PDA

View Full Version : What is the actual accuracy improvment from a free float rail


Artery
05-19-2009, 1:43 AM
So everyone says that a FF rail improves accuracy by free floating the barrel. While I have no doubt this is true from my experience with bolt action rifles whats the actual improvement (if any) for a AR. Does anyone have before/after data or pictures?

tiger222
05-19-2009, 6:35 AM
From what I understand, free floating only helps when the barrel is under sling pressure...

To add, a Colt trained armorer told me the AR's technically can never be free floated due to the gas tube -

However, on non AR rifles, I have found that pressure on the handguard touching the barrel did affect accuracy.

On a military rifle I think the effect is not important. But if you are looking for precision it will remove one variable.

scidx
05-19-2009, 7:48 AM
To piggy-back...
When a projectile is fired through a barrel, the metal reciprocates; or waves. It's kind of like when you were a kid and you flipped a jump rope to watch the wave travel to the other end. A barrel is expectedly designed to continue the wave throughout. Whenever you put pressure on the metal, you interupt the wave cycle. An AR has set pressure from the gas block. Free float rails or guards help but can not offer pure free float.

Geo
05-19-2009, 8:02 AM
If you are an unskilled shot, no amount of accurizing will help.

grahlaika
05-19-2009, 8:17 AM
Free-floating is an art more than it is a science. Some barrels work well being supported, others work better being free-floated. Accuracy means repeatability, and non-free floating barrels can be just as accurate as free floating ones. All you need to do is to find the right load for your barrel to minimize the variations in harmonics, and you get accuracy. Precision, on the other hand, is a different issue.

SuperSet
05-19-2009, 8:33 AM
It's supposed to be about 0.5 MOA. Molon on ARFCOM posted about this a while back and this guy's findings were similar.

http://www.rifleshootermag.com/new_products/RS_floatfree_200804/index.html

hybridatsun350
05-19-2009, 8:33 AM
You're groups will shrink by precisely 1/2" if you go to a free-float tube. Lol, just kidding, but it certainly can't hurt, right? :)

phamkl
05-19-2009, 9:04 AM
[skip to last line if you don't care for theories]

Free floating in bolt guns is usually a shortcut as a full bed will almost always result in more accuracy. Free floating allows the barrel to vibrate in exactly the same manner every time. If something is attached to the barrel then the differential heating/cooling process will add an element of randomness into the mix because slight changes in the structure result in different vibration characteristics.

In a fully bedded action, vibrations are dampened throughout, if the barrel flings the bullet somewhere, the magnitude of the "fling" is less than it would be on a floated barrel. The placement of a suspension piece, for accurization, should dampen the wave such that there is a node at the muzzle so that the rifle doesn't fling bullets anywhere. Since different loads cause different vibrations, this is the idea behind different guns preferring different bullets. And since no two barrels are exactly alike on a microscopic level, different barrels in the same batch could have different wave propagation characteristics, which is why some guns are just randomly accurate (more precise manufacturing will result in more consistency between barrels.)



So, so long as you choose the right bullet, theoretically you'll get the most accuracy out of any gun regardless of what the barrel touches (assuming you don't superheat the barrel but if you're going for accuracy where this would matter, you probably aren't shooting mags off in minutes at a time.)

Practically though, since we can't really bed an AR action, the freest floating barrel will let your barrel vibrate exactly the same for every bullet and therefore will give you the most consistency in shot placement.

Artery
05-19-2009, 10:39 AM
It's supposed to be about 0.5 MOA. Molon on ARFCOM posted about this a while back and this guy's findings were similar.

http://www.rifleshootermag.com/new_products/RS_floatfree_200804/index.html

Thank you! Actual data rather than postulation is refreshing.

.5in is pretty significant... I think I'm going to take the plunge and get one. I'm the kind of guy that isn't really into the tacti-cool stuff (I don't care about flashlights lasers and whatever) but ~.5in of accuracy is a huge improvement.

DarkHorse
05-19-2009, 11:00 AM
Thank you! Actual data rather than postulation is refreshing.

.5in is pretty significant... I think I'm going to take the plunge and get one. I'm the kind of guy that isn't really into the tacti-cool stuff (I don't care about flashlights lasers and whatever) but ~.5in of accuracy is a huge improvement.

There are free-float tubes that don't have rails. Just tubes. Like the internet.

Artery
05-19-2009, 11:04 AM
There are free-float tubes that don't have rails. Just tubes. Like the internet.

I fear that much like how the internet is a series of tubes too many ARs are becoming a series of rails... :eek:

The FF hand guard I'm looking at is the DD omega rail and truth be told they're a couple things I'd like to be able to mount like a bipod mount or maybe a sling attachment

dchang0
05-19-2009, 11:27 AM
You're groups will shrink by precisely 1/2" if you go to a free-float tube. Lol, just kidding, but it certainly can't hurt, right? :)

Woo hoo! I'm gonna buy TWO free-floats then and shrink my groups by 1 whole MOA!

ar15barrels
05-19-2009, 3:37 PM
http://ar15barrels.com/tech/freefloat.jpg

dchang0
05-19-2009, 5:16 PM
Randall, you are freakin' wealth of information!

cmace22
05-19-2009, 7:50 PM
If you are an unskilled shot, no amount of accurizing will help.

We are all wiser from your wealth of knowledge, grasshopper :rolleyes:

norcal-ar
05-19-2009, 8:38 PM
look for the most recent edition of Guns and Ammo "Book of the AR-15" they did this test and it showed that it helped quite a bit but remember the guy who wrote the article is an excellent shooter and was using match grade ammo on all of his test.

ar15barrels
05-19-2009, 8:45 PM
Randall, you are freakin' wealth of information!

Credit Molon on arfcom for that graphic. :thumbsup: