So I ordered an AR-10 build kit from Seekins to build a nice "precision" gun. I'd like to also build an upper with a shorter 308 barrel and with a lighter handguard. Problem is that Seekins kit come with the warning "we do not recommend interchanging our receivers with other SR25 receivers to ensure the best receivers fit." Is that just a standard CYA or are their receiver sets really that tight. If it isnt a big deal, what have you guys used that works?
Seekins SP10 upper compatibility
- Thread starter srt-4_uk
- Start date
AR10s are far from standard if at all with some basic possible congruencies. An upper from an SP10 will not fit on anything else.
AR10s do not work like AR15s, which do have some compatibility.
Some exceptions where some large frames do work are...LMT, Larue, and KAC. Where I’ve seen a larue upper be used with an LMT MWS lower.
If you wish to get an upper build with an SP10 compatible upper that will work with your lower, you need to buy a build kit from Seekins and the needed parts and a barrel from Seekins to ensure correct headspace if you wish to reuse your existing bcg.
If you build a whole new Upper using using the Seekins build kit, you can actually use any upper parts you want as long as they are matched, such as JP parts for example.
Here is my build using JP parts and Seekins build kit. In my case I used a Krieger barrel and JP bcg, bolt and SLR gas block.
AR10s do not work like AR15s, which do have some compatibility.
Some exceptions where some large frames do work are...LMT, Larue, and KAC. Where I’ve seen a larue upper be used with an LMT MWS lower.
If you wish to get an upper build with an SP10 compatible upper that will work with your lower, you need to buy a build kit from Seekins and the needed parts and a barrel from Seekins to ensure correct headspace if you wish to reuse your existing bcg.
If you build a whole new Upper using using the Seekins build kit, you can actually use any upper parts you want as long as they are matched, such as JP parts for example.
Here is my build using JP parts and Seekins build kit. In my case I used a Krieger barrel and JP bcg, bolt and SLR gas block.
Sorry I wasn't clear. I bought the SP10 upper, lower, handguard kit to build a 6.5CM.
I'd like to build another complete upper to drop onto my Seekins SP10 lower, but Seekins only sells kits so I can't get their upper.
Has anyone put a different mfg upper onto their SP10 lower or do I have to do another complete build? I'm aware there isn't a "standard" but I also know that some uppers can go onto different lowers. Just curious if anyone had done it with a Seekins.
I'd like to build another complete upper to drop onto my Seekins SP10 lower, but Seekins only sells kits so I can't get their upper.
Has anyone put a different mfg upper onto their SP10 lower or do I have to do another complete build? I'm aware there isn't a "standard" but I also know that some uppers can go onto different lowers. Just curious if anyone had done it with a Seekins.
You can’t. Glen’s stuff is highly proprietary and unique. You’ll have to buy a whole new kit.
That said, call them and see if they will split it for you. They are usually really helpful.
I was a bit redundant and not clear on my other post, sorry.
That said, call them and see if they will split it for you. They are usually really helpful.
I was a bit redundant and not clear on my other post, sorry.
Been curious about this in the past but not where I could check a couple. Looks like an Armalite would fit but it won't (at least one of the older ones), close but pins were off a hair. A complete LaRue PredatOBR upper went right on with tight lockup (a little gap in the fit) and seemed to cycle/dry fire as it should. A stripped Matrix went on but was loose and with sloppier fit than the LaRue. Not saying you should do it or that it can/can't be done but there's a quick test of 3 different uppers on an SP10. There are other mfgs with similar patterns and one or more might be fine but easiest is probably to try to get an actual Seekins upper.
Wonder why they dont sell a striped upper.
Whos barrel extension did you use and how tight or loose was it in the seekins upper?
Whos barrel extension did you use and how tight or loose was it in the seekins upper?
If you're going to have to go with something other than Seekins, you might be ahead of the game to just build another lower. And then another, and then ......... Plus if you get another SP10 upper it's going to be for the big SP3R handguard.
The barrel extension is from Krieger, that’s where I got the barrel, it’s headspaced to a JP bolt. They can also sell you a JP bolt. The bcg is JP. I used a SCS for the buffer/spring.
The tolerance was fine it wasn’t loose or too tight. I didn’t have to modify anything at all for it all to fit.
Moot point since I think the only way to get a large frame LaRue upper is to buy the ultimate upper kit making it more than the complete Seekins builders set. And I know physically fitting isn't the whole story, but I'm curious, what is it about a LaRue upper that makes it not work on a SP10 lower?
Damn, this thread reminds me I want to get a Maten receiver set while there are still a few available!
Damn, this thread reminds me I want to get a Maten receiver set while there are still a few available!
Last edited:
Well shit, when I tried and OBR, I could not get the thing to close. Good to know.
Haven't fired it that way but just for kicks I stuck 10rds in a pmag and cycled them through w/o any issues. Gets me to thinking though. It would be neat if Seekins offered a large frame upper with a more typical barrel nut/handguard setup. I know that's not what the SP10 is intended to be and there's probably a reason they don't offer but for those with an SP10 lower it would be nice to be able to build another upper for it.
At any rate, this thread cost me $600+ for a Maten receiver/handguard set!
At any rate, this thread cost me $600+ for a Maten receiver/handguard set!
