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Posted: 10/10/2011 4:23:33 PM EDT
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I recently purchased a Colt LE6920 with the 16.1 inch barrel and wanted to ask a few questions about the rail system i was looking to add. I currently have an aimpoint PRO that ive added to the flat top area and am considering replacing the stock with a Magpul option. I like the KAC rails and am not considering any other rails at the moment. Price is not an issue but type of rail is. Ive done some research and looked around on these forums but could not find the answer to my questions concerning KAC rails. I only plan on adding a light onto the rail system but want the real estate for possible future options. Im used to using a free float barrel with long guns for accuracy but not sure what the advantage would be on a carbine.
M4 Carbine RAS -does the lack of free float present any issues -does this come with the KAC delta ring as I want to replace the one that comes with the colt i prefer twist over the akward tension system that colt uses. -does this fit up snug to the front sight or does it require a low profile gas block. RAS Free-Floating Barrel (Medium) - can a flip uo iron sight mounted on the end of the rail be considered accurate since its not attatched to the barrel -are the free float RAS systems that difficult to remove for dissasembly -is the increase in accuracy worth the added expense and how much can the rifle be banged around with a system like this and maintain zero Thanks for any help and if anyone could post pictures of their LE6920 and kac rail system it would be appreciated, please label what rail system your using as well. |
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The KAC RAS also has a clamp that grabs onto the barrel nut, so it doesn't rely solely on the tension of the delta ring to hold it there. It also has a leaf spring that goes underneath the handguard cap behind the FSB, providing additional stability. You can also remove the bottom part of the rail without disturbing the top rail (incase you have an optic on the top rail) in order to clean the surface of your barrel and for periodic inspection.
I can't say enough good things about KAC rail. The "drawback" is that it's on the "heavier" side (but it's very relative and subjective) and it does not come with holes for sling swivels 
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Quoted:
I recently purchased a Colt LE6920 with the 16.1 inch barrel and wanted to ask a few questions about the rail system i was looking to add. I currently have an aimpoint PRO that ive added to the flat top area and am considering replacing the stock with a Magpul option. I like the KAC rails and am not considering any other rails at the moment. Price is not an issue but type of rail is. Ive done some research and looked around on these forums but could not find the answer to my questions concerning KAC rails. I only plan on adding a light onto the rail system but want the real estate for possible future options. Im used to using a free float barrel with long guns for accuracy but not sure what the advantage would be on a carbine. M4 Carbine RAS -does the lack of free float present any issues -does this come with the KAC delta ring as I want to replace the one that comes with the colt i prefer twist over the akward tension system that colt uses. -does this fit up snug to the front sight or does it require a low profile gas block. RAS Free-Floating Barrel (Medium) - can a flip uo iron sight mounted on the end of the rail be considered accurate since its not attatched to the barrel -are the free float RAS systems that difficult to remove for dissasembly -is the increase in accuracy worth the added expense and how much can the rifle be banged around with a system like this and maintain zero Thanks for any help and if anyone could post pictures of their LE6920 and kac rail system it would be appreciated, please label what rail system your using as well. Go to the M4 picture thread in the AR Tech forum and you'll see more pictures of the KAC RAS than you ever want to in your life. That, or army.mil is a good source for them, too. The KAC M4 RAS is the standard US military rail system. A "KAC delta ring" is no different from the Colt unit, and all delta rings use the "awkward tension system" as that has been a part of the design since 1959. It works perfectly fine. The M4 RAS doesn't just use spring tension to keep it locked like many drop in rail systems out there. Not only does spring tension keep the top rail locked in, but there is a "claw" on the rear of the rail that locks in to the stock barrel nut and screws down, as well as a leaf spring that slides under the front handguard cap making the KAC RAS one of the easiest to install, but sturdiest rail attachments on the market. The bottom rail, however, is only held in with spring tension unless using the "UK SAS" bottom rail which locks in like the top rail. As the M4 RAS is a "drop in" rail system, no modifications or disassembly are required to the stock 6920. It is a simple handguard replacement. The FF RAS are much more difficult to install, as they require the complete disassembly of the barrel and replacement of the stock barrel nut with the rail system's barrel nut. Rail mounted front sights work fine as a BUIS, but are not the best solution for getting the most accuracy out of