Crimping Groove, Cannelure?

[Pat Cannon]

What's the difference between a 'crimping groove' and a cannelure? Or is it like Clark Kent and Superman?

[John T]

Nothing. same as same as.

there is little need to worry about cannelure unless you "have too" load to sammi.

[Seismic Sam]

Well, actually, you DO need to worry about crimping, both taper crimp on auto bullets, and roll crimp on cannelure bullets all the time. On the taper crimp on auto bullets, the case neck grip has to be tight enough to keep the bullet in place when it slams into the feed ramp and chambers itself. If recoil in the mag started to make the bullet come out, and then on the next to the last shot that loosened bullet got slammed all the way down to the powder, you could have a kaboom. That's the most likely scenario for Vlad's kaboom, although no one will ever know for sure. The results aren't quite so awful for revolver bullets with cannelures, but if you do not have tight enough roll crimp, the bullet can get pulled forward by the recoil on hot loads, and potentially stick out of the cylinder and jam the gun up. With the Smith 500, you really have to crimp those bullets in tight to get them to stay put.

[Pat Cannon]

Why we're on the subject you guys can critique my crimp. This is a 125gr Montana Gold JHP in .357.
Pardon the pocket lint:



Also, is there a purpose to the vertical grooves in the cannelure?

[Rem700]

Me thinks Clark Kent - Superman
In basic I think of it as the area of the bullet that the cartridge case is to be crimped, That area referred to on a jacketed bullet as the cannelure and on a cast bullet the crimp groove.

[Rem700]

Vertical grooves, Dont really know perhaps more surface area for the cartridge case to grab.
In general I use enough crimp that when the cartridge is pushed against a surface with my thumb and with my weight on it the OAL length doesnt change. Crude but generally seems to work as a rule of thumb for use in repeating arms.
Its also possible to over crimp and end up with loose bullets.
I do also load single shot rifle rounds with no crimp but thats a whole other topic.

[Rem700]

One more reason some dont like loading mixed headstamps = different brass thickness which varies crimp tension.

[870TC]

Vertical grooves come from the tool used to make the cannelure in j-bullets, no magic reason for its appearance. In cast bullets, the crimping groove is designed right into the the mold so it does not need to be added later...some swaged lead bullets can be seen with the vertical lines added later.

[1911fan]

Technical differences, a cannelure was not intended as a crimping groove in the beginning, it was found to work as one, and thus located to what the manufacturer thought would be a good place, but in a rifle, you crimp to optimum OAL for your rifle, not to the groove.

The original intent of the cannelure comes from trying to hold jackets and cores together when jacketed bullets were just coming into use. Lots of bullets would open the jacket, the light jacket would snag on fur,clothing or whatever, and the heavy lead core would just separate. If they stuck together, they worked better and the idea of controlled expansion was born.


Crimping grooves are just that, the place to crimp a handgun or rifle round when OAL is critical to function. They are often cut different with a distinct edge to the groove for the case mouth to fit into.





The word cannelure is from the concept of using heavy siege guns to collapse guard towers and walls by smashing a horizontal line across the bottom of the wall above the foundation, this would destroy the structural integrity of the dry laid stonewalls which would cause the upper works to collapse down.