I'll just quote from High Power Rifle Accuracy by Douglas Arnold:
"Barrel life will be extended if boattail bullets are used primarily, rather than flat-base bullets. The difference can be as much as 60 percent longer barrel life and is the reason, besides better ballistic coefficient related factors, why the military has used boattail bullets for years in small arms ammunition."
I wasn't aware that boattails could give such greater barrel life. It appears to be a valid point that given two bullets of the same weight, the boattail one will likely have less bearing surface and thus less wear on the rifling. Could this be the only factor, or is there some other hot-gas boattail voodoo involved? Anyone even thought about this one and can substantiate?
============================== "I'd love to be the one to disappoint you when I don't fall down" --Fred Durst
Posts: 759 | Location: St Cloud, MN | Registered: 17 January 2005
Barrel life will be extended if boattail bullets are used primarily, rather than flat-base bullets. The difference can be as much as 60 percent longer barrel life and is the reason, besides better ballistic coefficient related factors, why the military has used boattail bullets for years in small arms ammunition."
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Posts: 28849 | Location: western Nebraska | Registered: 27 May 2003
A flat based bullet with the same amount of powder and the same type will give a little more velocity than a BT. But a BT bullet will give a better flight in long distances than a FB,thus better accuracy at those ranges. The only thing that i can thik of is with barrel life,a constant and profound use of boat tails will corrode the throat to some degree. vangunsmith
Posts: 442 | Location: Idaho | Registered: 16 December 2005
More BS, only after they drop below the speed of sound? As a general rule if two bullets of the same weight and caliber, one a flatbase and the other a boatail are fired at the same velocity, the BT will have a greater ballistic coefficient. Long before the boatail reaches 1,100fps, it is kicking the flatbase bullets butt in flatter trajectory and wind bucking ability. If you reference balistic tables you will see that it does take a few hundred yards to develop a real advantage, but it does happen long before the bullet becomes unstable. That happens when the bullet drops below the speed of sound.
Point, you are sorta' right, as you state it. As "a general rule" most BT bullets of specific weights do have good BC shapes and a good BC counts at all speeds. But trajectory comparisons between bullets of different BCs were not implied or intended in my response.
The BOAT TAIL shape - in and of itself - only comes into play below the speed of sound. At that speed the sonic-wave drag stops and the vacuum on the bullet's base shifts from the bullet's full diameter to the smaller diameter of the boat tail. This significantly reduces the effect of the vacuum following the bullet.
To confirm this would require that we shoot two bullets with the same BC, one a flat base and one with a BT, at identical velocities. They need not be the same weitht nor even the same diameter, only the same speed. There will be no trajectory difference between the two until they drop below the speed of sound. After that, the BT would be significantly better, but not before.
Posts: 1615 | Location: South Western North Carolina | Registered: 16 September 2005
Hmmm... Two bullets with same caliber, weight, material, and nose profile: one with BT will have higher BC than one with FB. So it is kind of moot to argue that BT has no bearing on trajectory.
I'm actually with you all on this. In fact, a lot of what he writes in this book comes off pretty self-righteous/arrogant. I'd never heard of the barrel life argument before. I always thought that the military switched to boattails due to better ballistics, esp in squad/heavy machine guns.
Next time you get into the book store or gunshop, take a peek at this book. He also claims that "the amount of neck tension on the bullet has little effect on accuracy" which I also don't agree with. Consistent neck tension has been shown (to me anyway) to be a factor in consistent velocities and thus consistent downrange behavior. I'm glad I just borrowed this one...
I rarely load boattails, myself. The flat bases work just fine for me.
============================== "I'd love to be the one to disappoint you when I don't fall down" --Fred Durst
Posts: 759 | Location: St Cloud, MN | Registered: 17 January 2005
He might just be a little mixed up between the military use of ball powder vs the military use of boat tails. It seems logical to me that using ball powder will increase bbl life, but using a boat tail bullet should hardly be a factor.
I do wonder if a FMJ boat tail will tumble better upon impact than a flat base. I could certainly see that as a military reason for using boat tails over flat based bullets.
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"Beware of the Free Market. There are only two ways you can make that work. Either you bring the world's standard of living up to match ours, or lower ours to meet their's. You know which way it will go." by My Great Grandfather, 1960
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Posts: 8421 | Location: adamstown, pa | Registered: 16 December 2003
Jake, didn't say to compare two bullets "with same weight, shape, caliber, composition, etc." ONLY discussed two with the same BC, no matter the caliber, etc.
