Lee Factory Crimp Question 9mm

[LiveLife]

Try to adjust your seat & crimp die to give you a finished case mouth measurement of:

9mm = .376".
.40 S&W = .421".
.45 ACP = .471".

That will match most factory taper-crimp I have measured.

rc, Thanks for the information, but can you explain how you calculated the measurement or is it based on calculation and lots of experience.

The reason why I am asking is that you get a different number when subtracting the bullet diameter from the suggested measurement. I am not questioning the suggested measurement, just trying to understand the calculation

rcmodel can give his reasons but calculating taper crimp is something I learned from rcmodel while lurking for years on THR.

What I realized from amount of taper crimp rcmodel often suggested is that it's twice the thickness of average case wall of .010"-.011". So adding .021" to the diameter of the bullet will give you:

.355" + .021" = .376"

.400" + .021" = .421"

.451" + .021" = .472" (although I typically use more around .471" - maybe 45ACP brass walls are thinner?)

 

[Walkalong]

Using magnification, I just adjust the crimp so that all the shortest/skinniest cases get the bell removed completely, which means the longer/fatter ones will get a hair more crimp, which is usually about .001ish. .002 won't hurt. No need for any more.

 

[dickttx]

I only reload for 9mm, 38 Super, 38/357, 41 Mag, 45 ACP, and 45 Colt, but I have a FCD for each of those, and use it every time I load. And I only load lead.
Using one die to seat and crimp is OK if you never change bullets. If you do change bullets it takes longer to reset the die than to load the rounds. Unless you have a separate seat/crimp die for each bullet.
But maybe that is why all my shots don't go into a single hole. Darn, never used that excuse before. Now I will NEVER not use a FCD.

 

[Potatohead]

Ahhh, to crimp or not to crimp, and how much. That is the golden question in this here reloading it seems.

What I realized from amount of taper crimp rcmodel often suggested is that it's twice the thickness of average case wall of .010"-.011". So adding .021" to the diameter of the bullet will give you:

Just to clarify, RC never said the .021 thing specifically. I only know because he told me that.

 

[LiveLife]

No. I don't believe rcmodel specified that.

Adding the average of .021" to the diameter of the bullet is to simply things (As you figured from my posts, I am "numbers" oriented reloader - it's a curse I tell you ).

But the kicker is that case wall thickness is not consistent from headstamp to headstamp, and even for same headstamp. They are no longer .010" thick and can vary from .011" to .013". I have seen inconsistencies where a part of case neck was .010" and another part of the same case was .012".

 

[Potatohead]

Right on...and I could tell by your post that you weren't saying he did. So really I just probably shouldn't even have mentioned it. My bad.

 

[LiveLife]

Oh no, not at all. I think taper crimp for 9mm is often misunderstood topic and some reloaders use too much that reduces neck tension, cuts into plating, cause headspacing issues, leaks more high pressure gas at the case mouth, etc. rcmodel's explanation years ago helped me determine a "method" of adding about .021" to the diameter of the bullet that seems to have worked for me over the years.

If I want to squeeze out even more accuracy, I will use even less taper crimp of .377"-.378" with .356" sized bullets to reduce high pressure gas at the case mouth.

 

[Potatohead]

Yes, I fall into the 377 area mostly. Just a touch.