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Frankengun II-The Lightweight

I’ve always toyed with the idea of building a lightweight AR carbine but never got around to it.  Recently while building Frankengun 1 I was looking over my pile of parts I decided I had enough parts to try and build  as light a rifle/carbine as I could get without spending a pile of money on expensive custom parts.  I had not set budget in mind when I started bit I didn’t see spending a lot of money on something that was made simply to play with. When all was said and done I was surprised how inexpensive one could duplicate this rifle. See the Edited to Add at the bottom for prices.

Piles of parts

The Upper Parts…

Upper receiver-I picked up stripped Anderson ” lightweight sporter” upper from AIM last winter while driving through Ohio. This is a flattop but doesn’t have a forward assist or ejection port/dust cover like the A3/M4 flat top uppers have. It does have the shell deflector however.

Forward assists (aka jam buttons) came about during Vietnam to allow the shooter to seat the bolt when it jammed. Original M16s were not issued with cleaning kits and the powder used at the time tended to foul the action quickly (that’s a long story).  It is debatable whether something that evolved for a full auto rifle out of those circumstances in a jungle war 50 years ago is even relevant  to a civilian rifle today.  The same goes for the ejection port cover.  The absence of those features cuts 2.2 ounces off the weight.  Weight 6.6 oz

Flat top sporter upper with thin barrel and Cav Arms lower

Barrel- the barrel is a thin profile 16″ carbine barrel from an earlier build. I bought it from Model 1 Sales back in the 1990s.  Unlike the more common M4 profile that is thick and thin in places, this thin barrel weighs 3.8 ozs less.  Weight: 22.9 oz  Note: there are “pencil” barrels that weigh even less than this barrel. One made by Faxon is said to weigh 19 ozs. It also costs around $180 if you can find one in stock. Palmetto State Armory sells a couple “pencil” barrels, one in stainless and one in black for around $100. Reports are that they weigh around 21 ozs.

Gas Block-I was kind of surprised that a standard A2 front sight block weighs 4.5 oz. A low profile railed block weights a hefty 7.4 oz. I have an A2 FSB that was cut down my removing the sight part, it weighs 3.4oz. My choice was a short low profile aluminum Trinity Force gas block with a total weight with the gas tube of only 1.4 oz. Bought from sportsmans guide online.

Gas blocks-R to L Trinity Force Aluminum, A2, rail block and a cut down A2

Flash Hider: A friend of mine cuts down regular AR flash hiders and then threads them. He uses them as thread protectors and as “mud guards” on various rifles to protect the crown and muzzle. I’ve found they work very well as a mini flash hider. The cut down flash hider is 1.1 oz which is .8 oz lighter than a regular one. You can see the difference in the photo above.  An alternative is to simply use a thread cap/protector or grind/mill the threads off. Why do you need a flash hider on a sporter? You don’t.

Sights:  It never made sense to me to have light weight rifle or carbine and then hang pounds worth of optics on it. Kind of defeats the point.  Use iron sights.  I had a pair of Magpul BUIS (back up iron sights) on another rifle but I found a similar style of polymer sights on sale at sportsmans guide made by Omega pretty cheap. I will try them. If they work I’ll keep them. The Omegas weigh 2.2 ozs.


Omega Sights, very light weight

Hand guards:  One could use conventional hand guards which upon weighing I found the original A1 type hand guards to be the lightest. However, when you add the front sight base, retaining plate, barrel nut and appropriate hardware the weight is over 12 ounces.  I started looking around and found a carbon fiber free float hand guard at Delta Team Tactical.com which is  advertised at 5 ounces for the 12″ long one. I ordered it.  Big surprise upon arrival was that is actually weighed 12.2 ounces with the the full length metal rail, 3 side rails and the barrel nut.  The barrel nut itself weighs 3 ozs. I took all the rails off and without the nut, the tube itself weighs 3 oz.  I took one of the side rails, cut it down and installed it on the top to hold the front sight.  By removing the rails I cut the weight down to 7 ounces. That will work and I don’t think your are going to find a carbon fiber handguard any less expensive.  An  alternative might be to order a shorter aluminum free float rail with key mod or M-lok holes in it. I don’t think it would lighter but it might get close.

Carbon fiber tube with rails, end cap and barrel nut was over 12 ozs to begin with. Take all the rails off to get the weight down.

