Does a shorter barrel need less powder?

[Droppin Deuces]

Considering that most AR data I'm finding is created using 20-24" barrels, is it safe to assume that a 16" barrel can produce optimum velocities using less powder? Is there a rule of thumb for what % to reduce by?

For instance, if 25.3 grains of Varget produces ideal velocities in a 24" barrel, I will probably get a lot of blast out of a 16", right?

[Droppin Deuces]

I guess what I'm asking is if there is data specific to different barrel lengths.

[mif_slim]

Suppose to but I personally just notice more flash! HAHAH...oh and, slower velocity

[Sky_DiveR]

You would use faster burning powder and/or a heavier bullet so that it would completely consume itself within the shorter barrel....
In theory.

[J-cat]

It's not less powder but a different burning rate you should consider. A faster powder will be consumed more efficiently inside that short barrel.

[smoothy8500]

I use IMR 4198. It gives gives me good results in a 10" bbl with a 5" flash hider.

[Divernhunter]

This subject comes up ever so often when I talk to people about guns/reloading. This is the facts for reloading with todays powders. What works best(for speed of bullet) in a long barrel will also give you the most speed out of a short barrel given the same bullet(weight, shape etc).

I used to think shorter barrel better to use faster powder. But that is not the case. I read an article about it and then I tried it with several cartridges and a bunch of different powders all at max loading. I used 223/5.56 and 308win/257Roberts/454casull/25-06 barrels with 22-26" and then 10-15" closed chamber(Encore pistol). I used as many as 10+ powders with all cartridges loaded the same. The ones that gave the most speed in the long barrels also gave the most in the short barrels.

In the 223 I found that Win748 or H335 was best in both with a 55gr bullet. With a 40gr bullet the Win748 or Benchmark was best. In the 308 Win748 was best with 150gr bullets as well with 125-130gr bullets but Benchrest was also excellent with the lighter bullets. In the 44mag and 454Casull H-110 beat out all others including 2400. The 257roberts with 100gr bullets did best with H-414 and I know that Win760 is suppose to be the same but did not show it in my guns. The 257Roberst also did very well with IMR4064.

As far as accuracy my loads all were very good HOWEVER other guns may show a preference for another powder for accuracy.

Powders I used included win748 & 760.Varget/benchmark/IMR4198 & 4227 &4064 & 4895 & 3031 & 4350 & 4831 & 7828 & 7828SSC maybe a few others I forgot now. I also used H-110 & 332 & 335 & 450 & 414 & 4350 & 4831 & 4895 and also maybe some I forgot now. I also used RL15 & 19 & 22 & BL-(C)2.

So there you have it, what the article stated also also proved that the powder that does the best in the long barrel also does best in the shorter barrel with hand weighted loads over my chronograph.

[Sky_DiveR]

Interesting. Guess I gotta get me a Chrono. I never woulda guessed. At least the fireball would be pretty impressive. Wonder if it has any adverse effects on the barrel.

[J-cat]

Velocity is not the primary or only consideration. Muzzle blast, flash, recoil, etc. are also important. Shooting a full load of Varget outa a 10" barrel is not very pleasant. I use QuickLoad to match the powder to the barrel length I'm using and it works really well.

[Droppin Deuces]

Wow, very good info. Thanks for the in-depth response!

I went out today and had pretty darned good results with Varget(lowered it by .3 grain below the book's suggestion) and came up with several 3/4" groups, and was also striking a 4" swinger at 415 yards very consistently. I hadn't tried shooting that far with my previous loads, but these results seem pretty good to me. Other than me, I think my scope is my gun's biggest limitation right now(3-9x with 1/2" clicks).

Can't wait to work up some more rounds and see what happens!

[vacaman]

I always was taught you should pick a powder\load that will complete it's BURN before the Bullet exits the Barrel...so while Divernhunter may get good results with the same powders, did he use less powder?

I mean it makes sense...what good would the powder load do if it is still expanding after the bullet exits the muzzle??

[Droppin Deuces]

I've been having good results with Varget the past few outings. It has taken me out to 600 yards and beyond with some very consistent results(even out to 885 with some big holdover) packed behind Sierra 69 HPBT. I also notice that it gives a noticeably softer recoil than BL-C(2).

I just ordered 8lbs of 4198 to see how that compares to Varget. I still have it stuck in my head that a faster burning powder will give me better results in a shorter(16") barrel. I guess we'll see how that works out. If nothing else, I'll have a lot of powder to build plinking rounds for my standard AR.

[sonnyt650]

Look over the famous pressure chart for an AR on ar15barrels.com which show a peak that quickly decays before the carbine gas port, followed by a slower decay. Due to the laws of physics (thermodynamics?) I don't think the shape of that curve can vary much. All powders are limited by the peak pressure, just that peak will be earlier and narrower or later and wider. It's the volume underneath that determines the velocity of the bullet where ideally you want a powder that's quick to start up the peak and right before the gas port it drops off significantly -- again might be against the laws of physics. Since for that diagram the peak dies within a handful of inches from the chamber and there's quite a bit of barrel left, I think you won't get any better loads than what the factory provides for their 24" barrels. I'm guessing that faster powder just means that peak that died so long ago decayed faster too.

[TMC]

If your goal is produce the same velocity with a given powder/bullet out of a shorter barrel you will need increase the powder charge, not decrease it.

A given load will go slower out of a shorter barrel compared to a longer one because there is less time for the gas presser to accelerate the bullet.

Its an easy test, take any load and two rifles with different barrel lengths, say a 16 and 20 and shoot them over a chronograph, you will see it instantly.

[Droppin Deuces]

If your goal is produce the same velocity with a given powder/bullet out of a shorter barrel you will need increase the powder charge, not decrease it.

A given load will go slower out of a shorter barrel compared to a longer one because there is less time for the gas presser to accelerate the bullet.

Its an easy test, take any load and two rifles with different barrel lengths, say a 16 and 20 and shoot them over a chronograph, you will see it instantly.

This I understand. What I was wondering was whether or not a normal charge tested in a 24" barrel amounted to wasted powder in a 16" barrel.
But sonnyt650's response more or less answered that for me.