Mod. 14-3 cylinder blow by

[Yochim]

I have a pre 1980 Mod. 14-3, and am getting blow by (powder and burn marks) on each fired shell and in each hole of the cylinder toward the center part closest to the pin which it revolves around.
Any ideas on what could be causing that?

 

[OFT II]

Welcome to the forum. What ammo are you using? It sounds like light hand loads that don't expand the case and seal the cylinder.

 

[Inusuit]

Yes, likely an ammo problem. Either loads are too light or maybe Tula steel cased? So the cases are not, as OFT II says, expanding to seal the chambers.

 

[Yochim]

I started using hand loads, 125 gr. X-Treme plated flat nose with Titegroup. I started with 3.8 gr. and worked my way up to 4.8 gr., trying to get the fps up to the 900-1000 range. All of the powder weights had the same blow by/powder burns in the same place. I then bought a box of Sig Sauer 125 gr., and they did the same thing. Also, the Sig ammo says on the box, 900 fps, but the most I got out of 10 rounds was 805.9, and a low of a couple of rounds in the 652-663 range. It just doesn't seem like an ammo issue.

 

[bigggbbruce]

I get those to, I just scrub the cylinder when cleaning.

 

[epj]

Somehow this seems like a pretty normal condition. I haven't fired a revolver yet that didn't have some degree of blow by around the front of the cylinder. As long as it isn't excessive, I wouldn't worry about it all that much. If the B/C gap is excessive, then some action might be warranted.

 

[Yochim]

I expect and have always had blow by in front of the cylinder due to the gap between it and the barrel, but I was concerned about the constant and consistent blow by/burn in the same spot on the shells and inside portion of the cylinder toward the center.

 

[bountyhunter]

Welcome to the forum. What ammo are you using? It sounds like light hand loads that don't expand the case and seal the cylinder.

+1 I used to buy reloads and the ones with weak powder charge would show the burn pattern around the sides from not expanding.

 

[Yochim]

With that in mind, perhaps my "role crimp" is too tight. In order to remove a bullet, it takes me 2 good raps with my removal hammer, so If I lessen the crimp and decrease the COL slightly to compensate, perhaps the case will expand more and seal it off.
But, that doesn't explain why the factory Sig Sauer ammo did the same thing. You would think their loads would be crimped properly and have a sufficient powder charge to expand the shell and reach the advertised FPS of 900, although they did not. They actually averaged under 800.

 

[reddog81]

I don't think less crimp will help. If anything, less crimp will equal less pressure and more blow by.

With that said I've never paid that much attention to how sooty a case looks.

I'm surprised by the extreme spread on the Sig ammo. If the barrel is a 6" inch I would have guessed the average velocity to be closer to the advertised amount.

 

[Yochim]

Me too. I wonder if somehow the cylinders have gotten out of perfect round somehow, causing a little loss of pressure when fired. The gun is well over 40 years old, and although it hasn't been shot much in the last 40 years, I can't remember how much I used to shoot it back then.

 

[Yochim]

I read in several places that .38 specials, and perhaps other revolver ammo need a "tapered" crimp, not a roll crimp. The die set I am using is a roll crimp the more you crimp it, that is why I mentioned that I might lessen the crimp to decrease the roll, then shorten the COL slightly to compensate for the reduced crimp. With less of a roll crimp, perhaps the shell will expand more flatly to the cylinder walls.

 

[Alk8944]

Yochim,

What you could do is just shoot the gun and stop trying to fix something that is not broken! .38 Spl. is a relatively low pressure load in standard pressure particularly. For that matter, all revolver cartridges, except the magnums, are low pressure cartridges and you will get some gas blow-back around the case. This is completely normal, quit worrying about it!!!!

 

[epj]

Since the soot marks are always at the bottom of the cylinder charge hole, ie closest to the center, it's possible your forcing cone is not cut parallel to the cylinder face.

 

[alwslate]

I load light 38 spl plinking loads with cast bullets and always roll
crimp them. The brass gets smoked up no matter which gun I shoot
them in. So does the face of the cyl as well as the top strap of the
gun. In fact the entire area of the gun close to the brl-cyl gap along
with the fingers of my support hand that is in front of my firing(right)
hand. I've always considered it to be normal for the last fifty years.

 

[Yochim]

Thanks for all of the information and ideas about what is going on with my K38. As a result, I guess I just won't worry about it any more.
But, I am curious about one thing stated by epj above. What is the "forcing cone"?

 

[Yochim]

Never mind, I just googled it and figured out what the "forcing cone" is.
Thanks to all.