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My department got two brand new Bushmaster ARs (generic M4 profile, semi-auto). I checked the barrel nut torque and they were both north of 40lbs.
Everything else looks normal. Well factory oiled (we did not clean & re-lube ).
Bench functions seemed very stiff/tight, triggers seem gritty & creepy.
We also purchased some additional D&H mags (from PSA).
Had a bench issue with full (30rnd) Bushmaster mag not seating/locking easily. De-loaded 2 rounds and that seemed to work.

At the range, w/Winchester .223 target ammo, they both repeatedly failed to go into battery (from 28rnd D&H mags) and one made a jam with the round badly bent & stuck above the bolt face and half into the chamber, most were under the bolt face and into the chamber. Determined after five or six attempts that the 1st gun did not like having the bolt release smacked, need to be pressed. They both chambered better if we pulled charging handle back and let them fly instead of releasing a locked-back bolt. However did not run 100% on that method either. Cycling into battery seemed better with only one real FTF.

I am not a great or heavily experienced rifle shot and we were not taking a lot of time although my partner is retired Marine. We only brought elevation up one click on one gun, the other was fine. After a few (30 rnds each gun) we were about 4"x5-shot groups at only 50 yards w/bench, w/irons, w/o sandbags. Ran about 40 rnds thru each and then 10 rnds of Hornady TAP (duty ammo) in each to confirm functionality (laugh) & POI (same). Coincidentally 1st round of TAP blew out a primer so we did a field strip but never did find the primer. We also had an issue with trigger locked in forward position but bolt seemed full forward (forward assist had no resistance). Found that switching gun to safe and then back to fire made an unusual click and it was then functional.

Not happy yet with mag seating, feeding, functionality or accuracy. I would not want to rely on either gun, but we must.

I've assembled Palmetto State Armory ARs for my self and shot seasoned department Colts etc... never had numerous issues like this.

So this morning I'm reading old posts about "break in period" and asking how many rounds do you think for break in? Or is something wrong with me or these rifles? Or should we start over with Colts?
 

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When you "checked barrel torque" did you maybe move the nut so the gas tube is binding? See if it rattles a bit with the bolt to the rear.

I assume you lubed the rifles properly, used known good mags and ammo, etc.

Check and make sure the right type buffers and springs are in the tubes.
 
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I hate hearing this about LE purchased guns.

Not a smartaleck answer at all: Colt M4s can be found retail for around $1000. I would expect they could be department purchased for less than that. Sell or return the Bushmasters.

An M4 should not need a breakin period, they should run absolutely 100% right out of the box. Look, building an AR rifle ain't rocket science, Colt has been doing it for well over 50 years.

+1 to 1KPerDay's question about the gas tube/barrel nut alignment. Pull the uppers, remove the handguards. Run the BCGs in and out slowly by hand. Feel and listen as the end of the gas tube enters the gas key on the bolt carrier. There should be no more than a very slight touch/rub between the tube and key as it enters. It helps if you place your thumb and index finger very lightly on the gas tube right where it enters the uppper receiver as you do this. If you can feel the gas tube bend and feel a scrape as it enters the key, it's not aligned properly and can cause function problems.

BTW, when you have a stoppage where the bolt rides over the base of a cartridge and ends up smashed against the middle of the cartridge case, usually with the round fed halfway and a big dent in the side of the case, that's called a "bolt over base stoppage" AKA a "BOB" and is one of the worst types of stoppages to have with an AR because immediate action- SPORTS or "tap rack bang" won't clear it. It takes level 2 remedial action to clear that stoppage. It is ALWAYS the result of a bad magazine. When you have a BOB, do yourself a favor- remove and download that mag and then immediately smash it. Run over it with a cruiser. Never let that magazine get back on duty, because it will have BOBs again at the worst possible time.

HTH
 
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I will say that my department approves the use of Colts and Bushmasters. That being said ALL the malfunctions that I've seen on the line has been with Bushmasters. These are personal purchase Bushmasters mostly, but that shouldn't make any difference.

