View Full Version : AR-15 Decreasing back up sight radius for increased ergonomic comfort.
So here is the deal on my mostly stock 16" Colt AR-15 model 6920 I have been thinking recently on the ideal white light and mount. After seeing many examples and holding a few I want to put a pistol style light (TLR-1, X300, or similar) ahead of the FSB at the 12:00 position.
The rifle is primarily a home defense rifle. But I would like to be able to make hits out to 200 yards. It will have an AimPoint pro RDS on it prior to this modification.
This seems advantageous as its lightweight, easy to flash or turn on, casts a barrel shadow down, and will not reflect back as much if you put the rifle barrel against a doorway that the side of the light was in if it was between 9-12 or 12-3.
However even with the stock set to the shortest setting given my anatomy my arm reaching to the end of the front sight is almost straight. This feels very uncomfortable. After looking at some free float tubes, along with a low profile gas block I could use a 9" free float tube with a top rail that would end right about where the stock FSB ends. Put the white light at the very and and a front iron sight about 2.5" back from the stock carbine position.
This allows me a little bend in my arm that I normally have but still gives me perfect position to activate the light.
Seems allot for just a white light but I would have the added benefit of a free float hand guard and be able to add a VFG, AFG, or hand stop as well.
The irons will be used for backup with a RDS and be fixed with a 1/3 co witness.
Thoughts and comments?
Failure2Stop
08-20-13, 16:33
A 12:00 light is really the optimal position for a light, so you are on track there.
You certainly can go with a FF and put a front sight behind the light, the reduced sight radius will not really make much difference at 200.
The concern about arm reach makes me assume either of 2 things:
(1) You have very short arms
-or-
(2) You are shooting a carbine from a squared shoulder position.
If (1) is true, then you really don't have much choice in the matter and are going to need to reduce the reach to the light in order to activate it.
If (2) is true, I highly recommend adopting a more bladed/athletic/boxer stance. The "SMG" stance does not support carbine employment as well as a modern carbine stance:
http://img25.imageshack.us/img25/9936/daniel2bdefense2b014vi.jpg
I would say I have short arms (not very short).
I am using a squared stance. I might try a more bladed stance. But if I loose very little with the 2.5" reduction in sight radius It might not be worth changing my stance.
So here is the deal on my mostly stock 16" Colt AR-15 model 6920 I have been thinking recently on the ideal white light and mount. After seeing many examples and holding a few I want to put a pistol style light (TLR-1, X300, or similar) ahead of the FSB at the 12:00 position.
The rifle is primarily a home defense rifle. But I would like to be able to make hits out to 200 yards. It will have an AimPoint pro RDS on it prior to this modification.
This seems advantageous as its lightweight, easy to flash or turn on, casts a barrel shadow down, and will not reflect back as much if you put the rifle barrel against a doorway that the side of the light was in if it was between 9-12 or 12-3.
However even with the stock set to the shortest setting given my anatomy my arm reaching to the end of the front sight is almost straight. This feels very uncomfortable. After looking at some free float tubes, along with a low profile gas block I could use a 9" free float tube with a top rail that would end right about where the stock FSB ends. Put the white light at the very and and a front iron sight about 2.5" back from the stock carbine position.
This allows me a little bend in my arm that I normally have but still gives me perfect position to activate the light.
Seems allot for just a white light but I would have the added benefit of a free float hand guard and be able to add a VFG, AFG, or hand stop as well.
The irons will be used for backup with a RDS and be fixed with a 1/3 co witness.
Thoughts and comments?
Everyone has an opinion. Here is mine. Maybe I misunderstand you but I would not consider fixed irons with the PRO. The beauty of an RDS is a FOV that encourages rapid engagement. If used correctly you are only looking at the target. A fixed rear takes that away for me. I cannot imagine a situation where co witness would be of any value to me. Too much to think about. The dot either works or doesn't. If it quits throw it off. I feel the same way about a light mounted in front of the sight. I really like the Inforce WML/Thorntail mount combination. The angled switch on the rear of the light is about as ergonomic as it gets. It puts the light between 10 and 11 o'clock. It is not as bright as the lights you mention but 200 lumens inside of a house is plenty for me. I am not a fan of the wires cluttering up the fore end with remote switches. Look at the Troy Alpha rails or similar. I would buy a longer rail than you think you need. Troy sells an 11" and 13" with a built in flip up sight. A naked rail allows you to mount things where you want them and not have the bulk of a quad rail. I hope my advise is worth more than you paid for it! GH
Failure2Stop
08-20-13, 16:55
I would say I have short arms (not very short).
