Upper ID And Troubleshooting

[Iraqgunz]

Can anyone ID this upper/ barrel configuration as being legit or was it pieced together. The upper receiver itself is marked LMT. The barrel is stamped on the top approx. mid way down 5.56 NATO 1/7 CB. The FSB is marked on the right side 2A I1. The bolt and bolt carrier have no markings and I believe that they are Bushmaster.

One of our guys had this upper and was using it at some point. Today when I took it to the range for testing it was malfunction city. The fired cartridge would extract, but not fully eject and then a live round would attempt to feed. Since I do not deal with these super shorties much I am reaching out to the other RKI's here. The buffer is a standard H buffer.

1. Does this need an H2 to cycle properly?
2. Is there a possibility that the gas port is not correct? The FSB appears to be completely solid and straight. Any input is greatly appreciated.

1579

1578

[spamsammich]

Are the FSB pins tapered and is it parked under the FSB?

[Iraqgunz]

The pins do not appear to be tapered but rather straight. I have not removed the FSB so I do not know if it is parkerized or not. I also do not want to remove it unless it is necessary. The barrel does not look cheap and is actually very thick.


Are the FSB pins tapered and is it parked under the FSB?

[Eric]

During live fire, does it lock open after the last round? If not, that points toward insufficient gas. After a good scrubbing/lube I would also look at rebuilding the bolt.

[Iraqgunz]

It doesn't get to the last round as every other round it jams as I indicated. I have already checked the gas rings and extractor. The ejector feels strong as well. What I need to know has to do more with these short uppers and whether or not this was pieced together or if it was done right.


During live fire, does it lock open after the last round? If not, that points toward insufficient gas. After a good scrubbing/lube I would also look at rebuilding the bolt.

[Robb Jensen]

Looks like a factory LMT 10.5" barrel.

If it's dumping the fired case before complete ejection then the extractor is bad and/or you need more extractor tension. I'd also test it for short stroking loading 1 round per mag with several mags to make sure it can lock back on an empty mag.

It should run well with .223 pressure ammo with a CAR buffer and with 5.56mm NATO pressure ammo good with a H buffer.

Those pins on the FSB are straight and can be removed installed from either side.

[Iraqgunz]

gotm4,

It looked as if it was still clinging to the extractor just not ejecting out. The extractor is strong and has an O-ring on it. I am going to to the 1 round test later. I was using MILSPEC M855 ammo in the test. Also, the gas rings are new as I put them (McFarland) on. I may actually try it again in about 20 mins. and I'll let you know what happens.


Looks like a factory LMT 10.5" barrel.

If it's dumping the fired case before complete ejection then the extractor is bad and/or you need more extractor tension. I'd also test it for short stroking loading 1 round per mag with several mags to make sure it can lock back on an empty mag.

It should run well with .223 pressure ammo with a CAR buffer and with 5.56mm NATO pressure ammo good with a H buffer.

Those pins on the FSB are straight and can be removed installed from either side.

[Robb Jensen]

Sounds like you may need a new ejector and spring. Or to pull the one that in the bolt now and give it a good cleaning. Do you have another bolt to try?

[Iraqgunz]

Robb,

Just got back from the range. I went ahead and replaced the extractor even though it felt ok and put the O-ring back on. Then I loaded one round in 8 mags and they all fired and ejected fine. Loaded up a few with 30 rounds and it ate it up without a problem. Looks like the extractor was indeed weak. It even went through 2 mags of the Bulgy SS109 w/o a problem as well.


Sounds like you may need a new ejector and spring. Or to pull the one that in the bolt now and give it a good cleaning. Do you have another bolt to try?