[clancy12]

I just got my new RCBS 40SW/10mm die set today and I am having difficulty getting the taper crimp figured out. How can you tell if it's crimped too much/not enough on a taper crimp? Thanks.

[Walkalong]

It needs to be enough to remove the bell and maybe a hair more. Just get the case anywhere from laying flat against the bullet to a slight (.001 to .002) indention.

[rfwobbly]

Walkalong told you right.

Another way is to make up 5 or so test cartridges (no powder; no primer). It's the body of the seating die that places the crimp, so you'll move the die body progressively lower until your test rounds are able to drop into and out of the barrel (removed from the gun) using only their weight. Then lock down the die body right there.

More crimp IS NOT better.

https://lh3.googleusercontent.com/_E3bV2jGIaSg/TVbEega-GWI/AAAAAAAACHQ/NlHiWfC8ANM/40_S%26W.jpg

Usually, the resulting crimp will measure .002 or .003 smaller than the maximum case mouth spec given in your manual. So right at the case mouth where your manual gives .423" (10.74mm) will end up at ~.420". Notice that this measurement is taken only on the last 1/32" of the case mouth.

If you have some factory-made ammo that chambers really well, you might measure their case mouth diameter as a comparison.

Hope this helps! ;)

[243winxb]

Seat a bullet to the correct COL. Back out the seating stem. Then with the round in the fully raised ram, screw the die in by hand, crimping as you go. Can not over crimp this way if brass is all the same length. Final test, will round drop in to the barrels chamber? If not, a hair more taper crimp is needed.:)

[clancy12]

Thanks for the input everyone, now it makes a lot more sense.

[buck460XVR]

Seat a bullet to the correct COL. Back out the seating stem. Then with the round in the fully raised ram, screw the die in by hand, crimping as you go..:)

This is how I adjust the crimp on my .45ACP rounds. Turn the crimping die down(with the seating stem turned up) until I can no longer turn it by HAND. I then turn the seating stem down til it touches the bullet and lock it down. Without exception, this has always worked for me with my Colt Government.

[mdi]

For semi-auto reloading "crimping" is misleading. Mebbe we should say "De-Flaring" because you are not "crimping" in the sense of the word, just removing flare from case mouth.

[noylj]

+1 RFWobbly: If you have some factory-made ammo that chambers really well, you might measure their case mouth diameter as a comparison.

This is the way to go with taper crimp and roll crimp.
If you seat and crimp in one step, you have to first get the COL right (for me, this involves making one or two inert rounds, seat the bullet, raise the seating stem up all the way the adjust the die body until I have removed just enough bell/flare so the round slides into the barrel. Then raise the die body up so there will be no more crimp and adjust seating stem until the inert round fits the magazine and feeds and chambers--I load the longest COL that meets those criteria). At this point, I adjust the seating stem back up all the way and turn the die body down until I know longer feel any bell/flare. You can use a caliper to measure it, but your fingers are more sensitive. When you get the inert round functioning, you then use it to finalize the die and seating stem positions.
Personally, I prefer to separate the two activites.