your iron sights. As to whether or not the FF is worth it, it depends on your use and application, which you have not stated. However, given that you mentioned that you're using an Aimpoint PRO, my first inclination is that with the type of shooting you plan to do and the capabilities of the optic, you won't notice a significant difference. FF is more important in precision work and firing from supported positions. If you're using the Aimpoint properly, you're working in a more "run and gun" performance envelope, where you're not going to be putting a lot of pressure on a bipod or on your handguards in supported shooting positions, or using heavy sling tension that will move the barrel relative to your POA. It also doesn't sound like you're going for small groups, as the Aimpoint is not the ideal optic for shooting groups with. ~Augee |
My Colt SP6920 with KAC M4 RAS rails, Aimpoint M2 on LaRue cantilever QD mount, my carbine is exactly the same as yours except for different markings, it doesn't have law enforcement wordings The lack of free float is no problem with my intended self defense range of point blank up to 100 or so yards which most gunfights take place (ref. read the Ammo Oracle). No the KAC RAS doesn't include a delta ring, it doesn't need one, the Colt delta ring are one of the best out there same used with the military issued M4 carbines. KAC have an internal mounting bracket that locks on the barrel nut under the delta ring which make it solid without any movements. The RAS rail fits very snug with the front handguard cap, no need to replace the factory front sight-gas block. I don't prefer any free floating rails for production quality barrels, I have another Colt 6721 carbine with a LaRue free float rails but I'm using a higher quality barrel with a thicker barrel profile. The RAS free floating barrel installation requires the barrel to be removed from the upper receiver, this requires tools such as an upper receiver action block, shop table vise, and a handguard installation wrench. I did my own free floating rail installation myself because I have the required tools, if you don't have the tools just send it to a gunsmith like ADCO and have them install it. KAC RAS Non Free Floating Installation Instructions - pdf file link AR15.com Ammo Oracle - link ADCO - link |
| Great info guys thanks for the help, Alpha-Romeo3 your setup is more or less what im going for except i plan on using kac rails and and thinking about a magpul stock ctr i even have the same surefire. Im considering getting the socom 14.5 inch next year but not sure if it really makes a difference. Also i didnt know the KAC delta ring wasnt a screw off thats a good bit of info im used to using a m11 mod 0 but i never had to dissasemble that portion of it the armorer usually does that bit :) |
Last year's picture of my other Colt 6721 HBAR carbine with my same KAC M4 carbine RAS rails and Magpul CTR stock with optional enhanced 0.70" rubber butt-pad Quoted:
Great info guys thanks for the help, Alpha-Romeo3 your setup is more or less what im going for except i plan on using kac rails and and thinking about a magpul stock ctr i even have the same surefire. Im considering getting the socom 14.5 inch next year but not sure if it really makes a difference. I have a CTR stock on my other 6721 carbine, it's better than the factory Colt M4 stock with virtually no movement, plus the QD sling mount and integrated rubber butt-pad, I'm very satisfied with my CTR, but my SP6920 is my M4 carbine clone so I prefer the look of the M4 stock on it. I don't have experience with the 14.5" SOCOM barrel but I have a similar medium contour profile 16" midlength gas system barrel, I would only use this heavier profile barrels for SHTF/ war conditions but for home and self defense the standard M4 barrel of the 6920 are a better choice, lighter, handier, and could be carried for long periods of time. |
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The RO921HB (otherwise known as the M4A1 otherwise known as SOCOM profile) barrel is really only useful if you're running heavy volumes of FA through your barrel regularly, or you've got fewer suppressors than rifles you want to suppress and want to minimize POI shift with and without the suppressor without re-zeroing your optics on a regular basis.
Otherwise it's just 4 extra ounces of weight in the most inconvenient place possible - up front. I personally happen to fall into the latter category, so I use RO921HB barrels when possible - but before I really got into suppressed shooting, I actually avoided the M4A1 profile barrels because the weight was superfluous. Now that I've got two suppressors that run back and forth between half a dozen (at least) uppers, I try to use RO921HB barrels to minimize the POI shift as the thicker barrel is stiffer and won't "droop" as much with the weight of the suppressor when it gets hot (not too many rounds when suppressed). If I weren't running suppressed I'd dump all of my SOCOM profile barrels for gov't profile. ~Augee |
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If you don't mind a brand new KAC M4 RAS rials with minor blemish, most of the time are not even seen because of rail panels, KAC sells these for around $150 with 3 full length 11-rib rail panels.
http://www.knightarmco.com/shop/index.php?main_page=product_info&cPath=2&products_id=32 |
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