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Posted: 11/10/2010 6:53:05 PM EDT
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I had a so called "brilliant" idea the other day that I could work up 5.56 NATO loads by obtaining some live NATO rounds, pulling the bullets, decapping, swaging, and repriming, then loading, seating, and crimping with my own bullets and powder. That way I would be comparing apples to apples.
I figured that I could then compare case head expansion between my reloads, which would be using unfired brass, and the actual NATO rounds. That would give me an upper limit to what loads I can use. Now I'm reading about how multiple reloadings can work harden the brass and lead to destructive failure after a couple reloads and I'm thinking that sticking to .223 pressures may not be such a bad idea. FWIW, I'm using TAC and the 75gr Hornady HPBT bullets and working this up as my 2000+ round reserve "just in case." Thus far 24.0 gr of TAC is giving me nearly MOA accuracy at 100 yds out of an untuned AR15, so I could be best off sticking with what I've got and not blowing myself up. For folks with a .223 chamber, 24.0 grains is over the recommended max load, so do not use that! I'm being deliberately vague to keep ignorant folks from trying something that I'm beginning to think might be kinda stupid. On the other hand, if someone else has done this before, or thinks it might have merit, I'm interested to know. |
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"I had a so called "brilliant" idea the other day that I could work up 5.56 NATO loads by obtaining some live NATO rounds, pulling the bullets, decapping, swaging, and repriming, then loading, seating, and crimping with my own bullets and powder. That way I would be comparing apples to apples."
Do these NATO loads involve crimped primers? |
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Actually, I would deliberately remove the crimp and primer so that I could reprime with the primer I intend to use on MY load. I would also be using 75gr instead of 55gr bullets. Perhaps not so much apples to apples as I thought. I imagine the heavier bullet and different powder might change the pressure curve and make case head expansion comparisons less reliable.
I shoot a rifle-length gas system, so I'm not too worried about loosing primers. That is a consideration for the carbine though... |
| As you likely know, not all brass is created equal. If you want to use case head expansion to estimate pressure in a cartridge, you really need to use identical brass. In the past, the advice I read to was purchase some full power loads from a manufacturer like Federal, and then purchase some of their brass too. I've not seen 5.56 NATO headstamp brass available for sale unfired very often. I think that using 5.56 NATO rounds that I've disassembled for the brass is going to get me pretty close to the once-fired military brass I'm planning to use for my loads. |
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Quoted:
I had a so called "brilliant" idea the other day that I could work up 5.56 NATO loads by obtaining some live NATO rounds, pulling the bullets, decapping, swaging, and repriming, then loading, seating, and crimping with my own bullets and powder. That way I would be comparing apples to apples. I figured that I could then compare case head expansion between my reloads, which would be using unfired brass, and the actual NATO rounds. That would give me an upper limit to what loads I can use. Now I'm reading about how multiple reloadings can work harden the brass and lead to destructive failure after a couple reloads and I'm thinking that sticking to .223 pressures may not be such a bad idea. FWIW, I'm using TAC and the 75gr Hornady HPBT bullets and working this up as my 2000+ round reserve "just in case." Thus far 24.0 gr of TAC is giving me nearly MOA accuracy at 100 yds out of an untuned AR15, so I could be best off sticking with what I've got and not blowing myself up. For folks with a .223 chamber, 24.0 grains is over the recommended max load, so do not use that! I'm being deliberately vague to keep ignorant folks from trying something that I'm beginning to think might be kinda stupid. On the other hand, if someone else has done this before, or thinks it might have merit, I'm interested to know. Where are the apples? The cases are the only component common to both loads, and they will need to have the primer crimps removed first. Everything is else is different. I think you mistakenly believe that there is a difference between LC brass and .223 Rem brass. Mostly there's not, except for one import that has really heavy cases. LC, Winchester, and WCC are essentially the same. Lapua is very close. Remington brass is about the same capacity but the shoulders are annealed to a softer state. |
