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Old May 4, 2005, 08:51 PM   #6
Sturm
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Join Date: March 2, 2005
Location: Central Texas
Posts: 584
Tj, you can do this in one or two operations, depending on the amount of time you want to spend doing it. I'll start with auto pstol cartridges first. I seat and crimp in 2 seperate operations and my equipment is what I consider precision. I seat my bullets about .001" short of the actual desired finished length because I have found that the the taper crimp die lengthens them about .001". Of course this is nitpicken. If you have your seating die adjusted correctly it is going to provide tension when it removes the bell from the expander (second) operation and the bullet will be fairly snug at this point, So at this point, I measure as close as possible to the casemouth to get a dimension and taper crimp to .002" less than that diameter for .40 and .45, and .001" or between .001 and .002 with 9mm and you can read .0015" on your dial caliper. Same thing it's the middle of .001 and .002"!

A while back a fairly new reloader posted a technique he had been wondering about using and after I thought about and investigated it a little, I found it to be very sound practice. With your dial calipers, measure the case wall thickness at the mouth and you can determine the finished crimp diameter and manufacturers case thickness variations are negated. Say your case thickness measurement is .011" with a .45 ACP case and you want .002" of taper crimp, it's easy, you just use this simple formula. Casewall thickness X 2 + bullet diameter (.451 in this case) and subtract .002" (amount of desired crimp), .011" X 2 = .022" + .451 = .473 - .002" = .471" for your taper crimp diameter with that particular brand of brass. See, you can teach an old dog new tricks! One other thing worth noting is that Commercially Hard cast bullets usually run about .001" larger in diameter than Jacketed. Some choose not to taper crimp because adequate tension (bullet pull) is aleady there. But, if you want some taper crimp with a bullet that is oversized already by .001", A thousandth of an inch will most likely get you want you want. You can use the formula and adjust the bullet and taper crimp values.

For revolvers, there is a very simple way to get a perfect crimp. First, buy a REDDING Profile Crimp die. Yeah, I'm more than happy to help you part with some money here, you'll thank me later, and so will your group sizes! A heavy roll crimp as you see recommended for even target loads by some, means different things to various reloaders. As with pistol loads, what you are trying to do here is achieve bullet pull (tension) on the shank of the bullet, and if the expander is slightly large in diameter, most of the crimp will only come from rolling the casemouth brass into the bullets cannelure. Fairly easy to overdo this, btw. What the Profile crimp die will do for you is to size the brass down in diameter as your crimping, like a taper crimp die, but it will also still give the roll crimp with it, when you need it for heavy magnum loads. Then you have the best of both worlds. You know you will get adequate bullet pull and you have a roll crimp to assist that and also lock the brass into the cannelure. Until you get a REDDING Profile Crimp die and using the one you have, adjust in very small increments. First just allowing the brass to barely touch the crimp ring. Lower the ram and rotate the crimp die 1/8th turn deeper and look closely at the result at this point. Use a magnifying glass if you have one and if it needs more crimp go to 1/16th turn and repeat with each depth rotation a liitle less than the previous one until you reach your goal. One thing I also do, is to trim brass occasionally for the purpose of getting consistent lengths with my cases for crimping and I seat bullets that will put the casemouth into the middle of the cannelure. The Loading manuals will give you C.O.A.L. in most cases some don't. My personal philosophy is to get reloading manuals that do, and that also provide pressure data for that load. If your cases are max. length it is not necessary to trim to recommended trim length. .005" will do, you'll just have to trim again sooner. But for a game load or wanting that ultra satisfying magnum group, you might find it worthwile. What you don't want, is so much roll crimp, the casemouth is distorted and if you see the crimp ring below the casemouth on the brass and it appears to be wanting to be a different curvature from the brass below that ring, you have gone too far. Here's an example with .357 Mag. My brass is 1.290" in length. I am going to trim to 1.285" and use the procedure for seating and crimping in 2 operations crimping the brass into the middle of the cannelure. After I have seated and crimped my COAL is 1.585 with brand X of bullet, but the manual say's 1.590. First, I'm not likely to worry about such a small variation. But say my COAL was 1.580" and I was using a max. charge of powder, I would divide 1.580 by 1.590 to get the percentage of variation and I would find that my load is 99.4% of the reloading manuals recommendation. I still want a maximum charge because I have previously worked it up and started from a minimum charge. In this case I'll use VV data with a 158 gr. SPEER JHP, be the VV data I have is the most recent and it complies easily with SAAMI guidelines. The max. charge is 16.3 grains, so I'll multiply by .99 to adjust the powder charge for the variation in length. The calculater says, 16.137 and until digital scales get that accurate, I just measure 16.1 with my RCBS RC-130 powder scale.

It appears that I have done it again on the long post thing, so I hope it helps!
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