The reason the problem is more common with the 45lc rifle is because the makers all use the maximum SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) specs when they ream the chambers for the gun. They do this so the gun will more likely cycle with a broad spectrum of ammo's. This is why semi-auto pistol with match grade guns are finicky about the ammo they will run. The match grade chambers are tight.
I do warranty work for EMF. They import the Rossi M92 as well. Over the years the EMF folks have had me do chamber cast on various rifles because the customer insisted the chambers were bad. One feller bought an EMF 92 and before he ever shot it sent it to Doug Turnbull for color-case work. Once he shot it with his CAS loads he found that the cases would swell but only on one side. This to him indicated a bulged chamber. He sent the rifle to me along with some of his bulged fired brass to verify this. I did a chamber cast and found the chamber to be within SAAMI spec. and the cases were truly bulged but not beyond SAAMI. Think about this. If the chamber was bulged and the brass was bulged to match extraction would be difficult. Not the case here. The fired bulged brass would easily chamber and fall right out if the open rifle was held vertical. The brass was bulged because that was the softest or the thinnest area of the case, not because the chamber was bad. He insisted, they gave him his money back and I bought a Doug Turnbull CC-ed rifle on the cheap from them.
More recently, they had a feller send me a 92 and a 73 for the same reason. He insisted the chambers were too big on both. I cast both guns and both guns were within SAAMI. He still insist that they are bad, that SAAMI spec are not correct and the industry should do something about it.
This diagram shows both cartridge and chamber dimensions. Please note that unless noted all diameters are +.004 and there .200" inside the chamber the nominal is .4862. If you add .004 to that the chamber can be as large as .4902 and still be in spec. I believe this all came about when the industry changed from the non rebated old balloon style cases like the one shown to the modern rebated rim swagged brass. Notice the max bullet dia. .456. Modern 45lc bullets run to only about .454 max with the majority at .452. The current ammo specs don't fill the chambers like the old balloon case ammo. So hard brass and down loaded CAS ammo will exhibit these problems.
This 45LC blow-by in the rifle problem has been going on for so long now I believe the IMR folks came out with their Trailboss powder just to combat this. A good book charge of Trailboss and a 250 grain bullet crimped well in a Win or Starline case seems to be the solution for some folks. Win or Starline cases are somewhat softer brass than most of the others. Some folks only neck size their once fired rifle brass. For BP, there are some folks using 44-40 brass blown out to 45 and claim it works well. 44-40 brass is really thin.
For the most part the blow-by is negligible for CAS loads because accuracy is not needed. But, if you are getting blow-by you can be sure the pressures are fluctuating which means you POI is deviating, too.
I will say though, I've had some CAS rifles in 45lc sent to me because they were no longer extracting consistently. What I found was a build up of fouling under the extractor that was holding it off enough to not let it hook the rims.
Steve Young aka Nate Kiowa Jones Sass# 6765
Steve's Guns aka "Rossi 92 Specialists"
4525 Alamosa st.
Port Arthur TX 77642
www.stevesgunz.com
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