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Barrel twist effect on bullet

 
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  #1  
Old 06-22-2006, 07:16 PM
hjl hjl is offline
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Barrel twist effect on bullet

If you have a 30 inch barrel chambered for 7mm RUM with a 1-7 twist {to use 200 gn wildcat bullets one day}.
What effect does the twist have on a 162 gn amax at 3200-3300 fps on accuracy & expansion on light game to 500 yards?
What effect does the twist have on a 140 gn nozler bt @ 3500 fps on accuracy & expansion on light game to 500 yards?
What effect does the twist have on a 120 gn nozler bt @3800-3900 fps on accuracy & expansion on light game to 500 yards?
Thank you for your replys.
Regards
hjl
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  #2  
Old 06-23-2006, 01:25 AM
 
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Re: Barrel twist effect on bullet

<font class="small">Code:</font><hr /><pre>
Vel -- Twist ---- RPM
----------------------------

3300 7 339,428
3500 7 360,000
3900 7 401,142
</pre><hr />

If you're a BR shooter, you want the slowest twist the stabilizes the bullet. For LRH it likely doesn't matter unless you spin the bullet so fast it explodes from the centripetal acceleration.

Personally I wouldn't build a custom gun for shooting ULD/heavy pills just to burn out the barrel on vermin loads. That's why I have three 300 RUMS.

If you want a BR pontification from the expert, take a look at BB on Twist
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  #3  
Old 06-23-2006, 07:06 AM
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Re: Barrel twist effect on bullet

I don't know how tough Nosler's are. But alot of longer range bullets come apart &gt;310Krpm. If they stay together, then they'll be fine.
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  #4  
Old 06-23-2006, 07:24 AM
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Re: Barrel twist effect on bullet

You will tear the A-Max bullets apart at around 3050 to 3100 fps in most cases with a 1-7 twist. At least that is the case with a Lilja 1-7 twist 3 groove.

The Ballistic Tips will take it and accuracy will be good. Expansion will be violent to say the least. I have shot the 140 gr Accubonds to a solid 3700 fps in my 7mm AMs with good accuracy.

I would recommend a 1-10 if this is the bullet you would want to use all the time, in fact a 1-12 would probably be even better.


Your really playing with the RUM using bullets of 140 gr and lighter, you will see little advantage over some of the smaller 7mm magnums. Bullets in the 160 gr range and higher really make these big cases settle down and produce good consistancy.

Just my opinion,

Kirby Allen(50)
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  #5  
Old 06-23-2006, 07:13 PM
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Re: Barrel twist effect on bullet

hjl, i don't think you need a 7 twist even for the 200 wildcats. an 8 will be more than enough and a 9 will work 99% of the time.the problem with a 7 twist is most have a lilja 3 groove and that's just not enough rifling, in my opinion. a 5 or 6 groove would work better, especially if it's a canted land design. personally i think a 180 berger is a better bullet and a 9 twist will work best with the 160-180 gr bullet weights.i agree about the lighter weight bullets,just a waste of time with this cartridge.
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  #6  
Old 06-28-2006, 04:54 AM
hjl hjl is offline
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Re: Barrel twist effect on bullet

Thank you for your reply.
If I want to use 120gn -180gn bullets I should get a 1-9 twist is this right?
If I want to use a 200gn wildcat will the 1-9 twist work?
Regards
hjl
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  #7  
Old 06-28-2006, 07:46 AM
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Re: Barrel twist effect on bullet

In most cases yes it will work very well. With the velocity potential of your RUM you should not have a problem with a true 1-9 twist barrel.

Kirby Allen(50)
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Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

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