West Hurley model 1928 Thompson misfires

[dksusmc]

I have a West Hurley model 1928 Thompson produced in the 70s that I have owned for over 5 years.  It has run flawlessly until a few months ago when it started misfiring after 1-6 rounds of automatic fire. The round chambers, but the firing pin does not penetrate the primer far enough to detonate the round.  See the attached picture. The casings on the right fired normally; the rounds on the left failed to fire. I can take the unfired rounds, put them in my 1911 and fire them without a problem.  I have done a thorough cleaning multiple times and cannot see any problem that would be causing this.  Does anyone have any ideas about what is happening?

[inertord]

Have you disassembled the bolt and cleaned/examined the firing pin and hammer? 

[ppgcowboy]

New Spring?

[DINK]

As mentioned above, have you completely disassembled the bolt and thoroughly cleaned all the parts and the channels and slots they run in?  This includes the extractor as well as all the firing pin assembly parts.  Also, the front of the receiver is difficult to get to and hard to see into, but it can get fouled and need thorough cleaning.  There's a narrow channel that the extractor runs in that is hard to clean out without a long dental pick or pointy piece of wire.  Also the area around the back of the chamber is hard to get at but can accumulate fouling.  The front of the chamber has a sharp corner that the mouth of the casing headspaces on and it's hard to clean thoroughly.  You can run a couple of sections of cleaning rod in through the back of the receiver with a nice new .45 brass brush on it and then chuck the other end into a pistol drill to clean out the chamber.

If everything is squeaky clean and lubed, then a new spring is cheap insurance (as noted above) and they should be changed out every five thousand rounds or so anyway.  The firing pin in the Thompson is powered by the force of the bolt coming forward, so anything that robs that action of energy will cause light hits like you are experiencing.

 

[reconbob]

       Fire the gun in semi and make sure that the bolt stays locked fully to the rear

everytime. If the gun was dirty, or if there is a blockage of the firing pin or extractor,

the gun would not shoot at all. Not light-strike after 5-6 rounds. If the barrel is getting

shot out and losing power (because the bullet does not tightly seal the bore) you could

be getting short recoil, the bolt does not recoil back as far, has less power moving forward

and you could get the light hits.

My $0.02

Bob

 

[Chief762]

I was having much the same issue with my WH28. Sometimes on the first round, other times not. Sometimes it would run just fine. I suspected that the hammer pin was sometimes sliding over just a bit and hitting the blish lock slot because a small chip was evident in the slot where the pin should pass by. Thus slowing down the bolt enough to make a light primer hit. As seen from the picture, Paul Krough added hammer pin pads to the front of the bolt pocket to keep the pin centered up. Although he installed a new barrel, he also rechambered and headspaced the original WH barrel. Some were known to be unnecesssarily tight. I haven’t had a light primer hit since PK redid my gun.

I know he’s not taking in new work, but maybe John Andrusky? Hope this helps you find the reason.

[deerslayer]

West hurleys have tight chambers that slow the bolt and rob energy.  Causing missfires.  Could be your problem. 

[jpw43]

6 hours ago, Chief762 said:

I was having much the same issue with my WH28. Sometimes on the first round, other times not. Sometimes it would run just fine. I suspected that the hammer pin was sometimes sliding over just a bit and hitting the blish lock slot because a small chip was evident in the slot where the pin should pass by. Thus slowing down the bolt enough to make a light primer hit. As seen from the picture, Paul Krough added hammer pin pads to the front of the bolt pocket to keep the pin centered up. Although he installed a new barrel, he also rechambered and headspaced the original WH barrel. Some were known to be unnecesssarily tight. I haven’t had a light primer hit since PK redid my gun.

I know he’s not taking in new work, but maybe John Andrusky? Hope this helps you find the reason.

I had a similar problem with my WH. The hammer pin was doing just what you describe.

PK fixed the Blish lock slots and I never had that problem again.

[Rimcrew]

Looks like you are using reloads.  Make sure the primers are fully seated.  High primers will do exactly what you are experiencing.

[ppgcowboy]

Has the original poster even tried any of the suggestions offered here?

[full auto 45]

Clean and replace the recoil spring. Check the feed lips on your mags.

[parts]

when it is on single does it still not hit the primer hard enough ?

[TSMGguy]

One post. Never came back.

[ppgcowboy]

9 minutes ago, TSMGguy said:

One post. Never came back.

My point

[Ryo]

Too bad.. it's always nice to find out issues.

My WH is the opposite.. loose tolerances.. can get run away until I fixed it.