Is my barrel clocking?

[rojasray]

Benelli MP90s




Can you guys tell somewhat of a clockwise twist to the extractor notch on the barrel not lining up with the notch on the slide? Can this affect feeding or extracting because I seem to be having issues with it with CCI SV.

Can someone with the same pistol please post a pic for comparison?

[Rover]

CCI SV is fatter than Euro ammo.

[rojasray]

Yes, but is my barrel clocking?

[Gwhite]

The MIT collegiate team has about 25 Benellis. Most will work with CCI SV, but no where near all of them. I'm slowly amassing a list of things that can impact functioning. My goal is to eventually get them all tuned up so they will work with any ammo, but I have a lot to learn before that is going to happen.

The problem you show in the photo is a bit unusual. The barrel in the Benelli is held in place by two screws located underneath, inside the weight compartment. If you look at the exploded diagram, the barrel is turned down in the middle, with a sloping transition at each end. I believe the screws each clamp on the opposing slopes at either end of the barrel, and by jockeying back & forth between the two, that's how you can adjust the headspace. I don't recall seeing any sort of flat or groove to hold it from rotating, but there could be. I've never had one completely out of a pistol. We've had one pistol where the barrel had come loose, and student would get misfires. You could slide the barrel back & forth a little with firm thumb pressure. Yours could be getting close to that point.

I have been warned by Larry Carter that if the rear face of the outer portion of the frame holding the barrel gets hammered down enough by the slide, the headspace can be reduced to the point where you can get slam fires. On most Benellis, the barrel is inset slightly as shown in your photo. The sum of the depth of the cutout in the bolt face and the depth of the inset of the barrel needs to be between 0.040" and 0.045".

If you need to tighten and/or adjust the screws, I would be very careful. The screws are short, and there's not a lot of metal holding them. If you just crank them tight, you run the risk of stripping the threads. The nominal torque for a 5mm set screw is 4.7 N•m, which is 41.6 inch•pounds. I used a torque screw driver set for 25 inch•pounds to be safe, but with a dab of medium strength liquid blue Locktite (#242) for added insurance. I'm not sure how much the pistol has been fired since the repair, but so far so good... If it comes loose again, I'll try 30 inch•pounds.

[FredB]

Gwhite,

A couple of notes:

1. Larry Carter told me that the Benelli barrels are a press fit in the frame, and they can be a tight fit or not. He said you sometimes can loosen the 2 screws and still not be able to move/remove the barrel, and that he had designed a special press for that situation. He also said that head space was critical when replacing the barrel.

2. I had a Benelli that fed and extracted unreliably with just about every ammo, but simply hated CCI SV. I sent it back to Larry thinking that the chamber needed to be a little enlarged. Instead it appears that he slightly chamfered the chamber mouth at the bottom. That pretty much cured the problems and then it loved CCI SV, although it was still somewhat ammo sensitive.

HTH

[Gwhite]

Fred,

Thanks fro the info. I'm constantly learning.

We have a large collection of spare magazines, and can frequently find a combination of magazine & pistol that works well with a particular ammo. We mostly use CCI and RWS Target Rifle. However, I don't like fussy pistols, so I've been studying the problem for a while (as time permits). My personal Benelli is very forgiving, and will work fine with any magazine. When I've swap my slide onto a fussy Benelli, they have always worked fine. So, there are subtle differences in the slides that can have a big impact on functioning.

The main thing I've found is a big difference in how smooth the slide feels when it is pulled back. Things I've identified:

1) Machining marks on the bottom of the slide: This is where the hammer presses on a rib underneath the slide. Some are smoother than others. A light stoning can help.

2) Machining marks on the top of the disconnector: This is on the newer versions that have a small arm that sticks up to operate the disconnector. Again, a little polishing can help.

3) Bolt Stop pin too long: This is the little black plate that holds the firing pin and the recoil spring tube in place. The tube is retained by a pin that sticks up from the plate into a slot in the bottom of the recoil spring tube. If the pin is too long, it rubs on the spring, and you can actually feel it as a periodically increasing & decreasing drag on the tube as you run it in & out. The pin should stick up about 0.042" from the plate. I've found some as long as 0.050", and replacing them with a shorter one makes a big difference to the smoothness of the slide operation. We have spares I can pick through, but there's no reason you couldn't (carefully) stone one down.

4) Rough or damaged Recoil Spring Tube: Sometimes the students forget to close the slide before they remove the takedown block. That means the tube will slam back against the stop pin with considerable force. If the tube doesn't launch itself across the room, it will raise a burr that will cause drag. I've also found some tubes where the slot was a bit rough. Replacing the tube or stoning the rough bits smooth can help a lot.

5) Clean Chamber: Depending on the ammo, the chamber can get gunked up quickly. See this thread about how we keep our chambers clean without much fuss: http://www.targettalk.org/viewtopic.php ... sh#p186896.

6) Dirty or stiff extractor: Rare, but sometimes this can happen. I've hardly ever had to replace an extractor (which is good, because they can be a real pain to get out). Often, a bit of light oil/solvent and a lot of manual cycling will do the trick.

7) Proper Lubrication: The Benellis are fussier about lubrication than some pistols. I discovered mine will not function well at all if I use grease on the slide instead of oil. I made up a set of notes we keep posted over the cleaning area (see attached file).

Hope this helps folks. I really like my Benelli, but so does my daughter. I shoot a Pardini, so she can use the Benelli. I really ought to get another one, but I'm in Massachusetts, and new ones are no longer legal for sale.