Advantages of boat tail?

[STLRN]

FS2K

Dr Fackler tested the theory that the round tip deformed. Apparently there was the initial thought that deformation was part of the design and that was part of its mechanism of lethality. Go to the below link and it shows when tested the round's tip didn't deform. Also somewhere on the net there are X-rays of post firing 5.45 projectiles. What those show is that the steel insert moved forward and this causes the lead in the round to flow forward asymmetrically, causing the early yaw.



http://www.btammolabs.com/fackler/ak..._potential.pdf

[Art Eatman]

'Scuse me, but if we're through with the "why" of boat-tailed bullets...

Art

[44 AMP]

Yes, this one has been around a while, and I think with good reason. However, the reason doesn't have much practical applicability for most shooters.

There is more of the throat exposed behind the boattail to hot gas than with flatbase bullets, coupled with the fact that boattails were used more often in high performance rounds, which are often notorious for short throat life.

I don't think there is much of a difference but it is logical that for very high volume shooters with a premium on accuracy it could be a factor. I doubt it would be anything significant for ordinary shooters. Maybe you could get a Mythbuster to take this one on. It would be boring to watch, so the TV guys wouldn't be interested, but think about the shooters!

Take two identical rifles, with identical ammo, except rifle A gets boattail bullets, and rifle B gets flatbase. Everything else the same, and shoot until the barrels show signs of wearing out. Then check the round count. Do this say 5 or maybe 10 times so you would have a good average, then you could have some valid basis for either busting the myth or not. Oh, yeah, get some ammo/bullet company to sponser it, unless you are well enough off to pay for it out of pocket.

[HiltonFarmer]

Take two identical rifles, with identical ammo, except rifle A gets boattail bullets, and rifle B gets flatbase. Everything else the same, and shoot until the barrels show signs of wearing out. Then check the round count. Do this say 5 or maybe 10 times so you would have a good average, then you could have some valid basis for either busting the myth or not. Oh, yeah, get some ammo/bullet company to sponser it, unless you are well enough off to pay for it out of pocket.

Sign me up AMP. I'll make some calls and see if we can't get this set up.

That would be an awesome test.

HiltonFarmer

[Jimro]

There is more of the throat exposed behind the boattail to hot gas than with flatbase bullets, coupled with the fact that boattails were used more often in high performance rounds, which are often notorious for short throat life.

I don't understand, the gas pushing the boat tail has to push it just as far as it pushes the flat base bullet. The gasses have the same amount of time and area to work on the throat and bore.

A lot of benchrest shooter using flat based bullets also rebarrel quite often.

I have now officially beaten this horse, shot it to death, and bludgeoned the corpse into ground round. I will stop now.

Jimro

[drmiller100]

the "funny" thing is that different readers all have completely different conclusions.

boattails erode the barrel faster then flat base bullets.
boattails by definition have much different noses on the front of them.
boattails are more accurate at long range.
boattails are less accurate at close range.

all of the above are factoids, and are incorrect conclusions in and of themselves.

what is true is that a boattail will usually have a lower coefficient of drag then a similar flat base, and compared to a similar flat base bullet will travel slightly faster at long distances because of that.
because they are faster at long range, they will shoot somewhat flatter.

[30Cal]

I think I saw the throat erosion horse move....

I grabbed this off Culvers page a couple years back (www.jouster.com). Maj Culver studied Ordnance at the Naval Post Graduate School and is a pretty knowledgeable guy... This is about .30-06 military ammo, but I think it fits the bill almost perfectly.

