Need to free float?

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  • rvb

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    In a recent discussion*, I mentioned I like long float tubes on my ARs to cover as much of the barrel as possible. The idea is I want to keep the barrel from touching anything I might use as a rest, which could throw the point of impact off. Anecdotally I mentioned witnessing a fellow 3-gun competition miss by approximately 3 feet at 200 yards, when his barrel was hitting the peak of a simulated "rooftop" shooting position.

    Folks didnt believe the claim, so, always wanting to add to my personal experience and knowledge, I decided to do an experiment and see for myself how important it is to keep the barrel from hitting your rest.

    I set up using a ~15"-tall wood rest, on a target at 100 yards. Every round fired used the same point of aim. The rest was a little tall for my usual prone position, a situation common in practical shooting... that you don't get an "ideal" position.

    I used my 3-gun rifle. It uses an 18" WOA SPR barrel, JP extended (15") free float Handguards, and vortex genII PST 1-6. The barrel's pretty thick... It uses a 3/4" gas block, and the profile is thicker than that all the way back to the chamber. Notice the hand guards extend past the rifle-length gas system. Ammo was 55gr hand loads.

    image_zpsmorurozj.jpeg


    Group A, 5 rounds. Fired in my "typical" position, with weak hand holding the tube against the rest to keep it on target in recoil. My first couple of rounds were the high/low fliers, as I didn't get in to a good position with the improvised rest, so I fired 5 instead of 3.

    Group B, 3 rounds. Fired with the barrel resting on the rest. I put no weight on it other than gravity, keeping my weak hand back under the stock.

    Group C, 3 rounds. Fired holding the gun against the rest like I did in group A, only with the barrel on the rest vs the Hand guards. This was awkward, trying to reach out that far.

    Group D, 3 rounds. Fired with the barrel against the rest, putting just a rediculous amount of pressure down on it.

    image_zpsoaon1tcq.jpeg



    Measured from the center of group A, the groups impacted higher by the following amounts:
    B: 5.5"
    C: 15"
    D: 20"

    Some observations/thoughts...
    -- I was surprised group B hit so much higher. I expected 1-2", not 5". Perhaps part of this was from letting the gun recoil (lift) vs holding it down. In hindsight, I should have also tried a gravity-only hold resting on the Hand guards.
    -- I thought later I should have tried a lot of pressure on the hand guards to see if perhaps some of the flex was in the barrel nut or receiver vs the barrel.
    -- Groups A and C are the most representative of what could happen in a match were I to hold accidentally resting the barrel on a prop vs the Handguards... 15 MOA of "why the hell didn't I connect, I called a good hit?!"
    -- I wouldn't expect such a big difference with a standard barrel-mounted front sight. It would move with the barrel. I might try to repeat that someday with my hbar'd A2.

    i expected some shift in POI, but this frankly shocked me. Of course, every gun, barrel, and ammo combination could be different. It does reafirm my opinion that an ideal setup should use as long of a float tube as possible to "protect" the barrel from touching a rest.

    *https://www.indianagunowners.com/forums/long-guns/438168-my-perfect-ar15-setup-3.html#post7128490

    -rvb
     
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    Gabriel

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    Good post.

    You think this would be common knowledge, but I see people using the barrel as a rest quite a bit.

    I'd like to see a similar test with the handguard mounted front sights (maybe versus the barrel mounted). I've always thought they defeated the purpose of the free float handguard. One of my rifles has sights mounted that way (granted it is back up to an optic) and always figured my accuracy would be significantly affected if I shot it slung up or with the handguard against a rest.
     

    rvb

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    Good post.

    You think this would be common knowledge, but I see people using the barrel as a rest quite a bit.

    I'd like to see a similar test with the handguard mounted front sights (maybe versus the barrel mounted). I've always thought they defeated the purpose of the free float handguard. One of my rifles has sights mounted that way (granted it is back up to an optic) and always figured my accuracy would be significantly affected if I shot it slung up or with the handguard against a rest.

    It's a good idea, and worth testing for your equipment, but i think results from such a test would vary wildly depending on the hardware. The first HGs I had on the above rifle were trash. They had a very poorly designed mount, and it didn't take much pressure to bend them. If I'd have had irons on them, they'd have never held a zero, never mind pressure from sling or rest.

    I'm a big fan of the JP HGs, as well as BCM. I've certainly not used all the HGs available out there, but those have proven a couple of times to be rock solid. I put my upper with the BCM HGs in a vice block, put a straight edge along the top, and squeezed the barrel and HGs together as hard as I could and saw no deflection in the HGs, only the barrel. I've done similar tests with the JP.

