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View Full Version : M-Lok rail recommendation as URX 3.1 replacement


gunf1ghter
03-16-16, 20:31
Hey guys,

One of my SBR uppers is an AAC 9" 300BLK with the factory installed KAC URX 3.1 rail. The upper is rock solid but I despise the chunky KAC rail and am itching to replace the rail with an M-Lok model but can't find anything at the same 8 inch length as the URX.

Would it be better to go 7.0 or is there a chance that I could get a 9" rail to work on the 9" barrel and still have clearance for my suppressor?

I could/would go keymod but I have several other rifles with keymod and was itching to try an M-Lok setup.

Thanks.
jackblack73
03-16-16, 22:04
I have the same upper and have thought about changing the chunky URX too. Although I might not just because I don't want to deal with that barrel nut. I didn't see too many 8" MLOK rails out there, but an SLR was at the top of my list. Can't remember the model though. More recently I've noticed the Fortis Rev II looks pretty nice.
scooter22
03-16-16, 22:30
KAC URX4
titsonritz
03-16-16, 22:35
KAC URX4

They are Keymod
M4Guru
03-16-16, 22:47
Not anymore. KAC has been shipping M-LOK URX4s for a couple months. I don't know if the 8" is available yet, but the 10" and 13" are.

https://www.boltcarrier.com/product/urx-4-556-ibn-10-75-rail-assembly-mlok
Jwknutson17
03-16-16, 22:50
They are Keymod

They are also MLOK. I just picked up my SR25 MLOK and would have to say it is one of the best feeling rails I have picked up.
PorkchopExpress
03-16-16, 23:30
I've had 2 SLR 8" mlok rails on my 9", love them both. Started with the ultralight solo, which is extremely light and slim. Recently swapped it for one of their new ION series to try out.
titsonritz
03-16-16, 23:55
Not anymore. KAC has been shipping M-LOK URX4s for a couple months. I don't know if the 8" is available yet, but the 10" and 13" are.

https://www.boltcarrier.com/product/urx-4-556-ibn-10-75-rail-assembly-mlok


They are also MLOK. I just picked up my SR25 MLOK and would have to say it is one of the best feeling rails I have picked up.

Well I guess I'm behind the times, thanks for the update.
gunf1ghter
03-17-16, 00:05
Thanks guys for all the ideas. I didn't know about KAC making mlok so that is one idea. SLR 8" looks like it could be perfect but out of stock.

If I knew that a 9 handguard would work and have enough clearance for my 51T mount and Saker I would probably just get the Midwest industries or Geissele rail.
Primus Pilum
03-17-16, 00:46
As a kac fanatic, go with the mk8.

The urx 3.1 is still one of the top rails on the market, there is no way I would replace it with anything.
jstalford
03-17-16, 00:58
ALG has an 8"


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themonk
03-17-16, 06:20
I am in the same boat and have been looking for a replacement for a few years. FYI- the URX4 is an 8.5" rail and the URX3.1 is 8". Depending on what suppressor you run this can be an issue.

There are very few 8" rails on the market. ALG & SLR are really the only decent ones if you want to call them that. I dont think they are in the same league as the Knights.
gunf1ghter
03-17-16, 08:12
As a kac fanatic, go with the mk8.

The urx 3.1 is still one of the top rails on the market, there is no way I would replace it with anything.

I'll be selling the URX 3.1 once I get it replaced.
gunf1ghter
03-17-16, 08:41
ALG has an 8"


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Yeah, I'm not a fan of the "smooth rail" concept any more than I'm a fail of the chunky rail. I like the rail to be as minimal as possible and I'll add the stuff to it as I see fit.

For a good reference of what I actually do like, I love the keymod rails that are on my BCM uppers. It's better than pretty much any other keymod rail I have tried. I can put a few panels on it near the forward grip and put on any other mounts/qds, etc, that I need. I also like that it's seven sided.
M4Guru
03-17-16, 10:19
http://www.megaarms.com/ar-15/ar-15-hand-guards/wedge-lock-ar-15-hand-guard/nggallery/thumbnails

If you like the KMR, the Mega Wedge Lock feels very similar in the hand. 7" and 9", no 8" at this time.
gunf1ghter
03-17-16, 10:30
http://www.megaarms.com/ar-15/ar-15-hand-guards/wedge-lock-ar-15-hand-guard/nggallery/thumbnails

If you like the KMR, the Mega Wedge Lock feels very similar in the hand. 7" and 9", no 8" at this time.

Yeah, same problem, hardly anyone making 8" guards even with the prevalence of 9" barrel 300BLK SBRs out there. I would just put a 7" hand guard on it but the only reason I can justify the expense of changing it out is to get as much forward grip on it as possible.
samuse
03-17-16, 14:08
As a kac fanatic, go with the mk8.

The urx 3.1 is still one of the top rails on the market, there is no way I would replace it with anything.

I agree. The 3.1 is the best rail I've ever used and I hope KAC keeps making 'em. I have three and want to pick up one more...
gunf1ghter
03-17-16, 14:43
I agree. The 3.1 is the best rail I've ever used and I hope KAC keeps making 'em. I have three and want to pick up one more...

If you need a short one I will sell you the one I have as soon as I find something to replace it with that meets my needs. I know plenty of guys that still love quad rails, but I hate those too.
wickedyz
03-17-16, 14:55
They are also MLOK. I just picked up my SR25 MLOK and would have to say it is one of the best feeling rails I have picked up.

