View Full Version : 300 AAC built upper issue FTE/FTF
Finely got time to take my AAC built upper 300 out today, I will not fire more than one or two rounds before a FTF, or a FTE. I'm using a both Remington 220 gr OTM subsonic, and CMMG 175 grain subsonic both ammo have the same issues, my setup is a AAC 16" and I'm running a 762SD suppressor. I'm not sure whats the exact cause, but it doesnt want to feed out of the mag, has a hard time picking up a new round, out of the mag when its being charged. Then sometimes it requires a recock it to get it to fire then if it does eject it will either work as it should or the case will get stuck sideways, causing a jam. If it does manage to eject, it will fail to pick up the next round. First time I have ever had these issues with any caliber AR, I did notice it was very stiff and requires some "force" to get it to lock up, empty even. Does it need more break in, different bolt, buffer spring? Not sure where to start on this one, but if it needs a break in, it will take a while, at this rate.
Thanks
Finely got time to take my AAC built upper 300 out today, I will not fire more than one or two rounds before a FTF, or a FTE. I'm using a both Remington 220 gr OTM subsonic, and CMMG 175 grain subsonic both ammo have the same issues, my setup is a AAC 16" and I'm running a 762SD suppressor. I'm not sure whats the exact cause, but it doesnt want to feed out of the mag, has a hard time picking up a new round, out of the mag when its being charged. Then sometimes it requires a recock it to get it to fire then if it does eject it will either work as it should or the case will get stuck sideways, causing a jam. If it does manage to eject, it will fail to pick up the next round. First time I have ever had these issues with any caliber AR, I did notice it was very stiff and requires some "force" to get it to lock up, empty even. Does it need more break in, different bolt, buffer spring? Not sure where to start on this one, but if it needs a break in, it will take a while, at this rate.
Thanks
Sounds like it could be short stroking. What magazines are you using? What buffer and what Buffer spring? Dose it pick up a round every time you manually charge it with no problem? Is the bolt group well lubed? Sorry about all the questions but we need this info to get down to your problem.
No idea but I would start with a different buffer and spring. If not them a different bcg. Process of elimination and narrow it down.
When you say lock up, is this empty? If so, I would first clean it well, inspect and lube, work the charge handle and release from full compression(empty) and if it's not reliably cycling and locking up unassisted, you need to contact AAC. Otherwise, yes, sounds like a gas issue to me. I would check mags as well, try others.
This is a tech question, and I will move it over there for some of the Smiths and gun plumbers.--it's still an AR
Sounds like it could be short stroking. What magazines are you using? What buffer and what Buffer spring? Dose it pick up a round every time you manually charge it with no problem? Is the bolt group well lubed? Sorry about all the questions but we need this info to get down to your problem.
No problem, USGI 30's and a 20's. Magpul 30, I have tried maybe 7 or 8 different mags, bolt and carrier dripping with Break Free, No it does not pick up rounds very well at all, no real consistancy. Does not matter ifs under gas pressure or being manually charged. GI buffer spring H1 buffer. Even when its being operated manually, empty (no round) it still seems reel tight going into lock. When it does fire the empty case seems to get caught in the upper, sometimes it just wont extact, and tries to jam a loaded round into a empty case. About the only thing is hasnt done is double feed.
When you say lock up, is this empty? If so, I would first clean it well, inspect and lube, work the charge handle and release from full compression(empty) and if it's not reliably cycling and locking up unassisted, you need to contact AAC. Otherwise, yes, sounds like a gas issue to me. I would check mags as well, try others.
This is a tech question, and I will move it over there for some of the Smiths and gun plumbers.--it's still an AR
Sorry and thanks.
Robb Jensen
02-12-12, 09:01
Try that upper on a known working lower.
I wish I had it to look at - it is the kind of thing I could instantly debug.
When it is empty - and with a known good spring and with lube, if you pull the charging handle back an inch, and let go - will the bolt lock into the barrel extension? If yes, then that is fine. If no, then the bolt, barrel extension, carrier, upper, or cam-pin is bad. The easiest thing to try is another carrier assembly from one of your 5.56mm rifles and see if that changes it. If it does, then change one part at a time to isolate. If it does not, then if the carrier rubs in the upper, it is the upper. If the carrier does not rub in the upper, then it is the barrel extension.
You can also send it back to AAC - but I am trying to save you time.
I wish I had it to look at - it is the kind of thing I could instantly debug.
