bigedp51 is spot on with his explanation for why you get flattened primers with loads that are not near maximum.
I experienced this over two decades ago loading for my M1a. I was given advice by a Distinguished HM gunsmith to leave the sizing lube on my cases, that is fire lubricated cases, and my cases would last, basically forever. And basically, that was true, I never had a case head separation after lubing my M1a cases. What I also found that the primers on my loads where now rounded whereas with the dry cases, the primers were flattened. Obviously the pressure had not changed one way or another, so what was happening was that with dry cases, the case is stuck to the chamber walls, the primer backs out, expands like a muffin, and the case side walls stretch, stuffing the expanded primer back in the pocket. With a lubricated case the case must slide to the bolt face, stuffing the primer in the pocket, well before pressures are high enough to expand the primer or stretch the case.
Also, given that the sidewalls are not stretched, the cases don't experience case head separation. Typical advice is to reload cases no more than five times in a Garand/M1a and toss the case. This is due to case head separation. These mechanisms are hard on cases but I took one set of LC 66 twenty three firings without a case head separation. These sectioned cases are mine, along the way, some cases experienced case neck splits, body splits, and I sectioned them to see what was going on in the interior. R refers to the number or times reloaded. R5 is five times reloaded, R22, twenty two times reloaded. The FAL case, which I think was once fired, or a couple times fired, in a buddy's FAL, shows obvious signs of case head separations.
Now this is what happens when you have the case sidewall carry load: the case stretches and fails.
These cases were fired dry, five times in a buddy's M1a. You can see why the advice to load five times and toss is good advice, if you fire dry cases in these actions.
Many in the shooting community believe that lubricated cases raise combustion pressures and this is without foundation.
What lubricated cases due do is to full load the bolt face as parasitic friction between the case and chamber is eliminated. What also happens is that you will see the true transition from rounded to flattened primers in a gas gun. When developing loads, I lubricate all my cases. I don't want false indications of safe pressures, which dry cases in dry chambers will give you. The pressure does not go away with dry cases, the barrel chamber and case are carrying more of the load than they should. And, because the case is carrying load through the sidewalls (stretching the case, remember) the bolt face is not fully loaded, which gives a false safe pressure indication. I want stiff bolt lift when I hit a maximum load, I don't want pressure indications disguised by the friction between case and chamber. I want to see the transition when primers go from round to flat, and I don't want to stretch my cases.
Anyone thinking that oiled cases causes high pressures in your rifle is wrong. Oil revealed your overpressure loads because now, with the bolt fully loaded, you are having sticky extraction. Your loads were always too hot but parasitic friction between case and chamber disguised the pressure indications.
Recently I have been doing load testing in a 30-30. The difference in headspace between new cases and the sloppily cut chamber is amazing. New cases properly headspace in my 30-30 Wilson gage, and yet after firing, they are 0.017"above the gage "No Go". Cases are not meant to stretch much more than 0.006" and had I fired these cases dry, it is likely I would have experienced case separations on the first firing. As it was, because I had fired these cases lubed, they slide to the bolt face and I won't have any side wall thinning. Belted magnums are just as bad and I fireformed all my new, hideously expensive 300 H&H cases lubed. They all fireformed perfectly to the chamber. Hopefully everyone knows that shoulder headspace is not controlled with belted magnums and belted magnum chambers vary considerably. The previous owner to my rifle experienced case head separations in three loadings, I think some of my cases are there, and not a sign of sidewall separation to be seen.
Now I am going to add some real speculation on this. I think lubed cases produce more accurate results. Dry cases load the action in unpredictable ways as the friction between case and chamber varies. With lubricated cases I am loading the action the same way each shot and so the action dynamics should be more consistent shot to shot.
I experienced this over two decades ago loading for my M1a. I was given advice by a Distinguished HM gunsmith to leave the sizing lube on my cases, that is fire lubricated cases, and my cases would last, basically forever. And basically, that was true, I never had a case head separation after lubing my M1a cases. What I also found that the primers on my loads where now rounded whereas with the dry cases, the primers were flattened. Obviously the pressure had not changed one way or another, so what was happening was that with dry cases, the case is stuck to the chamber walls, the primer backs out, expands like a muffin, and the case side walls stretch, stuffing the expanded primer back in the pocket. With a lubricated case the case must slide to the bolt face, stuffing the primer in the pocket, well before pressures are high enough to expand the primer or stretch the case.
Also, given that the sidewalls are not stretched, the cases don't experience case head separation. Typical advice is to reload cases no more than five times in a Garand/M1a and toss the case. This is due to case head separation. These mechanisms are hard on cases but I took one set of LC 66 twenty three firings without a case head separation. These sectioned cases are mine, along the way, some cases experienced case neck splits, body splits, and I sectioned them to see what was going on in the interior. R refers to the number or times reloaded. R5 is five times reloaded, R22, twenty two times reloaded. The FAL case, which I think was once fired, or a couple times fired, in a buddy's FAL, shows obvious signs of case head separations.
Now this is what happens when you have the case sidewall carry load: the case stretches and fails.
These cases were fired dry, five times in a buddy's M1a. You can see why the advice to load five times and toss is good advice, if you fire dry cases in these actions.
Many in the shooting community believe that lubricated cases raise combustion pressures and this is without foundation.
What lubricated cases due do is to full load the bolt face as parasitic friction between the case and chamber is eliminated. What also happens is that you will see the true transition from rounded to flattened primers in a gas gun. When developing loads, I lubricate all my cases. I don't want false indications of safe pressures, which dry cases in dry chambers will give you. The pressure does not go away with dry cases, the barrel chamber and case are carrying more of the load than they should. And, because the case is carrying load through the sidewalls (stretching the case, remember) the bolt face is not fully loaded, which gives a false safe pressure indication. I want stiff bolt lift when I hit a maximum load, I don't want pressure indications disguised by the friction between case and chamber. I want to see the transition when primers go from round to flat, and I don't want to stretch my cases.
Anyone thinking that oiled cases causes high pressures in your rifle is wrong. Oil revealed your overpressure loads because now, with the bolt fully loaded, you are having sticky extraction. Your loads were always too hot but parasitic friction between case and chamber disguised the pressure indications.
Recently I have been doing load testing in a 30-30. The difference in headspace between new cases and the sloppily cut chamber is amazing. New cases properly headspace in my 30-30 Wilson gage, and yet after firing, they are 0.017"above the gage "No Go". Cases are not meant to stretch much more than 0.006" and had I fired these cases dry, it is likely I would have experienced case separations on the first firing. As it was, because I had fired these cases lubed, they slide to the bolt face and I won't have any side wall thinning. Belted magnums are just as bad and I fireformed all my new, hideously expensive 300 H&H cases lubed. They all fireformed perfectly to the chamber. Hopefully everyone knows that shoulder headspace is not controlled with belted magnums and belted magnum chambers vary considerably. The previous owner to my rifle experienced case head separations in three loadings, I think some of my cases are there, and not a sign of sidewall separation to be seen.
Now I am going to add some real speculation on this. I think lubed cases produce more accurate results. Dry cases load the action in unpredictable ways as the friction between case and chamber varies. With lubricated cases I am loading the action the same way each shot and so the action dynamics should be more consistent shot to shot.
