I bought a used upper from a local classifieds. The trouble with that is there is no way to function check in a parking lot. When I got it home I installed it on a lower that I know functions properly. When I chambered the first round, it did not go fully into battery. I forward assisted it in. Uh oh.... Took it apart, inspected and re-lubed. Chambered again and it went fully in but slower than it should. Uh oh again.

Took it out shooting today and I could only fire on round at a time. I had to manually cycle with the charging handle. Not only that, but it had a hard time stripping the next round from the mag. I had to sling shot twice per round. Put the lower on another 300blk upper and it functioned as it should with the same mag.I did not swap BCGs though. Probably should have to eliminate the possibility.

So my theory is that the chamber is out of spec and possibly the buffer spring that came with the upper is not strong enough to strip the next round for some reason. It did better as the mag emptied.

What say you?

Edit: Just swapped buffer springs and it strips off fine. Chamber is still tight though.

quote:

The trouble with that is there is no way to function check in a parking lot.

Sure you can, but wear hearing pro, they're way loud in parking lots. And it's very surprising. When I bought a Draco mini and tested it in the driveway, the guy was surprised as shit!

just kidding, don't do that.

Was it an assembled upper, or did the guy build it himself? Pistol length gas I assume?

Sounds like buffer/recoil spring. Buy another and start there. I’ll bet the seller just grabbed a 556 spring and threw it in with the package.

I will swap in a new spring. Would that also have to do with the bolt being unable to fully extract a spent casing?

I think the seller said he bought it built. Pistol length on my SBR lower.

A couple of thoughts:

1. The buffer spring is in the lower. If the lower works with your other uppers.... it wouldn't be high on my list of suspects.

2. The first thing that I would do is to be absolutely sure that the chamber is clean . Make sure there is no residue from shooting a bunch of Wolf or Tula lacquered cases. Is the area where the locking lugs clear of debris?

3. If you've done the above with no luck.... I'd see how a different bolt control fits. Do the bolts look the same dimensions ?

4> Please let us know how you eventually fix this issue....so we can all learn !

Thanks, mike

Sometime this weekend I'll do a side x side comparison with one of my 300 blk uppers that does work well.

I bought a used, no name, home built, 300blk carbine from my local LGS.
Couldn’t get more than two or three rounds down range w/o a double feed. I swapped the BCG out with one of my other AR’s and it worked fine. The troublesome BCG worked fine in my 223/5.56 rifles.
And I had tried different mags, buffer spring, etc.
I know you don’t really have this option, but my LGS made good on the BCG.

Who makes the barrel? Will a cartridge freely drop in the chamber by hand? How long is the barrel? What length gas system?

Scrub the heck out of the chamber when cleaning it.

If all else fails, check the gas tube. Blackout is dirty.

I agree....especially if a suppressor was used !!

quote:

Originally posted by heavyd:
Who makes the barrel? Will a cartridge freely drop in the chamber by hand? How long is the barrel? What length gas system?

Scrub the heck out of the chamber when cleaning it.

If all else fails, check the gas tube. Blackout is dirty.

quote:

Originally posted by heavyd:
Who makes the barrel? Will a cartridge freely drop in the chamber by hand? How long is the barrel? What length gas system?

Scrub the heck out of the chamber when cleaning it.

If all else fails, check the gas tube. Blackout is dirty.

A round does not slip easily into the chamber. In fact, I had to morter it out. My other ARs don't do that.

Sounds like either a small chamber or a rough chamber or a dirty chamber.

Don't waste your money on parts until you're sure that barrel and chamber is clean ..really clean ! Soak that baby in your favorite solvent ! mike

They make a bronze chamber brush for 556. I don't know about 300 BO , but a 556 chamber brush wouldn't do any harm,...it seems to me.

Status report ??

First off I did not see rather you posted on the type of ammunition, sub - supersonic ammunition, reloads or factory. Second buy a case check gauge and check your ammunition first. If you are rolling your own, odds are that the length and shoulder are too long. Second are you shooting blkout ammo or did you get a box of variant ammo. Remember that you will most likely have to re-spring and buffer to get the blackout to run on your lower. and you may also have to do it again to run sub verses supersonic ammunition. Just my two cents, Big

I can almost guarantee that you need to O ring the BCG. This happened to my 300 blackout build. It would fire one shot, and not go to battery fully.

I O ringed the BCG and 0 failures since.

I'd start by cleaning the upper, especially the chamber. Then I'd visually inspect every part for wear, tear and tightness.

Given your complaint of a tight chamber, I would concur with the above recommendation to gauge the chamber and bolt combo. I assume the bolt came with the upper. Also check that the gas tube is properly aligned, the gas key is tight, and the extractor claw is in good condition. I'd also check and see what spring and insert the extractor has in it.

What buffer is in the lower you are using?
What do the barrel markings say?

Model 1 sales "300 Fireball" barrels have REALLY short throats, shorter than any of the 8 or 10 rifles and pistols I've owned in various branded 300/221's.