Revolver Misfires: Brass-related?

[swjones503]

I have a Ruger Speed Six 357 in Stainless. The gun seems nice and tight, but every once in a while, I get a misfire.

Being a cheapskate, I hold on to my brass forever. Some of it has morphed into something like Weatherby brass...as in, belted-magnum. Not caused by overpressure, more like adding up the normal minute expansion caused by standard pressure over dozens of reloadings.

Can that raised shoulder, about 1/10" above the rim, be causing the blow of the firing pin to be cushioned by the case moving forward gradually?

Pin extension above the recoil shield seems to be something like .035, +/- .005. Space between the brass head and r.shield measures about .011" with the cylinder held forward. BC gap measures at .007" with the cylinder held back.

Any ideas?

 

[BBBBill]

Used up brass, end shake, headspace, firing pin protrusion all can contribute. Are you saying that the raised shoulder keeps the brass from fully seating? How can the cylinder close on that. If the endshake is bad enough to allow the cylinder to close over the ballooned cases, your headspace may be off. I don't have my specs handy to reference, so I'm talking from memory here. I think the headspace is supposed to be .060"-.066" on the Ruger Six series. End shake should be held to .001"-.003" and barrel-cylinder gap at .004"-.006". Firing pin protrusion should be .050"-.055". Dfariswheel should come along and confirm or correct anything I've misstated.

 

[rcmodel]

If the reloads drop all the way into the chambers, it is unlikely to be old brass related.

However, there is this:

http://www.thehighroad.org/showthread.php?t=563715&highlight=colt+commando

rc

 

[murf]

measure the rim thickness on a misfire case and compare to a fired case rim. do the same comparison for the primer pocket depth.

murf

 

[Jim K]

When dealing with old cases, there could be several problems, including the primer pocket being forced deeper by the primer seater so the anvils lose support.

Really, after two or three thousand reloads, those old balloon head copper cases made in 1897 just wear out.

Jim

 

[btg3]

I bought 500 rds of mixed headstamp re-manufactured .38spl that fired fine in Speed Six and Service Six revolvers, but not a 642. Of course there was a difference in the guns, but the primer was also recessed in this lot of ammo.

 

[swjones503]

Looking closer

OK. I measured things a little more closely.
Firing pin protrusion is only .040"....010" short.
Cylinder to recoil shield is .060"...about right.
My end-shake is running about .005", which is too much.
With brass in place, the space between an "average" case and the recoil shield is about .006-.007".
With about .005" primer seated below the head...I'm only left with about .028 firing pin travel after it hits the surface to ignite the primer.

Per rcmodel's question...the brass goes all the way into the chamber.
With the bevels on the head, I found it difficult to get an accurate measurement of the head thickness, so I just measured from the head to the recoil shield (w/o the spent primer).

Looks like I can improve things with the end-shake and the firing pin.
Thank you all for your input , it helped to clarify things.