18" 7mm SAUM twist rate

[HydroCarbon]

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]

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]

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.

 

[Corvalliscory]

1in8 and be done as long as you don't plan on shooting anything crazy...

 

[HydroCarbon]

Thanks for all of your input, I appreciate it. I plan on starting out with Berger's and ELD-X.

 

[Aoudad shooter1975]

1-8...no doubt...

 

[Ksduckhntr]

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.

 

[North Idaho Hunter]

1-8 all the way, I have seen no ill effects going 1-8 in 7's running 160 class bullets. I would much rather over stabilize then under!

 

[FrogFire7]

I always go fast twist... there is no down side!

 

[Elk Hunter 338]

built tons with 8 twist.. guys are hammering the 180 hybrids out of them!!

 

[Buttermilk]

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.

 

[HydroCarbon]

Gonna go with 1:8. Thanks all for the help! The Berger Stability Calculator is a cool tool. I'll keep you guys posted.

 

[Kimber7man]

For those that have used them: is the 180 hybrid as reliable as the 215 hybrid for elk? And how does the 180 compare to the 175 elite hunter? Thanks

 

[Elk Hunter 338]

They're probably the best for the 284 cal!!