Rail length on 16" carbine - Page 1

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[ARCHIVED THREAD] - Rail length on 16" carbine (Page 1 of 2)

Posted: 1/16/2021 1:43:00 AM EDT

I thought that this topic would have been beaten to death, but a search doesn't pull anything up recently and what I did find in a general search was several years old.

What is the preferred rail length on a 16" carbine and why?

Let's take for example a BCM MCMR 13" versus 15" rail.

The 15" rail would be the choice if one were using a suppressor, or needed a ton of space for accessories.

The 13" rail leaves a bit more barrel exposed, but if one were not using a suppressor and did not need the space of the 15", is there any reason that I am missing to not get the 13"?

Thanks.

Posted: 1/16/2021 1:48:35 AM EDT

[#1]

And yes, I read the What Rail Length Do I Need? A Guide thread.

But that is "a thread discussing the basics of rail length compared to barrel length."

I know what a 13" versus 15" rail is on a 16" barrel (BCM has pics on their website).

I am interested in the "why" one versus the other. Is the point simply to cover up as much barrel as possible? Or at some point does excess rail just add weight and bulk?

Posted: 1/16/2021 1:59:44 AM EDT

[#2]

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Quoted:
And yes, I read the What Rail Length Do I Need? A Guide thread.

But that is "a thread discussing the basics of rail length compared to barrel length."

I know what a 13" versus 15" rail is on a 16" barrel (BCM has pics on their website).

I am interested in the "why" one versus the other. Is the point simply to cover up as much barrel as possible? Or at some point does excess rail just add weight and bulk?

View Quote

Gives you more room for mounting stuff, gives you a longer sight radius if using irons, and probably most useful, it gives you more working space and better control for your support hand. Tradeoff is a bit of weight.

Everybody's needs are different, but personally I like to run as much handguard as I can, especially with M-Lok (or Keymod), where the weight increase of a couple inches ain't that big. Quad pic rails, different story.

Posted: 1/16/2021 2:16:13 AM EDT

[#3]

Quote History

Quoted:

Gives you more room for mounting stuff, gives you a longer sight radius if using irons, and probably most useful, it gives you more working space and better control for your support hand. Tradeoff is a bit of weight.

Everybody's needs are different, but personally I like to run as much handguard as I can, especially with M-Lok (or Keymod), where the weight increase of a couple inches ain't that big. Quad pic rails, different story.

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Thanks, yeah I am moving from a Larue quad rail and have a 13" BCM MCMR on backorder. I am debating changing the order to a 15" MCMR.

Anyone have a preference for the 13"?

Posted: 1/16/2021 2:18:48 AM EDT

[#4]

I'm rocking a 13" rail on my 16" middy that doesn't have FSB.

Posted: 1/16/2021 2:27:43 AM EDT

[#5]

I think that with a 13" I can keep the light back a bit further to centralize weight and not have a huge shadow from the rail (yes I know the barrel produces a shadow).

Posted: 1/16/2021 2:34:33 AM EDT

[#6]

I run a 10" rail on my 12" setup (plus can).

13" hand guard on 16" is only about an inch more barrel. Still easy enough to adjust gas block

Posted: 1/16/2021 2:38:58 AM EDT

[#7]

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I run a 10" rail on my 12" setup (plus can).

13" hand guard on 16" is only about an inch more barrel. Still easy enough to adjust gas block

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Yeah, I have a BCM 11.5" with a 10" rail. I have the light back a bit to both protect the bezel and keep it from getting coated with carbon (it is maybe even with the end of the flash suppressor).

Just trying to decide if that's how much barrel coverage that I want on the 16" rifle....

Posted: 1/16/2021 5:58:16 AM EDT

[#8]

At some point you reach the longest you want your arm out. For me thats 13” and I doubt it’s much longer for many people.

Posted: 1/16/2021 9:42:19 AM EDT

[#9]

I ran a 15" on a middy 16 for about a year. Went back to a 13" It just balances better for me. AND I think it looks better.

Posted: 1/16/2021 11:08:08 AM EDT

[#10]

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I ran a 15" on a middy 16 for about a year. Went back to a 13" It just balances better for me. AND I think it looks better.

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I think that might be where I am at.

I need to pick up some miscellaneous parts. I should check out some rifles at the LGS and spend some money there.

