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29K views 44 replies 17 participants last post by  Rocky Raab  
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#1 ·
My reloading book uses a 26" barrel when generating the data for the 7mm-08. My model 7 7mm-08 has a 20" barrel.

Does this mean that my gun will be more more efficient with a faster powder? I have read though that the powder is usually fully combusted within an inch or so of the chamber...then what about muzzle flash?

I have also read that slower powders are louder and have more blast..is this true?

My reloading and powder experience is very limited, only IMR4350 for a 30-06 and H380 for a .22-250

A bit open ended but please share your thoughts, especially if you have experince with this gun and caliber.

Thanks!
 
#2 ·
Use the book data and powders. You will realize slightly less velocity because the bullet will have a bit less time to accelerate in a shorter barrel, and you will have a bit more blast because the gas will be at a higher pressure at bullet exit, but the best powder for a long barrel will almost always be the best powder for a shorter barrel, also.

It's a myth that shorter barrels require faster powders in a given cartridge. Faster powders will reach their pressure peak faster, but also subside faster, giving less overall bullet acceleration than a powder that delivers a smooth, long pressure curve.

It's also a myth that muzzle flash is caused by powder that is still burning (or that re-ignites) after bullet exit. Muzzle flash is caused by the spontaneous ignition of unburnt flammable gases that are released by the previous combustion of the powder. There isn't enough oxygen released by the powder to burn all the fuel that is also released. The excess fuel gas ignites when it mixes with oxygen in the air.

Not all the powder always burns in the barrel, due to a variety of factors; but what doesn't burn is either ejected unburnt or left behind. It almost never burns afterwards.

That is all a bit oversimplified, but the basics are true: The best powder for a cartridge is independent of barrel length (within reason); and, muzzle blast/flash is not related to unburnt powder kernels.
 
#3 ·
Hrm. Didn't know this. Thanks Rocky.

There can be better powders if there's a really major difference in barrel length, I've found. Like, a 4" barrel vs a 16" barrel. I've had a .40 S&W load that was, in a carbine and at a max load, slower than the expected velocity of the minimum load. I believe we tested it in a Glock 22 as well and it was running at about expected velocity.
 
#4 ·
Rocky covered the technical side pretty well. Efficiency? A sharp stick uses less powder, think about it..... we are in the field to get an animal, efficiency be darned.

All centerfire rifles are loud enough to damage your hearing. Yes the shorter barrel will be a tad louder, but the difference isn't going to protect your hearing. Use hearing protection when you can.
 
#5 ·
KO's example is why I qualified my "best powder for a cartridge is independent of barrel length" summary statement with the words "within reason." A 400% change in barrel length rather changes the equation, no question about it. But in MOST situations, the statement holds.
 
#12 ·
GrapeNuts said:
Thanks..

Now a question about bullet preference. Will a 139 gr Hornady Interbond give me the needed expansion from this gun or should I stick to standard cup and core due to the lower velocity? Rig is meant for mixed terrain whitetails at 250yds or less.
Click to expand...
Under those conditions the 139gr Interlock is just about perfect in a 7mm-08, and so is the 154gr Interlock for that matter. I've used both in the 7mm-08, and 7mm RM for well over 20years, and have had excellent results with both from 20ft to 400yds on deer and antelope.

Interbonds are a response to market trends. The perception that megadollar bullets are a necessity for deer size game is a real stretch, to say the least. The 7-08 just isn't that hard on bullets.
 
#7 · (Edited)
Ko,

The key is Rocky's parenthetical "within reason". I have a reference to a 1954 publication in which rifle ammunition fired in a very short barrel was shown to bulge the bullet base, ruining accuracy. In other words, peak pressure is so great the muzzle blast can actually deform a bullet base if it runs out of barrel near that peak.


Grapenuts,

To answer your original question a little more completely, no, the powder does not all burn in that first few inches. Peak pressure is reached then, however. That is due to pretty much all of the powder having started burning and being actively contributing gas to the pressure at that distance. Many powders that are slow enough will still have a few percent trying to finish burning when the bullet exits.

