what is the real problem with seat/crimp dies

[mikeyr]

I just got a bullet feeder for my 650 and i would like to keep using the powder cop. For historical reference, I used a combo seat/crimp die for a good 10+ years until I got Dillon dies a few years back and changed over to separate seat and crimp dies. I don't remember any issues from when I used a seat/crimp die but I keep reading they are not ideal. I am setting up my 650 to be a dedicated 9mm press, my second 650 will be other calibers.

[sunnysmarine]

a separate crimp die gives better results during seating especially with varying case wall thickness from brand to brand and how brass can thicken or thin over many reloadings, Less damage distortion to the sides of the bullets and less chance of the case bulging from to much crimp pressure

[jessdigs]

I have never had a problem with the combo seat/crimp die, but I do like the separate crimp die.
Even if I have to do it on the rock chucker with a fcd.
My rcbs 270 weatherby dies don't crimp at all, and that's a lot of recoil, so I ordered a custom fcd for it. I believe the crimp is important and you get better adjustment from a separate crimp die.

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[ar15barrels]

I just got a bullet feeder for my 650 and i would like to keep using the powder cop. For historical reference, I used a combo seat/crimp die for a good 10+ years until I got Dillon dies a few years back and changed over to separate seat and crimp dies. I don't remember any issues from when I used a seat/crimp die but I keep reading they are not ideal. I am setting up my 650 to be a dedicated 9mm press, my second 650 will be other calibers.

Seating while crimping tends to tear the bullet jacket as the bullet is STILL being pushed into the case AS the crimp is pushed against the case.
This matters less on a cannelure where you have a place for the crimp to push into than it does on non-cannelured jackets.
If you keep the crimp pretty mild, there realistically won't be a problem.
The problem will occur with heavy crimps.

[at_liberty]

You may have to sort head stamps to get a consistent crimp within a batch. Measure the typical case thickness to find your groupings.

[mikeyr]

this is plinking ammo, i don't want to get into sorting head stamps and like that, i do that for 45ACP not 9mm. So I will stay with the separate seat and crimp dies. I just bought a Rube Goldberg looking thing to allow my bullet feeder AND powder cop, we will see how it works, its a new toolhead and lots of little parts, if it does not work then I will lose the powder cop to stay with separate dies.

Thanks for the explanations why the combo dies are finicky, that explains why I don't remember any issues, when I started shooting 9mm I bought 3,000 cases from Starline so my brass was consistent until I started picking up range brass also.

[fguffey]

what is the real problem with seat/crimp dies

The advantage/disadvantage is not know to Internet reloadeers. Before reloaders started reloading on the Internet Lyman said crimping was a bad habit. They did not like the ideal the bullet was moving down at the same time the case mouth was being locked onto the bullet. They thought seating the bullet caused the neck of the case to expand; I understand that does not make any sense to an Internet reloader because they use neck tension. In the old days the neck had bullet hold and was measured in pounds. And now? There is no way to measure neck tension.

For immediate acceptance in the Internet world of reloading purchase cases with neck tension. I purchase cases with bullet hold because I measure bullet hold in pounds.

Many reloaders have seated bullets with a crimp that would not allow the bolt to close. The failure is caused by seating the bullet whole crimping; again too much crimp causes the shoulder/case body juncture to bulge.

Later Dillon started makin separate dies for crimping and for seating. Problem, the RL550B press had 4 positions. I will not use a progressive press without a lockout die, when 2 dies are used when seating and crimping there is no place for the lockout die or the powder die.

MY RCBS Piggy Back and Piggy Back 11 have 5 positions.

So/I made an arrangement with Dillon, they said it was OK for me to use my dies with their press because I was not starting over with new dies.

F. Guffey

[hambam105]

OP, when you wrote the following:
"I don't remember any issues from when I used a seat/crimp die but..."

Were you using cast or FMJ bullets without crimping issue before, and are you currently experiencing crimping problems with plated bullets?

[bruce381]

Seating while crimping tends to tear the bullet jacket as the bullet is STILL being pushed into the case AS the crimp is pushed against the case.
This matters less on a cannelure where you have a place for the crimp to push into than it does on non-cannelured jackets.
If you keep the crimp pretty mild, there realistically won't be a problem.
The problem will occur with heavy crimps.

good advice