Powder Load and Barrel Length?

T

Tony C

New member
I hope I can pose this question well. I have been reloading pistol for 8+ years, but less than 100 rounds into rifle, and it seems like I am starting all over again. :D

My question is a pressure thing. It makes sense to me that the same levels of powder fired out of a 26" barrel would generate higher pressures in a shorter barrel.

So, I'm looking at the Hornady manual for 223 Remington, 55 grain FMJ. Looking at Varget, it says that max is 26.4 grains, giving around 3,200 FPS. Their test barrel is a 26" 1/12" twist Remington 700.

My rifle is a 16" (after flash hider) M4/AR15. We know that the same 26.4 grains giving close to 3,200 FPS out of a 26" barrel and bolt action, will give a less FPS out of my 16" barrel in a semi-automatic. But does the pressure change also? Is it greater?

Summing this up, in a shorter barrel, does the pressure increase at the same number of powder grains over a longer-barreled rifle? Can I load closer to the max as I am trying to get a faster FPS result? I'm not trying to get crazy here or push things to the limit, but I am trying to get close to the FPS results from my reloads as I do out of factory ammunition.

I do know to watch for signs of pressure in the cartridge and primer.

Thanks for your help,
Tony C.
 
It makes sense to me that the same levels of powder fired out of a 26" barrel would generate higher pressures in a shorter barrel.
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Maybe I'm not quite getting the question, but I don't think there is any 'pressure' difference regardless of barrel length. The bullet simply exits the barrel sooner when shorter, and any FPS gains are lost over something longer. The powder has more chance to burn completely in a long barrel but peak pressure should be the same.

There's certainly a port pressure difference with a carbine vs rifle length gas system, one reason why the latter has less felt recoil. The bolt simply pushes back with less force.

If you're trying to get a 55gr pill to hustle along at 3,200fps out of a 16" barrel, good luck. Mine run about 2800fps.
 
Chris in VA

Chris, thanks.

No, with American Eagle 5.56 I'm getting an avg. of 2,880 fps and my first reloads of 24.0 grains of Varget and 55 grain FMJ bullets, gave me 2,588. I just want to get closer to the 2,800 without causing pressure issues.
 
The max pressure in any cartridge will be within a few inches, probably less, of when the bullet leaves the case. The velocity will continue to increase until you get to some impractical barrel length. There's no way to "make up" for barrel length without dangerously increasing pressure.
 
"...a 26" barrel would generate higher pressures in a shorter barrel..." The barrel doesn't generate anything. The pressure is chamber pressure. The only difference between a 26" barrel and a 16" is the muzzle velocity. 10 more inches to spin the bullet and have it pushed by the expanding gases.
"...You are below the "starting load."..." Not according to Hodgdon. 25.5 of Varget is the start load for a 55 grain jacketed. 27.5(compressed) is max. Compressed is nothing to worry about. Mind you, Tony C does need to work up the load.
 
Jim Watson / T. O'Heir

When you say I'm below the starting load, you are choosing only the highest of the three loads for 55 grain bullets on the Hodgdon website and none of which matches the bullets I am using. My bullet is a FMJ w/cannelure. You are starting with, what appears to be the Speer Spitzer Softpoint w/o cannelure.

The Hornday manual says that Varget, when using a 55 grain FMJ w/Cannelure has a starting load of 22.8 grains and a max load of 26.4. This puts me smack in the middle of the load data.

So why did you choose the starting load of 25.5 grains? When the data varies so much from manual to manual to website, how did you decide to start with the largest starting load?

Thanks
 
Back to the original question.
The chamber pressure will basically be the same regardless of barrel length BUT the pressure has longer to act on the bullet in a longer barrel. Hence, the higher velocity from a longer barrel.
Very small cases MAY actually show lower velocities from longer barrels vs/ shorter barrels simply because the powder doesn't produce enough gas to continue to accelerate the bullet in the longer bore. 22 rimfire is an example of this.
Regarding the variation in published data: Each barrel, bullet type, and powder lot is slightly different. Data collected from test barrels is going to be different from your particular barrel as is the results from your particular lot of powder. The idea of start loads is beginning at a level deemed safe and working up to a level determined to be safe or adequate by the loader. Using multiple sources allows some wiggle room. I keep a minimum of 2 current manuals-one from my favorite bullet manufacturer and a Lyman.
 
Barrel length will not make any difference in powder choice. The load that shows best speed from a 26" barrel will also be the fastest from a 16" barrel. It will be slower in the 16" barrel. Not because it generates less pressure, but because the pressure has less time to accelerate the bullet before it leaves the muzzle.
 
