Years ago, I was shooting my new Ruger .22 Mk II stainless steel bull-barrel target pistol for the first time. I was really cranking some rounds through it in rapid fire, reloading the mag, and rapid firing again. I was using inexpensive uncoated-lead US-made .22 LR fodder (maybe Thunderbolts or something like that). I soon noticed that the bullets were beginning to spread all over the place on the target. Looking at the muzzle, I noticed large pieces of lead adhered to the bore. When cleaning the bore with a patch jag, I actually was pounding sizeable chunks of lead out of the barrel. I had never experienced this when shooting the same kind of ammo and similar rates of fire from my standard Ruger Mark I carbon steel pistol.

I suspect that possibly stainless steel has a higher coefficient of friction than carbon steel, resulting in the lead "sticking" to the barrel in a hot barrel. I've since used only copper-washed bullets and haven't seen the problem again.

Has anyone else experienced more severe lead fouling in stainless barrels as compared to typical carbon steel barrels?

Early stinless barrels did have the reputation of being a good bit less smooth than carbon steel....but i doubt that was the problem. Some .22ammo is less well lubed than others (dry lube) and rapid firing does heat things up a bit, so it more likely that the lube on those bullets just failed.

I've gotten the same problem with good barrels and cheap ammo today, stinless of carbon steel doesn't seem to make a bit of difference.

My son had the same problem with Thunderbolt ammo in his S&W 22A pistol. These rounds shot fine in our rifles, but it would lead the barrel so badly in the 22A that you couldn't get a cleaning rod in the barrel - long chunks of lead would get knocked out when we cleaned it (he found it was leading badly when he literally couldn't hit a 1 ft square target at 5 ft!). Other ammo shoots great. Two of our rifles have carbon barrels, one stainless, but the 22A is carbon steel. It's not a steel issue; just a matter of how a bullet interacts with a particular barrel.

I've noticed big differences in the accuracy of different .22 LR ammo. My Mark II 4 3/4 carbon standard loves the Winchester Dynapoints, and my Ruger 10/22 Carbine carbon loves the federal copper washed stuff, it also shoots the CCI Velocitor very well.