Wear in an M4?

[Sticks]

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?

[Littlelebowski]

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.

[markm]

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?

Almost every other part on the gun would have to wear out and be replaced twice before that would be an issue.

[arptsprt]

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.

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.

[TurretGunner]

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?

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.

[Iraqgunz]

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,

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.

[drck1000]

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.

[Iraqgunz]

As much as I hate to admit it, Bushmaster has a "Field" gage for 30.00.

http://www.bushmaster.com/products.asp?cat=15

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.

[Heavy Metal]

Oh yay!

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!

[Grumpy MSG]

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.