TargetTalk

Are there any obvious or known issues that could cause a FAS601 to double (or triple) fire? If there's anything I should pay especial attention to on disassembly it would be helpful to know in advance.

Step 1 is to check the cases. If there are no firing pin marks, you are getting slam fires, probably from inadequate headspace.

If there are firing pin marks, it could be from "hammer follow", which occurs with too light recoil and/or too much drag. If the bolt doesn't come back far enough to cock the hammer, but DOES come back far enough to feed the next round, when the bolt closes, the hammer will be pushing on the firing pin, and the round can fire. I'm not sure at what point in the recoil the hammer cocks, but you should be able to see if this is a possibility by cycling an empty pistol. It may just be that the ammo you are using is too weak, or the pistol is too dirty/un-lubricated to cycle properly. I have a couple pistols that react this way to recent Federal .22 standard velocity ammo (#711B).

The third option is inadequate sear engagement. I'm not familiar with the trigger in the 601, but on many pistols, that can be (mis)adjusted. I couldn't find any reference to adjusting the 601 sear in a quick search.

I did come across this posting: https://bullshooter.blogspot.com/2006/0 ... autos.html

There is no mention of any issues like what you describe.

Also check the firing pin itself and it’s spring. Finally be sure the fp channel is clean. Most of my experience was with 602 pistols and they often had firing pin problems.

Dr Jim

Thanks for the suggestions. I believe I've got it sorted out. The upper screw (hex socket) on the hammer housing has a very narrow range of workable adjustment. Too far in and the sear won't catch. Too far out and you can't get the hammer housing in without hitting the bar from the trigger that trips the sear. I ran through a couple of magazines in the yard, but out of consideration for the neighbors I'll wait until I can get to the range to give it a more thorough workout.