Going to a faster powder accomplishes several things. You will increase ballistic efficiency, the percent of the energy stored in the powder that is converted to kinetic energy in the bullet. In connection with that, you can't put as much stored powder energy into a case with a fast powder because it would create too great a peak pressure, so you generally end up using less powder by weight and save money. You reduce the pressure at the muzzle, which has several benefits: it reduces muzzle blast, it reduces recoil, and it reduces the amount of blast-propelling on the base of the bullet that can exaggerate errors due to bullet base or muzzle asymmetry and any bullet out-of-balance condition.

The muzzle blast effects take some further explaining. The effect on accuracy happens because muzzle and bullet base symmetry ensure the blast acts uniformly on the bullet base as it exits. Without those, the blast will start to escape from one side of the bullet base before the other and the bullet will be slightly tipped by that, which the bullet has to recover from in flight. Additionally, if the bullet mass is at all eccentric, after leaving the muzzle, instead of continuing along a trajectory in line with the bore axis, it will start to spin about its center of mass instead. The shift from spinning on the bore axis to spinning around the center of mass is called bullet jump. That is because the bullet moves over slightly to find that new rotation axis. During and after the jump, the bullet is no longer quite centered over the muzzle blast, and so, again, it can be slightly blown off course or tipped by the asymmetrically applied pressure. It's one of those things that wouldn't matter if every bullet had same error and started out oriented so they jumped the same amount and in the same direction every time, but that isn't how it works.

The recoil difference is due to two things. Half or more of the powder gets blown down the tube with the bullet, plus the evolving gas has no less mass than the powder generating it (mass can neither be created or destroyed except in nuclear reactions), so the more powder you put in the case, the more recoil you have from accelerating its mass down the tube. The more significant effect, though, is rocket effect. That is the rearward propulsion of the gun due to the rapid acceleration of the mass of the gas in the barrel once the bullet exits. So this is a push that occurs after the bullet is clear of the muzzle. It can be responsible for up to 40% of total recoil. Venting muzzle pressure before the bullet clears the muzzle is how muzzle brakes reduce recoil even when their holes just vent sideways and equally in all directions. If you have a smaller charge of a faster powder that produces less gas mass and exhausts out the muzzle at a lower pressure, you can cut the rocket effect down. In another forum I once helped a fellow looking for a low recoil load for his kids reduce the recoil of his light load from 14 ft-lbs to 11 ft-lbs just by changing powders, but not giving up any bullet velocity.

The drawback to a smaller charge of a faster powder is it will usually leave more empty space in the case. That can reduce ignition consistency, so it isn't always the best thing to do. The fact you are lowering muzzle pressure also costs you some velocity. You end up having to decide what trade-offs are suitable in your gun?
 
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#14 ·
unclenick said:
Going to a faster powder accomplishes several things. You will increase ballistic efficiency, the percent of the energy stored in the powder that is converted to kinetic energy in the bullet. In connection with that, you can't put as much stored powder energy into a case with a fast powder because it would create too great a peak pressure, so you generally end up using less powder by weight and save money. You reduce the pressure at the muzzle, which has several benefits: it reduces muzzle blast, it reduces recoil, and it reduces the amount of blast-propelling on the base of the bullet that can exaggerate errors due to bullet base or muzzle asymmetry and any bullet out-of-balance condition.

The muzzle blast effects take some further explaining. The effect on accuracy happens because muzzle and bullet base symmetry ensure the blast acts uniformly on the bullet base as it exits. Without those, the blast will start to escape from one side of the bullet base before the other and the bullet will be slightly tipped by that, which the bullet has to recover from in flight.
...
The drawback to a smaller charge of a faster powder is it will usually leave more empty space in the case. That can reduce ignition consistency, so it isn't always the best thing to do. The fact you are lowering muzzle pressure also costs you some velocity. You end up having to decide what trade-offs are suitable in your gun?
Click to expand...
Following unclenick's explanation it seems obvious to me that, contrary to Rocky Raab's assertion, excessive muzzle blast is detrimental to both accuracy and recoil. Therefore, ideally every load would be tuned to the barrel length, with shorter barrels getting smaller amounts of faster powder so that a full burn is complete before the bullet leaves the muzzle. Of course this will reduce muzzle velocity, but that's already an accepted tradeoff of shorter barrels.

