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Posted: 4/21/2015 9:06:43 PM EDT
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A buddy of mine was in the shop and said he didn't see the need to float. No way you are going to bend that barrel ! Sooo, I took him over to my Peterson head machine with a 7 inch solid column. (a Folgers coffee can is 6 1/2 inches in diameter) I put an indicator on it and then leaned hard up against it(I am 6' 210) The needle moved .0007. He said yea but you do not put that much weight on a barrel. Well I had to have an answer. I took my 16 inch heavy barrel rifle and weighed it at the front edge of the hand guard. It weighed exactly 4 lbs. The rifle weighs 7lbs 7 ounces with empty mag. I mounted 2 different brands of heavy barrels(.880 under handguard), an M-4 profile and a pencil light. I chucked the barrel up by the extension, in my lathe, put an indicator on the end of the barrel just before the threads. I took an exact 4 lb weight and placed it on top of the barrel at 1 inch increments. Here is the deflection I got measured from the shoulder. Heavy at 2'' .0005, M-4 .0005, pencil .0008. Heavy at 3'' .001, M4 .0012, pencil .0015 Heavy at 4'' .0015, M-4 .0017, pencil .002. Heavy at 5'' .002, M-4 .0026, pencil .003 Heavy at 6'' .003 M-4 .0037, pencil .0042. Heavy at 7'' .0035, M-4 .0045, pencil .0051. I did one of my fluted heavy barrels and it had .0002 more deflection than non fluted, thru the range.
Here is the math. 100 yards is 3600 inches. .0035 barrel deflection in 16 inches is a potential change of impact of .787 inches. The further out the worse it gets.Engagement of 50 yards or less, not that big a deal. If 3/4 of an inch is important to you, you should float. Craig |
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A buddy of mine was in the shop and said he didn't see the need to float. No way you are going to bend that barrel ! Sooo, I took him over to my Peterson head machine with a 7 inch solid column. (a Folgers coffee can is 6 1/2 inches in diameter) I put an indicator on it and then leaned hard up against it(I am 6' 210) The needle moved .0007. He said yea but you do not put that much weight on a barrel. Well I had to have an answer. I took my 16 inch heavy barrel rifle and weighed it at the front edge of the hand guard. It weighed exactly 4 lbs. The rifle weighs 7lbs 7 ounces with empty mag. I mounted 2 different brands of heavy barrels(.880 under handguard), an M-4 profile and a pencil light. I chucked the barrel up by the extension, in my lathe, put an indicator on the end of the barrel just before the threads. I took an exact 4 lb weight and placed it on top of the barrel at 1 inch increments. Here is the deflection I got measured from the shoulder. Heavy at 2'' .0005, M-4 .0005, pencil .0008. Heavy at 3'' .001, M4 .0012, pencil .0015 Heavy at 4'' .0015, M-4 .0017, pencil .002. Heavy at 5'' .002, M-4 .0026, pencil .003 Heavy at 6'' .003 M-4 .0037, pencil .0042. Heavy at 7'' .0035, M-4 .0045, pencil .0051. I did one of my fluted heavy barrels and it had .0002 more deflection than non fluted, thru the range. Here is the math. 100 yards is 3600 inches. .0035 barrel deflection in 16 inches is a potential change of impact of .787 inches. The further out the worse it gets.Engagement of 50 yards or less, not that big a deal. If 3/4 of an inch is important to you, you should float. Craig Nice work. |
| Interesting data. I conducted a similar test a few years ago. Thanks for posting that. I always chuckle when people say fluting makes a barrel stronger! I will say it's more rigid compared to the same WEIGHT barrel, but not the same diameter. I just don't say anything anymore. |
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Quoted: A buddy of mine was in the shop and said he didn't see the need to float. No way you are going to bend that barrel ! Sooo, I took him over to my Peterson head machine with a 7 inch solid column. (a Folgers coffee can is 6 1/2 inches in diameter) I put an indicator on it and then leaned hard up against it(I am 6' 210) The needle moved .0007. He said yea but you do not put that much weight on a barrel. Well I had to have an answer. I took my 16 inch heavy barrel rifle and weighed it at the front edge of the hand guard. It weighed exactly 4 lbs. The rifle weighs 7lbs 7 ounces with empty mag. I mounted 2 different brands of heavy barrels(.880 under handguard), an M-4 profile and a pencil light. I chucked the barrel up by the extension, in my lathe, put an indicator on the end of the barrel just before the threads. I took an exact 4 lb weight and placed it on top of the barrel at 1 inch increments. Here is the deflection I got measured from the shoulder. Heavy at 2'' .0005, M-4 .0005, pencil .0008. Heavy at 3'' .001, M4 .0012, pencil .0015 Heavy at 4'' .0015, M-4 .0017, pencil .002. Heavy at 5'' .002, M-4 .0026, pencil .003 Heavy at 6'' .003 M-4 .0037, pencil .0042. Heavy at 7'' .0035, M-4 .0045, pencil .0051. I did one of my fluted heavy barrels and it had .0002 more deflection than non fluted, thru the range. Here is the math. 100 yards is 3600 inches. .0035 barrel deflection in 16 inches is a potential change of impact of .787 inches. The further out the worse it gets.Engagement of 50 yards or less, not that big a deal. If 3/4 of an inch is important to you, you should float. Craig |
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Great post and data. It's not just deflection, although that is a very important factor. Its also that pressure on the barrel changes its resonant frequency and harmonics during firing.
