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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
brass showing pressure signs at lower powder charges with subseqent firings
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<blockquote data-quote="Brent" data-source="post: 33322" data-attributes="member: 99"><p>Jon,</p><p></p><p>With my 30-338 Lapua Imp I worked up and settled on 90gr RL25 with the 210 JLK seated .005 into the lands, 3.820 or there abouts. MV was about 3200 with a 215M.</p><p></p><p>I'm shooting 88gr and a 210M, with MV about 3165 now. I've loaded the brass 7 times now, FL sized each time, bump less than .002 and had to drop a bushing size in order to retain the .001 neck tension after the 5th firing, as necks were harder and just didn't pull down enough with the .331 bushing any longer. My headspace though, it has always remained the exact same thing since the first firing, fired, and sized. </p><p></p><p>Mines a tight neck, turned for .002 total clearance, and so far I've managed to get away without anealing yet. I need to after the 3rd or 4th firing on them though, just put it off and kept loading. </p><p></p><p>My Retumbo load had to be cut back too, it was way too hot to keep loading at the charge I started with as well. About 96gr is where I maxed out before at about 3250 fps. Now I'm at 90gr, and about 3180 at the same pressure...</p><p></p><p>So far, my thoughts on it lead me to wonder if the throat roughening up after a couple hundred rounds results in a loss of efficency. I can't trace it to anything else. I've been monitoring chamber pressure with the Oehler M43 and Southwest Products PressureTrace, so the comparisons are based off the before and after PSI numbers as well as their corresponding MV averages. Powder lot #'s, primers, OAL and everything were identical, I even waited for temperature to approach the same as the tests done last fall. Even then, the lower pressure loads were fired in warmer temps. I had wondered if the cold (+20 deg) was reducing the bore diameter enough that that was some of the cause, but it was not. Originally the pressures were "way" off the scale, 75-80,000 psi where they normally were about 68-70k psi. Half, well almost half of my psi problem was a result of excessive fouling because I shot it until I had over 100 rounds through it to see when accuracy would fall off. Never the less, I still had to drop the load, pressure just did not come down all the way like I'd hoped. </p><p></p><p>When I get new brass, I'll see what effect it has on this all over again, anealing these will be interesting also.</p><p></p><p>I kind of do the same thing as you on the load development end, but instead of the MV "flat spot", I look for velocity points where the POI shifts up then down or the opposite, the flat sopt there. Hopefully the MV isn't erratic there when I'm done. Optimally I'm looking for a range to load that my POI is stable after shifting high, and I have enough capacity (pressure range) left to load higher until the POI shift moves down or flattens off before moving up again. Keeping the loads ES in mind, MV shift points, POI shift direction, and temperature effect on the loads MV, you pretty well know where to load for a certain temp range and if one end of the range will stack errors and go vertical much faster than the other that may cancel some of them out if you fell into that range. </p><p></p><p>Unfortunately a couple of my good loads don't produce a low POI shift with an increase in MV due to harmonics, just flattened out and went lower if you backed off MV, which just coumpounds the problem. I've got to recheck everything again with it in the new stock now.</p></blockquote><p></p>
[QUOTE="Brent, post: 33322, member: 99"] Jon, With my 30-338 Lapua Imp I worked up and settled on 90gr RL25 with the 210 JLK seated .005 into the lands, 3.820 or there abouts. MV was about 3200 with a 215M. I'm shooting 88gr and a 210M, with MV about 3165 now. I've loaded the brass 7 times now, FL sized each time, bump less than .002 and had to drop a bushing size in order to retain the .001 neck tension after the 5th firing, as necks were harder and just didn't pull down enough with the .331 bushing any longer. My headspace though, it has always remained the exact same thing since the first firing, fired, and sized. Mines a tight neck, turned for .002 total clearance, and so far I've managed to get away without anealing yet. I need to after the 3rd or 4th firing on them though, just put it off and kept loading. My Retumbo load had to be cut back too, it was way too hot to keep loading at the charge I started with as well. About 96gr is where I maxed out before at about 3250 fps. Now I'm at 90gr, and about 3180 at the same pressure... So far, my thoughts on it lead me to wonder if the throat roughening up after a couple hundred rounds results in a loss of efficency. I can't trace it to anything else. I've been monitoring chamber pressure with the Oehler M43 and Southwest Products PressureTrace, so the comparisons are based off the before and after PSI numbers as well as their corresponding MV averages. Powder lot #'s, primers, OAL and everything were identical, I even waited for temperature to approach the same as the tests done last fall. Even then, the lower pressure loads were fired in warmer temps. I had wondered if the cold (+20 deg) was reducing the bore diameter enough that that was some of the cause, but it was not. Originally the pressures were "way" off the scale, 75-80,000 psi where they normally were about 68-70k psi. Half, well almost half of my psi problem was a result of excessive fouling because I shot it until I had over 100 rounds through it to see when accuracy would fall off. Never the less, I still had to drop the load, pressure just did not come down all the way like I'd hoped. When I get new brass, I'll see what effect it has on this all over again, anealing these will be interesting also. I kind of do the same thing as you on the load development end, but instead of the MV "flat spot", I look for velocity points where the POI shifts up then down or the opposite, the flat sopt there. Hopefully the MV isn't erratic there when I'm done. Optimally I'm looking for a range to load that my POI is stable after shifting high, and I have enough capacity (pressure range) left to load higher until the POI shift moves down or flattens off before moving up again. Keeping the loads ES in mind, MV shift points, POI shift direction, and temperature effect on the loads MV, you pretty well know where to load for a certain temp range and if one end of the range will stack errors and go vertical much faster than the other that may cancel some of them out if you fell into that range. Unfortunately a couple of my good loads don't produce a low POI shift with an increase in MV due to harmonics, just flattened out and went lower if you backed off MV, which just coumpounds the problem. I've got to recheck everything again with it in the new stock now. [/QUOTE]
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brass showing pressure signs at lower powder charges with subseqent firings
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