Interchanging/Changing bolts

[andy t]

The AR manuals state to "never interchange bolts in an AR". What if I get a used bolt? Is there a process I need to go through to make sure the bolt is fine for use in a given upper? What is the reasoning behind that warning?

Thanks,

Andrew.

[Snake RAH]

Go to a gunsmith/armorer and have him check headspace. If you were nearby me, I'd be happy to help you out.

Since all parts wear differently, and all parts aren't exactly the same dimensionally, the possibility for excessive headspace is there. Excessive headspace can cause kabooms at worst, crappy accuracy at best.

New bolts are $50 or so. As a result, I always get a new bolt with a new upper.

[andy t]

Snake,

How come headspace is not an issue with new bolts?
I am thinking of getting a new bolt. I am stuck between a FN Mil Spec bolt and MP tested bolt on G&R Tactical site. Is one better than the other?

Thanks!

[Robb Jensen]

Snake,

How come headspace is not an issue with new bolts?
I am thinking of getting a new bolt. I am stuck between a FN Mil Spec bolt and MP tested bolt on G&R Tactical site. Is one better than the other?

Thanks!

It can be an issue but usually isn't if neither the barrel or bolt have thousands of rounds through either or both of them. The biggest thing safety wise is you want to be damn sure when changing a bolt or barrel is that it won't close on a USGI Field gauge. Generally if a rifle/carbine needs a new barrel it's a good time to get a new bolt, these two parts should wear together.

Being a bit of a perfectionist I make sure it'll close on a GO gauge and will not close on a NO-GO gauge.

[jmart]

Assuming the wear accrues on the bolt lugs and the barrel extension, is there a rule of thumb that says how much headspace will increase over every 5,000 rounds or so? Will there be enough wear that say, on a new barrel extension/bolt combo that is headspaced properly (GO Guage=Yes, NO GO = No), will it wear enough that eventually the weapon would accept a NO GO or FIELD REJECT gauge? If so, in how many rounds? Also, I'm wondering how much of the wear occurs on the bolt vs how much on the barrel extension?

[Robb Jensen]

Assuming the wear accrues on the bolt lugs and the barrel extension, is there a rule of thumb that says how much headspace will increase over every 5,000 rounds or so? Will there be enough wear that say, on a new barrel extension/bolt combo that is headspaced properly (GO Guage=Yes, NO GO = No), will it wear enough that eventually the weapon would accept a NO GO or FIELD REJECT gauge? If so, in how many rounds? Also, I'm wondering how much of the wear occurs on the bolt vs how much on the barrel extension?

There's no real rule of thumb because of the different factors of how the rifle is shot and ammo used. If the rifle is shot a lot, check the headspace more often.

Example:

John A. is a benchrest/high power shooter and shoots his AR15 twice a month, he shoots 100 rounds at the range every session, all very slow well aimed fire (much less wear).

John B. is a 3gun shooter and shoots his AR15 twice a month, he shoots 100 rounds all in rapidfire. (much more wear)

[jmart]

There's no real rule of thumb because of the different factors of how the rifle is shot and ammo used. If the rifle is shot a lot, check the headspace more often.

Example:

John A. is a benchrest/high power shooter and shoots his AR15 twice a month, he shoots 100 rounds at the range every session, all very slow well aimed fire (much less wear).

John B. is a 3gun shooter and shoots his AR15 twice a month, he shoots 100 rounds all in rapidfire. (much more wear)


Fair enough, but still, doesn't the round count establish the wear? The only real difference I see in these two scenarios is that the 3gun shooter subjects his bolt and extension to higher heat. I'm guessing a couple hundred degrees higher, but as long as both are lubed adequately I would think the main cause of wear is round count (or each time the bolt engages and disengages). The 3 gun guy will wear it out sooner in calendar time, but the round count ought to be the final determinent of wear, at least that's how I envision things. That's not to say I'm correct.

[Snake RAH]

"Being a bit of a perfectionist I make sure it'll close on a GO gauge and will not close on a NO-GO gauge."

I'm not quite a perfectionist, but I adhere to this practice as well, on all bolts and barrels.

The 3 gun shooter will likely wear the bolt and barrel out faster (due to going to higher round counts in a shorter amount of time), but the benchrest/high power shooter may ditch the barrel and bolt combo at a lower round count, because his accuracy dropped off.

I have a Bushmaster carbine barrel with over 10,000 rounds through it running the original bolt. It's mainly gone through 3-gun matches, carbine matches, and carbine classes, one with a round count of 2200 rounds in two days. It still closes on the GO, but does not close on a NOGO. I figure I'll keep shooting it until 1) headspace gets beyond a NOGO, and/or 2) the bolt breaks (either lugs, pits, or crack at the cam pin).

I have a spare bolt for several of my guns. When the time comes to replace a bolt, I'll verify headspace. If the barrel won't headspace with a new bolt (close on GO, not close on NOGO), then I'll replace the barrel too. I think, however, I've got quite a bit more shooting to do before I get to that point.

[jmart]

"Being a bit of a perfectionist I make sure it'll close on a GO gauge and will not close on a NO-GO gauge."

I have a Bushmaster carbine barrel with over 10,000 rounds through it running the original bolt. It's mainly gone through 3-gun matches, carbine matches, and carbine classes, one with a round count of 2200 rounds in two days. It still closes on the GO, but does not close on a NOGO. I figure I'll keep shooting it until 1) headspace gets beyond a NOGO, and/or 2) the bolt breaks (either lugs, pits, or crack at the cam pin).



This is an interesting data point, 10,000 rounds and still within headspace spec. Just curious, is your bolt still original? Is it a BM bolt?

Some Headspace Gauge Specs (http://www.forsterproducts.com/Pages/gages.htm)