Keith crimp groves

[Nora]

What was Elmer's fascination with having huge crimp grooves in his designs? I'm presuming that it would aid in higher pressures before the boolit is released from the case. But was it as simple as that or is there more to it?

Nora

[OldBob]

I'm gonna step out on a limb here and say it was because he shot mostly revolvers with heavy loads and wanted a heavy crimp to be darn sure the boolits didn't move out and hang up the cylinder.

[AZ-Stew]

Add to OldBob's post: And to make sure his heavy loads of 2400 powder would ignite properly.

Regards,

Stew

[runfiverun]

and 2400 was a slower powder in those days.

[462]

I have to agree with OldBob. Ol' Elmer forgot more about reloading than I will ever know. I've had cylinders hang up a few times by not employing enough crimp on stout loads. The groove is there for a reason.

[Dale53]

A solid reason for the long sloping shape of the Keith crimping groove is that dies of the era seated the bullet and crimped in one step. If your bullet had a small crimp groove, it tended to push a ring of lead ahead of the crimp. This caused all kinds of problems. The Keith design helped to prevent that. Using the Keith crimp groove, as the bullet was seated and the case was being crimped (try to visualize what is happening inside the die) it ran onto the "slope" of the crimp groove which kept it from running a ring of lead ahead of the groove.

It was an excellent design, particularly for the day. It is less important today, when we are mostly using four die sets and seat the bullet in one stage and crimp it in another.

Dale53

[Bass Ackward]

I say that you hit the main reason.

Remember that bullets in that day were lead and tin. Elmer's mix of 16-1 produced a bullet of around 10 BHN. It was easier to fold brass into a larger space without deforming a soft slug than if you had a short steep curve with which to cram it in.

And then if it was too short and steep, it could be hard to tell just how much crimp you had. Cause if it bottomed out, you could actually reduce bullet tension by having the case bottom out and bow away and break contact with the bullet losing neck tension.

Another big reason for a long crimp (more room) is that it is more forgiving to variances in case length too. Hand gunners get lazy.

[462]

Dale and Bass,

Thanks for the enlightenment, gentlemen.

[Shuz]

I find it very interesting that many of the Lyman 429421 moulds that I have, exhibit different styles and lengths of crimp grooves as well as different dimensions on the driving bands, especially the front driving band. Even the ogive and meplat have differences. We are all aware of the round grease groove vs square grease groove difference. I've often wondered why Lyman made all the changes in the "Keith" bullet and still designated them all 429421!