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bb2007
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Posted: 2/15/2011 1:19:46 AM

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How much of an accuracy difference does installing a "Free Float" rail system make?

Standard 14.5" M4 Carbine (1:7 twist Chrome Lined, etc.)

Let's say the average M4 carbine shoots 2-3 moa with m855 or m193...will adding a free float rail system make it a 1-2 moa gun?

So much money is spent on rail systems (guilty here as well), but in the end...is there any real advantage over a MOE handguard? (besides operators that need to attach NVG stuff.)
Springer09
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Posted: 2/15/2011 1:21:22 AM
i would venture to say 1/2 moa
Cdenmark
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Posted: 2/15/2011 2:01:45 AM
[Last Edit: 2/15/2011 2:03:19 AM by Cdenmark]
Think it's more to the equation than just a HG swap. Trigger work, good consistent ammo and don't forget the shooter. M-4 is a battle carbine not a sniper rifle. FF probably won't hurt but I think it only matters if shooter is putting stress on the barrel when he or she shoots it anyway. Off a bench at 100 yds probably negligible. The shooter will probably be the difference.
reelserious
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Posted: 2/15/2011 9:09:31 AM
1/2 moa
SA80Dan
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Posted: 2/15/2011 9:41:12 AM
[Last Edit: 2/15/2011 10:06:48 AM by SA80Dan]
The whole point of a free float tube/rail is not to give you a fixed MOA accuracy increase, it is to insulate the barrel against external influences which can affect your POI. For instance, resting your rifle on a fence post, car hood, up against a wall etc - all this stuff can affect your point of impact - usually not by much, but it can do, nonetheless. The biggest one is if you use a sling to cinch the rifle up tight to stabilize a hold. If your barrel is not freefloated, this can significantly change the POI (by up to 3-4 MOA if you crank on it hard - i.e at 100 yards you can potentially pull your shots off target by 3-4 inches in an extreme case).
kavik
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Posted: 2/15/2011 9:57:58 AM
Originally Posted By SA80Dan:
(up to 3-4 MOA if you crank on it hard).


dylang32
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Posted: 2/15/2011 10:06:48 AM
Search is your friend! This is asked at least once a week.
bb2007
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Posted: 2/15/2011 10:32:08 AM
good to know. thanks.
Flatulence
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Posted: 2/15/2011 11:59:17 AM
My serch-fu is weak I guess 'cause I haven't found a thread showing accuracy w/ a free float while torqued down with a sling and non-free float torqued down with a sling.

I know that's pretty specific, but would you post the link that comes close to providing that info?
nhsport
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Posted: 2/15/2011 12:02:16 PM
Originally Posted By kavik:
Originally Posted By SA80Dan:
(up to 3-4 MOA if you crank on it hard).





I would be very surprised if it amounted to that much.

Remember that service rifle matches were shot by many in the "old" days (out to 600 yards) before free floats became common and those boys
put some serious strain on their slings. (of course the good guys also know where their zeros are also)

Most every before and after test I have seen was with a better grade of barrel and better trigger installed or other upgrades at the same time as the handguard update so
real info is a bit fuzzy.

As far as I can see the FF handguard can in no way hurt things

SA80Dan
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Posted: 2/15/2011 12:40:22 PM
Absolutely, that would be an extreme case but I have heard of it (I do shoot high power matches). Most deviations are going to be nowhere near that, but as you said - a freefloat can in no way hurt things.
MRW
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Posted: 2/15/2011 1:33:44 PM
Right now I'm stuck in a decision loop. I've got a Bushmaster gov't profile 20" barrel with regular handguards and I'm debating between the following

1. DCM style free float tube with regular handguards. This gives no rail, but does free float and gives a sling point
2. two-piece drop on rail. This does not free float but gives a spot for a bipod.
3. One piece free float rail. This free floats and gives a spot for a bipod.

the only reason not to do #3 is that I might use the upper for competition where the handguards must look original
Don't be so open-minded that your brains fall out.

General education should not be mere training of the hands to work, but training of the mind to properly reason. http://www.welltrainedmind.com/classed.php
Cdenmark
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Posted: 2/15/2011 3:22:49 PM
MRW, On a NM style rifle I think I'd use a NM style free float. Your rifle get what you want. Is it a flat top or an A-2? Not that it really matters, personally I don't put rails on 20 rifles just scopes. Ice cream comes in different flavors for a reason.
GHPorter
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Posted: 2/15/2011 3:32:42 PM
Originally Posted By bb2007:
How much of an accuracy difference does installing a "Free Float" rail system make?