I really like the feel of the URX 4, but I wish they would have put an anti-rotation system onto the rail.
BC98
03-17-16, 16:03
I really like the feel of the URX 4, but I wish they would have put an anti-rotation system onto the rail.

Have you had one turn?
gunf1ghter
03-19-16, 00:02
Unfortunately KAC only shows the 8.5 URX4 in Keymod on their website and I wants me some m-lok lovin.
Boba Fett v2
03-19-16, 00:28
Never thought I'd hear the URX 3.1 be referred to as "chunky".
jackblack73
03-19-16, 00:43
Never thought I'd hear the URX 3.1 be referred to as "chunky".

Why? It's clearly huge compared to many newer rails. Especially the 8" because it's so short I hold it where the picatinny is.
Boba Fett v2
03-19-16, 00:46
Why? It's clearly huge compared to many newer rails. Especially the 8" because it's so short I hold it where the picatinny is.
Maybe if you have girl hands. In that case I understand.

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Failure2Stop
03-19-16, 07:33
I really like the feel of the URX 4, but I wish they would have put an anti-rotation system onto the rail.
75+ ft/lbs of torque and thread sealant is pretty resistant to rotation.
gunf1ghter
03-19-16, 10:19
Why? It's clearly huge compared to many newer rails. Especially the 8" because it's so short I hold it where the picatinny is.

Yeah, same deal for me. It's not necessarily that there's anything "wrong" with it, it's just that I've taken multiple classes with the slimmer keymod rails and the URX feels chunky and alien like in my hand, I choke up all the way to where the picatinny section is and it feels awkward. I'd say I have medium/large hands, usually wear size L gloves.

It's great that people love the URX 3.1 so much, will hopefully make it easier for me to sell mine when I find a replacement in M-LOK.
1911-A1
03-20-16, 14:20
I've grown to hate the 3.1 screw and nut attachment method and the crappy selection of rail lengths they offer, and how they don't sit flush with the built-in rails. I'm switching to an MLOK URX4 when the 14" models hit the market.
Firefly
03-20-16, 14:53
Hmm....I adore my URX 3.1 rails. I keep my stuff relatively basic. And the 3.1 makes a lot of sense. Although I do want to put a Geissele rail on a project of mine.

That said I can't wait for stand alone SR25 MLok rails
gunf1ghter
03-20-16, 15:19
I found a SKU for URX 4 8.5 in m-lok. Out of stock but looks like it exists even though it isn't on the KAC website.
Jwknutson17
03-20-16, 15:44
Hmm....I adore my URX 3.1 rails. I keep my stuff relatively basic. And the 3.1 makes a lot of sense. Although I do want to put a Geissele rail on a project of mine.

That said I can't wait for stand alone SR25 MLok rails

The KAC SR25 MLok I have feels a lot like my Geissele MK1 and MK3 rails. Prob why I like it so much. Add in the URX3.1, and you just named my 4 favorite rails, hands down.
Firefly
03-20-16, 16:54
The KAC SR25 MLok I have feels a lot like my Geissele MK1 and MK3 rails. Prob why I like it so much. Add in the URX3.1, and you just named my 4 favorite rails, hands down.

Aww now I GOTTA get me that rail.
Apparently the 556 one is out but I would love to upgrade my ECC or do another build.
Or probably just save up....

My word, KAC is addictive.
gunf1ghter
03-22-16, 16:00
My local handy dandy armorers said that out of everything out there the only thing that is a direct replacement for the KAC is the SLR 8" M-Lok Rail.

They did however strongly suggest that if I'm open to going with a 7" rail I save my money and get a Midwest Industries 7" m-lok setup, which is cheaper than the SLR and which they will do the swap out on with the existing KAC rail for free. Comments?

We also checked and with the existing barrel it will not be possible to even go to an 8.5" rail (URX 4) without interfering with the 51T flash hider on the currently installed suppressor mounting system.
themonk
03-22-16, 16:14
SO they essentially said everything already stated in this thread. Personally I would not go to a 7" rail as you would be losing valuable length and IMHO I would not include MI in the same league as Knights, and I say that as someone who owns two MI rails.
gunf1ghter
03-22-16, 16:22
SO they essentially said everything already stated in this thread. Personally I would not go to a 7" rail as you would be losing valuable length and IMHO I would not include MI in the same league as Knights, and I say that as someone who owns two MI rails.

So you're arguing to just keep the URX 3.1? Or you are saying SLR is more in league with KAC than MI is? I get it that KAC is some of the best stuff out there. I just don't particularly like the URX 3.1 in the shorter length. I might be happy as a clam with it on a 11.5" or 16" barrel setup.

Well, it's 1" and they actually had one already set up, with the Magpul AFG for M-Lok installed it was not too much of a loss. The rail space is still a bit more useable since it's got 7 mount surfaces and you aren't losing 1.5" to the picatinny sections on the front like on the URX 3.1.

I'm debating it. They install the MI rail for free since they sell it. If I elect to go to the SLR they will charge me about $50 to do the swap which is worth it since I don't want to have to buy the KAC wrench.

They showed me the key system on the newer MI rails and said they aren't sure how SLR does anti rotation on their hand guards or if they do it at all.
themonk
03-22-16, 16:33
As I said above, ALG and SLR are the only game in town for 8" rails. SLR makes good stuff as does ALG, but they are not in the same conversation as geissele and Knights. If you really want out of the URX I would personally go with the SLR. They make good stuff and have great customer service.