The overwhelming criteria for this gun is to have the lightest, most compact, yet still reliable, bullet-launcher that I could. I want to keep traditional internal systems (carbine-length gas, standard receiver extension, no external piston, etc.) while minimizing the outward weight and profile. The intended use is for drills nights where I am on my feet for several hours but rarely get to shoot other than to demonstrate a drill. As such I want the lightest, most compact package possible strapped to me so that I deal with less fatigue but also with less issue of the gun getting in the way when moving around the range and other shooters. Light weight and reduced overall bulk are the goal. If it proves feasible there is a possibility of building a near-identical gun, perhaps in 300 BLK, as a suppressed home-defense carbine.
The Daniel Defense 10.3” lightweight barrel is the shortest I feel comfortable with, and since DD uses this length on their MK18s I'm pretty confident that they have the gas port figured out.
Given that barrel, I want to cover as much of it as I can while still maintaining a small, lightweight, profile. A DD 10.0 rail would cover more barrel but it would be more expensive, heavier (especially after adding rail covers), and would not allow many suppressors to be mounted if I chose/choose to go that route. The Troy TRX Extreme tube rectifies ALL of those shortcomings and with the inclusion of Mount-N-Slot accessory mounts is easily just as modular. The Troy version is lighter than the VTAC variant of the same handguard, and the holes vs. slots allows for QD sling attachment points to be recessed instead of act as warts.
I will put a Mount-N-Slot handstop at the furthest forward point on the handguard and hook it with my support-hand index finger to help pull the gun tight into my shoulder and also keep my hand from sliding forward in front of the muzzle.
I have no use for the forward assist, and I've used the Les Baer non-FA upper on another project, but found that like all things Baer their pointless obsession with tight fits makes them a non-starter. The MUR can be had without a FA, and somewhat counter-intuitively is actually lighter than the standard M4 upper in that configuration (although still slightly heavier than the Baer).
I prefer fixed iron sights when combined with a RDS in a lower 1/3 mount, and since this upper will most likely eventually wear an H-1 in a Daniel Defense mount, the Daniel Defense fixed front and rear iron sights mate up nicely. To start I'm considering using it irons-only for a bit.
While there are many quality BCGs available on the market, I have come to believe that only Colt really does it right. And given that the premium is only $40 or so over competing products I am willing to absorb that cost. As of now I have no use for whale-jizz coatings on anything, let alone a BCG and since I can't have the Colt and the whale-jizz anyway that makes it an even easier choice. If I got the route of building a suppressed version I *may* entertain alternate carriers but the bolt itself will still be Colt.
BCM Gunfighter charging handles go in all my personal guns now. Having experienced issues with almost every other handle on the market, and finally being sold when I couldn't run a PRI in the rain but switched on a GF-equipped carbine and had no trouble, they are the de-facto handle for me now. Considering going with the Mod 5 on this one as an experiment and in keeping with the light/compact design criteria.
Light will be either the M600 or M300, depending on what I find best suits my needs, but leaning heavily towards the 300 unless it puts the lens somewhere that gets a lot of blast or if I find it not be bright enough. Mount-N-Slot for the mount.
The lower I'm a little less settled on. I know that it will have a BAD-ASS 45* safety, Noveske receiver endplate sling mount, and a BAD Lever. To start out with I'm going to keep with the light and compact theme and use a CAR stock and a Troy Battleax grip and see how those work.
The sling will be my VTAC 1-to-2-point convertible and attach to the Noveske at the rear and a Magpul RSA on the top rail of the TRX. I will also have a QD socket in the TRX for convenience and flexibility later.
First disappointment, the MUR-1s does not weigh as advertised. The Vltor website repsesents that “MUR-1S (shell deflector only) weighs less than 8 oz.” This either means that this is weighed without the dust cover and associated hardware or it is flat out wrong. There has been some conjecture that the part used to be billet and now is forged and that this may account for the difference, but the end result is the same: the MUR-1s weighs almost exactly the same as the standard M4 flattop upper with forward assist, meaning it’s essentially a $100 premium for nothing.