All that being said. After checking that the gas tube hasn't been pinched, I'd return them to Bushmaster and make them see that they work.
 
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I don't like current model Bushmasters. My favorites are BCM and Spikes. I had a couple of newer bushmasters a few years ago and I was not happy at the quality. I don't own them anymore.

Tony.
 

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Maybe it's just me . . but I have had two BMs over the last 5 years or so . . both were a major PIA.

I have a Noveske and a Stag Arms . .

Both have been awesome . .
 
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Ok call me a grumpy old fart but who strips down a rifle too check the barrel nut and doesn't clean/grease/oil a new rifle...... I'm I the only one that thinks is this odd. The nut can't turn because the gas tube gets in the way so why even bother too check...

Firearms run of springs, grease, oil and ammo take away any one you want and you get sluggish or no operation.......


D&H mags? I don't know who they are but anytime I go too the range with any new too me weapon I take mag's that I know work this is too make sure the weapon works, after that if I have something new too add too the mix I at least have a base line.....


Go back too the gun shack inspect and clean the weapons real good give it a good greasing and oiling, then find some mag's you know will work load'm up and get them zero'd then put some rounds down range.
 

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No offense but I'll echo other people's concerns on torquing a barrel nut with a gas tube in place.
No info on how the firearm was lubricated and using mags with no prior history.

I'm all for inspecting and lubricationg a new firearm but barrel nut torque isn't one of those steps that I would perform even though I'm equipped and knowledgeable on the subject.

My Noveske and Stag have several thousand rounds through each of them without a single failure.
 

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All things considered, your department's shortest trek from A to B would be to return those rifles and whatever came with them to the vendor and get your $$$ back. Buy Colt Defense, Model 6920, USGI magazines or P-Mags, don't try to work in them, just clean, lube & shoot. Beware anything recently shipped under the "Bushmaster" badge.
 

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I agree about barrel torqueing. We have had 3 carbines with loose barrel nuts (from the factory (one colt, 2 S&W). Obviously the barrel won't come off (or the nut), but when shooting the recoil/harmonics cause the barrel to whip making zeroing impossible.

We check all new carbines by removing the gas tube, making sure the nut is snugged down before deploying,
 
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Checkout Lewis Machine Tool Co. they make IMHO some of the best AR platform rifles out there. The customer service is excellent also. I believe most of there sales are Government or law enforcement.

JMPWNG2
 

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Sounds like your gas tubes are both misaligned and it's causing a hiccup in the bolts forward movement. It's easy to do if you use a torque wrench to check the nut. Should be an easy fit.
 
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I agree about barrel torqueing. We have had 3 carbines with loose barrel nuts (from the factory (one colt, 2 S&W). Obviously the barrel won't come off (or the nut), but when shooting the recoil/harmonics cause the barrel to whip making zeroing impossible.

We check all new carbines by removing the gas tube, making sure the nut is snugged down before deploying,
That's interesting... I have a buddy with an upper that won't zero. I'll have to check that. GI3
 
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Discussion Starter #17
UPDATE:
Checked gas tubes in upper receivers. One gun had significant free play up/down, left/right. The other had free play but not as much. Found no drag on the bolt carriers when engaging the gas tubes. No evidence of significant wear on gas tubes or BC tubes (only 50rnds each gun).

I stripped, cleaned and re-lubed both guns (I didn't ask, I just went and did it).

Ran a bout 100rnds in each gun this weekend and no issues or incidents. Full magazines even seated well. We did no further bench or sighting work. Shot a qualification string (20rnds) swapped rifles between shooters and shot a second qualification string, then a few mags on forward movement drills. All target ammo, the two Bushmaster mags and two D&H.

It would seem the clean & lube was the answer however I reserve putting faith in these guns until after at least a few hundred more "proofing rounds" and sighting work at the range.

I think this article was the inspiration to check the barrel nuts: http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/

Thanks to everyone who contributed input!
 

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Often guns and machine tools are shipped with preservative grease and/or oil on them. It's best to clean it off and properly lube before use. If it was lube and not preservative, you'd be out some time and supplies.
 
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