Load development for shorter barrel ?

[Scatt_Nasty]

Recently had the Savage .308 cut to 18 inches with a brake. Prior to the cut it could toss 42.5 gr (4064) 168 SMK's sub .5 MOA and the 175's on top of 43. gr .8 MOA.

Now I'm lucky if I get 1 MOA out of the 43 gr 175's.

Anyone notice accuracy loss with a chop or have any advice on some 175gr loads for a short barrel ?

 

[Fred_C_Dobbs]

Re: Load development for shorter barrel ?

The "conventional wisdom" is that the shorter barrel should be more accurate because its relative stiffness is higher than a longer barrel with the same profile. Maybe you just need to adjust your charge. What was the original barrel length?

 

[Scatt_Nasty]

Re: Load development for shorter barrel ?

Original length was 24 inches.

 

[Greg Langelius *]

Re: Load development for shorter barrel ?

When you alter the barrel's length, you also alter its harmonics, and load development needs to be repeated for the new length.

Greg

 

[RobertB]

Re: Load development for shorter barrel ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">When you alter the barrel's length, you also alter its harmonics, and load development needs to be repeated for the new length.

Greg </div></div> This is the truth. Work up a new load and if the smith did a good job you should be fine.

 

[Fred_C_Dobbs]

Re: Load development for shorter barrel ?

FYCN, is it possible you swapped the charges when you listed them in the OP; that you're really loading 43gr with the 168 and 42.5 with the 175? I ask because I'm looking at your barrel times in QuickLoad and it makes more sense (to me, anyway) if I swap the charges. Swapped, your barrel times match to within 0.006 ms. As you listed them, they're separated by 0.61 ms.

Anyway, I also looked at the barrel times with the barrel cut back to 18". Here's the charges QuickLoad/Optimum Barrel Time predicts:

The faster accuracy node:
168gr SMK (0.9886/0.988) 43.7gr - 55.6K psi - 2519 fps
The slower accuracy node:
168gr SMK (1.0774/1.076) 41.1gr - 46.4K psi - 2371 fps

The faster accuracy node:
175gr SMK (0.9886/0.989) 43.3gr - 58.1K psi - 2498 fps
The slower accuracy node:
175gr SMK (1.0774/1.077) 40.7gr - 48.2K psi - 2351 fps

The first number in parenthesis is the OBT-predicted accuracy node (in thousandths of a second). The second number is QL's predicted barrel time for that charge weight. QL/OBT has to be tweaked for factors like actual case capacity and seating depth -- which I obviously didn't do in this case -- but I find it's normally within a tenth or two of a sweet spot.

 

[Scatt_Nasty]

Re: Load development for shorter barrel ?

thanks for the replies. I will work up a new load.