crimp??


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poor man
February 19, 2013, 11:48 AM
ok before the "pros" jump on me... i DO have the manual for the RCBS dies im using.... BUT im looking at my 9mm loads and i dont see the crimp. i mic the case before loading and after and they are the same. so just for tests i put a fired case in the die and pushed a bullet into it, its as tight as a "real" load and measures the same, so is my die not set right? without destroying cases how do i tell if my crimp is set right????

PS: ive been loading the 9mm this was for a long time and never had any troubles BUT id like to do it 100% right if i can

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rcmodel
February 19, 2013, 11:53 AM
The taper-crimp on a 9mm should not be visable.

But to set the die properly, keep adjusting it down and measureing the case mouths of the loaded rounds.

Proper amount of taper-crimp for the 9mm should measure .376".

rc

bds
February 19, 2013, 12:13 PM
BUT im looking at my 9mm loads and i dont see the crimp. i mic the case before loading and after and they are the same.
You won't.

My resized cases measure around .373" and when I apply a "neutral taper crimp" which returns the flare back to flat, I measure .376" for .355" diameter bullet (.355" + .021") and .377" for .356 diameter bullet (.356 + .021") - see left picture below.

Slight negative taper crimp often used on factory jacketed loads may be around .373" - .374" which will indent the bullet surface (picture in the middle).

(Picture not to scale)
http://www.thehighroad.org/attachment.php?attachmentid=173616&d=1350671953

mdi
February 19, 2013, 12:49 PM
For new reloaders the term "crimp" is misleading. No crimp is needed on a semi-auto cartridge, nor is one wanted as the case headspaces on the case mouth. You are just using a taper crimp die to straighten out the case mouth to insure good chambering. BDS's pic is an excellent depiction of "crimps". I use just enough "mouth straightening" on my semi-auto reloads to pass the "Plunk test", like the pic on the far left...

45lcshooter
February 19, 2013, 01:33 PM
I've never crimped straight walled semi auto cases. Straight walled pistol cases such as 38/357, 45lc get rolled crimp because of the groves.

Walkalong
February 19, 2013, 01:37 PM
I adjust the "taper crimp" for auto pistol calibers so the shortest cases will get the bell removed completely, which means the longest cases will get about .001 indention.

http://www.thehighroad.org/attachment.php?attachmentid=153244&d=1322011199

poor man
February 19, 2013, 03:12 PM
thanks i didnt figure i was doing too much wrong as nothing jumped up and bit me.... and they seem to be fairly accurate (as steady as i can be) :(

dmazur
February 19, 2013, 03:49 PM
Too much crimp in cases like 9mm, .45 ACP which are supposed to headspace on the mouth can reduce the force it takes to push the bullet back into the case.

This is counter-intuitive, as most think more crimp will fix a "loose bullet setback" issue.

Case "tension" is what retains bullets in these calibers. If the case is too large/bullet too small, crimping can't fix it.

Some straight-wall cartridges, such as .44 Remington Magnum, may require a firm roll crimp. (Depending on powder and load.) It can be related to getting proper ignition with H110, and also about preventing "bullet pull" due to recoil.

You may already be aware that there is more to crimp than just "one size fits all", but if you weren't, there it is... :)

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