I am reloading for Bullseye competition and was told to ensure that the crimp on the 45 ACP was no more than 0.469.
Couple of questions:
1. How does one measure the crimp?
2. Does "no more than 0.469" mean that the measured crimp of 0.470 is OK (because you are crimping from 0.472 or thereabouts) or is it the other way around i.e., the crimp diameter is 0.468 or 0.467 …?

Thank you

Jas

Using RCBS dies, i set the crimp by feel & how the round chambers. With the COL set on the round, ram fully up,turn the taper crimp die down by hand as tight as you can. You will feel it crimp. Drop the round into the barrel. Does the round chamber fully? If not, screw down the taper crimp die a tiny amount at a time till it does. Use brass of the same lot & brand so trim length is close to the same. I have never trimmed 45acp brass.

I never could get a accurate read on my 45 acp or 9mm. I just keep screwin the die down till they went and tighten it down. I might be on the extractor too. I dont know. Do you have to have a micrometer to measure it? It must be pretty close cause I ve shot thousands of rounds setting crimp like that.

quote:

Originally posted by Jas Madhavan:
45 ACP
1. How does one measure the crimp?
2. Does "no more than 0.469" mean that the measured crimp of 0.470 is OK (because you are crimping from 0.472 or thereabouts) or is it the other way around i.e., the crimp diameter is 0.468 or 0.467 …? ...

You sure have received some confusing and totally incorrect information along the way. No wonder you are having a hard time trying to understand what to do.

First off, the 45ACP "Headspaces" off the Case Mouth. So, the main thing is to make sure the Case is the correct length and that would be by measuring it with a 0.001" capable Caliper. If it is too long - Trim it to the proper length. The inexpensive Lee Case length Gauge/Trimmer is excellent for this and will make them all the same length.

You can also drop a Resized but not Flaired Case into the Chamber as shown in 243win's flicks. The Case Head needs to be nearly Flush and barely below. If it sticks out too far, the Case needs to be Trimmed.
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Next, you only want to straighten the Case Mouth, not Crimp it in any at all. Your Die Set probably came with a Taper Crimp(or a Profile Crimp which is slightly different), but I doub't it came with a Roll Crimp(since the Case Headspaces off the Case Mouth).

So, you Seat a bullet and then begin checking the Taper Crimp. You can either measure it with the Calipers(which should be the same diameter measurement as 1/8" back of the Case Mouth) or lay it on a piece of Glass and look to see if the Case Mouth is holding it up. If it still needs a bit more Taper, re-adjust and check it again.

It is really that simple. However doing it incorrectly can cause Jams and one of the ways mentioned has the potential to put you in an Over Pressure Condition.

Best of luck to you.

Jas Madhavan, It would be nice if barrels and ammo were right on spec. but they are not. Some have a lot of slop, or very tight. One rule does not fit all. Measure the case mouth/crimp with a vernier caliper, if you want to. SAAMI Chamber & Cartridger Drawings link This works for me in 3 Gold Cups & M645 & 1911s >

Just put enough crimp on it to keep the bullet in place. If you think you have too much you're probably right. The case headspaces of of the mouth. If you crimp too much it slide into the chamber, not enough your bullet moves when it loads.

In all the years I've reloaded I've never found a 45 acp case that measured the .898 length that it is suppose to be. They are all shorter.

The NRA done a real good test of taper crimp and roll crimp on 45 acp with lead semi wadcutters. They had a heavy rifle bolt action test vehicle. It turned out the best accuracy in their test came from a .020 roll crimp. With lead you can use your barrel for a gage and seat the bullet until the head of the case is flush with the back of the barrel hood.

I think the only way to get cases that head space on the chamber shoulder would be to have a barrel that not chambered yet, hand fit it to the slide during all the tricks like in Jerry Kuhnhausen's book. Then reamer the chamber to fit your brass because like I said you won't find 45 acp brass that is long enough.

I would not seat jacketed bullets to headspace the cartridge as that will raise the pressure.

The only match semi auto barrel I've ever bought that I had to trim cases for length to fit was a Kart 9mm match barrel.