I was thinking this was not a free floating rail but a friend says it is.
The KAC M4 RAS is a two part rail, a top half and a bottom half. The top half contains the top rail and the side rails. The bottom half has the lower rail.
The top half clamps to the barrel nut so in effect I guess the top half is as much of a free floating rail as any of the other free floating rails that clamp to the barrel nut.
But the bottom half of the KAC M4 RAS does not clamp to the barrel nut (it’s removable so a grenade launcher can be attached).
Well my friend says that the bottom half of the KAC M4 RAS can not put upward pressure on the barrel because when you put upward pressure on the bottom half of the KAC rail it presses against the top half of the rail which is locked to the barrel nut.
Yep, F2S is obviously right. It’s not a FF rail. While the design may mitigate some of the POI shift issues with non free floating rails, it still does not qualify as being free floating. Another example is the Surefire M73. Somewhere along the line Surefire marketed it as a FF rail even though it was not so (they have since stopped). It does do an outstanding job of avoiding problems with non FF’s, but it still is what it is. Same for the KAC.
It’s rigid but not freefloating. With freefloating there is no foward of the barrel nut contact with the barrel/handguard cap.
Sometimes with freefloat tubes you still have to be careful that there isn’t anything contacting the gas block if the gas block is covered by the freefloat tube/rail. If there’s contact there it’ll cause all kinds of accuracy problems.
What’s really confusing is how non-free floating rails or handguards could have that much of an impact on accuracy. The military has tens of thousands of KAC M4 RAS equiped M4’s not to mention M4 carbines with the factory plastic handguards. This can’t be causing all kinds of accuracy problems otherwise our troops wouldn’t be able to hit anything. How are Marine recruits managing to qualify at 500 yards with iron sights without free floating rails?
I just can’t help but wonder if this free floating rail business isn’t all snake oil.
I would really like to see a study that shows any significant real world POI difference between a non-free floating and free floating rail on a carbine.
Watch a rifle that was filmed with a hi-speed camera firing a round, watch what the barrel does. Then think about something contacting the barrel during this process, then rethink your last post
hehe… anyone who uses a VFG can make a non-FF carbine walk all over the place, particularly if they’re a really hard holder. I can crank an M4’s POI down several inches at 100 just by varying the tension I’m pulling back on the VFG with. The difference is, my FF gun will shoot to the same POI whether I’m locked up on it tight putting rounds downrange offhand while moving, or holding it much less firmly while sitting/prone/whatever.
This has been done to death. There are many advantages to FF rails, not the least of which is minimizing POI change as accessories are mounted and dismounted, and there is even some evidence to show that non-FF guns’ bolts break sooner because of uneven loading on the bolt lugs caused by pressure from a VFG or heavy accessories mounted on the handguard.
Your intuitions are misleading you. Accomplished shooters on both the military / civilian side nearly unanimously advocate the use of FF rails.
Most of us who have used both don’t need to “see a study.” Our experience is the study.
Here are a few things to think about / areas where FF rails shine:
When a bipod is rail mounted.
When shooting off a rigid improvised rest.
When putting extensive pressure on a rail mounted sling.
When bearing down on the forearm to control recoil.
When the barrel / rail gets hot and the metal starts to “move.”
Think about barrel harmonics and its effect. With a non-FF rail, the barrel will “vibrate” differently based on your grip on the rail. With a FF rail your grip pressure and placement has less of an effect.
This may sound all academic but I can assure you it is also observable in practice.
Its not a FF rail because both the top and bottom contact the handguard cap which contact the barrel, thus putting stress on it
Theres a reason why the sopmod block II has the DD RIS II in it, even the .mil know the need for a FF rail if you want an easy to install one get the DD omega rail, its one of the best investments you can make.
Not trying to say the M4/M5 RAS is bad but alot has changed since it came out
A non-free floated AR will have quite a difference of of POI from zero depending on how you’re shooting it and how you sighted it in i.e. prone on the mag, prone off a bipod, handheld, sandbagged on a bench. You’ll see a shift if you shoot in a position different from how you zeroed the gun. A freefloated gun will have essentially no change.
It’s the same reason precision rifles (bolt guns) have they’re actions bedded and the barrel free floated.
Anything that touchs the barrel will influence the way the round fly’s. Those recruits are taught to do everything the same way for each shot. Even at the 200 where they are shooting in three different positions the seven common factors to a good shooting postion are used. If you took arifle off the line and changed the handguards to a FF rail the POI would be different. They do influence the strike of the round, they just do it for every round!!
