Question on Barrel/Rail/Suppressor Clearance

[Mr.Goodtimes]

I'm in the planning process of putting together my first SBR and am wondering, would a Larue 11.0 Rail work with a BCM 11.5in barrel and AAC M42k or Mini? If not that then would it work with a Surefire Can on one of their mounts with the little spacer at the back?

I have not seen this setup anywhere so I'm thinking that I may have to go with a 12.5 in barrel. I wan't to stick with the 11.0 rail length as not only is that my preferred length, I'm on a bit of a budget and already have a larue 11.0.

Cheers,

Goodtimes

[rob_s]

General rule of thumb on the AAC cans is 1" difference between stated rail length and stated barrel length. Obviously this does not apply to reflex models.

So a 9.5 rail on a 10.5" barrel. 11.5 rail on 12.5" barrel. 7.0 rail on an 8" barrel (like the Noveske 300 BLK).

[Mr.Goodtimes]

Thanks Rob. Do you know if one of the surefire cans (either Mini or K) would work with one of the extended adapters such as this one:

http://i55.tinypic.com/11s2npy.jpg

[todd.k]

The SF silencer will mount all the way to the back of that brake. You will need a 12" barrel to use an 11" rail and mount a silencer.

[Mr.Goodtimes]

Thanks Rob and Todd. It looks like I'll be going with a 12.5in barrel as I really want to stick with the 11in rail.

Todd I've been considering one of your new 12.5in general purpose uppers. Do you guys do semi custom orders? What I'm looking for is the upper minus handguards and barrel nut with a low pro gas block pinned to the barrel. I would by a basic complete upper but I would rather not spend the money on handguards and an A2 FSB that are going to come off anyway.

If not will yall be offering your 12.5 hammer forged barrels for sale anytime soon? I would be all over one to go with a matched upper/lower.

[rob_s]

A 12.5" barrel and an 11.0 rail make for a pretty safe combination for all but reflex cans like the Ops, Inc. and the AAC SPR-M4 type. You'll have a small gap but it's a non-issue for all but aesthetic reasons.

[Mr.Goodtimes]

Is there still any advantage to using a reflex can these days anyways? Regardless, though, I'm going to be using a mini can to keep weight down. I'm also waiting to see some stuff about the new cans that Knights is releasing before I make a decision.

[rob_s]

The reflex cans to tend to have better noise-reduction:added-length but it really depends on the design.
SPR-M4 (http://www.advanced-armament.com/product.aspx?pid=198)
Length added: 4.90"
Length added: 4.90"
M4-2000 (http://www.advanced-armament.com/product.aspx?pid=197)
Length added: 5.10"
Sound Reduction: 32-34dB


However, a reflex can I make in my garage is probably going to be less effective than an M4-2000, for example, so it's not just about the overall design.

There are also other considerations like the gun/rail being used. In my case I bought a 6933, a 9.0 rail system, and an Ops, Inc. 15th model (at least I think it's a 15th) and they all interface together perfectly.

Current configuration
http://i134.photobucket.com/albums/q111/rob_s/gun%20stuff/00f44f58.jpg


original configuration

without can
http://i134.photobucket.com/albums/q111/rob_s/gun%20stuff/DSC_1757-Small.jpg

with can
http://i134.photobucket.com/albums/q111/rob_s/gun%20stuff/DSC_1758-Small.jpg

[Mr.Goodtimes]

I thought I'd bump this thread. I'm pretty indecisive these days about what I want for my SBR. I'm having trouble deciding mostly because of trying to figure out what can/rail combo I want to use. Using my superhuman reasoning skills, if you (rob_s) used an OPS can on an 11.5in barrel with 9.0 rail, would it be safe to say that I could use the same can on a 12.5in barrel with a 10in DD Lite rail?

EDIT: If I can use a 12.5 in barrel with 10.0 Lite Rail and OPS 15th then I think I may have my mind made up. I've heard nothing but good things about OPS products.

Also, Rob, how would you say your OPS can compares with others on the market such as the M4-2000 and surefire cans?

[rob_s]

I think your math is sound, but can't guarantee it.

I'm not really a can guy, as I've discovered since buying mine. The Ops can is fine, it's just old tech, especially in the mounting department.

Were I starting form scratch today I'd be looking at the 762SD-N-6 can from AAC as a do-all, and probably mount it on a 10.5" barrel (something like this (http://noveskerifleworks.com/cgi-bin/imcart/display.cgi?item_id=lslp-556-sb&cat=136&page=1&search=&since=&status=)) but that's really staring to screw with your math! My one caveat with that system is that the Noveske rail is heavy in comparison to others, but they are the only ones making lengths that are logical when combined with a can.

