I am wondering what is the correct BCG for the GAU-5/A/A, a chrome M16 without FA notches maybe ? Chrome or Phos, FA notched or no notches ??   I've seen pics with all different combos so I'm scratching my head. Thanks

(Just throwing this out, take it for what its worth)
GAU5; thats an Air Force thing right?
I think that they had 603 and 604 uppers, some with A1 flash hiders and some with CAR moderators.

For a while there the Air Force was using whatever they could get their hands on...

So "both"?

Since I believe the GAU-5/A/A was adopted after  1968, the military, including the Air Force, standardized on the phostated, notched carrier.

According to retro black rifle, retroguy is correct. That's what I have in mine, soon to be completed.

Yes an Air Force version, all the pics from the 1970 raid show the dust cover closed and if it isn't you can't see the BCG clear enough to tell what it is. Like I said I've heard chrome no FA notches and Phos with FA notches, someone has to know what they were issued with ?

It doesn't matter.  I've seen them with slick chrome, F/A botched chrome, and phosphate.

But RetroBlackRifle also notes in the Mix-Master Franken Carbine section that the more unusual it seems, the more likely it was used, re-used & re-re-re-used by the AF ‘smiths.

Point is: do what you like, it’s probably correct. Most correct is the phosphate FA notched as noted, but I would bet anything chrome smoothies got reused.

Almost all of the GAUs we had at my unit had chrome BCGs in them until about 2003-2004 when all of them along with the M16s and A1s were upgraded to phosphate BCGs.  Few years later we upgraded to M4s and all of our GAUs were shipped back to Lackland.

We had GAUs with 11.5" barrels with the XM177 style flash hider, 16" pencil barrels, 14.5" pencil barrels, and M4 barrels.  Stocks were a mix of aluminum and plastic, all CAR style.  Handguards were mostly skinny rounds, had one set of M4 style that strangely enough weren't on the carbine with the M4 barrel.

There was an effort in the mid-90s to rebarrel to 1/7 14.5 inch (GUU-5P overstamp) but both the skinny and M4 profile barrels in the supply system had Carbine ramps which were between M16 and M4 size in width.  Some were missed because this was left up to local CATM and was a TCTO (no money provided) as opposed to the despicable CAPCO kits foisted on by June Sims (who got a Form 1000 cash award) for the M16A2 "upgrade"....I submitted a Form 1000 saying lets just rebarrel the 604s to 1/7 and put an A2 rear sight in and Big AF said A2 conversion was a done deal already (with Lowest Bidder CrapCo) and cut a check to the Warner-Robbins Item Manager for "saving money" as opposed to buying new A2s from FN (yes June I saw the Puff Piece in Airman Magazine).

"Almost all of the GAUs we had at my unit had chrome BCGs in them until about 2003-2004 when all of them along with the M16s and A1s were upgraded to phosphate BCGs."

Josh were those chrome BCGs FA notched or un notched ? I'm guessing both ? which was the most common and original ? Thanks

I don't recall.  Probably a mix of both.

Thanks I'm trying to make this build period correct for 1970 original issue. The M16 Phos is the cheapest and easiest, but I've seen some images and heard chrome smoothie is correct for original issue 1970 GAU-5/A/A ?

I wasn't even alive in 1970, much less in the AF, so no idea.

I found this which points to phosphate with FA notches. So I guess we have a winner !

"The bolt and bolt carrier had gone through some changes as well. The original AR-15 had a chrome plated bolt and bolt carrier. The XM16E1 used the same with the addition of the forward assist notches. This was a proprietary “hard” chrome plating process that was quite expensive. It was found that the chrome did wear off and chip and eventually corroded. It had also prematurely worn the internal dry film lube inside the upper receiver. The original purpose of chrome plating was to make it easier to clean. This it did, but there was a better way to go about this.

There are no remaining records that state the exact time when the chrome plating process ceased, but it is safe to say in the 1967 time period the chrome plating was dropped in favor of a more durable and cheaper manganese phosphate which was black in color. The inside of the bolt carrier and carrier key remain chrome plated. Both the smooth side as well as the forward assist notched versions of the bolt carrier was produced in chrome plating and eventually both changed to the new finish. In 1966 Colt stopped manufacturing the smooth sided carriers due to lack of interchangeability with the XM16E1/M16A1 rifles."

Thanks everyone for your assitance

Keep in mind a lot of the GAUs were parts guns.  I don't think I've ever seen one that was factory stamped as a GAU.