Posted: 1/16/2021 11:32:37 AM EDT

[#11]

I am replacing my middy with a 10" m-lok handguard. The GB will peek out a wee bit but that doesn't bother me. I don't see the need for adding weight and I like the look and handling.

Posted: 1/16/2021 6:06:58 PM EDT

[#12]

13" is as long as like. I'm not real tall and shoot squared up and reaching out to the end of a 13 or 15" rail isn't my thing.

The only two carbines I have with a rail are 7" with a FSB. Works better for me working structures with the light.

Posted: 1/16/2021 6:22:00 PM EDT

[#13]

I got both.

The 15 is slightly my preference because my light has a pressure switch, which lets me mount the light further forward and out of the way. Also, less chance of the barrel resting on barricades.

Posted: 1/16/2021 6:43:55 PM EDT

[#14]

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I got both.

The 15 is slightly my preference because my light has a pressure switch, which lets me mount the light further forward and out of the way. Also, less chance of the barrel resting on barricades.

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Just visited my friendly LGS. They recommend as long of a rail as possible for coverage and at a very slight weight increase. They know their stuff and I trust their advice. Also got to handle a 14.5 with 13” rail which is about the same coverage of a 15” rail on a 16”.

A 15” would also give me more coverage to prevent burns when it is slung.

I think I am gravitating toward the 15” rail.

So far the reasons to not get the 15” are that it looks goofy and there are several additional grams of weight.

The reasons not to get a 13” are potentially limiting options, exposed barrel (burns when slung and barricades), can’t get light as far forward to get it away from the pressure pad VFG area, etc,

Posted: 1/16/2021 6:54:39 PM EDT

[#15]

I’m traditionally a “7” on a carbine, 9” on midlength, 12” on rifle length” guy, because I do prefer a pinned front sight base to something mounted to a rail.
That said, I do have other lengths and one advantage to a 15” one is that I can mount a light (Surefire 300u) on the 12-o’clock rail and still have my front sight (LMT) pretty far forward right behind it. It does have a very natural feel to it with no noticeable shadow cast from the light.

Posted: 1/16/2021 8:20:48 PM EDT

[#16]

15" is my preference. I prefer a long handguard for many reasons. You can lay or lean a hot barrel against anything without burning anything. You can rest the handguard on anything without applying pressure against the barrel and affecting your POI (yes even slight pressure can flex a barrel if it is long and/or thin). What's the point of a free float barrel if you can't rest the weapon while keeping the barrel free floating? The difference in weight is very little in comparison to a shorter handguard. It's not always about attaching crap, it's about being able to place your support hand anywhere you want without touching a hot barrel.

There are logical reasons for having a shorter handguard though. If you change muzzle devices relatively often you want to be able to clamp the barrel in a vice unless you have one of those nifty reaction rods.

Posted: 1/17/2021 2:41:27 AM EDT

[#17]

Just visited my friendly LGS. They recommend as long of a rail as possible for coverage and at a very slight weight increase. They know their stuff and I trust their advice. Also got to handle a 14.5 with 13” rail which is about the same coverage of a 15” rail on a 16”.

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Coverage for what?

Posted: 1/17/2021 2:48:41 AM EDT

[#18]

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Coverage for what?

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It was mentioned above. Barrel coverage for barricades, hot barrel, placement of lights, etc.

Posted: 1/17/2021 5:33:34 AM EDT

[#19]

IMO there is just one legitimate reason to go 15" and that is to mount a bipod further forward. The more forward the bipod, the finer control you have of the muzzle via the stock. This requires a stiff enough rail to make use of the length. I can only reach irons and bipod tension adjustment easily on a 13" or 14" rail. 15" is specialized and requires me getting out of my shooting position to adjust the bipod or deploy front BUIS. Trying to get rid of weapon light shadow is pointless and just makes the gun front heavy and requires use of a pressure pad because you cant easy reach the rear button with a thumb if your light is at the front of a 15" rail.

Posted: 1/17/2021 10:30:07 AM EDT

[#20]

I am partial to 13 or 13.5 on a 16" barrel. It gives plenty of room mount anything I would ever mount and stretch my arm out. Plus it leaves enough barrel exposed that I can see where the muzzle actually is. Normally that isn't really a big deal but it gives piece of mind when shooting through small openings (vtac barrier, portal in armored car, etc).