[Rodman24]

I recently built out a 10.3" DD with an M4-2000 and a 9" Troy TRX Extreme. The overall length is 1" shy of my 16" with the AAC brake.

Dirty little SOB.

http://farm7.static.flickr.com/6006/5871550398_57febae2d3_b.jpg.

[rob_s]

Rodman that looks like a well thought out AR. One or two minor things I'd change personally but very well thought out. I like to see logic and reason employed in these things. Good job.

[Rodman24]

Rodman that looks like a well thought out AR. One or two minor things I'd change personally but very well thought out. I like to see logic and reason employed in these things. Good job.

Thanks. Don't mean to hijack the thread, but to answer your question about the thought process...

This was meant be more of a HD/fun to shoot set up. I wanted to keep it as short as my 16" but suppressed. I think I can pick out a couple of items that I think you might do differently: stock and oversized mag release, maybe EOTECH vs Aimpoint.

I changed out the oversized mag release and installed a KAC ambi-release (I'm a LH shooter) which I very pleased with. My concern with the oversized release is that it might promote an accidental release. It's never been an issue, but since it sticks out a little further I removed it just to be safe.

The UBR is heavier, but I really like the balance.

I'm actually building an identical lower for my 16" upper. I'd like to have them set up the same way unless there's a very good reason. At the moment this lower is host to both uppers.

Also installed is the BAD-ASS ST. I love the short throw.

MIAD grip - I've tried many others, but the MIAD fits the bill for me.

Trigger is a JP sigle stage. Another personal preference item I suppose.

As for the upper itself, I went with the full rise Aimpoint mount from LaRue (lower 1/3 cowitness). I wanted it to be as quick into action as possible. I might move to a flip up on the rear but I arlready had the DD fixed rear. I know some prefer stay with fixed sights when using red dot sights, but I'm also thinking about potential snags. That's why I went with the KAC micro front sight (which I like very much). Right now the two don't necessarily make sense together, but I think I would be more concerned with snagging the front.

I don't have my light solution figured out at this point. I'm currently working with a rail section mounted at 7:30 (which you can barely see in this pic). This provides a pretty good position for middle finger toggle activation for my TR-3 (thinking of a lower profile light like the X-300). So far I'm pleased with this positioning. It doesn't interfere with my grip and the front of the rail section actually provides a point for me apply pressure with my index finger (pulled snuggly to my shoulder).

[rob_s]

I like your carbine so much that I posted a link to your post on my facebook fan page. and your description of your reasonings makes it even better.

I get a lot of grief for jumping on newbies, and I have no idea if you're a newbie or not, but you obviously engaged your brain when you put that gun together and it shows. Congratulations. and a satan-hander to boot! :D

[Rodman24]

I like your carbine so much that I posted a link to your post on my facebook fan page. and your description of your reasonings makes it even better.

I get a lot of grief for jumping on newbies, and I have no idea if you're a newbie or not, but you obviously engaged your brain when you put that gun together and it shows. Congratulations. and a satan-hander to boot! :D

Thanks for the compliment. As much as I would like to say I'm not a newbie, I guess I am. I've really only been working with the AR platform for about 2 years.

I've been fortunate enough to have time and opportunity to learn from those who have experience, and enough money to try out equipment for myself. I'm always interested in learning and thinking things through.

[Mr.Goodtimes]

Rodman's rifle is a very well thought out bean. One reason I'm taking so long to decide with my SBR is because I'm making it a very well thought out piece. I don't have much money and the money I do have is going into quality components so I need to make sure I get it right the first time. My goal is a lightweight, general purpose rifle. I want a suppressor not for the CDI factor but because I look at it as a viable item for a home defense/cqb rifle. My goal with my SBR is to have a gun that when suppressed, is the same length or shorter than my 16in gun with a surefire brake.

Options I'm considering:

1. 12.5in bbl w/ DD MK18 RIS II and SPR-M4
2. 12.5in bbl w/ DD Lite Rail 10.0 and OPS Inc. 15th
3. 12.5in bbl w/ Larue Tactical 11.0 and AAC M4-2000

Option 3 would be the cheapest for me as I already have a Larue 11.0 however, I'm not positive this is what I want to do as option 1 would work better for when I put together my 16in precision upper. Option 2 I'm not sure about as I think the OPS cans may be kind of loud when compared to other more modern designs. Also, I'm a little uneasy with their warranty of only two years when AAC offers a lifetime warranty, plus the can is made entirely of inconell where the OPS is all SS. I also greatly prefer AAC's mounting options. I only wish I could get the M.I.T.E.R. mount as a brake instead of FH.

While I really like the SPR-M4, I like the extra rail space afforded to me by the Larue 11.0 rail system. This would also be nice as both my SBR and SPR would use the same rail.