Regarding the case space presumably you can use inert fillers or buffers to solve that problem.

Which leads to a few questions:

1. Are there any manuals that suggest loads by barrel length?
2. Are there any manuals or recipes for very short-barreled rifles -- e.g., 8" .223 -- where perhaps you have to switch to slower pistol powders to get a full burn before the muzzle?
3. Are there any standards for measuring or quantifying muzzle blast?
 
#8 ·
Either the Interbond or the standard non-bonded version of the same bullet will be exemplary deer bullets, Grapenuts. You'd be hard-pressed to detect any forensic differences on two identical dead deer shot with either. If you already have one, there's no reason whatever to buy the other in its place.
 
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#9 ·
Thanks Rocky, I get the feeling you didn't start playing with firearms just yesterday.

I have to ask though, in your response about the 139 bullets, did you allow for my decreased velocity? I may even load 150gr just to help me be certain of good penetration.

Stepping down from an '06 and am little shy about shooting smaller bullets at deer.
 
#10 ·
Yes, I did. The difference in velocity you might see (and there are no hard and fast rules in this) is roughly 25 fps per inch of barrel. Of course, it might be a bit more or a bit less. Nothing to lose sleep over.

Read some of the early stories about the 250 Savage. Back when, using bullets that were MUCH inferior to today's, that little .25-cal bullet weighing 100 grains and launching at 2800 fps knocked 'em deader than Pet Rocks. Compared to that, you're overgunned!
 
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#13 ·
Rocky Raab said:
Yes, I did. The difference in velocity you might see (and there are no hard and fast rules in this) is roughly 25 fps per inch of barrel. Of course, it might be a bit more or a bit less. Nothing to lose sleep over.

Read some of the early stories about the 250 Savage. Back when, using bullets that were MUCH inferior to today's, that little .25-cal bullet weighing 100 grains and launching at 2800 fps knocked 'em deader than Pet Rocks. Compared to that, you're overgunned!
Click to expand...
Hey rock ButchB here, my very first rifle was a savage 99 with the rotary magazine in 250 savage, or 250-3000 as it was still called then. That win 100gr silvertipped bullet made alot of deer meat for my family. Put the little bullet where it belongs and the deer die. Big hole little hole it don't matter. I bang my head on the bed post every night for ever selling that rifle to this very day.:eek:
 
#11 ·
Actually, if those "early stories" were prior to 1932, they referred to the original 87 grain bullet at 3000 fps. Even though that load performed very well, some people insisted that a heavier bullet would surely be better just because it was heavier, so the 100 grain at 2800 fps was introduced in factory ammo in 1932. Some have claimed the heavier bullet sort of "took the luster off the 250/3000".
 
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#15 ·
The Lyman reloading manual has loads for short barreled handguns such as the T/C Encore for cartridges ranging from the .22 Hornet to the .450 Marlin. The manual states the barrel length used for each cartridge.
 
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#16 ·
dbooksta, you mixed peaches and pomegranates there. Excess muzzle blast is indeed detrimental to both accuracy and recoil, just as unclenick described. Powder choice can indeed influence muzzle blast. But muzzle blast is not velocity.

Powder is essentially consumed by the time the pressure peaks. One of the major reasons that the pressure drops off rather sharply is that there is little if any powder left to burn and produce more gas. That doesn't mean that all powder always burns, because some might not, for several reasons too technical to detail here. But it is safe to say that all that is going to burn has just about done so by the pressure peak.

What happens after that is the high pressure continues to exert a tremendous push on the bullet all the way to the muzzle. That pressure drops due to the increase in bore volume and also because the cold barrel cools it, but it stays as high as 10,000 to 40,000 psi even at the muzzle. That is much more than needed to keep accelerating the bullet, so the bullet does keep accelerating.

