Benelli MP90S firing pin recoil hangup

[-TT-]

Following up to my (fixed!) extractor issue, I still experienced an occasional alibi. The frequency went down from 1 in 20 to maybe 1 in 50, still way over the zero alibis I used to have.

Realized the source was the back surface of the firing pin. See the photo - where the hammer has dented the FP butt end, also raising a bit of a ridge where the FP slides over the hammer when recocking it under recoil. That's a new FP on the right, and an old one on the left.

There was a pretty significant hiccup in the action, as the hammer kind of falls "into the ditch" only to then have to "clear the ridge". I corrected it by carefully filing off the high spots, and radiusing/polishing the surface with 1000 then 2000 grit. The gun cycles cleanly and reliably again.

My question - is this common, and everyone has to touch up their Benelli FP regularly? They're incredibly reliable otherwise, I've only had to replace one in ~15000 shots. Maybe I should I just consider replacing as soon as it starts to dent like this, or I feel the "hitch" when cocking?

[Gwhite]

The original Benelli firing pins were flat on the back end. They also use to break frequently.... Part of the problem was that unless the face of the hammer and the rear face of the firing pin were perfect square, the hammer could hit the back of the firing pin off center, which put a lot of undo stress on it.

When I started maintaining Benellis for the team I help coach, I found a bag with the remains of about 20 broken firing pins. Here's a picture of the common failure modes that also shows the square shape of the original pin design:

The top two broke near the back, possibly from the problem I mentioned. The lower two had the tips break off.

Larry Carter came up with an improved firing pin design that has a radiused back end, and yours looks like a Benelli attempt to emulate that. At least the photo doesn't look like the ones I've bought recently from Larry. The idea is that the hammer is guaranteed to hit closer to the center of the pin, reducing any sideways stress. Larry's has more of a raised round bump rather than a cylindrical section, and are certainly much more reliable that the old factory design. He also consulted with a heat treating expert to make sure they were strong & hard without being brittle. It looks like yours are a bit softer.

You can keep an eye on yours & clean it up as needed, but you might want to get a spare or two from Larry as well.

[-TT-]

Interesting yes, the one on the left in my photo is the Benelli FP that was original to the gun. After a year, it broke at the front, just as the flat part emerges from the round shaft (sort of like the ones at the bottom of your photo)

The one in the gun now (not photographed) was purchased when I bought the gun (about 1.5 years ago), and is the one that's peening rather a lot and which I smoothed. I'm not sure if it's Larry's - it closely resembles the original.

The one on the right is Larry's, purchased maybe a few months ago. It closely resembles my others, too, but has a darker finish. Can you post a photo of yours, that look different?

I'm still not quite confident in the FP that I smoothed. Thinking to just replace it with the new one I have, and watch how the new one wears. Hopefully it is improved, or at least less vulnerable.



I guess one actually *wants* the FP to be a little softer than the hammer. At least it's easily replaced, and relatively inexpensive.

[Gwhite]

I'll try to get pictures in the next day or so. I should have one of the older ones and the "new" LGI version.

[-TT-]

Thanks. I looked at my new pins and the bag is marked 104P-G0042502. I suspect this is an updated Benelli-sourced 104P-G0042501 part, since Larry's designs usually have "LGI" at the end.

[Gwhite]

That's definitely a new number, but Larry sold me several of his design under the old Benelli number. Due to one thing an another, he's occasionally had trouble getting parts in a timely fashion, so he may have just dumped his in the same bin & not bothered to assign a new part number and modify the web site.

In any event, it turns out I had examples of all three variations:

I've had good luck with his design, and based on your experience, I will be asking if I can still get his version the next time I need any. The way the back end of Larry's is shaped, it pretty much guarantees that the hammer will hit on the centerline of the pin. I think they may also be a little harder than the new Benelli pins, because they don't seem to deform as much as yours has.

[-TT-]

Mine are definitely type "C", and I agree that I like the look of the LGI type "B" curve. Thanks very much for the comparison!

Is it the angle of the photo, or does the "B" shoe ride a little bit farther above the plane of the bolt when installed? The ones I have all sit squarely on the center flat surface.

[Gwhite]

Maybe just a tiny bit, but not that I've noticed. When Larry first came out with them and I bought some, he claimed nobody had ever broken one of the new ones. With the team using several, I think we had one let go within a year, but the rest are going strong.

One problem we have is that some students are in the habit of pulling the trigger until the pistol goes "click" in standard pistol timed & rapid fire. That means they are regularly dry firing without the adapter, which puts a lot of added stress on the firing pins.

[-TT-]

Called DeAnna and she reports they are out of stock on the LGI design.

I've swapped out my dinged one for a fresh Benelli pin and will watch how it goes more carefully. Maybe I had one that didn't get a full heat treat, or something.

P.S. Teach those students well. :-) They should be pacing themselves, not counting-to-six. Ok, I guess I do that sometimes. But only in slow fire!

[Gwhite]

Did DeAnna mention if they plan to get more made? I hope they don't consider the factory version "adequate".

[-TT-]

She didn't say when, but she did say that she expected them to be available at some future time. The Benelli units were in stock. I suggest you put in a second request, to improve the odds of the LGI ones. :-)

[Gwhite]

Will do. Once the collegiate national championships are over in March, I will probably drive up to Maine with several Hammerli air pistols that need an overhaul.

[10M_Stan]

FWIW, here is an image of a new firing pin for a MP90S I received 12/2017 (from Larry's):