Powder coating and keyholing

[Ritchie]

I've been working with powder coated bullets recently. Results are:
Gun: Beretta M92FS Compact

Bullet: Lee 124 gr. TC tumble lube, sized .358 in all instances.

Previous load: conventional lube sizing with Rooster Red lube. 4.0 grains of
AA#2. This load produced 2 to 4 keyholes in each magazine. Full profile
keyholes were frequently produced at as little as one meter distance.
Variations in powder charge resulted in no change in keyholing.

Light load: bullet powder coated with Harbor Freight red. 4.0 grains of
AA#2. Noticeably improved accuracy, closer to point of aim. Far fewer
keyholes but not entirely elimated. Fairly clean barrel.

Heavy load: bullet powder coated as above. 6.0 grains of Power Pistol .
Improved accuracy, even closer to point of aim. Fairly clean barrel. Shot
80 rounds, keyholing NONE.

Discussion: Typically, the 9mm Para seems to have "generous" dimensions
in the throat and leade. Jacketed, copper plated, and powder coated lead
bullets have less trouble with poor accuracy and keyholing than do greased
lead bullets. It turns out that conventional lead bullets are a challenge for
handloaders in 9mm. I speculate that when a bullet occasionally yaws on
leaving the case mouth, the base of the bullet drags on or is pushed into the
side of the throat/leade. In the case of the greased lead bullet, the base area
is smeared or otherwise distorted. The bullet with a coating over all has less
friction and greater surface protection, so does not suffer so much damage.
With powder coated or plated bullets, these treatments do little to increase
structural strength, but do protect the entire surface. It has not been possible
to recover fired bullets, but I would be most interested to examine keyholers
that were not greatly damaged in recovery.

 

[Rottweiler]

I don't think its the powder coating causing the keyholing. I had the similar results with that bullet both sized and conventional lubed and tumble lubed in a SIG 226 years ago in the pre-powder coat days. I even played with the powder charge like you did. You had better results than I did. my keyholing got worse with heavier charges.

A fellow shooter gave me a handful of his 124 gr. round nosed cast to try. No keyholing. I swapped that TL mold for a non TL mold on castboolits.com

 

[Havok7416]

.358 certainly seems a bit large for a 9mm bullet, but I am aware that some guns have oversize bores. If that is not your problem it could be the charge. Can you duplicate the loads you tested, but with conventional lead? That would be my starting point to ensure consistency

 

[243winxb]

Lee 9mm 124 gr TL Cast bullet

Bullet Design?

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[noylj]

0.357-0.358" is a very nice size for 9mm cast lead bullets--just as 0.356-0.357" is a very nice size for 9mm jacketed bullets. They work great in even 0.355" groove barrels.
Keyholing, in my experience, has been due to bullets being undersized or some damage to bullet or muzzle.
You get up to high pressure, and you MAY obdurate the bullet to fill the bore and eliminate keyholing/leading.
Do you know your barrel's groove diameter? Are you sure your bullets are at least 0.001" larger than groove diameter? I have no idea if ideal for powder coated bullets is the same or if the bullet before coating should be at least that large.
Pretty bullet. Yours?

 

[Ritchie]

I may not have been clear enough-powder coating does not cause keyholing, it reduces it! The groove dia. is right at .356". The Lee 124 gr. bullet in regular lubed form flies sideways no matter what the charge. The Lee 105 SWC works very well in conventional lubed form except in fairly heavy loads. This did not prepare me for the difficulty with the heavier bullet. I have suggested some ideas for what might be happening to cause these problems, and the reasons that some changes might work to reduce problems. If anyone has more information on this phenomenon, feel free to chip in.

 

[Ritchie]

_243winxb_ Yes, that's the one. Shake in a plastic sandwich box, pick out with needle nose pliers, bake in a Goodwill toaster oven. On the screen they need to be cracked loose after cooking but that's not a problem. The base of the bullet is mostly covered with coating. Size after they're cool.

 

[tyeo098]

...did you slug your bore?