Vltor MUR-1s weighs 8.4 oz. complete
Dust cover and associated hardware weighs 0.7 oz.
Standard M4 upper receiver weighs 8.6 oz. complete
Les Baer non-forward assist upper weighs 7.5 oz. complete
this is the part I was hoping to avoid using by buying the MUR but is now back on the list
Turns out the Troy grip, something I had on hand already for a woman/kid gun, weighs 2.6 oz. Pretty light huh? Except that a MOE weighs 2.7, and the tiny profile of the Troy makes it unusable for me. It would have been GREAT for the intended application of the woman or child, but I actually find it hard to hit the magazine release set up this way.
I will not sacrifice function on this gun for weight/bulk savings. I may go back to the MOE, or I may finally experiment with trimming down and re-profiling the A2.
Troy Grip - 2.6 oz.
A1 Grip - 3.2 oz.
A2 Grip - 2.3 oz.
TD BG-17 - 3.7 oz.
Magpul MOE - 2.7 oz.
On the plus side, the CAR stock saves nearly 4 oz. vs. the MOE with pad, and while my focus was largely on how bad the Troy was, there doesn't appear to be any detriment to using it in dryfire. Obviously range time will be better, but I'm confident enough in it at this point to keep it on the gun until I get the project finished. Unlike the pistol grip.
Magpul MOE Stock - 8.3 oz.
CAR Stock - 4.6 oz.
Additionally, it turns out my fears RE: the Baer upper were well founded as it just flat doesn’t want to mount to any of the 7 lower receivers I have tried it on. We are not talking about hard to fit, we are talking about literally bash the pivot and takedown pins in with a rubber mallet. This is a no-go, but may be salvageable.
Tried Just the pins in the upper without the lower and while tight they were nowhere near as tight as when assembling with a lower. Put the upper on 6 different stripped lowers and the front lug for the pivot pin was too wide for ALL OF THEM. Couldn't even get it seated on the lowers far enough to get the pin in. Had to start with the upper rotated forward just to get the pin started and then closed the two halves to get the takrledown pin in. Couldn't get either pin in all the way with just my hands but in spite of pushing them in by hand had to pound them out once in.
Rear lug hole is round (should be oval). Finally just got the calipers on it. It's .245" ID. Interestingly the pin fits tighter in the rear hole but the front lug is the fat one. Pivot pin hole is .248" ID. FWIW, in most lowers I've now tried this in I cannot even pound the pins in without a rubber mallet, so this is nowhere near normal tight. Front, pivot, lug is 0.505" wide, rear is 0.50" wide. I used a drill an ¼” bit to open up the holes, and appear to be making some progress in this. The Baer upper alone is starting to look like it needs it’s own page.
Attempting to fit the Baer upper to a variety of lowers
Parts on hand to this point:
Daniel Defense 10.3” lightweight barrel markings
Daniel Defense 10.3” lightweight barel : 1 lbs. 0.3 oz.
Vltor MUR, Troy TRX Extreme 9.0, Daniel Defense 10.3” lightweight barrel
Battle Arms Development Ambi 45* Short Throw Selector
Parts still rolling in, but getting very, very close to being done.
BCM Gunfighter MOD 5 & 0.625” front sight base
I chose the Mod 5 because it is lower profile than the Mod 3 or 4 and seemed more in line with the project focus. The 0.625” front sight base will eventually get cut down to almost nothing and pinned in place if the project turns out the way I expect it to. Alternately, I may notch the top/front of the Troy handguard to allow for the FSB to protrude, but the cut-down and Daniel Defense front sight will weigh less overall.
Complete collection of parts for initial iteration of upper
Above parts dry-fit into complete upper to check for compatibility.
All should be go for final assembly.