Bolt and Charging Handle:  I used a standard bolt and charging handle. There are light weight bolts available but they tend to cost a lot of money. A standard charging handle with a standard latch is the lightest you are going to find.  I weighed a number of bolts and handles. They averaged about 12.2 ozs

Lower Parts:

Lower: The lower was a toss up between a polymer Calvary Arms (acquired in 2008 but now offered by gwacsarmory.com and called the CAV 15) and a conventional aluminum lower built as a carbine. The Cav 15 is a one piece molded unit that includes the stock and pistol grip. Unlike conventional rifle lowers it does not need a separate buffer tube. It also uses a carbine buffer and spring saving additional weight.  A conventional aluminum lower needs a buffer tube, buffer and spring in addition to a stock. The  Cav Arms lower is 23.7 ounces with the spring which is  5.2 ounces lighter than the aluminum lower.  An alternative would be a regular polymer lower but with the buffer tube, pistol grip and stock. I doubt it would be less weight than the Cav Arms.

Cav Arms (top) vs. metal carbine lower (bottom)

Buffer and Spring: One of the variables one has to be aware of is the weight of the buffer. Buffers can affect the cycling and operation of the rifle.  I’ve accumulated a number of buffers over the years from various rifles and parts kits. I never paid them much attention as long as the rifle they were in functioned properly.  As I pulled them out of my parts box or various rifles and weighed them I was surprised at the variation in weight. The lightest one was 1.6 oz while the heaviest was 4.6. The others ranged from 2.8-3.4 ozs.  The average buffer is about 3.0 oz.  The 3.4 oz buffer is be considered a “heavy” or H1 buffer while the 4.6 oz is referred to as a H2.   The difference of 3 oz between the lightest and heaviest is significant in terms of total weight but one has to match the buffer to the rifle.  A light buffer in a very light rifle may not necessarily be the best combination in terms of recoil, function, durability etc.  While good for the bottom line weight, this rifle will need to be tested* to find the best buffer.

Buffers vary widely in weight. Lightest on far left, H1 next to it. The heaviest (H2) is the third from left/black one with the white tip.                                                   

Lower Parts Kit: I used a standard lower parts kit in my Cav Arms lower.  If one wanted to cut weight even further there are some parts kits that use plastic (polymer) hammers and other parts. There are also some kits that used titanium parts and pins which tend to be very expensive. I am not looking at the ultimate light weight just a functional light rifle made with off the shelf parts.

The Result

Put all together I came up with a total weight of 4 lbs 15 oz.  That’s using the lightest buffer I had. Anything else would put it over 5 lbs.  It feels very, very light particularly compared to most other carbines which are over 6 lbs.  I haven’t shot it yet** but plan to in the near future. Overall I was pretty happy at how it turned out and how it looks.  I should also note that the upper can be put on any AR lower so tests with it on a regular carbine lower is also in the works and the subject of another article.

The end result. A functional sub 5 lb carbine

Final thoughts: The only other thing this lightweight needs is a sling and some ammo. To keep it light as possible my thought is to get a 1″ wide light weight nylon strap, add a plastic buckle and then attach it with paracord loops. Can’t get much lighter than that. To keep with the light weight sporter theme, a 5 or 10 round flush fitting plastic mag would be light to carry. Remember this is a sporter rifle not a battle rifle.

So how practical is this rifle? I think it kind of depends on one’s expectations. It might be practical as a walk in the woods rifle, or a carry on a horse, bicycle,  ATV, motorcycle or bush plane. Perhaps it would be useful on a long trek on foot where weight is a consideration.  It might have some use for a child or small person to shoot and handle though less weight means more recoil. From that standpoint it might serve useful as a carry often, shoot seldom type tool.

**UPDATE 4/14/17- The rifle has been fired and tested and went through 140 rounds without a problem. It is quite mild and fun to shoot.

*The light weight buffer functioned perfectly.

Edited to Add….

I’ve been asked about how much it cost to build this rifle. It is kind of hard to tell since I already had many of the parts which were taken from other things. I will however attempt to break it down if you had to buy all the parts today.  I didn’t intend this to be a budget build but it just turned out that way.

Cav Arms lower and lower parts kit-$179– Note: these are now offered here http://www.gwacsarmory.com/cav-15-mkii-ar15-polymer-stripped-lower-receiver-black-ar-15/. They are $129 plus shipping plus transfer fee, plus you need a lower parts kit ($40+), approximate total $179. I would guess with shipping and transfer cost the actual price would be just over $200.  UPDATE 4/14/17…check for blemished Cav 15 lowers frow gwacsarmory for $85.

