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StrangerDanger

Benelli M4 -- The Trigger Disconnect Sucks

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After 10,000 rounds through my M4, I feel I can say that the weakest link I've found in the platform is the trigger disconnect.

 

When you fire a round in the M4, and the BCG cycles to the rear, the disconnector is working properly. You could pull the trigger at this point and the hammer will not fall.

However, as the BCG begins to move forward and the shell elevator drops, the disconnector is now disengaged. During this time while the BCG is still moving forward into battery, you can pull the trigger and the hammer will fall.

What you end up with is a chambered round and the hammer down against the rear of the BCG. to clear this, you must manually chamber a fresh round to recock the hammer. The live round that was chambered is then ejected.

 

I've installed a lighter bolt handle that weighs 8 grams opposed to the 12 gram factory handle. This has sped up the action slightly. You must have a solid stance with the M4, or you can hear that the weapon is cycling slower than usual.

Running the weapon wet with oil helps also.

 

Some would say, just slow down. However, if I have my followup shot in sight, I'd like to take it without inducing this type of failure. The recoil reduction of the M4 is so great that shooting follow up shots like performing double taps with a pistol is easy. As fast as you can pull the trigger, you can keep the weapon on target. Even with high brass loads.

 

You can cause this failure by hand (without a live round) by cycling the weapon. As soon as the elevator drops, there is about 2 inches of BCG travel that the disconnector is disconnected.

 

I contacted Benelli about this years ago. I thought there was something wrong with it. They basically gave me the line, "It is what it is." It was inspected by Benelli when I had the 4 port barrel replaced and they said it was fine too.

 

An aftermarket fix would be awesome. I don't know how it would be done though. The disconnector would have to be based on BCG placement rather than on the shell elevator.

 

Anyone else experience this?

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After 10,000 rounds through my M4, I feel I can say that the weakest link I've found in the platform is the trigger disconnect.

 

When you fire a round in the M4, and the BCG cycles to the rear, the disconnector is working properly. You could pull the trigger at this point and the hammer will not fall.

However, as the BCG begins to move forward and the shell elevator drops, the disconnector is now disengaged. During this time while the BCG is still moving forward into battery, you can pull the trigger and the hammer will fall.

What you end up with is a chambered round and the hammer down against the rear of the BCG. to clear this, you must manually chamber a fresh round to recock the hammer. The live round that was chambered is then ejected.

 

I've installed a lighter bolt handle that weighs 8 grams opposed to the 12 gram factory handle. This has sped up the action slightly. You must have a solid stance with the M4, or you can hear that the weapon is cycling slower than usual.

Running the weapon wet with oil helps also.

 

Some would say, just slow down. However, if I have my followup shot in sight, I'd like to take it without inducing this type of failure. The recoil reduction of the M4 is so great that shooting follow up shots like performing double taps with a pistol is easy. As fast as you can pull the trigger, you can keep the weapon on target. Even with high brass loads.

 

You can cause this failure by hand (without a live round) by cycling the weapon. As soon as the elevator drops, there is about 2 inches of BCG travel that the disconnector is disconnected.

 

I contacted Benelli about this years ago. I thought there was something wrong with it. They basically gave me the line, "It is what it is." It was inspected by Benelli when I had the 4 port barrel replaced and they said it was fine too.

 

An aftermarket fix would be awesome. I don't know how it would be done though. The disconnector would have to be based on BCG placement rather than on the shell elevator.

 

Anyone else experience this?

 

I have, but VERY rarely.

 

ETA, what bolt-handle are you using?

Edited by Unobtanium

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I have also long stated that the M4 trigger sucks and is the weakest link, I suppose this is just another reason why, although to my knowledge I have not encountered this specific problem.

 

I also use the titanium charging handle, and my bolt carrier stays dripping wet with the best lube on the market, so I am doing my part to avoid the "issue".

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I have a Design Concepts bolt handle. Luckily I snagged it at Christmas. They're hard to get. I figure Kip will provide a great replacement. He may be aiming for stock weight though rather than a ultra lightweight model.

 

When I used the GG&G bolt handle years ago, I could hear the BCG moving much more slowly. I'd estimate cycle time was around 0.25 seconds. The stock unit was probably around 0.20 and the Titanium model is slightly faster.

