Could use opinion on what could be causing this...

[AR_ART]

Picked up a pre-owned ACR and having some issues. I can only describe it as, its not ejecting the previous round before the next round is trying to go in. This is happening consistently, exact same scenario...

Here's the scenario. Load up a magazine, insert in mag well, let the slide go and shoot. First shot goes bang. I pull the trigger again, but nothing, I turn the rife and this is what I see;

http://inlinethumb08.webshots.com/17607/2376025150101902256S600x600Q85.jpg

http://inlinethumb40.webshots.com/46887/2048492300101902256S600x600Q85.jpg

And this is what its doing to the cases. The case on the left is the first round from magazine. The complete cartridge is next in the queue. Note that damaged case;

http://inlinethumb03.webshots.com/49858/2310890820101902256S600x600Q85.jpg

I checked to make sure that the "U" was facing up on the piston setting, I tried different magazines and anywhere from a full 30 round mag, to only 5 rounds to only 2 rounds with the exact same results.

I checked to see if the barrel was fully seated. I noticed a couple things compared to my first ACR. This one the barrel seems to come out and go back in very easy. My first one was a very snug fit. I don't know if thats okay/normal.

I examined the piston and piston block which all seemed to be in good condition.

It appears to me that possibly there is something wrong with the piston system, so its not driving the bolt back far enough. Its moving just far enough back to start to load the next round but not enough to eject the case. Again, this happens every time as noted

Any thoughts would be greatly appreciated.

[Delfuego]

I dont an ACR, but you may look at http://www.acrforum.com

One person mention the gas regulator.

[ChunkyMonkey]

I sold the ACR due to 2 things.. broken charging handle (covered by manufacturer) and constant misfeed on any kind of ammo. Try load up your mag to 28 max.. it seemed help me a bit.

Up to SCAR and don't look back.

[AR_ART]

I have a SCAR and gotta say when I had my first ACR, I'd have gone with the ACR hands down. I never had any type of FTE or FTF. Thing was solid! would eat any ammo or magazine.

With this one... Well, I gotta agree. I've totally taken it down and can't find anything "obvious"......



I sold the ACR due to 2 things.. broken charging handle (covered by manufacturer) and constant misfeed on any kind of ammo. Try load up your mag to 28 max.. it seemed help me a bit.

Up to SCAR and don't look back.

[BPTactical]

It appears to be short cycling. Anything inhibiting rearward travel of the bolt?
Ejector clean?
Obvious unusual wear anyplace?

[AR_ART]

I'm not intimately familiar with piston driven rifles, but I took it down and watched how the parts worked.

I removed the piston block, and stuck a dewey rod in the piston chamber. I pushed down and watched the BCG in the ejection port. I noted that the when the guide-rod spring was fully compressed, the BCG was only half-way open.

I then removed the guide rod spring and repeated my test. This time I could move the BCG all the way open via the piston rod.

So, I'm wondering if the guide rod is supposed to go all the way back OR the rod only opens it part way and the momentum opens it completely?

Checked the things you suggested and it looks good....




It appears to be short cycling. Anything inhibiting rearward travel of the bolt?
Ejector clean?
Obvious unusual wear anyplace?

[ray1970]

Bert will probably slap me for this, but I am going to disagree with him about the short cycling. It seems to me that if the bolt has traveled rearward enough to pick up the next round out of the magazine it has probably gone far enough back to eject the spent round.

Personally, I would take a good look at the ejector and make sure it is functioning as it should.

Of course, I'm damn sure no gunsmith. :-)

[Hoser]

Factory ammo or reloads?

[AR_ART]

Used both reloads and new factory ammo. Just to check, I ran the same ammo in my SCAR 16 without issue.

Interesting thought that it might be the ejector. I can see where you are coming from, but I too am no gunsmith but won't discount anything. I'll give it a quick take down and look...



Factory ammo or reloads?

