View Full Version : peening on breech face

July 10, 2009, 08:47 PM
Was looking at some of the older posts and came across a post about peening on a breech face. What is this. My Ruger MK2 after about 8 to 10 thousand rounds has what I would term blast erosion on the breech and the bolt face without adverse affect. Is this the same thing?

July 10, 2009, 10:13 PM
Noooooo. Peening is when the metal is deformed in some way as a result of the repetitive hammering of the action opening and closing. It can take the form of mushrooming, denting, or bulging. All or most of the metal is still there, it is just relocated.

July 10, 2009, 11:44 PM
Also many in many rimfires the firing pin will hit just above the chamber and peen in an area. This will usually cause problems on chambering and extraction. Not all rimfires do this but many do, use snap caps.

July 11, 2009, 01:57 AM
Ruger MKs have a firing pin stop to prevent them from damaging the breech face.

July 11, 2009, 06:38 AM
Which falls out unnoticed on a lot of them and then are dry fired resulting in damage. When reassembling be sure to check that little pin. Don't ask how I know.

July 11, 2009, 06:54 PM
Hey Drail look at my last post. I still feel like an idiot

July 11, 2009, 09:10 PM
Hey finrot, don't feel too bad. A lot of what looks like damaged metal on these guns is simply accumulated very hard fouling which will come off with a pick. I use a piece of heavy gauge copper wire that I sharpen to a point and pick the fouling off of the bolt face and the extractor groove and forward part of the reciever. These guns will run really dirty for a very long time but eventually you need to get that crud out of the nooks and crannies. Rimfire ammo is filthy stuff. I have three MK IIs, one of which has been shot almost to death since about 1982. It still prints nice groups though. A truly amazing pistol for the price. Whenever I hear the term "peened breechface" I think of an old 1927 Argentine 1911 that a guy brought into my shop that had apparently spent it's military life in an armory where they stored racks of pistols on a rack with steel rods running up the barrels which slammed into the breechface. The breechface was beat up so bad that the primer would flow into the dents and cause extraction failures. We replaced it with a Springfield Armory slide. It turned out to be a very accurate pistol after some other work and a new barrel. Those 27 Argentines were made from some very good steel. But if you ever think about buying one (or anything from a military armory) look at the breechface carefully under a good light.