View Full Version : Why wouldn't a non free float barrel be better than a FF barrel......
SW-Shooter
10-26-09, 03:38
Why wouldn't a non free float barrel be better than a FF barrel when it comes to better accuracy and less POI shift when using a suppressor.
Would there be any stabilization of the barrel by having more mass to "lean" against and would it benefit from less flex and shift in POI? Has anyone ever examined this cause and effect?
Just being nerdy.
Belmont31R
10-26-09, 05:26
Why wouldn't a non free float barrel be better than a FF barrel when it comes to better accuracy and less POI shift when using a suppressor.
Would there be any stabilization of the barrel by having more mass to "lean" against and would it benefit from less flex and shift in POI? Has anyone ever examined this cause and effect?
Just being nerdy.
Most accuracy issues from non-FF rails are because of the inconsistent pressure on the rails. Any force on the rail is going to affect the barrel also.
FF forearm allows consistent barrel harmonics because there is no pressure on it.
Most accuracy issues from non-FF rails are because of the inconsistent pressure on the rails. Any force on the rail is going to affect the barrel also.
FF forearm allows consistent barrel harmonics because there is no pressure on it.
agreed!
Most accuracy issues from non-FF rails are because of the inconsistent pressure on the rails. Any force on the rail is going to affect the barrel also.
FF forearm allows consistent barrel harmonics because there is no pressure on it.
yes. but this is not true in ALL cases. some barrels, due to various issues, will perform better with a certain amount of consistent force applied to the barrel, generally from a single direction.
finding this "sweet spot" is mostly luck as you try different combinations of pressure and location, along with projectile weight and type as well as propellant type and amount.
anyway, non-FF handguards are probably not going to be considered "consistent" in the way or amount of pressure they apply to the barrel...
The barrel acts as a tuning fork when fired. It vibrates at it's specific resonance. Applying a outside force on it may or may not help. It depends on whether the bullet exits the muzzle at a midpoint of the vibration, i.e. when it's centered, as opposed to one of the outer extremes. Target rifle makers now tune the barrel with dampeners, or determine by experiment what length a particular profile can use best.
Since a force on the barrel may actually dampen or stop the oscillations, the use of a free float is no guarantee of an improvement on accuracy beyond preventing the sling pressure from shifting the actual muzzle. From what little knowledge I can pick up. a free float handguard is considered a 1/2 MOA improver at best. Significant for a precision shooter, unimpressive for the fielded cost. The advantage for a soldier is as a platform for accessories, not a major increase in accuracy.
Now add the weight, dynamics, and change of point of impact for a suppressor to the barrel harmonics model. A suppressor oscillating on the end of a barrel probably doesn't move significantly enough to change trajectory as much as the impact of baffles.
Those who shoot the combination with any frequency haven't made much noise about it being a problem. :D
Why wouldn't a non free float barrel be better than a FF barrel when it comes to better accuracy and less POI shift when using a suppressor.
Would there be any stabilization of the barrel by having more mass to "lean" against and would it benefit from less flex and shift in POI? Has anyone ever examined this cause and effect?
Just being nerdy.
From my experience of 20 years of shooting AR's in across the course Service Rifle and other competitions the issue isn't accuracy with regards to non-FF vs. FF, it is point of impact shift, especially when in the slung tight position (primarily prone position). When the AR is shot from a bench with the forend on a rest and the rest is placed as close as possible to the mag well you'll see essentially no accuracy difference between an AR with non-FF handguards vs. the same AR with a FF handguard. But repeat that with both non-FF and FF slung up and fire both from a prone position and you will see a significant difference in change of point of impact, more so with a 20 inch barrel compared to a 16 or shorter barrel AR, and the point of impact shift with the non-FF will be inconsistent and drive you nuts.
Don
What difference does a heavy bbl make in this subject?
What difference does a heavy bbl make in this subject?
In terms of point of impact shift a heavy barrel will help to reduce it but will not eliminate it. In terms of accuracy it won't make a difference. I have a disgustingly lightweight 16" stainless BM fluted barrel that is incredibly accurate from the bench (3/8th MOA with my handloads). Accuracy is dependent on barrel manufacture quality and the combination of other factors such throat lead suitable to the specific bullet you are shooting, chamber concentricity, chamber dimension consistency, bolt face alignment i.e., truly perpendicular to the bore CL, etc.
There is a lot more that contributes to accuracy but too many variables to address here.
Don
SW-Shooter
10-27-09, 02:37
You guy's are leaving out the added weight of a suppressor.
Why isn't the current AR platform molded as one lower/upper unit utilizing current lightweight aluminum materials. Makes sense to mold it all as one piece with rails included, quick attach barrel and you'd be on your way.
Someone has to have the capabilities.
Alaskapopo
10-27-09, 02:47
yes. but this is not true in ALL cases. some barrels, due to various issues, will perform better with a certain amount of consistent force applied to the barrel, generally from a single direction.
.
I believe what you are talking about applies to bolt action rifles and not really AR's due to the way the barrels and receivers work. Bolt guns are set in a stock where a AR has the barrel and action all in one cohesive unit.
Slinging a 20" AR barrel on a qualification course is exactly the problem I consistently faced every time - sighting in was a wasted effort until I just let it rest on my forearm, no sling at all. Once the barrel was unstressed and left to gravity, it settled down.
Considering the three years in high school shooting International .22 with slings, jackets, and mats, it was a frustrating moment. I had never shot a flexy flier before - the stock on a conventional firearm prevents the influence.
Shooting the HK91, with a bolt guide welded on and bigger .308 hammer forged barrel, the sling wasn't a problem. It only crops up on AR's when LD target competition methods are used. I didn't sling up on live fire tactical training because the standard was to remove it in combat.
