I've teased this project in the pictures thread, but I have managed to bubba together a "free floated" RDB. A little background...
I bought the RDB defender in the summer of 2020. For a year, I fought with the thing, trying to get it to hold zero for more than 2 range sessions. I first ran it with a holosun 503C and Leupold D-EVO, and every range visit it seemed like I had to rezero both optics. In the begining, I could identify root cause: I had to re-red loctite the optic rail front screws 2 separate times after it worked loose after a few magazines, and I had a loose muzzle device one range visit as well. But after I got the optic rail to stay put, it still felt like I couldn't get the rifle to group consistently. I assumed that it was me, but I would switch over to a buddy's rifle and hit 1 MOA targets no problem with ease. I threw an LPVO on the RDB, hoping that it was the $1000 DEVO that wouldn't hold zero, but I had the same experience of wandering zeros.
At some point, I decided I was frustrated enough to sell the thing, but the local gun shop wanted 40% off the top and mucking around with a private sale was unappealing. So I decided that the RDB was worth more to me as an experiment than as cash and started cutting.
...........START RANT. SCROLL DOWN TO SKIP......................................................................................................
I had identified a couple of areas where I thought the RDB design really showcased KT's "oversights," for lack of a better word:
- Non-free floated handguard was a mistake, period. Even if it didn't make that much of a difference on THIS particular design (and it actually does), there is no reason to be building a gun in the mid 2010s without taking into consideration all the things learned in the decades of AR development. It's free R&D, and yet not a single KT 5.56 design takes this into account.
- The pencil barrel in and of itself is fine, IF it is properly manufactured and heat treated. I have a sneaking suspicion that the KT barrels are neither. Would a normal profile barrel help? I don't know. There is enough crap glued to the end of the barrel that the harmonics are all fubar anyway, but maybe it would help with heat deflection and handguard pressure.
- The optics rail being integral to the barrel assembly is a really cool idea, IF and only IF, you have access to barrel swap kits. Having the optic stay zeroed to the barrel while you swap from a 10" 300AAC SBR to a 17" 5.56 pencil to a 24" 6.5CM or 6mm ARC sounds really amazing. Too bad the ONLY things KT has actually released for the RDB as an upgrade to the base 2013 model in 9 years are a few CA compliant stocks, the survivor/"drink your pee", and the defender handguard. KT, as usual, failed to deliver on any of the hype-train future upgrade selling points. Which is fine. They seem to be doing perfectly fine and I can respect the decision to focus resources on making a smaller number of products and not expanding the company purely to meet demand. BUT, back to the main topic, there ARE NO BARREL SWAP KITS. Which means having the aluminium optics rail half-floating on the steel barrel/gas block assembly is insane. The whole reason they have that silly spring washer in the back is because they couldn't figure out how to build a rigid assembly out of materials with different coefficients of expansion. When they got to that point, the engineer should have stepped back and thought about the alternatives.
- Barrel to receiver lockup is sloppy, at least on my RDB. That means you can't put the optics rail on the receiver because you can grab the barrel and wiggle it up and down when it is pinned together with the 2 QD pins.
I can't believe we're even having this argument: build the most precise gun you can so that when you put it in the hands of a tired, sleep deprived, IED-near-missed grunt with a concussion, the extra 3-4 MOA of hand shake and adrenaline doesn't turn your hostage target into a shot patterning board.
Maybe the sub-par accuracy is a compromise due to the better trigger? Not from where I'm sitting. The relocated sear is brilliant, and the rear ejection is awesome: I totally agree, but why should that make the gun more or less precise? As far as I know, the long bolt travel and sear at the handguard shouldn't really have anything to do with how well the bolt locks up or how the barrel behaves.
Maybe there is just an inherent limitation to piston driven designs? The m27 is allegedly a 2 MOA rifle running m855 (a mediocre performing round) and it's piston driven, so you can certainly make a piston gun that shoots just fine if you put a nice barrel and a free float handguard on it.
I just don't understand how a brand new, from scratch designed $1300 (MSRP in 2015 ) rifle could really be acceptable printing 3-4 MOA from a vise.
So the first thing I did was make a real free floated handguard. It took a month to work up the courage to go full bubba, but I eventually got out the hacksaw and cut away the front of the plastic lower above the trigger group. I did this to expose the metal receiver "ears" where the front pin goes through. Then I welded on two extensions that the handguard would mount to, removing the connection to the gas block that all the RDB handguards (even the LI Raptor/Rhino) suffer from.
I ordered a bunch of handguards for ARs and AKs (almost bought a FNC rail) and found a super slim keymod AK long front rail worked the best. A little more hacksaw-based carnage and I had a hanguard that would fit over the receiver extension. Excellent.
With the new handguard, the RDB started taking on a L86A2 LSW vibe and I liked what I saw...
Next victim: that damn optics rail!
I used a torch to get the OEM optics rail off (after I finally got those darn screws to stay put...) and had to figure out how to mount an optic to the monstrosity. I really wanted to mount the rail to the receiver but the lockup between the barrel/chamber and the reciever has 2-3 mm of vertical play in it that made that a complete non-starter. I thought about welding up a better fitment at the front end of the receiver, but there was no guarantee that I could get it tight enough to hold zero.
So, AK gas block style it is. I scavenged some pic rail from the parts drawer and kitbashed out a mount for the 503c.
Time to hit the range!