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Posted: 3/22/2013 9:22:09 AM EDT
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With the powder shortage, I'm not able to get my favorite H-335 for .223 loading, so I'm using WC-844.
I loaded 10 each of 24.0 gr. up to 25.4 gr. (in .2 gr. increments) and test fired them all at 50 yards. Somewhere between 24.6 and 25.2, the primers were backing out to the bolt face, nothing more. Accuracy was best at 24.8 to 25.2, at least it seemed that way. AR 15, 16 inch, 1/9 twist, EOTech 551, 62 gr. pulls, CCI SRM primer, various once loaded brass, 2.235 to 2.240 OACL, NO CRONO. Is this the way to get the best load for plinking and 200 yd. shooting? I'm going to load 2,000 rounds and want to get it right. Thank you. |
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With that combination of components I would load three cartridges at each charge, and increment each charge 0.4 grains. When I reached a load that appeared to be maximum, I would back up and load the next to last charge weight.
I would spend the absolute minimum amount of effort and components on finding a charge weight for that ammunition. |
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With that combination of components I would load three cartridges at each charge, and increment each charge 0.4 grains. When I reached a load that appeared to be maximum, I would back up and load the next to last charge weight. I would spend the absolute minimum amount of effort and components on finding a charge weight for that ammunition. How far do you go until you determine it's at maximum load ? Some might say the first signs of any flattening (but still some curve) Others might want to see complete flattening and crater of pin strike area What's the good stopping point? |
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SteelonSteel, I'm not sure I'm following the headspace thing. At some point, shouldn't I get some movement
of the primer? After all, the crimp is removed so there's only pressure holding the primer in. It's not flattining out the fireing pin divit at all. Thanks for the opinions. So you think crono's the way? Hate to buy one for this. |
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The sure fire way is to measure case head expansion with a micrometer. If a charge causes the diameter to change, that means it yielded. Back down 1/2 grain, or maybe 0.3 grains in a .223 Rem case.
I've seen all sorts of recommendations about tolerable diameter change, from a half thousandth to 1.5 thousandth's. Any measurable change means the head yielded. If there is no change, then we have a reasonable expectation that the primer pocket didn't expand and will continue to hold primers. However, we also need to know whether a yielded head is unsafe, too. Maybe that's important for the guy that intends to load his brass one time. The strain is [change in diameter] / [original diameter], and full hard cartridge brass is good for about 67 to 78 ksi yield strength. The elastic modulus is 16 million lbf/in^2. So, assuming the case head is in full hard condition, the strain at yield is about 67/16000 = 0.0042. Assume the case head is 0.378 inches diameter, so the change in diameter at yield is 0.0042(0.378) = 0.0016 inches, or 0.002 inches on a thousandth's mike. (In a perfect world, the head can deflect to 0.0015 inches, then "spring back" to its original dimension, but the stress-strain relation is not really linear, so it will return along a hysteresis path to a slightly larger dimension.) If the case head is not strengthened to full hard condition, then a smaller change in diameter is allowable. We usually don't know the hardness of any part of our cases, just whether they are "hard" or "soft". So, stopping before any yielding is detected is conservative and frugal if the cost of brass is a consideration. One other detail to note. Cartridge brass in full hard condition has a very small allowable plastic range between yielding and failure, so exceeding the yield stress at the case head is a bad idea. Properties of Olin Alloy 260 Don't place bets that every company uses this same alloy. |
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OK, in a way, I'm sorry I asked! I thought I'd be able to find a good load useing published data and accuracy vs primer movement.
I am clearly following data received on this forum and my extensive collection of reloading books. I am wrong it seems. I've read dozens of threads on reloading on this site and never remember reading about "casehead expantion" in working up a load from published data. I am...after all, just wanting to fine tune a load, not create a new powder or caliber. Thank you for all the technical explanations, but I think I'll stick to a more "tried and true" way of loading these rounds. Safety, observation, and working up slowly from published data, should get me there for these plinkers. I will by the way, measure my brass along the way and use that as a tell as well. Great forum and tons of good info, thanks! |
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Dunno if this helps, but a quick google search showed a couple of folks who clearly have experience using this powder. There seemed to be agreement that lot to lot variation was far greater than H33, and was significant.
Assuming its not a brass issue . . . if your H335 didn't (or won't) back the primers out at similar loads, then there's obviously a difference between this powder and your old friend. |
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Quoted:
OK, in a way, I'm sorry I asked! I thought I'd be able to find a good load useing published data and accuracy vs primer movement. I am clearly following data received on this forum and my extensive collection of reloading books. I am wrong it seems. I've read dozens of threads on reloading on this site and never remember reading about "casehead expantion" in working up a load from published data. I am...after all, just wanting to fine tune a load, not create a new powder or caliber. Thank you for all the technical explanations, but I think I'll stick to a more "tried and true" way of loading these rounds. Safety, observation, and working up slowly from published data, should get me there for these plinkers. I will by the way, measure my brass along the way and use that as a tell as well. Great forum and tons of good info, thanks! Quantitative information always trumps "that looks about right", but in this game, we aren't usually starting with enough known information to make those decisions from real measurements. However, the first part of the method I described is easy to find documented, the problem is that there is no universal agreement on the rule of thumb to use. Some very experienced handloaders recommend zero measurable case head expansion, and that flat grates on other equally experienced reloaders that load hotter and intend to continue loading that way. You can bet they understand what is happening, and chances are they don't care if their brass is good for more than one or two reloads. It's acceptable risk and they manage that risk. I posted the rest of that for Scorpius as I knew he could sort through the numbers without  .
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Thank you, this is definitely a big help. It's beginning to make more sense now. I'm going to use
what I've learned here today, along with the experiance I've already got, to work up a good 3 or 4 loads tonight and fire them tomorrow. At least my original testing narrowed down the loads I can use for these bullets. I'll check former posts again and double check others loads. I'm going to incorporate something I've not done before, and that's measure my fired cases for pressure signs. Thanks for the help and I'll post my results for others to look at. |
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You need 2 to 4 thosandths headspace, the shoulder to case head lenth. Much more and the primer pops back to the boltface before the main charge goes off. The pressure of he main charge then drives the case head rearward reseating the primer which now can look flat even if the pressure was ok. Some dies at cam over will give 8 thousandths free headspace which is excessive. That's 8 thou of air behind the headstamp and boltface as the ejector is pushinf the case shoulder to the chamber shoulder.
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I agree 100% with Smith.
No way I'd load 2000 rounds of anything in a rifle without chronographing the load. As to your other issues with primers "backing out", I also agree that your die setup may not be correct. Primers might flatten, but they should not be "backing out" on you. Get a case gage, and use it correctly. In the absence of a case gage, a good indicator will get you the information you need. http://www.larrywillis.com/ |
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Why do you think a chronograph is so important?
If the load is accurate and is not over pressure it is a GOOD load. What will knowing the velocity do for you other than give you an idea of trajectory, which you can figure out by shooting anyway. I would shoot my groups at 100 yards but I would also use optics (a scope) for the load development. Once you find the most accurate load you can get with that selection of components does it really matter what the velocity is? The OP DID say it was "plinking ammo". |
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give you an idea of trajectory The answer's in the question. You don't need to know the trajectory of .223 ammo being used for plinking and 200 yard shooting. This is what the OP specified. My AR sighted in 1" high at 100 yards is also 1" high at 200 yards. This due to the fact that the sight line is nearly 3" above the bore. |
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