Monday, April 27, 2015

Bullet setback

Bullet setback is one of the concerns in reloading modern, high pressure, small case capacity, semi-automatic pistol cartridges.

Image from HERE
The mechanism of the pistol slams the nose of the bullet against a feed ramp, exerting forces that push backwards on the actual bullet.  If that bullet moves in the case, it reduces the free volume of the round.  Same energy in a substantially smaller volume results in much higher pressures.

Revolver cartridges are not subject to this issue.  They do not get slammed by the mechanism.  Also, most revolver cartridges were designed during the black powder era.  Black powder has much lower power density so more volume was required to create a viable round.  The transition to smokeless powder kept the exterior dimensions so there is ample volume within the case.

Ironically, the problem with high power revolver rounds is the bullet walking forward which will lock up the cylinder when the nose of the bullet starts to stick out.


One way to prevent the bullet from moving back in the case is to emboss dimples or grooves in the case.

This is a photo essay on how to modify a commercially available tool to do just that.

Hornady Cam-Lock bullet puller, PN 392165-12 on the left and a 7/16" bolt that was trimmed to length to function as an anvil on the right.  This tool will be modified so it can be used to press cannelures into 40 S&W cases.

This is what the collet-anvil look like when put together.  The anvil is about 0.030" (0.70mm) subflush to the fingers of the collet.  The bolt does not need to be a hardened bolt.  I cut the bolt with a hacksaw and finessed the fit with a 10" file.
The collet was file hard so it needed to be softened.

The tips of the fingers were softened by lifting the collet up on the anvil and heating the tips with a MAPP gas torch.  The anvil serves as a heat sink and keeps the base of the fingers from getting too hot. 
The base of the anvil (head of the bolt) was clamped in a vice and the ends of the fingers were peened with a hammer at the location of the arrows.
Two views of what the case looks like after processing through the ERJ case cannelure tool.

The details need a little bit of polishing to soften the embossments but I am very happy with the results.

Except for filing the anvil to size, the job took less time than writing this blog entry.


  1. Smart move, and a nice way to 'fix' the problem with .40s...

  2. Smart move, and a nice way to 'fix' the problem with .40s...