My ideal length, if Geissele would make it, is 12.625 so that I could use it on an FSB build with no mods. Unfortunately, not too many companies make that (Midwest, SKD come to mind).

15 on a 16 inch barrel just looks too long to me. 13.5 on a 14.5 inch barrel is about the limit for my sense of aesthetics.

Posted: 1/17/2021 11:20:10 AM EDT

[#21]

12" is as far as I can reach Prone without sling tension. On my feet, about 10". I vote 12.5 - 13", unless you want an SMLE aesthetic.

Posted: 1/17/2021 11:46:42 AM EDT

[#22]

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Quoted:
IMO there is just one legitimate reason to go 15" and that is to mount a bipod further forward. The more forward the bipod, the finer control you have of the muzzle via the stock. This requires a stiff enough rail to make use of the length. I can only reach irons and bipod tension adjustment easily on a 13" or 14" rail. 15" is specialized and requires me getting out of my shooting position to adjust the bipod or deploy front BUIS. Trying to get rid of weapon light shadow is pointless and just makes the gun front heavy and requires use of a pressure pad because you cant easy reach the rear button with a thumb if your light is at the front of a 15" rail.

View Quote

A 3-9 scope and bipod are part of the plan for this rifle. It will primarily have a red dot sight on it, but I will occasionally use a scope and bipod on it.

This rifle currently has a Larue 12” quad rail on it.

Posted: 1/17/2021 4:57:30 PM EDT

[#23]

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12" is as far as I can reach Prone without sling tension. On my feet, about 10". I vote 12.5 - 13", unless you want an SMLE aesthetic.

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Sage advice. On my 16" builds, a 12" modular rail is all I can actually use with a precision "Recce" barrel. In fact, on one rifle with a carbine A2 fixed gas block sight on a 16" barrel, I still use a 7" free float quad and can just push a rail mounted scout weapon light ahead of the fixed sight to avoid its shadow.

Less is more. Anything else is just adding space that won't get used and weight that can be avoided. More weight out front tends to upset the balance, too. And, as pointed out by another poster, its nice to be able to clamp the barrel behind the muzzle device for maintenance or upgrades.

Posted: 1/17/2021 5:06:44 PM EDT

[#24]

Measured my rail and its only 12".... I wouldn't go to 15" on a 16" gun

Posted: 1/18/2021 2:11:11 AM EDT

[#25]

There are four reasons to get a 15" rail; aesthetics, longer back-up iron sight radius, more rail space and to cover as much of the barrel as possible. Here are a few points you might want to consider before getting one.

You say that a 15" rail on a 16" barrel looks goofy (bad aesthetics) and it weighs more.

The 13" BCM MCMR you say you have on backorder is actually 13.4" long.

A 15" rail on a 16" barrel will give you about 1/2" of exposed barrel if it's threaded (about 1/2" of barrel and a muzzle device threaded onto the last bit). That still leaves 2.25"+ of muzzle device and barrel exposed (depending on how long your muzzle device is) versus 3.85"+ if you go with the 13" BCM MCMR (13.4" long). That's only 1.6" more exposed.

Unless you have a compact light or don't mind the light out beside your muzzle device you're going to have to mount it 1"-2.5" back from the front of a 15" rail on a 16" barrel (depending on how long your light is).

Your hand is not going to be able to get too much farther forward than the back of the light. So unless you want a longer back-up iron sight radius or have some else you can mount by/in front of the light (bi-pod, DBAL, barrier/hand stop, sling swivel mount, etc.) it will be wasted rail space.

I like the way a 15" handguard looks on a 16" barrel as well as the longer buis radius and I'm using a little bit of that extra rail space but because I mounted a light about even with the end of the barrel/beginning of the muzzle device I only have about 12.5" of grippable surface.

Posted: 1/18/2021 2:31:51 AM EDT

[#26]

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Measured my rail and its only 12".... I wouldn't go to 15" on a 16" gun

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Same, I think that 13-14 is the perfect length for a 16 inch barrel. Plus when looking at weights, there is just no need at all for any reason for that extra space just to have more weight for dead space. really.

Posted: 1/18/2021 2:47:37 AM EDT

[#27]

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I’m traditionally a “7” on a carbine, 9” on midlength, 12” on rifle length” guy, because I do prefer a pinned front sight base to something mounted to a rail.
That said, I do have other lengths and one advantage to a 15” one is that I can mount a light (Surefire 300u) on the 12-o’clock rail and still have my front sight (LMT) pretty far forward right behind it. It does have a very natural feel to it with no noticeable shadow cast from the light.

