Some of this may be a repeat, but maybe this will bring some of this together:


Based on the "Slabside Reciever" you can tell that this rebuild would have been based on a very early model, most likely it would have been a GAU-5A.



This rebuild was based on a GAU-5AA. In addition to the barrel upgrade, the original aluminum buttstock has also been replaced.



This is a classic example of a USAF M16 being converted into a Carbine. Based on the barrel, this would have been an early conversion.



This is another classic example of a USAF M16 being converted into a Carbine. Based on the barrel, this would have been a later conversion.



This appears to be a real mix of parts. The Lower is from a USAF M16. The Upper is a late model A1 with Round FA and BD, not something that you should find in early USAF inventory. The Buttstock, A2 Grip, Handguards, and Barrel would have been add ons during the rebuild.



This is the million dollar question; Is this a Colt Model 653? Is this a USAF GAU-5P? Is this a stock model or a rebuild?



A collection of Early and Late parts. Started off as an early A1 Lower. Add a Plastic Buttstock, Late Model A1 Upper, Carbine Handguards, and an M4 Barrel.



A collection of mostly Late parts. Started off as an A1 Lower. Add a Plastic Buttstock, A2 Upper, Carbine Handguards, and an M4 Barrel.


This does not cover all of the GUUs that are out there, but I think it hits a lot of the various configurations.


Based on the additional photos and info provided, I can rule out some of the explanations that I have heard:
1. GAU is used for a rebuild of an earlier GAU model, and GUU is used for the other rebuilds, FALSE. Pics show a GAU-5AA rebuilt and remarked as GUU-5P.

2. GAU is for rebuilds using a Barrel with 1/12 twist rate, and GUU is used for rebuilds using a Barrel with a 1/7 twist rate, FALSE. GUU markings have been found on Carbine Rebuilds that have Barrels with a 1/12 twist rate.

So far the only one that I can not rule out is that a Colt Model 653 could have been designated by the USAF as a GAU-5P.

Thanks again to everyone for all of the input, while we may not have a 100% answer on the GAUs and GUUs, I think we are ruling out some of the rumors.

Great job with the builds, best of luck on the new builds,
"Capt Richardson"

PS: there are pics of at least 2 GUUs that do have a tappered slip ring on them, they are posted in the USAF Section of the Carbine Guide. I did not post them here because they are not the clearest when it comes to the other features.

So basically you could slap just about any style of short barrel, on any style lower and it would be a nearly accurate copy of a GAU?

Quoted: So basically you could slap just about any style of short barrel, on any style lower and it would be a nearly accurate copy of a GAU GUU?

Seems like it.

Most seem to have an upper with A1 type field sights, slick side or otherwise.

I think my favorites are the weapons with the slick side uppers and M4 barrels, very unique.

Quoted: Quoted: ETA: Pic of my GUU-gery i29.photobucket.com/albums/c286/turnerhicks/Misc/IMG_0686.jpg Nice build and nice pic!

Hey Quib..... Note the correct handguard slip ring in the above photos?







I guess I should put an M4 barrel on here..

Quoted: So basically you could slap just about any style of short barrel, on any style lower and it would be a nearly accurate copy of a GAU?

Requirements for a GAU/GUU

1. Short barrel
2. Collapsible stock
3. UNDER NO CIRCUMSTANCES are you allowed  to have any method to the madness of how you configure the rifle (other than numbers 1&2 above).

Also, the lowers are not completely slick sided, they do have the bump out for the push pin detent.

Quoted: Quoted: Quoted: ETA: Pic of my GUU-gery i29.photobucket.com/albums/c286/turnerhicks/Misc/IMG_0686.jpg Nice build and nice pic!   Hey Quib..... Note the correct handguard slip ring in the above photos? coloradoshooting.org/ipw-web/gallery/albums/bbadmin-Album-1/cmt_car_a1_30.sized.jpg I guess I should put an M4 barrel on here..

Ah, camon' Lance........you gonna bust my balls all over again!
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CH139,
Good catch, GAUs actually have some method to the madness. GUUs on the other hand have absolutely no method to the madness!


Lancelot,
Very nice Stick!

Throw an Aluminum Buttstock on that in place of the plastic one, and you would have a very nice Colt Model 653 Replica (taking into account the 16" barrel limitations).

