Roll Crimp Question .40 S&W

[Branden967]

I got on a roll one night I ran a batch of about 600 rounds mixed brass with a very light to no crimp OAL' 1.128. I like the charge and they functioned fine but I am worried about the bullet set back / kaboom etc. Id like to go back and add a hair more of a crimp to that batch. Is it possible to run them through the seater die one more time to add that or should I pull them all and start over? Id also be shrinking the OAL down too to 1.125 which my other piece prefers.

Any helps would be greatly appreciated.

Technical data if needed:
Press is LNL
Current charge 5.4 w231 @ OAL 1.128
Desired (more crimp) @ 5.4 OAL 1.125

Thanks-

[pdq_wizzard]

don't roll crimp, taper crimp if anything, the only thing you should roll crimp is revolvers. most pistols space on the case mouth so if you roll crimp the case will be to deep. and that will give you high pressure (that could give you a kaboom)

I don't think the recoil of a auto loader will give you setback if you sized the brass.

[mjmagee67]

Two options 1-get a Lee FCD(Factory Crimp Die) and just run them through a crimp cycle. 2-take one or two bullets and repeatedly cycle them through your gun and measure for any change in length. Obviously follow all safety precautions carefully. If you get any setback you need more crimp. I prefer crimping with a FCD independent of seating.


Yes no roll crimp on 40, it's a taper crimp.

[Branden967]

don't roll crimp, taper crimp if anything, the only thing you should roll crimp is revolvers. most pistols space on the case mouth so if you roll crimp the case will be to deep. and that will give you high pressure (that could give you a kaboom)

I don't think the recoil of a auto loader will give you setback if you sized the brass.

This whole ordeal started when I ran a couple of rounds though gun to test them. When I charged the gun and the same round 4/5 time I got may a .002 to .005 set back max. But when I inserted a load magazine and release the slide via the button I would get a huge set back. So I figure more crimp was needed.

[Bill Steele]

40S&W is a taper crimp cartridge, not a roll crimp. The round headspaces on the mouth of the case, hence the taper crimp.

In a taper crimp round, the crimp doesn't add neck tension, in fact for the most part it reduces neck tension. Lead is softer and has less spring than brass. As you run the case up into the crimp die, the bullet is compressed along with the case being sized down. As you remove the round out of the die, the brass springs back more than the lead, hence your reduced neck tension.

In a round that uses a taper crimp, the sizing die is what determines neck tension and hence bullet security. Thinner brass will provide less neck tension for a given bullet than thicker brass. That is, the hole the bullet is seated into is smaller when the brass is thicker. So if some of your rounds have insufficient neck tension, you can either sort your headstamps and use the thicker brands (like Fiocchi, CBC, PMC, etc.) or get another sizing die that sizes the brass a little smaller.

Specific to your question on length, you can run your rounds through the seater to seat deeper. You run the risk of shaving a little of your bullets if your crimp is already too much. If you crimped correctly the first time (which is to just take the bell out), taking the extra 3 thousandths off the remaining rounds should not be a problem.

[pdq_wizzard]

This whole ordeal started when I ran a couple of rounds though gun to test them. When I charged the gun and the same round 4/5 time I got may a .002 to .005 set back max. But when I inserted a load magazine and release the slide via the button I would get a huge set back. So I figure more crimp was needed.

what kind of dies are you using? you could try and run the die down just a half turn and see how that works, but don't so a roll crimp.

I use a Hornady taper crimp on my .40 and .45 I load mostly lead for my .45 so the taper crimp helps uniform the loads so they cycle.

[huckberry668]

Yes, you can crimp it once more w/o having to do-over the whole process. Sounds like you're using the seater die to seat and crimp in 1 step. Just remove the seating stem and readjust the die 1/16 of a turn lower till you get your desired crimp. Don't crimp too much or you'll lose accuracy.

it really shouldn't set the bullets back from chambering force. sounds like your sizing die may not be sizing the brass down enough.

[mjmagee67]

You can also just recrimp by raising the bullet seating adjustment all the way up and screwing the die in 1/4 turn and repress a few and try in your gun again. Taper crimping absolutely adds neck tension!

[Branden967]

I am using the Hornday dies. All the brass runs through the redding GRX to get the bulge out first then goes as follows.
station 1 Full-length Sizing Die
station 2 Adjustable Case Mouth Expander Die (where I overdid it)
station 3 Powder
station 4 Bullet Seater Die

Ive read enough to understand the difference between a roll crimp and a taper crimp but (without sounding dumb) Im still confused on how to spot the difference. Going for a taper crimp its essentially the absences of the roll of the top. Correct? And to get a taper crimp (or more tension) its not achieved by the seater die but by the sizing die? Wouldnt the expander die kill that?

[Bill Steele]

..Ive read enough to understand the difference between a roll crimp and a taper crimp but (without sounding dumb) Im still confused on how to spot the difference. Going for a taper crimp its essentially the absences of the roll of the top. Correct? And to get a taper crimp (or more tension) its not achieved by the seater die but by the sizing die? Wouldnt the expander die kill that?

Correct, getting the belling out is what you are after with the taper crimp. A roll crimp is used for calibers that headspace on the case rim (like a .38spl round). The roll style crimp is put into a cannelure (a channel in the bullet) and is used to secure the bullet during recoil. If you set the taper crimp down far enough it will start to look like a roll crimp and it will pinch the case mouth into the bullet damaging it.

Correct, the sizer die is what determines your neck tension. If you are not getting enough tension, then a few things might help: as suggested, try screwing the sizer down closer to the shell plate, or use thicker brass headstamps when loading jacketed bullets (i.e. .400" bullets, you can save the thinner headstapms like R-P, TZZ, Starline, etc. for lead and plated (i.e. .401" bullets)), if you have an expander ball on the decap stem (most straight walled handgun caliber dies don't), you can have it turned down .001"-.002" and your problems will likely fade away as well, finally get a sizer that sizes more (Dillon dies are usually a little tighter).

The belling die is there to just bell the case enough so you don't shave the bullet while seating. You don't want to bell any more than that. The taper crimp is then set to just take that belling out after the bullet is set (essentially returning the case to straight).

Finally, a little bullet setback during the feed and chambering is pretty common. A good way to test to see if your neck tension is adequate is just push down with your thumb on the finished round, the bullet should stay firm.

You get it well.