Posted: 5/27/2002 8:05:53 PM EST
I got a Bushy M-4 to go with my Dissipator. Finally got to take them both out today and my M-4 sucks!! I couldnt get off more than four shots in a row before it would either double feed, fail to eject, fail to feed, or fail to lock the bolt back after last the last round in the mag. I have both 20rd and 30rd USGI new mags with green followers. My Dissipator functioned 100% with the same mags thru 200rds. The M-4 got 200rds thru her as well, but fired single shot 90% of the time, or if I was lucky I'd get 2 to 4rds thru her before she would malfunction again! Both Bushy's were new in box from the same dealer. The only thing I saw that may be causing the probs, is the bolt on the M-4. It looks very rough on the sides, like tooling or machining marks running most of the length of both sides of the bolt. The Dissipator's bolt is completely smooth like it should be. I really like the M-4, but I am dissapointed with her. Any similar probs with the M-4 Bushy out there? I'm taking her back to my dealer tomorrow to send it back to Bushmaster. I Have never had any probs with my Dissipator! Any advise or suggestions are welcome! Thanks in advance.
Sounds like you already found the problem. You should have swapped bolts to see if you get the same results from the dissapator. This way you'd know if it were the rifle or just the bolt/carrier, plus it'd be easier to just ship the bolt/carrier than the whole rifle. I have 3 bushys, the newest is an M4 from February (this year). I've already put over 3000 rounds through with no hiccups (except dirty mag problems).
Vinnie, I thought about that but wasnt sure about head space issues. I know they are mil spec but I wasnt sure. In almost ten yrs in the military, I never thought about the ability to swap bolts. Thanks for the reply...I'll have to look into that. I hate having problems with an expensive new toy!! I guess with as many rifles that Bushmaster puts out, they're bound to let a few bad or unfinished rifles or parts leave the factory. Hopefully she'll be running like the Dissipator soon!
You could be short stroking. Pull the bolt out of the carrier and make sure that the gaps in the rings are offset from each other.
If you aren't locking to the rear on the last round, you are definately short stroking. The rough surface on the carrier probably isn't the problem. It only really contacts the inside along 4 small rails which are usually visible after a few hundred rounds. Most notable on either side of the carrier key on top.
With that being said, your problem is most likely either weak ammo (not likely) or a gas system problem. Because the weapon is brand new, there is a good chance that it was assembled improperly. The gas tube may have been incorrectly installed or damaged on installation. Check your carrier key for proper installation as well (that small tube on top of your carrier that is secured by two hex bolts). It should be solid and staked into position. If there is any movement at all, that's your problem. All of this assumes that you have properly lubed the weapon as well. You could try putting some CLP or your lube of preference on the bolt carrier paying special attention to the areas that have slight wear marks visible.
The double feeding can also be caused by a bad ejector (that spring loaded plunger opposite you extractor on the bolt). Check to see that it is generally the same height as the surface of the lugs or just barely below them. Also check to see if is moves in freely. Occasionally, you see some installed that are out of spec (too short) and they won't generate enough force to adequately eject the round from the weapon. If the round is coming out of the chamber, the extractor is doing it's job.
If the "double feed" you describe means that the old casing stays in the chamber, and a new round is stripped and fed behind it, your extractor is bad. Check for debris under the spring and free movement. Also check for burrs or a broken lip. The rifle is new and this shouldn't be an issue, but check it just to be thorough.
Since this rifle is new, I would really consider calling Bushmaster and complaining. They should fix it for you IMHO.
Well you said both Carbines were new, so there wouldn't be any wear (no head space issue because of wear). If there was a installation error of the barrel causeing the head space issue, then she still wouldn't run right with the "good" bolt. If it is the bolt/carrier, then the dissy would run fouled up.
I wonder is the markings on the bolt are causeing a gas leak? It is the bolt and not the bolt carrier you are talking about right?
If it's the bolt, and to cut down on the time the weapon is down, I'd order a new one (50 bucks) tell them about the problem and have that replaced. It's nice to have a spare bolt around anyways.
Gus Fisher, a long time Marine Corp Rifle Team Equipment armorer claims with great authority, that on an otherwise properly working rifle, the alignment of the gas check rings are unimportant. Those gaps close up nicely under assembly and firing pressure. If there is something else essentially wrong with your rifle, ring alignment may be the straw that broke the camel's back however.
Gus went on to describe a test they did at the RTE shop in Quantico. They set up a service rifle in full on match service rifle trim, and using the same shooter, had him fire groups with the rings either aligned or offset taking great pains to ensure the shooter did not know which condition was the case and thus removing shooter bias from the test. They found no functional difference in reliability and that the more accurate groups tended to be fired with the rings aligned rather than offset.
So, I'd second the advice to switch carriers between the two carbines and see if that has any effect. If that clears up the problem, then you know the problem is in the bolt carrier group. If it doesn't clear it up, then you may want to examine the buffer spring. There were a few reports that Bushmaster was shipping full length A2 buffer springs with their carbine stocks. The standard spring is too long and offers too much resistance for the M4 telescoping style buffer systems. The result was short stroking, failure to eject, failure to feed, failure to hold the bolt open on the final round, etc.
Assuming this is the Post Ban M4, it uses a full length A2 buffer/buffer tube/buffer spring.
This may very well be the case. However, I also purchased a Bushmaster M4 style that had very similar failures out of box. I'll explain. It was a 14.5" complete upper with permanant phantom flash suppressor. From the start I'd get MAYBE two or three successive rounds without a failure. Often (but not always) it would not eject the fired round and would try to feed a new round. This went on for about 90 rounds before I stopped from frustration. I took it home and did some major searching (military tech manuals and online) trying to figure out what the problem was. As it turns out, my gas rings had all three gaps aligned and the extractor spring was a standard A2 with the blue insert. I offset the rings and replaced the spring with a HD with black insert. That carbine had zero problems in several hundred rounds following.