IMHO, if you are going to stick an M4 Barrel on it, then you are going to have to hang a M203 off of it! PLEASE DON'T, that is to nice to mess with!


BMick325,
YOU NAILED IT BROTHER! If it looks like it was made from the spare parts pile, call it a GUU-5P!


CH139,
Good call on the Lower Receiver.

I left that infamous pic of the Female SP out, because all of my sources say that it is a GAU-5P, not a GUU-5P. However I have never seen anything that positively defines what a GAU-5P is, and I have never seen the markings on that Carbine, so who knows maybe it is a GUU-5P!


Quib,
Also a very nice set of Sticks!

Lancelot is just jealous because you have 2! I am also jealous, so how about you loan me one, after all you can only shoot one at a time, right!


Thanks again everyone, this is always fun and educational!
"Capt Richardson"

Quoted: Quib, Also a very nice set of Sticks! Lancelot is just jealous because you have 2! I am also jealous, so how about you loan me one, after all you can only shoot one at a time, right!

Thanks.

Yea, I know Lancelot is just jealous………he always was.

Sorry, can’t give up the slick side GAUclone, that one belongs to my son!

Quoted: Quoted: Quib, Also a very nice set of Sticks! Lancelot is just jealous because you have 2! I am also jealous, so how about you loan me one, after all you can only shoot one at a time, right! Thanks. Yea, I know Lancelot is just jealous………he always was. Sorry, can’t give up the slick side GAUclone, that one belongs to my son!

Yup, its all true.

Everyone needs to keep in mind that the Air Force got hind tit for ground weapons forever.  CATM folks have had to be both very smart and very quick to be able to supply the real needs Airmen have had for personal weapons for a long time.  In 1989, I saw about 12 different configurations of the "GAU-5" (that's what the SPs that carried then called 'em, whether they technically wer or not) in the hands of people from different units TDY to Panama to support us while Noriega was going bugnuts.  It was entirely because CATM troops made what they had work however they could.  Bad barrel?  Find one and install it.  Damaged upper?  Here's one!  'Course it doesn't look like the uppers on all the other shorties, but it works.

Really, that's one of the biggest reasons for the variety you see in the GAU/GUU series of weapons.

well here is my days contribution.  i also have TO 11W3-5-5-42-1 on PFD if anyone wants a copy.  it covers a little about the GAU-5A GAU-5A/A and GUU-5P  send me an email with your email and ill send it to ya.  maybe a site staff can add it to the referance.

barrel 62378 10" 1/12
barrel 62488 11.5" 1/12
barrel 64632 14.5" 1/7not for sure if its a lightweight .625 or standard .75
barrel 64698 14.5 1/7 m203 campatable.  dont know if it has an m4 barrel extension (ramps) yet.  if it does have the ramps what about the receiver not having the ramp expension cuts?

in the maintenace parts list when looking up a replacement barrel for teh gau-5a and gau-5a/a its says the barrel has been replaced by barrel 64698 the 14.5 1/7

I was an SP in the AF back in the early 80's, and we had some at Minot with the 10.5 and 11.5 barrels.  They were great for getting in and out of a patrol car, had the alum. buttstock, man I wish I had one!@!!!!!

Would Norrells Grayish Black be an appropriate finish on a lower or upper with a GUU build?

Thanks.

So no more 'Franken-ARs', they are simply 'GAU/GUU' clones?

Quoted: Would Norrells Grayish Black be an appropriate finish on a lower or upper with a GUU build? Thanks.

Yes.

Remember they are for the most part based on Colt components, and a lot of them are "early" components as well so Colt grey is correct. (Although a lot would never know the difference.)

Quoted: i just did a quick search of GUU-4/p and got very litle info from it.  from what i got it was an experamental version with a .221 fireball.  looks like i will be talking with the engineer some more on this.   i just found a holster for a .38 revolver that is labled GUU-1/P.   www.ljmilitaria.com/weapons__sheaths__holsters__and_etc_.htm

