When is a bolt "old"?

[opngrnd]

BLUF: Is a bolt with 2746 rounds too old for a new barrel?

Backstory: I answered an ad on the E&E and sold a complete 20" BCM upper with BCG, CH, etc included. After receiving payment, I was giving it a quick cleaning and once over and noticed the extractor spring was broken. I wasn't going to have time to function test before my opportunity to ship the upper, and I didn't have a 5-coil Sprinco on hand, so I swapped the bolt with a new Sionics bolt and shipped it. (I did have 4-coil springs on hand.) I'm thinking about throwing the used bolt in a carrier and using it for a different project. I figure I can mic the fired cases and check them against cases fired from a factory Colt like I do with most builds, and drive on. What say you? Is there a general number when you stop reusing bolts?

I'll note that when my service rifles were sent in for new barrels, they kept the same bolt. I found it interesting they replaced barrels but not bolts.

[georgeib]

I'm sure someone will come along with the precise specs, but my tendency would be to measure the lug length and bolt face to lug depth on a new bolt, and see how it compares to your used one. I'd bet you're good to go though.

[Joe Mamma]

I am not an expert. But off of the top of my head, I do not recall hearing about any recommended replacement schedule for AR bolts based on round counts.

Personally, my general rule for round counts when I consider AR 223/5.56 bolts to have crossed a line and be potentially problematic are:

5,000 rounds when used in carbine length gas systems,
7,500 rounds when used in mid-length gas systems, and
10,000 rounds when used in rifle gas systems.

I know there are lots of bolts with more than double or triple these number of rounds that are working perfectly. But these are just my personal numbers.

So in my opinion, your bolt with 2,746 rounds from a rifle length gas system (I assume it's a rifle length system) probably has plenty of life left in it.

I do try to change my extractor springs (and extractor inserts and o-rings) every 2,500 rounds, and extractors every 5,000 rounds. But that's being very conservative.

I consider the bolt and its related parts to be the most important thing on an AR that affects reliability (in a gun that was already working reliably). So I track rounds on those parts very carefully, and replace them according to my schedule.

Joe Mamma

[Diamondback]

I am not an expert. But off of the top of my head, I do not recall hearing about any recommended replacement schedule for AR bolts based on round counts.

Personally, my general rule for round counts when I consider AR 223/5.56 bolts to have crossed a line and be potentially problematic are:

5,000 rounds when used in carbine length gas systems,
7,500 rounds when used in mid-length gas systems, and
10,000 rounds when used in rifle gas systems.

I know there are lots of bolts with more than double or triple these number of rounds that are working perfectly. But these are just my personal numbers.

So in my opinion, your bolt with 2,746 rounds from a rifle length gas system (I assume it's a rifle length system) probably has plenty of life left in it.

I do try to change my extractor springs (and extractor inserts and o-rings) every 2,500 rounds, and extractors every 5,000 rounds. But that's being very conservative.

I consider the bolt and its related parts to be the most important thing on an AR that affects reliability (in a gun that was already working reliably). So I track rounds on those parts very carefully, and replace them according to my schedule.

Joe Mamma

Offtopic, tangent, would you mind sharing your entire Preventative Maintenance regimen stem-to-stern for us who are still in the "baby's first steps" stages?

[turnburglar]

I think if it head spaces fine, and there are no visible cracks in the lugs; it gets run. Worst case scenario you crack a lug after a few cases.

[GH41]

If I built with used parts I would have a field gauge. Wear patterns between the bolt and extension are unique. When you start mixing used parts from different rifles it encourages accelerated wear. Enough to hurt anything??? Maybe maybe not.

[Joe Mamma]

Offtopic, tangent, would you mind sharing your entire Preventative Maintenance regimen stem-to-stern for us who are still in the "baby's first steps" stages?

Diamondback, send me your email address via PM, and I will be happy to send it to you as a pdf document (or some other format if you want).

I have thought about posting the information from time to time because I have never seen a good preventive maintenance and parts replacement schedule *anywhere*. That's why I created my own.

I'm sure many would find it helpful. But I'm also sure it would start all sorts of arguing (because these things always do on the internet), and I don't want to deal with that. So I don't plan on posting it anywhere.

Joe Mamma

[26 Inf]

send me your email address via PM, and I will be happy to send it to you as a pdf document

Joe Mamma

Got it! Thanks!

[Triple X]

Diamondback, send me your email address via PM, and I will be happy to send it to you as a pdf document (or some other format if you want).

I have thought about posting the information from time to time because I have never seen a good preventive maintenance and parts replacement schedule *anywhere*. That's why I created my own.

I'm sure many would find it helpful. But I'm also sure it would start all sorts of arguing (because these things always do on the internet), and I don't want to deal with that. So I don't plan on posting it anywhere.

Joe Mamma

I'd like a copy also please.
Sent you a PM

[lysander]

5,000 rounds when used in carbine length gas systems,
7,500 rounds when used in mid-length gas systems, and
10,000 rounds when used in rifle gas systems.

Must be nice to have deep pockets.

The Army studies on M4 reliability give the bolt 10,000 to 12,000 rounds MRBF, M16 bolt 13,000 to 15,000 MRBF. On average they replace the bolt every other trip to the depot for overhaul (one tour is approximately 6000 rounds).

And the bolt is not the top replacement item. The top 4 items are:

Barrels
Bolts
Ejector springs
Hammer springs

All of the other parts last in excess of 30,000 rounds.

I just inspect bolts for cracks with every cleaning. If you are paraniod about cracked lugs, replace with the barrel, it makes headspacing easier too.