257 Weatherby

Kgkimerer

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has anyone wildcatted a 257 Roy to 6.5/257 Roy. Lots more Bullets in 6.5. Just curious
 

257Tony

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I never have, but lots of guys have done it, or neck down the 270 WBY. Basically, you end up with the same case capacity and performance as a 264 WM, but with fewer brass choices.
 

Kgkimerer

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I never have, but lots of guys have done it, or neck down the 270 WBY. Basically, you end up with the same case capacity and performance as a 264 WM, but with fewer brass choices.
About what I guessed for performance. Hmmmmm. This is a possibility.
 

sable tireur

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http://www.mcwhorterrifles.com/

The reamers are set up for shooting the heavier for caliber bullets as opposed to the lighter weight varmint bullets. Typically the 6.5mm 140 grain Bergers as well as most others. This is a terrific hunting cartridge.
 

RockyMtnMT

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We built a 257 Weatherby and had a proper twist barrel put on it so that it can shoot a bullet that does the cartridge justice. We installed a 7" twist. This rifle went with us to Africa last weed and was responsible for animals from jackel to trophy bull eland.

Steve
 

MagnumManiac

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We built a 257 Weatherby and had a proper twist barrel put on it so that it can shoot a bullet that does the cartridge justice. We installed a 7" twist. This rifle went with us to Africa last weed and was responsible for animals from jackel to trophy bull eland.

Steve
What bullet NEEDS a 7” twist in 1/4 bore?
Even the 115gr Berger is fine in a 10” twist.

Interesting.

Cheers.
:confused:
 

RockyMtnMT

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We have a 128g Hammer Hunter for the 7" twist. This bullet is 1.506" long.

When I say a proper twist what I mean is a twist for the 25 cal that is relative to the bore and other calibers that are used for long range. Compared to 6.5mm in an 8 twist a 7 twist in the 25cal is relatively similar. The standard 10" twist that is in the 25 cals is the worst/slowest proportional to caliber twist rate of all the calibers. Next is the standard 10" twist in the 270cal. The 270 in 10 is much more proportionally better than the 10" twist in the 25cal, but still a handicap for the 270.

The 115g Berger is not fully stable in a 10" twist barrel, according to their twist rate calculator. That bullet needs 9.5" twist to be fully stable.

There is a difference between ballistic stability and stability for terminal performance. Marginally stable bullets can and will shoot very accurately to extreme range. When it matters what the bullet needs to do after impact, full stability makes a huge difference. The rotational force of a bullet is what keeps a bullet from tipping or wobbling. The faster it is spinning the better it is at staying point oriented forward without yaw or tipping to the side. In air the rotational vel has little or almost no degradation throughout its trajectory. As soon as that bullet touches something the rotational vel rapidly declines and the bullet will yaw or tumble as soon as the spin slows enough to allow it. If the starting stability is marginal there is a good chance that the bullet is flying with some yaw and the chance for bullet failure on impact is greatly increased. If the bullet is not hitting straight to the target then there is a very good chance that fluid will not get into the hollow cavity in the nose and cause the needed expansion for proper terminal performance. We do not test other brand bullets but I can say with certainty that many of the bullet failures that we read about are due to lack of stability not poor bullet performance.

1.5sg is considered fully stable for ballistics. Elevation or air density will play a large roll in determining whether or not a bullet is fully stable for ballistic flight. Higher elevation requires less rotational vel to stabilize a bullet due to the lower air density. This does not mean that the bullet is spinning with higher rpm's. A particular bullet may be unstable at sea level but fully stable at 10,000' above sea level. It is still the same rpm's at both elevations. We have figured out from testing that elevation is not a good indicator of stability for terminal performance. Problem is that on impact the bullet slows it's rpm's the same at any elevation. The higher rpm's will keep a bullet longer after impact and give proper terminal performance.

It is our recommendation that bullet stability for hunting should be 1.5sg at sea level min for good terminal performance. Better terminal performance is at 2.0sg. Our recent trip to Africa with nine different rifles running a variety of Hammer Bullets from 25cal up through 37cal showed straight line penetration on all animal impacts regardless of animal orientation and bone impacts. The one common with all of the rifles used was stability factor above 1.5sg.

Sorry about the long windedness of my response. As a bullet maker/hunter I am passionate about terminal performance on game. It is the reason we started making bullets. When we started testing our bullets the data that we accumulated answered a lot of old questions about past performances before we started making bullets. Our data is not unique to our bullets and should be paid attention to no matter what bullet you are using. We owe good terminal performance to the animals that we hunt.

Steve
 

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