This was assuming I did my part and didn't basically limp wrist it. If you purposely let the weapon roll with the recoil, you can hear and feel the carrier moving more sluggishly.

 

I have some concern that if you reduced the weight too much, the ARGO system would batter the BCG. Or slam the BCG to the rear. I'm not sure if the ARGO was tuned for a specific weight when paired with the main spring inside the receiver extension. I believe the ARGO is more forgiving though.

 

Design Concepts was 8 grams

Stock was 12.5 grams

GG&G was 24.5 grams

*These were according to my Dillon electronic reloading scale. I can't recall the exact amount, but those are within half a gram.

 

These weights are miniscule compared to the combined weight of the BCG though.

 

What lube are you using? I have a few bottles of LaRue's machine gun oil that I haven't tried out yet.

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I have a Design Concepts bolt handle. Luckily I snagged it at Christmas. They're hard to get. I figure Kip will provide a great replacement. He may be aiming for stock weight though rather than a ultra lightweight model.

 

When I used the GG&G bolt handle years ago, I could hear the BCG moving much more slowly. I'd estimate cycle time was around 0.25 seconds. The stock unit was probably around 0.20 and the Titanium model is slightly faster.

This was assuming I did my part and didn't basically limp wrist it. If you purposely let the weapon roll with the recoil, you can hear and feel the carrier moving more sluggishly.

 

I have some concern that if you reduced the weight too much, the ARGO system would batter the BCG. Or slam the BCG to the rear. I'm not sure if the ARGO was tuned for a specific weight when paired with the main spring inside the receiver extension. I believe the ARGO is more forgiving though.

 

Design Concepts was 8 grams

Stock was 12.5 grams

GG&G was 24.5 grams

*These were according to my Dillon electronic reloading scale. I can't recall the exact amount, but those are within half a gram.

 

These weights are miniscule compared to the combined weight of the BCG though.

 

What lube are you using? I have a few bottles of LaRue's machine gun oil that I haven't tried out yet.

 

Yet another reason the GG&G handle sucks, and I use the same lube that you have sitting unused next to you. :)

 

P1012616.JPG

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Guest cleefurd
After 10,000 rounds through my M4, I feel I can say that the weakest link I've found in the platform is the trigger disconnect.

 

When you fire a round in the M4, and the BCG cycles to the rear, the disconnector is working properly. You could pull the trigger at this point and the hammer will not fall.

However, as the BCG begins to move forward and the shell elevator drops, the disconnector is now disengaged. During this time while the BCG is still moving forward into battery, you can pull the trigger and the hammer will fall.

What you end up with is a chambered round and the hammer down against the rear of the BCG. to clear this, you must manually chamber a fresh round to recock the hammer. The live round that was chambered is then ejected.

 

I've installed a lighter bolt handle that weighs 8 grams opposed to the 12 gram factory handle. This has sped up the action slightly. You must have a solid stance with the M4, or you can hear that the weapon is cycling slower than usual.

Running the weapon wet with oil helps also.

 

Some would say, just slow down. However, if I have my followup shot in sight, I'd like to take it without inducing this type of failure. The recoil reduction of the M4 is so great that shooting follow up shots like performing double taps with a pistol is easy. As fast as you can pull the trigger, you can keep the weapon on target. Even with high brass loads.

 

You can cause this failure by hand (without a live round) by cycling the weapon. As soon as the elevator drops, there is about 2 inches of BCG travel that the disconnector is disconnected.

 

I contacted Benelli about this years ago. I thought there was something wrong with it. They basically gave me the line, "It is what it is." It was inspected by Benelli when I had the 4 port barrel replaced and they said it was fine too.

 

An aftermarket fix would be awesome. I don't know how it would be done though. The disconnector would have to be based on BCG placement rather than on the shell elevator.

 

Anyone else experience this?

