.308 Short Barrel (16") loads for semi auto

[tlend]

Looking for some experience out there! I've loaded lots of .308, but only for bolt rifles. My new endeavor is reloads for a 16" barrel M1A. None of my manuals list a 16" barrel, and the shortest mentioned is a 22". I know I should expect a velocity drop, but what ball park am I looking for? I have about 800 surplus .308 144gr bullets that I want to use up and figured this would be a good opportunity. I don't know what else to use them for so I figured I'd make some plinking ammo. (I've never actually heard of 144 gr, but I weighed several of them, and they were between 142.8 and 144.3. They were packaged in a large plastic bag and sealed, no other markings)

The data I was looking at shows about 2600/2650fps for a 22" barrel semi auto. What would that correspond to in a 16"? I'm using IMR 4895 and just looking for some plinking stuff. I'm trying to do as much work on the front end as possible before actually making a round, so whatever input you have is appreciated.

 

[ILikeLead]

Go read this short article and it will give you some guidance...especially last section.

http://www.chuckhawks.com/rifle_barrel.htm



I once saw an experiment where these fellas took pistol calibers and long barrels and chronographed bullets as they cut off one inch at a time. But that was for pistol calibers.

 

[Bwana John]

Try a slightly faster powder for shorter barrel length.

 

[cheygriz]

Hodgdon BL-C #2, or H-335. Regardless of barrel length.

 

[JASmith]

Looking for some experience out there! I've loaded lots of .308, but only for bolt rifles. My new endeavor is reloads for a 16" barrel M1A. None of my manuals list a 16" barrel, and the shortest mentioned is a 22". I know I should expect a velocity drop, but what ball park am I looking for? I have about 800 surplus .308 144gr bullets that I want to use up and figured this would be a good opportunity. I don't know what else to use them for so I figured I'd make some plinking ammo. (I've never actually heard of 144 gr, but I weighed several of them, and they were between 142.8 and 144.3. They were packaged in a large plastic bag and sealed, no other markings)

The data I was looking at shows about 2600/2650fps for a 22" barrel semi auto. What would that correspond to in a 16"? I'm using IMR 4895 and just looking for some plinking stuff. I'm trying to do as much work on the front end as possible before actually making a round, so whatever input you have is appreciated.

I just posted a velocity estimator that might help: http://shootersnotes.com/applications/velocity-estimator/

The case volume isn't always readily available in the reloading references. For the .308 Winchester, try 55.8 grs of water and a case length of 2.015 inches.

You will also need to enter a reference load that uses the same powder but with a charge weight equal to or greater than the one you use in your load. Same for the bullet, it will need to be the same weight or heavier than the one you use and more likely even better if its the same brand. Barrel length for reference load is needed along with your barrel length.

Let me know how it goes!

Thanks!

 

[tlend]

awesome information, especially the on-line velocity estimator from JASmith. I didn't even consider a faster powder, I just assumed IMR4895 for M1A. Thank you all! I'll post range results when I get out there again.

 

[41 Mag]

I shoot a Ruger Compact 308 bolt action that has a 16.5" barrel. I have used the Hodgdon pistol data for loads since they are for a 15" barrel. It might be a good place to look for powders that might not be listed in the standard rifle loads and the velocities are pretty close to what I can expect as well.

The one thing you still need to consider with the auto is the pressure curve, I don't know just how they might effect your M1A since I have no experience with BLC-2 or H-335 in an auto loader. I do know neither shot as good as H-4895 or RL-15 from my rifle. I would look into anyway before I loaded up a bunch and messed up my rifle. Of course the powders I have used might not work well in it either.

 

[tlend]

Range Report/Follow up

Well I borrowed some data from about 10 different sources, and THR members were so helpful I wanted to follow up with my results.

Rifle:
Springfield M1A Socom II with a 16" barrel

The load development:

I started by chronographing Factory ammo out of the short barrel to see where it measured vs. posted factory velocity. My biggest problem was finding data specific to semi-auto/short barrel firearms since I knew it would have different results than the .308 bolt action with a 24" barrel (duh!)

Ideally, I would have used the same bullet weight, but since I stopped by the gun store on the way to the range I was stuck with what they had.

I used Hornady 168gr TAP which had a factory posted velocity of 2700fps. I chrono'd 10 rounds and found the average velocity out of my firearm was 2475fps.

Armed with this data I returned home with some sense of expectations for my own handloads (but with a much lighter bullet). I used data from a web site posted by JASmith (post #5) and figured I could expect at least a 200 fps drop from posted load data. I knew I wanted to start conservative and worked out a starting load of 41.5gr of IMR4895 behind the 144gr FMJ. Posted velocity indicated 2500fps which is a comfortable mid-range load.

When I got to the range, the load chrono'd avg 2255fps with ES of 44 and they printed low on the target (at 100 yds). I kept raising my load by 1.0gr and played around with a couple until I worked up to 44.0gr of IMR 4895. That load behind a 144gr FMJ shot a 2 in group at 100 yds with open sights and had an avg velocity of 2530fps. I'm sure the rifle is capable of better grouping than that, but I'm not. No signs of overpressure and the rounds were very comfortable/low recoil. Of course I could push that little bullet a lot faster, even out of such a short barrel, but I had to ask myself..... Why? They hit where I was aiming with plenty power to knockdown anything I'll ever point it at. And I don't anticipate using it beyond 100 yds anytime soon. If I do, I'll work up a new load

Anyway, thanks for everyone's help, its been a blast! Can't wait to start something else after I load a few hundred of these and get em all stripped up.

 

[SilentVectorX]

WHOA! 2" with a stock SOCOM is already really impressive. I also own a SOCOM II and am trying to find good loads for it, but I'm currently limited by those bloated CQB irons.

What is the filled-to-overflow capacity of a fired case? QuickLoad would be more accurate with a measured value rather than a guess.

 

[JASmith]

Are you looking for the nominal case capacity, or the case capacity for your rifle?

If the first, QL already has that in the database. If the second, one will need to measure.

And yes, it will make a difference, but that difference will be trumped by a good chronograph session with enough repetitions that you have understand the variability of your loads.

The average and standard deviation will tell you how far the estimators are from target. If within one standard deviation, very little complaints are needed. If more than 3 standard deviations out, should start looking at tweaking the calculations and double checking your input.

(E. g., plus or minus 50 ft/sec is most likely a normal difference between the prediction and the measured average.)

 

[rcmodel]

Try a slightly faster powder for shorter barrel length.

I didn't even consider a faster powder,

Nor should you consider it.

Whatever powder gives the highest velocity in a long barrel will also give the highest velocity in a short barrel.

The only differance you might note by using faster powder would be less muzzle blast, and less velocity.

rc

 

[JASmith]

...The only differance you might note by using faster powder would be less muzzle blast, and less velocity.
rc

RC makes a good point.

One of the nice features of QuickLoad is that it makes a nice printout of velocity vs barrel length. I have in fact used that feature in a short study of how to minimize muzzle blast in a pistol-length .223, but wasn't in a position to verify with real tests...

 

[zeke]

Recently bought a used socom. Apparently not used very much. Got a HUGE accuracy improvement by checking , then recutting the muzzle crown.