Shipping today. I need another LF AR like I need a hole in my head. I'll check how it fits the SP10.
Just as an update. Seekins responded back. They dont sell uppers separately. They said they based the design off the SR25 but due do varying tolerances, dont know what will or wont fit.
Given the lack of precision I need for the short 308, I'll probably just build an Aero and call it a day.
Given the lack of precision I need for the short 308, I'll probably just build an Aero and call it a day.
The Maten came in and fit nicely but the SP10 pins are .003 larger and, despite hole alignment, wouldn't go in. Not going to modify (unless I come across another Maten upper for cheap) but I'd bet the Maten with the holes reamed a tad would work just fine.
Per Glen Seekins, it’s their own. The used to use armalite, but had issues with availability.
Kinda off topic but is there a Handguard similar to the Seekins one on the Sp10 that fits the Lr 308 pattern (in this case a Stag 10)? I know Seekins doesn't make one. We have retarded gun laws up here in Canada and AR15/AR10s are limited to being used at a range but somehow the Stag 10 isn't considered an AR10 and I can use it anywhere that it's safe to shoot. Anyways, I can't seem to find a nice flat bottom handguard for it. Hell, someone oughta make one with an integrated full-length RRS dovetail...
Yes, I am replying to an old thread, but hey, I did search.
Anyone gotten another brand complete upper to work with their Seekins SP10?
I ask as I just got a used Seekins SP10 this week!
I am wanting a 6.5 CM upper for it.
Anyone gotten another brand complete upper to work with their Seekins SP10?
I ask as I just got a used Seekins SP10 this week!
I am wanting a 6.5 CM upper for it.
Reviving this but anyone confirm on an upper alternative for their sp10? I have a 22 creed barrel coming in and want to build another upper to run on my sp10.
Tried digging through your post history to avoid reviving a dead thread, but it seems you're *fairly* active and thus there was a lot to dig through, so I figured I'd ask here in case anyone else has similar questions. How have you liked / change this build since putting it together? I'm coming from an extended upper LMT MWS which is an absolute pig to carry around and just picked up a builders kit courtesry of @coraxdefence. My plan is to run a 20" Proof 6.5cm barrel to try to keep weight down, but I'm clueless on what to run for a bcg / buffer setup.
Do you plan to run suppressed? That will dictate your buffer spring and buffer weight. Keep in mind the buffer tube too.
I believe proof uses a JP bolt, call them to confirm.
The most flexibility I found has been with a JP full mass BCG or VMOS bcg and their g2 silent capture. You can configure the VMOS and silent capture weight, H2, H3, etc.
To get the best performance of a 65cm I’d go with 22” barrel.
Your bolt should have a small diameter firing pin.
The adjustable gas block should be a good brand like Superlative Arms or something similar.
Here is what proof recommends on their site.
Recommended components:
Full Mass Bolt Carrier Group
Full Mass Buffer
Adjustable Gas Block
* All barrels with Intermediate, Rifle +1, Rifle +2, and Rifle +3 gas systems include the proper gas tube.
* Our AR-10 barrels use a deep feed system that makes the feed ramps compatible with the feed ramps in the lower receivers of both DPMS and Armalite style rifles.
* It is recommended to double check and ensure proper headspace before firing your rifle.
Plan to run it suppressed 90% of the time. Was leaning towards a ultra 5 unless you think there's a reason to step up to the 7. It turns out I'm not the first in line for the builders kit, so this project may turn into buying a complete SP10 and then dropping the barrel I want into it.
This is exactly what I did. I had an sp10 and when that barrel shit the bed I put on a Krieger.
Craddock precision does good work when you are ready for it. All you do is send the upper and they can do the rest. They key is headspace, +2 gas system, and adjustable GB.
Will tell you that the ultra 7 is the ticket vs 5. I have a 5 and 7. My gun works best with a 7. If your running suppresses a good gas block, full mass bcg and heavy buffer will be best. Be prepared to keep the bcg and everything else quite wet with oil.
Suppressed gets the gas guns super dirty. Clean the gun and bcg after each suppressed session. I don’t use my can as often because of how nasty it gets.
Managed to get a builders kit so this build is back on my radar. Appreciate the suggestion for the 7 over the 5, just ordered it. For the buffer tube, what is best? My plan was to use a Vltor A5 tube. Is that the correct length? I know LMT's 308 tube is *ever* so slightly different in length, so wanted to ask what the best option is here.
I run a JP H2 SCS in all my SP10's with exceptional results, that way you can run a standard carbine Buffer Tube or rifle length with the spacer that is provided.
I've lurked some of your posts on other SP10 threads. Seeing as you've put more than a couple of these together, is there any benefit to running a rifle length tube with the spacer, or is it simplest to run in a normal carbine tube? Planning to go JP FMOS BCG, Proof 20" 6.5CM (+2 gas), Seekins adjustable gas block and Ultra 7 can.
JP SCS have a fixed rate of travel so it makes absolutely no difference what your tube length is, so honestly the Carbine Tube has the advantage because you don't need a spacer.
You're good, it will put you exactly 1" past your handguard from the crown of your muzzle. It would look like this with a MB on.
Just be aware it's going to kick a shit tune of Carbon on your handguard so better go with black..
