Short Cycling Issues On Mid length BCM Upper

[gemini1]

If your rifle had 300 trouble free rounds and only started to have issues afterwards then something has either gotten loose as suggested earlier, or something might have gotten stuck somewhere. But if you said that the gas block set screw is a SOB to loosen, then the block could not have gotten loose or shifted. Now, have you check the lower and made sure that the BCG is not hitting or scraping anything that may cause the bolt from freely moving back? have you tried pulling the charging handle all the way back to allow the bolt catch to hold the bolt on an empty mag? and does the bolt move smoothly? You mentioned that you also shot those 45 grain winchester varmint rounds? what are the chances that it could have fragmented before leaving the barrel and somehow a piece got lodge in the gas port hole? You might as well try spraying the gas tube with a brake cleaner and use an air compressor to give it a good blow of high pressure air.
Also, I would call/email BCM first, just to make sure if they'll cover warranty if you try removing/loosening anything.

[dieselpower]

wow..BCM used a two piece clamp on gas block. Its not that btw. The gas block will only cause this and also leave evidence that its the problem...so no residue = good gas block for the most part.

Short stroking normally doesnt make the bolt catch in the wrong place...a bad magazine does...

take the upper off ...
Insert a magazine with 1 round in it...watch the bolt release arms operation. strip that round out..watch the operation...

if you feel this is a short stroking issue...

flip the upper over. Look closely at the end of the gas tube, does it still have a little bulge at the end? If not replace your gas tube.

Look closely the BCG gas key. Look inside of it and use compressed air to clean it out.
Look around the edge were the gas key is held against the BCG...do you see little streaks...this is the sign of a lose gas key. Can you wiggle the gas key? this is the sign of a broken gas key bolt...and if the gas key bolts are staked in place the head of the gas key bolt will not move...which is why I dont stake my gas key bolt heads...I am not going to war so I want the ability to check the torque and replace the bolts every 10,000 rounds.

Check the back of the buffer tube for dirt and crap

check the buffers end tip...is it smashed and possibly dragging on the tubes walls slowing the whole DI system down.

Replace that spring...

Check action spring (2) for kinks and
free length Free length should be
RIFLE: 11 3/4 Inches (29 85 cm)
minimum to 13 1./2 inches (34 29 cm)
maximum

CARBINE: 10 1/16 inches (25.56 cm)
minimum to 11 1/4 inches (28.58 cm)
maximum. Do not attempt to adjust
spring length

Check the sides of the tube for signs of dragging by the buffer..could be a bent tube.

use a ton of bore cleaner on the barrel...could have a piece of copper fouling the gas port. so use compressed air the opposite way...as in through the gas tube blasting the debris into the barrel...the more PSI the better. I used to use 140psi in my armory.

check for scraping and dragging inside the upper, clean the hell out of it.

Check the Forward assist pawl arm..is it fully retracted?

Download both my TM links..the -10 is a must, the -23 is good to have. Print out the -10 and stick it in a 3-ring binder.

Good luck.

[ar15barrels]

Do you know of any guys you would recommend to look it over?

Where are you located?

[USFSFire]

Alright guys real quick I just got back from sending a couple rounds down range. The first 10 fired flawlessly, slipped in a new mag hit the catch and fired another 10 rounds. At the end of the last 10 I checked the bolt and it was caught but not at the face of the bolt. Every round or two after that was short cycling. I am located in North County San Diego. Diesel power- I am going to check out everything that you mentioned right now.

[USFSFire]

OK hopefully this picture post works I am not too computer savvy. Anyways there is a little powder residue on the underside of the gas tube rear of the gas block, not too much though. Also I tried with several mags to place one round in the chamber and manually eject it. When I pulled back the charging handle very slowly the BCG meets some resistance and can get stuck before it goes all the way to the rear. This "resistance" is felt with all mags I have used with the exception of magpul. C products, colt, and KAY all had this issue. Magpul had resistance but did not get stuck. When I take out the magazine the BCG remains stuck in the position.

[USFSFire]

Also there is some marks inside the upper receiver on some of the abrupt edges.

[USFSFire]

http://i1322.photobucket.com/albums/u580/GlobeHotshot1990/068.jpg

[264Grendel]

Take it to parallax tactical

[Revolver Ocelot]

Had a similar problem with a 20 " upper. New gas rings fixed it. This was after 1000+ rounds though. Rings didnt even look bad.

Have you tried the drop test on your bolt carrier?

[USFSFire]

Rings look fine, I read many other posts about the issue but it seems nobody ever posts the resolved issue. Idk if this is referred to the drop test or not but on one of the many posts I read someone suggested disassembling the BCG, inserting the bolt, holding it vertically and seeing if it falls out. It didn't I also tried calling parallax today several time with no answer, left a message though

[torquefliteterror]

Rings look fine, I read many other posts about the issue but it seems nobody ever posts the resolved issue. Idk if this is referred to the drop test or not but on one of the many posts I read someone suggested disassembling the BCG, inserting the bolt, holding it vertically and seeing if it falls out. It didn't I also tried calling parallax today several time with no answer, left a message though

Do you have another recoil spring you can swap out? I know it sounds weird, but I had one that was actually binding and it would not let the bolt go back far enough.... I went ahead an swapped it out with another one and it worked fine.

[264Grendel]

Rings look fine, I read many other posts about the issue but it seems nobody ever posts the resolved issue. Idk if this is referred to the drop test or not but on one of the many posts I read someone suggested disassembling the BCG, inserting the bolt, holding it vertically and seeing if it falls out. It didn't I also tried calling parallax today several time with no answer, left a message though

Saturdays are a bad day to call parallax. They are really busy and i think understaffed.

[USFSFire]

Yea I swapped buffer springs and I had the same issue.

[dieselpower]

what gets me is this isnt home built. I would say the wrong spring was used for the bolt catch spring, but it worked fine for a while.

Did everything look good when you took it apart and watched the magazine act on the bolt catch? Did you do this with different magazines?

[USFSFire]

Yea I thought I used the wrong spring too, then I went bought a new spring kit, triple checked it, installed it and same issues ensued. The bolt had enough friction to get stuck with all mags except magpul which seem to have the lowest profile follower. I contacted BCM and explained my issue and they told me to send the bolt to them for inspection. This was on the 5th so we'll see...