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Super Fast Twist Barrels for Hammer Bullets
- Thread starter nksmfamjp
- Start date
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Now it's going to take me even longer to get my barrels if you keep sending everyone there! 
Kidding. Ken is a great guy and runs a solid outfit. I've got six of his barrels in the office right now waiting to be chambered.
I remembered reading or hearing something about the benchrest guys using the slowest twist rate possible to stabilize the bullets they were shooting. Might have even been one of Erik Cortina's interviews.
I did step up to a 1:8 for my .338 Norma since I use monos for hunting. Curious to see what it does for the 300 OTM's.
Might as well order a Borden action and Seb NEO front rest so you can really have a lot to look forward to the next year.
Mike Matteson
Well-Known Member
Watching
TXAoudadKlr
Well-Known Member
Originally to bring up subsonic bullets to the same RPM's as super sonic rounds in standard twist rates to increase stability. A side effect was the added RPMs had an increase in terminal performance of subsonic bullets. With greater wound churning with bullets like maker, Barnes and discreet ballistics bullets,
Kevin with Q used a 12.5" 1:3 barrel "Fix" in 8.6Blk to kill a Cape buffalo using a 210gr Barnes spinning 500k RPM
I, too, went with 1:8" for my .338 Thor (.338 NMI) primarily to propel the Berger 250/300, but I have not done the load development yet.
WOWZER!
We are running several platforms with 4+gains of twist. 6mm to .460, including consecutive barrel blanks with the only change being how large of a gain. The picture is a 300WM: shots 4,5,6 from a new barrel during break in. 200yd target. We came out of solids for a bit- but the Hammers look pretty worthy of trying them again.
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Let's see if we got this right... please chime in. Going from 12-8 (which we have operating). Just using simple linear values.
Using a .338cal for base line- an 8T and a 12T- a .75inch bullet contact area:
In this example the bullet will engrave by +.0105 as compared to the land width.
It will gain (+/-).0025" of width per 1" of gain over its 12inches.
If I extend that to 24inches it would be (+/-) .00125" of width per 1" of gain over the 24"
If I turn this into percentages a change of +/-17% occurs. Can that potentially translate into 17% less initial pressure? If a longer lead reduces pressure less initial twist should reduce pressure.
Anecdotal (new term I have heard describing our results) wise- our back to back comparisons have yielded more velocity on less powder- Anecdotal only and 3rd party.
A few years back at K2M John B (don't want to mis-spell a last name) a guy known for a carriage mounted 50cal- took third without a spotter. He was shooting a lighter bullet at a higher velocity than other competitors - a true outlier- with a slower twist rate comparatively speaking. Speed was used to stabilize his bullet as the bullet he was using required a book 9T (though actually 7.5T was required)- his velocity allowed him to shoot a 13T.
HARPERC
Well-Known Member
I read that previously, and wondered if it holds true across the spectrum of case capacities, and bullets.For what it's worth, Applied Ballistics did a test years ago on twist rate and its effect on muzzle velocity. Here's an excerpt of their findings:
How Muzzle Velocity Changes with Different Barrel Twist Rates « Daily Bulletin
Many barrel-makers mark the twist rate and bore dimensions on their barrel blanks. Does muzzle velocity change with faster or slower barrel twist rates? Absolutely, but much less than you might think. Faster twist rates do slow down bullets somewhat, but the speed loss is NOT that significant.bulletin.accurateshooter.com
My own thought is twist rate needs to be considered in light of end goals.
I haven't seen accuracy of hunting rifles impacted to the point of being unserviceable. BR competitors, and those chasing velocity for velocity sake, can have different needs.
For what it's worth, Applied Ballistics did a test years ago on twist rate and its effect on muzzle velocity. Here's an excerpt of their findings:
How Muzzle Velocity Changes with Different Barrel Twist Rates « Daily Bulletin
Many barrel-makers mark the twist rate and bore dimensions on their barrel blanks. Does muzzle velocity change with faster or slower barrel twist rates? Absolutely, but much less than you might think. Faster twist rates do slow down bullets somewhat, but the speed loss is NOT that significant.
While this is good data the test is done with a 308win pushing 175s 2650fps from 8-12 twist barrels.
I suspect the results would be quite a bit different if he had tested a 26Nosler or some other hot rod cartridge with hammers or light for caliber cup and core bullets that produce almost twice that velocity in the upper 4000s.
