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If I had it to do over again, although there were no 20” ones available when I got mine, I would get a 20”. I like the idea of the extra velocity for potentially punching through armor.

I came to this conclusion when thinking about building a 20” AR for potentially defeating armor, but to decide to build my 20” AR more for a DMR role. Lugging its heavy ass around all day for the small advantage it might give me in potentially being able to defeat armor doesn’t seem worth it. But a 20” RFB and the minuscule weight penalty offered by those 3”, in a package that I’m guessing is around the size of 14.5” AR (or less), that is a much more appealing idea.

(Adding a pic of 20” AR build because I got a new optic and don’t have any IRL friends around to show that give a **** about such things.)
55235
 

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It depends on how you intended to use your RDB. If you just want to visit the range and shoot for groups, I don't think 20 or 17 would differ much.

The 5.56 round is designed to travel fast in order to deliver the intended effect in the military world. So if you want to use your RDB for hunting, it makes more sense to have a longer barrel.

I have used both M16A1 (20 inch barrel) and M4A1 (16 inch barrel) in the military and when we go to range with them we use different zeroing target for M4 and M16. Guess what? The zeroing standard is the same for them, merely adjustment is different. They both need to shoot a group fits in a 1 inch circle and I don't see how M16 is more accurate than M4 or the other way around. M16 has a muzzle velocity of 3100 and M4 is 2970, M16 has an effective range of 550 meters for individual target and M4 has 500 meters.

One last thing, use the ammo that is designed for the task, if you are shooting groups, the weight of the bullet will affect your accuracy more than the barrel length.
 

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I personally am in the 20" barrel club, and I was blessed with finding one at Classic Firearms. It may just be me, but shooting my 20" RDB is a much more pleasurable experience than shooting my 16" AR, less blast, less concussion, and I swear it's just a hair quieter. Additionally once both my AR & RDB have a their accessories (optic and a weapon light) on, the RDB is MUCH better balanced and still shorter overal. The upshot of all that is while the AR is more mechanically accurate (free floted barrel) I have better offhand or "practical accuracy" with the RDB because she balances SO much better. Plus if I can get a little better performance with a 20" I'll take it.
 

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I personally am in the 20" barrel club, and I was blessed with finding one at Classic Firearms. It may just be me, but shooting my 20" RDB is a much more pleasurable experience than shooting my 16" AR, less blast, less concussion, and I swear it's just a hair quieter. Additionally once both my AR & RDB have a their accessories (optic and a weapon light) on, the RDB is MUCH better balanced and still shorter overal. The upshot of all that is while the AR is more mechanically accurate (free floted barrel) I have better offhand or "practical accuracy" with the RDB because she balances SO much better. Plus if I can get a little better performance with a 20" I'll take it.
I honestly see no difference having a free floated handgaurd vs not in the Rdb. My Ar15 (and Mdrx) has the freefloat handgaurd and I regularly shoot groups between the Rdb and my Ar.Im just not seeing it.
 

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I honestly see no difference having a free floated handgaurd vs not in the Rdb. My Ar15 (and Mdrx) has the freefloat handgaurd and I regularly shoot groups between the Rdb and my Ar.Im just not seeing it.
If you’re not seeing differences in the groups you shoot between your AR and your RDB, your AR is trash.

*Edit because that sounds incredibly harsh and I’m not trying to be a phallus. The accuracy of the RDB is nowhere near that of the AR. It’s not to say that the RDB is a bad rifle, I love mine and wouldn’t say that, it’s just the RDB ain’t no DMR. Of course it’s also possible, albeit ridiculously unlikely, that you got a sub-MOA RDB.
 

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It may just be me, but shooting my 20" RDB is a much more pleasurable experience than shooting my 16" AR, less blast, less concussion, and I swear it's just a hair quieter.
It’s not just you, longer barrels are quieter for the same reason shorter barrels are louder; more time and volume to burn the powder inside the barrel. Same applies to flash, and a bigger boom almost always accompanies a bigger flash.

The RDB could potentially be slightly quieter than a DI AR because of the mechanisms of operation, but unless you have a can on it you will likely never be able to discern that particular difference in noise.
 

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If you’re not seeing differences in the groups you shoot between your AR and your RDB, your AR is trash.

*Edit because that sounds incredibly harsh and I’m not trying to be a phallus. The accuracy of the RDB is nowhere near that of the AR. It’s not to say that the RDB is a bad rifle, I love mine and wouldn’t say that, it’s just the RDB ain’t no DMR. Of course it’s also possible, albeit ridiculously unlikely, that you got a sub-MOA RDB.
It is a preproduction 1:9. Same twist as my Ar. Butt I'm also not getting sub moa out of my Mdr. Best Ive gotta so far is (RDB) around 1moa with Fiocchi Extrema 50gr (5shot groups with a 3x Prisim).

I believe Dmrs are typically 1.5moa..Which..I can get with almost all of my rifles to average 1.5moa in 5 shot groups (not typical blasting rounds tho..), usually with match ammo in my 308s.556s I don't usually get match ammo)
 

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Does anyone know if Kel-Tec will sell me a 17" RDB Barrel? I will call them on Monday but that's 36 hours away.
 

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It is a preproduction 1:9. Same twist as my Ar. Butt I'm also not getting sub moa out of my Mdr. Best Ive gotta so far is (RDB) around 1moa with Fiocchi Extrema 50gr (5shot groups with a 3x Prisim).

I believe Dmrs are typically 1.5moa..Which..I can get with almost all of my rifles to average 1.5moa in 5 shot groups (not typical blasting rounds tho..), usually with match ammo in my 308s.556s I don't usually get match ammo)
You should have bought a lottery ticket the day you bought your RDB, sounds like it was your lucky day!
 
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