In practice, that would mandate a difference in nose shape but that does happen, doesn't it? I mean, not all boat tails have the same BC so their other design criteria do come into play, right? And certainly no one said a BT, nor a high BC has no effect on trajectory.
The original issue was a specific question of the effect of the advantages of a boat tail vs. flat base.
Posts: 1615 | Location: South Western North Carolina | Registered: 16 September 2005
actually if my memory serves - it was either PO ackley or the military that found boat tails decreased barrel life smoewhat. Something to to with tha gas column behind the bullet getting stuck between the boattail and the barrel. Been a long time since i read about that though
If anything should be taken from this thread it is that you can't believe the crap in the gun mags. With the information available online now, the print media is slowly fading into the shadows. Ask the editors at the major newspapers. These folks will print almost anything just to get people to read their magazines. With being able to chat with gunsmiths and other shooters about their knowlede and experiences at your fingertips everyday, why would you subscribe to this garbage? Most of the writers for the mags are just that, WRITERS, not shooters.
I'd thought about the general timeframe connection between the switch to boattails and different powder. This could all be related. If anything I would tend to agree with butchloc in theory. The shape of the boattail would tend to funnel hot gasses into the crevice between the barrel and the bullet. Hell, maybe none of it matters one bit as long as you allow prudent time for the barrel to cool off between shots - I think that's the big cause of barrel erosion, not bullet shape, etc.
The worst part is that this guy is not writing for a magazine. This is a big book on rifle accuracy, supposedly from a gunsmith/wildcatter/handloader/CEO of Arnold Arms which built tackdriving rifles (all their stuff shoots into the .2's and .3's, you know...). It would have been nice if he provided some kind of testing or basis for statements like these.
============================== "I'd love to be the one to disappoint you when I don't fall down" --Fred Durst
Posts: 759 | Location: St Cloud, MN | Registered: 17 January 2005
I think he has made a non-sequiter leap from armour-piercing U.S. military boat-tail bullets to all boat-tail bullets in general.
The U.S. military did find that the use of the 173-grain armour piercing bullets in the .30-'06 could increase barrel accuracy-life as much as from 200-300% over the use of the 150 gr. military flat-base bullet.
That life increase was NOT, however, attributed to the shape of the bullet-base, but to the harder, non-distorting core of the armour-piercing projectile.
They were NOT trying to increase barrel life when they discovered that....they were doing routine acceptance testing of ammo lots from the various U.S. military manufacturers. They found that the barrels used for testing the ammo (to see that it met required "figure-of-merit" specs) lasted several times as long if fired with just the armour-piercing rounds.
Beyond that, I cannot remember the details, but the info is available from the NRA if they are willing to dig it up. They did publish the results in the American Rifleman during the 1960's.
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Posts: 9685 | Location: Cave Creek 85331, USA | Registered: 17 August 2001
Originally posted by Alberta Canuck: I think he has made a non-sequiter leap from armour-piercing U.S. military boat-tail bullets to all boat-tail bullets in general.
The U.S. military did find that the use of the 173-grain armour piercing bullets in the .30-'06 could increase barrel accuracy-life as much as from 200-300% over the use of the 150 gr. military flat-base bullet.
That life increase was NOT, however, attributed to the shape of the bullet-base, but to the harder, non-distorting core of the armour-piercing projectile.
They were NOT trying to increase barrel life when they discovered that....they were doing routine testing of ammo lots from the various U.S. military manufacturers. They found that the barrels used for testing the ammo (to see that it met required "figure-of-merit" specs) lasted several times as long if fired with just the armour-piercing rounds.
Beyond that, I cannot remember the details, but the info is available from the NRA if they are willing to dig it up. They did publish the results in the American Rifleman during the 1960's.
That is the most logical explaination I have heard to date. Thank you.
______________________________
Well, they really aren't debates... more like horse and pony shows... without the pony... just the whores.
1955, Top tax rate, 92%... unemployment, 4%.
"Beware of the Free Market. There are only two ways you can make that work. Either you bring the world's standard of living up to match ours, or lower ours to meet their's. You know which way it will go." by My Great Grandfather, 1960
Protection for Monsanto is Persecution of Farmers.
Posts: 8421 | Location: adamstown, pa | Registered: 16 December 2003
