New builds 2019 40 SW AR Pistol


Hello, All
Couple builds going on this year, including an AR Pistol in 40SW. Not much experience so I would probably go with a complete upper on one of my standard AR lowers with a magwell block/ glock mags, anyone have recent experience good or bad with the various .40 uppers out there? Recommendations? Indoor range/ rockpit gun. Thinking in the 8" range for barrel, red dot type optics, arm brace. Budget build.


I haven’t tried a .40 yet, but have had good luck with the Sylvan arms 9mm mag adapter. My upper is a Faxon, I’m pretty sure they also have .40, .45, and 10mm uppers. They are top notch uppers and I’ve had zero issues with mine.


Did you buy the complete upper?

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I’ve done both, complete uppers and parts.


are the bcg’s and barrel extensions pretty standard or are they proprietary? Uppers? Any good tips to save me some aggravation?

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The receiver is basically the same. Just uses a barrel and BCG, plus a different buffer. Everything else should be the same.


BCG: Prices from 99 up to several hundred. I am steering away from the $99 one

Brownells has a Stern Defense for $142,

everyone has lots of choices for around $150-$175. Seems like this is the most expensive part of the build, (other then trigger and optics!) advice?
Barrel: Joe Bobs has KVP barrels on sale for $79, any negatives on the KVP?


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I’m really interested to see what you end up with. I am wanting an Angstadt Arms, and will probably go with them I guess. I just can’t decide between 9mm or 40.


Haven’t committed to a special lower, building on a Anderson multi caliber lower I had bought on sale a while back, Aero upper. using mag well blocks, two piece type with jig to cut glock mags for mil spec mag release.
most of the parts have arrived, still waiting on BCG and charging handle, aiming device. Put a 9" guard on it last night 7" in the mail.
This is coming out low budget finding lots if parts on sale. Ebay for the pistol brace and tube, Joe Bob’s for the barrel and comp.


Ron Williams with RMW XTREME

For me was the only way to go, I had him build me a 10mm Upper. I sent him the Upper and handguard he did the rest. Was a dream to work with.

It’s also Direct Impingement not blow back. With the 10mm that is a big deal because the mass needed for blowback also increases felt recoil.



Whats the price?

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Let’s see I provided the bootleg Upper and SLR handguard (left overs from other builds) then paid about $600.
That was the Upper. Lower was left over parts and put together with some new stuff. Total was like $1,000. Would of course be more if I didn’t have “the AR parts bin”


May go to a rifle sometime, love the 10mm cartridge. Your build looks cool. This is an attempt to see how a blow back system works on the platform. What works and what doesn’t. So far betting the magwell block feed ramp is going to be the focal point of some tinkering.
Easy to convert to something else if I’m not happy, got a solid receiver build papered as “Other”.


Think I’m hitting close to the $500 mark less any optics.
Might just throw a $150.00 green laser and a $180.00 Viper red dot on it. Fun at the gravel pit


Hope it works out well for you.


Lots of parts to re-purpose if it don’t!


I contacted mr. Williams about 10 years ago to do the exact same thing. My dumbass never followed through though. I have always kicked myself about not doing it. They didn’t have the G20/21 lowers back then. I was pricing it to finish using UZI mags.


Yeah I have the Quarter Circle 10 lower. I only have 1 negative. I keep fussing with it but I can’t get the last round bolt hold open to work 100%. I here the same from a lot of people that it is spiratic at best.


So first range report. Functioned well. Little tinkering with the TorqMag magwell block. Put a Sightmark LowPro mini green laser and Sightmark R spec reflex. Both had good reviews and appear to be solidly constructed budget range optics, $129/ ea. Only downside so far no LRBHO, and it looks dorky with the little mag hanging out the big magwell.
QUESTION: Moving forward, would my millspec upper fit on a 9/40 lower if I wanted to swap the lower out with a pistol caliber lower?

40 SW Build

Upper $39.00
Barrel $79.00
Bolt Carrier $143.00
7.5 oz buffer/spring $39.00
Torkmag adapter block $69.00
charging handle $12.00
tube/ pistol brace $45.00
grip $15.00
guard $20.00
brake $30.00
Lower $69.00
parts kit $12.00
parts kit $39.00
optic $129.00
laser $129.00
Sub Total $869.00
tax $78.21
shipping (est) $50.00
Total $997.21