What besided not enough twist can cause a Keyhole?

MPFD

MPFD

Well-known member
When I was shooting yesterday, I had a round that by all means should have worked fine print a perfect keyhole. Could the bullet have been made improperly, causing it to yaw and destabilize?
 
How did the other rounds shoot? Maybe just a defective bullet?

The only other time I've seen it is when velocity was really low. Maybe a light powder drop?
 
Keyholes are a result of unstable projectiles. Any number of factors can cause the instability. Most common is incorrect twist but, a bullet with the center of mass offset from the spin axis will be unstable as well.
 
What bullet were you shooting at what velocity in what twist? I have seen bullets keyhole when they were coming apart due to being spun to fast.
 
The Stevens yesterday 1-9 twist key holed a 55 grain Varmint Nightmare. The heavy premium bullets shot fine. But 55 with a good load of Benchmark shot a terrible group with one bullet that Key holed...
 
Specifically "varmint Nightmare" I haven't used, but with other "inexpensive varmint" bullet(Dogtowns) here is what I have witnessed with 2 different rifles.
1) They are cheap, production tollerances are not stellar. So maybe a bad lot of bullets.
2) Dogtowns in particular, have a VERY light jacket! I went round and round with Midway, exchanged several emails and phone calls. They claim that "AS LONG AS YOU KEEP THEM UNDER 4000FPS, THEY'LL OUTSHOOT YOUR BEST BARREL". Well, maybe if you are using a 12/14 twist. What the truth is, is they have a RPM ceiling of about 230,000rpm. Meaning with your 9 twist you have to limit them to less than 3000 fps(depending upon barrel smoothness).

Probably you are spinning them apart, but they haven't yet "puffed". Just leaked enough core to start them tumbling.

Remember that Velocity really means nothing for bullets, RPM is the destroyer.
Here is a RPM calc for you.
MV * 720 / Twist

So: 3000fps * 720 / 9 === 240,000 RPM
 
A nicked crown and a barrel full of copper will cause bullets to keyhole.

As previously stated, a rough 1-9 barrel will eat up jackets and cause fouling to accumulate quicker.

If your barrel does copper foul quickly, it is easily determined by looking down the muzzle with a flashlight, the copper streaks will be very obvious.

Montana Extreme Copper Killer gets copper out real fast when used on one of the Montana Extreme Plastic brushes. The technique used is 15 strokes using the plastic brush with solvent re-applied every 5th stroke. Let sit for 15 minutes, dry patch out, you are done.

Good luck!
 
No, its been real easy to clean up I use Sweet's 7.62 and I'm not finding much copper. I think it was just a bad bullet. That is the only one I have seen do this and I probably shot 18-15 of them through it...
 
Probably just a bad bullet or bullets in causing the large group-a worn out bore and undersize bullets are other things that will produce keyholes. TTT
 
I have had a lot of the Dogtown & Varmnint nitemare 55g JSP bullets tumble with various loads, not all the time but they do it in the 1/9" & 1/12" twists in my guns.
 
a guy at the range swears by his dogtown bullets but when I shoot them in my rifles they do produce wierd shapes and not perfect holes in the paper....have also seen these bullets vaporize at 3400.
 


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