Parts for SR-762 builds

[eunichron]

Primary Arms discount on the SR-762 lowers is up again. $69.99 while they last. I have all the receivers I need for the builds I want, so I won't be purchasing more.

I did finally get a response from Ruger customer service regarding parts availability. They only confirmed that they no longer have parts available for purchase, and that any Armalite upper should mate with their lower.

A few of the parts I ordered from Numrich/Gun Parts Corp arrived today. Pivot pins and bolt catch roll pins. The pivot pins are Ruger OEM part #NS01066 and measure at 1.3500" long, not including the head. They are .2745" wide. This matches dimensions I've seen for Armalite pins. I think it is safe to say any Armalite compatible pins are good to go for these Ruger lowers.

The bolt catch roll pin is listed in the manual for both the SR-556 and SR-762, and it measures within spec for a standard AR15 bolt catch roll pin. I paid $7 each for these Ruger OEM pins, don't pay that much. Use whatever you can salvage from a parts kit or order them from McMaster-Carr (3/32" x 1/2" coiled spring pin part #91598A204).

Next steps will be ordering one each of the Stag10 and DB10 uppers and some more Armalite small parts to see how they match up.

[Armed Eye Doc]

You are giving some excellent information on a large frame receiver that will be useful for some unknown lurker in the future.  You are what this forum is about.

[Armed Eye Doc]

Diamondback DB10 and Ruger SR762 will mate to each other and cycle.  I was not in a place to test fire though.

Top is a Ruger upper on a DB lower.  Bottom is reversed.

[98Z5V]

Good info!  So, you won't get any info from Matrix Aerospace about these now, because they changed their own design.  However,Matrix made all those uppers and lowers for Ruger,  from 2013 to 2018.  With that said, you can follow what other Matrix owners had to do to complete their receiver sets and get them running.

Here's my .338 Federal Matrix gun:

 

[Belt Fed]

The takedown pin on the last Aero lower i built was too short. it still worked but does not come even with the hole.

Edited October 12 by Belt Fed

[eunichron]

On 10/11/2026 at 3:51 PM, Armed Eye Doc said:

Diamondback DB10 and Ruger SR762 will mate to each other and cycle.  I was not in a place to test fire though.

Top is a Ruger upper on a DB lower.  Bottom is reversed.

Excellent!

My only update is that I have no updates at the moment. Great to have confirmation on the DB10 upper, but they're out of stock on the website at the moment, so I haven't been able to get an order in. I have a Stag 10 upper on order that's estimated to ship in the next few weeks. I've been finishing up some AR15 builds while I wait on stock notifications.

[98Z5V]

I've got a couple STAGs and one Matrix.  The Matrix was identical to the SR-762.  I can mate them together next week and see if they fit.

[eunichron]

Update: Of mice and men and LPKs...

Sorry, bit of a wall of text ahead so here's the tl;dr - don't bother buying a bundled LPK. It'll be better to piece together your own buying single parts. Armalite pins, LR-308/SR-25 bolt catch, LR-308/SR-25 magazine catch. The rest can be AR15 parts.

I ordered one each of an AR10(A) and AR10(B) lower parts kit from EveryGunPart. Great place to deal with, the parts kits were shipped quick. No complaints about them as a vendor. These are probably the fanciest LPKs I've ever purchased, and I've assembled thousands of ARs at this point (former SOT). 

The good news - Armalite pivot and takedown pins will work in the Ruger. They fit dimensionally, the one small difference is the heads of the Armalite pivot pins were milled slightly smaller, making for a little gap between the head of the pin and the receiver spring housing. Not a big deal, it doesn't even show up well in photos. I'll tack that up to variance in tolerances. I'll be sticking with the Ruger factory pins because of the nicer fit, and because I'm salty I spent so much on them compared to the Armalite pins. 

I ordered one of each kit because there was still at least one unknown; the bolt catch. Ruger told me the lowers use a standard AR10 lower parts kit, but didn't specify A or B pattern. I assumed A pattern since that is the Armalite pattern that uses LR-308/SR-25 magazines, same as the Ruger, but photos of the factory assembled SR-762 lowers look like they use either a DPMS/LR-308 or Armalite B pattern bolt catch. I bought the B pattern parts kit just to test the information I got direct from Ruger.