With the last of the parts in-hand, I sat down to assemble the completed upper. I installed the gas tube in the gas block, then the barrel was attached to the upper using the supplied Troy barrel nut and the A2 flash hider was added to the barrel, then the two assemblies were combined before installing the TRX Extreme. I finished up by installing the front and rear sight before dropping in the bolt and charging handle. At this point I married the upper to my Colt 6933 lower which is currently wearing a Tango Down BG-17 grip and a CAR-style stock body, as well as a Tactical Link BAttery Assist Lever. The current receiver endplate is from Daniel Defense with the QD socket, but I will be replacing that with a similar product from Noveske so that the buttstock can lock in the closed position.
Complete, functional, carbine weighs 5 lbs 7.4 oz.
Same carbine with added T-1 in DD mount weighs 5 lbs 12.1 oz.
There are still changes to be made. I have a Magpul K-Grip on order which will replace the BG-17. I also have a BAD-ASS 45* throw safety that will replace the stock unit in the Colt lower at the same time as the grip. I am expecting a Mount-N-Slot hand stop to go at the very leading edge of the handguard, both to give me added traction to pull against but also to keep my hand from sliding forward past the muzzle. The sling I will be using is my Blue Force Gear Vickers Combat Applications Sling which I have converted to a 2-to--1-point cervertible sling so I will also add a Magpul Rail Sling Adapter at the top rear of the TRX handguard to accept the HK snaphook when used in 2-point mode.
I am considering purchasing a 9mm upper and having the gas tube hole drilled to replace the MUR, but for now I think this is a good configuration to test proof of concept and worry about tinkering with the minutia later on. Eventually I’m also hoping to swap out the rail, stock, and grip for versions of same in tan just to keep the heat down on the gun when it sits out in the hot sun.
I got to put some rounds through the gun in the above configuration. We ran a modified version of the Hackathorn Standards which I modified to work with the carbine. "The Hack" calls for several weak-hand-only strings with the handgun, and we fired those strings weak hand only with the carbine as well, which is where the lightweight nature of this gun really came in handy. I had no malfunctions while shooting, but several times when dropping the bolt on a fresh magazine it didn't go into battery and hung up with the round pushed partway out of the magazine. Those issues may track back to a worn action spring since this is a lower that gets a lot of use in various configurations. The round count for this session was 200 rounds.
A few more parts came in to get the project tweaked and finished up. Those parts are the Magpul MOE-K as well as a flat-top Rock River Arms 9mm upper with a gas tube hole drilled by ADCO. According to Magpul's website the MOE-K is intended for PDW style guns where the shooting hand is brought in closer to the body, which seems applicable for this project. Additionally, the 9mm upper receiver lacks the forward assist and brass deflector of the standard M4 upper, neither of which are of particular importance, meaning lighter overall weight.
Magpul MOE-K pistol grip
Rock River Arms 9mm upper receiver
I got the new parts mounted up, and put the whole assembly on the scale. As this project was coming together the goal in the back of my mind, secondary to meeting the needs of the intended application, was to hit 5.5 lbs with optic and irons, and this gun came in just under the unofficial goal at 5 lbs 7.4 oz.!
5 lbs 2.6 oz. with irons only
raises the question of whether 5 lbs flat with irons only would be possible
Goal Met! 5 lbs 7.4 oz.with irons and optic
With Magpul RSA and Tactical Link BAL added back to the gun
This is the configuration that I'll run the gun in when I get it out to the range
This past Tuesday night I put 56... well would have been 56... rounds through the gun. Somewhere near the 24th round of the first magazine the empty case got stuck in the chamber and required mortaring to clear. Fortunately it popped out with the first try. I've been shooting the WPA steel-cased ammunition in the hopes that it would cure the chronic stuck case issues I was encountering with the Wolf ammo in virtually all of my guns. Hopefully this is just an isolated incident but time will tell.