    I could try the test you mentioned with my gun with BUIS. I'm confident they'd do pretty well, but I also consider them for back-up and a couple MOA variation I could live with.

    my ARs using BCM HGs...
    image_zps4hfoorej.jpeg


    I was using the short .223, making good hits at 300 standing using a post for support, after I had done the test above, and didn't have to worry about pressure from the post throwing my rounds into never never land... But I was using the dot, not the irons...

    -rvb
     
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    Gabriel

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    It's a good idea, and worth testing for your equipment, but i think results from such a test would vary wildly depending on the hardware. The first HGs I had on the above rifle were trash. They had a very poorly designed mount, and it didn't take much pressure to bend them. If I'd have had irons on them, they'd have never held a zero, never mind pressure from sling or rest.

    I'm a big fan of the JP HGs, as well as BCM. I've certainly not used all the HGs available out there, but those have proven a couple of times to be rock solid. I put my upper with the BCM HGs in a vice block, put a straight edge along the top, and squeezed the barrel and HGs together as hard as I could and saw no deflection in the HGs, only the barrel. I've done similar tests with the JP.

    I could try the test you mentioned with my gun with BUIS. I'm confident they'd do pretty well, but I also consider them for back-up and a couple MOA variation I could live with.

    my ARs using BCM HGs...


    I was using the short .223, making good hits at 300 standing using a post for support, after I had done the test above, and didn't have to worry about pressure from the post throwing my rounds into never never land... But I was using the dot, not the irons...

    -rvb

    Exactly. Since the optic is on the receiver, it won't make a diffeence. I'm, guessing you oculd pull thta front sight around quite a bit on a support or sling. You are also correct that equipment would make abig difference. I have a DD quad rail on one, a BCM on another, and Seekins on a third. I'd bet the DD would be the hardest to pull around.
     

    DanVoils

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    Nice post. All of my hand guards are free floated with the exception of 2 of my 22's. They live for plinking more than anything else. People seem to think that barrel flex is only for the pencil barrels and not for every barrel. Thanks for showing them wrong.
     

    Cerberus

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    Have shot many thousands of rounds with the old tried and true iron sights and non free floated barrels over the past many years. Have even rest on the barrel many times. Granted I never pressed down on the barrel, but I never had a point to prove either by doing so.
     

    55fairlane

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    As far as AR rifles I can't 100% give you an answer, but all my 3 position small bore guns,free floating is a must....I have helped guys at the club,the POI was just moving all the place,the dollar bill test showed the barrel was touching, sand paper away,shot group closed right up.....knowing this.....
     

    Cerberus

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    As far as AR rifles I can't 100% give you an answer, but all my 3 position small bore guns,free floating is a must....I have helped guys at the club,the POI was just moving all the place,the dollar bill test showed the barrel was touching, sand paper away,shot group closed right up.....knowing this.....

    I don't actually think that the question is whether or not there is any POI shift if you rest your barrel vs not. It's how much. Yes, everyone knows there will be some shift, and long range shots are better to not have the barrel rested if avoidable. The posting that started this in another thread was simply a claim that resting (implies only gravity pressure) caused a 3 ft shift in POI at 200 yds. Now under testing it seems that some moderate pressure had to be applied to get the POI shift that was alluded to. Some time in the next week or so, it will be the 30 year anniversary of me learning to use proper sling tension in firing a rifle on a KD range, and in case you don't know this, the USMC does not use free floated rifles for general issue. Never had a problem qualifying and even shined at 500 meters. Have even spent the years since then shooting under some quite austere conditions and have never had a problem in hitting targets, and now I shoot monthly with a great bunch of folks that for the most part shoot ARs in the "issue" style, being that there are exactly 4 free floats out of about 2 dozen ARs. Granted we don't frequently shoot off rested barrels other than to see POI shifts on 100 yd paper, but we do commonly shoot off sand bags resting around about the FSP area and 500 yds is usually hit with regularity by most.
     

    rvb

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    First, I didn't test fixed irons (barrel mounted). I even said I wouldn't expect as much shift since the sight would move with the barrel. So you're making arguments that aren't relevant to my experiment. In the other thread, we were discussing floated barrels, and this started when I gave reasons why I like the FF HGs to be as long as possible to make sure the barrel stays off anything I might use as a rest.

