Over-spinning bullet…until they come apart

[FireFlyFishing]

Did anyone notice that a 55 grain .Projectile from a 20 inch barrel requires a 1:14 twist? Why use a 1:7 twist that stabilizes a 77+ grain Projectile in a 12 inch barrel? Just a commoner, but what about common sense? YMMV.

Is this a riddle?

 

[M118LR]

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?

 

[M118LR]

Statistics may lie, mathematics not so much. Yet I still wack the beads on my Old Abacus. LOL.

 

[FireFlyFishing]

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]

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,

 

[sedancowboy]

I don't think I can get this gun up to this velocity as it has a 22" barrel. Hodgon's data is from a 24".

Walk me through your formula if you don't mind.

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]

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

I used the same formula as @lancetkenyon above, but with more steps to get me to his simplified version.

 

[Greatgrandad]

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 the

calculator.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.

 

[Huntaddict]

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.

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]

Did anyone notice that a 55 grain .Projectile from a 20 inch barrel requires a 1:14 twist? Why use a 1:7 twist that stabilizes a 77+ grain Projectile in a 12 inch barrel? Just a commoner, but what about common sense? YMMV.

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.

 

[HARPERC]

I have vaporized two 6mm 85gr V-Max.
1:7" 6SST @ 3650+. 378,425 rpm was too much for the thin varmint jacket.

First shot, I didn't know what happened.
Second shot, I kept both eyes open figuring out what went down with shot #1.
Seeing a cloud of dust raise and a rainbow like shimmer about 10' off the muzzle was really cool.

Sometimes its a steady pattern of uncalled flyers making one scratch their head.

 

[M118LR]

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.

We seem to have a distance to target resolution. Not to mention a differing purpose. If the Projectile is only going to travel 100 yards barrel length, twist rate, and Projectile weight ain't really relevant. So those that are determined to over spin their Projectile speed on. Now folks that want their Projectile to reach the steel plate at the 1K Red cloud range at Fort Stewart need to do a bit more math. Like Forest says, stupid is as stupid does.. Overspin your Projectile and what is the result?

 

[FireFlyFishing]

 

[M118LR]

So do you have something to answer my original questions or some information that benefits the group on this subject?

Firefly, I don't see any parameters for barrel length to velocity, or barrel length to twist rate in your calculations. Nor is there any variance of a flat base to boat tail Projectile. If your goal is to spin the jacket off you are doing well! Notice you haven't even mentioned bearing surface. What is the goal of this thread? I may be able to give more focused input once I understand?