Gunsmithing 308 combo barrel supersonic and subsonic

[KCAK]

I am new to the form and have really enjoyed the posts and information presented here. I have a question about barrel twists. my friend has a Rem 700 AAC-SD with the 1 in 10 twist. We were able to load up 180 grain Hornady SP subsonic with Trail Boss. I see that many people have done that combo succesfull here on the form. We also tried the 220 grain Hornady Sp but were not able to see stable flight. My question is what twist will reliably stablize 220 grain round nose bullets, and still be safe to shoot standard match ammo (175 smk @2650 fps ) at supersonic speed. I have a BAT ACTION model HRPIC. Its a switch barrel gun. I have 2 barrels for it now. 280 rem 28" long 1 in 9 twist # 6 and a 243 28" long 1 in 8 twist #6. I have thoughts of 2 more barrels i want to build for it. 30.06 24" 1 in 9.5 twist. that one is set in stone. the other one i am not sure about. i want a 308 about 18" that will shoot 220 round nose subsonic and be able to use standard match ammo interchangably. I have been told that 1 in 8 twist would be to fast for this purpose. Excesive CUP presure ect. I have heard of 1 in 9.3 twist barrels for fast 338 bullets (300 grain SMK ) What about 1 in 9 twist for a 308. Any thoughts would help. thanks

 

[bohem]

Re: 308 combo barrel supersonic and subsonic

I have an 8.5tw 308 that shoots in the 0.3's from a 10.2lb hunting rifle. It handles 168-208 Amax's at supersonic speeds with no issue. I've shot subsonic 240 SMK's and 250RNFP cast from it no issue.

Cold weather subsonic testing was done at -930' DA and there was ample stability.

The 308 doesn't have enough snot to "blow up" 155+gr bullets from that twist rate.