Jump to content
High Exposure

Questions on Building a Pistol Caliber AR

Recommended Posts

Ok, so....

 

I was gonna add this request on the LW 9mm AR thread in the AR Sub-forum:

 

http://njgunforums.com/forum/index.php/topic/72207-buying-building-9mm-lightweight-complete-upper/#entry911839

 

but I thought it would detract from Tuk-Tuk's post so I decided a new thread was in order.

 

I want to build a .40 S&W AR that takes Glock mags. I have to give my MP5 back to the Dept armory soon and I want something for steel matches.

 

I know 9mm would be easier but .40 suits me for a number of reasons - primarily that's what the rest of my Glocks are, ergo my Glock mags as well, and it's the caliber I keep in abundance along with .223/5.56.

 

It looks like unless I want a Rock River or Olympic Arms upper (hint: I do not) I will have to piece an upper together myself for this project - but I have little experience with pistol caliber ARs.

 

What do I need to know?

 

Lower will be a QC10 Small Frame Glock Lower:

What action spring and buffer do I need?

Does it use a standard receiver extension?

Standard AR trigger or something special?

Anything else I don't know?

 

Upper Receiver make is still undecided:

Do I need a particular upper receiver?

Planning on getting a .40 BCG and barrel from QC10 when they become available, but just in case, who else makes quality 16" .40 AR Barrels and .40 AR BCGs?

I know they are straight blowback, so is it simply install the barrel with no gas block/tube/system?

Who makes a muzzle break/comp in .40?

Anything else I don't know?

Share this post


Link to post
Share on other sites

I'll take a stab at a couple of those..

 

-Yes it will most likely be gas blowback, My 9mm carbine is gas blowback and all pistol caliber BCG's Ive seen are blowback. I'm only aware of RRA and Olympic arms when it comes to 40 cal BCG's. ..no gas block needed

 

I don't see why you could not use a heavy buffer and a standard spring, you could always call double diamond supply and ask.

 

http://www.gunbroker.com/Auction/ViewItem.aspx?Item=437905034

In this gunbroker ad at the bottom of the description it says, "all you will need to complete this is a standard lower parts kit"....bonus

Share this post


Link to post
Share on other sites

What are the possibilities for a piston driven system?  I heard they are extremely reliable and have the same half life as uranium?

 

I have not seen a piston kit for a pistol caliber carbine. If you look at the BCG the gas key is a slanted nub, only ment to ride in the same slot as the charging handle. All blowback

Share this post


Link to post
Share on other sites

Check out Just Right Carbines out of NY. They make ar style carbines in 9mm, 40sw, and 45 acp. They sell parts too, not sure if they are proprietary design, but they have something to look at.

Would you consider buying a build pistol caliber rifle? They are priced well and accept glock mags.

Any other requirements or preferences?

Share this post


Link to post
Share on other sites

The big issue is the .40 part. I know I could get a 9mm setup but I want to see how feasible .40 would be as that is what all my Glocks are. I don't want to buy 10 new 9mm mags or stock another caliber.

 

I have the QC10 lower that takes 9mm/.40 Glock mags. That's the easy part - it comes with all the necessary unique (non-standard AR) parts already installed.

 

QC10 will be making .40 bolts for Glock mags and .40 barrels eventually (so they say) I just don't know of I can use an standard AR upper, barrel nut, action spring, or what kind of buffer to use.

 

If .40 just isn't feasible, then I will have to go 9mm with it.

Share this post


Link to post
Share on other sites

QC10 will be making .40 bolts for Glock mags and .40 barrels eventually (so they say) I just don't know of I can use an standard AR upper, barrel nut, action spring, or what kind of buffer to use.

 

I emailed them asking what lengths they are going to offer .40 barrels in since their 9mm barrels are only up to 10.5" but have yet to receive a response in the past 3 days from them. Also asked if they have any better time frame on the availability of said .40 components. Ill update if/when I do get a response.

 

I am really interested in doing this as well now that I have the G35, although if it doesn't come through I already stock 9mm so its not a disaster.

Share this post


Link to post
Share on other sites

Depends on whether you want a blowback .40 (brutal) or a soft shooting DI upper.

 

Ron Williams can make you a .40 DI upper (or any caliber you want).

 

Rudy @ Macon Armory can build a .40 blowback upper.

 

You can get in touch with either of them through arfcom or thier web sites.

 

But to answer some of your questions:

 

The QC10 receiver is the nuts. You will HAVE to have the bolt ramp "thinned" by the gunsmith (or ADCO) to fit through the glock mag feed lips. If getting a DI setup, they will do that for you.

 

Standard receiver extension and standard guts. But Action spring and buffer depends on the caliber and recoil system. Blowback will need a buffer heavier than shit to soak up the bolt inertia and you WILL feel all that mass banging back and forth. With my DI 9mm, i'm using a RCA lightweight bolt, wolff lightweight spring, taccom delrin buffer and an adjustable gas key turned down to limit gas and its softer than a mouse pissing on cotton.

 

Use standard AR trigger (i like the Geissele 3G in mine, a very fast action trigger). If a DI setup, the bolt will come ramped as usual. If a blowback setup, make sure you get the bolt ramped by a gunsmith/ADCO. If not, you will break trigger pins. All the more reason to not get blowback.

 

Upper receiver doesn't matter. I replaced the original standard RMW upper receiver with an ultralight 2A Armament Balios Lite. But i also thought about using a Spartan side charge for fun. With a DI upper, you use so many *standard* AR parts, you can use all the special goodies out there (except for gas block/tube, thats always the propriatary part).

