Lightest possible AR pistol

Minuteman · Jul 28, 2014

What components to build the lightest possible (but still reliable) AR pistol in 300BLK?

I'm going to guess:

Magnesium upper, lower, bolt&carrier. 10.5" carbin fiber barrel, no stock, but spectra sling. Poly 'iron' sights.

If these are lightest; what hand guards (or just leave the off?). Flattop, piccatinny rail?

What magazines/ammo are the lightest.

Any recommended alternatives?

Pinecone · Jul 29, 2014

Magnesium bolt would be interesting. And not a good way.

Bolt carrier needs a certain amount of mass to work properly.

IMBLITZVT · Jul 29, 2014

So you want to make the lightest possible AR15 which was designed already to be light. However you want to switch out the light standard ammo with heavy 300BLK?

However to add, I would think a something like the Burris fast fire would be lighter than a front and rear Iron sight... but I could be wrong. Either way, I don't think I would want Irons on an AR pistol with no arm brace, IMHO.

BradMacc82 · Jul 29, 2014

IMBLITZVT said:
So you want to make the lightest possible AR15 which was designed already to be light. However you want to switch out the light standard ammo with heavy 300BLK?

Considering the terminal ballistics of 5.56 thru a 10.5" barrel, I'd be willing to accept a little trade-off of the increased weight of 300BLK ammo. The terminal ballistics of 300BLK thru a 10.5" barrel inspires more confidence IMO.

photoracer · Jul 29, 2014

Lighter = hard to hold and inaccurate most of the time, weight = accuracy because the polar moment of inertia makes it steadier to hold on target. Going to need a serious muzzle brake to tame the recoil and barrel flip. No free lunch. Weight = reliability as the heavy bolt is what reduces the felt recoil in combination with the buffer and spring. There are no magnesium BCGs as far as I know and they would not be an acceptable material anyway. I don't know anyone who makes CF sleeved AR barrels although there are lots of makers of CF sleeved barrels for other firearm types out there. I have an aluminum sleeved barrel in .22LR in one of my ARs. Handguard could be either carbon fiber or undersized modular aluminum with lots of holes (ALG Defense for one).

Minuteman · Jul 29, 2014

Good discussion, thanks for the input.

I've been reading and discussing a bit off-line. I'm now thinking a normal aluminum upper/lower receiver is best. There is some Magnesium-Alloy, but it's really expensive and not as proven. How about no buffer/spring/tube at all. Just an ultra-light sling like a simple web strap, or few strings of 550 cord or Spectra cord. Carbon-fiber pistol grip and small or no forearm protector. No flashsuppressor or muzzle break. No picatinny rail, just a simple reddot, like the DocIII or Burris Fastfire (great suggestion). I don't even need a brass deflector, forward assist or dust cover. Just barebones minimum.

But I do think the caliber is important and 300BLK or 7.62x39 are probably best, much better than .22LR or 5.56 at the 10.5" length.

In hindsight, perhaps the FN5.7 pistol might be an even better alternative than all of this specialized build. ?

Blaster229 · Jul 29, 2014

There are carbon fiber barrels??

Decoy · Jul 29, 2014

Any reason you chose 10.5 for barrel length?

clandestine · Jul 29, 2014

Unless its a .22 it needs a buffer tube unless your using a aftermarket piston/charger setup.

New Frontier Armory Polymer Lower
Ranier Arms 8.2" .300 Barrel (Have ADCO Dimple the Barrel like Knights does to PDW's)
SLR Rifleworks Nitrided .750 Set Screw Gas Block (Have Adco Pin it)
Boomfab Titanuim Carrier (Youll Need the Adjustable Gas Block for this)
Superior Shooting Solutions Flaw Wire Buffer Spring
SSA or SSA-E Trigger
Standard Carbine Buffer (NOT an H Buffer)
Magpul MBUS2 Polymer Sights
7" M.I. GEN 2 SS Handguard (Lightest 7" Rail Out there)
Magpul MOE K Grip
Standard AR15 Charger
I Kick Hippies Sling Plate
Standard AR Pistol Buffer Tube
MAG Tactical Magnesium Flat Top Upper (Lightest NON Polymer Upper)

Decoy · Jul 29, 2014

clandestine said:
Unless its a .22 it needs a buffer tube unless your using a aftermarket piston/charger setup.

New Frontier Armory Polymer Lower
Ranier Arms 8.2" .300 Barrel (Have ADCO Dimple the Barrel like Knights does to PDW's)
SLR Rifleworks Nitrided .750 Set Screw Gas Block (Have Adco Pin it)
Boomfab Titanuim Carrier (Youll Need the Adjustable Gas Block for this)
Superior Shooting Solutions Flaw Wire Buffer Spring
SSA or SSA-E Trigger
Standard Carbine Buffer (NOT an H Buffer)
Magpul MBUS2 Polymer Sights
7" M.I. GEN 2 SS Handguard (Lightest 7" Rail Out there)
Magpul MOE K Grip
Standard AR15 Charger
I Kick Hippies Sling Plate
Standard AR Pistol Buffer Tube
MAG Tactical Magnesium Flat Top Upper (Lightest NON Polymer Upper)

Personal preference, I would move up to a 9 or 10 inch M.I. GEN 2 SS rail and add a Novekse KX5 to tame the beast. I know it will add some weight but good it's a trade off. Again just personal preference. (also gives you a little more rail space if you have an aggressive shooting stance.)

clandestine · Jul 29, 2014

Decoy said:
Personal preference, I would move up to a 9 or 10 inch M.I. GEN 2 SS rail and add a Novekse KX5 to tame the beast. I know it will add some weight but good it's a trade off. Again just personal preference. (also gives you a little more rail space if you have an aggressive shooting stance.)

