Chamber diameter - GP100

[8ring]

I measured the end of the chambers on my GP-100 and noticed that the diameters were about .355". I couldn't make a 9mm plated bullet go through the chamber without stopping. I load .358" lead bullets and .357" plateds.

Would this chamber size affect performance or accuracy? It seems that the bullets would be swaged to a diameter smaller than the barrel before they reach the forcing cone. However, there are no signs of wear or roughness at the front of the chambers and no lead or powder accumulates there.

Is this normal? If not, what are the usual chamber diameters for a 38/357?

Thanks for the advice.

Chris

 

[Chuck Perry]

I've never heard of this trouble with the GP. Ruger single action 45 Colt's have been notorious for having too small chamber throats. Brownell's makes a tool specifically for opening them to proper size. I would assume as you that your revolver is in need of help. Ruger will probably not make it right; according to reports on the web the aforementioned 45 problem was deemed within factory specs by Ruger, and they would not correct it. It was up to the individual owners to fix it themselves, or pay a smith to do it.

 

[stans]

Chamber throats really should be 0.357" to 0.358". With undersized chamber throats, lead bullets are going to be swaged undersized, then sort of rattle down the 0.357" groove diameter barrel. Don't expect much in the way of accuracy! You could have a gunsmith slug the barrel, then ream the chamber throats to matching diameter.

 

[Mal H]

As stans said the only real way to measure your chamber throats is by slugging them. It is almost impossible to get a good reading with a caliper in the throat. It will usually indicate undersized that way.

I just slugged my GP-100 and found the throats to be .3577 which is fairly normal. But measuring them with a caliper, I got anywhere from .350 to .353.

 

[only1asterisk]

Better undersized than oversized! If they do slug undersize, this is something can can be fixed. Too big is more of a pain to fix.

David

 

[8ring]

Thanks for the advice. I shot some 140 gr. lead 357 loads on Sunday and they were actually fairly accurate. My 158 gr. copper plated 357 loads were all over the paper.

I'll take it to a local shop that has a machinist and ask him to measure the chambers. If they're tight, I'll ask him to open them to .358" and polish them.

I'll report on the outcome.

Chris

 

[stans]

I have tried copper plated bullets in 357 Magnum and 45 ACP. They worked fairly well in 45 ACP, but I have not been able to get really good accuracy in any of my 357's. The bullets are Berry's and I taper crimp all plated rounds.