Parts for SR-762 builds

[eunichron]

Hey all. So, I'm not new to this forum, been coming here for over a decade, but I suppose there was a backend change at some point and lost my account. Anyway...

I (maybe stupidly) jumped on Primary Arms' recent deal on stripped SR-762 lowers. Bought a pair of them for some builds I've had in mind. I'm no stranger to building large frame ARs, and thought it wouldn't be too difficult to find parts to finish the receivers and find matching uppers even with the rifles being out of production for several years.

My hope was to find some Ruger or AR10A small parts to do some further test fitting to see what sticks... Numrich has a decent amount of Ruger small parts, but no takedown pins in stock. I reached out to Ruger but have not received a response yet. No dice on any Armalite small parts A or B series.

Down to brass tacks... I'm looking for a source on these parts in order to finish the receivers and build a couple rifles:

• Small parts in general, but especially pivot and takedown pins, including springs - the takedown detent spring is longer on the Ruger since it is installed through the rear of the receiver.
• Bolt catch - as best I can tell an AR10A bolt catch should fit
• Upper receiver with DPMS threads - I've looked at the Centurion Mk11 and HTX Concepts SR25. Both look promising. I know the likelihood of them using the same pin size is next to nil.

Thanks.

[eunichron]

Centurion got back to me and confirmed their Mk11 upper will not mate with the SR-762 lower. He did lead me on to the Stag10 upper, which I've seen mentioned in other forums, but no confirmations that it does mate with the SR-762. Looks like OpticsPlanet has a few Stag10 uppers in stock, might pick one up for some test fitting.

Edited Tuesday at 02:13 PM by eunichron
more information

[Armed Eye Doc]

That's good information for the next guy looking to do the same.  I saw those lowers.  I was tempted but I have a couple of Diamondback large frame receiver sets for future projects.

[Armed Eye Doc]

FYI, Diamondback is Armalite pattern and will not work for you.

[98Z5V]

12 hours ago, eunichron said:

the Stag10 upper,

The Aero Precision-produced STAG-10 uppers should work.  I have two of them (full receiver sets), and I actually prefer them over the standard M5 sets.

They are Armalite/SR-25 cut, SR-25 pins and threading, which is DPMS-sized.

Aero Precision sent out the STAG-10 lowers with takedown and pivot pins, just to make sure they worked with the lowers. They were specific to the lowers themselves, due to the lower machining.

The important measurement for you to get is the diameter of the pin hole, and the width across the lower receiver at both those pin locations.  On the Ruger.   If you can get me that information, I can point you in the direction of pins that will work. 

Welcome back.  

[98Z5V]

Oh, for the takedown detent and spring, AR15 parts will work.  The key is cutting a piece of stiff wire to the proper length to take up that extra distance.  On the original DPMS LR-308 lower parts kit, they used a stainless steel rod, sized properly, with standard AR15 pin and spring. Detent goes in, spring goes in, rod goes in, from the back.

That later changed, for DPMS, and both went in from the bottom, and were captured by the pistol grip. 

Edited Wednesday at 01:59 AM by 98Z5V

[eunichron]

51 minutes ago, 98Z5V said:

The important measurement for you to get is the diameter of the pin hole, and the width across the lower receiver at both those pin locations.  On the Ruger.   If you can get me that information, I can point you in the direction of pins that will work. 

I'm on the road right now so can't gage the pin holes for a couple days, but I did test fit my MATEN upper (a newer Zev production) on the Ruger after getting them home. The Mega's pins are just slightly oversized for the Ruger's pin holes. They will fit with some force, so that leads me to believe the Ruger receivers are sized for Armalite pins.

I'll know for sure come Friday.

1 hour ago, 98Z5V said:

The key is cutting a piece of stiff wire to the proper length to take up that extra distance.  On the original DPMS LR-308 lower parts kit, they used a stainless steel rod, sized properly, with standard AR15 pin and spring. Detent goes in, spring goes in, rod goes in, from the back.

