"A" Preventative Maintenance Program

[toddackerman]

Depending on your firing schedule I would check the the throat every 1500 rounds, as well as action spring length. The barrels could last 50 or 60 thousand rounds, but the chambers go in as little as 8 grand. Even less if your doing alot of Frangible shooting.

Since Crane says you can have bolt shear in as little as 4 grand with a harsh schedule its going to be up to you to modify the schedule depening on your use.

But your baseline is good.

Throat erosion is something to be concerned with, but I question how important it is in CQB weapons. When I shot Bench Rest, we would bring the barrel back about 1/8" every 5,000 rounds or so to have "Fresh Land and Grooves" to contact the bullet bearing surface. Those were .308's.

I have 6400 rounds on my MRP barrel, and even though I haven't checked the throat, it is still shooting sub MOA (checked it 3 days ago), which tells me something. The head space is still well within tolerance.

Tack

[LukeMacGillie]

I dont know this for sure, but I really do think that the throat erroision was the reason that the Rangers were back to the old Vietnam SOP of having a cleaning rod taped to the weapon in the early days of the GWOT.

Throat errosion is the first thing I check when Agents have extraction issues, and 8 times out of 10 its the throat, allowing the round to seat too deep, not a bad extractor/ejector.

But I end up replacing the entire upper and bolt.

Some of the folks who I support are on the bolt a week and upper a month plan

[Diz]

Yeah, this can get real technical real quick!

I think the thing to shoot for is a nice average, sorta in the middle of the bell curve, as it were.

It sounds like a good chrome lined bbl is capable of much more than 10K and the chamber might be the critical wear point. On the CQB-R report I believe they had something on the average of 1-2 thou larger headspace after a hard10K rounds. On the other hand, there was also significant errosion at the gas port which you normally might not think about.

I believe you are right, in that the initial focus should be on hard wear items that typically wear out much sooner than bolts or bbls. The bolt parts, especially the extraction system, the buffer spring, the mag springs, etc. Then there is the bolt carrier keyway staking, and the reciever extension staking.

Then you have to cull out any problem mags. And try to find some decent ammo.

And last, but not least, find a good lube and cleaning system.

Aye Carumba.

[Hawkeye]

D,

Just keep in mind when reading those reports, to differentiate between full auto fire and semi auto. I'm sure you are, but just saying it for posterity. Full auto fire is going to wear on the throat, gas port, bolt, etc.. harder/different than semi auto fire.

[Shihan]

Diz these questions have been asked quite a few times on here in the past with quite abit of decent replies. If you cant find them in a search let me know and I will help you look. Also when your done please post you findings as this is Goos Sh-T!

[Diz]

Absolutely right on the full auto part, as well as suppressors. I know these two factors are gonna really fry your piece.

It's kinda like shooting for a target here. We really don't know how many rounds we will get out of our components, but we have a pretty good idea of how many it takes to trash a rifle under extreme conditions.

At the other extreme, we have all heard stories of guys getting 20K or more through a rifle, with the same bolt and bbl.

[Diz]

OK I did do a search for PM. And I think gotm4's reply should be a sticky. (I did read through all of those, BTW.)

-3K for complete bolt re-build, head space check, and buffer spring check.

-Bolt and barrel until a headspace down check, then replace as a unit.

-Complete overhaul at 10-15K including all the above, plus FCG springs.

Sounds pretty good to me. My apologies for not checking first.

[AR15barrels]

You can't really fix a number to barrel life.

Assuming that the other parts of your shooting system are in order, when the barrel stops hitting what you are aiming at, it's probably time to replace it.

For highpower shooters, this might only be a few thousand rounds.
Threegun shooters will go longer on a barrel.
Slow-fire plinkers will go a long long time before wearing a barrel out.

If you don't shoot much beyond 100-150 yards, you probably won't even notice when your barrel IS getting worn out.

[Diz]

Good point. I never specified that I am talking about using my carbine as an in-close defense weapon, probably not shooting past 100m. So even with significant chamber/bore wear, I can still get 1 minute-of-bad guy.

What got me thinking this way wuz the Crane SOPMOD report where they were talking about going to round-count -vs- maint intervals for M-4 inspections. Which makes sense for high-mileage short-bbl guns that are at high risk of failure before std maint interval.

Another point seems to be the gas port errosion on a carbine length gas sysytem. We are pretty much stuck with it. Although heavier buffers seem to help by increasing dwell time. It would also seem to make sense to drill the gas port before chrome lining, with a careful finish reaming to size?

[Hawkeye]

Diz, the minor issue with the carbine length gas system is one reason I have become a fan of the midlength system.