 

Blowback does not require any gas block or tube and there are "Dedicated blowback receivers"  out there that dont have the gas tube hole drilled (not that its critical to have/not have it). You WILL need a dedicated blowback bolt which is the harder part. Any gunsmith can ream a barrel, but machining a bolt natively for the 40 cartridge head is the bigger hurdle. For DI, they can just ream out a 5.56 or 7.62. to accept the larger diameter. I use a NiB 5.45 bolt in my DI-9 and it works great.

 

Muzzle brakes really dont exists for pistol carbines. They neither produce enough gas to run one, nor is there much demand for them to fuel production.

 

You can NOT use piston system with pistol calibers. Although DI uppers are avaialble for 9mm, 40, 357sig, 45 and a slew of other variants, thier gas systems are no standard 5.56 carbine, mid or even pistol length systems. Some will be close, others not even remotely close. Without the standard lengths, you dont have enough room to run the piston between the block and the bolt.

Share this post


Link to post
Share on other sites

Good info, thanks!

 

Don't want a piston gun, so no worries there. ;)

 

Right now I am leaning towards a DI system. Is there a difference in gas system lengths? Does it mimic DI AR systems?

 

QC10 says they are going to make .40 Bolts. I just don't know if it will be a DI or a blowback system.

 

I may end up with blowback first since that may be easier to source and cheaper, then have a DI upper built down the road.

 

Do you have website info for the two guys you mentioned above?

 

ETA: Disregard the web addy request:

 

Ron Williams: http://www.rmwxtreme.com/

Share this post


Link to post
Share on other sites

To clear up some confusion regarding blowback vs DI chamber and bolt differences, a pic is in order. The bolts and chambers are arranged differently since there are different needs for both. Since a blowback is just as its name implies, there is no need for a locking rotating bolt assembly that a standard gas operated ar15 uses. As such, the blowback bolt is a single piece carrier and breech face whereas the DI bolt is standard ar15 components. Similarly the blowback barrel has a different barrel extension that lacks the locking lugs and is mostly flat faced. Feed ramps are generally built into the mag block for conversions and lower receiver for dedicated receivers.





You know what standard DI parts look like, but here is a blowback bolt vs di comparison.






s_Bolts04615.jpg

Share this post


Link to post
Share on other sites

Its a Ron Williams upper on an old ddles glock lower. Ron did all the bolt machining as he originally supplied the bolt with the upper. Glock lowers are common enough that they know what to do if you are building the rifle around one, just let them know since not every build will need the extra machining. Colt mag lowers do not. Ron also makes his own large frame block mag ar15 lower for G21 mags for his popular DI 45 upper.

Share this post


Link to post
Share on other sites

No problem. when I ordered my DI upper several years ago, I originally told Ron I wanted to build a lightweight 9mm competition gun to shoot at steel matches at various clubs. he turned the barrel down to a lightweight .625" profile to keep weight down, put on a simple target crown and milled the bolt for the glock mags and tested.

 

now one thing to keep in mind for the 9mm DI system is that there is not enough gas in standard factory loads to run a DI upper. With 9mm, it's really for the reloader who can tune the load to optimally run the system. The gas block is so close to the chamber to extract every bit of pressure that the fast burning factory powders just don't have enough had volume to drive the system. I have to load a combination with a slightly slower burning powder in order to get the bolt to cycle. Its not a stout load by any means, just at a slower powder. I understand that other calibers don't have this issue and so they are more popular for di systems for people who don't reload. 40 and 45 don't require any special loads.

 

when I initially got the upper, I had to do some experimentation and Ron worked with me to establish a baseline load combination given the components that I use. With my bullet on hand, he suggested some powders with starting loads and overall length values to try and Tailor from there. he was pretty much spot on and I only play with the loads enough to get it shooting soft enough to be functional but not reduce excess recoil.

 

function wise it runs fantastic. I have the occasional fail to eject but I think that is due to the short nature of the 9mm case in the long 556 action where sometimes the shell slips off the extractor before it fully clears the election port and stove pipes but it's a rarity. I used to use a blunt truncated cone jhp type round from Montana gold and occasionally that would have a feed issue because of that flat nose getting hung up on the locking lugs in the barrel extension. Once I switch to a real FMJ load, those occasional feed jams went away. but the real test is that I use it for competition events and it runs great and if it didn't I would not be able to comfortably run this gun for that type of shooting.

 

fast forward to today, I decided to add some extra lately goodies to the recoil system since these kind of parts are becoming quite popular, mature, and prolific. Since the gas block on these di carbines are proprietary, you really can't add an aftermarket adjustable gas block. Fortunately rubber city armory makes a lightweight bolt carrier with an integrated adjustable gas key 2 adjust gas entering the bolt carrier. I sent one of those off to Ron to mill so it fits the Glock feed lips and added a wolff reduced power carbine spring with a Taccom Ultralite Delrin buffer. All that together with my current di 9mm load, I had to adjust the gas down quite a bit to limit the amount of gas that I previously needed a minimum in order to soften up the recoil with the ultralight weight recoil assembly. with several ounces shaved off the recoil assembly and the gas tuned down from its previous setting, both primary and secondary coil impulses are a lot softer in this gun. It's very comical how soft it shoots especially compared to a hard thumping blowback action 9 mm rifle.

 

all in all it's been an excellent rifle and a joy to shoot and very successful in competition amongst with how light the gun is and how soft the recoil is. I have about six thousand rounds down the pipe of this gun and I only really shoot it at matches and try to go as much as I can.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.



×
×
  • Create New...