roll crimp and taper crimp


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Old 10-17-2011, 12:22 PM   #1
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Default roll crimp and taper crimp

can some one explain to me the difference, and uses for each. I currently have dies set up to crip on my cannelure bullets with my 357 and 357 max, which i believe is a roll crimp, but i would like to get carbide 44 mag dies,usually use rcbs dies, and there are options for a rill or taper crimp, and now im wondering if i may be doing something wrong with the other dies or if the kind of crimp is specific to the bullet, ie taper crimp might be for bullets without cannelure?

Help!



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Old 10-17-2011, 01:12 PM   #2
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Roll crimp is for revolver loads, they head space on the rim. Taper crimp for semi-auto that head space on the case mouth.



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Old 10-17-2011, 01:47 PM   #3
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n8ball, I have the same dies and for my .44 mag loads I just carefully followed the directions for the roll crimping process. So far so good.

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Old 10-17-2011, 01:51 PM   #4
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Bottle neck cases head space on the shoulder so you can either roll or taper them. Straight wall cases for revolvers are roll crimped. You're fine with your 357 and 44 cases being roll crimped. If in doubt you can always look at a factory case to see how it's crimped.

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Old 10-17-2011, 02:12 PM   #5
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jeepejeep, that is exactly what I did with my .44 mag loads. After simply following the directions for the roll crimping process with my RCBS die I used a magnifying glass to examine one of my loads and compare it with a factory round. They looked the same so I felt good about it. My loads fired just fine and grouped well and the seating depth for the rounds in the chamber didn't change when the gun was fired.

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Old 10-17-2011, 02:27 PM   #6
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Quote:
Originally Posted by jeepejeep View Post
Bottle neck cases head space on the shoulder so you can either roll or taper them. Straight wall cases for revolvers are roll crimped. You're fine with your 357 and 44 cases being roll crimped. If in doubt you can always look at a factory case to see how it's crimped.
You don't roll crimp bottleneck cases, even if they headspace on the shoulder. Most people don't even crimp bottleneck cases. I use the Lee factory crimp die for .223.

.357 Sig headspaces on the mouth, not the shoulder.
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Old 10-17-2011, 04:45 PM   #7
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Role crimp works best with a bullet with a canalure (A ring cut/pressed around a bullet that was made for crimping, I've got a tool to do that someplace.) or into the crimp grove of a lead bullet. The very edge of the case mouth is pushed into the bullet.
Taper crimp work with most every bullet type and cones the casing into the bullet, but so very little.

A crimp is beneficial for weapons that will exert pressure on the bullet that could push the bullet deeper into the case, not good! This would include auto-loaders, tubular magazines and heavy recoiling revolvers.

Auto-loaders, there is a possibility of the bullet being shoved in as it hits the feed ramp. I use a 'Lee Factory Crimp Die' for my 40s and 45s. I DO NOT crimp any of my bottle necked rounds. Neck tension works very well. (I do polish the expanding ball for smoother operation and this does make them a tad smaller.)

Tubular magazines, with the spring pressure and recoil, the bullet could be pushed in. I have no weapons with this type of magazine (that I shoot).

Revolvers, I have never had a problem with set back in any of my .44 mags in the last 38 years of shooting.

My view, if anyone would care. For proper role crimping, the brass must be trimmed to the same length, no variation, and the seating die with crimp must be set just right or the brass will wrinkle and/or the loads will be inconsistent. Some powders need a crimp for proper ignition, I don't use them.

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Old 10-17-2011, 04:58 PM   #8
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Quote:
Originally Posted by robocop10mm View Post
You don't roll crimp bottleneck cases, even if they headspace on the shoulder. Most people don't even crimp bottleneck cases. I use the Lee factory crimp die for .223.

.357 Sig headspaces on the mouth, not the shoulder.
Expanding this.
Rimmed cases, headspace on the rim.
Belted cases, headspace on the belt.
Most rimless or rebated rimed cases, headspace on the shoulder.
Some odd ones, 30 cal carbine and 9MMs, are tapered cases and headspace on the case body (considered better for automatic fired weapons, I view it as a fix for a non existent problem at best. I'm doubtful if the 9X19, 9X17 cases are actually tapered cases by most manufactures anymore.)
The barrels seam to always have a forward chamber edge for headspacing.

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Old 10-18-2011, 12:23 PM   #9
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gotcha, i did notice that you can get straight wall case dies, iie. 44 mag, that taper crimp, i was looking over the dies on midways site. i know i still have alot to learn, wish my dad and his knowledge were still here, you guys are all very helpful, i have been learning alot on this site.

i guess ithe next step is to figure out head space on my firearms? I dont use any heavy loads right now, and i have only set up the 357 dies to roll crimp according to the rcbs paperwork.

If you over crimp, will the primer flatten out like high pressure loads? it seems by my naked eye that the crimp is now set properly after some trial and error.

i know i need to do something different with my 45 acp dies, i was using semiwad cutters and had a few feed jams, one of the jams seated the bullet further in to the case just by the working slide.

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Old 10-18-2011, 01:54 PM   #10
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You don't need to figure out your head space. On 357 or 44 the case rim is where your head space is so there's no problems there. If the cases are so long that they don't chamber (I've never seen this with .357) you'd need to trim them.
The .45 head spaces on the case neck and needs a good, tight taper crimp. I'm not sure, but in order to over crimp would take a lot of force on the press handle and you'd know you were doing it. As long as the case mouth is turned into the channel lure on your revolver cases you should be good. With a taper crimp it's harder to tell but with no channel lure you'd have to really press the case into the bullet a lot to make high pressure. After you crimp, look closely and be sure you can see and feel the case mouth edge all around the bullet. Press the nose of the bullet against your bench pretty hard. The bullet should not move into the case. If it does, crimp a little harder. Some trial and error.



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