Alright guys, the day has come!! My GM Hydramatic M16A1 parts kit has arrived.

I can't even describe the feeling I had when I first pulled it out of the box. This has been my holy grail for several years, and I finally got it. It is all I thought it could be and more.

I am a SE Michigan native, and I've always lived within 20 miles of the old Hydramatic plant at Willow Run. Always been fascinated by the Hydramatic M16A1.

For those who would like a little backstory as to how I aquired this upper, check HERE

Below is as good of a description as I can give. I tried to get good pics, but working with an iPhone has its limitations.

Please share any thoughts or input you have, I really want to pick this upper apart.

Here's a general shot of the parts I got, all of which came off of an LE GM Hydramatic. Complete upper w/ charging handle, no BCG, type D stock w/ tube, buffer, spring and screw, A1 grip and brown nylon sling.


Here are some shots of the stock assembly, grip and sling. Pretty standard. The buffer has a deep wine colored pad, almost black, and has a deep dimple on the face. Stock screw is typical drainhole style, but has a dot of green on the threads as opposed to red. Grip is wide bottom, and has a 4 and a plus marked inside. Also has a C mark in the recess on top. Sling is typical as well.










Next we will examine the receiver. The color is a dark charcoal grey with a hint of green tint. Lugs are NOT black. There are a couple light handlingarks that show through to a light gold color. The charging handle is a perfect match in color, and wears through to light gold as well. Slip ring is a touch darker, but is also wearing through to gold in a couple light marks.

Here is the right side of the receiver.


Bottom.


Sight wheel and arrow markings.


Port door area. Typical stuff here.


Front lug is recessed. Taper cuts on the sides of the lugs kind of cut into the pin holes, haven't seen that before.


Forging flash on rear of carry handle.


I found a couple forging flaws. May be unique to GM's, maybe not. Worth noting though.
You can see from this angle there is a raised area at the top of the recess below the sight wheel.


Another angle of the flaw. There is also another flaw just like it on the opposite side of the recess (not pictured).


Here is the "blister" flaw somebob pointed out to me a few weeks ago on a couple other uppers. Note the raised area around the rear sight screw. Kinda hard to see.


Here is the front of the carry handle. You can see the slight greenish-goldfish tint on the machine marks.


The forward assist has a 1 in a small circle. It is not as recessed as others I have seen, and the 1 is raised a bit, but it is definitely a 1.


I found that the snap ring is broken, and a weld has come apart on the weld spring, which is rubbing on the front of the receiver next to the gas tube hole. No biggie to replace those.


Charging handle is interesting. There are six little dimples on the rear in a horizontal line. Never seen this before.


Machining looks similar to Colts.




You can kinda see the gold showing through on the sides.



Next up is the barrel and FSB.

Barrel is MP C marked.



Here I a shot of the forge mark on the bayo lug. Can't make it out, as it is cut off, but it is either 2-3 letters in a circle, or a design of some kind.


ETA: Here is a better pic of the bayonet lug forge mark. It is a sideways M over P in a circle. Any thoughts on this would be great.


Here is the right side forge code on the FSB above the barrel. Looks to be a sideways 19, or a 9, or a 6 from the other way. Might even be a G. Kinda hard to tell.



Here is the left side forge mark. Looks like an 8, or maybe a B.


Rear of FSB, forging flash.


Front of FSB, forging flash.


Rear of Bayonet lug, doesn't look machined, but doesn't have pronounced flashing either.


Barrel has no other marks. Bore looks like new, strong rifling with no evidence of throat erosion. Chamber needs a scrub, but I'm sure it will clean up nicely.

Gas tube is standard late style, nothing special here.


Handguards are both L and R marked, with immaculate heat shields.

Left side has kind of a swirly finish, looks like it might mottle nicely.


Right side is a bit different, similar finish, just not swirly.


Both handguards are marked with a 4 and plus, just like the A1 pistol grip. Kinda hard to see.


Here are a couple of shots with one of the demil GM receivers I have. The color isn't an exact match, but it's in the ballpark.