Clearly, that means that a short barrel allows less time for acceleration to happen or for pressure to drop, so short barrels generate less velocity but higher blast and jet effect. Conversely, a longer barrel generates more velocity but less blast.

The reason the manuals don't list loads for different barrel lengths is that (as I claimed at first) the optimum load is essentially independent of barrel length - within reason.
 
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#22 ·
Rocky Raab said:
The reason the manuals don't list loads for different barrel lengths is that (as I claimed at first) the optimum load is essentially independent of barrel length - within reason.
Click to expand...
I appreciate your explanation, but I have two problems with that conclusion:

1. I thought the best way to determine when I'm approaching the maximum load is to look at the muzzle velocity vs. what is shown in the manual. But as you noted the shorter the barrel, the lower the muzzle velocity for the same pressure. I have seen rules of thumb regarding how much velocity you lose as you shorten the barrel, but none of my manuals say anything like "Reduce maximum load velocity by x fps for each inch shorter than our test barrel, which was y inches long." So is everyone with short barrels just supposed to give up on quantifiable limits and just look for the pressure signs as they work up loads?

2. We shoot .44 magnum out of a 3.5" snubby and a 10" hunter revolver; or .223 in a 8" SBR vs. a 24" bench rifle? Is a tripling of length "within reason"?
 
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#17 ·
Its been quite a few years since I read the article and don't remember who wrote it or where it was published but it studied this very subject.I believe they started with a 28 in barrel and cut off an inch at a time chronographing several different loads using powders of fast to slow burning rates.I think they ended up at 16 in barrel length.They found, as Rocky has said,the optimum powder for a long barrel is also optimum in a short barrel in conventional rifles.
 
#18 · (Edited)
GrapeNuts, here's a specific reccomendation you can try if you like :

try the Hornaday 139 gr Interlocks, seated in the channelure, with a good firm roll crimp, (and if you decide to crimp, be sure to trim to length every time, even new brass) try some Varget powder, (I'd start around 47-48 grs and work up until you lose the accuracy, or til pressure signs show), and lite it with a magnum primer ....this combination should work in your short bbl, and will be relatively temperature insensitive....the mag primer, and the crimp, will both contribute to getting a good sized fire going early....... you should wind up around 2750-2800 fps and that'll take care of your specified chores......
 
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#19 ·
I find this thread most interesting.
Most of (practically all)of my load developement for hunting is by trial and error.
My particular rifle was a Springfield Krag 30/40,with a 21 inch barrel.I'm a woods hunter.
All data that I encountered was for 26 or 30 inch barrels.
My first trial load was with IMR3031,and it was pretty good.I then tried a lot of IMR 4198 loads,because it is faster,for my shorter barrel.
The origional load,for long barreled rifles,is best for my shortie,too.
Amen,Rocky
Frank
 
#20 ·
I think that is generally true, as Rocky said, "within reason". Even in a .357 snubby revolver a max load of H-110 will run a bit faster than a max load of Unique, albeit with a lot more muzzle blast, flash and recoil. This notion of faster powder for shorter barrels is just one of the many things which seem to "stand to reason" but which doesn't actually pan out in practice.
 
#23 · (Edited by Moderator)
Basically all the above is true and gets somewhat deep and one can literally spend thousands of bucks on ammo, propellant, primers and testing and maybe will learn something quicker or slower.
There is a better way which are some excellent computer programs are available today that allows you to "test at your desk" so to speak.
The program I am familiar with is Quickload and it has been a God send for me so to speak.

You can program in many variables such as barrel length, bullet weight, bullet by manufacturer, about all the available propellants, and start changing these at your computer.

