Now that suppressors are becoming more common, many shooters are looking to shorten and thread the barrel on their existing .308 rifle. Shortening the barrel helps to offset the length and weight of the added silencer. But how short to cut? Barry Bass of Silencer Tech provided TGR the results of his testing.
Tempature was 49 degrees when we started and had risen to 52 when we were done. Ammunition used were factory 150 gr. American Eagle and 180 gr. Sierra with 42 gr. of Varget powder and Lapua brass. All ammo was weighed to get the closest consistency in weight for the test.
Using a CED chronograph – two shots were fired and velocity averaged:
Barrel 150 gr. 180 gr.
24” 2745 2532
23” 2732 2524
22” 2686 2481
21” 2774 2501
20” 2732 2514
19” 2701 2460
18” 2701 2445
In the past I have seen velocities do this where they will drop off and then come back higher with a shorter barrel. Harmonics – drag – sweet spot – I don’t know…..
For example, a 300 WSM 21” barrel will have a better velocity than a 24”.
On the .308 testing stopped at 18″ due to the drop in velocity. Going down to a 16″ barrel is not ideal.
The velocity dropped off on the 180 drastically. I shot another 2 to verify at the two extra shots were the same.
We also had a 16” AR10 with which we shot the same ammo and came up with 2500 with the 150 in a two shot group.
I know it will not be a 800 yard gun but I think out too 500 it will still be very good and with the 1 in 10 twist it should still be very good for subsonic loads as well (10 gr. of Trail Boss and a 180 gr. bullet).
On the project gun, we will get the crown squared and cut to 11 deg. thread and install a custom Silencer Tech suppressor on it.
We have found there is a sweet spot on every caliber:
- 223 = 18”
- 300WSM = 21”- 22”
- 22LR = 10”
- 9mm = 11”
- 308 = 20”
Different powder and bullets can change this but these barrel lengths seem legitimate. I have seen cutting one inch can make as much as 100 fps plus loss in velocity, I call that the point of no return, and I think that was fixing to happen with the 308 that is why we stopped at 18″. We noticed that the SD between shots were getting closer as well.
For custom suppressors contact Barry Bass at www.SilencerTech.com
by Mike Coker
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