    And in in the other thread, maybe you understood it to be a gravity-only type "rest" as in my group B, but no, group C is what I was trying to communicate that I saw happen. Most folks in 3-gun style matches will try to hold the gun against the rest to keep it from moving off target in recoil. It's not an excessive hold, just using the WH to hold both the rest and gun. On a solid rest failing to do so is just asking the gun to bounce off target. That my group C, a "typical" type hold for me put the round 15" high perfectly proves my point in the other thread; at 200 it would have been 2.5 feet high, and that's with a fairly thick profile barrel, not the light weight ones many 3-gunners prefer. It was the exact technique I used for group A, only where the rest touched the gun changed.

    I hope that that clairifies what I was saying. GRoups A/C are the heart of the test. Groups B I would never use outside of a bench rest type application. D was the only one that I pressed down in a manner I considered excessive.

    -rvb
     

    rvb

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    In this video you can see the simulated rooftop with the 200 yd flash targets where I witnessed the gentleman send rounds about 3 feet high. Unfortunately the angle obscures my weak hand grip on the HGs/rest. The barricade near the end shows both myself and my competitor / good friend using very similar techiques holding the HGs against the rest for the fastest possible follow up shots. Had I let the barrel touch the support, I'd still be standing there trying to hit the targets..... The barricade was a little high for me, I had to stand tall to reach; The front hold clamping the gun to the rest was doing almost all the work, I couldn't really lean into it....

    https://m.youtube.com/watch?v=19STpWMucJY

    -rvb
     

    rhino

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    I'm glad rvb took the time to create evidence to show people who don't believe how much POI can change when you apply pressure to an AR barrel.

    I learned this lesson during one of my first three gun matches back in the mid 1990s. I was shooting my brother's Colt Sporter with a pencil barrel and getting good hits at 50 yards offhand. Then on another stages where we shot from a bench at 1 and 2 inch circles, I used one of those bipods that clips on the barrel at the same location as the front sight tower. All of my hits were 2-3 inches high at 50 yards, but POI went back to normal as soon as I shot offhand again.

    Freefloat tubes are mandatory equipment in my opinion, either for sport or defense.
     

    Cerberus

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    First, I didn't test fixed irons (barrel mounted). I even said I wouldn't expect as much shift since the sight would move with the barrel. So you're making arguments that aren't relevant to my experiment. In the other thread, we were discussing floated barrels, and this started when I gave reasons why I like the FF HGs to be as long as possible to make sure the barrel stays off anything I might use as a rest.

    This is your quote from the other thread;
    after having shot some 3-gun and high power and seeing how far off target you can throw a round either through resting the barrel/handguards on a prop for stability or through sling pressure, I want all my barrels FF. In fact, I should have included in the list HGs that extend to cover the barrel as much as possible to avoid putting the barrel in contact with a rest. That's quite important to me.

    I watched a guy throw all his rounds about 3 feet high at 200 yds because his barrel was resting on the "roof peak" at a match. With a sling, I've pulled the shot 5-6 moa off zero with just a change in sling tension on my non-FF A2 I shoot in HP.

    Yes, you did have to force the excessive POI shift. Resting will give you a couple inches POI shift using you barrel as a crowbar will give you 15MOA shift. And how do you apply sling pressure to a barrel on a free floated barrel?
     

    rhino

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    Yes, you did have to force the excessive POI shift. Resting will give you a couple inches POI shift using you barrel as a crowbar will give you 15MOA shift. And how do you apply sling pressure to a barrel on a free floated barrel?


    He clearly referred to a NON-free floated barrel in that quote:

    after having shot some 3-gun and high power and seeing how far off target you can throw a round either through resting the barrel/handguards on a prop for stability or through sling pressure, I want all my barrels FF. In fact, I should have included in the list HGs that extend to cover the barrel as much as possible to avoid putting the barrel in contact with a rest. That's quite important to me.

    I watched a guy throw all his rounds about 3 feet high at 200 yds because his barrel was resting on the "roof peak" at a match. With a sling, I've pulled the shot 5-6 moa off zero with just a change in sling tension on my non-FF A2 I shoot in HP.

    -rvb
     

    rhino

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    Some other factors will come into play as well for affecting how much deflection is observed. A barrel that has a smaller outer diameter is going to bend more than a thicker barrel with the same stress applied. The distance from the receiver to where the barrel is pressing against a support will play a big role as well. The farther from the upper receiver (i.e. a longer bending moment arm), the greater the deflection with all other factors the same.
     