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I was in the safe already while working on another rifle, and remembered this thread, figured I'd post a couple pics of a 15" rail on a 16" midlength gas barrel.
Like mentioned, I have a light mounted at 12-o'clock and a fixed sight mounted behind it. I do like this configuration.
This gives me the longest realistic sight radius while still having the light out front, but I don't think a 2" shorter rail would really be that much of a hindrance to be honest. In fact I have to reach a little bit more forward than I'd prefer, to activate the light while in a shooting position. It's not awkward, and some people who prefer their VFG way out front would probably like it better, but you can see I have my foregrip mounted roughly halfway down the rail as that's where it seemed the most comfortable on this particular setup. I use the foregrip more like a handstop anyway.
If you're not doing something silly with your light like I do, and if you're simply looking for the most barrel coverage and longest sight radius possible, go for it. The weight difference between a 13" and a 15" rail is negligible, even with it being weight way out front.

Posted: 1/18/2021 10:44:05 AM EDT

[#28]

The longer the better usually. If you are resting the barrel on a rooftop or log or something similar, you need as much rail as possible. Also, the longer rail will cover more of a hot barrel preventing hands and clothes from touching it. Iron sight radius and more real estate too. The only downside is weight which from a 13" to 15" is maybe 2 oz.

Posted: 1/18/2021 11:07:00 AM EDT

[#29]

Quote History

Quoted:
There are four reasons to get a 15" rail; aesthetics, longer back-up iron sight radius, more rail space and to cover as much of the barrel as possible. Here are a few points you might want to consider before getting one.

You say that a 15" rail on a 16" barrel looks goofy (bad aesthetics) and it weighs more.

The 13" BCM MCMR you say you have on backorder is actually 13.4" long.

A 15" rail on a 16" barrel will give you about 1/2" of exposed barrel if it's threaded (about 1/2" of barrel and a muzzle device threaded onto the last bit). That still leaves 2.25"+ of muzzle device and barrel exposed (depending on how long your muzzle device is) versus 3.85"+ if you go with the 13" BCM MCMR (13.4" long). That's only 1.6" more exposed.

Unless you have a compact light or don't mind the light out beside your muzzle device you're going to have to mount it 1"-2.5" back from the front of a 15" rail on a 16" barrel (depending on how long your light is).

Your hand is not going to be able to get too much farther forward than the back of the light. So unless you want a longer back-up iron sight radius or have some else you can mount by/in front of the light (bi-pod, DBAL, barrier/hand stop, sling swivel mount, etc.) it will be wasted rail space.

I like the way a 15" handguard looks on a 16" barrel as well as the longer buis radius and I'm using a little bit of that extra rail space but because I mounted a light about even with the end of the barrel/beginning of the muzzle device I only have about 12.5" of grippable surface.

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Very good points and you put numbers (measurements) on it.

I will do some measuring to see if my preferred light (PLHv2, SR-07, Arisaka offset mount) would be in front of my support hand on a 13” versus 15”. On my rifles I use a Magpul VFG as a hand stop.

Posted: 1/18/2021 5:53:35 PM EDT

[#30]

From the front of my light to the end of the tailcap (including cord plug) is 6.5”.

A 15” rail with the front of the light lined up with the end of the rail would put the light forward of where I normally grip the rifle. There would be a very slight overlap with the cable and plug but that allows for more of a grip than with the light body there.

A13.4” rail would overlap my grip with the end of the light body, the rear of the tailcap and plug.

My preferred grip is in the 7-10” range from the receiver (ie, 3” forward of the VFG).

Looks like the 15” rail would give me a more clear area for my support hand.

Posted: 1/18/2021 7:42:43 PM EDT

[#31]

Call me paranoid, but for a heavy use carbine, 13.5 is about the longest I’d go regardless of barrel length. Being able to extend your sight radius or stick your light out and extra few inches isn’t worth the squeeze for me... Regardless of mounting interface (or monolithic in the case of LMT) your rail is still a beam that acts as a lever when you smash it, rest it, load a bipod, etc. A longer lever means more force. More force can result in failure or permanent deformation in extreme cases. We are dealing with aluminum after all.

