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Discussion Starter #1
I don't have access to a chronograph at this time and I don't want to spend the money. And I just need a rough rule of thumb or experience with this matter.

So what should I expect the muzzle velocity difference to be when using a
Rock River AR15 with a 16 inch barrel 1 in 9” rate twist instead of a
Remington 700 26”, 1 in 12” twist (Hornady Data used from their reloading book)?
My guess is a loss of 150 fps.

I reloaded the 223 Rem using Hornady Data:
55 gr #2266 SP w/c
B.C. 0.235 C.O.L.: 2.200”
Varget 25.5 gr
Velocity per book 3100 FPS
 

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Quickload suggests that load, with a 16" barrel, will come in right at 2900fps and with a 26" barrel, velocity would be around 3240fps. A gain of roughly 350fps, or 35fps per inch of increased barrel length. That's a lot, but then again, the .223 Rem really needs more than a 16" barrel to burn all of the powder it can hold.

Incidentally, QL shows that as being a 110% compressed charge. A slightly faster powder, like H322 or IMR4198, might be in order. Both show the same velocity and higher ballistic efficiency, without being compressed so much. Particularly if you do most of your shooting with the 16" barrel, the Varget load is not ideal.
 

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Jason got it right in principle. The only fly in the ointment is that the Hornady case is likely to go into the AR with more like 30 grains water capacity than QuickLOAD's default 28.8, and to eject with more like 30.5 grains water capacity. I base that just on having measured cases fired through my own AR. The result I got is 3092 fps for the long barrel and 2732 fps for the short, so 360 fps difference. I also have a second, slightly faster powder file for Varget based on some other measurements I made, and it adds a couple percent to pressure and about 40 fps. Yours should wind up in that range somewhere.

How much you lose will vary a little with the powder choice. I find Varget is really a little slow burning for best work with the 55 grain bullets, though some get good accuracy from it anyway. In my guns it does best with match bullet weights from 69 grains and up. With 55 grain bullets I have an easier time getting accuracy out of something like Reloader 10X, which, at just 22-22.4 grains (less expensive to use) gives you the same pressure as my two Varget models, respectively, but adds 43 fps to the long barrel and 51 fps to the short barrel velocity. So it produces slightly less velocity difference at 352 fps.

There are other choices that nudge the velocity higher, but waste more powder. If I try to keep the charge at about 90% case fill, for loading ease, and burning at over 95% in the shorter tube, then Reloader 10X seems like the best compromise and it is a known good accuracy powder in the .223.

Your particular load may wind up needing more or less powder than predicted because of chamber tolerance differences. For example, the Lyman #49 manual has a 55 grain spire point seated all the way out at 2.26" COL (which should lower pressure as compared to 2.20"), but gives 25 grains of Varget as the maximum load using Remington cases. So, as with my two models, there seems to be a little lot-to-lot variation in Varget's burning speed or case capacity difference brand-to-brand or both working in concert.

If you decide to try RL15, Start at 20 grians and work up to an accuracy sweet spot. If you are sticking to Varget, try using a drop tube to load the cases, as that will pack the powder in better. Regardless of your powder choice, if you want a good systematic method of finding sweet spot loads, look at Dan Newberry's site.

As to actual velocities, you do need a chronograph to measure them with much resolution. You can build a ballistic pendulum or two separated disks spun by a synchronous motor if you have AC power at your firing line, but it's a lot of trouble to do either and the resolution is enough lower that you have to take and average a lot of readings to get to a reasonably precise result.

I've both read of and seen enough people having error trouble with the cheap chronographs that I'm not inclined to recommend any of them. You don't need a $750 PVM-21, but I think it is worth saving up your pennies for the CED M2 ($199 last time I looked). You can get a sense of how it compares to others on this thread at the Sniper's Hide. I also have an Oehler 35P (I set up two chronographs for velocity loss determinations to learn BC's). Like one of the posts in the SH thread, my CED and Oehler track almost perfectly.
 

