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Discussion Starter #1 (Edited)
Shot around 550 rounds through my ACR yesterday, now I've got this on the back of my barrel where the lugs ride in before locking. It's not just the two spots, it's all the way around the barrel in varying degrees.



To me, this is unacceptable wear in a critical area of the firearm. This sort of wear is why I dumped my MSAR 556 and bad mouthed the company at every chance I got. I took quite a hit on that one, selling a gun I paid 2K for for less than 900.

I don't get a new gun often, in fact I sold my carry pistol so that I could afford this one and to see this kind of wear coming on it so soon is a huge let down, not to mention depressing. My SCAR is pushing 5K rounds and doesn't show this type of wear, it's very slight on the SCAR, and in two specific places. But the ACR is already looking like a worn out pile of junk.

The edges are no longer crisp, they're rounded, with flats in them. It looks like someone took a punch and gave each edge a good whack. My barrel was tightened in correctly before you ask. 7 clicks. And I witness marked it so that I could see if it moved during live fire. IT didn't.

This is not a barrel locking issue, as I recall the MSAR damaged it's self like that because the timing in the carrier where the cam pin rides was way off in terms of how long it should be vs. when the bolt actually needed to start turning to lock.

I want to see some high round count barrels from the rear where the wear on mine is taking place.

So if it isn't too much trouble, someone with a better camera than I. Please take a good photograph of your ACR's barrel.

I'd also like to know how many times I can remove my barrel before it negatively impacts the locking mech.
 

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Same issue on mine. Believe its due to the barrel not being torqued down all the way. I've contacted BM about it a couple weeks ago, haven't heard back.

On yours, open the bolt, line up your witness mark, and try to see if there's any rotational movement in the barrel to receiver fitment. And if there is, can you measure the diameter of the barrel indexing pin and the slot in the trunnion it fits into?
 

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Discussion Starter #3 (Edited)
There is no rotational movement in the barrel to receiver fitment.

I can tell you exactly why it's doing it based on past experiences with other clones that have done it.

It's because they didn't machine the cut out right where the cam pin rides. If it's off by even .0001 it can completely fuck up a system like this.

All I can conclude from this experience is that the naysayers were 100% dead on when they said that this thing is a poorly designed hunk of junk. I'll listen to the ex-military armorers next time when they try to sway me away from buying a gun, especially a gun designed by a coast guardsman and his buddies that can't even make a magazine that works right without tearing up another 2K plus rifle. (SCAR)

Now I'm stuck with the POS, and Sportsmans warehouse doesn't offer any warranty or return policy like other gun stores do.. I wonder why that is, I think it's because they know none of their stuff works.

I would swap this thing for a beat to shit demo SCAR in a heart beat if given the chance. But it doesn't work that way in the greedy ass gun world, I'll end up trading it for a worthless Glock or something along those lines.

There won't be anymore American designed weapons coming into my house, I've had it with poorly designed, and poorly made American guns.
 

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Here are some pics of a barrel that has had 1400 rounds put thru it, and has been removed and put back on at least 500 times. I love to show everyone how easy this comes apart.
please try and take more pics of your barrel so I can see what exactly you are talking about. Have you contacted bushmaster about this?
 

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Discussion Starter #5 (Edited)
I plan to come first thing Monday morning.

Here's a slightly better picture, still doesn't show the true extent of bare metal showing through.


You can see the rounded edges towards the top of the lugs if you look hard enough, it's like a U shape in the picture where it should be a 90" angle.

I just ran out and put another 60 rounds through it, the peening is considerably worse.

It's a real shame because I shoot really well with this gun.

This peening only goes maybe 10% of the way into the lug, only towards the top, it's like it's wearing in so that the bolt can rotate freely into the channel. I see no reason why it could pose a problem. Bolt lugs show no wear.. it just bugs the hell out of me being a brand new gun and already having these kinds of problems.

So what should I do? Keep it and shoot it until it fails? or send it in and lose it for god knows how long for them to just look it over and say.. meh it's ok.
 