I hope this sheds some light for the hive on original Hydramatic upper configuration. If anyone wants pics of a specific part or something I might have missed, don't hesitate to mention it. I can take more pics tomorrow if needed.

Also feel free th point out anything you observe that jumps out at you. I'm sure I missed something.

Thank you for looking, I'm glad to be able to share my new baby!!

cool.  the 4 dots on the charging handle is something i've seen before.  mostly on the bronze anodized charging handles.  they look like vise marks or something.

Wow, you noticed much more than I did when I saw them in the shop.  Didn't notice the forging flaw in the carry handle recess, didn't notice the row of dots on the back of the charging handle, and I didn't pay that close attention to the hand guards.  What's funny is I traded for 2 charging handles from boywonder777 with the row of dots because the color match, one for me and one for my friend (2 on left):



Do your right hand guards have this texture?  I put one on my bronze rifle just because I thought it looked different:



Is this what the "+" looks like?  I think I put one of these on my bronze rifle too one of the "swirly" hand guards on mine just because it was different:



ETA:  Also, others have said GM or H&R had identification markings on the stock where it meets the receiver, is there anything there?  Is that a rivet holding the sling swivel on?

ETA: Here's a post I made about the hand guards: Link

ETA: Thanks for posting this, I think it is a really cool story with you living so close to the plant.  When you look at the way the finish wears on your upper, slip ring, and charging handle I think you have a very new condition one of those "bronze" uppers that show up from time to time.  You might just leave the snap ring + weld spring alone, I would be afraid of scuffing the finish taking it apart and it documents quality control at GM.  I think you have a really cool piece of history there, you might be ahead of the curve here.



ETA:  The tacked M16 guide says rivets were introduced around 1970, if GM rifles all came with type "D" stocks and that stock really came off a GM it gives us an idea of when it was made.  Has anyone else come across "D" stocks with a rivet holding the swivel on?

Great write up and pictures - fun to see, and thanks for stepping up and saving a piece of retro history.  If we all do our parts we can all become poor together!

So looks like sling swivels were replaced?  Rivets I assume from what I can see - they look pretty fresh.  Hope you aren't planning on buffing out the furniture to get some mottling!

Thanks again for the post... great job!

Very nice looking upper, kinda wish I had one of my own for some reason, even though I've told myself I'm done building AR's.

Interesting about the dots on the back of the CH. I've seen them on some of mine before but did not think much of it.

I cllicked on this thread because I carried a GM Hydramatic Div. M16 in basic and Ft. Jackson, SC in 1975.

I thought it had a sort of greenish tint to the finish on the upper and lower receiver and wondered if yours would look the same.

It shot pretty good I guess.  I shot expert with it.  One guy in the platoon shot a higher score than I did (by 3 points).

Note the droopy 3, seems to be more common on but not exclusive to these receivers.

I thought about this after you mentioned it before, and I am leaning towards leaving it. The snap ring seems tight in the barrel nut recess, but it is missing about 1/3rd of it. Think I will have any problems with it coming off?



ETA: I love this pic! The color variations are awesome. Looks like the one on the far left has the similar green tint as mine. The gold one next to it looks similar just worn down to more gold.



While I am thrilled with the 98% condition of my setup, I really like the worn gold look. I have a bunch of gold aluminum parts I've been collecting to eventually do a build like this. Was gonna do my GAU build in worn gold, but I have a nice original finish 604 upper that I don't want to mess with, so grey it is....

Oh, btw Bob, email me your info so I can send that trigger guard out to you.

WOW...great upper assembly!!  

She's a beauty and will make a great build.

What are your plans for finishing this build?  She'd look great with a NDS M16A1 lower with "GM Hydra-Matic" markings applied by Indent.  

I have a braceman lower with GM legend, all milled out. Just need to send it off to Victor for coating, then I will be assembling this bad lad!

I'll keep everybody posted when I get everything finished up within the next month.

Wow! Very Very NICE! So glad for you.

Nice score Mike. Thanks for all the detailed info too. I'm still looking for the same. Tried bidding on #2 but someone had deeper pockets then me! Looking forward to seeing the finished product.

