Quarter Bore Lovin’

[Mike D Texas]

It's somewhat dependent on how fast you plan to launch them. If you're shooting them in something like a 25 Creedmoor where the speeds could be in the 2700-2900fps range you'll likely want a 7.5tw but if you're shooting them in a 25-284, 25 PRC, 25 SAUM, 25 WSM, 257 Wby, or any other wildcat where velocities will be 3000 to as much as 3300+ then an 8tw will due.

The concern with using faster then an 8tw in things that'll launch these 3100 to 3300 or maybe even faster is the bullet RPM starts getting over 300,000 and at 300K that's when bad things start happening to bullets in flight.

I talked to Hornady and Bartlein quite a bit before I ordered my barrel and both thought an 8tw was the way to go with the 25 SAUM I'm having built to shoot the 134 ELD-M's.

Elevation would have some affect on this. I don’t know about ELDMs but 135 Bergers are marginal on stability with an 8 twist between 3000-3300fps at sea level.


If you have the opportunity I would go 7 twist and be done with it.

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[B23]

1.50 is considered fully stabilized so, for me, I can live with 1.49 but I don't think I want to chance it with bullets spinning 340,000 RPM. Also, my base elevation is nearly 2K and goes up from there. Even at 25 Creedmoor speeds the fastest twist I'd use would be 7.5tw

Also, under 1.50 doesn't mean bullets won't still shoot well, you just won't be getting the maximum BC of the bullet. I shoot Berger 75gr VLD's from a 9tw Lilja 22-6mm and per Berger's twist stability calculator my SG is 1.24 and that rifle shoots about as good as anything I have.

 

[Brandon.miller.4]

For what it's worth I shoot a 25-284 with a 7.5 twist at 2950ish and have zero issues. 133 bergers

 

[Mike D Texas]

1.50 is considered fully stabilized so, for me, I can live with 1.49 but I don't think I want to chance it with bullets spinning 340,000 RPM. Also, my base elevation is nearly 2K and goes up from there. Even at 25 Creedmoor speeds the fastest twist I'd use would be 7.5tw

Also, under 1.50 doesn't mean bullets won't still shoot well, you just won't be getting the maximum BC of the bullet. I shoot Berger 75gr VLD's from a 9tw Lilja 22-6mm and per Berger's twist stability calculator my SG is 1.24 and that rifle shoots about as good as anything I have.

Personally I’m confident that Berger Hybrid jackets are thick enough to hold up under higher RPMs.

And FWIW I have a 7 twist 22-250AI that I have successfully used 55 grain Hornady VMAX bullets at 3950fps (if my calculation is correct that’s about 409,000 rpm) with acceptable accuracy and absolutely devastating terminal results on varmints.

I’ll be using a 7 twist barrel on my 257Wby with 135 Hybrids at ~3200fps.


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[B23]

Personally I’m confident that Berger Hybrid jackets are thick enough to hold up under higher RPMs.

And FWIW I have a 7 twist 22-250AI that I have successfully used 55 grain Hornady VMAX bullets at 3950fps (if my calculation is correct that’s about 409,000 rpm) with acceptable accuracy and absolutely devastating terminal results on varmints.

I’ll be using a 7 twist barrel on my 257Wby with 135 Hybrids at ~3200fps.

The smaller shorter lighter bullets tend to handle the high RPM's a lot better than the long heavy for caliber bullets do.

 

[Steelbanger78]

Just finished my 25 SST build, thanks for the info!

 

[JordanF]

Just finished my 25 SST build, thanks for the info!

Any updates on this? I’m wanting to have A 20” proof carbon barrel made and I’m wondering what kind of velocity to expect with 134eldm’s

 

[Steelbanger78]

Im 100ish rounds in and finally started gaining some velocity. Nice groups with Staball HD but showed signs of pressure around 2850. N565 at 3000 fps has been the best so far but some more testing next weekend, with H4831sc and H1000.

 

[JordanF]

Im 100ish rounds in and finally started gaining some velocity. Nice groups with Staball HD but showed signs of pressure around 2850. N565 at 3000 fps has been the best so far but some more testing next weekend, with H4831sc and H1000.

Sounds like it’s going well! What brand and length barrel is that?

 

[Steelbanger78]

It's an OMR barrel (they use Shillen blanks I believe). Ive been super impressed with it, I've messed with some Christensen and even a couple Proof carbon barrels and got decent groups out of both once it was warmed up but it always seemed the cold bore was off, no hint of that with the OMR. Ive shot 12 rounds pretty much as far as they could be loaded with zero impact shift. 1 is a small sample size but I'd definitely try one again.