Benelli M4 Feeding Problems

[Jogusto]

You are not familiar with the ID system based on the information you have provided. For clarification, look up a diagram of an ID system and then take your M4's BCG apart. There is no ID system. Remove the pistons and you got nothin'. They don't "assist". They do it all.

.

 

You are quite correct. I am familiar with the ID system but I stand corrected.

 

Even so, it's still true that the gas piston stroke length is insufficient to unlock the bolt. The piston has to slam it pretty hard to send it sailing back against the recoil spring, far enough to unlock the breech and release the chamber pressure, which should provide the remaining oomph required to fully rack the bolt. I'd love to see someone make a high speed movie of an M4 cycling, with one of those new Casio camcorders at 1000 fps so we can see what it looks like!

 

Back to the issue at hand: failure to lift shells and hanging up the bolt. Careful examination will reveal that the shell being released onto the shell carrier also operates the carrier release/magazine catch, via its shell head lip, and that's what prevents more than one shell from exiting at a time. The lip of the shell actually presses the lever from the inside against spring tension.

 

When the bolt moves forward, the shell lifter engagement finger (not the official name) enters a detent in the underside of the BC. This serves to transmit additional force thru the BC to the shell lifter, ostensibly lifting the shell up and into position for feeding.

 

The problem seems to be the friction of the shell, being squeezed slightly by the carrier release lever, varying more or less, and when it is "more" -- as determined by the fit and finish of the ammo itself, especially the shell head lip -- the bolt is unable to overcome the resistance and hangs up.

 

This delicate balance seems to be necessary for the usual reasons. Too strong a recoil spring, and the bolt will not travel back far enough during the eject part of the cycle. Too weak, and we have this situation, where the shell lifter seems to cause the bolt to hang up.

 

I tried to prove my thesis with some experimentation. By hand polishing the lip on the offending samples, I can make my M4 cycle flawlessly. QED.

 

(This may be why the inexplicable, transient FTFs occur -- ammo variations, but not in the DEQs or the weight of the shot load!)

 

Yes, it's true, I am somewhat disappointed to have purchased the M4 based solely on reputation and raves, in this forum and elsewhere, only to discover the operating principles are relying on a somewhat tenuous balance of forces, moreso that I would ever have thought for the touted "reliability" of the weapon. Flying off the handle? no, not in the sense most people use that expression... Disappointed? Sure...

 

I'll give her a few hundred more break-in rounds, then choose my ammo carefully to ensure I have the most reliably-cycling ammo. I still love the way she shoots, and my wife is just crazy about it too! I'll need to try ERdept's fix for shortening the Length of Pull (nice hack, ERdept!).

 

In the meantime, if anyone has further insights into this shell lifter hangup issue, especially a robust fix for it, I'm all ears and TIA!

[Unobtanium]

You are quite correct. I am familiar with the ID system but I stand corrected.

 

Even so, it's still true that the gas piston stroke length is insufficient to unlock the bolt. The piston has to slam it pretty hard to send it sailing back against the recoil spring, far enough to unlock the breech and release the chamber pressure, which should provide the remaining oomph required to fully rack the bolt. I'd love to see someone make a high speed movie of an M4 cycling, with one of those new Casio camcorders at 1000 fps so we can see what it looks like!

 

Back to the issue at hand: failure to lift shells and hanging up the bolt. Careful examination will reveal that the shell being released onto the shell carrier also operates the carrier release/magazine catch, via its shell head lip, and that's what prevents more than one shell from exiting at a time. The lip of the shell actually presses the lever from the inside against spring tension.

 

When the bolt moves forward, the shell lifter engagement finger (not the official name) enters a detent in the underside of the BC. This serves to transmit additional force thru the BC to the shell lifter, ostensibly lifting the shell up and into position for feeding.

 

The problem seems to be the friction of the shell, being squeezed slightly by the carrier release lever, varying more or less, and when it is "more" -- as determined by the fit and finish of the ammo itself, especially the shell head lip -- the bolt is unable to overcome the resistance and hangs up.

 

This delicate balance seems to be necessary for the usual reasons. Too strong a recoil spring, and the bolt will not travel back far enough during the eject part of the cycle. Too weak, and we have this situation, where the shell lifter seems to cause the bolt to hang up.

 

I tried to prove my thesis with some experimentation. By hand polishing the lip on the offending samples, I can make my M4 cycle flawlessly. QED.

