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Benelli M4 -- Refinish Time!

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Took the five weapons out today/tonight.


Noveske Build

Boringly reliable. Eats even Wolff without an issue.


Glock 36

Not a single problem.



Botched the install of the Ejector and made the rifle unusable. Fixed the issue, but it missed out on testing.


9mm AR15 Build

Huge problems at the beginning. Short stroking no matter the ammo type. Took my ball and went home. Stole the JP Enterprises silent buffer out of the MRP and dropped it in the 9mm build. Knocked out the weight in the bolt carrier. Stacked about $2.25 worth of quarters in the receiver extension to act as a spacer. With this arrangement, I need to install the upper receiver with both pins removed since I have to press the buffer into the receiver. Took the pistol out tonight again and ran through 300 rounds of various reloads. I had a couple jams randomly, but it was running pretty well. I still need to tweak some things to get it 100% reliable.


Benelli M4

Started out having some issues where the bolt carrier would stick at the rear of the stroke. I'd have to hit the handle with the palm of my hand to get it to go forward and continue loading the round. I went through about 300 rounds of high brass #4 bird shot, a few boxes of slugs and buckshot. I even ran about 50 #8 value pack crap through it.


Cycling was pretty reliable by the end of the firing strings. By the end, I could barely touch the handguards it was so hot. My shoulder is feeling the love now.

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SD -


On the M4. Do you attribute the cycling issues to the boron layer changing tolerance on the bolt carrier/rails/receiver only?


How thick is the boron layer?


Any friction in the movement of the gas pistons at all or free floaters like they are stock?

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I think I've localized the hang up to the breech bolt latch and the notch on the bottom of the bolt carrier. The breech bolt latch was one of the parts WMD did not coat, so it is still stock. I think I have a spare breech bolt latch in my box, so I'm going to see if it exhibits the same stoppage. When I manually pull the bolt to the rear, allow the bolt to move forward about half an inch, then retract the bolt to the rear again, the latch will bind up. I have to either push the bolt very hard to get it to go forward, or retract it all the way to the rear again.


The pistons have free play in them, but they are still tighter than stock. I may sand them some more. The weapon didn't seem to have any issues with the pistons when firing. There was no sign of short stroking.


Nickel Boron can be coated up to .004" thick. That doesn't mean everything is coated to that thickness though.

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Fixed the pistons. Used my poor man's lathe (chucked each piston up in my hand drill) and spun them inside some 1200 grit sandpaper for a few minutes. I kept test fitting until they fit perfectly. Now the M4 has that telltale rattle can sound when tipping the muzzle.


I'm wondering if the tight fit of the pistons was slowing the bolt travel to the point that it was hanging up on the latch.


One thing that worked out really well was the weapon light mount. I didn't have any issues with it getting in the way of my support hand. The few times I reached out for the button, it was easy to find. It also handled all the recoil I could throw at it.

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I'd have to look at the mechanics of the pistons again, but this friction could have a big effect. Not just on slowing down the pistol from the pressure that does exist but letting the argo vent the gas otherwise as it builds pressure and doesn't move as fast as the system is designed for it to move the pistons.


These are interesting developments. Curious if that fixes it or if other things come up.


For those that may do this later, if it turns out it is the pistons, to sand them before having them coated


Did you have any of the argo parts or the gas chambers on the barrel coated?

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No coating on the ARGO plugs or the barrel itself. Mainly because I couldn't get the ejector out of the barrel without a major PITA. Fitment would have been a nightmare if the insides of the piston housing was coated. Even though I sanded down some of the finish, I didn't sand all the way through it. So the Nickel Boron is still present on the piston "rings." It just has a polished look now.


The pistons are meant to free float, but have a relatively tight seal. No force should be required to move the pistons fore and aft. When I went through my 300 rounds, there was some resistance. I was hoping the finish would polish out by itself. This didn't happen, so I figured I'd polish them until they fit. It only took about 3 minutes for each piston with the poor man's lathe.


I didn't have a breech latch spare. I think I recently ordered one from Brownells, but it's in limbo. I polished the engagement point on the bolt carrier, but didn't detect any discernible difference. I'll take it out and test it again when my shoulder can take another round.

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  • 2 weeks later...

Can you take a picture of the weapon, cleared of course, straight down the barrel so I can see the profile of where your light sits, etc?