That was exactly my thought if I wasn't able to source an original lengthened spring. I did find this listing for BAD pins with an option for a rear location spring. I might just reach out to them and see if they'd be willing to send me a few springs.

[98Z5V]

1 hour ago, eunichron said:

I did find this listing for BAD pins with an option for a rear location spring.

They will not steer you wrong.  I've been a devotee of them since May 2010.  They make great stuff, don't lie, do what they say and say what they do...   

I was waiting for your measurements before I suggested them, directly.  

Great people, great parts.  

Edited Wednesday at 03:15 AM by 98Z5V

[eunichron]

Got some measurements in. Won't be able to take a pin gauge to the holes to confirm the caliper measurement until next week, but I'm pretty confident in these measurements.

• Takedown/pivot pin hole: .2770/.2775
• Receiver width at the pivot pin hole: 1.3335
• Receiver width at takedown pin hole: 1.1325

For s&gs and comparison's sake I took some pics of it next to my Mega lower:

 

[eunichron]

From the information I have that points to an Armalite pattern lower parts kit... which Armalite doesn't sell direct anymore.

Any guidance on where to find one, at least the pins, is most appreciated.

[Armed Eye Doc]

11 minutes ago, eunichron said:

Armalite pattern lower parts kit

Here is an AR10B LPK

https://everygunpart.com/armalite-ar-10-b-lower-parts-kit-minus-trigger-and-grip-10lrpk-armalite-parts/

And the AR10A LPK

https://everygunpart.com/armalite-ar10-a-lower-parts-kit-no-trigger-grip-a10lrpk-armalite-parts/

I don't know the difference between them or if the pins you are wanting will fit your Ruger, but they are available.  Everygunpart.com is a good company to buy from.  That is who Armalite farmed out their parts retail to.

That Ruger is definitely an Armalite cut lower.

[Armed Eye Doc]

It will be a couple of weeks, but I may be able to see if a Ruger will work with a Diamondback.  I'll have to ask my brother to bring his wife's Ruger.

[shooterrex]

1 hour ago, Armed Eye Doc said:

It will be a couple of weeks, but I may be able to see if a Ruger will work with a Diamondback.  I'll have to ask my brother to bring his wife's Ruger.

Or ask @Belt Fed I know he has Diamondbacks and I would be surprised if he doesn't have a Ruger. at least he can measure the Diamondbacks. 

[eunichron]

I know some topics on other forums discuss Matrix being the OEM for both Ruger and Diamondback and that they're more or less interchangeable, but that was all pre-2021. It seems Diamondback has changed their uppers since then and they're now Armalite threaded. I'd really like to stick with DPMS threads on the upper for more compatibility.

I know there are companies that will sell an Armalite barrel nut with their handguards. So that brings up something else I've never been clear on; barrel extensions and headspace. I know they used to be different between DPMS and the AR10B, but did Armalite go with DPMS dimensions on the barrels for the AR10A? I.e. will an 18tpi upper and barrel nut work on a DPMS pattern barrel?

12 hours ago, Armed Eye Doc said:

Here is an AR10B LPK

https://everygunpart.com/armalite-ar-10-b-lower-parts-kit-minus-trigger-and-grip-10lrpk-armalite-parts/

And the AR10A LPK

https://everygunpart.com/armalite-ar10-a-lower-parts-kit-no-trigger-grip-a10lrpk-armalite-parts/

I don't know how much time I spent looking around everygunpart and didn't find those. Thanks.

[98Z5V]

On 9/26/2026 at 4:04 PM, eunichron said:

• Takedown/pivot pin hole: .2770/.2775
• Receiver width at the pivot pin hole: 1.3335
• Receiver width at takedown pin hole: 1.1325

I have BAD Enhanced pins in my Aero M5 7mm-08 gun.  The diameter works for what you listed, but the Aero M5 receiver has difference widths across the hole.

Pivot pin area width on the M5 = 1.550"

Takedown area width on the M5 is 1.0335"

Both BAD pins protrude out of the other side of the lower, when snapped in place, by 0.069"...