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Discussion Starter #5
Interesting. I estimated 2900 fps.

Quickload suggests that load, with a 16" barrel, will come in right at 2900fps and with a 26" barrel, velocity would be around 3240fps. A gain of roughly 350fps, or 35fps per inch of increased barrel length. That's a lot, but then again, the .223 Rem really needs more than a 16" barrel to burn all of the powder it can hold.

Incidentally, QL shows that as being a 110% compressed charge. A slightly faster powder, like H322 or IMR4198, might be in order. Both show the same velocity and higher ballistic efficiency, without being compressed so much. Particularly if you do most of your shooting with the 16" barrel, the Varget load is not ideal.


Interesting. I estimated 2900 fps: http://www.thehighroad.org/showthread.php?t=538300

200 fps muzzle velocity loss
so instead of 3100 fps for a 26 inch barrel I may be getting 2900 fps for a 16 inch barrel.

(10 inch difference / 2 inches) time 40 FPS = 200 fps change.

Quickload is very impressive. Thanks for running the numbers.

Before reading your response I went out and bought BL-C(2). A quicker burn rate makes sense in the shorter barrel.
 

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I was going to suggest that powder, as well. The quicker powder will be a little more efficient, not be as compressed, and possibly result in less muzzle flash.
 

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Discussion Starter #7
Excellent Information Nick

Seriously.
It took me almost two hours to get through your post. I had to pause and read almost all of Dan's web sight and did some more reading on the reviews of the Chrono you mentioned before getting to the end of your post. Also the review on Quickload.

Funny how one good question leads to several leads on fascinating information.

I will have to adjust my load development method from just the ladder method.

Reloader 10X I may try later. I will have to work with the BL-C(2). I do have to admit the Varget is accurate.
 

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Discussion Starter #8
Here are the recent results of BL-C2 and Nikon M223 scope

I was going to suggest that powder, as well. The quicker powder will be a little more efficient, not be as compressed, and possibly result in less muzzle flash.
I took my M223 Nikon scope and my 16" AR to the range Wednesday with the new load.

BLC2 27.0 gr Hornady Book has 27.4 at 3200 fps
Bullet 55 gr #2267 BT-FMJ w/c

Estimated 2900 fps for my 16" barrel AR15.

Zeroed at 100 yds
Went to 300 yard range next.

Used the BDC Bullet Drop Compensation reticle on the M223 Nikon scope and found quite a big spread of about 15 holes. Looks like about 2.5 inches on average below target. I shot quite a few to see the rough average with a visual.

Then I took the info from Handloads.com using 2900 fps and used the turret knobs to move the elevation up 12 inches. Minus 12.09 per Handloads info.

I hit almost bullseye off by about an inch. Next target total miss then next one about an inch and a half off.

Yea I know maybe luck on the first one using the turret for elevation adjustment. Maybe pure skill:rolleyes:

Here is the interesting part:
When I plugged in the 3140 fps that Nikon recommends for bullet velocity with a 55 gr bullet into the Handloaders.com program it moved the 300 yrd drop from -12 to -9.45 that is the 2.5 inch difference rough average that I needed.

Accuracy observation using the M223 scope:
I do better with crosshairs using the turret for elevation.
I'm all over with my group using the circle reticle for the Bullet Drop Compensation. I have heard of this before on debates over BDC.



Data I plugged into the Handloads.com Ballistic Calculator:

Elevation 4500 ft.
Temp. 92 f
Sight Height 2.5
BC .243
55 gr

Velocities: 2900 fps and 3140 for comparison.

Do I like this New Nikon Scope? YES
 

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Don't overlook the very real possibility that the 1/4-minute clicks on the scope aren't really 1/4 minute. One of my Nikon's clicks is reasonably close to 1/4-minute, but the other one's isn't anywhere in the same county as 1/4-minute.
 

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Quickload suggests that load, with a 16" barrel, will come in right at 2900fps and with a 26" barrel, velocity would be around 3240fps. A gain of roughly 350fps, or 35fps per inch of increased barrel length. That's a lot, but then again, the .223 Rem really needs more than a 16" barrel to burn all of the powder it can hold.

