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Buildus Interruptus - Printable Version

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Buildus Interruptus - PVBoom - 06-15-2020

So after 2 years and change I am finally putting together the 2 Grendel builds I got parts for.
A rifle and a pistol

BOM (and original prices paid back in 2017/2018 for historical purposes)


Rifle Build (New) 6.5 Grendel


  1. Faxon 18" .750 Nitrided (mid length) 195 GB0
  2. Monster bolt 55 GB
  3. Magpul MOE FDE Rifle stock 68 Amazon
  4. Larue Cheek RISR
  5. Spikes gas tube med. melonite 16 Joe Bob Outfitters
  6. Geissele LPK 42 Brownells
  7. A2 Rifle Stock Completion Kit 38 Joe Bob Outfitters
  8. BCM Gunfighter CH mod 4 50 Brownells
  9. AP Enhanced Upper/MLOK HG 15 219 GraniteRidge
  10. Sharps Blem NPR BCG 139 GraniteRidge
  11. JTM Pistol Grip 12 Seal 6 Tactical
  12. Superlative Arms adj gas block 90 Midway
  13. VG6 Gamma 65 55 Brownells
  14. Magpul BAD Lever 28 Brownells
  15. Cerakote Diamond Lower 67 Cerakoters
  16. Larue MBT Trigger 99 Larue Divorce Sale
  17. [FONT=&amp]UTG Leapers Light Recon M-LOK legs 38 OpticsPlanet[/FONT]
  18. [FONT=&amp]AADMOUNT 30 mm blem 229 Aadland[/FONT]
  19. SWFA SS HD 3-9x42 450 SWFA

The lower is a Diamond Series billet aluminum from SOCOM, I bought back in 2000.
It has extra screws for trigger adjusting and upper/lower lockup.
It also has a non-standard bolt release installation with no external lugs for the pin.

For some inane reason I chose a metallic blue finish. Don't ask why.
So when I decided to make this build, I wanted FDE, so I had it Cerakoted locally.

Here are the instructions the lower came with:

[ATTACH=CONFIG]16317[/ATTACH]

I didn't find these until after I got stymied on the bolt release. So I didn't do any of the other suggested mods.

So this has halted my build, I ordered some pins and set screws from Brownells that I think should work.
I checked with a caliper using a takedown pin detent which fit through the bolt release pin holes
The hole for the pin goes forward through the lower to where it is scalloped out for the name. At that end, there are threads.

So here is a look at the lower and the issue. The lower is complete, except for the bolt release and the Larue RISR.

[ATTACH=CONFIG]16315[/ATTACH]

Later on I got the barrel in and seated, but I will do some more checking before I red loctite it in.

Here is the lower with AP M4E1 upper and handguard (barrel not in)

[ATTACH=CONFIG]16316[/ATTACH]

Buildus Interruptus - Lemonaid - 06-15-2020

It's unclear to me what your problem with the bolt release is. More details please.

Buildus Interruptus - PVBoom - 06-15-2020

Lemonaid Wrote:It's unclear to me what your problem with the bolt release is. More details please.

Mil spec lowers have external lugs to take the retention pin of the bolt release/catch. Mine doesn't.
Look at the picture of my lower, increase magnification as needed. The vertical slot above the mag release/catch is where it mounts.
The retention pin holes are internal to the lower, not external as per mil spec.

Buildus Interruptus - VASCAR2 - 06-16-2020

It looks like the long pin rest in a slot of the lower receiver and held in place by a screw just to the rear of the mag well. I figure the screw holds the pivot pin in the correct location in the lower receiver. A picture of the top of the receiver would confirm there is room for the long pin to accept the bolt catch lever in the correct position. Looks like the extra screw hole is the method of retaining the bolt catch pin compared to the traditional lower receiver. This is the first time I’ve seen a lower receiver configured in this way but once the upper and lower are pinned together the bolt catch just needs a pivot point because it can only move a small amount with the upper and lower pinned together.

Buildus Interruptus - PVBoom - 06-16-2020

Yeah, here is a shot showing where the long pin goes, and the threaded end to take a set screw.

[ATTACH=CONFIG]16318[/ATTACH]

Buildus Interruptus - PVBoom - 06-26-2020

OK. An update. I did a lot more reading here, on lapping and barrel mounting. I also found a discussion about some chamber polishing due to dirty chambers with spurs in them. This was for Faxon GB barrels which were scraping the ejected brass. That drove me down a paranoid rathole so I was working on some polishing to take care of that. Anyways, I got all of that done and mounted the barrel. I think I am OK with the chamber end.