I avoid Pig devices unless necessary. They often over-gass when its not needed. They are very effective at pushing the concussion away from the shooter though.

The other killer for me is they make installing a silencer more tedious.

You can achieve the same look and concussion redirecting effects with a YHM Q.D. Mount and a Shield Cover but without the over-gassing issue.

I mean no offense to people who like the Pig devices, but 9/10 the guys who install them don't get the reason they exist.

Minuteman · Jul 29, 2014

Blaster229 said:
There are carbon fiber barrels??

Yes. They are actually pencil thin metal barrels wrapped tightly in carbon. Much better and lighter I read.

Decoy said:
Any reason you chose 10.5 for barrel length?

I've read that 300Blk was designed to burn all its powder in 9", so 10" or a tad more seems ideal to me.

clandestine said:
Unless its a .22 it needs a buffer tube unless your using a aftermarket piston/charger setup.

New Frontier Armory Polymer Lower
Ranier Arms 8.2" .300 Barrel (Have ADCO Dimple the Barrel like Knights does to PDW's)
SLR Rifleworks Nitrided .750 Set Screw Gas Block (Have Adco Pin it)
Boomfab Titanuim Carrier (Youll Need the Adjustable Gas Block for this)
Superior Shooting Solutions Flaw Wire Buffer Spring
SSA or SSA-E Trigger
Standard Carbine Buffer (NOT an H Buffer)
Magpul MBUS2 Polymer Sights
7" M.I. GEN 2 SS Handguard (Lightest 7" Rail Out there)
Magpul MOE K Grip
Standard AR15 Charger
I Kick Hippies Sling Plate
Standard AR Pistol Buffer Tube
MAG Tactical Magnesium Flat Top Upper (Lightest NON Polymer Upper)

Wow, great specs list for an ultra light AR in 300Blk. Thanks!

I've fired a sig P556 pistol without a buffer/tube, works fine and little recoil. Not possible in an AR style pistol?

clandestine · Jul 29, 2014

Minuteman said:
Yes. They are actually pencil thin metal barrels wrapped tightly in carbon. Much better and lighter I read.

I've read that 300Blk was designed to burn all its powder in 9", so 10" or a tad more seems ideal to me.

Wow, great specs list for an ultra light AR in 300Blk. Thanks!

I've fired a sig P556 pistol without a buffer/tube, works fine and little recoil. Not possible in an AR style pistol?

The P556 is a Swiss/SIG 55x design/clone. Different Animal and does not use a buffer tube in the design.

Speed3 · Jul 29, 2014

Nice list for a pistol build, thanks.

4095fanatic · Jul 29, 2014

Most of my research suggested 300BLK has a sweet spot somewhere between 8"-9". If you want as light as possible, I'd go shorter than 10.5". Can't cite references due to work computer restrictions banning me from going to most sites (not sure why this one is OK), but a quick google search on 300 blk barrel length statistics should turn up plenty.

Biggfoot44 · Jul 30, 2014

For wt per se : Carbon fibre lower and upper. Gunsmoke Enterprises Gen II tube/ spring/ carrier. If a 5.56 , I'd say 7.5in pencil bbl, will defer to Chad on .300 bbl config. Plain round free float carbon fiber handgaurd. Whichever is lightest red dot sight.

Of course more beyond single priority of weight, it would be a good trade off of price , durability , and constant spring replacement to switch to conventional alum recievers , conventional tube/ buffer/ carrier at expense of a little more weight.

Pinecone · Jul 30, 2014

Minuteman said:
Yes. They are actually pencil thin metal barrels wrapped tightly in carbon. Much better and lighter I read.

But carbon is an insulator, so if you shot rapidly, the metal barrel heats up a LOT. And heat is what causes barrels to degrade and need replacing.

Carbon wrapped barrels are a good idea for a hunting rifle, where you carry a lot and only shoot a few rounds per season, but for a tactical type firearm, they are not so good.

IMBLITZVT · Jul 30, 2014

Minuteman said:
In hindsight, perhaps the FN5.7 pistol might be an even better alternative than all of this specialized build. ?

A FN5.7 would seem to be to be an all around better solution IMO.

Assuming you have a receiver already. Why not do something with a Sig Brace and closer to an SBR and get a FN5.7.

I don't think a really light AR pistol would prove to be a lot of fun to shoot and will cost an sh@tload to build. I see an expensive build for a gun that will not prove very useful or fun. Kind of cool, yeah... but a FN5.7 is a cool gun too!

photoracer · Jul 31, 2014

Blaster229 said:
There are carbon fiber barrels??

Carbon fiber sleeved, they have a liner of stainless steel in the middle that the bullet goes down. There is a company in, I think Montana, that makes carbon fiber sleeved big game and sniper barrels and they have won at least one major sniper competition the last I heard.

photoracer · Jul 31, 2014

Minuteman said:
Good discussion, thanks for the input.

I've been reading and discussing a bit off-line. I'm now thinking a normal aluminum upper/lower receiver is best. There is some Magnesium-Alloy, but it's really expensive and not as proven. How about no buffer/spring/tube at all. Just an ultra-light sling like a simple web strap, or few strings of 550 cord or Spectra cord. Carbon-fiber pistol grip and small or no forearm protector. No flashsuppressor or muzzle break. No picatinny rail, just a simple reddot, like the DocIII or Burris Fastfire (great suggestion). I don't even need a brass deflector, forward assist or dust cover. Just barebones minimum.

But I do think the caliber is important and 300BLK or 7.62x39 are probably best, much better than .22LR or 5.56 at the 10.5" length.

In hindsight, perhaps the FN5.7 pistol might be an even better alternative than all of this specialized build. ?

No buffer tube, buffer, and spring and you have a single shot pistol. Action will not cycle.

Lightest possible AR pistol

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