Anyone ever do 1:9 308 finished at 20" ? How do they shoot?
Gunsmithing 1: 9 twist 308
- Thread starter Grizzly23
- Start date
Did someone give you a bbl? Why would you unless you were shooting heavies subsonic? 308 is challenged enough with a 10 or 12 twist;-)
I wouldnt go more then a 1:10 on a 308 for shooting 168-200gr bullets, Sub sonics with a heavy 240 a 1:8 works well. It all depends on what bullet you want to shoot.
Casey
Casey
I'm shooting a 1: 10 now but having new bbl made they don't do 1:10
I'm also going to shoot 175 & 178 gr most so I guess 1:12 is it I should also say it will be 20 in .
We've done lots of 8 twists in 16-20" 308's specifically for shooting subsonic 308. It runs full speed, and subsonic 220SMK's amazingly well. The factory twist on DTA covert 308's we sell are all 1:8.
No gas systems. Bolt guns.
This is not exactly answering your question:
Southern Precision Rifles (fantastic but hyper busy folks) built a trued Rem 700 with stainless Brux 1:8 cut to 27in on it. It shoots 1/2 MOA at 200 yards with factory Hornday 178 Superformance, surplus Lake City LR 175's. Hand loaded Lapua Scenar L 175's and Lapua Scenar 185's shoot 1/4 MOA; and of course factory Lapua 200gr sub-sonic all land in a 3in circle at 100 yards.
Southern Precision Rifles (fantastic but hyper busy folks) built a trued Rem 700 with stainless Brux 1:8 cut to 27in on it. It shoots 1/2 MOA at 200 yards with factory Hornday 178 Superformance, surplus Lake City LR 175's. Hand loaded Lapua Scenar L 175's and Lapua Scenar 185's shoot 1/4 MOA; and of course factory Lapua 200gr sub-sonic all land in a 3in circle at 100 yards.
Long barrels aren't conducive to subsonic accuracy. The DTA barrels we've sold and made around 16-18" produce sub-MOA with subs. A really bad group is about 1.25 MOA. Not sure why, but longer barrels don't play well with sub loads.
Long barrels and slower bullets exaggerate bad form usually is the problem. Long dwell time.
That's the reason my 22 trainer has a 26" barrel. It makes my mistakes look worse on paper so it's easier to see and correct them
While I agree, I believe there is a lot more to it than that. I spend a lot of time chasing rimfire accuracy, so I know all about how difficult it can be... yet going from a long barrel to a shorter barrel in smallbore benchrest doesn't seem to make a 2-3MOA difference in accuracy. There's a powder burn rate thing, or bullet friction thing going on there with the longer tubes. I ran out of analytical equipment capability to find what it was specifically, but I am quite positive it was not simply bad form.
I agree. I was just suggesting part of the equation.
My WAG is the muzzle exit pressure becomes inconsistent with a long barrel. All the powder is burned, with chamber pressure is dropping bullet friction is becoming a greater component, so you get inconsistent exit timing (dropping out of the node).
That's what I've read from others that seemed to have a stronger grasp on the physics of internal ballistics than I. Seemed logical!
Great info, was looking at some solid copper bullet and need that twist: GS CUSTOM BULLETS - 308197SP204 Technical Data
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