Pierced primers

[crowellrw]

So... I took my girl friend out to the shooting range for the first time last night. We had a bunch of 38 special ammo that I loaded up, 158 gr SWC, 5 gr Unique. They were just a little hot for her S&W 642(?) snubbie. She shot one round and I finished the other four in the cylinder. When I ejected the spent cases I noticed burnt powder on the frame where the firing pin comes through. On close examination, see picture, the primers on three of the five cases appear to be pierced. My son has put about one hundred of these through his Ruger security six with no problems, I checked the primers on the last fifty he fired when I got home.

What could be the cause of this?

It feels like there is a bur on firing pin but that could be a result of the pierced primers.

bc

 

[Old Fuff]

I would start by pulling a bullet from one of the remaining cartridges, and check to see that the charge is 5 grains (check it on a scale) and that the powder is indeed Unique.

If that checks out O.K. get some feeler guages and measure the distance from the rear cylinder face to the breech face. Then (after checking to be sure the cylinder is unloaded) pull the trigger and hold it back while using the feeler guages again to check the distance from the rear cylinder face to the front of the firing pin. Subtract the second measurement from the first, and that will show what the firing pin protrusion is. You may have a firing pin that's too long, or has a damaged nose. But if that seems to be the case it's time to send the gun back to Smith & Wesson and let them fix it.

 

[wcwhitey]

Check the container to see if it is the "Cleaner burning Unique" from Alliant. The 5.0 Grain under a 158 SWC is considered hot with the newer formula. The standard pressure weight is 4.2 and the +P is 4.5 grains. I loaded the 5 grains for years and never had a problem but did take note that alot of the formulations that I went by have changed recently. This may be overly cautious by the loading manuals but it has changed. Bill

 

[earplug]

What Primer brand

Might be to late to save the burred firing pin. But...?
Some primer brands have soft cups to ensure detonation with light firing pin blows. Federal is known for soft cups.
A change in primers may fix the problem. A harder cup.
Did the cases extract ok? Did the recoil feel hotter then factory?
Did the reloader use the same primers when shooting the Ruger?

 

[Sundles]

Guns are individuals and a number of factors can cause what you experienced.

A few weeks back, I was shooting a bunch of different commercial 357 loads in a bunch of different revolvers. I had one S&W mod. 66 that would peirce primers with Remington Golden Saber ammo. That same revolver would not peirce primers with any other brands of ammo and NONE of the other test guns would pierce primers on the Golden Saber ammo, so go figure.

 

[Steve C]

You have a good picture of the fired case primer end. The primer looks pretty ordinary to me. I've seen pierce primers and there's a hole completely through them. There doesn't look like any other pressure signs.

Pull one of the cartridges and recheck your charge weight just in case the setting had slipped on the powder measure. Speer #13 lists from 4.7 to 5.2grs as +P loads for Unique with any of their 158gr lead bullets and you are within that range at 5.0grs.

There are several things that could make the primers leak. The burr you mentioned could be the culprit, a longer firing pin intrusion could put a deeper dent in the primer.

You may want to drop your load down to 4.4 to 4.5 grs for a standard velocity round. It will be a little more pleasant to shoot in the lighweight 642.

 

[crowellrw]

Thanks for all of your input.

The distance from the breech face to the cylinder is 0.067" and the firing pin protrusion is 0.047". I don't know if that is OK or not. Is the specification for firing pin protrusion available somewhere on line?

The load is maybe as much as 5.1 gr of Unique but not more. I was setting up a new loader and was using a scale to watch the powder drop as I went along. I was using load data from an old (mid eighties) Sierra Bullets manual. The load was for there 158 gr jacketed bullets. The powder is from the mid eighties as well so it isn't a new formula confusing things.

I will definitely be loading much lighter loads for the S&W.

What do you think about a file and a lite hand to get rid of the existing bur on the firing pin?

Thanks again for the help.

bc