DougGuy
This has been the week for chamber weirdness it seems. Had a couple of problem children come in that would not chamber even factory ammo half the time.
One was the cylinder of a S&W Model 22-4 of 1917 Classic. In .45acp. In the customer's own words:The cylinder came in and I could not get a .471" gage pin all the way down in some of the chambers, none of my assorted dummies would chamber. Surprisingly, all of the throats were .4525" on the nose and very even at that! After computing chamber depth to be .819" using my self made headspace micrometer, I set a collet depth stop on a Manson reamer that I had Dave grind the throat section off, this one is strictly for cutting the chamber depth and diameter. I used this modded reamer and was surprised at the metal it removed. It filled the flutes completely in each hole. It wasn't just a shave, the chambers were seriously undersized and egg shaped as well. Once the reamer finished it's work, a .474" gage pin would go all the way down to the headspace ledge and turn, this is as it should be.The chambers are smaller than SAAMI maximum. Enough so that factory ammo with full metal jackets chamber with few problems using moon clips. But my cast lead reloads only go in about 1/2 to 2/3 of the way. My reloads plunk in a case gauge and in my Ruger SR1911. I end up trying to swage them down smaller and simply cannot do it for this gun.
After adding the chamfer to the back, polishing and rebluing the holes, I could hold a speedloader 6" to 8" above the cylinder and drop it onto the cylinder where 9 out of 10 attempts had it falling fully into the chambers like butter. I am sure the customer will have a big grin on his face the first time or two he takes this gun out to the range!
The other one was a Springfield EMP in 9mm caliber. This one came in and none of my dummies would plunk, none of his handloads would plunk, I pulled one of his dummies and the boolit was down to .353" on one side and in the case all eccentric. The chamber would take a .379" gage pin at the largest. If you subtract the .012" case walls from the gage pin's diameter, you come up with .355" which will be too small to perform well in the barrel once fired. His empty cases were .379" and barely fit in the chamber.
Dave Manson sent me a finishing reamer with the throat section made onto it so it cuts the chamber and the throat, which worked great in the chamber, after reaming, the chamber was .382" at the headspace ledge, which is perfectly acceptable. But after pinning out the throat it wasn't quite to my satisfaction so I used another modified Manson reamer, this one ground down from a 35 caliber rifle throater (cuts a larger throat) and I throated the barrel with this to get enough .358" freebore to finish the job.
This gun had been sent back to Springfield twice, and they either failed or refused to address the less than SAAMI spec chamber, or the issues the customer was having with it.
As important as the throat diameters are, this just goes to show that throats can be and often are just one part of the problem..... Revolver chambers that are cut with uneven reamers are different in volume as well as size, these will definitely contribute to pressure variables when the gun is fired, not only can extraction be improved by finish reaming the chambers -IF- they are undersized, but groups will improve also when all of the chambers and throats are identical in size and volume!
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. Pistol accuracy appears to be better, but the idiot pulling the trigger had some failures. Getting old is a b**ch! Thanks Doug for your good work.
