I think I’ve stumbled upon my 3rd worn out gas tube. By worn out I mean on the carrier key end where there’s a larger diameter band that seals in the carrier key.
A few years back I had two mid-length BCM tubes that wore down on that area to the point where the gas leakage cause soft/short stroking. I have a BCM SOCOM Carbine factory upper that’s several years old. It has always been excessively soft on bolt speed/cycling, but I could never figure out why. I even dropped down to a carbine H2 buffer system from the A5 Vltor to improve cycling.
Yesterday I went to clean this gun (which I recently started shooting more often) and noticed the gas tube has no visible step up in diameter on the end that sticks into the gas key.
This would be my 3rd BCM gas tube from 5+ years ago that has failed prematurely. None of these had excessive firing schedules at all.
(Anyone know who has Colt carbine gas tubes in stock?) Brownells and Arms Unlimited are out of stock.
Yeah, there isn’t much Colt stock anywhere right now. Sorry I can’t help you, but as a potential alternative, you might give a Wilson Combat gas tube a shot.
In case you didn’t know, there is a guage for that measurement, if you’re at all curious.
I’m interested in pulling the tube an measuring it, but I don’t want to be stuck with no replacement for months. The gun does run good, but the tube finally explains the sluggish bolt speed I’d noticed for years.
That guage allows you to measure it in the upper Mark. I check mine every time I clean them. I’m guessing this is more of a thing than most of us realize, otherwise that gauge woudln’t exist. Interesting you posted your observations on this topic.
I’m too cheap to buy the gauge, but I could see it being handy. Usually I look for that shiny band around the tube where no fouling has accumulated… just a rough visual check.
Someone posted the diameter measurements here years ago.
Either that, a tight inner diameter, or a slight misalignment would be my guesses. @markm, you could check for misalignment by sliding the BCG onto the gas tube (with the upper off the lower) and see if you see or feel any significant difference is resistance compared to other uppers. If it turns out to be the gas key, you could either get the carrier rekeyed, or use one the carriers off your spare BCGs.
Nitrided tubes do last longer here, and would be something I’d look at for sure.
Going though several tubes sounds gas key related, likely alignment but who knows.
To check strip the carrier down and slide it back and forth to check to contact with the tube… if it’s strong and moves the tube at all you’ve got an issue and you should bend it a little. Hold the upper muzzle down and drop the empty carrier and make sure it bounces (doesn’t work assembled with the bolt in).
I though that on the first one. But after 3 bad tubes (all different guns), I’m speculating that there were some tubes with soft steel a few years back.
Thanks!
I generally check that with all my guns, and I definitely was checking this on the first two after replacing the bad tubes. The replacements haven’t given me any problems.
3 different guns/BGGs. I had suspicions that there were bad tubes, and I thought it was only mid-length, but this 3rd gun in carbine exceeds the coincidence threshold on the problem.
It’s not been that uncommon for me to see tubes that need to be replaced. Not something I see regularly, but often enough it doesn’t surprise me anymore. At this point, I think Murphy strikes more often than most people give him credit for. While giving PMI a few years ago, I was explaining that joes should check for loose gas keys during cleaning, and the random rifle I used for the demonstration had a loose gas key.
Most modern rail/handguards cover up the tube in front of the receiver (unlike the old delta rings). On my first bad tube, I could have figured out the problem sooner, but all the leaking gas fouling was hidden under the rail.
