Diamondback/Ruger SR762 upper swap

[2grim4U]

So... bought a SR762 a while back. Like the weapon but... got the itch to do something in a new upper. It took a lot of digging to find an upper that would fit because the Ruger uses a kinda hybrid upper with DPMS threads for the barrel nut, but the tapered (instead of radiused) lower/rear similar to Armalite. The original Ruger upper and lower forgings have Cerro Forge marks, so this shouldn't be too hard, right? Noooo. After some searching on one of the Ruger forums, someone had sourced finished uppers using the same forging that Ruger used from a company called Matrix Aerospace. Emailed Matrix, no joy there. Another compatible upper was an upper from Stag, but the profile was not the same and it didn't look right despite fitting the Ruger SR762 lower. Then, in a holy grail moment, I found the exact same upper that Matrix no longer sold from Daimondback. They were blowing them out at $79 and they had 9 in stock. I bought all of them.

They showed up and the fit and contour match is exactly the same as the original SR762 upper. Had the same Cerro Forge mark, BUT they were machined for a DI gas tube. Perfect! Now I have the challenge of trying to figure out what bolt carrier, barrel, nut, and handguard are going to be compatible with Diamondback/Ruger SR762 bastard that I'm trying to put together.

With 9 uppers to put together, well maybe 2 or 3, I have 2 calibers in mind: 6.5 CM (duh), and 7mm-08 (huh?). Maybe another 7.62N.

I haven't been able to find a one shop stop source of information to determine whit parts will fit which pattern large frame AR's with actual dimensions. The barrel nut threads are definately DPMS Ø and pitch, but I haven't found any info on the barrel extension OD/length to determine if there is any difference between Armalite and DPMS patterns as far as the barrel extension. Same for the bolt carrier. About all I've come away with so far is that the bolt has to match the barrel extension and Armalite/DPMS bolts/extensions are definitely different.

Any direction or sources of information greatly appreciated. Or, if anyone has some time to tell me what they have and post some pics and dimensions, I'll eventually figure it out. Hell, send me enough pics/dimensions and I'll model it in CAD and share.

 

[2grim4U]

Chime in if I'm wrong...

From what I've found out, if the upper is threaded for a DPMS barrel nut, then a DPMS pattern barrel/extension is used. So far, so good.

As far as the bolt carrier, all AR-10 clones are the same dimensions regardless if they are Armalite, DPMS, etc. However, the bolt is specific to Armalite or DPMS pattern. Not going to take any risks here, I'll buy a matching DPMS pattern BCG. Probably going with a matching JP HP bolt and a steel lightweight carrier.

Handguards are another matter. Different for Armalite and DPMS. Since it has DPMS threads, then I need to use a DPMS pattern handguard? Not so easy. Apparently DPMS manufactured a standard height pic rail upper and a low profile pic upper. The pic rail height dimensions on my Diamondback upper matches the original Roger SR762 pic rail height, but the dimension falls midway between the dimensions given on Midwests website. Looks like I'll have to call Midway for clarification.

The ejection port cover and forward assist are generic AR-10 pieces. Got those from Brownells and they fit perfect.

As far as who to get a barrel from, lots of choices. I do want to go with the 7mm-08 build first but there's not a lot of choices out there in this caliber. It's funny this caliber isn't more prolific in gas guns. Huge selection of 7mm bullets to choose from and 7mm caliber has great external ballistics. Did some load development a while back in a custom 700 action in 7mm-08 and we were getting just shy of 2,900 fps with 180gr slugs and Lapua SRP brass. No scary signs of overpressure. This was with a 24" barrel and a can attached. Not expecting the same results in a gas gun, but it's not going to stop me from trying. I'd be happy with this velocity with a 160gr slug in a GG.

 

[Raivkka]

Be interested to hear how this all works out for you.
I have the same rifle and I bought an extra upper and handguard from Matrix Aero several years ago.
Haven't built it yet but will someday.

 

[2grim4U]

Be interested to hear how this all works out for you.
I have the same rifle and I bought an extra upper and handguard from Matrix Aero several years ago.
Haven't built it yet but will someday.

It's unfortunate there hasn't been better standardization of the AR-10 platform. It seems that manufacturers make changes or adjustments just for the sake of being different. I can understand this from a business standpoint because you (as a business owner) want your customers to be chained to your company when it comes time to upgrade or buy parts for the weapon you purchase. But it makes it a pain in the ass when you want to build an AR-10.

The good thing is there are only a few manufacturers that have nothing in common with the DPMS platform, which is by far the most abundant. With the exception of Rock Rivers Arms, almost all bolt carriers have the same exterior dimensions with respect to how they fit inside the upper receiver. But, there are subtle differences with how some parts work together. Things like the bolt catch, firing pin, bolt to bolt carrier fit, and the pivot and takedown pins appear to be common gotchas...

Even though Ruger killed off the SR762, I think it was a business decision and not something wrong, or with insurmountable problems to fix. I have had no issues with mine. My only gripe was the recoil (fixed with a cheap muzzle brake), and the so so trigger. I could have spent a little time with some Wolf springs and a diamond hone and made the trigger work pretty well, but I just tossed in a Geissele SSA-E. Accuracy has typically been in the .2 to 1 mil range depending on the ammo and how bad of a day I'm having. Reliability has been good even with old surplus Indian ammo. Mags are mostly Magpul but I have some CPD (Duramag) magazines that I've become a fan of lately.