This is known as an unintended consequence. Mixing two different disciplines can cause problems not forseen by either proponent. They are not always compatible, in spite of the expertise of someone suggesting it.
As for a single one piece AR, that sort of complete redesign is difficult at best. A review of modern military designs of the last fifty years shows some interest in removing the bolt for cleaning. Changing the AR enough to make a one piece receiver and remove the bolt introduces so many other changes it's no longer an AR, it's something else. And the AR doesn't suffer from tactical inaccuracy with the separate parts - that's a LD competition shooting perspective, which brings us back to unintended consequences . . .
Slinging a 20" AR barrel on a qualification course is exactly the problem I consistently faced every time... [snip] It only crops up on AR's when LD target competition methods are used.
One option, if you're required to retain the original AR plastic handguards, is to use an under the handguards free float tube. They are designed to allow a free floating handguard that has the appearance of a stock assembly. The forend cap (that holds the forward end of the handguards in place) is attached to the free float under tube and the sling swivel is attached to the free float under tube as well rather than the front sight base. They are legal for CMP (Civilian Marksmanship Program) wherein the AR must retain an external original configuration appearance. DPMS sells a very good under the handguard free float tube, see:
http://www.dpmsinc.com/store/products/?prod=630&cat=1526
Don
You guy's are leaving out the added weight of a suppressor.
Why isn't the current AR platform molded as one lower/upper unit utilizing current lightweight aluminum materials. Makes sense to mold it all as one piece with rails included, quick attach barrel and you'd be on your way.
Someone has to have the capabilities.
What does a single receiver instead of an upper/lower have to do with anything (ignoring how virtually all modern rifles have moved away from this...)?
-B
you'll never have a complete AR being 1 pc.....lowers need to be removeable to get the buffer out for changing weights, and trigger assemblies have to go in and so on. the closest thing to a single receiver you're going to get is the Lewis Machine & Tool MRP (monolithic rail platform) or VLTOR VIS. The LMT has a proprietary barrel clamping system that uses a torque wrench and you can change barrels in just a few minutes. swap your bolt out and change your magazine and you're good. The VLTOR doesn't have quite such a fast barrel changing but it is a very nice system and costs half of the LMT. Downside (if there is one) is that the rail and upper receiver are welded together, but welds are typically stronger than the metal around them.
SW-Shooter
10-27-09, 23:31
I'm just looking to ask questions about the evolution of the AR design. I like to know the principle characteristics and what makes the design tick. I know the basics and advanced aspects of the design, I'd like to build a better mousetrap.
Uppers with integrated rails take a lot of stress off the barrel. They are one piece and allow the barrel to free float. Integrating the lower isn't necessary - there is very little accuracy to be gained, especially for the engineering involved and the resulting fraction of a MOA improvement.
Firearms for military use have to be 1) cost effective to make 2) only nominally accurate 3) simple to take down for operator maintenance and armorer repair. Attempting modifications to improve accuracy often result in serious impacts on those factors, usually to the detriment of the overall usefulness. They make work well on a range, but tactically restrict the user.
The M4 is a direct result of the A2 being too much rifle for the infantry in today's urban warfare, LIC situations. In response to a need for a longer distance weapon, the M14 and Squad Designated Marksman are used, but they supplement the squad and platoon capability - not substitute it.
Arming the teams and squads with super accurate rifles isn't going to increase lethality much for the cost - 2MOA gets the job done and has for a long time. It's why they practice on man sized targets - which I expect would bore most precision shooters to tears. 16" ten rings don't look very challenging.
But, doing that while moving, in the dark, with return fire, that gets the adrenaline going. It's much more of what the AR was designed to address.
Long distance is a nice sport, but only a very small part of the mission.
I believe what you are talking about applies to bolt action rifles and not really AR's due to the way the barrels and receivers work. Bolt guns are set in a stock where a AR has the barrel and action all in one cohesive unit.
if you remove the handguard (and the gas tube) there is no difference between the bolt rifle and AR in regard to barrel impingement, harmonics, etc.
One option, if you're required to retain the original AR plastic handguards, is to use an under the handguards free float tube. They are designed to allow a free floating handguard that has the appearance of a stock assembly. The forend cap (that holds the forward end of the handguards in place) is attached to the free float under tube and the sling swivel is attached to the free float under tube as well rather than the front sight base. They are legal for CMP (Civilian Marksmanship Program) wherein the AR must retain an external original configuration appearance. DPMS sells a very good under the handguard free float tube, see:
http://www.dpmsinc.com/store/products/?prod=630&cat=1526
Don
this is how I had my DCM (Department of Civilian Marksmanship) bushmaster upper set up with a Douglas SS barrel.
SW-Shooter
10-28-09, 13:58
I know this is off topic but wouldn't the 6.8 round be optimal for use in Afghanistan? I'm about to tackle a build and I just want to cover all of the essentials without mistake , I want to make sure I build a better rifle, something that will outlast the test of time.
I'm just not certain of the direction I should take. Or if there is a better mousetrap yet to be conjured.
I know this is off topic but wouldn't the 6.8 round be optimal for use in Afghanistan? I'm about to tackle a build and I just want to cover all of the essentials without mistake , I want to make sure I build a better rifle, something that will outlast the test of time.
I'm just not certain of the direction I should take. Or if there is a better mousetrap yet to be conjured.
Are you going to Afghanistan?
-B
I know this is off topic but wouldn't the 6.8 round be optimal for use in Afghanistan? I'm about to tackle a build and I just want to cover all of the essentials without mistake , I want to make sure I build a better rifle, something that will outlast the test of time.
I'm just not certain of the direction I should take. Or if there is a better mousetrap yet to be conjured.
Just get a SCAR then.
You and most people won't notice a difference in accuracy with or without one.
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