I'd love to see some pics of the lower in its current state.

Will Victor anodize completed former 80% lowers?  

Here's a shot of it when I took it out for function test about a month ago. It has another upper setup on it obviously, but the lower worked perfectly.




It's since been stripped and cleaned, and waiting on this upper to send out to Victor for color comparison. I'll see if I can dig up a pic or two of the ugly millwork inside.



As of recently, yes. $50 + return ship.

Awesome!  

Holy Cow, that's beautiful!!!

I"m greenish/bronze with envy

Nice score!


That hand guard with the swirls should be easy to mottle up. Sand and buff.

Don't sand that hand guard please  I think the user MacAttack's 'bronze' upper has the same style hand guard.  We should do a little more research first.  

Upon further inspection this evening, I have figured out what the bayonet lug forge code is. The code is sideways, with the top toward the receiver and bottom toward the muzzle. You can just make out the two letters M and F inside a circle. The M sits right on top of the F, and the machine cut runs just adjacent to the letters. I guess the F could also be a P, but it looks more like a F. "MP" would actually make more sense, considering the barrel markings.

Any thoughts?



ETA 2: The forge code on the bayo lug is definitely M over P in a circle.

Won't be messing with the HG. I was originally just saying it looks like it will mottle.

Here's the hand guard, to me it looks like frosting that was put on a still warm cake.  (is there a word for that?)



Here's the thread:

http://www.ar15.com/archive/topic.html?b=3&f=123&t=526471

I'm away from home right now, I'll take a closer look at my stuff over the weekend.

Bob, that is exactly what my left side HG looks like, swirly like. I wonder what the right side looks like.

Also, by the looks of it, the upper in question in Mac Attack's thread linked above is nearly identical to mine. Same FSB markings, barrel markings, receiver color etc.

AR15guy's upper looks almost the same, the only differences I can see is the FSB marks are slightly different, and the finish looks darker.

I'm beginning to think that a lot of uppers that people think are H&R's are actually GM's.

Wasn't saying do it, but thats the ones that can done. Drain hole, non LR marked (mine weren't marked, i see these are) and swirly underneath. Thats what one of my mottled sets started out as..

One thing I've noticed is the port door pads on these are not as "crisp" as a colt door.  The corners are rounded and it just looks 'off' ever so slightly.  I compared what I thought was my H&R upper and I found the same forging flaw on the right side on the inside corner of the indent of the carry handle, and have the same flaw on the left side.  The port door is also the sissy rounded square pad.

Does it go through to stringy glass fibers or to the broad "flakes" of fibers?  Any pics?

What happened to all the pictures ?
A otherwise good thread has been lost.

Pics are back up.

Look on this thread at my pics.

http://www.ar15.com/forums/t_3_123/571477_Got_Mottling_.html

I didn't even notice that the port door pad has rounded edges. Good eye!

Would love to see some pics of your upper for comparison.

I recall that slightly greenish tinge on the Hydramatics; hadn't thought about it in years.  Nice catch!

BTW, when I was in Basic at Ft. Ord in the summer of '70, the DI's made a point of issuing Hydramatics to south paws.  The claim was that they ejected more to the front, so a lefty wasn't getting his own brass down his shirt.
I've never heard this elsewhere since, and it does cross my mind that the DI's may simply have made it up to keep the lefties from bitching...

Anyone here recall a difference in ejection pattern with the Hydras?

Enjoy yer rifle,
Moon

I would like to call on anyone with an A1 upper, barreled or not, that has forging flash and/or no Colt proofs to break them out and share some pics and info in this thread if you are willing. Or, if you have an MP C marked barrel with forging flash on the fsb and some forge marks, it would be great to see these as well. It would be great to have more uppers to compare and contrast. If you would rather email me directly, that's cool too.

I've already got some theories brewing on the differences between some of the uppers that have already been shared, and their origins, whether GM or H&R. The more examples we have to compare, the better we can begin to understand what we have.

Thank you to those who have already shared, and I hope to see more.

Thanks guys!!

