The gun may just be on the small side of the spec. End of chamber diameter spec for a 16ga is .742 to .732. The end of my Brownells plug gage is .735. When chamber reamers got dull they sharpened them each sharpening made them smaller. Check the chamber length with a barrel wall thickness gauge. The indicator will change direction at the end of the chamber. My 12ga Brownells plug told me an LC Smith had 2in chambers. BWT showed it to be 2 3/4in
Well, I tried every test mentioned. Measureing with a depth caliper simply didn't work. While the chamber looks like it is stepped, the caliper end rod never was able to catch on it. It is apparently a very short radius or cone. A bore gauge pushed in stopped suddenly at the step, and measured 0.731. My Brownell gauge also measures exactly .735 at the front (yes, we have a winner!). To confirm, I tried a Magtech brass case and a Cheddite 2-1/2 inch case. They both measured within .003-.004 of 2-1/2" and were new and unused. With the extractors retracted on dismounted barrels, they both pushed in easily until flush. The trouble appears to be tight chambers and bores.
I have a set of 28" inserts in 28 gauge I recieved on a Parker I bought which really didn't need them. They are a two diameter design and the front has been turned to fit the chokes and the two rear sections are supposed to fit inside the normal bore. The muzzle ends fit well but the steps on the barrel section are oversized by a few thousanths. I need to hone or bore the barrel slightly for some pits in the back half (barrel walls are very thick) and plan to take them down a few thousandth's until the inserts have a proper friction fit. I this doesn't take the barrels enough to cean them up, I will likely use the inserts and shoot light 28's in it. Closest I will likely ever get to buying a hammer 28.
