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  #1  
Old 05-01-2013, 12:34 PM
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Compressed powder loads


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The old timers talked about the infringing of powder in the cartridge case.
Your thoughts about this.
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  #2  
Old 05-01-2013, 01:44 PM
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More thoughts around about this topic than I have words for, there are a multitude of factors involved. BP actually requires a bit of compression, it definitely does not want air space behind the bullet. There a few smokeless powders that work best with a bit of compression, others that you better not, such as Trailboss. There are many, many factors at work with interior ballistics, not the least of which are case size relative to the bore, case shape, and seating depth, all of which relate back to the burn speed of the powder involved. For example I use charges of A1680 in my Max which are not in the book, yet I get pressures notably reduced from theoretical book values with great velocities. A very complicated topic with no concrete answers. GW
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Old 05-01-2013, 01:45 PM
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Think they meant intrusion of the bullet into the powder capacity. This happens when bullets of greater length, usually associated with greater weight, are seated deeply into the case to meet maximum cartridge overall length.
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  #4  
Old 05-02-2013, 11:46 AM
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That's what I thought also.
I've yet to determine the consequences of compressed powder loads. Good or not good.
When I develope a load, say using 4350 in my 7x57, I keep the powder level at the base of the neck of the cartridge.
An after thought, I have a Ruger # 1 International in 7x57. Short barrel.
What is more efficient, a slow burning powder (relativly) like 4831 or a faster burner like Varget?
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Old 05-02-2013, 02:42 PM
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Unclenick and internal ballastics experts will tell you the powder is consumed in the first couple inches of the bore and the rest of the barrel is used for expansion of the gasses and stabilization of the bullet.

The slower burners will spread the pressure spike out longer, which in my way of thinking, gives a better burn (efficiency?), yet the faster ones consuming the propellant quicker provide a kick in the pants to get the projectile down bore.

That said - tried all sorts of powder/bullet combinations in my Brazilan Mod 1909 7x57 and found equal loads of either IMR 4350 or VV N550 with 160 or 162 bullets to give best accuracy.
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  #6  
Old 05-03-2013, 11:39 AM
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I agree.
I'm thinking that a faster burning powder, like 4320 may be more efficient than a slower burner like 4831 in my short barreled # 1 International.
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  #7  
Old 05-04-2013, 09:51 AM
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As a, maybe, consideration for you.
Relatively speaking, slower powders and especially extruded ones, will TEND to have more throat erosion due to a sandblasting effect. Whether or not the average Joe would notice is up for debate.
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  #8  
Old 05-05-2013, 11:54 AM
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I'm in total agreement about the erosion issue.
My question is about the barrell length.
Are faster burning powders more efficient than slower ones in a short barrell?
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  #9  
Old 05-05-2013, 01:29 PM
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Depends on what you mean by efficient. If you mean is a larger percentage of the energy contained in the powder is converted to kinetic energy then yes. However more powder and more potential energy can often be contained in the case with slower powders before pressures reaches the guns limits. Generally the same powder that produces greatest velocities (energy) with a long barrel also produces the greatest velocity in a short barrel.

Unburned powder is not the primary source of throat erosion. Powder simply isn't hard enough to erode steel. The main cause of throat erosion is heat. Why then do some slower powders tend to increase erosion? Because larger charges are being used. If one were comparing 10 grains of a faster powder against 30 grains of a slower powder which would you expect to produce the most erosion, a 10 grain charge or a 30 grain charge. There is little comparative difference in the amount of energy in most powders on a weight by weight basis and most of that is due to nitroglycerine content. A 30 grain charge funneled through the same size throat as a 10 grain charge is going to expose the throat to much more heating. Also repeated heating and cooling produces micro-cracks in the metal which in turn increases degradation of the steel. The steel becomes 'burned' just as steel heated to hot and too long in fabrication can become burned.

This is more obvious in artillery using separated of bagged charges where shorter ranges use smaller charges of the same powder with very conspicuous improvements in barrel life. This is why artillery barrel life is commonly rated in terms of "equivalent full charge" (EFC). It is also why 'overbore' small arms cartridges commonly experience increased erosion regardless of the powder.
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  #10  
Old 05-06-2013, 11:29 AM
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Exactly my thought.
The slower burning powder is not confined to the cartridge case, the burn is completed in the throat area.
In my thinking, this is energy wasted.
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  #11  
Old 05-06-2013, 11:46 AM
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As long as the powder is burning, it's creating heat, hence expanding gases.

In my findings, compressed loads (in rifles) of slow powders can be more accurate than loads of less than 100% case capacity with faster powders using the same projectile and rifle when trying to achieve the same velocity.

No, wait, did that make sense?

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  #12  
Old 05-06-2013, 01:12 PM
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Quote:
Originally Posted by Easternhunter View Post
The old timers talked about the infringing of powder in the cartridge case.
Your thoughts about this.
An interesting question.