Edit: I forgot to add the single most valueable thing about this program is you can see how much propellant is burned before exiting the barrel. You can start off with a long barrel and shorten it in the program you it will tell you the % of propellant burned. It will allow you to identify a propellant that burns completely in your barrel length because for every % that is not burned it is just blown out the muzzle. Even pistol propellant will not burn completely and indoor ranges have to sweek the floor in front of the firing line to remove the unburned propellant that is blown out the muzzle and if not done will cause a fire when spark hits it. Thusly you can change propellants on the computer, identify which ones work at 99% or greater for your barrel length. I have also found that propellants that give a long pressure curve on the low end of the range gives me the best accuracy.
The program calculates your chamber pressure, muzzle pressure, velocity etc and chronographing in every load I have check so far is amazingly close to the velocity the program tells you it has.

For instance the M1 Garand has a port pressure requirement to make it operate correctly. Too low it will short cycle, too much it will overdrive gas system and there are thousands of articles about M1 Garand loads but I also have a Tanker Garand and the port is now six inches closer to the chamber than a rack grade thus my port pressures were out the top.

I got in and adjusted the program and plugged in different propellants until I found a combo that would still give me velocity without excess chamber pressure.

I figure I have saved several thousand bucks by the use of Quickload. There are I am sure other programs but I have yet to see them so will stay with Quickload for the time being.

Whoops Edit required: I forgot to mention the best feature of Quickload. You can start off with a 26" barrel and check to see how much propellant is burned in %. You can reduce the barrel length an watch the % lower thus you need to select a faster propellant. Remember for every % not burned it is wasted as blown out the muzzle.
You can also determine pressure curves and as stated a long slow curve is what you are looking for and I have found keeping those loads on the low side gives best accuracy most of the time.
 
#24 ·
dbooksta, that's why this is still almost as much art as science. Unless you have pressure-measuring gear (which is now available to reloaders) you are operating as much by blind feel as quantifiable results.

Humpy, the one feature of QuickLoad that is absolute balderdash is that % of powder burned thing. "Powder burning all the way to the muzzle or beyond" is probably the most persistent myth in reloading. It simply does not happen that way. Period. As I explained in this very thread, everything that is going to burn has just about done so by the pressure peak. If it were otherwise, the pressure would continue to rise or remain high. It doesn't. Pressure after the peak drops just about as we'd expect a static pressure to drop with a change in volume and temperature - which proves that there is no additional burning.
 
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#25 ·
Rocky Raab said:
As I explained in this very thread, everything that is going to burn has just about done so by the pressure peak. If it were otherwise, the pressure would continue to rise or remain high. It doesn't. Pressure after the peak drops just about as we'd expect a static pressure to drop with a change in volume and temperature - which proves that there is no additional burning.
Click to expand...
That is not a conclusive theoretical argument: After all, if the bullet traveling down the barrel opens up bore volume more quickly than the burning powder can produce gas, then it's possible for the pressure to fall off while powder is still burning.

The lower the ratio of (gas production) vs. (change in bore volume due to bullet travel) the more your pressure curve following peak pressure (which imparts maximum acceleration to the bullet) would resemble a "static" pressure profile. Complicating matters further is the fact that powder burn rate is a function of pressure. Without knowing the burn rate as a function of pressure one couldn't integrate over the pressure curve to determine powder consumption. I can imagine pressure/burn-rate functions that give a sharp initial pressure but then tail off very slowly.

Granted, in practice it may be that even the slowest powder is completely burned within an inch or two of bullet travel, but can you provide any support for that claim -- especially since, as you note, many people believe otherwise?
 
#26 ·
In so much as I have personally seen unburned propellant laying on the floor from handguns in indoor ranges that when swept up will readily burn, it therefore follows all propellant even though double based does not ignite.

As well I have observed unburned rifle propellant on large sheets of white paper in front of a muzzle after firing rifles which also follows that it did not burn in the barrel.

I have also observed unburned propellant and removed same with cleaning patch throughout the entire length of a barrel.

In light of the fact indoor ranges were required to be vacuumed at Aberdeen Proving Ground after rifle firing leads me to believe all propellant does not burn in rifle barrels.

Questions for Mr. Raab: WC852 was a propellant used in 30.06 ball ammunition production. There are two designations for WC852 (fast and slow), could you enlighten us as to why the same propellant number would be designated fast and slow?