Been reviewing this for some time now;

 

The malfanction being demonstratable during elevator drop is coincidental, paralleling the instance when the bolt carrier is not obstructing the release of the hammer. The hammer configuration or cocking surface of the bolt would need to be modified in order to extennnnnd the period of transition in which the "interference" between the bolt carrier and hammer exist. While this can be improved upon, two perils begin to creep into the mix. Focusing soley on the hammer, the region requiring additional material would rapidly present a condition where-in the hammer would pre-maturely strike the the aft vicinity of the bolt carrier below the firing pin...preventing proper ignition/primer strike. Mods to the bolt carrier would entail weld-up/fitment, or an upgraded part (gulp).

 

In "as equipped configuration", only three remedies exist;

 

  • Ensure disconnector spring and plunger are clean, well lubed, and not fatigued (plunger spring)
  • Slow down
  • Consider the upcoming "carriercomp" improved replacement hammer.

Our pending hammer DOES have minute geometry revisions which facilitate diminishing this period of essential overlapping/conflicting "modes" of ability... to a noticable degree, while not to an extent which renders the trigger group inoperable by design/revision.

 

 

Hope this made sense, and sheds light on carriercomp's relentless intent to address public pursuit of meaningful enhancement to the M4 platform.

Kip

Edited by cleefurd

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This type of thing happened to me after installing the GGG handle. I went back to factory and Seems much improved.

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Kip, awesome news. This is exactly what I wanted to hear. I had hoped these parts would be more than just US made parts. I definitely plan on buying these parts. Another portion of the weapon to inspect is the recoil spring. If the spring is weak, the cyclic rate of the weapon will be significantly reduced.

 

I never noticed how weak my main spring was. In fact, neither did Benelli. When I had my M4 serviced by Benelli, it had approximately 10,000 round on it at the time. When I procured a second M4, I was surprised to feel how much firmer the spring was when retracting the bolt handle.

 

I've been considering getting a new receiver extension so I could send the tube off to Robar to have the interior coated in NP3 Plus. Plus the Recoil Spring Plunger. I figure it might help with the cyclic rate.

 

ben-M4.gif

 

Kip, we want a Titanium part #120. ;)

 

It might be a good idea that some of these springs being replaced at the time that the disconnector and hammer are replaced.

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Guest cleefurd
I can't find part #120. :o

I couldn't either at first. Just as I was about to tell him "ya got me"... I found it. The black # closest to the center of the page.

Appears to be the recoil tube.

Not sure how well suited ti is to the app, with respect to the abuse the pivoting arm and plunger dish out inside .

The off axis forces might not be kind to it unless it (ti) were internally coated, with a plunger that bore a compatible coating as well.

 

Sure could speed things up a bit w/o having to resort to a spring so strong that light loads malfunctioned. (the coatings approach would speed it up... the ti housing would have no effect)

 

Hmmmm.

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I couldn't either at first. Just as I was about to tell him "ya got me"... I found it. The black # closest to the center of the page.

Appears to be the recoil tube.

Not sure how well suited ti is to the app, with respect to the abuse the pivoting arm and plunger dish out inside .

The off axis forces might not be kind to it unless it (ti) were internally coated, with a plunger that bore a compatible coating as well.

 

Sure could speed things up a bit w/o having to resort to a spring so strong that light loads malfunctioned. (the coatings approach would speed it up... the ti housing would have no effect)

 

Hmmmm.

 

Doh! Thanks for pointing it out to me Kip.:) From the two recoil tubes I have seen, M4 and SuperNova Tactical, I wouldn't think Ti would be a good choice here. I'm sure that the stock ones are hardened for wear resistance but they most likely help to balance the weapon. IIRC, they are fairly thick and substantial and with the kind of weight reduction I would expect with titanium, it may well just throw the balance off some. Maybe not but it would be a concern. It would be interesting to feel the weight difference.

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The off color made it harder to see. The black colors are parts Brownells doesn't stock.

 

Overall, this issue is addressing three separate issues;

 

1. Nominal weight reduction

2. Reliability enhancement

3. Increased cyclic rate/lock time

 

Titanium might not even be needed honestly. An aluminum tube with a steel insert where the buffer reciprocates in it would work. Cheaper and would weigh less.

 

It's debatable on if the reduction in weight would be a good thing or not. Given the location of the receiver extension. It might make the weapon have the perception of being front heavy, even though it would be overall lighter.

