18" 7mm SAUM twist rate

HydroCarbon

Member
Joined
Mar 28, 2011
Messages
16
Location
Douglas, Wyoming
I'm really wanting to do a short barreled 7saum. I'm not just sure what twist rate to go with, my plan is to shoot 162 - 175gr bullets. I've read a bunch of different threads on here, as well as, rokslide, accurate shooter, snipers hide and others. What I'm finding is that none of these really talk about short barrels. When I do a twist rate calculator, a 1-9 or 1-9.5 twist is the answer. I'm thinking a 1-8 will fit the bill.

Here's my thought process:
  • 18" barrel, minus 2.5 for the shank, leaves 15.5'' to get the bullet spinning
    • 1-9 twist: 1 and a little over 2/3rds of rotation in the barrel
    • 1-8 twist: almost 2 full twists before leaving the barrel
Here's my plan:
  • Tikka T3X action
  • Mesa Altitude stock
  • CarbonSix 18" Sendaro barrel
  • New Bottom metal
Am I right in this line of thinking, do I go 1-8 or what?
Thank you for your input!
 

grouse

Well-Known Member
LRH Team Member
Joined
Oct 15, 2010
Messages
2,604
Location
Outside
I don’t think you can go wrong with a little faster twist. It won’t hurt anything. I’m interested to see how this build goes. Good luck.
 

jebel

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Joined
Jun 15, 2018
Messages
340
Location
Oregon
The bullet will be spun to the engraved rifling rate no matter the length of your barrel. Focus on the particular bullets you want to shoot and the rate they require to be stabilized, not the barrel length.

You mention the weight class of bullets you prefer, but not the particular bullets. Something around 1:9 is likely good for Berger and Hornady bullets in the 162-175 weight range. You’d need faster for some heavier than that range. Hammer Hunters or Absolute Hammers in the 155gr class would need 1:8.5.
 

Ksduckhntr

Well-Known Member
Joined
Jun 18, 2017
Messages
272
I’m building the exact same rifle and went with 1/8. I don’t plan to shoot anything above the 170 range but what does it hurt to have a little faster twist.
 

Buttermilk

Well-Known Member
Joined
Dec 19, 2005
Messages
673
Location
Good Ol' Oklahoma
I’ve got a 17.5” bbl with a 1:9” twist in my 7mm RSAUM.
If I were to do another it would likely have a faster twist. I’d probably do something in the 8.5” range even if I only shot 162-168 gr bullets. If I were to shoot 175-195, I would go faster.

The Berger stability calculator will help you decide a good twist rate.

I get 2830 to 2850 fps with 162-168 gr bullets from my 17.5” barrel.
 
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