Polymer AR 5.56 Pistol Project

[JDub]

Greetings Horde!!

I finally got off my duff and started my 80% lower pistol project. (Thanks to our fine legislators here in sunny CA. Single-Shot handgun exemption just got outlawed)

I wanted to do Grendel but am starting out 5.56 'cause it's mostly a just a range toy.

Naturally, I'd never dream of completing my build without the advice and consent of you guys here. Especially since am a total newb when it comes to anything < 16".

So let's kick this off, shall we?

Parts list:

JMT Gen2 Polymer 80% lower - FDE - $100
PSA lower parts kit with Magpul MOE K2 grip - FDE - $65
Phase 5 Hex2 Pistol buffer tube - Standard carbine buffer and spring - $60 (This lets you get the LOP out to 9.5" as opposed to the 7" LOP of the buffer alone)
Radical Firearms Upper 10.5" CrMo 1/7 5.56 chamber barrel, 9" free-float handguards(no-namo), Carbine gas, A2 flash hider - $240 (no bcg or charging handle) w/Coupon Code "SUMMERTIME" (10%) Had to buy SB15 with it.
Sigtac SB15 Wrist Stabilizer - $130
Magpul MBUS 2 front and rear BUIS - Black(Who gets light-colored sights? JK) - $80


So here are the questions that are swimming around in my head:

1) What bcg should I use? I have an AR15 one sitting around but should I get a FA BCG? What are your thoughts on NiB (Ares Armor has a NiB FA BGC for $99)?

2) Should I go with a heavier buffer? I have a JP Silent Capture Spring in my 20" HBAR. Should I start out with that instead of the standard carbine buffer and spring?

3) Thinking about upgrading my muzzle device and am considering either a Kaw Valley Linear Comp, Kineti-Tech muzzle brake with Sound Redirect (think muzzle brake with krink style shroud), and the infamous Noveske KX3/KX5. Will my gas system really benefit from having the KX3/5? I do want to divert the muzzle blast down range(which all of these will do) but is the flaming pig really worth it?

4) Should I be looking at an adjustable gas block? JBO has a Kies clamp-on one for about $40.



I am concerned about the polymer lower failing around the buffer tower. Either at the rear take-down pin holes or the threads. That's why I'm so concerned about the gas system.

Part of me just wants to see what happens while my inner cheapskate wants to take the cautious approach. I suppose $100 isn't too high a price to pay considering that taking my family out to Thai food tonight cost $85...sheesh. (My buddy likes to say that you're really only renting the food! Ew.)

FYI, the reason I'm going 80% polymer is:

1) Want to do 80% but don't want the complications of going aluminum. I'm a newb after all.
2) Best way to obtain an AR pistol in CA, as far as I'm concerned.
3) I get to stick it to the man. No 10-day waiting period, no registration and no registration fee. God I hate paying bureaucrats to protect me from myself.

BTW, obtaining an AR pistol is not easy here and getting a SBR is impossible for regular folks...here's a snip from the Calguns.net forums:

Here are the ways to obtain an AR Pistol in CA:

1. purchase a complete pistol from a LGS that will SSE transfer. make sure they mark it down as Single-shot and not semi-auto OR
2. PPT from someone who already has one. OR
3. (the option you are inquiring about) build from an 80% lower. follow steps in this order:

I. complete the 80% lower. document process if so inclined
II. Install a magazine lock.
III. Install a ZERO-ROUND magazine, or SLED.
IV. Install a lower parts kit and buffer tube assembly. any buffer tube (A2, Carbine, pistol) is acceptable per ATF guidance.
V. Once complete, purchase necessary components to have a complete pistol upper
VI. Marry upper and lower receivers together.
VII. Once pistol is assembled COMPLETELY, it now (provided you followed the previous steps) is a non-roster pistol in a single shot exemption configuration...aka LEGAL
VIII. You are now free to conduct any gunsmithing you wish...aka remove the ZERO-ROUND magazine or SLED and install a 10 round magazine.


Anyways, thanks for letting me share my excitement and questions!

[VASCAR2]

Just curious on your choice of 1:7 twist 10.5" barrel. With velocity being the limiting factor in 223/5.56 I think I would shoot bullets on the lighter side compared to the heavier side of 224 bullets. A 1:9 twist will handle from 50 grains to 69 grain match bullets. I think the 65 grain game king or 60 grain V-Max might work for larger critters and defense but still use the light bullet for small varmints.

Generally the lighter bullets are cheaper and if you don't plan on shooting anything less than 55 grains you should be OK. I assume a 10.5 5.56 barrel would still stabilize 77 grain SMK or 75 grain Tap but I have no first hand experience with less than 16" barrels. I guess it boils down to your intended use.

[JDub]

Just curious on your choice of 1:7 twist 10.5" barrel. With velocity being the limiting factor in 223/5.56 I think I would shoot bullets on the lighter side compared to the heavier side of 224 bullets. A 1:9 twist will handle from 50 grains to 69 grain match bullets. I think the 65 grain game king or 60 grain V-Max might work for larger critters and defense but still use the light bullet for small varmints.

Generally the lighter bullets are cheaper and if you don't plan on shooting anything less than 55 grains you should be OK. I assume a 10.5 5.56 barrel would still stabilize 77 grain SMK or 75 grain Tap but I have no first hand experience with less than 16" barrels. I guess it boils down to your intended use.

