Well, I've heard of bullet tumble, but just found it hard to believe, until today. I'm posting this in the "ar15" room because it gets alot of traffic, and therefore can help any doubting Thomas's out there like myself. I went to the indoor range today and took the beater pistol which is a S+W 22A. After about 600 rounds I started noticing heavier smoke and powder embers leaving the barrel, of course I ignored this and pressed on. At about 650 rounds I lost all ability to form a group, and noticed holes the shape of bullet side profiles. I checked the gun over and found nothing wrong. I came home and did an internet search on "bullet tumble" and came up with this........"The only way powder can cause a bullet to be unbalanced before it leaves
the muzzle is for it to change the bullet's shape.  One way that can
happen is the powder is just barely ignited and not completely burns.  You
can determine this if the bore is very, dirty after shooting H380, but much
cleaner after shooting other powders.  If there's enough powder residue in
the bore to distort the bullet as it rides over the clumps of powder
fouling, that could cause the bullet to tumble.

One solution may be to use a hotter primer with H380 powder.  That'll
help burn the powder more completely and reduce, if not eliminate, powder
fouling.

The other way powder can change a bullet's shape is that it burns so fast
initially, it slams the bullet into the rifling too hard and the bullet's
rear part enlarges in diameter non-uniformly as it starts into the rifling.
But this typically just causes larger groups, not keyholing bullets.".............I think the dirty bore deforming the lead bullet I was shooting ,explains the tumble I was seeing today.yarchive.net/gun/ammo/bullet_tumble.html

Follow up on the take down of the S+W22A. Broken firing pin in 3 pieces, and firing pin spring in 2 pieces.

I have run wheel guns to the point that the lead has just clogged the rifling (used the wrong lead for casting).  When this happens, the bullet no longer engages the rifling, and is just push straight threw the barrel with out spinning, Hence tumbling and key holing.

If you plan on shooting this much lead/ or plated ammo threw the pistol, then invest in a Bore snake that you can run down the bore every few hundred rounds.  This will prevent the fouling from build up, and creating high ammo pressure in the pistol and causing damage.