In case that's the problem, I have ordered a new spring/guide rod assembly, and a new firing pin spring. However, after only 1500 rounds, I'd think the spring would not be that well worn.james481 said:Hmm, I guess I'm not sure on this one, but I doubt that the problem is in the "rails" on the slide. I believe that those rails are there to pick the next round out of the magazine, and only the firing pin hits the catch. The first thing that I would check is your recoil spring. If it's worn out, it will cause exactly the situation you describe.
James
I wish that were the problem, because I'd just remove the loaded chamber indicator if it came down to it. Alas, I can get the slide to stick without any round chambered, or coming into contact with the indicator.Matches said:Sometimes the slide on my M9 does the same thing. I have not taken my pistol apart as far as you have. I have noticed that last 1/8 inch is about when the round meets the loaded chamber indicator. It would seem the slide doesnt have enough energy to force the round up over this protrusion. If a stonger spring was available I would seriously consider trying it. Does anybody have any other ideas.
Matches
Th0r, thanks for your insights here. It sounds like this is the right line of investigation for me. Unfortunately, the guide rod/recoil spring assy. and FP spring I ordered from USASteyr was cancelled because they were out of stock. I thought it was too good to be true when their website took my order.Th0r said:There is no sticking of the slide or any internal parts. The recoil sping is just too weak. Once worn, the recoil spring lacks alot of power in it's resting position. But once the recoil spring reaches it's uncompressed postition the firing pin spring is reachingthe end of it's compression. The worn, uncompressed recoil spring and the compressed firing pin spring (plus the step up needed to lock the barrel/chamber/round in place) cancel each other out.
[snip]
It only took my gun 600rds and now I've noticed the developing problem. The gun REALLY needs a stronger spring in my opinion. At least another 2lbs. Until a stronger spring it made, I've opted for a new spring with a couple washers between the base of the guide rod and spring.
Thanks very much for your insights. My example of the "creep close" was just to show that I could reproduce the out-of-battery condition at will even without a round chambered. In actual use, however, the slide will fail to go into battery in about 1 out of three rounds. This is after I meticulously detail stripped and cleaned the barrel, chamber, and action.ShelbyV8 said:With a round in the chamber the M40 will always hang up about 1/8 to 1/16 out of battery on a creep close. The striker is being cocked and the LRI is being cammed. Does it feed properly when the slide is released by the slide release or when pulled all the way to the rear and released. If so the problem is possibly that the ammo is not hot enough to fully cycle the slide. If the chamber is clean and the slide working smoothly try hotter loads.
No affect. The recoil spring is under a compressive load (~displacement x spring constant) and until the force is high enough to cause the slide to move, you have not overcomed the initial compressive force and thus no increase in load on the recoil spring and no fatigue etc. I'm assuming your slide wasn't opening when you were carrying since the frame plus full mag is probably less than 3 pounds. Not sure what the recoil spring load is but I would guess it is more than 12 pounds and you have to overcome friction in the slide for it to move.Matsaleh said:I just had a thought (call the papers!)...
I have been using a ClipDraw http://www.clipdraw.com/ to carry my S40 on a daily basis for about the last 6 months. The clip is mounted on the side of the slide, not the frame. It occurred to me that the weight of the gun+loaded mag puts constant pressure on the recoil spring that is not normal in a regular holster, where the entire gun is supported.
Is it possible that this constant, but slight, pressure on the recoil spring might have weakended it, causing my current failures?
Thanks.
Ok. Thanks very much for your reply.uncle_walty said:No affect. The recoil spring is under a compressive load (~displacement x spring constant) and until the force is high enough to cause the slide to move, you have not overcomed the initial compressive force and thus no increase in load on the recoil spring and no fatigue etc. I'm assuming your slide wasn't opening when you were carrying since the frame plus full mag is probably less than 3 pounds. Not sure what the recoil spring load is but I would guess it is more than 12 pounds and you have to overcome friction in the slide for it to move.
My suspicions were correct. The "protrusions" I mention above were really small nicks or cuts in the rails that feed a round into the chamber. I think they were catching on the edge of the mag ever so slightly. I used my Dremel and some polishing compound to very gradually smooth out the raised metal, and voila, no more misfires! After 100 rounds of testing with my carry ammo and two other kinds, I am now back to carrying my S40 full time.Matsaleh said:I then disassembled the gun and looked for areas of wear or protrusions on which the slide might catch. In the center of the slide, beneath the firing pin channel, there is a pair of "rails" that contact the "catch" (#10 on the USASteyr schematic). At the rear end of these rails, right at the point where they bevel up into the slide proper, there are two wear marks. I ran my finger over those marks, and there is a barely perceptible protrusion that catches my finger. there is also a protrusion on either side of the rails, so that it appears as if the metal has been flattened and widened ever so slightly, like it has been deformed by the strike of a hammer.
I suspect that this is the cause of my slide sticking.
/That's good info too. FWIW, I investigated that possiblity in my own case but it was not to be. However, I can easily see how it could contribute in general. The contact area between the FP spring and the inside of the striker does not appear to be as finely machined as the inside of the FP chamber.Los36 said:Matsaleh-
I'm happy to hear that you solved your problem.
I'd like to add that recently, after a cleaning, when I would gently cycle the slide by hand, the slide would not fully go into battery. I was able to completely cure this by lubricating the inside of the firing pin, where the spring is. I believe that if this area is totally dry, the friction of the compressed firing pin spring on the inside surface of the firing pin is a major contributor to the problem.