I've heard others say that the gas port on their Bushmasters needed to be opened up to allow reliable function. This isn't something I'd attempt myself, just another possibility.
It's likely the buffer spring causing the problem, as others have said.
I've had lots of problems with my BUSHY and one of the things they did last time was debur the carrier---you could see where carrier was scraping upper so you might want to take a good look inside upper.I still have to try it out with the carrier work and new bolt.I think the carrier was causing problems seeing as I'm on my 3rd upper in about 1000 rounds.Bushmaster will service it in a timely manner and you can just keep sending it back til it works or your warranty runs out.
When you say that you replaced the spring with a HD with black insert, please humor me; what is that & do they have a site?
I am not an armorer but this is the way it was explained to me. M4s supposedly require a stiffer extractor spring and a stiffer insert for the spring as well due to the shorter gas tube length with the 16" and 14.5" barrel. The usual AR-15/M-16 insert is blue, but the M4 insert is black.
Specialized Armament (and probably many others) sell these stiff spring/insert combos.
From the SAW website here are the ones I purchased for my M4gery:
If link doesn't work visit www.sawlesales.com click on Specialty Products, then click on the "SA05006
EXTRACTOR SPRING ASSY, HEAVY DUTY (W/ BLACK INSERT) (S.A.W.)"
HBAR16 hit it on the head in his above post. I should have written Heavy Duty but got sloppy, sorry. I actually bought mine from a member here who was buying them in bulk from SAW. They aren't easy to come by. I even called Colt and they didn't have any available. They gave me about three places to call that might have had them, none did.
Here is a basic explanation of what happen. With the 14.5" barrel, the gas pressure is stronger. It pushes the bolt back fast enough so that when it unlocks, the centrifigal force of it spinning causes the extractor to open up slightly. There are actually plans to change the bolt design to eliminate this problem. When it opens up, it lets go of the case, and the case is not ejected properly and often remains jammed between the bolt and the locking lugs.
Now this can be "fixed" in multiple ways.
1.Colt (and other spring manufacturers) makes a heavy duty spring. It's a slightly different color, sometimes it looks copper colored. Colt also has a heavy duty insert that goes inside the spring. In the standard M16/AR15 the insert is blue. The heavy duty insert is black and noticeably harder. This extra spring pressure keeps the extractor in place, counteracting that problematic centrifigal force. They're about $5 each, give or take.
2.You can purchase a D-Fender ring that goes around the spring underneath the extractor. It's basically a wedge shaped piece of rubber. This essentially increases the pressure under the extractor just like a heavy spring, maybe even more pressure. Cost, about $15.
3.You can go to your local hardware stor and purchase a small polymer O-ring. I don't remember the inside/outside diameters, but it's easy enough to take your spring with you and make sure that the O-ring will just fit around the spring. This acts exactly like a D-Fender but isn't a "specialty" item. Cost is about 12cents each.
I actually used both 1 and 3. As long as I used the HD spring and insert, there was no noticable difference in the way the case is ejected with or without the rubber O-ring. But for 12 cents it was cheap insurance.
Hope that helps.
I've shot a number of new bushys...
MY GUESS IS SHORT STROKING.
Two of them acted that way when new, and it turned out they were tight and they were pretty dry.
Lube the bolt, bolt lugs, and bolt carrier. You might even be able to feel the difference when you move the bolt in the bolt carrier. One of them was fine then did that as it got dirtier and dryer.
Lube, Lube ,Lube and will go away with a few more rounds.
Thanks to all for the replies and info. I took the rifle to my dealer and he gave me a new bolt/carrier in trade for the original one. Presto!!!! she runs like a champ now...put 300rds through her today without a single malfunction of any kind. As I stated earlier, the bolt carrier looked really rough, almost like they didn't finish machining it at the factory. The new bolt carrier is completely smooth. Now when charging her, she is smooth as butter, before she felt gritty and rough during charging. I forgot to mention that with the original bolt carrier, it would sometimes hang up about 1/2 way thru charging her and the carrier would get stuck in that position and was a major pain to send it home again. No problems at all now that she has the new bolt and carrier. I've been handling these babies for almost ten years and never had any problems before...I also have never had a carrier that was as rough as the original. Thanks again to all who replied!
Got all excited whn I saw HBAR 16's response re the heavy duty springs at SAW Sales. The springs are easy to find, but only Colt has the black inserts, apparently. Stayed excited right up to the order form with a $50 MINIMUM ORDER.
Oh well, you sell Colt stuff; I suppose you get as arrogant as Colt. Guess I'm stuck w/my HD springs from Wolf, and blue inserts.
You can always try to get together a larger order with a couple of guys to cover the $50 minimum. Also, keep a lookout here on the exchange boards. The guy I bought from sold a couple of dozen at least. Try searching the exchange for extractors and see what pops up. Someone who was selling them might still have one that they'd sell.
A piece of 6mm surgical tubing, cut to 1/16" is also another alternative.
send $7.00 to m16pigtail for WOLFF M4 with black insert. price includes postage.
addy on web site
Something else you can check. I had all sorts of problems with a new Bushmaster 20" Flattop. My problem turned out to be the gas tube had not been pinned into the front sight at the factory. Check that, if its not pinned then it flops /turns around and you won't get the full measure of gas back into the receiver.
After I pinned the gas tube its running like a sewing machine.
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