4895 was routinely manufactured by Radford AAP for many years and then production suspended. Could you explain why.

How are the loads developed at LC AAP for the different projectiles they manufacture.

Could you tell us why the 168 7.62 Match ammo initially loaded in the early 1980s by LC AAP was matched at a different facility. What facility that was. Who did the loading of the development rounds. What the equipment consisted of that the development rounds were assembled with.

Can you tell us why the M16A1E1 barrels failure at Aberdeen PG was blamed on propellant and what the failure consisted of?

Can you tell us why LC lots 60-1 thru 60-5 performed much better than previous and subsequent lots when loaded with the 173 Match bullet?
 
#27 ·
GrapeNuts said:
My reloading book uses a 26" barrel when generating the data for the 7mm-08. My model 7 7mm-08 has a 20" barrel.

Does this mean that my gun will be more more efficient with a faster powder? I have read though that the powder is usually fully combusted within an inch or so of the chamber...then what about muzzle flash?

I have also read that slower powders are louder and have more blast..is this true?

My reloading and powder experience is very limited, only IMR4350 for a 30-06 and H380 for a .22-250

A bit open ended but please share your thoughts, especially if you have experince with this gun and caliber.

Thanks!
Click to expand...
GN,

I'm on the side of the better velocity powder in a longer barrel will also be the better velocity in a 5 to 6 inch shorter barrel. If you have a chronograph (or access to one), try several powders across the appropriate burn rate your 7-08 and see for yourself.

PS: It'll be a good excuse to get out and shoot more - Have fun!
 
#28 ·
If the bore volume increases rapidly, pressure drops rapidly as well. When the pressure and temperature drop to below the propellant's operating range, no further burning happens. Some propellant not fully ignited can go out (which is why we sometimes find partly burned kernels). As you correctly say, burn rate is dependent upon pressure and temp. Drop either or both too low and burning ends. Remember this is not like open-air burning. It all happens in three or four milliseconds, so even the slightest delay is equivalent to "not burning."

Humpy, read what I said. I never claimed that ALL the powder burns. I quite clearly said in several places "all the powder that is going to burn." Some never does, and that's what we find on the floor. The rest of your questions are irrelevant.
 
#29 · (Edited)
I personally don't worry about the % burning, as for my hunting use it is irrelevant if all the powder burns or not. All I care about is if the critter I'm aiming at dies. As an example, I shoot probably 3-5 rounds A YEAR out of my .35 Rem. No, I haven't bothered to re-sight it in each season either; I know the zero doesn't change with the synthetic stock.

At the end of the current 50-round batch, a new batch will get loaded. I will probably get around to cleaning the barrel, then, too :D Yes I know that sounds terrible but I'm shooting cast bullets and it's my experience that unless I get rained on, the lube / fouling leaves just enough grease in the bore that I don't have to worry about rust on the inside. Your climate may differ so don't take that as a blanket recommendation to never clean your gun.....

Last thing I shot with it was a turkey at about 90 yards and hit exactly where I was aiming.... a few deer and pigs here and there, and the unlucky raccoon, coyote, or jackrabbit on occasion. Then the season starts anew..... It did account for 3 pigs on one hunting trip and I think that's the most rounds that have ever been through at the deer camp, in one day.

One issue is that the powder I'm using is a bit slow for the purpose (Varget) so I get a fair amount of muzzle blast. Also there is some fiddling to get enough in the case; t's a tradeoff for not wanting to stock another powder and the time involved to work up loads again.

This is just one perspective and my needs are far different than the competition shooter who may put more rounds downrange in a day, than I will with the Marlin in the next decade or so. Or the shooter that's trying to hit something ten times farther away than the average shot I get at game. The percentages and efficiencies will doubtless be very important to some people. Just not with me, with this rifle, for it's intended use.

One person's perspective on the issue.....
 
#30 · (Edited by Moderator)
Mr. Raab,

So basically you are saying that all that will burn does quickly and the rest isn't burned so it therefore follows that Quickload saying a lower % of burn is correct and not balder dash thusly it is relevant.

