Small Pistol Primers Backing Out

[alamogunr]

I have a supply of Wolf Small Pistol Primers that have always given me trouble not firing every time. This first appeared in a S&W Model 65 that I had modified for DAO by bobbing the hammer. The primers that did not fire showed a shallow firing pin indent. At first I attributed this to hard cups. Others that I inquired of gave other reasons, such as light hammer strike due to lessoned mass because of the bobbed hammer. Some said it could be because of weak spring.

The only change I could make easily was to replace the mainspring. Made no difference.

A few days ago, I was talking with a person that is fairly knowledgeable, and told him of the problem. He had experience with Wolf small pistol primers and said he found that they were slightly short and had to be seated securely to the bottom of the pocket. Made sense to me since I had not investigated this condition. I took some empty .38 Special cases and primed them with the Wolf primers. Made sure they were seated all the way. Loaded them in the gun that had given me the most trouble and fired them. Each one fired but tied up the cylinder. Checking them, I found that in each one the primer had backed out enough to tie up the gun.

Why would popping the primer in an empty cartridge cause it to back out. This never happened when a loaded round fired. The only thought I have is that a loaded round causes the casing to be forced back against the recoil shield and reseat the primer. How far off base am I?

[gnostic]

Too light a charge will cause the primer to back out...

[mattw]

I am not sure why they back out, but that is to be expected. With wax bullets and primers you need to open the flash hole or this will happen as well. My wife has a custom bobbed S&W 38 that will not fire hard primers, mass was reduced to much for a good hard hit. I love Wolf primers, use a bunch... but not in every gun.

[alamogunr]

Both respondents confirmed what I suspected. I now remember reading the exact thing gnostic suggested but had forgotten it.

I'm going to load a bunch of .38's with the Wolf primers and H&G #50 WC's. That ought to tell me if the bobbed hammer is a factor.

Thanks to both.

[EMC45]

I've relegated the remainder of my Wolf SPP to semi autos. I had the same issue with them out of wheelguns.

[poppy42]

It’s got to do with physics. The way it was explained to me when I loaded round goes off the pressure of the round going down the barrel and out the muscle actually stops a primer from backing out. It happens all the time and it’s not just something with wolf primers! I actually posted a thread about a bad batch of CCI primers they didn’t go bang. CCI is supposed expert had me pull some of the remaining rounds and send them off to him just with the primers seated. He then proceeded to tell me that I didn’t see the primer is deep enough because they were all protruding from the face of the cases. Every case i’ve ever fired in the case that was not loaded backs the primaries out! No matter what the brand primer is! That has been my experience. Others may have different results.

[dtknowles]

Primers back out when the pressure is not enough to push the case back against the breach. When hit by the firing pin the primer can case move forward. If the case grips the side of the chamber and does not back up the primer will protrude. Low pressure and excessive headspace make this worse.

Tim

[poppy42]

Primers back out when the pressure is not enough to push the case back against the breach. When hit by the firing pin the primer can case move forward. If the case grips the side of the chamber and does not back up the primer will protrude. Low pressure and excessive headspace make this worse.

Tim

Thank you, that is what I was trying to say. Just didn’t quite come out explained the way I wanted to!

[Baltimoreed]

All primers back out except military crimped in primers. After a round is fired the pressure drops in the chamber as the bullet moves down the bbl, the case then contracts enough that it can also move backwards which reseats the primer. This primer movement causes the primer cratering that’s evident on hot reloads. When a too light charge of powder is used the primer still backs out but there isn’t enough pressure to move the case rearward to reseat it. Primer powered wax or rubber bullets need to have their primer holes enlarged to make them fire without locking up the revolver. The enlarged hole in the case allows the pressure from the primer ignition a place to go so it doesn’t back the primer out.

[DHDeal]

Tim beat me to it. The recoil process reseats the primers after they move. Not as noticeable (or noticeable at all) in a tight chambered rifle. The hammer whacks them forward and recoil whacks them back where they're supposed to go (assuming there aren't any mechanical problems with the gun).

The Russian primers (Wolff/PMC/Tula) are very good primers for accuracy in rifles. I've used many thousands of them and still have a bunch. The problem with them is they need a good hard seat in the pocket or you may experience what you've seen. I've had it happen only with small rifle/small rifle magnum primers. Large rifle have never given me any problems. I was in a benchrest rifle stage when I bought so many and have only come back around to handguns in the last 5 years or so. The Russian primers started to get scarce then and the American primers were available, so that's what I have stashed.