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I just slugged and measured my buddy's H&H .450 3 1/4 BPE double hammer rifle. Bore measures .447 and grove diameter is .4519 to .4520. Twist rate is 1 in 28 inches. I'm thinking a 275 to 300 grain lead projectile. I don't have the Greenhill formula so can anyone tell me if I'm in the right ballpark with the proper weight with this twist rate? The barrels or barrel flats doesn't give me any details. Thanks for any help.  

one of us 
Ballistic performance Bullet mass/type Velocity Energy 270 gr (17 g) Lead coppertubed 1,975 ft/s (602 m/s) 2,340 ft⋅lbf (3,170 J) 310 gr (20 g) Lead solid 1,800 ft/s (550 m/s) 2,240 ft⋅lbf (3,040 J) 325 gr (21 g) Lead coppertubed 1,775 ft/s (541 m/s) 2,280 ft⋅lbf (3,090 J) 350 gr (23 g) 2,150 ft/s (660 m/s) 2,340 ft⋅lbf (3,170 J) 365 gr (24 g) Lead solid 1,700 ft/s (520 m/s) 2,340 ft⋅lbf (3,170 J) Source(s): Barnes,[1] Kynoch[2] and Taylor.[3]  

one of us 
350 grains or lighter will stabilize well in a 33" ROT or longer at any velocity the rifle is capable. That gives you a wide margin, so I wouldn't worry about stability unless you start bumping up near 400 grains.  

one of us 
Length not weight is the key of finding max bullet for a given twist.  

one of us 
Dutch, Did anyone ever get you the Greenhill formula.? Note: There is a school of thought which holds that The constant value in the formula varies with velocity. So the twist rate formula when using Black Powder is different. I don't have my notes handy but will dig them up if you still need them
 

one of us 
The whitworth of civil war fame fired a 530 grain bullet in a .451 bore of 120 twist quite well. I would expect a plus .002 over groove bullet of modern flat nose profile of 450500 grains will work just fine. "The liberty enjoyed by the people of these states of worshiping Almighty God agreeably to their conscience, is not only among the choicest of their blessings, but also of their rights." ~George Washington  1789  

one of us 
https://wikimedia.org/api/rest...2fa21cc8fe7e6654d156 Just google it. Copy paste on this website is shall we say problematic. "The liberty enjoyed by the people of these states of worshiping Almighty God agreeably to their conscience, is not only among the choicest of their blessings, but also of their rights." ~George Washington  1789  

one of us 
=================================== Greenhill Formula (simplified) L=150 x D x D ___________ T (that is, 150 x D squared divided by T) L is the bullet length The number 150 is a constant used by Greenhill and works well at velocities in the vicinity of 1500 f.p.s. or greater. At 2800 f.p.s. the constant can be changed to 180 with good results. For Black Powder velocities use 125 as a constant instead of 150 Miller Formula: https://en.wikipedia.org/wiki/Miller_twist_rule  

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