the dept I work for has a couple of 40mm launchers.

we have one that is misfiring.

it was brought to me to diagnose. it appears the metal around the firing pin hole has swaged outward (.0015") and the primer will slighty high center on the protrusion.

it appears the receiver metal is MIM as it has several pot marks.

The action is very SW revolver.

while I have an idea of taking a drill bit by hand and removing the swaged metal and making a slight chamfer......

just wondering if someone has a better idea or direction?

the revolver action is very snappy, so its not light hammer strikes.







thanks in advance

__________________
if you're gonna be a bear...

Interesting piece.
Considering the value of opinions:
I would start by just stoning the area flat.
Can go more aggressive later, if needed.

__________________
-jwk-
US Army '72-'95

I would stone or file the firing pin hole flat. You don't want a chamfer that the primer could flow into. This is the same for a revolver. If you keep making the face of the recoil shield flat each time it burrs up, after 2 or 3 times it will stop doing that.

Also, make sure that the bottom of the hammer is not touching the rebound slide when it's all the way forward against the frame. If it is, the rebound slide will absorb some of the impact force, making for light strikes.

Make sure that when the hammer is all the way down with the hammer nose sticking out, that the hammer nose can wiggle a little bit. This shows that the hammer nose is not hitting the frame behind the firing pin hole.

All these things apply to a regular S&W revo as well.

Been a long time since I fired a m79. The only issue I can remember was with a certain lot of flare shells. Faulty ammo.
I agree with previous posters, stone it flat. I suppose the soft
Alloy and the hi-low pressure system of the 40mm ammo caused
this.

thanks for the intell.

I will not chamfer...but stone flat.

I checked the hammer while holding the trigger ...... the hammer is not in contact with the rebound slide.

also, the firing pin floats upon full contact with the inside of the receiver.

I would also guess that the tolerance of the rounds could be a factor. I have 3 rounds to test the launcher....they use a .38 Short Colt primed brass as the ignition source.

two of the primers are set deeper than the third. I asked to see the cases of the rounds that misfired.....but they have not surfaced.

thanks again

__________________
if you're gonna be a bear...

Sounds like you may need an extended firing pin. You can effectively lengthen the current firing pin by removing it from the hammer and grinding .010 off the face of the hammer, thus allowing it (and the firing pin) to go .010 more forward. When grinding, make sure to keep the face at the original angle. A belt sander or disk sander works well for this.

Measure the front to back thickness with a caliper before you start. You can check your progress to see how much has been removed. Then assemble the hammer nose to the hammer and recheck for firing pin wobble to make sure there is no interference in the new position.

thanks TG for the additional info.

I stoned it flat and ran the hammer about 50+ times and it pushed out a little more slag....which I flattened with the stone.

I hope to test fire this week and should I need a little more firing pin, I will definitely keep your method in mind.

take care

__________________
if you're gonna be a bear...