Twist rate for 338lm

[cudby]

Hi Everybody,


A question about twist rate:
I will be buying a 32" Barrel for my AIAW 338 Lapua M. and will be shooting Lapua Scenar 300 grs bullets. The goal is to hit a plus 2 KM (1,24 Mil).

The normal approach would be to go 1:10 in twist rate since that is recommended by the bullet manufactur on the bullets reloading guidance however; Bryan Litz recommend 1:11 in order to achieve a SG of 1,5.

So the question is; what speaks for getting a higher SG then 1,5?

I know that the BC G7 will benefit a 0.001 for each 0.1 the BC G7 goes higher than a SG of 1.5 according to Bryan Litz.

I was hoping someone in here would know if there are any valid data supporting getting an even higher SG than 1,5 when passing though transonic and flying in subsonic.

Hope you all will help me out, if you have any qualified knowledge on this.

Br
Christian
(from Denmark)

 

[Emouse]

Diver makes sense on this,...in essence, go out and shoot and collect real world data on your load and rifle at distance. Litz too acknowledges that shooting a faster than prescribed twist most likely will not do any harm with premium bullets. 9.35 twist is very specific and unless your using a cut or hammered barrel it just will not not be that exact. matter not if its a 9 or .35 more,...it will work fine.

Stress less on the transonic dynamic at this point and just go shoot to collect data. If your hitting a 2k your doing pretty damn fine in any case.

 

[cudby]

Currently I am shooting the standard AI barrel of 27" with 1:11 and my longest hit was at 1.710 meters (1.062 miles) with the 300 grs Lapua Scenar bullet. I would like my next barrel to have 32" and therefore just want to explore the what twist are best suited for this bullet?

(I know that AI are going with 1 : 9,35 now but that seems tight for the Lapua Scenar 300 grs bullet... but does it serve this bullet anything additional ... I don't know)

 

[Fursniper]

I'm in the process of Fireforming cases in my 338LM improved, a 32" Krieger with 9.3 twist. Shooting 300 bergers in a unformed case within an improved chamber I'm still getting sub moa groups and the barrel is not broken in yet (30 rounds). The 300 grainers seem to do fine with this faster twist especially considering the big void in the chamber that the brass shoulder & body is having to conform to during fireforming. I wasn't sure what to expect but so far I'm pretty pleased. I think this bodes well for what to expect when I can actually shoot a case that's shaped to the chamber (waiting on Whidden for my Ackley Improved dies).

 

[GIXXER2000]

I am shooting an AI-PSR Tooley 27in 1-9.3 M-40 Bartlein barrel. Getting 2730 fps with 300 Hybrids. My longest hit so far in 2445 yards on my 2nd shot. I was able to see bullet splash and 2825 yards but the light changed after the 2nd shot so never saw the other 3 shots. I am going to shoot the Tonopah 2 mile.

 

[Hoffer]

In my DA 25iHg for an example: My 38's, "projected" turbulent free subsonic air is near 4,200y and by then the CEP is and has gone all to hell.... That is way, way before I might be out of the transonic zone and it's effects.

What FPS are you projecting your turbulent free subsonic zone at?

 

[Fursniper]

Shooting my improved LM out to 2500 yards with 277 grainer solids in my 9.3 twist now with fireformed cases. Velocity is right at 3000fps, that puts me right at 25.1 mils with a DA of 8200. So far in calm air at a 36" target hitting 3 out of 5. Would like to improve on that but just not sure on the consistancy yet. I've seen a few bullets fall way short with the same hold, not sure what that's about yet but it's been fun trying to run it against the bigger guns...

 

[TripleBull]

I've taken the Scenar 250 grain out past a mile. That's into transonic - actually a bit into the subsonic. I get a muzzle velocity of about 3050 and see what I consider to be predictable ballistics to 1600 yards. At a mile, I need a little over a half mil more elevation than predicted by my app. My barrel is 10 twist, 28" and we shoot at 5000' ASL. I'm about to start loading 300 Bergers. It will be interesting to see how much their higher BC will yield for my gun.