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300 Win Mag Twist Rate Requirement

CRT2

LTC (ret)
Full Member
Minuteman
  • Jul 7, 2013
    940
    685
    Punta Gorda, FL
    Rifle: AI AXMC 300 Win Mag. Ammunition: 230 gr Berger Target Hybrid at 2826 fps (lightest bullet used is 200 gr Hornady ELD X). Per Berger the 230 gr Target Hybrid requires a 1/9.5 twist rate. I shoot in temperatures from 20 degrees - 95 degrees Fahrenheit and elevation is 1200 feet. Is there a down side going from a 1/10 twist to 1/9 or 1/9.5 twist?
     
    I formerly shot 240 Sierra match kings in a 9 twist. Been shooting 210 Berger and JLK vld bullets in the 9 twist barrels with absolutely no problems to a mile.
    To me, there is no downside.
    The few 230 hybrids I shot, shot much better than the 240 Sierras, and have a slight edge on the 210's especially going through transonic.
    If you ask why I'm not shooting hybrids now ? Gotta shoot up the stash of vld's first, and the rifles are throated for them.

    Best to you.
     
    I shoot my AXMC with a 26in 1-10 using the 215 Hybrids out to 1980 yards with very good accuracy. The temp range for me is 40 to 115 degrees and about 700 feet. If i were to go to the 230 Hybrids i would go 1-8.5 maybe 1-9 to get the spin rate on the bullet for for the transition though transonic.
     
    I shoot Berger 230 Tactical Hybrids in a 300 Win Mag, Bartlein 1:9. Stable at 1k. Formerly shot 240 SMK, Bergers are more consistent.
     
    I shoot Berger 230 Tactical Hybrids in a 300 Win Mag, Bartlein 1:9. Stable at 1k. Formerly shot 240 SMK, Bergers are more consistent.

    Berger 230 Tactical Hybrids are stable from a 1/10 twist at 2825 fps per the Berger twist-rate -calculator. The 230 Target Hybrids are not. Per Berger, the 230 gr Target Hybrids have a BC of .368 G7. However, at 20 degrees and with a 1/10 twist the adjusted BC is .348.

    Don't want to do a lot of testing and find that I should have replaced the 1/10 twist with a 1/9 to achieve long range stability - beyond 1000 yards.

    Your experience seems to support the 1/9 and I'm probably going with Bartlein - regardless the wait time.
     
    Would there be a disadvantage to using an faster twist rate for these heavier bullets, say, 1/8 or 1/7?

    Bullets start with no motion and accelerate to a forward motion and rotational velocity. Empirically, once the necessary RPM is reached there is little or no value to exceeding it and there are risks. Shorter twist causes higher RPM so requires more energy and it will take higher pressure to get there. Overspun bullets may fragment after leaving the barrel - see reports about self-disassembling 22-cal bullets when fired at more than 4k fps. There are formulas for estimating the necessary RPM. For 230/240 grain 30-cal bullets, those formulas tell us that 1:10 is marginal, 1:9 is good, and faster than 1:9 is not necessary. I do not recall ever seeing a 30-cal 1:7 barrel - based on available bullets I would expect little demand for them.

    quick google here and twist estimator here
     
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    Chandler Brothers (Col. Ret. USMC, Norman),(in 762), Crane, (in 338L), and some others tried it, short barrel fast twist, trying to make rotational twist overcome loss of velocity from short barrels.
    Attempt was to make a short handy SWS for several reasons. About the same time as Nick making his Desert Tactical bullpup.

    The short fast twist barrels suffered from varying barrel quality, one did fine, one didnt. And they ran into needing a special loading, that pressured correctly and burned all the powder in the barrel.
    The pressure issue to get the velocity created problems that blew up a few test guns, and field testing in 120-130° temps made it worse.
    Kinda ended the experiment for then. The experiment did continue with gain twist barrels, but, jury is still out.

    The Accurate Rifle magazine had several write ups on it, Snipershide had a few topics on it pre-Scout, and it's far enough in the past, they are pretty hard to find.

    The most current and lasting use of fast twist short barrels is the 8 twist shorties in 300 Blackout, there may be more, cant think of them this morning.

    The writer of the linked article on short barrel/fast twist isnt well thought of by many on the Hide, there are enough negative comments interspersed through here if you look hard enough. Several in the podcast post section.

    I personally like using the 9 twist in my 300 magnums, the added rotational velocity gives a little bit of edge at a mile, if the bullet jacket holds up as barrel wear and fouling starts to build. That has killed a few older Berger vld bullets for me in years gone by.

    The Hide is blessed to have people like Jim Boatwright and Alan and Dan Warner, who probably know more about barrel twist rates and results than the rest of the hide.
     
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    Stability going into transonic.

    Bullet style, shape, type seems to matter more going through and coming out into subsonic.
    My best results were with the 750 Amax in 50 cal, followed by the 300berger hybrid pointed in the 338 lapua. Doing ok with the 350 Sierra pointed in the 375.
    Still shooting 215 VLD bergers and jlk in the 300 (because I've got a ton of them), because I got stuck in the 2875 range with 230's and 240's, and the 2950 velocity with the 215 vld's has worked pretty good "so far" as long as i dont try to shoot them much past 1700. Sone days they make the mile stable, some days I dont know exactly what gremlin was out there.

    Got too many going at one time 375, 338, and 300.... the 300 gets left at home the most.
     
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    Hi,

    Here is IMO the "deal" with super fast twist rates.....