You can see that in slow motion photography. That change in harmonics alters the position of the muzzle at the moment the bullet leaves the barrel. The combination of deflection and harmonics from pressure or changes in dampening of the barrel has been shown to produce as much as a 6" difference in point of impact at 100 yards. The degree of shift varies depending on how and where you hold the handguard, whether you use a bipod, whether you preload it, and whether your support is hard or soft. Switching to a free float barrel eliminates virtually all of these variables. |
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Great post and data. It's not just deflection, although that is a very important factor. Its also that pressure on the barrel changes its resonant frequency and harmonics during firing. You can see that in slow motion photography. That change in harmonics alters the position of the muzzle at the moment the bullet leaves the barrel. The combination of deflection and harmonics from pressure or changes in dampening of the barrel has been shown to produce as much as a 6" difference in point of impact at 100 yards. The degree of shift varies depending on how and where you hold the handguard, whether you use a bipod, whether you preload it, and whether your support is hard or soft. Switching to a free float barrel eliminates virtually all of these variables. this -- it can be much greater than a 3/4" POA/POI deviance, even at really close ranges like 25m. Zero from a sandbag, then shoot unsupported prone and kneeling and watch how different each group is from the POA. As these deviations are angular, they get worse the farther you are from the target and become exponentially greater than 3/4". |
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Thanks for the info. I have a service rifle buddy that noted he can put several minutes of flex on a non-free floated gun when he slings in. Being 200 yards is the short range for him, that flex can make for a pretty substantial change in POI from POA. Hence why he (and most all competitive service rifle/ high power shooters) use free floated systems. |
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No exactly the opposite. His data shows force on a non floated hanguard will flex the barrel. Quoted:
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So... most AR's with floated barrels don't need them configured that way? I kinda already figured that, but it's trending anyway. No exactly the opposite. His data shows force on a non floated hanguard will flex the barrel. He is stating that most who configure their rifle that way would never see/notice the effects of non free float vs. free float. < 200yd 
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He is stating that most who configure their rifle that way would never see/notice the effects of non free float vs. free float. < 200yd Quoted:
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So... most AR's with floated barrels don't need them configured that way? I kinda already figured that, but it's trending anyway. No exactly the opposite. His data shows force on a non floated hanguard will flex the barrel. He is stating that most who configure their rifle that way would never see/notice the effects of non free float vs. free float. < 200yd Yes but I don't think it has to do with distance. I can certainly see the benefit of a FF rail at 100 yards. I see guys all the time at the local range that have these 20-24 inch heavy free floated barrels with all kinds of bells and whistles, 6-24x50 Barskas or another el cheapo scope that shoot a 30rd mag or 2 at 100 pretty quick and achieve basketball size groups. I think 
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| I did not mean to come across as floating not necessary. For ultimate accuracy it is. If your rifle is for self protection of your family, property or yourself, anything past 25 yards would probably not be considered self protection. At those distances it isn't as big an issue. As far as your question M4ger, I machined a fixture that I can put the upper assembly in and it will tell me if the barrel centerline is through the centerline of the upper. You would be amazed at how many are not. I made a cutter that goes in the upper that trues up the front surface where the barrel seats against. I also use the fixture to align the sights so a guy is at least on paper. Craig |
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The gas tube is free floating already. Quoted:
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Since we are on the subject, does the gas tube play a part in all this and if it does then why not as much as a rail attached to the gas block? The gas tube is free floating already. To me it doesn't seem to be but I'll take your word for it. |
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To me it doesn't seem to be but I'll take your word for it. Quoted:
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Since we are on the subject, does the gas tube play a part in all this and if it does then why not as much as a rail attached to the gas block? The gas tube is free floating already. To me it doesn't seem to be but I'll take your word for it. It does sort of "free float" inside the hole in the upper receiver. The AR15 isn't a true free float like a bolt action rifle, but it is as close as you can get. The biggest reason to use a free float hand guard is that any pressure on the hand guard will not move the barrel at the point where there would be contact. No pressure on the hand guard is going to affect the gas tube and It should be consistent from shot to shot. The biggest deviation in POI from shot to shot would be switching from standing to slinging up or from slinging up to loading a bipod. Not everyone is going to sling up or load a bipod but even small things like putting the hand guard against a barrier are going to change POI. The 3/4 MOA for the 4 pound example would be double that if you take in account both directions. The length of the hand guards and barrel diameter will alter that, I could see it being much more. As easy and cheap as it is to free float an AR15, there is no reason not to. |
| I would also contend that FF with iron sights or even a red dot with greater than 1 moa dot is probably a waste. The variability at short range doesn't really matter and at longer ranges the imprecision of the sighting mechanism renders the variability of a non-FF barrel moot. |
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I would also contend that FF with iron sights or even a red dot with greater than 1 moa dot is probably a waste. The variability at short range doesn't really matter and at longer ranges the imprecision of the sighting mechanism renders the variability of a non-FF barrel moot. And I would disagree. Although I understand your reasoning and maybe there is some truth in the fact many don't "need" to float. But in practice, however, even iron sighted rifles can and do reap benefits. The biggest being same POI regardless of rests, holds, or sling pressure as mentioned previously in this thread. Which is why freefloats are used by highpower shooters. I can sling up tightly and move POI by a couple or more inches in only 50yrds. I know this is an extreme example and can be mitigated by using consistent holds and rests for certain situations. But the beauty of freefloating is limiting those variables in the first place. Naturally it's up to the end user whether or not they think the benefit is worth it to them. But the benefits are there nonetheless. |
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Use a sling? Properly???
