Roll Crimp on 9mm

[Loyalist]

I recently purchased a used 3-die RCBS set in 9mm from the EE. It's the older grey box "Omark Industries" RCBS, part number 20509. I have started to use them yet, however, when cleaning the dies, I noticed that the seater/crimp die looks like it has a roll crimp. A Google search yielded very little on this part number, and the email back from RCBS stated that unless it's stamped "TC", it is a roll crimp.

So, my question is, should I try some roll crimp rounds (I'm casting if it matters) or just add a Lee taper crimp die to the collection and use the RCBS as a seater only?

I ask because a 9mm headspace a off the case mouth, and I would assume that a roll crimp would therefore cause me issues. If that is true, then WHY would they make roll crimps for 9mm?

 

[tjhaile]

I would get a separate crimp die anyway if you are loading on a progressive press. It is easier to adjust the two functions independently that way and no extra work.

That said, I doubt that your die is roll crimp because there is no reason for reason for such a thing to exist. If the die set is very old, it may not be labelled per current RCBS practice, which is how you may have received an incorrect answer. AFAIK, about the only time you would have a choice between roll and taper crimp dies would be for something like .38 Special, where the standard is roll crimp, but taper crimp is sometimes preferred for loading wadcutter bullets.

 

[Seagull]

I have heard of roll crimped 9mm but not common. Try and over crimp a piece of brass and you should be able to tell what your die is meant to do.

 

[BCRider]

Roll or taper you don't want a hard bitten in crimp in any case. Either can reduce the diameter to where it might become an issue for the headspacing. As is commonly presented the proper crimp for this is the minimum needed to just barely crimp the mouth in to straight with the rest of the case wall or just a hair inwards. You want to rely on the neck tension for the majority of the bullet retention.

Another issue with combination seating and crimping with one die in the case of cast bullets is that if you try to get a more aggresive crimp you can end up removing the flare from the mouth too early in the seating stroke. And if that occurs the lead can be plowed up and form a ridge ahead of the case lip. And this false lip can hold the rounds too far back depending on how tight or generous your chamber is cut. I ran into this with some .45acp with cast when the die got out of adjustment somehow. I got about 150 rounds that would shoot from one 1911 but not the other.

As a result of this and other issues I now seat and crimp in separate stations and life is a lot more cheery as a result. But if you're stuck with the one die adjust carefully and inspect often. This is only an issue with cast bullets and not even all cast designs. The smaller the cannelure groove the more at risk you are of plowing lead if you crimp in too early. With jacketed the hard copper avoids anything of this sort. But watch it with any plated bullets. Berrys suggests that a hard crimp can crack the plating and result in plating separation in flight. They recommend a soft or just barely non crimp.

A "plunk test" in your bore will also soon tell you how much you can get away with crimping. Start with a test dummy round with only a "no crimp" crimp and see how it clunks into position with a firm seating and drops out easily. Then increase the pinch of the crimp in stages until you find it tends to fall in with a little different sound and feel and maybe starts to sit more forward in the barrel. (field strip the gun and use the barrel only so you can see and feel better) When you go too far it'll actually drop in too far by a hair and taper pinch in place so it won't want to drop free as easily when you upend the barrel to drop out the round. When you feel this then clearly you've gone quite a bit too far with the crimp. Back it up so it's well into the hard edge to hard edge with no risk of the case lips wedging into the chamber's head spacing step.

 

[Loyalist]

Thanks for the suggestions guys. I'll order up at dedicated taper crimp from Lee, but will test out the crimp with plunk testing in the meantime.

This is my first time loading straight wall cases, so I might as well go through all the steps and learn the ins and outs

 

[nada]

you will need to make several dummies [ this is not a waste , pull the bullets & use as 2nds , aka guest ammo , or @ point & blast distance ]
this is something we all do for every diff bullet .

 

[bigedp51]

Normally any semi-auto cartridge is taper crimped and revolvers are roll crimped.

 

[Hamsta]

For plated bullets, if you ever use them, too much crimp could cut into the plating and promote some separation of the plating (Or jacketing) from the lead during travel in the barrel.

For 9mm, I just remove the flare plus tighten up maybe 0.002". Just use your fingernail. Compare to factory ammo.

 

[enefgee]

Get a Lee factory crimp die - life becomes easy - you get a solid taper crimp, (you NEED to crimp 9mm don't let anyone tell you otherwise) you can't over crimp, you can't collapse a case, and it post sizes the brass for perfect feeding.

 

[BCRider]

you can't over crimp,

Oh yes you can. If someone pinches the crimp in hard enough that the case mouth is smaller then the throat on the chamber then it won't headspace correctly on the lip where it's supposed to sit.

Granted it's hard to do with a taper crimp. But a suitably gorrila like setting of the die and a stubborn reefing on the handle will do it.

Or if someone goes for a strong roll crimp. A strong roll crimp as shown in the diagram and cartridge picture in biged's post above will allow the mouth of the casing to slip in and wedge into the headspacing shoulder and the result would be an incorrect seating of the casing. Or, more likely than wedging into place, is that it would headspace off the extractor hook. But that's a bad way to headspace with the results being hard on the extractor hook.