S&W 629 and Gas Cutting

[Mal Paso]

I was out in the boonies a few weeks ago with my Iphone and I saw a Cast Boolit thread in which there was a post that claimed that gas cutting on a S&W 629 was a myth.

Wrong!

I bought this gun used and the gas cutting had already started. It has progressed a little since with the 40,000+ rounds I put through it. S&W Forum says it progresses to a point and stops. My other 44 Mags don't have so much as a mark. I think rounding the front outside edge of the already thin cylinder creates the conditions.

Accuracy is very good. The barrel is like a mirror after the forcing cone.

[Flinchrock]

Just out of curiosity, what is your load?

[Mal Paso]

Most of the rounds I shot were 19g of 2400 behind a 250-260g Keith.

I have no idea what the previous owner used as the gas cutting started on his watch. The barrel was heavily leaded and the gas cut was filled with grime and missed by the gunsmith who looked it over. I think there is a narrow set of conditions under which the gas becomes a plasma cutter and would not blame it on my loads. 19g of 2400 in the 6 inch 44 is somewhat inefficient and doesn't warm the gun much.

I paid a bit too much as the market goes, what I learned was worth way more.

[Love Life]

Hit it with some JB weld.

[Plastikosmd]

Wow, looks like a good place for a crack to start and then failure? Not an expert in metal or gunsmithing, my disclaimer!

[dubber123]

I think I remember reading about a M29 test revolver one of the labs had, Speer perhaps, and they shot it until the forcing cone was virtually non existent, and the strap still wasn't cut dangerously through. I cannot recall the round count, but well over 100,000 rounds. They claimed accuracy was still excellent from the machine rest it was clamped in.

[osteodoc08]

It's a tool. Use it.

[44man]

Cylinder gap might be too tight. It also looks like cylinder alignment is off a little. Rounding the outside of the cylinder does nothing in any case.
Your concern is the cutting on the cone edge. Something is off, directing gas UP. I bet the cone and rifling is being worn oblong too.
Check to see if the cylinder front is faced square too. Had Dan Wesson guns with wobbly fronts. Set gap and rotate the cylinder and it would lock up. The smaller the gap the more the gas pressure will be.

[Mal Paso]

The gap is .006". Accuracy is excellent. The only thing I can see is the curve of the front outside edge of the cylinder enters the cylinder gap and increases the gap at the top edge. I think someone at the factory polished too much.

I really like the gun and have been keeping my eye out for another with a more symmetrical cylinder gap.

[Mal Paso]

Check this out too. This is lead deposited on the cylinder in a liquid state by the combustion gas and is soldered to the stainless. I have proof that boolits can be gas cut. Also explains why leading from poor boolit fit it so much harder to remove.

[too many things]

from what you say about the barrel being heavy leaded. would bet that the guy used jackets over the leading. increasing the pressure and getting a very heavy fire ring. They may have used a stone to remove the lead on the cylinder face. that would tend to remove metal too.

[MBTcustom]

44man hit the nail on the head. What is happening is that when they bored and threaded the hole in the frame for the barrel, it was a little higher than it needed to be, creating a situation where the bullet hits the barrel low in the throat (slightly). Either that or the chambers were reamed too close together (I've seen both situations).

This causes your gas seal to be lost at the top of the barrel. Gas cutting is certainly happening and the vaporized lead and hot gas is jetting directly upward and slightly to the right (your cylinder alignment is slightly off as well). The frame acts as a shield towards the front, allowing the hot gas/lead to wash backward over the cylinder. This is why you see lead deposits on top of the flute, to the RH side of the cylinder throat, and why the gas cutting in the forcing cone errs slightly to the right as seen in the pictures.
This would be easily seen with a borescope set to look straight ahead from the muzzle.

The bevel on the outside leading edge of the cylinder is purely cosmetic and has absolutely nothing to do with this situation. This is purely an alignment issue.

Now, that said, this doesn't mean your pistol is bad. You just came out on the short end of tolerance stack up. If it shoots straight, then don't worry about it.

[Mal Paso]

Actually that's a left side deposit but they are on all the flutes. The erosion on the cylinder face varies and in combination with the barrel erosion varies the deposits a little but it is on all the flutes.

Thanks for the input. I'm going to get a borescope and have a look. Sounds like I want to check cylinder alignment when picking the next gun.

Most of the damage was done before I got the gun. I fixed the kitchen table trigger job (with proper tools) and it's been a solid, crisp 2 1/4 pounds for years now. I reamed the .4285-.429 throats to .431 and shoot .431 boolits. The .429 groove bore is like a mirror, crisp rifling. Offhand I stay inside 4" at 25 yards and squeeze that down to 1 3/8" (6 shots) on occasion. I'm less accurate from bags, grip I think. If I can do better I'd like to. I never checked cylinder alignment as there wasn't much I could do to correct it but I could be more selective when I buy.

Thanks for the help. Sounds like I'll be bringing one more tool gunshopping.

The more I think about it I don't think all the cylinders have the same POI. I was careful selecting pilots when I reamed the throats but remember thinking how nice it would be to align the chamber/throat with the barrel.