Where to park the crimp groove in relation to the case mouth?

[greenjoytj]

Example: I am crimping my Lyman 452664 cast RNFP bevel base bullet.
This bullet has a classic deep groove and a 45 degree slope down out to the bullet side.

Where should the case mouth be in relation to the crimp groove to start the crimp?

I have been seating the bullet so the case mouth is even with the lower edge of the top drive band which puts the deepest part of the crimp groove flush with the case mouth.
Usually the case mouth clips the sharp upper edge of the crimp groove as it roll under this edge.

Should I be leaving a few thousands of and inch clearance for the case mouth to be rolled under so it doesn't clip the crimp groove edge?

On my last crimp session I took note of my COL before and after crimping and found the COL shortened by approximately 5 thou.
I didn’t think I was over crimping just trying to get the case mouth under the edge of the crimp groove to prevent the bullets from being pushed deeper in a tube magazine.
Redding die set was used.

I have no problem crimping bullets with a cannelure, I crimp to leave one forth of the nurling of the cannelure exposed.

[DAFzipper]

I usually set depth half way in the crimp groove. I rarely trim pistol brass and have given up on sorting by head stamp. Gives the greatest range for differing case length.

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[MSD MIke]

I like to put it right in the middle. This allow for case length variance while still keeping the case mouth within the crimp groove.

Mike

[C. Latch]

Your question is why I use a separate crimp die for .45 Colt.

Having said that, I seat and crimp with the same die for 38,357, and 45-70. Crimps aren't critical with lighter loads. With full power loads, just tweak your die settings until you're not getting shaving off the front driving band. Also consider that if you end up with a bunch of different molds, every one will have a slightly different crimp groove shape or depth. You'll often have to tweak your seating depth *AND* your crimp setting between bullets.

You can buy, for very little money, some thin shims with a 7/8" ID on amazon.com, and make a record of crimp settings between different bullets. You might, for example, have a custom mold with a deep crimp groove and set your dies for this groove, then you buy a Lee mold with a shallower groove. A couple of .010" shims under your seating die might be just what it takes to reduce your crimp when seating the latter bullets.

[Petrol & Powder]

I'm another reloader that seats and crimps in two operations. While those steps can be combined; it is just NOT WORTH the hassle.
SO, because I seat & crimp to two separate steps, it is much easier to "park the bullet" (to use the OP's terminology) in relation to the case mouth. I like set up the bullet seating depth so that the lip of the case mouth is close to the top of the crimp groove. When the top of the case is turned inward (roll crimp) it falls nicely into the crimp groove.
As others have started, if the case mouth ends up in the middle of the crimp groove that gives you the greatest allowance for variations in case length. However, I tend to err a little on the side of having the case mouth near the upper end of the case groove (bullet slightly deeper in case).

[onelight]

I am another that seats to the center of the crimp groove for the same reason as DAFzipper.

[Dusty Bannister]

In my preference for Semi-Auto firearms, I try to adjust for a mild taper crimp to ease chambering issues. The preference is for the ogive of the bullet to nearly touch the lands for easy chambering and extraction of a fired round.
for revolvers, I again like to have the ogive entering the reduced area of the cylinder chamber so the cartridge gets some support at the rear AND the front of the cartridge so the cartridge is centered in the chamber. As an alternative, for short bullets with a single lube groove, I will be more concerned with making sure that the case mouth fully covers the lube groove by having the case mouth just firmly nudge the edge of the groove for a smooth profile and dirt proof seal of the lube.

[greenjoytj]

Thanks everyone for you replies.

Just to clarify, I always bullet seat and crimp in two separate operations.

Next time I crimp I’ll figure out how many thou to leave between the case mouth and the edge of the crimp groove so the case can roll in with out scraping the corner edge of the crimp groove.

I never keep my dies locked at some known setting because I like to go through the set up process each time I use them. For me, I like to remain comfortable in setting up my die’s and not have the process turn into a fearful thing to do.

I do trim my pistol cases to the same length. It’s a one time operation for the straight wall pistol cases. I just wish I could find cases that when new were at least as long as the trim to lengths as mentioned in the reloading recipes.

[mdi]

I have been seating the bullet so the case mouth is even with the lower edge of the top drive band which puts the deepest part of the crimp groove flush with the case mouth.

Me too. One time, many years ago I looked closely at the crimp groove on some generic cast bullets I bought (1969?) and figgered the best seating depth would be with the case mouth edge even with the bottom of the groove (and the lip will lower as it is pushed inward)...

[lightman]

I usually seat the bullet where the case mouth is near the center of the crimp groove or just slightly deeper.

[Bazoo]

I set my depth so the mouth of the case hits maybe .010 lower than the driving band. So, 90% of the crimp groove. Then I set the crimp, and do both in the same operation. I like the mouth of the case just short (.005) of the driving band when loaded. That way I don't have any issues with a bit of runout, but can still get a good solid crimp.

Unlike most, I generally trim revolver brass and sort headstamps.

[USSR]

While I teach my students to seat and taper crimp in separate operations for pistol cartridges, with revolver cartridges I seat and crimp in one operation. Seating the bullet so the case mouth covers 1/2 to 3/4 of the crimp groove prior to crimping is a good place to be.

Don

[gwpercle]

In revolvers I crimp to cover most of the crimp groove , leave just enough clearance to not clip the upper band but getting a good solid roll crimp . I do these in two steps , seat then crimp .
Some boolits have deep wide crimp grooves and probably 1/2 to 3/4 deep crimp will hold but other designs have shallow and narrow grooves so each boolit & crimp needs to be looked at on an individual basis .

Semi-auto I taper crimp and have found that seating and taper crimping on flat sided boolits can be done in one step ...once you get the die adjusted properly .
Gary

[Tokarev]

To the OP: Where your best accuracy OAL leaves it. If it is above the case mouth, so be it. I did this with 150gr in 308 and got superb accuracy because there was that sweet bullet jump of 3-4 thou that my rifle liked.

[charlie b]

I seat and crimp separately for my revolvers. Lee FCD to me is the only way to go. I put the case mouth part way down the crimp groove. That way if I get a case that is a bit longer than normal it will still crimp in the groove.

For semi-auto I taper crimp. Just enough to hold the bullet. And do a plunk test to make sure it still head spaces on the case mouth.