 

(This may be why the inexplicable, transient FTFs occur -- ammo variations, but not in the DEQs or the weight of the shot load!)

 

Yes, it's true, I am somewhat disappointed to have purchased the M4 based solely on reputation and raves, in this forum and elsewhere, only to discover the operating principles are relying on a somewhat tenuous balance of forces, moreso that I would ever have thought for the touted "reliability" of the weapon. Flying off the handle? no, not in the sense most people use that expression... Disappointed? Sure...

 

I'll give her a few hundred more break-in rounds, then choose my ammo carefully to ensure I have the most reliably-cycling ammo. I still love the way she shoots, and my wife is just crazy about it too! I'll need to try ERdept's fix for shortening the Length of Pull (nice hack, ERdept!).

 

In the meantime, if anyone has further insights into this shell lifter hangup issue, especially a robust fix for it, I'm all ears and TIA!

 

 

I doubt this could be the cause, but check to see if maybe someone at Benelli fell asleep at the wheel and your mag-tube isn't screwed in all the way.

 

Also, as to the observation of the pistons, yep. That is the short-stroke piston design, you can see other examples of this design at work in the HK416, and other examples of it's kind, as well as plenty of other weapons.

[heckler&kochp2000]

I had the same problem with light loads, use only full power loads for the first 200 or 300 rounds and keep it extra lubricated during the breaking in process after 200 or so round it works good even with light loads . DUGGAN said if i left it pulled back and lubricated it up good that it would help, it seemed to work good.

 

I hope this helps!

Edited May 26, 2009 by heckler&kochp2000

[Niviticus]

I had lots of cycling issues with my new M4 as well. But after 200-300 rounds and plenty of lube its hasn't had a hiccup since. I'm currently at 900 rounds of walmart cheapies and about 200 rounds of buckshot/slugs. I seemed to only have problems with the cheap ammo. I agree with the others that you may just need to "break it in". I also noticed that if my stance/grip on the gun was lax it made the problem worse.

[Duggan]

I had the same problem with light loads, use only full power loads for the first 200 or 300 rounds and keep it extra lubricated during the breaking in process after 200 or so round it works good even with light loads . DUGGAN said if i left it pulled back and lubricated it up good that it would help, it seemed to work good.

 

I hope this helps!

 

I said to leave your gun with the bolt pulled back? Hmm ... that's how I leave my shotgun, but I don't know why I would say that would cure any cycling ailements ... however, lube absolutely is needed. Far too many people seem to be afraid of lube .... make that thing DRIP with some high quality, non-CLP lube, and I bet whatever problems you may or may not have at the initial shooting disappear after a few hundred rounds.

[Duggan]

Hmm... this may be true with your weapon, but I can very repeatably pull the bolt all the way back, then release it (NOT slowly, but suddenly), and get a hangup *every time* with certain of my Fiocchi rounds, and *never* get a hangup with the aluminum snap-caps. This would tend to argue against the theory that the ammo has nothing to do with it. Field shooting results also argue that the ammo does matter.

 

I appreciate that body motion after the recoil might help matters a bit, but the bolt still needs to stop and change direction even when firing. Releasing abruptly from a fully drawn-back position is much different? Hmmm... not sure. You could be on to something, but then it means inertial voodoo is required for completely reliable operation, including a shooter who not only jerks back (required for the Benelli inertial system to work), but also springs forward again to help the bolt overcome the "shelf".

 

Rather that debate whether the issue is a problem or a non-problem, I'd like to understand how many others out there have experienced this problem, especially in a relatively new M4. Certainly, the OP seems to be one. SD seems to be another, albeit after a larger number of rounds through. Any others?

 

This is not normal. If it won't even chamber certain rounds reliably then you have a serious problem from the sound of it, and this issue should be taken to benelli CS. Perhaps your BCG/lifter/bolt is somehow out of spec, or something is broken/loose and not causing things to happen as they should ... I've never, ever had a round that repeatedly would not cycle if I dropped the BCG from the rear.

 

I am perplexed, and I'm rather interested in the outcome to your problem.

[heckler&kochp2000]

I said to leave your gun with the bolt pulled back? Hmm ... that's how I leave my shotgun, but I don't know why I would say that would cure any cycling ailements ... however, lube absolutely is needed. Far too many people seem to be afraid of lube .... make that thing DRIP with some high quality, non-CLP lube, and I bet whatever problems you may or may not have at the initial shooting disappear after a few hundred rounds.