 

The linkage inside the receiver extension is pretty unique. All the torsional forces are mitigated at the plunger. If you look at the end of your bolt carrier's tail, you'll notice that it is rounded there. The plunger itself shows little to no wear (this is after 12,500 rounds of use on mine). The tail of the BCG doesn't rub along the edge. The plunger centers the linkage as it reciprocates.

 

The recoil extension spring tends to act like a live center for the plunger as well.

 

Inside the stock receiver extension, the finish is sub-par IMO. It's fairly rough when it should be a polished, coated/hardened surface.

 

The aluminum would be naturally lighter than the Titanium.

 

Aluminum holds up well on the M16 receiver extension quite well.

 

I'd like to see more scientific data on the relation between reduction of weight in the BCG and the receiver extension and how it increases cyclic time or reliability. Or, if it is battering the the BCG without a spring weight change. If it is determined that a lighter weight BCG package will increase cyclic rate, I'm sure a lighter weight plunger could be fabricated. Since we're talking about a 12 gram difference causing cyclic problems in a series of weapons with the GG&G handles.

 

From multiple sources, we've seen that minor changes in bolt carrier group weight has had negative side effects on multiple weapons. Such as the use of the GG&G bolt handle. The stock handle weighs in at 12 grams. The GG&G unit weighed 24.5 grams IRC. Since there are also many accounts of people not having any issues at all, I suspect that;

 

1. Subjects with negative effects have worn recoil springs.

2. Subjects with negative effects may be recoil sensitive. Purposely allowing the shotgun to move rearward causes the action to move sluggishly in my tests. This failure may also be tied to item #1.

3. Varying degrees of the weapon being broken in. I believe this has to do with the sub-par surface finishing inside the recoil spring extension.

4. Poor lubrication or climatic conditions.

5. Poor cleaning habits. The majority of the M4's have never had their recoil spring tube disassembled. As the BCG reciprocates, it transfers debris into the extension. This is a difficult assembly to properly clean without disassembling every 2,500 rounds or so. When I disassembled mine after 11,000 rounds, I emptied a quarter of a can of BreakFree down it to clean out all the collected oil and debris.

 

Naturally, these are unscientific tests, since there are many variables. Shooter, ammunition, location, release lot of weapons, lubricant/cleaning regiments.

 

I'm aware that most do not push these weapons to these limits. However, that never stops people from doing the modifications. Also, other benefits of such a project would easy to see. Enhanced reliability with lower dram loads would be the number one factor. The superior surface finish would leave users with a smoother operating weapon.

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My M4 was purchased in 2004. It is a 11703 model. Which has the gay recoil extension that the M1014 has. This prevents the collapsible stock from collapsing.

 

Since I just scored an awesome price on a collapsible stock (thanks HK), I figured it was time to upgrade this part.

 

I just came downstairs from my lair. The extension is history. It took me about an hour or so to break it free. I was worried it wouldn't give up the ghost very easily. I used a basic heat gun and roasted the **** out it. I rigged up the receiver in my vice and placed the heat gun so it would cook the extension near the receiver without me holding it.

 

You should take the recoil spring, recoil spring plug and the plunger out before roasting it to avoid damaging the spring mainly. This is pretty easy to do. At the base of the extension, use a pair of snap ring pliers to remove the snap ring. Then unscrew the recoil spring plug. It should be pretty easy to unscrew. It takes an odd shaped screw driver head. I just used the snap ring pliers points.

 

The 1 1/16 nut at the base of the receiver twists off normally. Lefty loosy when looking at the receiver from the top, extension pointed towards you. Common threading.

 

It took about 20 minutes of heat to get the nut off. This is why older posts opted for a torch. There is no way in **** a bic lighter would give you enough heat to do this job like I saw for another model of Benelli.

 

Then, it took another 20 minutes or so on the receiver extension to break it free. I used a 3/4" wrench on the flat spots on the extension. This was the hardest part to remove, since Benelli didn't give us a very solid wrenching surface. This also uses the lefty loosy thread patterns. I mention this because when you're trying to break locktite, it really would be nice to know which direction you should be twisting.

 

The receiver has the same green locktite that the magazine tube extension has. There is just a lot more thread to deal with. Hence the perception that it is harder to remove than the magazine extension.

 

I'd rate that it is harder to do. But not seriously hard.