Standard 14.5" M4 Carbine (1:7 twist Chrome Lined, etc.)

Let's say the average M4 carbine shoots 2-3 moa with m855 or m193...will adding a free float rail system make it a 1-2 moa gun?

So much money is spent on rail systems (guilty here as well), but in the end...is there any real advantage over a MOE handguard? (besides operators that need to attach NVG stuff.)


Nothing can make an M4 a 1-2 MOA gun if you're shooting GI ammo. The specs for both M855 and M193 don't get close enough to 1-2 MOA, and a 14.5" barrel is hardly the correct vehicle to produce tight groups, even with high quality, extremely accurate ammo. I do not see free floating helping practical accuracy in an M4.

Get a precision 20" or longer barrel. Get precision ammo. Put a free float on that upper and you can bring your groups down from "really good" to "nobody will believe I shot this!"

If you put a standard rail system on an M4, you get lots of options for mounting stuff, and you can actually reduce the impact of how much pressure you put on the barrel when you rest it; the bottom rail spreads the pressure out quite well, while a standard handguard makes it focus on the handguard cap.
"--you can't conquer a free man; the most you can do is kill him."
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Ghilly
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Posted: 2/15/2011 10:32:37 PM
Length of the barrel has zero to do with the accuracy it can produce. The only difference with a 14.5" high end barrel and a 24" high end barrel is a bit more FPS. With the same good ammo and a good bore the accuracy will be the same though slower FPS out of the shorter barrel. The Crown is also a huge deal. If you are talking iron sights the longer sight radius helps but with a scoped upper there is no difference.
Austin_Nichols
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Posted: 2/15/2011 11:51:58 PM
Originally Posted By Ghilly:
Length of the barrel has zero to do with the accuracy it can produce. The only difference with a 14.5" high end barrel and a 24" high end barrel is a bit more FPS. With the same good ammo and a good bore the accuracy will be the same though slower FPS out of the shorter barrel. The Crown is also a huge deal. If you are talking iron sights the longer sight radius helps but with a scoped upper there is no difference.


Correct.
Austin Nichols is.... Wild Turkey Kentucky Straight Bourbon Whiskey
1911smith
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Posted: 2/16/2011 12:11:06 AM
[Last Edit: 2/16/2011 12:12:03 AM by 1911smith]
Originally Posted By Austin_Nichols:
Originally Posted By Ghilly:
Length of the barrel has zero to do with the accuracy it can produce. The only difference with a 14.5" high end barrel and a 24" high end barrel is a bit more FPS. With the same good ammo and a good bore the accuracy will be the same though slower FPS out of the shorter barrel. The Crown is also a huge deal. If you are talking iron sights the longer sight radius helps but with a scoped upper there is no difference.


Correct.


Wrong........ if covering distances longer than 100 yards. Longer length barrels create more velocity creating a flatter trajectory over greater distances than considerably shorter barrels. Shorter barrels. 14.5" inches and below have more a challenge to stabilize heavier projectiles. If we're talking distances of say 100 yards or less. No, accuracy will not be greatly affected by 14.5 inch barrel.
" God Bless Our Snipers ".
Austin_Nichols
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Posted: 2/16/2011 2:36:18 AM
[Last Edit: 2/16/2011 2:38:00 AM by Austin_Nichols]
Originally Posted By 1911smith:
Originally Posted By Austin_Nichols:
Originally Posted By Ghilly:
Length of the barrel has zero to do with the accuracy it can produce. The only difference with a 14.5" high end barrel and a 24" high end barrel is a bit more FPS. With the same good ammo and a good bore the accuracy will be the same though slower FPS out of the shorter barrel. The Crown is also a huge deal. If you are talking iron sights the longer sight radius helps but with a scoped upper there is no difference.


Correct.


Wrong........ if covering distances longer than 100 yards. Longer length barrels create more velocity creating a flatter trajectory over greater distances than considerably shorter barrels. Shorter barrels. 14.5" inches and below have more a challenge to stabilize heavier projectiles. If we're talking distances of say 100 yards or less. No, accuracy will not be greatly affected by 14.5 inch barrel.