Just thought I’d throw this in there for the sake of gee-whiz…

The GUU-4P demonstrator was the designator assigned to a prototype survival gun developed in a joint venture by the USAF Armament lab (Eglin AFB) and Colt to satisfy a perceived need for a new small caliber survival weapon for air crews.
In 1968 the then head of the lab was a fellow named Dale Davis who envisioned a weapon that could be fired as accurately as a stocked rifle but used the shooters arm in lieu of a traditional stock to stabilize it during firing. The lab put together a wooden mockup of the design followed by a working model using a Remington XP100 in .221 Fireball (and later a .308). In December 1969, after some ergonomic changes, it was decided that 4 operational units should be manufactured for T&E by Colt Defense. These were to be made in .221 Fireball to essentially split the difference between the 5.56 and the .17 SPIW rounds that were being looked at for production guns. The official name for the project was the “Lightweight Rifle/Submachinegun” although it was also known as the IMP, or Individual Multipurpose Weapon, and simply “the arm pistol”. By Dec 1970 all 4 operational units had been delivered and underwent various testing and development including various caliber conversions. In the mid to late ‘70s it was determined that a survival weapon should be as quiet as possible so some of the units were converted to one of 3 experimental sub-sonic rounds designated as follows:
(T1) 7.62x28 cut down .30 carbine case w/ 7.62 ball loaded.
(T2) tapered 5.56mm case mated to 7.62 w/ ball loaded.
(T3) cut down 5.56mm case necked to 7.62 w/ ball loaded.
All three of these rounds were intended to be fired through Reed Knight designed silencers. Performance of this incarnation was satisfactory, but by the time the “bugs” were worked out of the system, the war in Viet Nam was over by several years and funding dried up. The official designator “Rifle, Caliber .221, GUU-4/P” was assigned to the final operational weapons in 1980-81 and after Eglin dropped small arms development in the mid 1980’s the remaining guns were split between various locations. Only one unit remains at Eglin today, it is on display at the Air Armament Museum located just outside the bases’ south gate.

Here is a drawing from an old edition of Jane’s Small Arms---

I was standing in the chow line yesterday behind a USAF M16A2 built up on a slick-side lower.

Then an hour later I had to fix another unit's M16A2 done on a restamped H&R M16 lower.

It's been a weird week.

Quoted: ...several years and funding dried up. The official designator “Rifle, Caliber .221, GUU-4/P” was assigned to the final operational weapons in 1980-81 and after Eglin dropped small arms development in the mid 1980’s the remaining guns were split between various locations. Only one unit remains at Eglin today, it is on display at the Air Armament Museum located just outside the bases’ south gate. Here is a drawing from an old edition of Jane’s Small Arms--- i61.photobucket.com/albums/h55/Schlafftablett/imp.jpg

Interesting.  So THIS is where Bushmaster got the idea for it's ARM pistol?  Were they somehow involved in the process (i.e. subcontractor or competing design) or did they just try to build a clone for the gun enthusiasts?

If I remember correctly, Bushmaster bought the rights to the thing after the USAF lost interest.  Bushmaster's first rifle was also reverse engineered from their pistol as well, which may be a little known fact to some.

Bushmaster Pistol and Rifle

when the M4 barrel is put onto the slick side upper what is done about the m4 feedramps?

Quoted: when the M4 barrel is put onto the slick side upper what is done about the m4 feedramps?

That is not a big problem.  What I see as a bigger issue is the M4 barrels now all have the 'F' front sight bases - what happens when you can't lower the front sight post enough for the fixed handled upper?  (I know one person this happened to using a Colt M4 barrel and a Colt M16A1 upper).

Quoted: Quoted: when the M4 barrel is put onto the slick side upper what is done about the m4 feedramps? That is not a big problem.  What I see as a bigger issue is the M4 barrels now all have the 'F' front sight bases - what happens when you can't lower the front sight post enough for the fixed handled upper?  (I know one person this happened to using a Colt M4 barrel and a Colt M16A1 upper).

Can you shorten the sight post?  I am building a GUU clone as well and it will have a Colt M4 barrel with a F marked front sight post so I am curious about this myself.

Quoted: Can you shorten the sight post?

Only to a point.  In Chuck's case he couldn't shorten it enough.

It's the like of the dice as to how the tolorances stack.  Will they work together or not?  You can't tell till you build it and take it to the range.

the F stamped shelf is machined .040 taller than a regualar one.  if ya take .040 of the FSP it should get ya in there

That reminds me of one of the numerous times I chose food and shelter over buying a gun; I could have bought an arm gun in 1981 for about $250...  Kicking myself is only a slight consolation. :(

From what I've seen of the arm gun by Bushmaster and the illustrations from Jane's, E.C. Ezell's "Small Arms of the World" and so on, Bushy did a great job of producing what Eglin was aiming for.