 

Also, I noted that the locktite did not smoke like the magazine tube extension does.

 

I gave the receiver a bath in BreakFree Powder Blast after the extension was removed. The threads were pretty clean.

 

Tools:

Vice (Mandatory)

Heat Gun or Torch (Mandatory)

Snap Ring Pliers (Mandatory)

3/4" Open Ended Wrench (Mandatory)

1 1/16" Closed Ended Wrench (Mandatory)

Wire Brush (Recommended)

Spray Solvent (Recommended)

 

The receiver extension doesn't weigh as much as I had expected. I'll try to weigh it tomorrow at work on our postal scale. However, I'd guess that it weighs about 8 ounces.

 

I was kind of worried that I wouldn't be able to get it off myself. I'd say that using a heatgun is probably the safest way to remove the tube since you're using a lower controlled amount of heat opposed to roasting it with a propane torch. Just be sure to pick a good vice point, use padding and do not force it. It will take some force to remove the extension, but enough heat will get the job done.

Edited by StrangerDanger

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Hey Kip,

The extension itself seems pretty straight forward to make. It's roughly 21mm in diameter and has an ID of approximately 16mm. The metric sizes seemed to make more sense for the italian gun.

 

There is a cheap fixed snap ring in the end of the unit that prevents the plunger from pushing all the way through.

 

The machining on this steel extension looks like a hack job compared to the work I've seen on your magazine tubes.

 

With your own tubes, you could set where you think the LOP should be on the collapsible stocks.

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That might work if it'll fit in that small of an area. Mostly the spring contacts the tube walls. Very little of the plunger contacts.

 

Surface finishing would be the best solution.

 

The design is really slick. There is very little side loading even though there is a huge geometry change in the cyclic motion. The pivot point on the cup of the plunger spreads the load while the recoil spring centers the plunger.

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Surprisingly I received the package today from Numrich Arms. It is in fact a 3 position recoil tube on the complete assembly. I'd wager the stripped unit is as well.

 

I'm glad I purchased the complete tube though, there are some minor design changes in the plunger. The finish on the plunger appears to be superior.

 

I haven't reassembled yet since I had to go to work.

 

Purchase with confidence.

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Just finished up my reinstall. It went fairly easy. There are a few things you should note before proceeding that will help you.

 

Note how deep the recoil tube is screwed into your weapon. You don't just bottom out the extension when screwing it in like on the magazine tube. So you're going to have to time the tube.

 

When I say time the tube, I mean you'll have to screw it in so that the stock isn't canted. If you try to screw the tube in all the way, it will eventually bottom out. However, when you attempt to screw the pistol grip assembly onto the weapon, the threads will not catch.

 

Rule of thumb is to screw the extension in so the leading edge of the threads is flush with the inner surface of the receiver. Once you're in the ballpark, attach the collapsible portion of the stock, and collapse it all the way. The comb of the stock will act as your index gauge as it will point at the rear sight housing.

 

You should still be twist the extension with the stock tail in place to finalize your adjustments. Once it is where you want it, tighten the locking nut with an open ended 1 1/16" wrench to secure the location. Remove the stock carefully, then use the closed ended 1 1/16" wrench to tighten the nut fully. Be careful that the extension itself isn't turning as you tighten the nut.

 

I used blue locktite on my reassembly. I would recommend everyone else do as well. Since the extension doesn't bottom out on it's threading, the only thing that keeps it in place is the tension of the locking nut. Therefor, thread locker is mandatory to secure this location on both the recoil tube threads and the locking nut.

 

The LOP improvement of the middle position when used with an Aimpoint T1 is vastly better. I probably won't use the fully extended length ever.

 

I'm still awaiting a Mesa Tactical QD rear sling mount to finish this build revision. I probably won't get it done until after I return from SHOT.

 

Stev

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Well, I ordered a stripped recoil tube from Numrich Arms today. The unit is only a 2 position tube. Fail. It's being returned. They weren't kidding about it being stripped. It doesn't even have the flexible ring that retains the plunger from pushing all the way through. I think it is part 49 from Brownells on the schematic.

 

I'll take a picture of all 3 styles of tube next to each other for identification purposes.

 

Buyer beware.

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