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Old December 3, 2009, 10:43 AM   #1
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How to get consitent taper crimp readings in .45auto?

Using a dial caliper, how do you get consistent readings for the taper crimp on, for example, .45auto?

I'm talking about the trouble I have actually taking a reading on a case.

So what I do is eyeball the case to see if I get a straight line reflection of my overhead fluorescent tubes.

For roll crimps, I look for a slight bend in the reflection at the mouth.

Otherwise, I find it nearly impossible to get consistent readings, even on the same case.

Do you guys use the fat part of the caliper, or the knife-edge part? Do you take readings with the case mouth horizontal or vertical?

Please know that I am not having any problem correctly crimping my cases. But I have read here and elsewhere about the importance of a correct crimp. Well, at the numbers thrown around in .45auto, say, .469 up to .472, there is no way one can accurately and consistently measure by hand such a fine range (4 thou) on the very end of a round object. I'm not planning to change my technique, just wondering how you guys take your measurements.

What gives?

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Old December 3, 2009, 11:00 AM   #2
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i have tried getting a reading for mine this past go round and it was difficult. i used the knife edge and really paid attention to where i measured. not worth it imo. i dont have an issue yet with col getting smaller in my 1911 so i am not worried.
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Old December 3, 2009, 11:08 AM   #3
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Here's what I do...

First of all, I trim my cases to get a uniform case length. Some people dont think its necessary to do this. But me, I dont mind doing it, and it helps with the taper crimp. Plus, I seat my LEAD bullets according to UncleNicks recommendations, so that I just headspace off of the bullet. It is supposed to reduce leading and increase accuracy with lead bullets. (and seems to work!)

When I have my cases ready for loading, I'll flare one, then run it through the taper crimp with out a bullet. I adjust my taper crimp die until I get a measurement of the case mouth equal to a case that has been sized. Once I get that, I just go to town primering, charging, seating, crimping... (repeat as necessary......!)
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Old December 3, 2009, 11:28 AM   #4
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I use the knife edge. I try to be consistant with it. Once the die is setup correctly I just leave it alone. Checking every once in a while.
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Old December 3, 2009, 08:07 PM   #5
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i use a digital caliper. some brass, like remington that is nickel plated, is very resistant to change. When I put it through my factory crimp die, it glides in and out like nothing happens. other kinds of brass, is different. I can always tell which is remington brass like this.
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Old December 3, 2009, 08:46 PM   #6
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Using the dial caliper I just use the wide part against the flared mouth... .475" sounds about right for jacketed bullets... and turn the LFCD in until I get .470"-.472" ...more or less straight with the discernable taper at all.

You just want to remove the flare.

Consider getting a loaded case gauge and drop them in occasionally while loading. You will get the feel between a flared, slightly flared, straight mouth pretty easy. I like a clean fit, absolutely no resistance.
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Old December 3, 2009, 10:27 PM   #7
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I try to take a few measurements with the knife edge. I try to keep a little pressure on the caliper as I slowly move it to the edge of the case. I find you can tell pretty well what the dimension is just as it slides off the case.

As long as it's in the ballpark I then measure the oal length and then push the bullet end hard, by hand, against the wooden edge of my bench. I push hard enough to make a little dent in the wood (fir). Then I remeasure, if it hasn't changeed oal it's tight enough.
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Old December 3, 2009, 11:03 PM   #8
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To get consistent crimp you will need two things: Same case length and same wall thickness coming at the mouth. This will mean brass that was trimmed uniform when new and has the same load history, and it will probably mean brass that is the same brand and maybe even the same lot.

Once you have that, the crimp is going to be as consistent as your press can make it. I like to see the brass bite into lead to prevent setback. For that purpose I measure the brass over the bullet just below the crimp, then look to see it is about four or five thousandths smaller immediately below the case mouth. If I have that, I believe I have an adequate crimp, and whatever it is exactly, that it will be the same from round to round.

If you want to replicate crimps precisely, you will need to get some chucking reamers and make some precise holes in some eighth inch metal plate in 0.001" increments and find the right hole for each brass brand that gives you the same height from the case head to the plate each time. It's a lot of trouble to go to, not to mention the expense of the reamers. If you headspace on the bullet, as mentioned earlier, that will set adequate start pressure up. Then you are relying on the crimp mainly to hold the bullet through feeding and its exact dimensions are less critical.
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Last edited by Unclenick; December 4, 2009 at 08:27 AM.
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Old December 4, 2009, 07:19 AM   #9
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Crimp on the .45 ACP round (or any round that headspaces on the case mouth) is not really a critical factor. I would concentrate more attention on ensuring that the case mouth has sufficient tensionon the bullet. Seat a bullet and try to push it back into the case (before crimping). You should not be able to move it no matter how hard you push. Once you get to this point the crimp is used only to remove the flare from expanding. Trimming ACP cases is kind of a waste because in time they just going to get shorter and most of the new cases I have measured are short to begin with. A heavy crimp is not going to stop setback and can actually make it worse.
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Old December 4, 2009, 08:14 AM   #10
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wondering how you guys take your measurements.
I don't. In fact, the idea is new to me, despite having been at this reloading business for many years.
My first reaction to the question was "why would you want to do that?". No criticism intended there; the quest for precision is part of the hobby and this, I can see, is another step toward that goal.
If I have any point to make, it's that I haven't found it necessary to add that step to my reloading regimen. I shoot a regular schedule of Bullseye matches and, consequently, load a LOT of .45s. They always chamber; they always go bang; I have my share of clean targets, so they shoot straight if I do.
The most that I do is, occasionally during a reloading session, drop a finished cartridge into a Wilson gauge.
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Old December 4, 2009, 02:04 PM   #11
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I am not going to change my methods (described in original post). I was just wondering how those of you who take the measurement actually do the measurement.

My method is visual inspection, and barrel check.
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Old December 4, 2009, 04:00 PM   #12
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Taper crimp

I use a micrometer. ......469/70
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