Bullet seating depth confusion.

[bowzette]

I think I found our the difference in seating depth even though the bullets are the same. I pulled a FM bullet and compared it to the X-Treme bullet-same company or common ownership. FM is loading or reloading with X-Treme brand bullets. Weight, length, and dia of the bullets are the same within statistical variances. The only difference is the FM bullet, ammo purchase 1-2 years ago has a single line crimping grove. The X-Treme bullet has a cannelure as used on jacketed bullets. The bottom edge of the cannelure on the X-Treme is placed a small amount higher than the crimping grove on the FM. Crimping to the middle of the cannelure or top edge of the cannelure results in the bullet being seated noticeably deeper using the X-Treme bullet than the FM. I assume FM/Xtreme made this crimping design change to be an improvement and created a cannelure to crimp the plated revolver rounds, at least the .38, as though it were a jackted bullet and not a lead bullet.
Question: Do I crimp at the middle of cannelure or close to the top edge of the cannelure or does it not matter?
Thanks

 

[Regaj]

You want the bullet seated deeply enough - and deep enough on the cannelure - so that every round gets a solid crimp.

A bullet seated too shallowly - say, near the bottom third of the cannelure - may end up with a weak crimp, as some cases simply don't have enough length to "roll over" into the cannelure.

A bullet seated too deeply - at the very top edge of the cannelure - may have a failed crimp if some of your cases are a smidge longer than the one you used to set your die... in which case you have overshot the cannelure.

You have to remember that absent benchrest-level attention-to-detail your cases are unlikely to be exactly, precisely, the same length. Since you're shooting mixed brass, I can pretty much guarantee it.

The good news is it doesn't much matter for handgun ammo. Certainly not for plinking and range ammo.

Generally, set your depth so the case mouth is about 3/4 into the the cannelure - biased towards the top, in other words - and you'll be good to go.

 

[bowzette]

Thanks Regai-is the info I needed.

 

[gwpercle]

In the 38 special / 357 magnum , when using bullets with no crimp place (groove or cannelure) or if for fitment reasons the bullet can't be seated and crimped there , use a taper crimp die from a 9mm Luger to apply a taper crimp to the smooth sided bullet area , works just fine.
Trying to roll crimp into a smooth side can bulge the case if not done just right.
Gary