Posted By Mac66 on December 22, 2016
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.
The Upper Parts…
Upper receiver-I picked up stripped Anderson “sporter” upper from AIM last winter while driving through Ohio. This “sporter” receiver was a flattop but didn’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
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.
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.
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.
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.
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. Am 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.
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: The lower was a toss up between a polymer Calvary Arms (acquired in 2008 but no longer made) and a conventional aluminum lower built as a carbine. The Cav Arms 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.
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.
Lower Parts Kit: I used a standard lower parts kit in my Cav Arms lower. It does not use a couple of the small pins used in a regular lower but the weight is barely measurable. 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.
Put all together I came up with a total weight of just under 5 pounds, 4 lbs 15 oz to be exact. 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.
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, or 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.