Kahr PM9 Barrel peening and replacement question

[skystud1]

I have an older Kahr which never had the barrel recall taken care of. The previous owner polished the barrel and I am not sure if they will fix it (plus I tinkered with it). The gun functions perfectly but peening visible after 50 rounds. Ground down peening and came back after another 50.

Three questions:

1. Will new barrel ( If I purchase one) fit old gun? I know recoil system different.
2. What causes the peening (Forward edge of barrel hood forming a vertical lip) The barrel or slide?
3. Can I fix peening on my own, with a dremel, sandpaper, file, etc?

Thanks!!

[TucsonMTB]

I believe the original problem was caused by a combination of soft materials and a loose fit. Mr. CJB will probably be along with a more definitive word soon, but . . . the only solution will require replacing the soft part (barrel and/or slide) and re-fitting.

The best people to do this are the good folks at Kahr. Because this is an older gun, it may have a lifetime warranty. In any event, historically Kahr has been quick to deal with genuine manufacturing and materials issues, regardless of the age or current ownership of the pistol.

Start with either email or a phone call. Email is usually better.

Email: service@kahr.com - Phone: (508)795-3919

Best of luck, but I don't think you will need much.

[skystud1]

I couldn't take it anymore and sent it to Kahr. Any idea if they will replace the barrel if it was tinkered with? Ie.. Filed down. What do they do for peening?

[jocko]

Nice infortmative post Tucson TB...

[skystud1]

Good move, I believe.

Hard to predict exactly what Kahr will do, but the results should be good. I am guessing both slide and barrel will be replaced. They like to make sure of the results and that is about the only way to be certain the problem is eliminated.

This may take a while, depending on their on hand stock of parts.

I was told around three weeks, so we shall wait and see. Man I feel bad for them if they are going to replace the slide. I have xs big dots installed and the rear sight set screws Re stripped. They better not charge me for new sights. Definitely never getting rid of this gun!

[FLBri]

If they replace your slide ... you will most likely still have the same sights on it if they are after market sights.

[CJB]

Ground down peening and came back after another 50

Mr. CJB will probably be along with a more definitive word soon

When you ground and/or filed down the deformation of the metal on the barrel, you made the problem worse.

Here's how it happens. Imagine a very tight fore/aft fit of the barrel to the slide, when the barrel is in "in battery" or locked to the slide. Lets say that fit is from "dead nuts zero" to maybe just one or two .001's of an inch. When the pistol is fired, the case will push on the breechface of the slide, and the slide will move in relation to the barrel. But really, since we have an excellently tight fit, the slide really cannot accelerate very much before it contacts the barrels locking surfaces, and the two move rearward together.

Now consider a rather sloppy fit. Say there is .005 inches of "free play" in the fit of the barrel to slide. Could even be more. But now, the slide has to move further before it contacts the locking surfaces on the barrel. And in that further movement, it accelerates to a greater speed. In so doing, when the two parts finally touch, there is more of a hammering effect.

That's one type of bad fit.

If you couple that with perhaps a no so stellar fit vertically... it makes the situation worse, because now your distributing that hammering effect on a smaller locking surface.

That's the second type of bad fit.

Now here's the final key to whats going on. Even though the slide is really moving independently of the barrel for a very short distance (the amount of slop in the fore/aft fit), both parts are moving rearward, from recoil, as this is happening. What often happens is that the barrel has gotten to the point where it is thinking about unlocking (rear of barrel tilting downward), so you get a bit of a "smear" effect to the metal deformation as well.

Metal hardness... or more like "toughness" can play a role, but the real problem is the fit of the parts. Metal hardness is something that is controlled on a very large scale. They don't heat treat barrels all that much, but instead use a metal that is tough, as it comes. The hammer forging process tends to work harden the metal as well. There could actually be some annealing that is done to the barrels to make them more easily machined... but I tend to think not. I have a raw Ruger hammer forged rifle barrel, with the hammering pattern still on its exterior (thats how I know its raw!). The outer surface is not all that hard, and machines well (or so says Clarke Custom, who fit it to a 10/22 for me). I'd expect somewhat the same on a pistol barrel... in the same league at least.

Some slides are selectively flame hardened. Colt does this. Browning High Powers are that way too, as also are the Sig P series slides. Very easy to see because the bluing wears very differently and takes on a different color as it wears, in the flame treated spots. Colt does the slide stop notch, the front of the slide at the recoil spring hood area, and the locking area "may" be selectively hardened. Sig does the slide locking surfaces, the notch and hood sections. I have no idea what Kahr does.

The fix - calls for examination of the slide, and seeing how a good barrel fits in it. You're into a new barrel, and perhaps a new slide. The slide is a maybe, as it could be absolutely fine.

The correct way of getting rid of the deformed metal, is to deform it back! Take out your hard punches and hammer and beat the metal back into place....

[skystud1]

Thanks a million, as that was the best post ever. I have to reread it later so I can truly grasp everything you mentioned. I guess my model Kahr is within recall range for the barrel. Hopefully they just throw in a new barrel and call it a day. Do they replace warranty items if there was a recall, even if I messed with it?

Well, now I know that peening means you need more metal not less. Ha thanks again bud!