When it is empty - and with a known good spring and with lube, if you pull the charging handle back an inch, and let go - will the bolt lock into the barrel extension? If yes, then that is fine. If no, then the bolt, barrel extension, carrier, upper, or cam-pin is bad. The easiest thing to try is another carrier assembly from one of your 5.56mm rifles and see if that changes it. If it does, then change one part at a time to isolate. If it does not, then if the carrier rubs in the upper, it is the upper. If the carrier does not rub in the upper, then it is the barrel extension.
You can also send it back to AAC - but I am trying to save you time.
Well I just "borrowed" a BCM bolt carrier, and bolt out of one of my known working 556's, and it ran 5 rounds no problem through one of my 20's, I used the one that didnt work worth a damn before. It now closes just fine, like any other AR I have ever dealth with, I did try it on the 556 doner rifle, and the problem followed, so something with the AAC bolt carrier group is not just kosher, I'm going to try it in different AR's of mine today, and see if its actually the bolt or what?
Well I just "borrowed" a BCM bolt carrier, and bolt out of one of my known working 556's, and it ran 5 rounds no problem through one of my 20's, I used the one that didnt work worth a damn before. It now closes just fine, like any other AR I have ever dealth with, I did try it on the 556 doner rifle, and the problem followed, so something with the AAC bolt carrier group is not just kosher, I'm going to try it in different AR's of mine today, and see if its actually the bolt or what?
You may want to take apart the BCG and inspect the rings...
Anytime I get a new gun, before shooting it I do the following(you may want to try the same)
Detail every aspect of the gun. Clean any grease/oil/carbon out and get the thing bone dry.
Lube liberally. For new guns, I(what some people would say) over-lube it. Just make sure your fireing pin and its channel are quite dry.
Inspect the gun. Check for burrs, fit, and lockup of everything. Use full power ammo. (556 for a 556) I remember reading here (not sure if accurate) that the subsonic is not loaded to the same pressure as the supersonic. You may need to run a couple hundred rounds of that through it first to wear the parts if you got tolerance stacking going on.
If you still have a problem, like rsilvers said, isolate 1 part at a time. If you cant figure it out, id send it back, but I'd try to break it in and figure it out first.
In future may want to shoot new barrels first with loadings before throwing can on in the (very) unlikely event they aren't being stabilized. More for an 8" than your 16". Others may find this unnecessary but just a thought.
No problem, USGI 30's and a 20's. Magpul 30, I have tried maybe 7 or 8 different mags, bolt and carrier dripping with Break Free, No it does not pick up rounds very well at all, no real consistancy. Does not matter ifs under gas pressure or being manually charged. GI buffer spring H1 buffer. Even when its being operated manually, empty (no round) it still seems reel tight going into lock. When it does fire the empty case seems to get caught in the upper, sometimes it just wont extact, and tries to jam a loaded round into a empty case. About the only thing is hasnt done is double feed.
That sounds like one of the issues on my M4. It could be an extractor problem. You could isolate this by trying a different Bolt carrier group and see if the issues still come up.
My apologies in advance for raising a thread from the dead...
I also have a new AAC 300blackout. But it's a 9" barrel.
It shoots really pleasant with nice accuracy.
However, I was also getting a lot of FTE during my first outing after putting it together. Tried a carbine buffer and H2. Same problem all around. Folks on 300blktalk.com mentioned that one finicky thing with the 300blkout is that there needs to be an o-ring on the extractor spring. Most BCG's, such as my DD do not come with one, or it is included as an option, but not installed form manufacturer. Adding the .01cent o-ring solved my FTE problems, and now she runs like a champ with sub and super sonics.
Can anyone else chime in?, and tell us if that is a common problem with 300blkout and running an original 556 BCG? just give it an extractor spring o-ring
i would try adding a o- ring to the ejector.if no results,then contact aac!
...if that is a common problem with 300blkout and running an original 556 BCG? just give it an extractor spring o-ring
An extra power extractor spring or O-ring is pretty standard on SBR's, at least the quality ones.
BufordTJustice
05-14-12, 18:49
An extra power extractor spring or O-ring is pretty standard on SBR's, at least the quality ones.
Agreed. I have a buddy who bought a 16" LW middy DD last year. It worked flawlessly. However, upon detail inspection of the bolt, it only included a polymer insert and what seemed to be a std power extractor spring. My buddy upgraded to a BCM spring with an insert for some insurance.
With the 300BLK being more finicky, a BCM extractor kit (or, my personal fav, a Springco XP extractor spring w/ insert) might be just what the doctor ordered.
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