Benelli m4 Gas piston O-ring / Full strip questions.

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P90Puma

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Did a (first time) total strip of the benelli today with a buddy who is an officer in the navy, after putting down ~70 rounds today, 400 rounds total through the shotgun.

One of the O-rings in the gas piston system had broken, is this just a regular O-ring that I can pick up at partsource/CT/etc?

Pretty cool gun, but man that trigger group is complicated compared to an AR15, no way was I going to take that apart (not that it suggests to anyways.)

Also the manual does not suggest to remove the follower/spring/mag tube assembly to cleaning, I read somewhere you use the bolt handle to take it apart, should I do so? If so, how?

Thanks.
 
You dont really need to take the mag follower out, but to do it a pair of needle nose pliers will work: and use it to squeeze the spring retainer at the end of the mag tube, then pull it strait out. It will be pretty tight even when squeezed with the pliers. (just make sure to keep a finger on TOP of the spring retainer because once its out of the top the spring will shoot out like a cannon)


The O-ring is probably a special high-temp O-ring, but the part number for it in the Benelli Manual is 270J. Brownells SHOULD be able to get it for you (Just checked, and they list it, but its backordered...)

this is the brownells SKU: 301-000-497 (factory part number on Brownells site is said to be: '70107' )


Normally the pistons dont really need to be disassembled for cleaning, maybe after 1000-2000 rounds or something.



Trigger group is pretty simple (Hammer, trigger disconnector) but its also got the shell lifter and shell advance mechanism built-in, so its got a few more parts. I wouldn't ever take the trigger group apart, just wipe it clean with a Q-Tip or something and then oil it up.
 
P90Puma said:
Excellent, thanks for the info.

I will try wolverine to see if they might have the part in stock, can't think of anyone else.
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They (or The Shooting Edge) should be able to order it for you. Although keep in mind getting aftermarket parts for Benelli's is quite difficult.

I tried getting another cheek piece for my M4's telestock after it was damaged from a drop, and after Emailing TSE, and waiting a good solid year (mean while using a jerry rigged fix), I ended up making my own replacement out of fibreglass cloth, epoxy, and some outdoor rated synthetic Leather. Now an O-ring would probably be a LOT more common of a part, so hopefully it shouldn't be too hard to get ahold of :p
 
P90Puma said:
One of the O-rings in the gas piston system had broken, is this just a regular O-ring that I can pick up at partsource/CT/etc?
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Yep, it is.

Just removed the assembly in my NEW "never fired" M4 to check it out and that O-ring came out busted too.

In the diving business we go through O-rings like s**t through a goose. These little black O-rings are all the same. Added claims increase the price and little else. I've replaced the "high temp" green O-rings in my HKMark23 with black garden variety ones and they work as well and last as long as the expensive green ones. Green being the color of money, I get the irony :D.

As to being broken, they may have been installed that way because the correct size was unavailable. For low pressure applications we "make em up" too. As you've already seen, they work fine.

The lowly O-ring is a marvelous little seal maker but claims about special properties are largely bunk. "Its size that matters" :D.
 
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Damn... I'm a little disappointed in reading about these O-Rings.

If Mossberg can completely eliminate the O-Ring in their semi-autos, I'd have thought Benelli could. Wow. I've got to check the schematics now.
 
G37 said:
Damn... I'm a little disappointed in reading about these O-Rings.

If Mossberg can completely eliminate the O-Ring in their semi-autos, I'd have thought Benelli could. Wow. I've got to check the schematics now.
Click to expand...

Assuming from the above post that you were to disassemble the piston assembly every 1500 rds or so and you had to replace both rings, you'd have enough rings in a $10.00 Princess Auto variety pack to do you 15,000 rds. I assure you being suckered into paying "gun part" prices for these things is completely unnecessary. If you find buying said variety pack a bit too much of a waste, find a sport diver who knows his ass from his elbow to go splits on one with you and he can make use of the big ones :D.

These are installed in a static part of the assembly by the way, so suffer no wear and even if there were enough heat generated to scorch em to hell, which I doubt, they'd maintain a seal till you pulled em out. The pressure differential across em has got to be really small. They probably do more to keep #### out of the fine threads of the static cylinder they're mounted on than anything else. If you're worried about the M4 breaking down in the middle of something important, I'd bet on it being due to something other than the O-rings.

The more you use O-rings the more you appreciate em. They're a hell of a lot easier and cheaper to maintain than a bunch of pricey, high tolerance parts. Operator replaceable and pennies apiece.
 
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