M1, Great thread. Thanks for posting all the detailed pics. Lots of great info for the retro archives

My lower has a greenish tinge to it.  I tried snapping a couple of decent pics of it, but Im a terrible photographer.  In the sunlight it's very noticeable.

Nice upper OP

I don't think I've seen one shifted over far enough to make the letters out like that, that's really cool.

I've heard this before - supposedly the cam pin slot is different slightly. You can modify the ejector by grinding a slight angle on it to acheive the same result. I have pics on my other computer, but they are likely still in the archives as well. That mod will make them eject at about 1:30 to 2:00 I understand.

Interesting. I have a GM bolt, and just found a GM carrier on the EE this week. When I get her all slapped together and get out to the range I'll let y'all know how the ejection pattern comes out.

Here is a comparison of two rear forging flash uppers and a Colt round forge no forge code upper.  In the past Engineer5 did a comparison with a "CK" forge Colt upper receiver, I will try to find a link.

ETA: Here is the post

Colt upper is on the top, same arrow, similar "R"

This shot shows the "blister" on the middle one pretty well


Mine has a very small bump in the carry handle recess, same size on each side, you really cannot see it in the picture.


I don't know what these charging handles came off, I traded them from boywonder777.  The other thing I noticed in your charging handle is the mark on the right side of the "T"

Two rows of dots depending on how the forging fit in the jig, didn't get all the paint off the top one

Nothing special on the left side.


There is another style forging that is similar to a "CK" "CH" forge upper, I will try to get some pictures later today.

ETA: Here is the other style that is similar to a "CH" Colt upper receiver, these don't show up as often as yours does.  This one was blasted and re-anodized, my friend Norrellsd it gray.  I think there are colt upper receivers with this style forging and no forge codes on the handle, am I right?  

Colt receiver has no charging handle, forging flash receiver has charging handle, front flash removed with tool marks that run side to side.


The shape of the cam pin bulge and where the mag well meets the carrier tube appear more rounded than a regular round forge receiver so I think of them as "very round."  This forging flash one is rebated, I have seen some forging flash receivers of this type that are not rebated


Arrow is different between the Colt and rear forging flash receiver, on both of these the vertical re-enforcement behind port door is wider at base than a regular round forge upper receiver, rounded area in front of port door is more rounded.


ETA:  I put my upper together from random parts, I just happened to choose similar hand guards as what came on MrM1A1's upper.  My "swirly" left hand guard does not have the plus / cross.  (Should we call it a Balkan cross?)  Went though a small pile of hand guards, found a swirly one with cross and number that will go on rocketresto's gold upper.

i took a look at a few hundred handguards today.  here's what i saw.

markings in that area
numbers from 1-11 with the cross.  
letters in that same area with no cross (A-K i think)
letters and cross

found them on L/R and no L/R marked handguards w/ the drainholes.  haven't had a chance to see if the non-drainholes have the same marking.

finish
smooth shiny
visible vertical ribs
"melty swirl"
leathery

the number cross doesn't seem to be tied to a particular finish.

haven't had a chance to look at the pistol grips yet for the cross.

looked at a few of my h&r uppers and they tend to have the number and cross handguards.  they few that didn't may have had the handguards switched around by me a long time ago.

do we know if colt owned the handguard molds and just contracted them out?  i know there were multiple manufacturers of the handguards with a lot of variation in the texture, mold, weight and thickness.

having found that on the non L/R marked drainhole hanguards, that would date them to 68 which is about the time GM/H&R got their contract fwiw.

Wait a minute, have you posted pictures of these yet?  

hehe i dug them out just to add some info to this thread.



