Why does my .357 always turn my left thumb black?

[Thundercleese]

After a day's worth of shooting (say 200 - 250 rounds of a mix of .38's and .357's), my left thumb always ends up black and sooty.

These days I hold it in the proper form - left thumb over right, pointing forward down the length of the cylinder.

Yet its always as if I'm getting blasted by something - I can't figure out how. It seems to become more obvious when I finish the day off with some 158 gr .357's. Each pull of the trigger, I can usually feel a quick sharp hot blast of something hitting the mid-digit knuckle on the thumb.

What gives? How the heck does cylinder gap blast make it all the way back there? As far as I know, the gun's in perfect timing.

 

[stans]

It just happens. Odds are, it is a combination of burnt powder residue, a little bit of lead, and a lot of vaporized bullet lube from cast lead bullets. It happened to me a couple of days ago when I put 100 rounds of cast LSWC loads through my S&W model 29-3. These were not exactly top loads either, nothing faster than 1100 feet per second, most were less.

 

[Thundercleese]

The mechanism behind it still kind of mystifies me. I mean, the blast from the cylinder gap goes sideways by necessity. Maybe just turbulence in the region causes hot stuff to blow a bit backwards?

Man, what must the 500 magnum be like. OUCH.

 

[Jim March]

Picture the hot gasses and crap coming sideways out the cylinder gap, and then forming a sort of "mini nuclear mushroom cloud head" right beside the gun. The tip of your thumb is inside the "head".

 

[Archie]

Probably.......

When the gasses escape from the cylinder - barrel juncture, a small bit of it hits the top strap. Most of that goes to the sides, but a finite amount runs the length of the top strap and hits the recoil shield. That gas goes to both sides, including where your thumb is hovering.

Be glad you ain't getting a full dose.

 

[DillHarris]

Pretty funny how this post just happens to come up when I was wondering the same thing myself. I noticed this happening to me for the first time this weekend. It just so happens this was the first time I've shot lead bullets (my very first reloads), so maybe it is from bullet lube.

 

[Thundercleese]

It was happening to me with jacketed soft points. 357 only. The 38's don't seem to have the oomph to do it.

 

[happy old sailor]

If you are shooting reloads: does you brass come out smokey? if so, add a little more crimp. other than that there are better answers above than i can provide.

i could be silly and say "use smokeless powder". seriously, some powders do burn quite a bit cleaner than others. do a search on this as it has been discussed several times.

if you are not reloading, ignore the above.