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M4 two port barrel replacement process


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Long post warning ....


After my ongoing discussion with Benelli customer service reps and following the efforts of another member here, Benelli has just replaced my "low recoil round" 4 gas port barrel with a two port barrel.


Since June, I have been trying to get a straight answer from Benelli on the low recoil barrels. I finally resigned myself that I would not get an answer from Benelli since they said there were no more two port barrels available and that the low recoil barrel 'should' be OK for any 2-3/4" or 3" load. Hearing of some other problems recently and then the news that another member successfully lobbied them a few weeks ago for a two port barrel, I recontacted Benelli to see what had changed.


In my call three weeks ago, the rep first said she knew nothing about it and that the other person must have had his own gunsmith work on his M4 since they had not done any barrel replacements. I relayed my previous efforts and showed that the other man's barrel had indeed been replaced by Benelli as he had posted on this forum. She seemed pleased with my level of detail and then did an about face and said she'd heard about the barrel changes and could now help with mine.


She stated that they'd been given a 'heads up' from the product manager and offered to read it. After pausing a bit to find it she said the memo was dated August 6, 2005 and stated the "Low Recoil barrels will no longer be shipped ... there have been long term reliability issues with the 'low recoil barrels'... the new barrel style will be used on all M4 series ... all new guns will now ship with this barrel ... it is rated from heavy 3" Magnum to light 2-3/4" loads". It seemed like it was an email from the way she accessed and read it aloud.


I told her this was definitely what I was calling about and she took my serial number to make sure I was affected. After 5 mins on hold she came back and said the replacement is only for the 11707 Law Enforcement guns, and not my 11703 model. She said the memo states it only affects the LE models since they are slightly different than the civilian guns, but she can still switch my barrel if I like. I said my understanding is the only difference is that the LE models have the notched/milled recoil tubes which allow the sliding stocks to retract while the civilian models have the solid tube which allow the stock to be placed at the full length only. She said that is correct. I said I didn't see how this would have any effect on the barrel issue as the LE and civilian should have the same problems with the 4 port barrels. She said yes she would think so too, but the memo only mentions that the LE are covered under the replacement.


She then asked again if I wanted to switch barrels and said she 'had' to advise me that if I switch, I may experience reliability problems with cycling tactical or low power loads. She asked if I understood this and still wanted to switch. I said yes of course.


I sent it back 2nd day, and waited a week to check on it. I then ran into their famous service when they looked up the RA and said nothing had been done ... "it will take several weeks ... our repair time is usually 6 to 9 weeks ... didn't anyone tell you?". She checked then said there was nothing she could do. I called back shortly asking to speak to the product manager as simply swapping barrels should not take two months. A short hold period and I'm right back in the customer service cue. This lady is very polite, checks and says she can't do anything about it, but she will pass me to a voicemail for her supervisor. I expected nothing to happen, but two hours later I got a call back. This lady said she was handling the M4 issues and said she thought the gunsmith was going to put a system in place to handle such quick turn issues. She said I'd hear back in a day or two with an update.


One week later and still no response, so I call again. The lady checks my RA and says "oh it shipped 5 days ago ... I see we didn't call you like we should have". It was scheduled to arrive the next day, but UPS lost it in one of their hubs! After spending the next day tracking it down, they finally put it on a midday truck and it was finally back in my hands by the end of last week.


In all, it was there and back in two and a half weeks. Had I not kept on top of it and gotten ahold of that one supervisor, I think it would still be sitting there in the 6 to 9 week repair line. And as with the whole incident since June, had I not kept pushing and seemingly proved I had been following the issue, they may not have admitted to the problem. It's ridiculous that the customer has to go through these motions when they are internally acknowledging the problems with the 4 port low recoil barrels.


Now that I have examined it, I have seen a few things I will show below ...

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In first examining the new two port barrel (part #81245), it looks externally the same as the four port barrel (#81246) with the screw in chokes. The bbl serial number is in the TM122XX range whereas my older four port barrel was TM100XX. From the rear, you can see just the two ports and I immediately noticed they are also smaller than the ports as used in the four port barrel.


New two port bbl



Older four port bbl




Comparing the sizes, I calculate the port diameters on the two port barrel are about 2.5mm (0.098"), while the four port barrels are about 3mm (0.118"). Adding up the total port area, I get a value of 9.8 sq. mm for the two port barrel, and 28.3 sq. mm for the four port barrel. This seems to be a significantly greater port area for the low recoil barrels that I would have expected.


The gas plug assemblies are also different between the two barrels. The assemblies on my new two port barrel now match the diagram in the parts manual, with a stepped pin (272J) retaining in the plug spacer (275J).



View of the two port gas plug assembly, looking down into the hole at the tip of the gas plug cap (273J), and from the front, looking at the pin holding in the spacer.





Comparing the assemblies in these pictures below (four port on top, two port on bottom), we see the four port model uses a large pin while the two port has pins with smaller, stepped ends.



The four port models also have much larger gas plug spacers and the pins pass through this spacer rather than simply retaining it, as is done on the two port models.




So despite the apparently much larger port area for the four port barrels, there were some changes made to the gas plug assemblies on the low recoil barrels as well. With both styles, the spring holding the gas plug cap closed seems extremely stout, so perhaps whatever changes were made were still not enough to allow the ARGO system to fully compensate for full power loads on the four port systems. I can't wait to try this new two port barrel out with a full assortment of loads to see what it will tolerate.



In closing, one other thing which has drawn my attention is the 'fouling' which surrounds the two ports in my new barrel. When recieved, there was some powder residue which I would have expected from a quick test firing upon reassembling with the new barrel. I noted what I thought was fouling or leading, particularly strong around the left port. I gave the barrel a quick cleaning last night and I definitely had traces of leading and plastic wad residue come out with a tight patch on a jag. The area around the ports was unaffected by this and I ended up giving it a more thorough cleaning with still no improvement. From the photos, there seems to be some shadowing which would indicate there is something on the barrel surface, though the more complete cleaning and brushing did not pull out any more residue to indicate it is leading or fouling. I'm getting a sinking feeling it is some pitting or surface defect around the ports. Perhaps the hardchrome did not take in that area or some parkerizing solution seeped in through the ports to etch the surface. Whatever it is, it was not affected by cleaning with Shooter's Choice, MPro7, Acetone or IPA. I vaguely recall another poster having some surface irregularity around the gas ports that looked like leading but would not come out (stevenb I think??). I don't recall hearing any resolution to that one ... I guess another call to Benelli may be in order :(

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