[JasonM]

Rodman's rifle is a very well thought out bean. One reason I'm taking so long to decide with my SBR is because I'm making it a very well thought out piece. I don't have much money and the money I do have is going into quality components so I need to make sure I get it right the first time. My goal is a lightweight, general purpose rifle. I want a suppressor not for the CDI factor but because I look at it as a viable item for a home defense/cqb rifle. My goal with my SBR is to have a gun that when suppressed, is the same length or shorter than my 16in gun with a surefire brake.

Options I'm considering:

1. 12.5in bbl w/ DD MK18 RIS II and SPR-M4
2. 12.5in bbl w/ DD Lite Rail 10.0 and OPS Inc. 15th
3. 12.5in bbl w/ Larue Tactical 11.0 and AAC M4-2000

Option 3 would be the cheapest for me as I already have a Larue 11.0 however, I'm not positive this is what I want to do as option 1 would work better for when I put together my 16in precision upper. Option 2 I'm not sure about as I think the OPS cans may be kind of loud when compared to other more modern designs. Also, I'm a little uneasy with their warranty of only two years when AAC offers a lifetime warranty, plus the can is made entirely of inconell where the OPS is all SS. I also greatly prefer AAC's mounting options. I only wish I could get the M.I.T.E.R. mount as a brake instead of FH.

While I really like the SPR-M4, I like the extra rail space afforded to me by the Larue 11.0 rail system. This would also be nice as both my SBR and SPR would use the same rail.


First, there IS a muzzle brake mount for the SPR/M4 - check with Randall at Allen Arms Tactical or Jeremy at Bullseye Indoor Range, or Bryon at Major Malfunction.

Of all your options mentioned, I'd go 11.5 bbl with DD RIS II rail and AAC M4-2000.

I am not a fan of the MITER system overall... you are limited in terms of mount choices, the mounts are more expensive, you are limited in terms of barrel lengths and rail combos.
It is longer and heavier than the M4-2000 and from a practical standpoint, you aren't going to notice 1, 2 or 3 dB when we are talking 5.56 guns. Plus, the tuning feature isn't guaranteed to get you a zero POI shift position. Shift will be minimal (within a few MOA) and completely repeatable with any good can.

Your idea of setting up the same rail on your SBR and SPR is a good one of you end up going that direction.

You can sell the Larue rail to make up some of the cost.

[rob_s]

Goodtimes, I certainly applaud your attempt to produce a well-thought-out end product. That's too lacking in these things for most folks (which is why Rodman's gun stood out to me, I think).

However, you can make yourself insane too, and the longer you wait the more new stuff comes out and derails what you're doing. At some point you have to put a pin in it and just jump.

I have to agree with Jason on the SPR-M4. I was going to go that route on a 6.8 upper and was going to use the same can for a 5.56, etc. and I just don't like the added length for no real perceptible benefit.

[Rodman24]

I agree with Jason and Rob. Jason's comment on the 11.5 with the RIS II but I would go with the M4-2000 - I think that would be a good combination. Rob's comment about avoiding what I call "Analysis Paralysis" is also worth noting. At some point you may have ideas that cross over from one purpose built rifle to the next.

I also like the idea of the 12.5 "General Purpose" with the Lite 10". That will likely be my next build (one of these days). The 12.5 will be a better range/class gun for both suppressed and non-suppressd use. You'll have a little longer dwell time and velocity (little cleaner too).

I would consider selling the LaRue to help finance the weapon you truly want. I still have unused parts sitting around. They're currently unused for a reason. If they don't fit with the build...so be it.

Think of it like this: You're committing to spend $1400+ solely for a suppressed SBR combination. I wouldn't skimp on any element of this build.

If you really have reason to use the LaRue that's great. I just assumed you may not REALLY want to use it on this one.

[johnson]

Yeah, the SPR/M4 is longer but does it even matter since most of it goes over the barrel?

[rob_s]

Yeah, the SPR/M4 is longer but does it even matter since most of it goes over the barrel?

IMO yes (https://docs.google.com/spreadsheet/pub?hl=en_US&hl=en_US&key=0Ajl2UPK0UHPscHdzd2hlZ2hOUXNHUnRyVUVVM3B0REE&output=html)

First of all it weighs 1.5 oz more, which doesn't sound like a lot until you add it to the end of the barrel. Second of all, while the M42k and SPRm4 are both supposed to add only 4" past the end of the mount, IIRC the SPR mount adds more past the muzzle.

[rob_s]

Rodman, I like it so much I'm copying it. I'm skipping the can for now and building an unsupressed version, but I'm doing the DD 10.3", Vltor MUR (no forward assist), 9.0 TRX Extreme, BADASS 45*, etc. I'm going to use a CAR stock and a single-point sling setup for now.

I think that if I like this configuration I'll make a twin that is setup for suppressing. Thanks for posting!