Here's the info from top down.  CH not original to uppers though they all have the "dots" on the rear

Upper 1
flash on rear
grind on front rounded portion
counterbored
no "bubble" by sight screw
some putting in recess of carry handle
circle 2 on forward assist
epc pad looks sharp
standard gas tube
MP C marked barrel, all inline on right side
FSB has flash, sideways 5 on right and circle mark on the lug
sling swivel roll pinned
cross 1 on Left HG
11 cross on Right HG
HGs L/R stamped

Upper 2
flash on rear
grind on front rounded portion
counterbored
no "bubble" by sight screw or flaw in recess of carry handle
circle 4 on forward assist
epc pad looks sharp
standard gas tube
MP C marked barrel, all inline on right side
FSB has flash, sideways 4 on right, upside down D on the left, and circle mark on the lug
sling swivel roll pinned
cross 1 on Left HG
no markings on Right HG (i may have swapped it out if the original was damaged)
HGs L/R stamped

Upper 3
flash on rear
grind on front rounded portion
counterbored
no "bubble" by sight screw
some putting in recess of carry handle
circle 8 on forward assist
epc pad looks sharp
standard gas tube
MP C marked barrel, all inline on right side
FSB has flash, sideways 3 on right, upside down A on the left and circle mark on the lug
sling swivel roll pinned
cross 2 on Left HG
4 cross on Right HG
HGs L/R stamped


Upper 4
flash on rear
grind on front rounded portion
counterbored
no "bubble" by sight screw
some putting in recess of carry handle
circle 4 on forward assist
epc pad looks sharp
standard gas tube
MP C marked barrel, all inline on right side
FSB has flash, sideways 5 on right and circle mark on the lug
sling swivel roll pinned
cross 3 on Left HG
6 cross on Right HG
HGs L/R stamped

so i went and looked at the pistol grips.  from your pic it looks like fat at the bottom grip.  none of my skinny all the way and skinny at the bottom grips have the number and cross but all the fat ones i have do.

if we find out that the cross manufacturer was specific to GM, that might explain the grip shape difference.

Lots of great info here. Thanks for posting.
Hopefully this can be stickied.

Interesting info on the handguards and their markings.

somebob, in your second pic, the middle one with the "blister" has another forging flaw like mine. I didn't think it was a flaw until I saw yours, I thought it was a ding or something. If you look toward the front of the receiver, just behind the gas tube port there is a small dent.
http://i1127.photobucket.com/albums/l626/somebob/bronze/IMG_9026.jpg

You can see the same dent in the same place on my receiver.

i can confirm my suspected GM upper has the same "ding" on the left side behind the slip ring

So which bolt catch would be correct for a lower on the upper, a standard catch or one like this?

Ooops. D/T

Both GM and H&R used the same bolt catches marked with a circled number. They also both used forward assists with the same markings. The rest of the lower parts are believed to have been produced in-house, or at least by different contractors, as the FCG parts, trigger, hammer, selector etc are marked with their own company specific markings.

"Both GM and H&R used the same bolt catches marked with a circled number. They also both used forward assists with the same markings. The rest of the lower parts are believed to have been produced in-house, or at least by different contractors, as the FCG parts, trigger, hammer, selector etc are marked with their own company specific markings."

Want to get back to TBR and see if there is any useful info there about subcontractor, sub-subs, etc.

Great thread, lots of great images and detailed comparison happening here. Thanks to Boywonder, Somebob & M1A for comparing parts. From the forging images it is pretty obvious that there are some common denominators that will help to define what was an H&R or GM assembly or former component of one.

Giving us a lot to think about.

Thank you

Alright, so we've got some good info going here!

I have had this grey/gold charging handle for a while, and haven't even thought about it till today. I took a close look at it next to my GM charging handle, and they have all of the same machining characteristics, including the row of six dimples on the back, and the little "vice mark" on the right end of the T. They look just like somebob's two pictured above.

The the grey left on the gold one I have is quite a bit lighter than my original GM, looks more like XM grey. Here's a couple side by side shots.






On another note, I received my GM carrier today! It is quite a bit rougher than I anticipated, and has been restaked, possibly in the field as the stake marks are really light. It will do though until I can find a nicer one more consistent with my upper's condition. I tossed my GM bolt in there, which is in a bit nicer condition, not quite as rough, and finished her off with Colt pins, and there she is!








All I need is to find a GM trigger, hammer, disconnector, pins and springs, and my whole rifle will be GM except the lower and a couple small pins and springs. Kick ass!