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I know these comments don't help with your issue:

I have just over 4000 rounds thru my ACR and I don't have any of the peening your showing / descriping on my bolt or barrel extension. If your barrel is tight, (my wrench is about 7 o'clock) then something is outta spec. I know this isn't what you want to hear, but a call to bushmaster is in order. Especially if the problem is getting worse with each shot fired.

I wish I could take photos of my set up, but I don't have a camera that can take close ups.
 

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Discussion Starter #7 (Edited)
My wrench bottoms out at about the 6 oclock position. I count 7 clicks, but 7 o clock? Should I hulk it on?


Think BMI will kill my warranty for adding a muzzle device that I can't get off myself?


ETA: The picture above has the same dents if you look carefully. I bet if you cleaned it you'd see shiny metal on those spots.




So maybe this is normal break in?
 

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What does the front and sides of the lugs on the bolt look like?

I also noted the same wear on the barrel extension in the ACR that went KABOOM. :confused:

Dave P
 

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Discussion Starter #9
They're good.

The ACR that went Kaboom shares the same exact wear pattern as mine and the other rifle pictured.

I'm starting to think that this is just normal break in and nobody is really paying attention to it.
 

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My wrench bottoms out at about the 6 oclock position. I count 7 clicks, but 7 o clock? Should I hulk it on?................................
This is the way I got it back from BFI last Oct when I sent it in for the recall. When I got it back, I put a witness mark on it. This is where I tighten it everytime I remove the barrel. (which is very rare) I usually pull the wrench until it stops. Then I put 1 more click in, which takes a little extra effort.

It works for me, and maybe the marks are normal wear on some rifles. Im due for a barrel removal type deep cleaning and will take a closer look then.
 

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There is no rotational movement in the barrel to receiver fitment.

I can tell you exactly why it's doing it based on past experiences with other clones that have done it.

It's because they didn't machine the cut out right where the cam pin rides. If it's off by even .0001 it can completely fuck up a system like this.
Thats what I'm thinking.

However, before you go off bashing Magpul for this, keep in mind BM are the ones making the rifle. And BM has proven that they can fuckup anything.

As for the PMags, they were designed long before the SCAR was in production for civilians. You should try an EMag, or blame FN for not designing a rifle that accepts ALL Standard AR mags. (FYI, their FS2000 can't accept USGI 20's.)
 

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Discussion Starter #12 (Edited)
Thats what I'm thinking.

However, before you go off bashing Magpul for this, keep in mind BM are the ones making the rifle. And BM has proven that they can fuckup anything.

As for the PMags, they were designed long before the SCAR was in production for civilians. You should try an EMag, or blame FN for not designing a rifle that accepts ALL Standard AR mags. (FYI, their FS2000 can't accept USGI 20's.)
Magpul admitted to altering their magazine design from STANAG dimensions themselves, They thought they knew better than the people who put a lot of thought into a universal .223 magazine years ago. The SCAR, F2K, Daewoo, along with a slew of other weapons are designed to take standard USGI magazines.

Enfield altered their magazine design too, as a result H&K not only had to come in and fix their rifle.. they also designed a whole new magazine to STANAG standards for a slew of European weapons. And it's funny how the three H&K 30s I've had since 05 have ran.. and ran... and ran.

Right now the best magazine on the market in my opinion is the Troy battle mag, it's what I dumped my alum. .223 magazines for, it's proved to be reliable after countless outings, and it fits my funky Euro-trash guns including the FS series without screwing up the rifle.

The Troy appears to be closer to STANAG specs than any of the Magpul mags. It even has a square cut on the back like real USGI mags do.


I've had USGI 20s in my FS, they lock and function fine. Actually they look kind of cool, like a bench rest magazine. I'd take a picture for you, but it looks like I'm going to have to trade my FS today for another basic ACR.

Being a recall gun I can just swap the bolt group, and barrel over to my post recall gun, and swap firing pins, gas plug, etc out before sending it back.