Incidentally, QL shows that as being a 110% compressed charge. A slightly faster powder, like H322 or IMR4198, might be in order. Both show the same velocity and higher ballistic efficiency, without being compressed so much. Particularly if you do most of your shooting with the 16" barrel, the Varget load is not ideal.
I supect a tad more due to the ARs gas operation...

375ish
 

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I don't have access to a chronograph at this time and I don't want to spend the money. And I just need a rough rule of thumb or experience with this matter.

So what should I expect the muzzle velocity difference to be when using a
Rock River AR15 with a 16 inch barrel 1 in 9” rate twist instead of a
Remington 700 26”, 1 in 12” twist (Hornady Data used from their reloading book)?
My guess is a loss of 150 fps.

I reloaded the 223 Rem using Hornady Data:
55 gr #2266 SP w/c
B.C. 0.235 C.O.L.: 2.200”
Varget 25.5 gr
Velocity per book 3100 FPS
i usually work on 25 fps per inch , so that would be 250. The other way is if it lists tke trajetory IE 1.5 inches high at 100 then you can calculate roughly what you have lost speed wise from the increased fall in point of impact.
 

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I took my M223 Nikon scope and my 16" AR to the range Wednesday with the new load...

Accuracy observation using the M223 scope:
I do better with crosshairs using the turret for elevation.
I'm all over with my group using the circle reticle for the Bullet Drop Compensation. I have heard of this before on debates over BDC.

Data I plugged into the Handloads.com Ballistic Calculator:

Elevation 4500 ft.
Temp. 92 f
Sight Height 2.5
BC .243
55 gr

Velocities: 2900 fps and 3140 for comparison.

Do I like this New Nikon Scope? YES
The shooting world is full of ironies, and the circle reticle arrangement on the BDC-type scopes is one of them. At ranges close enough to sight in for maximum PBR, the silly circles aren't needed. At longer ranges where you might benefit from them, they are simply too imprecise, as an aiming point, to result in good groups; you need fine wire lines to put on your target and the circles simply subtend too large an area, at those longer yardages. Using a ballistic calculator and predictable turret adjustments is the only way to go if you want to maintain good accuracy beyond whatever PBR you have chosen.

Good work looking at all the "science" and then getting out there on the range to make sure it all adds up. Isn't it great when your effort pays off? :)
 

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The velocity change per inch of barrel changes with the length of the barrel. The shorter it gets, the more you lose per inch. There are two reasons. One is that as the barrel gets shorter the pressure at the point of muzzle exit is higher and higher pressure accelerates more rapidly, so loosing an early inch cuts into acceleration more than losing a later inch, where the pressures are lower and more level. With BL-C(2) under a 55 grain bullet, if you are out at 24", then you see about 30 fps/in difference, but at 16" is is closer to 50 fps/in of barrel. That's why average seems high.

Another reason is the shorter the barrel gets, the bigger the percentage of barrel you are cutting off with one inch, so the bigger the portion of the total bullet acceleration you are eliminating.

Also, note that the .223 bullet is just plain going faster than a .30 cal. When you cut an inch off an inch from a 24" barrel for a bullet going 3200 fps, it causes a bigger loss in fps than making that same length change for a .30 cal bullet going 2700 fps.


SLCscottie,

BL-C(2) (cannister grade WC846) has been around for some time. It is a good powder, but like a lot of spherical propellants it is harder to ignite than stick powders and is more prone to erratic muzzle velocity as a result. At 100 yards, the resulting difference in vertical point of impact is almost invisible, but at 300 yards it tells a good bit more. You can see this by messing with muzzle velocities in your ballistics program to see the drop difference (the free online JBM calculators will do this for you, too). After subtracting the moa you got at 100 yards from the group at 300 yards, the remaining vertical dispersion is a good indicator of your velocity spread.

