I am beginning a 7mm custom rifle build. It will be chambered in either & Rem mag or a 7mm STW. What twist rate is the best for either one? I will use 150-160 grain bullets mostly. Thanks, 163bc
I would go 1:9 twist... allows you to use pretty much anything you'd want to in 7mm.
I'll be different and say 10 for those bullet weights.
I built a custom 7 STW and had Pac Nor do the work. I sent them three dummy rounds and they throated the barrel for that length at no extra charge also, minimum spec match, non turn neck chamber.
I went with a 1-11 twist to shoot the 140 & 150g Bullets. I am getting unheard of speeds due to the slower twist rate and my groups are like a benchrest rifle.
The only reason to get a 1-9 twist is to shoot a 175g or 180g Berger.
A 1-10 twist is the proper twist for 160-168g Bullets in 7mm caliber.
You should not over look a 28" 7 Mag barrel with a minimum spec chamber, throated for the bullet you intend to shoot. 160's will be chomping on 3200 fps with Retumbo with Fed 215's. The 7 STW set up in the same mannor, will be pushing the 160's right at 3300 fps out of a 26" minimum spec chamber.
Velocity is lost with large sloppy chambers, no getting around it.
My current 7mmstw has a Shilen 1-11 twist, it shoots 160gr Partitions very well at 3300 fps with a stout dose of IMR 7828.
9 twist.A good light bullet will shoot turned over fast; but a heavy one never will turned over too slow.
With todays designs getting longer,I prefer a fast twist.
Back in the day when the 7mm Weatherby came out, it was twisted at 12 and would not stabilize 160's,only the 139 as factory loaded by Weatherby.Some custom makers did 7mm Weatherby's with a 10 twist, which worked better.
Personally, I would not want a 7mm barrel with a twist slower than a 9 twist.The more I use 7 mags, the better I like heavy bullets.
To heck w/proper or 'ideal' - I K.I.S.S.
ROT's
6/6.5mm 8
7 9
30/338 10
350 12
22s - depends, a Fireball would get a slower twist as it would be on a diet of 40-50s and possibly 55s. Anything larger would get spun proper for 75s.......
NEVER had a Bad shooting rifle, due to over spinning bullets.
Shot in the 1s and 2s using an 8t 6BR w/both 68s and 105s, what is NOT to like about that?
Other things deserve contemplating IMHO but not twist rates.
Owned a few 7mags, 150s and up shot great in 9, had no use for light weight bullets in a 7RM.
YMMV.
I`d go with a 1 in 10". I have gone slower and stayed within the twist on bullets and the rifle shot fabulous. I`m all for building a custom rifle to suit my needs and wants. The slower twist has its advantages as well as the faster, it is give and take.
I would use a 9 inch twist.
I think a 10 would work just fine with bullets in the 160 grain class.
9 all the way as far as I'm concerned.
Dober
The only time the difference between a 9 and a ten would be significant is when the ten was too slow to stabilize a given bullet. Go with a nine and this would never happen. GD
9. You WILL want to shoot heavy bullets.