The photo below of the 4 receivers lined up are 1. Mega Arms with an LR-308 bolt catch, SR-762 #1 with an Armalite A pattern bolt catch, SR-762 with an Armalite B pattern bolt catch, and one of my generic DPMS pattern receivers with another LR-308 pattern bolt catch (pretty sure that was a CMMG kit, could also be from a Luth-AR kit, I don't remember). The Armalite B pattern bolt catch doesn't fit, it's just slightly too wide to fit in the bolt catch slot, and I won't even bother trying to modify or force it for the following reason.The actual lip/tab/notch that catches the magazine follower is a few hundredths short on the B pattern catch. It ain't gonna work. That's what I figured considering the B pattern guns were designed to use modified M14 mags, but I wanted to be sure anyway. I did dry fit the A pattern bolt catch and inserted a magazine (PMAG), which looks like it will work, but I won't be able to do more testing of the bolt catch until I get uppers in and built. Given that it looks like Ruger used LR-308 pattern bolt catch on the factory guns, I'd go with that.

Armalite A pattern bolt catch width: .445

DPMS/LR-308 bolt catch width: .442

Armalite B pattern bolt catch width: .411 +/- a few thousandths (this was really hard to measure because the tab is rounded, but it most often came in around .410)

The bad news...

Doing the bolt catch dry fitting presented an unexpected issue; magazine catches. Aside from the bolt catches the parts kits included standard AR15 spec parts, including the magazine catch. I don't know if this was EGP piecing the kits together, or if Armalite actually uses standard AR15 parts in their lowers, but this was the first time I'd seen an AR15 mag catch in a large frame parts kit. It's not going to work... it will install, it fits dimensionally, but the threaded portion of the mag catch is not long enough to seat properly in the magazine release and sits shallow. It works, but not good enough. I was planning to put Norgon Heavy ambi magazine releases in both lowers anyway, so I'll have to see how those fit, but I'm going to go ahead and assume that you should order an LR-308 magazine catch for these lowers.

So here's what I've gathered so far:

Takedown/pivot pins: Armalite pins are the proper pins. If you care about final fit and finish, try to track down some Ruger factory pins, but I'm pretty sure I bought the last ones. Any others I've seen since I ordered mine have been on scam sites that will steal your credit card info.

Bolt catch: Armalite A pattern or LR-308, remains to be seen which one will actually work in a function test but my gut feeling says LR-308 is the way to go.

Magazine catch: LR-308

Everything else: Standard AR15 parts will work, a spacer will be needed for the takedown pin detent and spring. I have a large collection of hex keys, 5/64 seems to be the perfect diameter to plug the hole. Length I'm guessing will need to be about 1/4", I'll refine that when I get to actually assembling.

On that topic of uppers... DB10 uppers are still out of stock. The STAG10 upper I have on order with OpticsPlanet keeps having its estimated ship date pushed back. I reached out to Stag for any information on when production might pick up, to which they said they aren't sure. I have some other things to decide before I complete these lowers, namely receiver extensions and stocks, but it looks like I won't be finishing these guns any time soon.

Edited Wednesday at 01:49 AM by eunichron

[98Z5V]

2 hours ago, eunichron said:

I ordered one of each kit because there was still at least one unknown; the bolt catch.

We have a Bolt Catch Study here,  right on the board.  That might have saved you some time. 

 

[eunichron]

7 hours ago, 98Z5V said:

We have a Bolt Catch Study here,  right on the board.  That might have saved you some time. 

 

Weird, I searched around before ordering and that thread never popped up.

[Armed Eye Doc]

Primary Arms has them on sale again but they dropped the price to $59.99.

https://www.primaryarms.com/ruger-ar10-762-stripped-lower-receiver

Edited yesterday at 12:46 AM by Armed Eye Doc

[Belt Fed]

2 hours ago, Armed Eye Doc said:

Primary Arms has them on sale again but they dropped the price to $59.99.

https://www.primaryarms.com/ruger-ar10-762-stripped-lower-receiver

That is a heckuva good price, i may have to order one of them or two. thanks for posting it.

[eunichron]

They were already a solid deal at $69.99. My only regret so far is the lack of options for uppers.