Crimping Dimensions

[LBussy]

When crimping is used, should a round be crimped to it's SAAMI dimensions? For instance in another thread someone mentioned crimping a 9mm round to 0.379" which if this diagram is correct, is the design dimension (9.65mm):

By Morgan Phoenix (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons. Retreved from: https://commons.wikimedia.org/wiki/File:9x19mm_Parabellum.svg

I've always had good luck by "slightly crimping" a round, enough to remove the bell mouth plus a little more, but this is far form scientific. The Lee instructions are not much help here. I've also not reloaded for lever actions or other guns where setback could be an issue.

This is an area where it never occurred to me that there might be explicit dimensions I could use.

 

[rodfac]

I've always had good luck by "slightly crimping" a round, enough to remove the bell mouth plus a little more.

That about says it all. And the phrase, 'a little bit more' means it's barely perceptible to the naked eye, in my case.

Crimping down to the thousandth of an inch assumes brass that's that precise; wishful thinking at best. I've spent some time trying to get precision crimps to that standard on 9mm as well as .45 ACP, and a number of other calibers as well, but could never see the results on target. For me it was a colossal waste of time for handguns, even match tuned ones.

A better use of time, in my opinion, is to buy top grade bullets, or perfect one's casting technique, so as to get a first rate bullet. Sorting brass by head stamp and lot # can also prove effective, as does assuring brass is the same length. But even these operations are very hard to see on target.

Precision rifle enthusiasts of the "F" class variety, or bench resters might be able to see a difference, but if my experience on the National Match Course is any indication, top competitors do not crimp whatsoever...it opens groups rather than improve them.

YMMV, Rod

 

[snakeye]

I have never used dimensions when crimping brass. Too many variances of various manufacture of brass....I just load up a couple of dummy rounds pull bullets and check them and set the crimp until I get a very slight mark in the bullets...then press check on the bench for any set back and I'm good to go.

 

[LBussy]

then press check on the bench for any set back and I'm good to go.

What do you mean by that?

I'm aware that for my uses, crimping is a placebo at best. I take some solace knowing that factory rounds are crimped and mine are too. I'm not a person who would notice the difference in groups between crimped and not - I don't do that type of shooting (although maybe someday).

 

[Nick_C_S]

What do you mean by that?

He likely means to take an assembled dummy round and press the nose against your load bench to see if the bullet sinks into the case.

I have never used dimensions when crimping brass.

Me neither (and for the reason snakeye mentioned). I've always crimped by feel and it has served me well. I can't explain it, but I know it when it's "right." Experience. Maybe a little luck too - who knows.

I started loading revolver rounds first (1984), where the roll-crimp is very "positive" and tangible. Moving to the taper crimped 45 ACP had me scratching my head a bit at first. But soon enough, I got over it and moved on - deciding not to overthink it any longer. It worked.

 

[LBussy]

But soon enough, I got over it and moved on - deciding not to overthink it any longer. It worked.

That's what I have been doing - but my desire for repeat-ability has me wondering what might be optimal. I guess I could find something that works and measure that but I thought I'd ask here first to see if there was a generally accepted method.

 

[mikld]

I measured the crimp on my 45 ACP reloads, once. I've been reloading semi-auto handgun ammo for only 18 years or so and with the single exception mentioned above I haven't measured (or considered) any "crimps". I learned the "plunk test" early and have never had it fail to tell me if my ammo is "crimped" enough (I don't actually crimp, I just remove any flare on the case mouth with a taper crimp die). I don't count my reloads but I have 5 favorite semi-autos, 3, 9mm and 2, 45 ACP that I shoot a lot (I know I've gone through 1,000 plated bullets, 1,100 Precision coated bullets, 500 RMR JHP, 500 Nosler JHP and about 75-80 lbs of cast bullets; 200 gr, 225 gr, and 125 gr).

 

[hdwhit]

LBussy wrote:
When crimping is used, should a round be crimped to it's SAAMI dimensions?

On a round that headspaces on the mouth of the cartridge, the case should be crimped only so much as to remove the flare (belling) of the case mouth created by the expander and thus allow the case to be chambered.

Whether that amount of crimp will produce a case mouth with a diameter exactly the SAAMI dimension is unclear. In straight-wall cases (and although the 9mm has a slight taper, pretty much everyone treats it as straight-wall case) most reloaders do not trim their brass from one reloading to the next as case lengthening is generally insignificant, so the length of the cases and consequently the diameter of the flared case mouth and the diameter of the crimped case mouth will vary.

I, for one, would not attempt to achieve a certain diameter on the mouth of my finished reloads if some other, slightly different, dimension is working just as well.

 

[higgite]

When crimping is used, should a round be crimped to it's SAAMI dimensions?

Only if you want it to fit in a SAAMI minimum chamber.

For instance in another thread someone mentioned crimping a 9mm round to 0.379" which if this diagram is correct, is the design dimension (9.65mm):

SAAMI case mouth dimension is from 9.473 to 9.653mm. But, as others have pointed out, if it's for your gun and fits your gun's chamber, there is no need to measure. I gauge my finished cartridges because I shoot them in multiple guns. ymmv