My reloading manuals form Barnes as compered to other cup “N” core manufactures manuals would suggest that it doesn't make much of a difference. I have found that my field results show not much difference from all copper bullets and lead bullets being seated deeply. My powders run (for the cartridge [ballistically the same as a 7mm Dakota)] from H4831 to H50BMG. Retumbo seems to give me the best results for all my bullet weights: 140gr to 180gr. Again, a mix of TSX and other cNc bullets. But, the last time I was out at the range, I was doing load development for a 175gr TSX a top Retumbo.

The first thing I ran into while reloading is how deep the bullet seats. I intentional started with a very reduced powder charge. About 15% of what I use for my 175gr SMK's and 12% for the Berger 180gr VLD's. Well... by the second shot I was at max pressure and a velocity 100fps short the above cNc bullets.

So I got some more H50BMG. I haven't reloaded yet, but I'm going for a full if not compressed powder charge to raise my muzzle velocity. The 175 TSX really does “infringe”. I'll be interested in seeing what happens. I'll post my results when I get a chance to get up to the range.
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  #13  
Old 05-07-2013, 11:50 AM
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It is interesting!
I realize that all rifles are different from one another.
I've always thought that the most effective burn was within the cartridge case.
Compressed loads seem to equate an overbore scenario, too much propellent in a given space.
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  #14  
Old 05-07-2013, 12:05 PM
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I am just reading Brownell's Pressure Factors.

"To demonstrate use of Figure 42 consider the 220-grain bullet seated to 1/8 inches as listed in Table X. The value of s/n is 1.125/0.34 = 3.31. Locating 3.31 on the horizontal scale of Figure 42 we read 1.3 for S at the top of the curve for the 30-06 cartridge. This agrees with the value of 1.30 listed in Table X. The pressure at this seating depth is 1.30 p(ref) or 1.30 (37,000) = 48,100 psia." Brownell

The meaning is that in this example, the intrusion (no compression) raises the pressure by a factor of 1.3. Of course, things are different if you change the powder at the same time.

Last edited by F2G1D; 05-07-2013 at 12:09 PM.
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Old 05-07-2013, 12:17 PM
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You just lost me bud.
Is too much propellent too much??
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  #16  
Old 05-07-2013, 12:19 PM
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Well if you want to know about overbore see this current thread: Overbore .

You will see there are two generally accepted definitions. I would guess its like you wrote here:
Quote:
Originally Posted by Easternhunter View Post
Compressed loads seem to equate an overbore scenario, too much propellent in a given space.
...If you are speaking in terms of economics. Meaning you could use less powder by using a faster powder that didn't take up so much case space. You would then be saving money. This predicated on the fact most powders with similar burning rate, from the same manufacture cost the same per pound (e.g. Varget, H4350, H4831 Retumbo etc...).

As for physics? Not necessarily. There are many compressed loads that give equal or greater muzzle velocity. Example: Up until the recent introduction of CFE 223, compressed loads of IMR 4320, IMR 4064 and Varget gave the highest muzzle velocities within a .308 Winchester and 150 to 155 grain bullets.
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Old 05-07-2013, 12:21 PM
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Quote:
Originally Posted by Easternhunter View Post
You just lost me bud.
Is too much propellent too much??
I think F2G1D is making the point that there is a differance between (not the same concept) "intrusion" and "compressed load".
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Last edited by mr glo; 05-07-2013 at 12:24 PM.
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  #18  
Old 05-07-2013, 12:37 PM
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overbore

More case capacity than is efficient for a caliber. Correct??
Why would not be the same scenario as a compressed load?
Compressing the propellent?
Ten pounds of stuff in a five pound bag.
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  #19  
Old 05-07-2013, 12:47 PM
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I just happened to be reading that sentence when I looked at the post. The point is that intrusion without compression can raise the pressure. A compressed load could be different. One example might be if the compression fractures the powder grains. Another difference might be that the bullet takes up a certain additional airspace, whereas the powder grains have 'intragranular airspace'. Compression achieved by seating the bullet deeper might be different than that achieved by using more powder, since in the first instance you could have increased the 'freebore' available to the bullet. The same 'freebore' effect might be achieved by simply seating the bullet deeper with no compression. Many factors have to be considered.

Last edited by F2G1D; 05-07-2013 at 12:54 PM.
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  #20  
Old 05-07-2013, 02:24 PM
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Quote:
Originally Posted by Easternhunter View Post
More case capacity than is efficient for a caliber. Correct??
Well no that's not correct, especially today with powders as slow as US869 and 20N29. The word usage , “efficient” is very subjective. Efficient to me may not be efficient to you.

Quote:
Originally Posted by Easternhunter View Post
Why would not be the same scenario as a compressed load?
F2G1D answers that very well in the above post.

Quote:
Originally Posted by Easternhunter View Post
Compressing the propellent?
Ten pounds of stuff in a five pound bag.
Yep, and some times its necessary. I'll try to reload my .284 Achilles this week and get out to the range. I'll try to get you field results in a week or so. I just looked again at Load From A Disk. 100% load density (LD) is at 83.5 grains of H50BMG. Unfortunately that will be to high a pressure. But I'm still interested as a mater of intrusion. Even US869 and 20N29 don't quite make it to 100% load density as predicted; about 95% LD.
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