To get better consistency from BL-C(2), you can try working with magnum primers. You seem to be filling the cases pretty well, so that may not help, but it can be worth a try. Knock the loads down 5% and work up with a magnum primer. You can simultaneously run the Newberry round robin at 300 yards.

Making no other change, you can also try the benchrest technique of deburring flash holes. That helped the performance of my .308 loads using Accurate 2520 years ago, actually cutting my M1A"s group size a whopping 40%, from about 1.2 moa to about 0.7 moa. It never made any difference with any stick powder I used in that gun, but because of that experience, even though it usually makes little difference, I always give it a try with any new powder just to see if I get an improvement? Newberry eschews all the benchrest methods, but I find they help in a minority of cases. You have to take it gun by gun.
 

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Discussion Starter #14
Thanks Broom

The shooting world is full of ironies, and the circle reticle arrangement on the BDC-type scopes is one of them. At ranges close enough to sight in for maximum PBR, the silly circles aren't needed. At longer ranges where you might benefit from them, they are simply too imprecise, as an aiming point, to result in good groups; you need fine wire lines to put on your target and the circles simply subtend too large an area, at those longer yardages. Using a ballistic calculator and predictable turret adjustments is the only way to go if you want to maintain good accuracy beyond whatever PBR you have chosen.

Good work looking at all the "science" and then getting out there on the range to make sure it all adds up. Isn't it great when your effort pays off? :)
Thanks. Plus it is a lot of fun. The original question generates more fascinating information that I have heard and not heard before.
 

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To take it up from where MZ5 left off, some scopes also have a transition near the center of the adjustment range, either side of which the moa per click is slightly different. This is due to the inside barrel riding the leading edge of the adjustment post in one direction and its trailing edge in the other. Sightron boasted of their fix for this when they first came out with their line a little over a decade ago, and I have to say the good old mil-dot reticule on my copy has served me very well.

I appreciate the idea behind the circle reticule, but don't find it works as well for me as the mil-dot, either. I suspect the problem is that the eye is very good at centering something in a circle, but not so good at holding off center. People can turn in some very good groups even with ghost rings, holding the front sight post in the center of the blurry rear sight aperture, but I wouldn't give two cents for their chances of placing the front sight consistently at, say 4:00 in the blurry aperture and half a front sight post width from center, then doing it consistently enough to get a good group. It would be easier with the scope reticule, but that doesn't cover the inbetweens very well.

BTW, like compensating with mil-dot hold-offs, correct parallax settings become important to making that circle reticule work, too.
 

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so true... I agree 100%

All reloaders should really get a chronograph
This has already been discussed, ad nauseum, but why would you think reloaders need a chronograph? If your loads function properly in your gun and they're very accurate, isn't that sufficient? Knowing your velocity is nice, but hardly necessary, simply because you loaded the components yourself. Consider that people have been loading and reloading for decades (centuries, if you count muzzle-loaders) without having any idea what velocity they were getting, and yet, their guns were safe and effective. Many hunters go afield each year with factory and handloaded ammo, completely oblivious to their exact velocity, and harvest game with surprising efficiency.

It's just a thought...
 

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I think that's usually true for all but benchrest 100 yard shooting, where muzzle velocity extreme spread has to be pretty gross to open a group up much. And that range covers most woods hunting in the East, where clear shots beyond that range are unusual. The game can't tell 100 fps difference one way or the other, at impact. At the other extreme, by the time you get to 1000 yards the 100 fps MV extreme spread that changes POI less than 1/4" at 100 yards can grow to a four foot difference in vertical POI, depending on the bullet and muzzle velocity. In that application you could be seriously short-changing your potential accuracy by not having a chronograph to help you develop more consistent loads. At the least, you'd be saving yourself a lot of load trial and error and unaccountable point losses.
 

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Uncle Nick,

Agreed that benchrest guys, and even varmint hunters, need, or benefit greatly from, a chronograph. For those who reload for fun, or hunting big game at normal ranges, it's just one of those things that is nice to know.
 
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