Over-spinning bullet…until they come apart
- Thread starter FireFlyFishing
- Start date
Help Support Long Range Hunting Forum
No, if you purposefully disregard the simple math of barrel length to velocity to bearing surface and Projectile weight do you think that you are going to make a breakthrough that defines mathematics? Why do you think that Uncle Sam pays all those engineers at proving grounds with funding way above common folks in yearly budgets that exceed lifetimes in a year of rounds expended? 
FireFlyFishing
Well-Known Member
No, if you purposefully disregard the simple math of barrel length to velocity to bearing surface and Projectile weight do you think that you are going to make a breakthrough that defines mathematics? Why do you think that Uncle Sam pays all those engineers at proving grounds with funding way above common folks in yearly budgets that exceed lifetimes in a year of rounds expended?
So do you have something to answer my original questions or some information that benefits the group on this subject?
Doom2
Well-Known Member
Generically speaking most cup and core bullets will survive up to around 280,000 to 300,000 RPM. Beyond that it's pretty much hit or miss. Throat and barrel conditions become critical. A velocity of ~3335 fps is going to be about 300K RPM in a 1 in 8 twist so that can be kind of a guide,
Velocity X 60 seconds \ .66ft = RPM Velocity in FPS X 60 \ Twist Rate in Feet = RPM
3900 X 60 = 234,000 \ .66 = 354,545 RPM
FireFlyFishing
Well-Known Member
I used the same formula as @lancetkenyon above, but with more steps to get me to his simplified version.
Greatgrandad
Well-Known Member
A bullet spinning apart is as much about the rate of spin as it is about bullet construction. Link to a calculator is below.
IME it is pretty difficult to spin apart modern bullets. It can be done but it is pretty extreme
I personally had a 22-250 ai - 24" 1:8 twist carbon bbl - running 75 grain AMAX at 3450 - they performed just fine.
Bullet Spin Rate Calculator - Calculator Academy
Source This Page Share This Page Close Enter the muzzle velocity (fps) and the barrel twist rate into the Calculator. The calculator will evaluate thecalculator.academy
A few of us have blown up a few thin jacketed bullets on a few occasions. I've watched more than a few old 50 grain Speer TNT bullets come apart mid flight when using a 26" 1/9" twist 223 and even more so in a 1/9" twist 22-250. Also, the "older" Berger 90's had a habit of not making it to the 1,000 yard target when fired hard from my 1/8" twist 22-250AI and some friends 1/7" twists. Sometimes, a few Varmint Grenades would live up to their names but earlier than desired.
Edit: One thing that did improve those old TNT's was a good moly coating, for after applying and when fired from our 223/5.56's, we noticed nearly zero premature separations.
Last edited:
Huntaddict
Well-Known Member
I hear you - a 1:9 twist is pretty tight for a 50 grain bullet. One of the reasons match bullets usually have thicker jackets....Surprised at the Bergers though...than 90 grain bullet should be ideal for that twist rate....its what I ran and never failed with AMAX's
lancetkenyon
Well-Known Member
So you are not limited to a 55gr bullet.
I shoot both 50gr VMax and 69 SMKs in my 11" AR15 pistol.
Plus, the faster the revolutions, the better terminal ballistics in game.
Last edited:
HARPERC
Well-Known Member
Sometimes its a steady pattern of uncalled flyers making one scratch their head.