Unhitch from rear swivel and cinch up good and tight and put all the damn pressure you can so the barrel stays steady. Damn sure gonna move any barrel that has sling fastened to it. Float tube takes the pressure. Similar with a bipod. Weight of the barrel on the bipod changes impact, also from angle of setup and amount of loading you apply to keep bipod in place. Not like it is some 30lb benchrest tripod rest that stays put is it? Have thought for years about radically lightening a service rifle float tube for classic look but precision performance. At $100+ just never took the action necessary. |
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as barrels get shorter the amount of leverage a sling can exert decreases IMHO a freefloat on a 10.5 barrel is more fashion than it is a requirement Take a handgun with a 6" barrel and shoot it with the barrel resting on a bag or rest and note the point of impact. Then shoot at the same target with your support hands resting on the same bag or rest and note the point of impact and then come to us with the conclusion as to whether pressure on a short barrel matters. I think it will change your mind about this being a fashion statement. If you support a handgun in a rest support only the frame and trigger guard area. If using a "V" rest, and you have no other option, place the handgun barrel in the "V" only at the point where the barrel attaches to the frame. That would be the same thing as barrel nut support on an AR. That is what a freefloat handguard does. |
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Great post and data. It's not just deflection, although that is a very important factor. Its also that pressure on the barrel changes its resonant frequency and harmonics during firing. You can see that in slow motion photography. That change in harmonics alters the position of the muzzle at the moment the bullet leaves the barrel. The combination of deflection and harmonics from pressure or changes in dampening of the barrel has been shown to produce as much as a 6" difference in point of impact at 100 yards. The degree of shift varies depending on how and where you hold the handguard, whether you use a bipod, whether you preload it, and whether your support is hard or soft. Switching to a free float barrel eliminates virtually all of these variables. I tried shooting a non free floated AR at an indoor range off of some rubber/kevlar blocks which are designed for backstops. Resting it on the block I was seeing a 4 - 5" change in point of impact at 25 yards. I wouldn't have believed it but it was repeatable. Rest the rifle on the block or put my hand between the block and the point of impact would change that much. |
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And I would disagree. Although I understand your reasoning and maybe there is some truth in the fact many don't "need" to float. But in practice, however, even iron sighted rifles can and do reap benefits. The biggest being same POI regardless of rests, holds, or sling pressure as mentioned previously in this thread. Which is why freefloats are used by highpower shooters. I can sling up tightly and move POI by a couple or more inches in only 50yrds. I know this is an extreme example and can be mitigated by using consistent holds and rests for certain situations. But the beauty of freefloating is limiting those variables in the first place. Naturally it's up to the end user whether or not they think the benefit is worth it to them. But the benefits are there nonetheless. Quoted:
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I would also contend that FF with iron sights or even a red dot with greater than 1 moa dot is probably a waste. The variability at short range doesn't really matter and at longer ranges the imprecision of the sighting mechanism renders the variability of a non-FF barrel moot. And I would disagree. Although I understand your reasoning and maybe there is some truth in the fact many don't "need" to float. But in practice, however, even iron sighted rifles can and do reap benefits. The biggest being same POI regardless of rests, holds, or sling pressure as mentioned previously in this thread. Which is why freefloats are used by highpower shooters. I can sling up tightly and move POI by a couple or more inches in only 50yrds. I know this is an extreme example and can be mitigated by using consistent holds and rests for certain situations. But the beauty of freefloating is limiting those variables in the first place. Naturally it's up to the end user whether or not they think the benefit is worth it to them. But the benefits are there nonetheless. 1. I have seen this with different types of firearms. 2. Some folks don't shoot well enough to notice or realize the difference so for them I truly believe that their money is better spent elsewhere. Keith |
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