How is the action/feeding going now?


Besides lathing your pistons, what other adjustments have you made since your last outing?

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I only had a couple stoppages with the #8 crap ammo. I bought some polishing compound recently. I've been buffing mainly the bolt carrier lately. Mainly on the rails, where the hammer rides and the notch that actuates the breech latch. The polishing compound is kind of slow going. I need to look into my technique to speed it up some. I've been using a cotton wheel and a Dremel.


Here are a couple older pictures showing how close the light is to the muzzle. The rear of the handguard limits how close you can make it without relieving the handguard.





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  • 1 month later...

Update after several months of use.


Still concerned with random stoppages, I decided to polish and rebuild the M4 from the ground up. Here is a description of the failures I'd randomly have;

When pushing the shell release button, a cartridge would eject onto the elevator anemically. When listening to this, I could hear that the shell was not being placed on the elevator with authority. When pulling the bolt handle to the rear to chamber the round, the bolt handle would hang up at the rear. I would then have to push the bolt handle forward with the palm of my hand in order to chamber the round. I then began my long trouble shooting phase of;


1. Replacing the magazine spring (no effect in function was observed.)

2. Replaced my carriercomp follower with a Brownells brand follower I had (no effect in function was observed.)

3. Replaced the receiver extension spring (no effect in function was observed.)


At this point I decided that I needed to start polishing components to smooth out anything that might be causing the action to hang up. I purchased some 800 and 1000 grit lapping compound and some 1500 grit wet/dry sandpaper.

4. I polished the bearing surfaces of the receiver extension's plunger with the 1500 grit sandpaper to almost a mirror finish. The action's feel was improved, but the failures were still present.

5. I polished the rails of the bolt carrier and along the bottom of the bolt carrier where the hammer makes contact. No noticeable difference was detected upon completion of this.

6. I tore apart the trigger pack completely. I polished the bosses around the shell elevator. I polished the shell elevator itself on the inside. The idea was to allow the shells to slide along the elevator easier. I also polished the front face of the trigger group where the rim of the case makes contact. I polished the inside face of the shell release lever. Polished the contact points of the breech latch. After this was all complete, no change in the failure rate was detected. The action was a lot smoother though.

7. I polished the inside of the receiver around where the shell elevator sits and along the front of the receiver near the magazine tube. No noticeable benefit was observed.

8. I removed the shell stop and polished the raised edges and along the front of the stop heavily. Loading and unloading became easier, but the problems still persisted.

9. I took the magazine tube apart and cleaned it extensively. There was some black crud visible inside the tube. I removed this crud from the spring as well. I took the follower and polished the contact points. Upon reassembly, the rounds were being shot onto the shell elevator with authority!


What is weird, I took another trigger pack from a friend's M4 and put it in. Most of the problems went away. So I purchased a new trigger pack from Brownells assuming that was the problem. The problems then persisted with the brand new trigger pack. FML.


I think the black crud inside the magazine tube might have been a byproduct of the Cerakoting process. I jammed a shop rag down it and pressed a Tornado brush through it and cleaned it out completely.


In the end, I ended up with a better weapon, since the polishing did not cut through the Nickel Boron finish, it just polished it to nearly a mirror on the contact points. It was just a serious PITA, and frustrating.

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This seems like a chapter out of my life with just about everything I do. Of course my career is based on very complex problem resolution and engineering. Seems like by the time it gets to me, every problem is this complex and convoluted.


When I am fiddling with things on my own time and end up in jackpots like this, my frustration runs overboard.


Glad it's operating now, though. How is cleaning the systems now compared to before the coating? How have lubrication requirements changed?

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It certainly was a bigger PITA than I expected. In the end, I paid about 300 - 350 dollars to have it refinished inside and out. Not bad really, for the complex order I had. Most won't be able to do this job themselves though. Pulling the receiver extension without damaging something takes some skill and specialized tooling. Then fitting everything back together and making it function properly can be a pain.


I lube the weapon the same way I always did -- rather heavy on the bolt carrier group and inside the receiver extension. Everything else gets a light coat. Contact points on the trigger pack get grease. The magazine and ARGO system are kept bone dry.


Cleaning is far easier than factory. The carbon just wipes off with a rag or q-tips.

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  • 3 weeks later...

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