I am using a squared stance. I might try a more bladed stance. But if I loose very little with the 2.5" reduction in sight radius It might not be worth changing my stance.
I'm not going to argue stance and performance, as it's ultimately frustrating on both sides, but I will simply say that there is a very good reason that those that shoot for a living have gone to bladed positions.
This comes from a guy that used to be a squared stance shooter.
http://i1097.photobucket.com/albums/g342/F2SConsulting/F2S%20Consulting%20LLC%20Practical%20Carbine%20Feb25-26%202012/DSC_0630.jpg
This dude is all of 5'5" tall, and shoots like a beast. His HG is 12" long.
One of the things that you lose with that 2.5" reduction is the fixed front sight. For a "serious" (spoken with a deep intonation and steely eyes) carbine, there are advantages to the old "A-frame". It is robust, it is always up, it won't ever go down, and it will always be in alignment with your barrel. Moving the front sight to the rail makes it susceptible to tube flex, which is way easier to accomplish than barrel flex, which is the big scary demon that drives us all to free-float tubes in the first place.
Anyway, shoot what you want, how you want.
Practically, the 2.5" reduction isn't the end of the world, and if you don't want to change your stance it isn't going to effect my bank account in the least.
Great question...
This is something that I have been struggling with as I have shorter arms. I prefer running the stock all the way out as I just feel that I have more control over the firearm.
As of right now I have a 12" rail on my Colt 6920. I don't know whether to have something set up for a pressure switch or purchase a light and mount at the 12 o'clock position.
FailuretoStop: Are you activating your light with your thumb or index finger?
I have taken classes from local instructors and am signed up for a Vickers class in December...I'm just hoping to actually see a better method to mount a light as of right now I can't figure out where would be best for me to mount it. Everything I have tried so far has me moving my support hand too much while I'm dry firing.
Any more thoughts?
I'm not going to argue stance and performance, as it's ultimately frustrating on both sides, but I will simply say that there is a very good reason that those that shoot for a living have gone to bladed positions.
This comes from a guy that used to be a squared stance shooter.
One of the things that you lose with that 2.5" reduction is the fixed front sight. For a "serious" (spoken with a deep intonation and steely eyes) carbine, there are advantages to the old "A-frame". It is robust, it is always up, it won't ever go down, and it will always be in alignment with your barrel. Moving the front sight to the rail makes it susceptible to tube flex, which is way easier to accomplish than barrel flex, which is the big scary demon that drives us all to free-float tubes in the first place.
Anyway, shoot what you want, how you want.
Practically, the 2.5" reduction isn't the end of the world, and if you don't want to change your stance it isn't going to effect my bank account in the least.
The counter to the bladed stance, is of course, you don't present your body armor to your target. Which probably isn't harped on as much in the civilian sector, but that was always what I was told. So if the OP has on something, that's something to consider too.
Off topic, but I'm slightly in the same boat as he is. I've seen the Centurion C4 rails, but I'm not a fan of the quad rail. Is there tube shape forearm that allows use with the FSP, extends past the FSP, but has more limited rail space? Only thing I can find is the Troy Battlerail (in carbine only, not middie)
So here is the deal on my mostly stock 16" Colt AR-15 model 6920 I have been thinking recently on the ideal white light and mount. After seeing many examples and holding a few I want to put a pistol style light (TLR-1, X300, or similar) ahead of the FSB at the 12:00 position.
The rifle is primarily a home defense rifle. But I would like to be able to make hits out to 200 yards. It will have an AimPoint pro RDS on it prior to this modification.
This seems advantageous as its lightweight, easy to flash or turn on, casts a barrel shadow down, and will not reflect back as much if you put the rifle barrel against a doorway that the side of the light was in if it was between 9-12 or 12-3.
However even with the stock set to the shortest setting given my anatomy my arm reaching to the end of the front sight is almost straight. This feels very uncomfortable. After looking at some free float tubes, along with a low profile gas block I could use a 9" free float tube with a top rail that would end right about where the stock FSB ends. Put the white light at the very and and a front iron sight about 2.5" back from the stock carbine position.
