Hey

So, I've been doing some research on the S&G 951. Actually on a few of the S&G locks. At some point I'm hoping to collect the 951, 833, 831, 826C and 826D. Options are sparse for buying, especially in the condition that I would ideally like as a collector, but it's a fun journey

My current bugbear is the 951. Up until today all I knew is that there are two versions:
* The 951, which is provided to US Military, and
* The 951C, which uses a different core (non restricted) and is supplied to the general public.
Now, you can find both of these. SecuritySnobs sells the 951C for just over $1,300, and the 951 can sometimes be found on eBay and the like. My main difficulty has been distinguishing the 951 from the 951C, especially from afar in an eBay listing. The other issue, which I only learned today, is that there are actually three cores in use:
The D4 keyway, for active US Military
The R1 keyway, for US Mil Contractors, and
The S1 keyway, which is for public/commercial sale.
I'm assuming that you can find both the D4 or the R1 in a 951 body, and the S1 in a 951C body. However of course on eBay a Mil body may have had its core replaced with an S1, or vice versa.
What I'm trying to figure out is:
1. How can you tell a 951 from a 951C? Are there any distinguishing marks on the key, body, or core that would identify one from the other?)
2. How can you tell an R1 or D4 cylinder from an S1? and
3. How can you tell the R1 and D4 from each other?
Here are some things that I've found out so far, which may or may not apply to all locks and may be incorrect for certain years etc, I'm not sure how true this is or how widely it applies:
1. At least some military body 951 locks have "US Government Property" stamped on the BACK of the lock. (Opposite side to the US Model 951 <Year> stamped on the reverse side)
2. Military (restricted) keyways have "US Military Property. Do not Dup" stamped onto them. Not sure if this applies to all, or just R1/D4?
3. Military cores are green (teflon coated?) whereas commercial are brass? (Least sure about this fact as I've heard conflicting evidence). Not sure whether this applies to all of them, or just the R1 or D4.
4. The Military bodies (951) have a UID stamped into both halves of the body to thwart destruction and recreation attacks, I'm not sure if the non-mil ones also have this number or ever whether all the mil ones do.
I'm also not sure whether all 951/951C cylinders have the Medeco Biaxial cylinder or whether some might have the regular Medeco? Also I've seen some videos where there is an anti-drill rod that you can access from the back of the core via a set screw, not sure if this is Mil. core only / just a Biaxial thing?
Some Medeco based padlocks such as the Hi-Shear and the 826 padlocks come with a little metal key tag that says something like "Control key, Do not issue, For maintenance use only". I'm not sure if the 951 is "supposed" to come with one of these new, but I've only ever seen them being sold with the plastic Medeco keycode card. Do those metal cards come with 951 locks or is that a deprecated feature?
Any knowledge or light that anyone could shed on this would be gratefully appreciated. I'd love to pick up one of these but I want to make sure that I'm buying what I expect, and I'd like to know what additional pictures I should be requesting to determine these details when contacting sellers. As an aside, if anybody has one of these that they want to sell, pop me a PM! Ideally I'd like it with the original box (AFAIK these S&Gs all come with a "To be opened by authorised security personnel only" box), operating instructions, chain, three keys including square head Control key, key fobs/tags, and it should be a 951 with the D4 (or R1, not sure of the difference) core, body stamped with UIDs and "US Government Property" on the back. I know that's a big ask and I realise I'll likely have to "settle" for less when I do eventually pick up one of these, but it's to be my centrepiece jewel of my S&G Military locks and probably my whole collection so the closer to this, the better.
(I'm also looking for an 831, 826C and 826D, just sayin'

Some resources / research links:
Photos showing the US Government Property stamp
Info on the keyways
A bit more info
Adrian Weber's video about his 951 (Including info on the UID stamping, and green core).
Another Adrian Weber video, this one about the 951's core (and that rod)
Screenshot of the body number stamp
Bonus round! - Some questions about other S&G locks:
1. Are the 826C and 826D supposed to come with the standard Medeco military compliment of three keys, two being round-bow Operation keys and one being a square headed Control key? I've seen auctions with various permutations including 2 keys (both round, one control and one operator) and 3 keys (all round bow, 2 operator and 1 control)
2. Which locks and/or cores are supposed to come with the metal key tag regarding "Control key, do not issue" - I've seen these at least with the Hi-shear, 833 and either 826C or 826D, but not sure if the same applies for the other of the 826, the 831 and the 951
3. Are all of these supposed to come with an S&G operations sheet (user manual)?
4. Do the 831, 833, and 826 variants come in a military and non-military version similar to the 951/C? And if so, what are the variants and how do we verify them?
5. I've noticed the 833 referred to as an 833C - is this the same as the 951 in that it comes in military (833) and civilian (833C) variants? What about the 831?
6. Are there any identifying features that I should look for in an 826 or 831 to tell which version is which? (such as the "US Government Property" or UID stamps on the 951)
Phew! Lot of questions I know. If it's any consolation, by filling in any of the blanks you'll be helping everyone

Quick update - I have a few updates on 'reliable authority' but feel free to correct if I'm wrong:
* Cylinder green colouring only started at the 833, so the 831 (and I assume the 826 variants) won't have this
* The metal "Control key, do not issue" key tag availability depends on issue date - apparently some 831 and 826 NIB were supplied with these and some weren't