[patrick0685]

simple...ill buy it off your hands for $100 cash money then you wont have the issue anymore









....other than that im no help

[BPTactical]

I'm not intimately familiar with piston driven rifles, but I took it down and watched how the parts worked.

I removed the piston block, and stuck a dewey rod in the piston chamber. I pushed down and watched the BCG in the ejection port. I noted that the when the guide-rod spring was fully compressed, the BCG was only half-way open.

I then removed the guide rod spring and repeated my test. This time I could move the BCG all the way open via the piston rod.

So, I'm wondering if the guide rod is supposed to go all the way back OR the rod only opens it part way and the momentum opens it completely?

Checked the things you suggested and it looks good....

Given this info I would be questioning if there is an error in the assembly.
I am only shooting in the dark here Ray, I have only fiddled with an ACR once or twice and that was in a retail environment.
Anxious to take a look though.....

[AR_ART]

If I can't figure it out it just may be coming your way. I'm going to check with Bushmaster themselves first and if they are no help, you'll be hearing from me... :)


Given this info I would be questioning if there is an error in the assembly.
I am only shooting in the dark here Ray, I have only fiddled with an ACR once or twice and that was in a retail environment.
Anxious to take a look though.....

[BPTactical]

If I can't figure it out it just may be coming your way. I'm going to check with Bushmaster themselves first and if they are no help, you'll be hearing from me... :)

The welcome mat is out if ya need!

[AR_ART]

Thanks! Its still might come your way. It appears the extractor is not "releasing" or letting the case go. I cycled it manually and it did not fling the round out. I check the bolt and ejector earlier and while its very stiff it seemed to work.

What makes operates the ejector? What makes it release the case?

[ray1970]

What makes operates the ejector? What makes it release the case?

The case should stay under the extractor until the ejector kicks it out of there. Is the ejector a plunger type like on the AR platform?

[BPTactical]

I can't make an accurate statement, like I said I have just casually fingered one.
An AR for example uses a spring loaded plunger on the opposite side of the bolt from the extractor. It is compressed when the round is stripped from the magazine and held compressed until the spent case clears the chamber. It then uses the extractor as a fulcrum and rotates the casing clear of the action.
An AK uses a section of rail on the left side of the receiver as an ejector. The casing is again held by the extractor and after firing this section of rail rotates the casing clear as the bolt travels rearward.

[AR_ART]

Woot! Thanks for the explanation! I think I found what's wrong, check this out;

http://inlinethumb33.webshots.com/48096/2741817870101902256S600x600Q85.jpg

The ejector is either stuck down inside or its broken. I pushed on it with a punch and it moves so it feels like the spring is still there!



I can't make an accurate statement, like I said I have just casually fingered one.
An AR for example uses a spring loaded plunger on the opposite side of the bolt from the extractor. It is compressed when the round is stripped from the magazine and held compressed until the spent case clears the chamber. It then uses the extractor as a fulcrum and rotates the casing clear of the action.
An AK uses a section of rail on the left side of the receiver as an ejector. The casing is again held by the extractor and after firing this section of rail rotates the casing clear as the bolt travels rearward.

[ray1970]

Yep. Definitely doesn't look good. Should be an easy fix. You'll be back up and running in no time. My guess would be it takes a standard AR spring and plunger.

[AR_ART]

Thanks for everyone's help and suggestions in getting this figured out!

[BPTactical]

Might be a little tricky to get out, when you get it out check the ejector and its bore for any burrs and address them as needed.
Probably wedged a piece of brass or such, causing it to stick.

[AR_ART]

Fixed!!!!!

Just got to get it out to the range and verify! I took the roll pin out and I fully expected the spring to pop out and fly across the room. It didn't the ejector came out once the roll pin was removed. Then without warning, the spring popped out. I soaked the bolt, dried it and blew air through the openings. Lubed and reassembled.

Seems to be working now!

Thanks for your help!


Might be a little tricky to get out, when you get it out check the ejector and its bore for any burrs and address them as needed.
Probably wedged a piece of brass or such, causing it to stick.

[BPTactical]

Another Happy Camper!