Another option is the New Frontier polymer lower. https://newfrontierarmory.com/shop/lw-15-complete-polymer-lower-receiver/  These are $129 plus shipping and transfer fee. They are complete and include the lower parts. Almost everything on it is plastic and is lighter than the Cav Arms. Problem is they are rarely in stock.

Upper stripped receiver-Anderson Lightweight Sporter  $39   http://www.aimsurplus.com/product.aspx?item=XANA3LWT  Add shipping. They are frequently out of stock but you can get on their notify list . They are sometimes available elsewhere at a higher cost. Another alternative is a complete slab sided upper from various makers. Prices vary widely but are usually much higher than the Anderson.  I would prefer a slick side upper without the shell deflector but couldn’t pass up the price of the Anderson. UPDATE 4/14/17-these are back in stock as of the update.

Barrel-$90  http://palmettostatearmory.com/psa-16-mid-length-5-56-nato-1-7-ss-pencil-barrel-5-56-nato-1-7-freedom.html.  The Freedom line is PSA’s budget line.  This barrel uses a .625 gas block unlike the .750 on  mine.  They also have black pencil barrel for $10 more. You can still buy a light weight barrel assembly from Model 1 sales but they are around $200 with shipping. Another alternative is the ultra light Faxon bbl for about the same price. I would go with the PSA bbl. If this barrel had been available when I started this build I probably would have bought it and kept the original barrel as an A1 Carbine.

Low Pro Gas Block – $20 UPDATE 4/14/17  PSA now has .625 gas blocks for their barrels.  Not aluminum but they will do. Delta Team Tactical now has aluminum .750 gas blocks

Mid length tube $8.00 https://www.deltateamtactical.com/Mid-Length-Stainless-Steel-Gas-Tube-AR15-AR-15_p_4578.html  or get one from PSA when you order the barrel and gas block

Carbon Fiber Free Float Handguard-$48  https://www.deltateamtactical.com/Carbon-fiber-Free-Float-Hand-Guard-12-Rifle-length-_p_4182.html

Back Up Iron Sights-$14  https://www.deltateamtactical.com/Omega-Mfg-Inc-Polymer-Backup-Sight-Set-Black-For-Picatinny-Rails_p_4472.html

Bolt/carrier and Charging Handle-$110                          AIM Surplus has a light weight bolt/carrier 8.9 oz-$110. http://www.aimsurplus.com/product.aspx?item=XAIMBCGN3LW&name=Light+Weight+AIM+AR+.223%2f5.56+Nitride+9310+MPI+Bolt+Carrier+Group&search=bolt+carrier

Buffer and Spring-$17  https://www.deltateamtactical.com/OMEGA-MFG-Universal-Fit-Buffer-Spring-Endplate-Castle-Nut-Kit–For-Buffer-Tube-Mil-Com-_p_4238.html  Don’t really need the tube, end plate, castle nut for this build but this is about as cheap as you are going to find a buffer and spring. UPDATE 4/14/17- Deltateamtactical now offers buffers and springs separately.

Flash Hider-$9  https://www.deltateamtactical.com/Omega-Mfg-AR-15-12×28-TPI-GI-Bird-Cage-Flash-HIder-556-223-A2_p_4632.html. An alternative is a simply a thread protector. or grind/turn the threads off your barrel. You don’t really need a flash hider on a lightweight rifle.

Delta Team Tactical has free shipping over $100 if you order all that stuff at the same time.


-Prices are rounded up to the nearest full dollar.

-Total cost does not include shipping costs, lower receiver transfer fees, taxes or tools need to build. I would estimate at least $100 more for the above taxs/fees/shipping etc.

-Total weight may be different than mine since I couldn’t find exact matches for what I used like the buffer and gas block. You can take weight out of a standard buffer to cut weight. The flash hider is full size not cut down like mine. You might try a thread protector to cut weight.

-It is likely that one could also save some weight by ordering a plastic lower parts kit from New Frontier. Good luck finding them in stock however.


About The Author

Mac created nylonrifles.com. It is the premier website and largest source of information on the internet about Remington nylon rifles. Mac spent 34 years in law enforcement, campus law enforcement and emergency management before he retired. He is a former Federal Firearms License holder and private investigator. He has a BS in Criminal Justice and Master's Degree in CJ and Security Administration. He has taught criminal justice at a college level and is certified and has taught numerous law enforcement, security and emergency management classes, including classes for the US Dept of Homeland Security. He currently is an emergency management and security consultant as well as being a Revolutionary War Veterans Association Appleseed rifle instructor. He is a Second Amendment Foundation Life Member and NRA Life Member and Range Safety Officer.


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