This allows me a little bend in my arm that I normally have but still gives me perfect position to activate the light.
Seems allot for just a white light but I would have the added benefit of a free float hand guard and be able to add a VFG, AFG, or hand stop as well.
The irons will be used for backup with a RDS and be fixed with a 1/3 co witness.
Thoughts and comments?
Buy this and you should achieve everything you're hoping for. You can leave the FSB, have room for a light at 12:00 and plenty of room to put your hand where it feels good. Room for a VFG underneath if you choose.
https://www.m4carbine.net/showthread.php?t=137059
If you want a full quad rail then check these out:
https://www.m4carbine.net/showthread.php?t=136639
https://www.m4carbine.net/showthread.php?t=136560
I bought the Troy version because I don't need the rail space. I've been pleased with it and it allows me to get my hand way out there. I need to add a light yet but I bought the rail with that 12:00 placement in mind.
The counter to the bladed stance, is of course, you don't present your body armor to your target. Which probably isn't harped on as much in the civilian sector, but that was always what I was told. So if the OP has on something, that's something to consider too.
Bladed doesn't mean sideways. You are pretty square to the target.
C4
Bladed doesn't mean sideways. You are pretty square to the target.
C4
Agreed, but in both the above pictures, the extended arm seems to open the armpit more. Just pointing out that more unprotected real estate could be exposed. Again, that's IF body armor and incoming fire are concerns. If this is for fun, body armor isn't a concern, competition, go for it. Do what works.
My input is that it allows me to run an X300u in such a way that the switch allows ambidextrous momentary or constant on, the control of which is mirrored both strong and support-side.
That is 500 OTF lumens of very nicely shaped hotspot and spill at a penalty of just a few ounces which is totally ambidextrous with momentary or constant on that is center-line to the gun and thus much friendlier when shooting over/around cover. If you can use the sights...you can use the light.
I cannot think of a better way.
Agreed, but in both the above pictures, the extended arm seems to open the armpit more. Just pointing out that more unprotected real estate could be exposed. Again, that's IF body armor and incoming fire are concerns. If this is for fun, body armor isn't a concern, competition, go for it. Do what works.
It's deceptive. About all that would be exposed to the frong is the lat and a tiny "grazing angle" bit of the arm-pit. Regardless you are already exposing your brachial and radial arteries, so I find the point moot to argue about that little bit of lat/pit.
This is for a home defense rifle that will not see competition. However like most HD firearms it will see hopefully only see range use.
I do not currently have body armor and there no immediate plans to buy.
Failure2Stop
08-21-13, 15:36
FailuretoStop: Are you activating your light with your thumb or index finger?
That's actually Kyle Defoor pictured.
I believe that he is using his thumb for activation.
I use my thumb for white-light tasks, though I prefer an M600 or M300 with tailcap actiation personally.
Failure2Stop
08-21-13, 15:52
The counter to the bladed stance, is of course, you don't present your body armor to your target. Which probably isn't harped on as much in the civilian sector, but that was always what I was told.
And the counter to that counter is that in combat, dudes are generally shot at angles, and body armor only covers a small amount of the body with rifle-stopping protection. The arms offer little resistance to military rifle calibers and offer basically no protection from lateral shots. Further, there are so many places that a shot can hit that will lead to death or grievous injury (face, neck, spine, descending aorta, major blood pathways of the arms and legs, etc) that when faced with a frontal threat at close range, the priority goes to killing the shit out of the threat. This is generally accomplished by a rapid, precision presentation followed my multiple rapid shots accurately placed into the threat in locations that are most likely to cause rapid or immediate incapacitation. This end is achieved by a forward balanced, aggressive stance.
As I said before, there is a reason that the folks that are at the tippy top of the "shooting dudes" game, and those that train those folks, for a living use this type of stance (see Larry Vickers, Kyle Lamb, Kyle Defoor, Mike Pannone, Dave Harrington, Paul Howe, Pat McNamara and Frank Proctor).
Speaking of Kyle Defoor, he has been experimenting with different sight radii on the AR. If I remember correctly, he found a 14.5 inch sight radius worked best. The rear as far to the rear as it could go and the front 14.5 inches out. He said he found a 5% increase in accuracy. It would also leave plenty of space for a 12 o'clock mounted light. All my AR's have a regular FSP, but when I do my next build it will be a Troy TRX and KAC sights.
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