Changing the bolt carrier from AA issue to M16 F/A style.........any issues?

[Smokepole50]

I have a Saber Defence 16" AA upper I bought many years ago. This rifle loves Hornaday 123gr A-max to the point of a ragged hole to 3/8" groups at 100 yards if I do my part. A while back I purchased some M16 bolt carriers for other projects and had one extra so today I installed it in my 16" Grendel. This (new) bolt carrier is mil spec and was made by R Guns. One thing I noticed is that the bolt carrier key on the new carrier seems to have a tighter/smaller hole for the gas tube than on the original carrier key I got with my upper from AA. It seems to align and fit fine over the gas tube and the bolt locks up fine but I am wondering if AA designed the carreir key opening larger for a reason like pressure venting. Am I concerned about nothing important? I would like to use this heavier carrier but I do not want to do anything that will affect accuracy.

Smokepole50

[bwaites]

I have a Saber Defence 16" AA upper I bought many years ago.
Smokepole50

Hmmm, it could be Sabre Defense, or AA, but not both. They both offered uppers, so either is a possibility. At one time, I believe, Alexander Arms was using Sabre Defense chrome lined barrels for some of their uppers, so it is possible you have a Chrome lined Sabre barrel in an AA upper.


The carrier key difference you've noted is probably nothing more than manufacturing tolerance issues. If it does not wear and contact on one side more than the other, it should not be an issue.


Many of us use M16 carriers and have been very happy with the increased weight which slows the bolt opening and improves timing a bit.

[Smokepole50]

Yes according to Bill it is a chrome lined Saber Defense barrel that he used on this AA upper. I guess I should have been more clear in how I stated that.

Any chance you know what the spec opening is for the carrier key? I did not put my calipers on the new key but you could see a bevel at the opening indicating a smaller hole for the gas tube to slide into. On the carred key that came from AA there was no bevel and the hole looked bigger. I will have to check the difference tomorrow.

[gastonglock21s]

Carrier key opening should be .1805-.1813" on the part that slides over the gas tube. It steps down to 2 smaller diameters after that and before intersecting the 45 degree hole that goes into the carrier. I wouldn't sweat it if it was even .182 as long as it functions well enough. I would change it if it was on the ragged edge of barely functioning (cycling) or if your upper was excessively dirty on the inside after a shooting session.

[Variable]

I don't remember my other AA orders, but I do remember my 10.5" upper coming with a FA carrier. I thought the other ones did too?

[Smokepole50]

I measured the two carrier key opening/bore with my calipers. The new R-Guns F/A carreir key measures .178 and the carrier key that came with my AA upper measures .179 soooo....

I guess I must have just seen an optical illusion caused by the difference in the new carrier key having a clean sharp bevel at its mouth and the older AA carrier key having the bevel some what rounded/smoothed off by the gas tube and dirty from firing the rifle. Looking closely I can actually see the bevel at the mouth of the AA provided carrier key which I did not see before. I guess I should use my eye glasses a bit more often or perhaps clean my bolt carrier more often.

Thanks for the measurement data. It makes me feel good to know the opening is the same.

Variable.......You might be remembering correctly depending on when you bought your uppers from AA. I have had this upper for quite awhile and it is possible that Bill was not building uppers at that time with F/A carreirs because the ATF had not ruled them OK to use back then.

[gastonglock21s]

I don't remember my other AA orders, but I do remember my 10.5" upper coming with a FA carrier. I thought the other ones did too?

My AA 16" chrome lined from last year came with the full profile bolt carrier group as well.

[Shivesy]

Carrier key opening should be .1805-.1813" on the part that slides over the gas tube. It steps down to 2 smaller diameters after that and before intersecting the 45 degree hole that goes into the carrier.

I'm impressed! I would never have thought that someone would ever need to know such information. Somewhere in life you had learned this information, you were asked about this information and for you to be able to remember those precise calculations, it's impressive! Above that someone decides to ask for this information and you to take the time to post the specifics of the question asked is even more impressive!! Thank you Sir.

[gastonglock21s]

I'm impressed! I would never have thought that someone would ever need to know such information. Somewhere in life you had learned this information, you were asked about this information and for you to be able to remember those precise calculations, it's impressive! Above that someone decides to ask for this information and you to take the time to post the specifics of the question asked is even more impressive!! Thank you Sir.

Glad to help when I can!

[gastonglock21s]

I measured the two carrier key opening/bore with my calipers. The new R-Guns F/A carreir key measures .178 and the carrier key that came with my AA upper measures .179 soooo....

I guess I must have just seen an optical illusion caused by the difference in the new carrier key having a clean sharp bevel at its mouth and the older AA carrier key having the bevel some what rounded/smoothed off by the gas tube and dirty from firing the rifle. Looking closely I can actually see the bevel at the mouth of the AA provided carrier key which I did not see before. I guess I should use my eye glasses a bit more often or perhaps clean my bolt carrier more often.

Thanks for the measurement data. It makes me feel good to know the opening is the same.

Variable.......You might be remembering correctly depending on when you bought your uppers from AA. I have had this upper for quite awhile and it is possible that Bill was not building uppers at that time with F/A carreirs because the ATF had not ruled them OK to use back then.

Glad to help.

I bet if you were to measure the bores on the keys with a bore gage or verify with pin gages they would likely be within the .1805-.1813 dimension. Accurately measuring a small id bore like that is not ideal with a caliper but you got to use what you got.