Yeah, I was thinking the exact same thing but it was part of the package. I would have preferred 1/9 or 1/8 but this is just a range toy. While 1/7 is sub-optimal for cheap 55gr ammo, I believe it'll be fine out to 100yd.

The other place I was looking at, Mas Defense, would have cost nearly $200 more to get the looser twist barrels...and this was without a free float hand guard.

It is really hard to get just what you want when you are working on the cheap. I have tried to keep the budget down while getting decent quality parts.

Part of me wanted to go whole hog and get the good stuff but then I have to realize that my application is nothing more than fooling around at the range.

[VASCAR2]

I've been there, life is full of compromise.

[JDub]

FYI, if anyone out there is considering a KX3, you might want to check out the GRG Krinkov-Style muzzle device:

http://www.amazon.com/Krinkov-Style-223-Muzzle-Balancer/dp/B00G3O95CQ?tag=viglink20251-20

It's what I ended up buying because, after all, I'm cheap and it was $40 shipped.

Unlike the KAK, it has the internal chamber just like the Flaming Pig.

[Ullr]

I finally got off my duff and started my 80% lower pistol project. (Thanks to our fine legislators here in sunny CA. Single-Shot handgun exemption just got outlawed)

How are you going to perform this build, given that the legal path has been removed?

[KentuckyBuddha]

What part of the legal path has been removed Ullr? The 80% lower bit, single shot in CA, or something else?

[burkew23]

What part of the legal path has been removed Ullr? The 80% lower bit, single shot in CA, or something else?

The Single Shot Exemption will no longer be allowed after Jan. 1st 2015, so we have until then to build our AR pistols. The 80% law (SB-808) will be voted on tomorrow and if passed would be retroactive and require anyone with a 80% build to register it. I really hope that one doesn't pass...

[KentuckyBuddha]

Oh wow! That is pretty extreme. You might be able to get a U-haul truck to the house before the enactment date on that bill though. LOL

Seriously though, condolences.

[JDub]

Well, there is still debate on whether the SSE exemption will outlaw 80% AR pistol builds. The law will still allow "Bolt-action and Break-top" single-shot firearms to be off-roster.

I can easily imagine that a side-charger with a single-shot sled qualifying as a single-shot, bolt-action firearm.

[JDub]

Well, looks like I'm done with the build.

I know this whole post would have been more appropriate for Arf.com but I hang around here more. Thanks for bearing with me...

Here it is...I'll just call it the "Budget Pistol":



And some single-shot lovin' close-up:



I received the upper from Radical Firearms this week. The free-float rail appears to be a Vector Optics and the upper a ??? (Anchor Harvey forged, at least). Melonited 1:7, carbine-gas, govt.-profile, barrel is of unknown origin. Low-pro gas block is not clamp-style. No bragging rights on the parts but this was a budget build and it was inexpensive. Turn around was 2.5 weeks.

I'm using an AR-15 BCG, GI charging handle and a JP silent capture buffer spring deal I swapped out from my other 5.56 Franken-gun. I wanted to put the JP spring/buffer in my Grendel but it has a PWS DI BGC (heavier than M16 BCG) and it is not compatible with it.

I'm using a UTG red dot I had laying around. Don't laugh, it was $50, holds zero and does co-witness. It's no aimpoint but this range toy ain't going into combat. Ironically, the Streamlight TLR-2s on the front (which I also had laying around) is about 5X the cost of the red-dot. One of these days I'll buy the EOtech I've always wanted to try out.

I'm giving the JMT Gen2 80% lower two thumbs-ups. Takedown pins were hella tight at first but have loosened up to tighter-than-any-7075-lower-I-own tight after lots of the ol' in-and-out and one range session. Still have to use a punch to disengage the rear pin because the pin is counter-sunk in the built-up polymer. All the pre-drilled holes lined up perfectly. No major obstacles for a first-time lower builder. Milling it out was a little nerve racking. But, it all came together after some dremel work here and there to get everything to fit in. I must admit is was a fun project and I plan on doing it again. The whole no-waiting-period, no-DROS, no-Fees thang is quite appealing.

Hope SB808 (required retroactive registration of non-serial-numbered guns) doesn't pass or I might lose this pistol in a boating accident.

During my first range session, I was having consistent failure-to-eject. I hope it's just a weak extractor spring. I installed a #60 o-ring around it as a stop-gap to see if that's really the problem. I swapped back and forth between magpul and lancer mags to no avail. The BCG did lock back on both empty mags. Also tried X193 and 62gr. FMJ in both mags and still had FTEjects.

[Wheelhorse]

Nice pistol and the price was right!

Those boating accidents can be a real bitch.

[JDub]

Nice pistol and the price was right!

Those boating accidents can be a real bitch.

Thanks! I'm resisting the urge to do a 7" pistol build now. I have about 50% of the parts laying around ...somebody help me!

[JDub]

Range report #2

O-ring fixed the FTEject problem like a dream. But the bolt was not achieving full lock-back after the last round consistently. The bolt catch was grabbing the bottom of the BCG instead of the bolt. So if a mag was inserted after this semi-lockback and the bolt released, a round would not be stripped from the mag. No FTFs, however.

I swapped out the JP silent capture buffer spring with a standard carbine buffer and spring and it started locking back normally.

So it looks like there might not be enough dwell time in this 10.5" with carbine gas to properly cycle the bolt or possibly just under gassed. I don't know what the gas port diameter is but that's something I could look into as well.