    LarryC

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    Some other factors will come into play as well for affecting how much deflection is observed. A barrel that has a smaller outer diameter is going to bend more than a thicker barrel with the same stress applied. The distance from the receiver to where the barrel is pressing against a support will play a big role as well. The farther from the upper receiver (i.e. a longer bending moment arm), the greater the deflection with all other factors the same.

    Can't disagree with your logic! However there is one more significant factor. The harmonics of the barrel, just like a guitar all firearms have motion when fired, that's why certain ammo is more accurate than others. Resting the barrel on any object regardless of the pressure applied will change the harmonics and affect the repeat accuracy. Obviously the old method of "bedding" the barrel significantly reduced the amount of harmonics, making the firearm more accurate and repeatable with different loads. I really don't know which can deliver the most accuracy, floating the barrel or properly bedding the barrel.

    I doubt there is any way to obtain test results to ascertain that. IMHO, free floating the barrel works well when a selection of an accurate load is used. However I don't know how different loads would be affected. (I have 3 AR / LR rifles all are free floating). I also don't see any way an AR style rifle could be properly bedded, so assume free floating is the only way to go.
     

    rhino

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    Can't disagree with your logic! However there is one more significant factor. The harmonics of the barrel, just like a guitar all firearms have motion when fired, that's why certain ammo is more accurate than others. Resting the barrel on any object regardless of the pressure applied will change the harmonics and affect the repeat accuracy. Obviously the old method of "bedding" the barrel significantly reduced the amount of harmonics, making the firearm more accurate and repeatable with different loads. I really don't know which can deliver the most accuracy, floating the barrel or properly bedding the barrel.

    I doubt there is any way to obtain test results to ascertain that. IMHO, free floating the barrel works well when a selection of an accurate load is used. However I don't know how different loads would be affected. (I have 3 AR / LR rifles all are free floating). I also don't see any way an AR style rifle could be properly bedded, so assume free floating is the only way to go.

    That's certainly true! However, I don't think it would have as much effect as stress applied to the barrel causing deflection of the muzzle. When the barrel of an AR oscillates as those waves propagate back and forth along the barrel, the magnitude of the vibrations (measured as the maximum deflection from the boreling of a wave crest/trough) is going to be relative small. Plus, if you get super lucky and the pressure is applied at a node (a spot along the barrel that does not move with the waves), then it will have no effect at all. You can actually determine where those nodes will be based on the length of the barrel.
     

    rvb

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    This is your quote from the other thread;
    after having shot some 3-gun and high power and seeing how far off target you can throw a round either through resting the barrel/handguards on a prop for stability or through sling pressure, I want all my barrels FF. In fact, I should have included in the list HGs that extend to cover the barrel as much as possible to avoid putting the barrel in contact with a rest. That's quite important to me.

    I watched a guy throw all his rounds about 3 feet high at 200 yds because his barrel was resting on the "roof peak" at a match. With a sling, I've pulled the shot 5-6 moa off zero with just a change in sling tension on my non-FF A2 I shoot in HP.

    Yes, you did have to force the excessive POI shift. Resting will give you a couple inches POI shift using you barrel as a crowbar will give you 15MOA shift. And how do you apply sling pressure to a barrel on a free floated barrel?

    Im not going to play the semantics game just so you can be argumentative. My normal hold on a rest = crowbar? Please.

    Sure. I may have used the word "resting" when using a "rest". I explained what I meant; which to me "resting" doesn't have to mean gravity only. It sounds like the others are on the same page. So keep waiving your BS flag that it's not possible to send a round so far off when "resting" the barrel on something, I'll let the evidence above speak for itself...

    -rvb
     

    rvb

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    Can't disagree with your logic! However there is one more significant factor. The harmonics of the barrel,

    I had harmonics in mind with my group D... Wondering if that why that was the only group that didn't see any vertical stringing; if by putting excessive pressure I took away the harmonics... ?

    -rvb
     

    rhino

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    I had harmonics in mind with my group D... Wondering if that why that was the only group that didn't see any vertical stringing; if by putting excessive pressure I took away the harmonics... ?

    -rvb

    You wouldn't take the harmonics away, but change them. You would essentially alter the fundamental frequency of the barrel by introducing an artificial node, effectively changing the length of the barrel with respect to vibrations. That would then alter the position of the resulting nodes, etc. etc. etc.

    Holy crap I'm a nerd.
     
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