So in your opinion what is the fastest one could expect to safely launch a 173 grain bullet from a 30 cal barrel and not have case failure or barrel failure?

How would you go about it?
 
#31 ·
Humpy, what is balderdash is the readout in Quickload that the powder burns for "x" inches, sometimes giving a number equal or longer than the barrel.. That, as I said, is not the way powder burns in a cartridge/gun at all. It may simply be poor choice of terminology. English is not the program writer's first language.

The relevance of burn rate, powder quantity, expansion ratio and several other factors is that all of them together affect the ultimate bullet velocity. The primary predictor for the end result is not the peak pressure achieved but the area under the pressure curve. A slow powder can safely use a heavier charge weight of powder than a fast one, generally. That added powder can release more gas, simply because more molecules are available. Even if it produces a slightly lower peak pressure, the added amount of gas can maintain pressure longer as the bullet moves down the barrel. That longer "push" produces higher muzzle velocity. "Longer push" is a simpler way to describe increased area under the pressure curve.

A higher pressure for longer time also does allow more powder to burn, even if not all of it does. The curve will be broader at the top when that happens, but will still signal burnout by a steep drop before the bullet has moved more than a few inches.

The absolute highest bullet speed would be achieved with a cast powder charge. The grain would have a hollow from primer to bullet, and the shape of the internal cavity would be crafted such that the burning surface would increase at a progressive rate to exactly compensate for the added volume of the chamber as the bullet moves down the bore. It would be, in short, a solid propellant rocket coupled to a piston bore. However, the only practical way I can envision to make it would be to cast the propellant, remove the core-shaping mandrel and then form the case shoulder and neck (assuming a bottleneck round). Priming and bullet seating would come after that.

Peak pressure in such a system would rise immediately to the allowed maximum and remain there until bullet exit. Fast bullet, but Oy-ve the muzzle blast! Probably not very accurate, either. That blast on the bullet base at exit would be bound to upset it randomly and throw it hither and yon.

Not a reloader friendly cartridge, either!
 
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#32 ·
Rocky, I think I'm starting to understand your point, which is: A very fast-burning powder would just provide a nudge, followed by reduced acceleration as it not longer produces gas. In contrast, slower-burning powders can continue peak acceleration along the length of the barrel because they can continue to fill the void left behind the bullet.

But I don't see how that addresses the concerns raised here, which center around finding the "best" powder for barrels of different lengths, where "best" may mean one or more of:
1. Most accurate
2. Highest muzzle velocity
3. Lowest muzzle blast

1. We know that excessive pressure at the muzzle can reduce accuracy. So take the "best" load for a 24" bbl and start chopping inches off the end of the bbl, and you're going to see increasing propellant pressure at the muzzle. So in principle I don't see why the most accurate load for one barrel length would be most accurate for shorter lengths.

2. We know max muzzle velocity will be achieved with the powder that can maintain the maximum pressure for the longest time. Assuming you have found this powder for a particular barrel, then YES it should also offer max muzzle velocity for any shorter barrel. 0But per #1 it will almost certainly NOT provide the best accuracy with shorter barrels, right?

3. You earlier said that two components of muzzle blast are muzzle pressure and reignition of double-base byproducts. You seem to be claiming that powder that is not burned before the bullet leaves the muzzle does not contribute to muzzle blast, correct? That's plausible, but still surprising to me: It means that powder, which burns easily under standard temp/pressure will somehow not burn or will extinguish after exposure to the high temperature and pressure in the barrel.

3a. Insofar as muzzle pressure contributes to muzzle blast, you will reduce muzzle blast using faster burning powders (albeit at the cost of lower muzzle velocities), correct? How much of muzzle blast is due to muzzle pressure?

3b. Insofar as reignition contributes to muzzle blast can't you reduce it by using powders with lower proportions of NG? Or can you provide the chemistry that can lead to reignition? I was under the impression that powders contain precise amounts of oxidizers to burn propellant, in which case reignition would suggest the powder is poorly formulated.
 
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