Chambers, Bolts and Brass

[joebush]

One of my favorite websites for quite some time has been varmintal.com. Al is a 30 year veteran of Lawrence Livermore National Laboratory where he conducted structural analysis of complex systems. Al has some interesting FEA models of rifle chambers and cartridge brass. One of Al's recommendations is to polish your chamber to reduce plastic strain in the case head and reduces the chance of case separation during subsequent reloads.

I feel this is logical and practical as the bolt components are designed to take the forces generated when firing and have no need to be "helped" by a "toothy" surface finish in the rifles chamber.

A quote from Al's: "Trying to use the weaker brass to lighten the load on the action and bolt face of a rifle by having the brass grip the chamber is analogous to using a car's radiator to protect the bumper in a front-end collision. A polished chamber minimizes case stretching, reduces case head separation, and increases case life."

On to my question. Does anyone here have experience with polished chambers in their AR? Any advice on how to do it? Any cautions?

[GLSHOOTER]

I'm no expert but I'll call BS on this one. The chambers should be smooth on a rifle but that will do nothing to reduce case head separation. If the case fits the chamber correctly it's stretch will be limited. Many guys induce this issue by shoving the shoulders back to far and re-firing the case over and over stretching it until the head case separation occurs.

The "toothy" surface will, in fact, lower bolt thrust to some extent. If you want to see it in action,( DON'T DO THIS!!) you could leave the sizing lube like RCBS Gorilla Snot on your case and fire it. The case will slam back into the bolt head as all the thrust is directed back since the case can't "grab" the chamber walls.

Look at a good rifle barrel, like BHW, and you will see these chambers are mirror smooth to start with. They could be polished up with a bore mop and some JB Bore Paste on a drill but that would be very cautiously done. Many guys do this and increase the size of the front of the chamber and get tuba shaped holes. Not good!!

If the chambers yields cases that look like gravel has been run over them then a polish is in order. In most cases it is not needed.

I'm sure a real experienced shooter or builder will get on here and tel you I am wrong and I may well be but I'll stick with my convictions on this one.

Greg