Re: Keyholing .38 spl wadcutters
I believe it is a wad cutter that can be used with either end in the case (??).
Things that make bullets tumble are wrong twist (but any 38SPL gun has the right twist for that bullet), a damaged barrel crown, bullets that are the wrong diameter (rifling in barrel looses grip on the bullet), voids in the bullets, bullets so soft the rifling strips the bullet rather than turn it, a leaded up barrel, cylinder timing off and bullet gets damaged trying to enter the barrel from the cylinder (spiting lead out the cylinder to barrel gap should show you that is the case, I would think).
Checkout the gun and if seems OK suspect the bullets (measure diameter and weigh some looking for an abundance of voids in that batch).