BM may be making the rifle, but reusing an inferior locking system for a piston driven gun isn't BM's fault. If they had been smart they would have used an AK style bolt, and locking lugs like the SIG 55X, and XCR series does. IF they had, we wouldn't be talking, or sweating over this kind of wear right now.

My AUG has similar wear that over time developed into this. v


If I could find the pictures I took of my LWRC M6 that also showed similar wear just from hand cycling I'd post it, I've also got slight peening in my SCAR and FS extentions. But it seems side by side that the lugs are rounded on the back of the SCAR, and FS extension to keep this kind of wear from happening. They also appear to be thinner, but this could be an optical illusion caused by the rounded lugs.


ETA: Another observation I just made is that in fact the lugs are thinner on the FS and SCAR, they're also rounded and swept back at a greater angle than the ACR. The bolt actually has a lot of play going into the lug channels, I can move it enough left, or right to account for any variance in the cam pin channel location. This would account for the lack of such damage to the FS, and SCAR.


I'll take some pictures as soon as the sun is up here of the F2K's barrel extension and bolt together.

ETA 2: Comparing the ACR to the F2K the ACR has no play in the lugs when the bolt is riding inside the channels before lockup, where as the F2K does. I can't wiggle the ACR bolt, but the F2K bolt will rotate left and right while inside the channels.

I can't get a good picture to demonstrate this in action, and actually a short video would be a better way to demonstrate it in action.

This leads me to believe that the peening we see on the ACR is a direct result of the original designer not taking such variances that mass production brings on into mind during the initial design.

This also leads me to believe that the peening is a purely cosmetic issue that will stop over time as the rifle wears in. I might take a file and change the profile of the edges that have damage to match the F2K's and SCARs lugs if after 1,200 rounds my barrel is still going strong.

The real area of concern would be the rear of the lugs that take a LOT of pressure when the gun is fired. and they all still have sharp corners
 

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Called BM today. They're sending me a shipping label in 7 to 10 days, and its going to a 3rd party in MI for repair. . . . :mad: Yea, this is going to be a fun one already.

Tempted to just junk the barrel and convert the gun to .300 AAC.

Its not a cosmetic issue, cause the backside of the lugs will be under shear and compression when the gun fires. Any reduction in material there can result in accelerated fatigue and failure. And since the lugs on mine with the worst damage are next to the extractor, (highest load stresses under firing) I'm going to play it safe.
 

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i have some mild peening, but mine appears to be purely cosmetic
 

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To the OP, sorry if I missed it, but what serial number range is your rifle in?
 

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Discussion Starter #16 (Edited)
I just got home with a brand new unfired rifle. SN# BL0020XX my old one is BL0027XX

Same peening in the same areas. This is a cosmetic issue as far as I'm concerned.

I've handled 8 guns with radically different Serial numbers, so far they've all had this issue.

I swapped my Firing pin, and piston assembly over to the new gun, and gave the old one to my girlfriend for her Spikes AR-15.

Of interest, this one bottoms out at 7 o clock, and requires ten clicks to lock the barrel on, and 11 clicks if you put some force behind it.
 

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Each one will have different numbers of clicks. It's just like a M240
 

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Both my ACR's have this "peening". One has over 3k rounds through it and the other is brand new, never fired. I wouldn't worry about this. I also checked some of my other guns and they have the same thing. Never the less have BM take a look anyway.
 

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FWIW, I just got home and check mine with serial number BL0054XX and the peening is present on one, maybe 2 extension lugs. Quite surprising really.

BTW, my barrel takes 6-7 clicks to secure. Also, compared against my AR, the AR's extension has lugs with curved channels that resemble a U instead of 90 degree corners like this |_| in the ACR.
 

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Just checked mine, very slight marks at about 600 rounds. My bolt has a fair amount of rotational play between the blot lugs and the barrel extension. I removed the recoil spring and slowly hand cycled it. I could feel a slight contact when I put pressure on the side of the bolt carrier. I will keep an eye on things.

Dave P
 
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