 

 

If they are how could i exchange them for 2 ports thru Benelli??

[Duggan]

You are quite correct. I am familiar with the ID system but I stand corrected.

 

Even so, it's still true that the gas piston stroke length is insufficient to unlock the bolt. The piston has to slam it pretty hard to send it sailing back against the recoil spring, far enough to unlock the breech and release the chamber pressure, which should provide the remaining oomph required to fully rack the bolt. I'd love to see someone make a high speed movie of an M4 cycling, with one of those new Casio camcorders at 1000 fps so we can see what it looks like!

 

Back to the issue at hand: failure to lift shells and hanging up the bolt. Careful examination will reveal that the shell being released onto the shell carrier also operates the carrier release/magazine catch, via its shell head lip, and that's what prevents more than one shell from exiting at a time. The lip of the shell actually presses the lever from the inside against spring tension.

 

When the bolt moves forward, the shell lifter engagement finger (not the official name) enters a detent in the underside of the BC. This serves to transmit additional force thru the BC to the shell lifter, ostensibly lifting the shell up and into position for feeding.

 

The problem seems to be the friction of the shell, being squeezed slightly by the carrier release lever, varying more or less, and when it is "more" -- as determined by the fit and finish of the ammo itself, especially the shell head lip -- the bolt is unable to overcome the resistance and hangs up.

 

This delicate balance seems to be necessary for the usual reasons. Too strong a recoil spring, and the bolt will not travel back far enough during the eject part of the cycle. Too weak, and we have this situation, where the shell lifter seems to cause the bolt to hang up.

 

I tried to prove my thesis with some experimentation. By hand polishing the lip on the offending samples, I can make my M4 cycle flawlessly. QED.

 

(This may be why the inexplicable, transient FTFs occur -- ammo variations, but not in the DEQs or the weight of the shot load!)

 

Yes, it's true, I am somewhat disappointed to have purchased the M4 based solely on reputation and raves, in this forum and elsewhere, only to discover the operating principles are relying on a somewhat tenuous balance of forces, moreso that I would ever have thought for the touted "reliability" of the weapon. Flying off the handle? no, not in the sense most people use that expression... Disappointed? Sure...

 

I'll give her a few hundred more break-in rounds, then choose my ammo carefully to ensure I have the most reliably-cycling ammo. I still love the way she shoots, and my wife is just crazy about it too! I'll need to try ERdept's fix for shortening the Length of Pull (nice hack, ERdept!).

 

In the meantime, if anyone has further insights into this shell lifter hangup issue, especially a robust fix for it, I'm all ears and TIA!

 

From what you've said here ... it seems like it's a matter of friction (needs more lube and/or break in, as the parts will wear into each other and get looser), or a matter of improper spring tension ... either in the mag tube or the recoil tube.

 

I would remove both springs and check to see if they are within spec ... If they are, I would lube the **** out of the bolt carrier and the receiver rails it slides in, and see if there is still too much friction ... again, without being there to see and feel the way the BCG handles it is hard to diagnose and offer definite solutions to phantom problems ...

[Duggan]

 

If they are how could i exchange them for 2 ports thru Benelli??

 

LOL sorry but that actually made me laugh out loud, no those are not the ports, but good guess! The ports are "holes" from the barrel (just past the chamber) into the gas piston housing ... you can see them if you use a light and look down your barrel.

[heckler&kochp2000]

LOL sorry but that actually made me laugh out loud, no those are not the ports, but good guess! The ports are "holes" from the barrel (just past the chamber) into the gas piston housing ... you can see them if you use a light and look down your barrel.

 

 

Åre these the ports?

Edited May 27, 2009 by heckler&kochp2000

[Duggan]

 

Åre these the ports?

 

Absolutely.

[Unobtanium]

How was this issue resolved? Was it resolved?

[Duggan]

Inquiring minds want to know!~

[Jogusto]

Well, sorry, I've been preoccupied with other matters elsewhere, but as for my own feeding problems, here's how it worked out...