Wow, my friend, you are completely wrong. Accuracy has nothing to do with barrel length, increased velocity notwithstanding. To clarify, additional fps does not make a barrel more accurate and I challenge you to offer science that proves otherwise. And how do shorter barrels have a problem "stabilizing heavier projectiles"? The issue is projectile "length", not weight, and unless the barrel is less than it's twist rate I fail to see your stabilization "challange" as described. Do some research, check out the ammo oracle on this site, and then report back.
Austin Nichols is.... Wild Turkey Kentucky Straight Bourbon Whiskey
Highandright
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Posted: 2/16/2011 8:28:41 AM
How much effect will wind come into play on a slower velosity bullet?
BRONZ
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Posted: 2/16/2011 8:57:21 AM
most and I mean most shooters wont know the difference.
BRONZ

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1911smith
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Posted: 2/16/2011 9:25:24 AM
Originally Posted By Austin_Nichols:
Originally Posted By 1911smith:
Originally Posted By Austin_Nichols:
Originally Posted By Ghilly:
Length of the barrel has zero to do with the accuracy it can produce. The only difference with a 14.5" high end barrel and a 24" high end barrel is a bit more FPS. With the same good ammo and a good bore the accuracy will be the same though slower FPS out of the shorter barrel. The Crown is also a huge deal. If you are talking iron sights the longer sight radius helps but with a scoped upper there is no difference.


Correct.


Wrong........ if covering distances longer than 100 yards. Longer length barrels create more velocity creating a flatter trajectory over greater distances than considerably shorter barrels. Shorter barrels. 14.5" inches and below have more a challenge to stabilize heavier projectiles. If we're talking distances of say 100 yards or less. No, accuracy will not be greatly affected by 14.5 inch barrel.


Wow, my friend, you are completely wrong. Accuracy has nothing to do with barrel length, increased velocity notwithstanding. To clarify, additional fps does not make a barrel more accurate and I challenge you to offer science that proves otherwise. And how do shorter barrels have a problem "stabilizing heavier projectiles"? The issue is projectile "length", not weight, and unless the barrel is less than it's twist rate I fail to see your stabilization "challange" as described. Do some research, check out the ammo oracle on this site, and then report back.


No, you can't do that, because increased velocity and flatter trajectories make a big difference when bucking the wind. Shorter barels will have to step down in trajectory weight to get to the velocity my longer barrel produces. Lighter projectiles run out of inertia quicker than heavier counterparts. No Oracle needed. That's hands on experience talking. If your framing your point within a shorter radious, then your oracle would prevail. At Greater distances the longer wand of my Mr. Wizard requires a lot less work of the shooter.

" God Bless Our Snipers ".
1911smith
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Posted: 2/16/2011 9:28:35 AM
Originally Posted By Highandright:
How much effect will wind come into play on a slower velosity bullet?


Depends on twist rate and bullet weight. Also depends on what day and tricks the wind is playing on that day.

" God Bless Our Snipers ".
Orion
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Posted: 2/16/2011 9:37:43 AM
Good topic because I am in the process of getting a 16" mid length barrel and was just going to go with a non-floated handguard. I WOULD like to get close to 1 MOA though because the farther off at 100 yards, the worse it is as the targets gets further out.
beltfed74
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Posted: 2/16/2011 10:31:57 AM
I shot benchrest in another life, we all shot shorter barrels. Even in HV Class, trajectory is meaningless as far as repeatability. Short tubes are stiffer, which aids in repeatablity.

This only includes LV,HV and Hunter Class stuff. The 1000yd guys were a different breed. Last I heard was velocity mattered a lot because when a bullet slows back down below subsonic accuracy starts degrading fast, the slower you get the worse. Atleast that was the theory 10 years or so ago.

As to answer the OP, everyone should have one free floated rig in the collection. Why? Just because.
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Posted: 2/16/2011 11:56:41 AM
[Last Edit: 2/16/2011 11:57:57 AM by Fields_Overseer]
Originally Posted By bb2007:
How much of an accuracy difference does installing a "Free Float" rail system make?

Standard 14.5" M4 Carbine (1:7 twist Chrome Lined, etc.)

Let's say the average M4 carbine shoots 2-3 moa with m855 or m193...will adding a free float rail system make it a 1-2 moa gun?

So much money is spent on rail systems (guilty here as well), but in the end...is there any real advantage over a MOE handguard? (besides operators that need to attach NVG stuff.)


depends on use. If you use a sling or bipod(puts force on the barrel) you will definitely notice a difference. It also lets the barrel vibrate without interuption wich also helps. Must have on a precision gun. If your shooting xm193 or clones, you wont notice much. Load up some mk262 or other match ammo and youll start to notice a difference.

If you have a match barrel, get a FF tube, if not, I wouldnt worry about it.
Primos
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Posted: 2/16/2011 12:12:27 PM
Originally Posted By BRONZ:
most and I mean most shooters wont know the difference.


But it gives me a chance to burn cash and hang stupid crap from 4 feet of picatinny rail.
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