Posted: 1/18/2021 8:16:15 PM EDT

[#32]

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Call me paranoid, but for a heavy use carbine, 13.5 is about the longest I’d go regardless of barrel length. Being able to extend your sight radius or stick your light out and extra few inches isn’t worth the squeeze for me... Regardless of mounting interface (or monolithic in the case of LMT) your rail is still a beam that acts as a lever when you smash it, rest it, load a bipod, etc. A longer lever means more force. More force can result in failure or permanent deformation in extreme cases. We are dealing with aluminum after all.

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What are the forces (in pounds or whatever) that make a 13.5” rail acceptable but disqualifies the 15”?

Just trying to understand if there is some science behind this or just your gut feeling.

Posted: 1/18/2021 8:20:05 PM EDT

[#33]

I went with 10.5", but I wanted to be able to use a bayonet. You can't go more than a small fraction of an ounce longer than that and have it be compatible with a bayonet lug.

It's long enough to completely cover the gas block (which I still have pinned, anyways) and lets me put the sling swivel at the end and still have the sling be usable as a shooting aid. I also like the balance, weight savings, and aesthetics better.

While longer sight radius for irons is nice, they will ultimately be just for backup on this rifle, so it's not a huge concern for me. A bit more real estate for accessories would be nice, but it should still suffice. Shorter is also stiffer, as I understand it, which is a good thing. I don't really extend my arm out as far as possible to shoot. I always found that very awkward and uncomfortable, even unnatural, so I don't do it and don't need the handguard way out there for that reason.

I had originally considered something like the Warblock on this rifle, in which case I would have gone with 9.3". With that or a FSB, that's as long as you can go on a mid-length regardless of overall barrel length. I'm glad I went the route I did instead, though.

The only future build that's a 16" mid-length that I'd go longer is the CWAR I want to do, and in that case I'd go with the 13" over the 15".

Posted: 1/18/2021 11:39:16 PM EDT

[#34]

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What are the forces (in pounds or whatever) that make a 13.5” rail acceptable but disqualifies the 15”?

Just trying to understand if there is some science behind this or just your gut feeling.

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Quoted:

Quoted:
Call me paranoid, but for a heavy use carbine, 13.5 is about the longest I’d go regardless of barrel length. Being able to extend your sight radius or stick your light out and extra few inches isn’t worth the squeeze for me... Regardless of mounting interface (or monolithic in the case of LMT) your rail is still a beam that acts as a lever when you smash it, rest it, load a bipod, etc. A longer lever means more force. More force can result in failure or permanent deformation in extreme cases. We are dealing with aluminum after all.

What are the forces (in pounds or whatever) that make a 13.5” rail acceptable but disqualifies the 15”?

Just trying to understand if there is some science behind this or just your gut feeling.

There is no data set that says “13.5 is fine but 13.5001 is unacceptable”. There are so many variables that contribute to strength and rigidity including material selection, geometry, material thickness, etc. My reasoning is just based on experience and simple physics.

Torque = (Distance from fulcrum) X (Force)

So the same force at a longer distance from the fulcrum (in this case, the barrel nut) will result in more torque applied.

Go ahead and open the nearest door to you... car door, bedroom door, whatever.

Now open the same door again, but instead of using the handle or knob, try pushing it open right next to the hinges. The door requires the same force to open, but it takes more effort on your part to move the door when the distance to the fulcrum(the hinges) is less.

Apply this to any lever. In this case, a rail. It will take less effort to apply the same amount of force (on the barrel nut) on a longer rail than it would a shorter rail of the same material, geometry, etc.

Simply put as bigstick just said, “shorter is stiffer”

Posted: 1/19/2021 12:40:06 AM EDT

[#35]

Quote History

Quoted:

There is no data set that says “13.5 is fine but 13.5001 is unacceptable”. There are so many variables that contribute to strength and rigidity including material selection, geometry, material thickness, etc. My reasoning is just based on experience and simple physics.

Torque = (Distance from fulcrum) X (Force)

So the same force at a longer distance from the fulcrum (in this case, the barrel nut) will result in more torque applied.

Go ahead and open the nearest door to you... car door, bedroom door, whatever.

Now open the same door again, but instead of using the handle or knob, try pushing it open right next to the hinges. The door requires the same force to open, but it takes more effort on your part to move the door when the distance to the fulcrum(the hinges) is less.

