Seekins SP10 upper compatibility

Aug 6, 2011
277
58
28
Nebraska
#1
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?
 

Saf3sh00t3r

Gen. Sum Tin Wong
Feb 10, 2017
1,671
30
48
San Antonio, TX
#2
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.

24671C00-7765-47B8-978D-918F7907D6B3.jpeg

5B95CA66-E383-4D5B-966B-D752C90D0549.jpeg
 
Aug 6, 2011
277
58
28
Nebraska
#3
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.
 

Saf3sh00t3r

Gen. Sum Tin Wong
Feb 10, 2017
1,671
30
48
San Antonio, TX
#4
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.
 

Waorani

Back to the Island
Feb 14, 2017
898
552
93
Auburn, AL
#5
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.
 
Aug 6, 2011
277
58
28
Nebraska
#6
I sent an email to Seekins to see if they would sell just the upper/handguard. If not, I can get a LaRue upper and cross my fingers that it works. If it doesn't work, looks like I'm building a LaRue. This 308 stuff is.........fun?
 

whatsupdoc

Duck season
Dec 12, 2017
407
242
43
Long Island NY
#7
Wonder why they dont sell a striped upper.
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.

View attachment 6978548

View attachment 6978549
Whos barrel extension did you use and how tight or loose was it in the seekins upper?
 

Waorani

Back to the Island
Feb 14, 2017
898
552
93
Auburn, AL
#8
I sent an email to Seekins to see if they would sell just the upper/handguard. If not, I can get a LaRue upper and cross my fingers that it works. If it doesn't work, looks like I'm building a LaRue. This 308 stuff is.........fun?
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.
 
Likes: XLR308

Saf3sh00t3r

Gen. Sum Tin Wong
Feb 10, 2017
1,671
30
48
San Antonio, TX
#9
I sent an email to Seekins to see if they would sell just the upper/handguard. If not, I can get a LaRue upper and cross my fingers that it works. If it doesn't work, looks like I'm building a LaRue. This 308 stuff is.........fun?
It won’t work. LMT and KAC, are the only ones that will work with Larue.
 

Saf3sh00t3r

Gen. Sum Tin Wong
Feb 10, 2017
1,671
30
48
San Antonio, TX
#10
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?
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.
 

Waorani

Back to the Island
Feb 14, 2017
898
552
93
Auburn, AL
#11
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!

IMG_0080.jpg
 
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Saf3sh00t3r

Gen. Sum Tin Wong
Feb 10, 2017
1,671
30
48
San Antonio, TX
#12
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!

View attachment 6978656
Well shit, when I tried and OBR, I could not get the thing to close. Good to know.
 

Waorani

Back to the Island
Feb 14, 2017
898
552
93
Auburn, AL
#13
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!
 
Aug 6, 2011
277
58
28
Nebraska
#18
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.
 

Waorani

Back to the Island
Feb 14, 2017
898
552
93
Auburn, AL
#19
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.