What determines when an M4 is “worn out”?
I understand less wear is always better, but does the relationship between the BCG and the upper matter, or only to the extent that excess friction to the point of failure is not created during cycling, and that the bolt is guided into the locking lucks of the barrel extension?
What exactly are the “critical” wear areas (if any, besides the bolt/barrel extension/throat) in the M4/AR-15?
In the military world “worn out” means that the weapon is not serviceable. The way that thisis determined is by inspections and gaging. Any part that fails is replaced until everything is corrected and serviceable.
I really can’t make sense of the remainder of your paragraph.
I think he means besides barrels wearing out and bolts breaking, what wears out on an AR? Does the BCG moving inside the upper receiver ever wear it out to the point that either the carrier or receiver is unserviceable?
Correct, how “Critical” is this area? It’s the only other thing I can think of wearing out besides the bolt breaking, gas-key coming loose, barrel shooting out, etc.
I’ve never seen one worn out but someone like IG would have a lot more experience than most in this subject. I’ve seen ARs from the 60’s that were still going strong even with the anno starting to fade. The weapons in the Philippines are all Vietnam era and they’re still using them on a large scale with mostly original parts. In an arms room in the US I’ve seen a Mk 12 SPR built on a well worn lower stamped XM-16. I don’t know how old that must be but if it still works then I’m not worried about one of my many ARs wearing out significantly.
Things that wear are springs. Even parts like the trigger hammer and disconnector can wear. If you examine your upper closely and the movement of the BCG it can only wear so much.
I have seen M16’s, A1’s and A2’s that have had years of service put on them and continue to function. People need to get around the concept that stuff wears out. The basis of the weapon may stay the same- lower receiver, upper, extension, but anything else will at some point need replacing.
the area most critical would most likely be the barrel but even then, it can be replaced.
Depends what you consider to be the rifle, and what are just parts you expect will wear out.
The lower receiver itself, which is legally the rifle, has a practically infinite life. In theory it should wear out at some point… but the round count would have to be extraordinary. I doubt you would do it in 100,000 rounds, although that’s just a guess.
throat erosion is something I hear a lot about. Never had a gun shot enough with it as an issue.
head spacing is key to be checked in guns that are re-barreled and I have read that the military armorers check it often (annual). We can all do this with a “go”, “no go” gauge.
in order of wear, I would think it would be, Springs, Cam, extractor, ejector, gas key and bolt, BCG…barrel should last 30,000+ rounds.
Filthy 14, a standard 16 inch Middy by BCM is over 40,000 rounds now. That gun isn’t even cleaned…hardly.
We don’t use a “go” or “no go” gage. We use a “field” gage. Throat erosion is measured with a bore erosion gage.
All weapon are to be fully inspected and gaged at least annually.
The gas key hardly ever wears and only needs replacing when someone dicks with it or drops it. There is no standard as to when a barrel will go out. It depends on rate of fire and lots of other variables.
I would think that the contact points between the bolt and the upper receiver would start to show excessive wear. We are talking steel against aluminum moving back and forth rapidly and frequently.
Or is there enough contact all around the bolt akin to a piston in an engine cylinder instead of just a couple of rails?
As IG already said, wear occurs to a point and then stops.
Almost every other part on the gun would have to wear out and be replaced twice before that would be an issue.
IG,
How important or necessary is it to check headspace after installing a new BCG? What are the variables that more or less mandate it? Round count? Like anything else, when in doubt, do it, but I am curious of your take. Thanks.
Unless you are shooting over 1000rnds a week, for YEARS, you are not going to wear out a reciver/BCG. Most shooters will never even wear out a barrel in their lifetimes.
I always do it. But, that’s me. I think it’s especially important considering people are mixing and matching parts from different vendors/ manufacturers.
IG - What headspace gages do you use/recommend? I’ve been looking for the field gages (field reject gage?), but I’ve only been able to find the go and no-go sets by Clymerm, Forster and a few others.
As much as I hate to admit it, Bushmaster has a “Field” gage for 30.00.
Oh yay:rolleyes:!
Look at your link near the bottom IG, they are selling green abrasive scouring pads to polish the tail of your bolt carrier!
Lets use an abrasive on a gas seal!
I can’t believe I.G. hasn’t mentioned the one thing that will cause a rifle to be worn out. Because it has the serial number on it, the lower receiver “is” the rifle. Any other parts could be replaced as needed. As far as a lower wearing out, I was a unit armorer in the early '80s and saw 5 rifles that were coded out for the same reason, excessive wear on the pin holes in the lower. They all displayed the same symptoms “fails function check”. On semi they would fire when you pulled the trigger (and hold it), cycled the bolt and would fire again when you released the bolt. When taken to General Support and checked with the pin gauge, the holes were enlarged. All five rifles were Hydramatic manufactured rifles and my speculation would be that they used a softer alloy of aluminum than Colt or H & R did. All were M16A1s manufactured in the early '70s, so they were about 12-15 years old at the time.