Apply this to any lever. In this case, a rail. It will take less effort to apply the same amount of force (on the barrel nut) on a longer rail than it would a shorter rail of the same material, geometry, etc.

Simply put as bigstick just said, “shorter is stiffer”

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Yeah, I get all that. But if that was really a significant factor in durability we would all be back to 7" rails.

Posted: 1/19/2021 1:15:02 AM EDT

[#36]

If the 13" BCM rail is not long enough to allow you to mount your light something like the picture below (so as to maximize the rail's grippable surface yet still have your light behind the blast of your muzzle device) and mounting a light on a 13" rail would make you have to alter your preferred grip (where as on a 15" it would not) then yes I'd say to go with the 15" rail (or if you really want a longer sight radius and/or more mountable surface for doo-dads).

Posted: 1/20/2021 7:47:31 PM EDT

[#37]

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Yeah, I get all that. But if that was really a significant factor in durability we would all be back to 7" rails.

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Some of us are very fond of 7" rails when a fixed A2 front sight is desired for absolute dependability. They are available as free float, too. Sometimes less is more. I do have longer modular rails with folded backup sights, too, but 12" is plenty for me.

Posted: 1/20/2021 7:55:07 PM EDT

[#38]

I use a 15 on 16. When shooting over barricades and banging it on stuff you keep from loading against the barrel. My hunting gun is the same way.

Posted: 1/20/2021 11:02:26 PM EDT

[#39]

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Some of us are very fond of 7" rails when a fixed A2 front sight is desired for absolute dependability. They are available as free float, too. Sometimes less is more. I do have longer modular rails with folded backup sights, too, but 12" is plenty for me.

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Some of us are very fond of 9" free float rails on a mid-length with fixed A2 sight.

Posted: 1/21/2021 11:42:13 AM EDT

[#40]

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Quoted:

Some of us are very fond of 7" rails when a fixed A2 front sight is desired for absolute dependability. They are available as free float, too. Sometimes less is more. I do have longer modular rails with folded backup sights, too, but 12" is plenty for me.

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How is that any more dependable than a longer handguard?

Posted: 1/21/2021 11:45:03 AM EDT

[#41]

Quote History

Quoted:
Call me paranoid, but for a heavy use carbine, 13.5 is about the longest I’d go regardless of barrel length. Being able to extend your sight radius or stick your light out and extra few inches isn’t worth the squeeze for me... Regardless of mounting interface (or monolithic in the case of LMT) your rail is still a beam that acts as a lever when you smash it, rest it, load a bipod, etc. A longer lever means more force. More force can result in failure or permanent deformation in extreme cases. We are dealing with aluminum after all.

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I’ve beat the absolute shit out of handguards 15” and longer without issue. In fact the only issues I’ve ever seen would have destroyed any length handguard.

Weird. Almost like this isn’t a problem.

Posted: 1/21/2021 11:57:46 AM EDT

[#42]

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Weird. Almost like this isn’t a problem.

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I agree that durability of 7, 9, 10, 13, and 15” rails is not a concern to me.

Posted: 2/8/2021 12:42:45 AM EDT

[#43]

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How is that any more dependable than a longer handguard?

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I'm referring to the virtual indestructibility if the A2 front sight. My point is the strength of the A2 tower front sight and its pinned attachment directly to the barrel with the rail behind it.

Posted: 2/9/2021 12:40:44 PM EDT

[#44]

Will a 13" rail allow for a bayonet...my 15" KMR is a no go with an M9.

Posted: 2/9/2021 1:14:13 PM EDT

[#45]

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Will a 13" rail allow for a bayonet...my 15" KMR is a no go with an M9.

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No, for a bayonet you need to stay right around 10”. The FSB needs to be pretty much exposed so the bayonet lug is well exposed.

Posted: 2/9/2021 3:30:21 PM EDT

[#46]

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No, for a bayonet you need to stay right around 10”. The FSB needs to be pretty much exposed so the bayonet lug is well exposed.

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A bayonet fits perfect on a mid length with fixed front sight assembly and 9” rail. So the above post is correct if you have a shaved FSA a 10” might work and still leave the bayonet lug exposed, but I have not tried it.

Posted: 2/9/2021 3:47:29 PM EDT

[#47]

I'm seriously considering an 18" SPRish-type build with a 17/17.5" handguard. Want to get the bipod out as far as possible, plus I just think it looks cool.
Not a lot available in that length though.