The one thing I like about the Ruger is that they use a forging from a well known forging supplier (Cerro Forge). And, the tail of the lower has a feature that I have not seen in very many AR-10 platform weapons. Ruger did do some smart things with the SR762. Just ahead of the threads for the buffer tube, there is a radiused support machined into the lower that supports the tail of the bolt carrier before it enters the buffer tube, much like Aero Precisions enhanced buffer tube. This keeps the bolt carrier aligned with the buffer tube before it enters. Nice touch.

I've read some horrible stories about buyers that have had serious problems with the SR762 and I wish I were able to actually see and analyze these 'problem children' to verify the fact that the issue is the fault of the weapon and not an owner that's a complete squid. There's also been a lot of inaccurate descriptions of how the hand guard and gas system attach. I've had mine apart down to stripping the barrel from the upper. It's overly complicated but not a fundamentally bad design.

For now, I'm looking and a Krieger barrel for the 7-08. I'm going to try to get my order in in the next few weeks. It's gonna cost me about $900 for the barrel, but there just isn't a whole lotta options out there, and the 7-08 will be my "show me the money" platform. The 7-08 may get put on the back burner for a 6.5CM just so I can get something together and make sure everything works.

Bolts and carriers for the Diamondback/Matrix upper are plentiful. Toolcraft and JP at the top of the list. Trigger will probably get swapped out for a Geissele High Speed Match. Got one of those in my 716 DMR G2 6.5 and am very pleased with it.

Optics and mount.... who knows yet. I might just borrow what I got on the SIG until I can verify that I haven't lost my mind.

 

[Hamm3r]

I am definitely interested in this. I like my SR762. It has shot very well for me and the gas piston was worked well for many different loads.
I like the idea of having another upper for it.
And like you, I put in the SSA-E trigger for a very nice improvement.
I wouldn't mind another upper with the piston setup though. Not set on it, but I like how it works on the SR762 for me.

 

[Islndbnd]

I am surprised that there is not more interest in building uppers for the Ruger. I would love to do a 6.5 CM upper for mine, so am anxious to see how this all goes for you. If you know of any other place to get one of the matrix uppers please post it.

 

[Raivkka]

At the start there were out of spec uppers. The bolt catch I believe it was. It would fail to hold the bolt back on last round. I could be wrong though. When I got my Ruger they immediately performed a warranty switch and I have never had problems with it. I have also put an Larue 2 stage trigger in it, no problems with that either.
I feel the recoil on that is pretty mild, I put a limbsaver butt pad on it. Seems good to me.
I found a company that has Amrmalite compatible setup, a Lothar SS barrel, BCD, Adj block, gas tube, thread protector for $677, this will be a DI setup. There prices just went up though.

I'm hoping the adjustable gas block will have enough adjustment to work with the stock buffer/buffer spring.

 

[Merle]

DPMS high profile and Armalite AR-10 are the same height. Any DPMS high profile handguard should work. The only difference between those two is the barrel nut thread pitch.

 

[GUNNER10]

Considering that most of the AR10 world is a case of who is copying who's homework, while trying not to get caught(sued), I wish you good luck in your adventure. I would suggest putting what does and does not work into a excel spreadsheet as there really is limited info on this subject.

 

[2grim4U]

So, I know this is an old thread, but with all of the chaos in the last year, most of my firearms projects got kicked to the curb with parts not being available, etc. I did manage to scrape together enough parts to build a 6.5CM and another 7.62N upper that fit the Ruger SR 7.62 lower. Parts were pretty straightforward. Diamondback went through an ownership change early last year and it looked like they were bailing out of the AR-10 clone market. Now, It looks like DB is back in the AR-10 clone business. They have uppers and lowers available.

The DB AR-10 clone appears to be compatible with the original Panther Arms/DPMS LR-308 excluding the actual upper and lowers, meaning all the parts that would fit a LR-308 should fit the Ruger/Diamondback. Uses the SR-25 pattern mags and the "DPMS Tall/High" handguard. The only issue I had to deal with is the pin for the dust cover is about .100" shallow. Don't know if this was a manufacturing oversight or DB uses a non-standard (as if there were any standard) dust cover pin. Both Uppers use Toolcraft BCG's, and I am using a 22" hybrid profile 6.5CM, and a 20" chrome plated 7.62N barrels, both from Criterion. I'm still contemplating a 7mm-08 upper. The 6.5CM is using a 15" PRI handguard and the 7.62N is using a 12.75" MI handguard. The 6.5 is using a Seekins adjustable gas block, and I think I have a Badger Ordnance block on the 7.62N.

The Ruger lower is using a Geissele adjustable match trigger, a LMT 308 DMR stock, Tubb flat wound buffer spring, and Ergo(?) vertical pistol grip.

I haven't had a lot of time at the range just because of the scarcity of reloading components. But I was able to functional test both uppers and get the optics on the paper. Both seem to function just fine.