 

First of all, there was nothing wrong with my particular M4 as far as I could see. I didn't measure the springs or anything like that, but it was well-lubed, kept clean, and had a few hundred rounds through it. Having discovered that the lip of the shotshells are being "grabbed" by the bolt carrier release lever on one side, and the receiver wall on the other, I started to look for ways to reduce friction that would impede forward bolt motion when the shell was on the carrier.

 

There are two spring-loaded levers pressing on the BC group as it is trying to slide forward and lift a shell up: the hammer and the shell lifter "assist finger" (for want of a better term... I don't have my parts diagram handy). There is also the carrier release lever, which also serves as the magazine catch. For all three of these parts, I carefully used some #5 and #6 polishing compound on a 1/2-inch cotton wheel (Dremel) and **carefully** did a little polishing, to change the black finish on these parts to a shiny metal sheen. I was careful not to change dimensions or shapes as I did this.

 

Upon reassembly and lubing, *voila*, problem solved. I have run 200 rounds through her at the range, including light target loads, heavy 00 buck magnums, LR slugs, full-house slugs, etc., all from widely varying manufacturers such as Estate, Remington, Federal, Winchester, and Fiocci. She also cycles manually without a hitch.

 

I think there is a lot of "folklore" about "running a few hundred rounds thru it to break it in"... and perhaps the net effect of this is to accomplish polishing of the parts in just the manner I've described. The Benelli, while a fine piece of machinery, is still mass-produced, and hand-polishing these parts isn't an option for the factory. As an engineer with 20 years of experience, I can understand that a stack-up of component tolerances (such as spring constants and parts dimensions and finishes) can produce a product which isn't as reliable as its brother from the same production line.

 

I'm happy to say that my M4 is working like a champ and I've had zero issues with it since my last posting. My wife loves to shoot it, which is my only problem: how to pry it out of her little hands, and where to hide the ammo so she doesn't shoot it all up!

[Jogusto]

PS> I'll try to post some pictures of what I did if I can get some time this weekend.

[Dom in Kenya]

 I own a Benelli M4 Super 90. On a routine change of ammunition from slugs to buckshot with no gun firing involved I was manually ejecting the slugs when the last round got stuck. I can’t pull back the bolt which is stuck and won’t budge. With a live round in the chamber what are my options to clear this issue? Can I disassemble the weapon with a live round in the chamber? Appreciate your feedback. 
 

 

[StrangerDanger]

10 minutes ago, Dom in Kenya said:

 I own a Benelli M4 Super 90. On a routine change of ammunition from slugs to buckshot with no gun firing involved I was manually ejecting the slugs when the last round got stuck. I can’t pull back the bolt which is stuck and won’t budge. With a live round in the chamber what are my options to clear this issue? Can I disassemble the weapon with a live round in the chamber? Appreciate your feedback. 
 

 

 Yes you can. To do this safely, put the M4 on safe. Unload any rounds from the magazine tube y pressing the inside face of the shell stop to allow the shell to eject into the palm of your hand. 
 

Now remove the trigger pack by pushing the trigger pin out, press the bolt release and pull the trigger pack free from the receiver. This will make it so that nothing can hit the firing pin. 

 

Remove the magazine cap and attempt to remove the barrel assembly. The bolt may be stuck and might try to prevent you from removing the barrel. At this point I would use a plastic dowel rod and hammer it against the bolt carrier in an attempt to unstick it. You can try using a rubber mallet to hit the barrel assembly to try to drive it out. 
 

When you get it apart, you need to inspect the bolt head, the round that was chambered, and the luge around the chamber. Is it extremely dirty or lacking oil? Is the rim of the round bent? Is the extractor claw deformed at all? When reassembling, cycle the bolt inside the receiver with the trigger pack removed. Note the tail end of the bolt carrier link and how it seats on the spring loaded plunger at the rear of the receiver. Does it cycle smoothly? Does it cycle correctly when the barrel assembly is installed into the receiver? The M4 likes to run wet with oil on the bearing points on the bolt carrier. You’ll note the rails the carrier rides inside the receiver on. This area should be heavily oiled. The rail should be heavily oiled as well. The head of the bolt should be oiled wet. The locking lugs in the barrel should also be oiled wet. 
 

The trigger pack should be brushed clean, and oiled on the moving points. The sear contact points should be greased lightly.  

Your pistons and ARGO plugs should be left dry. Oil will be burned off and create carbon build up quickly. Brush them clean with a wire brush and solvent, then leave them unoiled. They’re stainless, so they won’t rust.