[ATTACH=CONFIG]16365[/ATTACH]

So I lapped, and its questionable how much it helped, because it was tight as can be getting the tool down there (Brownells) on my cerakoted upper. So I lapped the cerakoted receiver face and think it did its job. I cleaned up the barrel end and receiver with some brake cleaning fluid, let it dry then mounted the barrel with anti-seize on the nut threads and loctite blue on the receiver. And a whole bunch of wiping up after I torgued it down because I used too much loctite. I did a torque to 30, loosen, torque to 35, loosen, torque to 40, loosen then final torque to 45.

[ATTACH=CONFIG]16366[/ATTACH]

In the meanwhile the pins and set screws came in and I got the bolt release/catch installed. It took a .75 inch pin, a .5 inch pin and a set screw to get it done.

I also reversed on the stock and buffer. I don't like the Magpul MOE rifle stock and want to go carbine. I also went back to what I wanted in the first place, a Luth-AR adjustable stock, the MBA-3 for carbine length. OK, its not the uber PRS. But its lighter (literally and fiscally) and I wanted to try it ever since I heard about the company. So I am doing that and you can't stop me... I think. I got the stock in, and of course their FDE doesn't match the Magpul FDE (which is what I had the upper/lower cerakoted in) so I broke out the Brownells rattle can and am taking care of it. The carbine buffer is en route and after everything dries I can continue assembling tomorrow.


I have also decided I don't want a pistol and am throwing those parts up for sale (barrel moved already). I am more in love with precision (and not getting concussed) and am hopping on Rebby's Lilja GB train for a 16". Its gonna get a lower quality upper lower, but I lapped it and it should be fine. That will also be carbine. I need to see what gas block is shorter, the Superlative or the Seekins, since the AP Atlas S-1 handguard is very slim (1.3" ID) so I will need the shorter AGB for the Lilja buiild. The other goes on this build (Faxon 18").

Buildus Interruptus - FLshooter - 06-27-2020

If you are looking for accuracy, a Lilja barrel is a great choice.

Buildus Interruptus - Croak - 06-28-2020

I'm a Marine. We like concussions. Thanks for the barrel!

Buildus Interruptus - PVBoom - 06-28-2020

Range ready, or it will be after I lube it up and work the action a bit.

[ATTACH=CONFIG]16373[/ATTACH][ATTACH=CONFIG]16374[/ATTACH][ATTACH=CONFIG]16375[/ATTACH][ATTACH=CONFIG]16376[/ATTACH]

I had to wait for some feeler gauges to arrive for fitting the AGB. I used the toothpick fall through method as described by Sundog.


Yeah, the FDE doesn't match. I will live with it.
The upper and rail are AP FDE.
I had the lower cerakoted and asked for Magpul FDE.
The mount, scope caps, ring and the Luth AR-3 stock were rattlecanned with Brownells alumina in the shade people said was closed to Magpul FDE.

No idea when I will be able to hit up a range, but after 2 years I got this done. Just sheer pleasure doing this. Learning what I needed to, dealing with each obstacle at a time.
I also went overboard and ordered stuff to do a 2nd Grendel build, switching from pistol build (which I wanted to do before) to a 16" rifle.

Final Parts list (minus the Dagger Defense offset BUIS I removed):

  1. [FONT=&amp]Faxon 18" .750 Nitrided (mid)[/FONT]
  2. AP Enhanced Upper/MLOK HG 15" FDE
  3. SOCOM/Diamond Lower cerakoted magpul FDE
  4. Monster bolt, Sharpes BCG
  5. [FONT=&amp]Larue MBT Trigger[/FONT]
  6. Spikes melonited gas tube
  7. [FONT=&amp]Superlative Arms AGB[/FONT]
  8. [FONT=&amp]Geissele LPK [/FONT]
  9. BCM Carbine buffer kit
  10. [FONT=&amp]BCM Gunfighter CH[/FONT]
  11. [FONT=&amp]VG6 Gamma 65 (got a CAGE for it also)[/FONT]
  12. AADMOUNT 30 mm mount, scope covers, throw lever
  13. SWFA SS HD 3-9 x 42
  14. Luth AR MBA-3 Stock w/ Limbsaver pad
  15. Royal Arms ARG Target Grip. I love the finger grooves on this for bench/target shooting, obviously not fit for all styles of shooting.


Buildus Interruptus - PVBoom - 07-27-2020

I swapped the mount to a LT204 LaRue C.A.N. QD SPR
I also did some cheek riser swapping between Luth-AR stocks.


[ATTACH=CONFIG]16517[/ATTACH][ATTACH=CONFIG]16518[/ATTACH][ATTACH=CONFIG]16519[/ATTACH]

Buildus Interruptus - VASCAR2 - 07-27-2020

Looks Good!

Buildus Interruptus - PVBoom - 10-27-2020

This saw some very light usage at the range. Test fired only, and I spent more time with the other Grendel.

Given the FDE variances, I am thinking of doing a Desert Fleck (Tropentarn) rattle can on this build.