    1. The pros and cons are completely dependent on projectile; not only the type but the design.
    1A) Some brands of jacketed projectiles can take the rpms and others cannot.
    1B) Some monolithic designs can increase BC quiet significantly (Testing still in process) and other designs do not take the increased rpms.

    2. There are some projectile designs that were not intended to transition, period..so it does not matter how fast you want to twist them.
    3. There are some projectiles that are designed to be stable within not only a velocity range but a gyroscopic stability range also.

    In ELR it should be looked at more like rimfire....Build the rifle to the projectile instead of ammo to the rifle.
    If the projectile you intend to run can handle the super fast twist rates then go for it.
    If the projectile you intend to run is not designed to transition then know that going into it.


    Sincerely,
    Theis
     
    Re @THEIS above...
    1C. Some monolithic's alloys wont take the rpms either, just like a shitty jacketed bullet wont...
    ?
     
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    @mckchome
    There was another issue with the short barrel fast twist rifles not readily recognized. Its not just with sb fast twist, it's a short barrel issue.
    And that is destroying suppressors with full power military ammunition designed to produce max velocity in long barrels. The burning powder exits the short muzzle into the can, and in the 338 tests, several cans were no longer serviceable in very few rounds.
    You see responsible can makers now qualifying their cans for barrel lengths in certain calibers.

    I know, weve gotten away from the OP's original question, of the AI AXMC, and any downside, I cant see a problem with a 9 with the bullets he listed, at all, it would be my choice, all things considered.
     
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    @mckchome

    I know, weve gotten away from the OP's original question, of the AI AXMC, and any downside, I cant see a problem with a 9 with the bullets he listed, at all, it would be my choice, all things considered.

    Information is essential to make a sound decision. Conversation with one riflesmith and he says 1/10 is good. Waiting on call from Mile High gunsmith to see if they will do it.
     
    The Berger 215 Hybrid boxes have "1-9" optimal twist rate" printed on them. I would follow their advice, they probably know a thing or two about bullets and twist rates.
     
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    The Berger 215 Hybrid boxes have "1-9" optimal twist rate" printed on them. I would follow their advice, they probably know a thing or two about bullets and twist rates.
    Yeah, I doubt Bryan Litz's knowledge base on this subject is overshadowed by any gunsmith on earth......
     
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    He has also exaggerated BCs on some bullets he was promoting.
    And promoted the 1-8 twist on 308s which hasnt quite worked out.
     
    He has also exaggerated BCs on some bullets he was promoting.
    And promoted the 1-8 twist on 308s which hasnt quite worked out.
    I don't remember saying he's perfect or never makes mistakes.

    I have no idea who you are or what your professional experience and qualifications are. I do know who Bryan Litz is (personally) and I know what his professional experience and qualifications are.

    Guess who I'm listening to on ballistics.
     
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    Hey smart guy I didnt offer you any advice on ballistics or share any govt test data with you so why dont you tone down your little flamer attitude.
     
    Hey smart guy I didnt offer you any advice on ballistics or share any govt test data with you so why dont you tone down your little flamer attitude.
    So you can trash talk someone but can't take it?

    Got it
     
    Spoke to Mile High Shooting and they are expecting some 1/9 twist 300 Win Mag blanks for AI AXMC by the end of the month.
     
    I chose the Proof 9.4 twist in my 300 wm build as well. I am only planning on shooting 215 Berger’s. IMHO, that is the best do all round to kill any game animal in North America.
     
    I think in real world experience, the super fast twist rates have shown you will limit your bullets to the heavies with those twists. You will spin the jacket off the lighter bullets. If you intend on only running 215 or more, faster is probably fine but if there is a chance you run a 185 or lighter, I would be concerned abt it.
     
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    Was performing more research and found this Hornady page: https://www.hornady.com/support/ballistic-coefficient

    They show a BC increase for their 212 ELD X when using 1/7 twist versus 1/10 twist. At Mach 2.25 with 1/10 the BC is .334 G7 whereas the 1/7 is .354 G7. At Mach 2.0 it is .326 versus .345. At Mach 1.75 it is .324 versus .341. Interesting read.

    Hi,

    I would suggest reading the hyperstablization theory paper in the resources section here.
    The Hornady numbers run pretty much directly inline with the 6% increase in BC that has been shown in the recent research testing we have done.

    Sincerely,
    Theis
     
    Hi,

    I would suggest reading the hyperstablization theory paper in the resources section here.
    The Hornady numbers run pretty much directly inline with the 6% increase in BC that has been shown in the recent research testing we have done.

    Sincerely,
    Theis
    I can see it clearly now, Hornady rediscovered the "banded-BCs" like Sierra did many decades ago.:ROFLMAO::LOL:

    You got it: right in the middle(y) higher RPMs means better stability (all other factors remaining the same) lending to higher BCs
     
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    I can see it clearly now, Hornady rediscovered the "banded-BCs" like Sierra did many decades ago.:ROFLMAO::LOL:

    1547528087694.png
     
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    Hi,

    I would suggest reading the hyperstablization theory paper in the resources section here.
    The Hornady numbers run pretty much directly inline with the 6% increase in BC that has been shown in the recent research testing we have done.

    Sincerely,
    Theis

    Thank you. Interesting read. As a Helicopter Pilot I understand some of the information, as a dumb Infantryman I deduce I need a 1/6 twist to achieve hyper stability. Also caught his caveat: "I restrict my comments here to “supersonic flight” simply because I have not yet had the opportunity to study adequately the transonic and subsonic flight of rifle bullets optimized".