The level of accuracy needed to qualify factors into this. You don’t have to be a sub-moa shooter, but you do have to understand and apply good fundementals.
I understand the principal of free floating but I’m talking about a carbine here.
The distance from the barrel nut to the handguard cap which contacts the barrel is about 6 inches.
I just can’t see where weight of the rifle resting in my hand could possibly impart any flex in a 6 inch section of barrel. Maybe if I had my hand wrapped through a sling attached to the back of the non-free floating rail and cinched it really tight but even then it’s attached at the back end of the rail and on the KAC M4 RAS the side rail is part of the upper half of the rail that’s clamped to the barrel nut. So basically I would have to flex the entire rail enough that it would deflect enough to push on the handguard cap.
I’ve tried to “wiggle” the top half of the KAC M4 RAS rail after it’s clamped to the barrel nut and I can’t see the handguard cap end move at all. It would have to move to impart any flex in the (6 inch section) of barrel.
I’m guessing it would probably take a 1000lb of force to deflect a 6 inch section of barrel.
And what about rifles like the M1 Garand, Springfield M1A, H&K G3, etc? These are pretty accurate rifles out of the box and they don’t have free floating barrels.
Stop hypothesizing and theorizing and go shooting. I can intentionally induce what I consider to be significant POI shift with non-FF rails. If you’re a good shot, you can too. If you’re not, you may not be able to notice. You have world class shooters who get paid to do the things we talk about on this forum telling you that FF rails are a measurable improvement over non-FF rails. As a matter of fact, if I could only do one thing to the standard issue (army wide, not USSOCOM rifles) M4, it would be to add a DD RISII.
It isn’t about the baseline mechanical precision of the weapon.
It’s about the user’s ability to flex the barrel in common use.
It is entirely possible to seriously flex the barrel with the KAC RAS with just hand and body pressure.
I have demonstrated it on numerous occasions.
Want to see POI shift? Take a non free float rail system like the KAC on an M4 with an aimpoint (M68 CCO). Zero the rifle, then shoot it standing. Then put a VFG on it and crank down on it reall good. Shoot the same string standing again. You’ll see POI shift unless you haven’t eaten your wheaties that morning. Same goes for leaning it on a wall, vehicle etc.
Free float rails, you will see nothing like the above. With the negligible difference in costs beteween the two rail types, it makes no sense to go non free float.
Actually a G3 does have a freefloated barrel. To get a M1 Garand or M1a/M14 to be anywhere near as accurate as a match barreled freefloated AR you’ll usually spend 2-3 times the cost of the AR. This is why the AR is King at Camp Perry. I’m not a Physicist but do have an understanding that physics applies to everything even though I don’t understand it all. Just because you don’t understand it doesn’t make it irrelevant.
OK. Not sure it will make any difference for me, but assuming I wanted to put a free floating rails on my LE6920’s, which ones should I go with?
I’ve got a couple DD Omega’s I was planning on EBAYing after I got KAC M4 RAS rails. The DD Omega’s clamp to the barrel nut with really small allen bolts. To me those bolts just looked too fragile. The KAC M4 RAS rails just seemed more sturdy.
I had thought about going with the Daniel Defense AR15 Lite Rail 7.0 until my friend convinced me that my KAC M4 Rails were just as good.
Only problem with the DD AR15 Rail 7.0 is I would have to have a gunsmith install it and I don’t want to take what are good shooting rifles and screw them up. You start taking barrels off and you get into headspace crap, torque wrenches, etc. I could probably do it, but I would rather pay someone that does that kind of stuff for a living.
I have done a good bit of work on my LE6920’s. I added LMT SOPMODS, Geissele SSA triggers, Hogue grips, Vickers slings, Aimpoint Comp ML3’s with Larue mounts, and Larue BUIS. I went through at least one and sometimes two of everything I changed before getting what I really should have got to start with. I’m happy with everything except for the rails and I could probably be happy with them if it wasn’t for this blasted forum.
It does kind of bug me that the DD AR15 Rail 7.0 does not have built in QD sockets. Would be much more slim-line if it did. I know the Larue rail does have QD sockets but I heard the Larue rail is put togather with epoxy. Is this true?
What would be a fair price for a gunsmith to install a DD AR15 Rail 7.0?