| Frankly, the "apple" is the case. Assuming that the case expansion actually reflects a reasonable estimate of max. pressure of the load, then case expansion should be relevant. However, I've been reading about case head expansion measurements and PSI vs. CUP and I find myself unconvinced that my "idea" is worth pursuing. I'm thinking that an accurate round is much better than an inaccurate round that blows up in my face under hot, dirty-barrel conditions. |
| I would stick to the published data as case head exspansion is just one sign of higher pressure.Unless you have access to pressure testing equipment you don't wanna just take a guess a what's to much. Also case head exspansion will vary with differant rifle chambers. |
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Quoted:
Frankly, the "apple" is the case. Assuming that the case expansion actually reflects a reasonable estimate of max. pressure of the load, then case expansion should be relevant. However, I've been reading about case head expansion measurements and PSI vs. CUP and I find myself unconvinced that my "idea" is worth pursuing. I'm thinking that an accurate round is much better than an inaccurate round that blows up in my face under hot, dirty-barrel conditions. There is no simple direct correlation between crusher pressure and pressure measured with piezo gages, and measuring head expansion in an attempt to correlate to those is pretty much a lost cause outside the lab. When measuring head expansion, a "no go" criteria is needed. I've seen everything ranging from no measurable expansion to 0.003 inches maximum. What we're trying to do by measuring head expansion is measure the strain in the head, so the first thing we need is an allowable strain. I would choose the strain where the case starts to yield, not necessarily the maximum elongation which is roughly 5% for full hard cartridge brass. The strain can be shown to be equal to the [change in case head diameter]/[original case head diameter]. If any change in diameter is measurable, that means the case has yielded slightly and as a result, the primer pocket is slightly larger. That's a pretty good cutoff for excellent case life. Some small change in diameter is okay, but it can't be determined by simply picking a number that applies to all cases. The equation I wrote above shows us that the original case head diameter has to be considered in each case. This is where a rule of thumb for maximum case head expansion starts to fall apart. Anyway, your instinct that a fast miss is still miss is good. I'll take accuracy. Besides that, and this is a drum I've beat the crap out of here, the difference in the trajectories of two bullets starting out 100 fps apart is not worth discussing inside 300 yards or so. |
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Crow if you are trying to duplicate, say M855, I am with you. IIRC I have a load at home I plan on testing. My prior attempts fell way short of 3,000 fps and I am using once fired Privi brass that was M855 initially. I can IM you the load or wait until I chrono. Posted Via AR15.Com Mobile |
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Here is what I do to make mil-spec rounds:
Use mil-spec brass. Use mil-spec bullet. Use mil-spec primer. Use mil-spec powder, or very close equivalent. Use chrono to compare known, fresh mil rounds with reloaded rounds, working up to velocities of mil rounds. Done. Anything else is guesswork. Or worse. FWIW, I personally take a great deal of care in prepping my cases, as well as ensuring the proper powder charge is thrown into each case. My Generic Mil-Equivalent rounds have proven to be considerably more consistent (and thus more accurate) than any milsurp ammo I have tried. I hasten to add that I have not tried every milsurp ammo type/mfr, but I can read the published accuracy specs, as well as see the dramatic difference between my mil-surp equivalents and common milsurp ammo. Whether you chose to load/emulate mil-type ammo or some other type, the main point is how well can you and your rifle shoot with it. Getting hits counts. Whatever ammo you use you must hit. You must also be able to use your sighting device(s) to make hits at varying ranges, sometimes with little warning, and and at dramatically different ranges. Give some thought to this when making up your general ammo. Also consider that you might have to accept ammo from another person, and share yours. How much different from the mil-spec standard ammo can your ammo afford to differ in such (SHTF) circumstances? How far off the target can you afford to be, if TSHTF? These are questions best answered by the individual. There is no one answer. As for myself, I will continue to crank out very good milsurp equivalents that match my iron sights, and the hash marks on my scopes. YMMV. |
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