The information below is from the  Colt Military Carbines Technical & Historical Guide , but I am reposting it here because I think it may help to bring all of the USAF Carbine info together.


USAF Carbines – Not So Easy To Figure Out!

In my research I have uncovered some controversy on exactly which models are which, and the USAF had a program of "Rebuilding" their carbines so it can be pretty challenging to figure out just exactly what is what.



*NOTES*
Colt Model 629's were donated/transferred from US Army inventory to USAF inventory following Vietnam. These Carbines have been identified as being designated either GAU-5A/B or GAU-5/B, however the exact designation is not clear. The majority of references do refer to them as GAU-5A/B.

Both the Colt Model 630 and Model 649 have been reported in various references as being the model that the GAU-5A/A was based on. So far the majority of references do refer to the Colt Model 649 as being the GAU-5A/A. Efforts are still underway to try and determine exactly which model the GAU-5A/A was based on.

GAU-5/P & GUU-5/P - there is controversy over whether the GUA-5/P was actually a USAF designation. It is also not 100% clear what the exact configuration was for either model. The data posted on the chart currently has the most support, but it is not 100% verified or agreed upon by all.

1st in the USAF Carbine Series
The first USAF Carbine was the GAU-5A which was based on the Colt Model 610.







2nd in the USAF Carbine Series
The next USAF Carbine was the GAU-5A/A which was based on either the Colt Model 630 or 649.





Based on a number of factors (BATF declaring the 4.5” Moderator as a Silencer and the inability to use a Blank Firing Adapter on the 4.5” Moderator) the in the early 1980’s the USAF removed the 4.5” Moderators on the GAU-5A/A’s which were still in service and replaced them with A1 Flash-Hiders.


3rd in the USAF Carbine Series
The next Carbine in the USAF series would have been the GAU-5P. While a number of references identify this USAF designation, they do not clearly identify if it was based on a stock Colt Model, if it was a USAF Rebuild, or if it was possibly both. One explanation would make the GAU-5P a Colt Model 653. Another explanation would make the GAU-5P the first of the USAF Rebuilds which would have replaced the barrels on the GAU-5A and the GAU-5AA with a 14.5" barrel.

Colt Model 653's have been confirmed to be in USAF inventory, however it is not clear if they were "Officially" given a GAU-5P designation.





If this is a GAU-5P, it would be based on a USAF rebuild.


4th in the USAF Carbine Series
This would have been the GUU-5P, which has been previously covered in this topic

Finally, some USAF Carbines simply do not fit "neatly" into any of the USAF Designations, and are a complete mix-match of parts. The "official" designation that we have given them is "USAF Mix-Master Franken-Carbines". This just goes to show that the USAF were masters of rebuilding and recycling! You will find many examples of these posted throughout the previous posts in this topic

Quoted: If I remember correctly, Bushmaster bought the rights to the thing after the USAF lost interest.  Bushmaster's first rifle was also reverse engineered from their pistol as well, which may be a little known fact to some. Bushmaster Pistol and Rifle

From what information I have that's about the size of it. I've been gathering info about this gun for about 2 years now in hopes of doing a comprehensive history on it.

Originally Posted By GHPorter That reminds me of one of the numerous times I chose food and shelter over buying a gun; I could have bought an arm gun in 1981 for about $250... Kicking myself is only a slight consolation. :( From what I've seen of the arm gun by Bushmaster and the illustrations from Jane's, E.C. Ezell's "Small Arms of the World" and so on, Bushy did a great job of producing what Eglin was aiming for.

While $250 is pretty good, I've seen them in the past 3 years NIB selling for $700. Now mind you, that's a rarity, but they are out there. The (BMAS) arm pistols do shoot fairly well, as do the rifles, but both have a nasty tendancy to spew shit in youir face with every shot.
Honestly, I'm not entirely sure how many mods, if any, that BMAS had to do from the original Colt 5.56 model. I din't mention it my earlier post, but when the operational units were built in .221, 2 non-functional models were also ordered in .17SPIW and  5.56 respectively. I've never seen any pics or even drawings on those, but I'd imagine the BMAS was really close to what Colt built.

...and the moderator.