In other news, I'm not sure about the MOE-K grip just yet. It may be too small for my long fingers. The angle seems nice but the length is wrong and needs work. I'll continue to play with it, but so far my go-to grip in general is turning out to be the Tango Down BG-17 on other guns and it may make it's way back to this one as well, in spite of the weight increase. I am NOT willing to sacrifice function for weight savings and if the MOE-K doesn't work out it will go away.
The good news is that other than the stuck case this thing is AWESOME for the intended purpose: a light, short, gun for carrying at drills nights. It was out of the way, it wasn't fatiguing on the sling, etc. Absolutely perfect for that application. Cardboard doesn't care about ballistics, so even if we were shooting at distance the short barrel would be a non-issue. Completely happy with the gun so far and just need to track the minor issues going forward.
I got all of the furniture changed out to tan this past couple of weeks. Troy TRX Extreme 9.0 in tan, Cavarms CAR stock in tan, and Troy fixed front and rear BUIS in tan. Partly an aesthetic choice, partly because tan guns stay cooler to the touch when sitting out in the Florida sun.
Due to another gun not cycling, I ran the PDW for TD1 at an EAG Tactical (Pat Rogers) carbine course. Just under 300 rounds of 55 grain WPA functioned without issue except on initial chambering. Several times the round failed to chamber when the bolt was dropped after a magazine was inserted. This never happened on the emergency reload, just on initial loading. I will need to investigate changing the action spring, and will detail clean the bolt/carrier group and the inside of the upper receiver before amply re-lubing just to check. The Cavarms CAR stock appears to have been sized for a commercial receiver extension based on the insane amount of wobble. While it is functionally insignificant it does get annoying at times. (note to self, pick up a commercial RE just to have on hand to check such things. The ID of the stock can be measured but fitting to the real thing is a better check)
Recoil on this little gun is stout. Significantly so with loads like XM193 or the excellent Asym 55 grain training ammo, but even with the low pressure WPA. Inconsequential on singles and doubles, but it becomes an issue during long strings of fire like the Mod Navy Qual or when firing a non-standard response. Since this was always intended as a carried-a-lot-shot-a-little I'm not really concerned about it, and the WPA would be my typical round of choice with this gun at the events I'd typically run it. The small, hard, buttpad of the CAR stock doesn't help either. Yes, this is still a 5.56 gun and no, it isn't kicking like a garand, but for those considering a similar project you should be aware that this probably isn't the best type of gun to run for three days at a carbine course.
Last weekend at the Carbine 0.5 course I got a chance to do a little further proof of concept testing. This little gun originally started out in the planning steps to be a 14.5", carbine-length gas, A1-profile barrel that was as light as possible without going NFA for a woman or a child to learn on. At last weekend's course we had a female shooter who started the class with a loaner gun from her boyfriend that she encountered issues with, so we transitioned her into what I thought was the best solution, a BCM midl-length lightweight with all-MOE furniture and an Aimpoint C3. As it turns out, even this gun was a bit heavy for her, so I took the PDW off and gave it to her. The CAR-style stock was less than ideal for a new shooter due to the less-forgiving pocket positioning as well as the fact that this little gun does kick pretty good. So we took the MOE off of the BCM and put it on here, and she loved it! She did comment that it kicked more, and was louder, but she also commented that it was worth it to get the reduced weight and easier handling. and by the end of the day she was hitting A/C steel targets at 200 yards from prone, lightweight barrel and GI trigger and all! She also did not appear to have any trouble with the rear sight being in the way of the optic, and frankly I didn't even think to mention it to her. Her performance across all categories improved with the small gun.
During the first part of the class when I was using the gun myself, I did have several failures to feed when initially loading the gun up. These came about when locking the bolt to the rear, inserting the magazine, and dropping the bolt using the bolt release. I need to check the action spring for shortening but I also think it's a good object lesson relative to that method of charging the gun, and room for evaluation in terms of how we drop the bolt at the end of an emergency reload as well.