How tight is tight?????

[Dick Herman]

Galling is much like surface contact welding. If there is a difference in the hardness of the steel screw (barrel) and the steel nut (receiver) galling should not occur. However using a thread lubricant greatly reduces the chance of galling AND improves the torquing efficiency.

[Olle]

Originally Posted by Dick Herman

Galling is much like surface contact welding. If there is a difference in the hardness of the steel screw (barrel) and the steel nut (receiver) galling should not occur. However using a thread lubricant greatly reduces the chance of galling AND improves the torquing efficiency.

I'd say it's very much like contact welding. Also, the increased friction and pressure cause microscopic tears in the surface, which will make them so rough that they don't want to slide anymore. I believe this is what happens in friction welding as well, right before the material starts heating up.

I have had the questionable pleasure of seeing that happen, and I thought I would never get the barrel off again. The shiny contact surfaces on the shoulders were dull and torn, just like if the parts had been welded and then pulled part again.

[Dick Herman]

Using a lubricant or an anti-seize compound reduces the friction. Some threading compounds incorporate graphite and copper to reduce friction. Friction and high contact stress are the enemies of all threaded members. Stainless steels and titanium are awful for galling when attempting to screw those type members together.

[Olle]

Originally Posted by Dick Herman

Using a lubricant or an anti-seize compound reduces the friction. Some threading compounds incorporate graphite and copper to reduce friction. Friction and high contact stress are the enemies of all threaded members. Stainless steels and titanium are awful for galling when attempting to screw those type members together.

Stainless can stick like the dickens, that's why the custom builders always build stainless guns with looses tolerances. If they even use stainless guns, I believe most prefer carbon steel.

I was playing with some of my guns yesterday, and once again I started wondering why Luger barrels "should" be torqued so much. Compare with, for example, an AK-47 where the barrel is pressed into the trunnion, and held in place by friction and a small cross pin. I have never heard about one coming loose. A Luger barrel is threaded so it can't be pulled straight out, so all that's really needed is enough torque to keep it from turning when you shoot. It's not like you're torquing the heads on a Top Fuel dragster, it only needs to be tight enough to stay put and it doesn't take much at all IMO.

[sheepherder]

Originally Posted by Olle

...an AK-47 where the barrel is pressed into the trunnion, and held in place by friction and a small cross pin...

I've run a 20 ton hydraulic press almost up to the limit to press the barrel out of the trunnion. And I had to drill the pin out.

[Olle]

Originally Posted by sheepherder

I've run a 20 ton hydraulic press almost up to the limit to press the barrel out of the trunnion. And I had to drill the pin out.

Yep, they do press them pretty darn good. Anyway, my point is that a barrel won't move as easily as one may think. Walther PP might be a better example of a pinned barrel, once you remove the pin you can tap the barrel out with hand tools. It still holds up well to .380, and I don't think the barrel would come loose shooting 9mm either.

It would actually be interesting to put a test assembly together with a hand tightened barrel and see what happens when you shoot it...

[rhuff]

Olle,

I bought a police turn-in S&W Mod. 66 revolver from a friend that said he couldn't hit anything with it. This gun is not a pinned and recessed model. On close examination, the barrel was unscrewing and the front sight was way off!! I removed the barrel and checked everything over, and the threads on the barrel and in the frame were in excellent condition. I cleaned everything up good, applied a bit of LocTite blue to the threads and put everything back together and aligned the barrel to the frame so that the front sight was aligned correctly. That was 2-3 years ago, and all is well, but I do check it every time I clean it after a range trip. Perhaps my gun was just a fluke, as I have not heard of another S&W revolver doing this.