Benelli MP90s Double Fire

[Rudi]

Good day!
I've put a couple 1000 Aguila standard rounds through this pistol in the year I've had it, it loves them. CCI not so much, several failures in the boxes I've tried. Last night I tried a magazine of RWS Pistol Match, Shots 2 went off as normal, and shot three automatically straight after which took me by surprise. Double fire. My trigger is measured and set at the 1000g standard. Post shot travel is about 1/4mm, how I've set it for 10 months now.
Anything I should consider checking? To be fair I didn't do a clean after my last Friday session (only 50 shots), that's the only thing I can think of, or the RWS had a hot round?
I know I could just ignore it as a one off, but would rather know where to check for signs of trouble further down the line.

Thanks as always, Rudi.

[Coolmeester]

If you have a black trigger unit, set 1st stage travel between the marked lines on the side of the adjusting screw. With newer silver trigger unit it isn't a problem.

If it doesn't help the trigger unit must be serviced and the springs need to be changed.

You won't need to clean .22 pistol until 1000-2000 rounds is fired.

[spektr]

It sounds like its dirty. CCI ammunition in eurospec chambers is a bit long.
Saami spec chambers are longer than Eurospec chambers.
That means the gun can fire when the bolt closes if its dirty

[-TT-]

A broken firing pin can do this, and is very easy to check by removing the bolt and taking the pin out. The pistol can often work (mostly) fine with a broken pin. You can check for gunk in the firing pin channel while you're in there.

Second possibility is slamfire as spektr mentions. The dimensions of CCI ammunition can perhaps make this an issue. This can be aggravated by a dirty bolt face. If it's not gunk, adjusting the headspace is a job for a gunsmith.

Third simple possibility is a dirty chamber, causing the cartridge to not fully seat when the bolt closes on it. A clean chamber is the single most important factor in keeping these pistols operating smoothly.

There are other possibilities, but these are easy to check, and rectify.

[Rudi]

Thanks both, I give a clean every 100 shots but did notice a little more gunk than usual after testing some other brands.
My early Benelli also doesn’t have a disconnector so that probably added to the issue.

[Gwhite]

Good day!
I've put a couple 1000 Aguila standard rounds through this pistol in the year I've had it, it loves them. CCI not so much, several failures in the boxes I've tried. Last night I tried a magazine of RWS Pistol Match, Shots 2 went off as normal, and shot three automatically straight after which took me by surprise. Double fire. My trigger is measured and set at the 1000g standard. Post shot travel is about 1/4mm, how I've set it for 10 months now.
Anything I should consider checking? To be fair I didn't do a clean after my last Friday session (only 50 shots), that's the only thing I can think of, or the RWS had a hot round?
I know I could just ignore it as a one off, but would rather know where to check for signs of trouble further down the line.

Thanks as always, Rudi.

If possible, the first thing to do is to find the case involved in the 2nd firing. Usually, they will not have a firing pin mark, in which case, what you have experience is a slam fire. Thinner/softer brass and extra touchy priming compounds can aggravate the problem, which is why it happened when you switched ammo. I have seen a couple Benellis slam fire shooting RWS, but also CCI. It can also happen if a burr or piece of dirt hits the rim just wrong.

If there IS a firing pin mark, but it's kind of shallow, then you need to take your bolt apart & clean the firing pin & the hole it lives in. In theory, the process of feeding a round into the chamber should push the firing pin fully back in place, so this is a bit of a long shot. Also, make sure your extractor isn't stuck. That can fire the rounds as well, although often early enough that the case head will blow.

If you have a regular looking firing pin dent, then something VERY unusual is going on with your trigger.

The Benellis are a bit odd, in that the headspace (gap for the rim) is set by the combination of the depth of the pocket on the bolt face, and the barrel position in the frame. Over time, the back of the frame around the barrel can get hammered by the bolt, slowly shrinking the headspace. If it gets too small, then you get slam fires. The sum of the depth of the bolt pocket, and the "set forward" of the barrel should be between 0.040” and 0.045”. The bolt pockets usually run around 0.036" +/- 0.002", so the barrel needs to be set forward ~ 0.005" or more to get enough headspace.

It is possible to re-adjust the barrel position, but it's not easy. It can depend on the vintage of the pistol, and how tight the barrel fits the frame. The screws that lock the barrel in place have threadlocker on them, and you have to heat them with a 700 degree soldering iron tip to have any chance of freeing them up. I've done this a couple times, and broken several "high strength" hex keys in the process. After you get them out, you want to use new screws when you put it back together, and torque them carefully. The length of the threads is short, and it would be easy to strip them. If Larry Carter was still around, I'd strongly recommend sending it to him. Some of the barrels are a press fit, and he had tooling to use a press. In some vintages, the fore & aft position is controlled by bevels cut in the barrel, and the screw tips are conical. The screws are spaced such that screwing them in & out pushes on the bevels, moving the barrel back & forth slightly.

Hopefully it's something simple like a sticky firing pin.

[Rudi]

Fantastic information. Thanks as always.
I’ve also noticed I may be over oiling and giving the crud a place to gather, certainly in the circle around the breach where the edge of the case sits , oiling in the slides especially after cleaning which creeps into the breech, I try to pop a drop of remoil but once the tip of the nozzle touches something it’s hard to release just a drop. I need to re-evaluate my cleaning schedule/routine

I didn’t have the empty case, but I certainly know what to look for now the next time, if it ever happens again.

I’d like to clean out my firing pin area and main spring, but I have a roll pin in the slide and not a standard solid pin, so I need to pick up a suitable punch.

[Gwhite]

You certainly want to scrape the edges of the pocket on the bolt face out with a toothpick. Any hard crud built up there could aggravate the headspace problem.

For tips on cleaning & lubricating, check out this: https://www.targettalk.org/viewtopic.php?t=57315

I haven't tried converting the roll pin versions to the solid pin, but it might be worth a try. The black retaining plate that holds the firing pin & recoil spring guide tube in place provides enough tension to keep the solid pin from shifting around, and it makes the bolt a lot easier to work on.