Tony C,

The Hodgdon manual usually runs loads at lower pressures than the powder company numbers. Just not always. It has to do with how the loads are worked up. The powder company uses a pressure test barrel all the way. Hornady uses commercial arms, then has the highest loads they limit themselves to tested to be sure they don't exceed the SAAMI maximum. The testing is expensive work, so it is avoided where possible.

I consider Varget on the slow side for a 55 grain bullet. It's happier with 69 grain match bullets and heavier, IME, and is better in the .308 than in the .223, IME. Take a look at Reloader 10X for 55's. You could use H335, which is canister grade WC844, the military 5.56 ball powder.

As stated previously, the pressure in the barrel peaks when the bullet is only about two inches down the tube, beyond which point the final length of the barrel isn't a pressure factor, so there is no pressure difference due to barrel length unless the barrel is shorter than 2".

Barrel%20Length%20Velocity%20Approximation_zpsvmsocp0k.gif
 
So why did you choose the starting load of 25.5 grains? When the data varies so much from manual to manual to website, how did you decide to start with the largest starting load?
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Tony,

I chose that load not because it was the highest but because it was for a conventional cup and core bullet most nearly similar to your Hornady. The other two 55 gr bullets they showed were the Sinterfire frangible and the Barnes TSX solid copper, which do not behave the same in the barrel.

Unclenick may "consider Varget on the slow side for a 55 grain bullet" but among Hodgdon powders it gives the highest velocity at maximum.
That may not make the powder happy but it would make me happy if I were trying to squeeze the most out of a carbine.

Unclenick,

Hodgdon is definitely a "powder company" even if only a repackager and distributor. Do they not do their own ballistic testing with standard lab gear? Or do they get their figures from the actual manufacturers?
 
Very small cases MAY actually show lower velocities from longer barrels vs/ shorter barrels simply because the powder doesn't produce enough gas to continue to accelerate the bullet in the longer bore. 22 rimfire is an example of this.
Click to expand...

Slightly off topic, but I seem to remember that a long time ago Remington was advertising their new Nylon 66 .22 long rifle semiautomatic as having a 19 5/8 inch barrel which was the "optimal" barrel lenght for that cartridge. They said anything longer and the bullet was actually beginning to slow down.

Not sure if true. Uncle Nick can probably answer.
 
Jim Watson said:
Hodgdon is definitely a "powder company" even if only a repackager and distributor. Do they not do their own ballistic testing with standard lab gear? Or do they get their figures from the actual manufacturers?
Click to expand...

This is actually at the heart of a dispute. You may have noticed that over the last few years all the Winchester powder data for powders that Hodgdon does not duplicate under one of their own names, has disappeared from Hodgdon's load data site. The Winchester powders that are the same as some Hodgdon powder still have data up (i.e., 231/HP38, 296/H110, 790/H414). That's because Hodgdon is packaging the same lots of both in the same containers so the pressure/velocity testing they have done for their powder then applies to both. But when Hodgdon took on the distribution of the Winchester brand, Winchester's brand owners agreed to keep up the pressure testing on their other powders and have not held up their end of that bargain. Thus, per their upgraded QC system, Hodgdon no longer considers the old test data current enough to continue taking on the liability involved with publishing loads based on it.

AFAIK, all the testing is contracted out. I once asked Hodgdon for a specific set of powder characteristics and got asked if I had any idea what it costs to have a lab characterize a powder completely. About $50K, according to the fellow I spoke with. So, no, they don't do that. They just have burn rate tests run to control the canister grade powder they package to ±3%. All of that is contracted out.

OTOH, Hodgdon lists only a starting load and a maximum load as fired from a standard test barrel in a universal receiver for most of their data. That means two test sets of ten each per load, unless an unexpected result occurs and a redux is required. This is unlike Hornady or Sierra who list a pile of loads for different velocities as fired from a production gun, and who list the same load for a variety of bullets of the same weight, none of which is likely to pan out very exactly. AFAIK, they only send their max loads out for pressure validation.


Mkl,

According to Geoffry Kolbe, depending on the particular loading, .22 LR stops accelerating somewhere between 16-19 inches down the tube. It's expansion ratio is very large. However, the loss of velocity immediately beyond that length is slow, so it seems more like extra length beyond 19 or 20 inches just isn't giving you added velocity. The fact it gives you a longer iron sight radius can be helpful, though.
 
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