FRANKFORD ARSENAL TEST OF .30-'06 CALIBER BARREL LIFE USING ISSUE U.S. ARMY BALL AND AP AMMUNITION
============================================================
Answer to a question asked on the CSP Board several years ago:
Dear XXXXXXX...
The short answer (as you have apparently just found out from personal experience) is that your barrel should be good for another 5000 rds (at least according to a Frankfort Arsenal Report conducted in the 1945/1946 timeframe.
Old wives tails had long held that a maximum barrel life with service ammunition was approximately 5000 rds or less. Some said as few as 3500. And just EVERYONE knew that using AP would trash your barrel in a heartbeat. On the flip side of the coin, most experts considered that M1 (172-gr) Ball, (essentially a precursor of the 172-grain FA Match 30-'06) to be extremely accurate, however according to urban legend, it was BOUND to "eat" barrels at an accelerated rate due to the 9 degree boat-tail that would allow hot gasses forward of the bullet base while the projectile was still in the bore!
As it turns out, virtually every old wives tale was pure unadulterated "Moose Manure", however some very high priced help published them as gospel. Clark Campbell in his excellent book "The '03 Springfield" parroted the widely held belief concerning the 172-grain match ammo being hard on the bore, and Phil Sharpe, one of the developers of the .357 Magnum Cartridge an a WWII Army Ordnance Officer and regular contributor to the "Dope Bag" in the American Rifleman) put out the information in his "Complete Guide to Handloading" that while the mild steel jackets of the WWII .30-'06 Ball wouldn't harm the bore of your favorite target rifle, he would not shoot .30 caliber M2 AP in his rifle under ANY circumstances... Just goes to show you how wrong you can be.
Frankford Arsenal grew weary of the stories and decided to conduct a test to determine if they were correct. Without going into great detail, they found that when using either M1 Ball (almost identical to the later M72 Match Ball) or M2 Armor Piercing, the accuracy actually improved up through the first 1000 rounds or so (don't hold my feet to the fire on the exact numbers as I don't have my references in front of me and am too lazy to dig 'em out right this second). They continued to fire the test (using a test rack) and it seemed that the accuracy "improvement" seemed to taper off after 1000 rounds, but the accuracy itself did NOT decrease. The accuracy continued to be excellent to outstanding through at least 8000 rounds. They finally ceased the test, not because the accuracy was declining, but because they simply got tired of firing, since the accuracy showed no sign of decreasing. FA estimated that the excellent accuracy should continue through at least 10,000 rounds and probably beyond.
This was NOT the case with the 150 grain M2 Ball however, it seems that the accuracy began to drop off after about 3500 - 4000 rounds (again don't hold my feet to the fire, I plan to write an article on this and will include the actual figures when I do). The only common thread to the barrel longevity I can personally see, is that both the M1 Ball (172 gr. Match) and the 165-168 gr. AP have a boat-tailed configuration (9 degree for the 172 and a much less obvious 6 degree for the AP).

So bottom line is that the BT bullet (173grs at 2550 fps) improved in accuracy in the first 1000rds, then stabilized to 8000+ rds. Accuracy with the flat base (150grs at 2750 fps) began to slip at 4-5k rds.

He goes on to say that if you shoot a boattail bullet at nominal velocities, you shouldn't see any appreciable difference in barrel life than if you shot flat base bullets. If anyone wants the entire post, I'll be glad to send it (talks about steel jacketed copper clad bullets, etc).

Ty

[44 AMP]

Jimro, what I meant was (here we go), since a boattail seals the bore further up on the bullet than a flatbase, gas is in contact with the barrel over a greater surface area. Therefore, more of the barrel is exposed to the heat and pressure at any given moment in the bullet's travel down the bore.

This is a physical fact beyond dispute. But does this small difference in the area of barrel steel actually have any real effect on the accuracy life expectancy of the barrel?

Seems like there are a large number of variables besides the bullet design, barrel steel, powder temp, pressure, etc. would all play a role. But the "myth" of boattails wearing out a barrel faster had to come from somewhere.

Perhaps it came from cast bullet experience, where having the gas reach past the base is a bad thing. Perhaps even though it doesn't melt a jacketed bullet the olt time shooters just knew there had to be something bad about it, and came up with the stories about shortened barrel life. Perhaps the alloys used in the earlier barrels was more "susceptable" to flame cutting.

I really have no idea if it true or not, but I am certain there is no practical differrence in the barrel life for most shooters, considering all the other factors involved, several of which would likely have a more siginificant influence on barrel life.

I have been a casual shooter for over 30 years, and have yet to shoot any rifle to the point of wearing out the barrel. Match shooters "worn out" barrels are often still capable of fine performance, just not the utimate edge that wins matches.

[JohnKSa]

This was NOT the case with the 150 grain M2 Ball however, it seems that the accuracy began to drop off after about 3500 - 4000 rounds (again don't hold my feet to the fire, I plan to write an article on this and will include the actual figures when I do). The only common thread to the barrel longevity I can personally see, is that both the M1 Ball (172 gr. Match) and the 165-168 gr. AP have a boat-tailed configuration (9 degree for the 172 and a much less obvious 6 degree for the AP).

That's not the ONLY common thread. One could easily interpret the test to mean that the barrel lasted longer when used with the heavier bullets. To test the hypothesis would take a much more controlled experiment.

Yes, this one has been around a while, and I think with good reason. However, the reason doesn't have much practical applicability for most shooters.

Agree and agree. Exactly as the benefits of the boattail (with the possible exception of easier bullet seating) don't have much practical applicability for most shooters.

[Art Eatman]

Okay, I know I'm not "most shooters". My own reason for using boattails in my '06 was for thecapability for a longer-range shot. Flattest trajectory I could get. My hunting typically was where a shot distance could vary from up-close to Ma Bell. Out of some 20+ deer with the '06, only two were really long shots; 450 and 350 yards. But, from knowing the rifle as I did, the shots seemed quite easy.

I probably would have made the kills with flat-based bullets. But, why not have every edge I can get? My 26" barrel gives me another bit of edge, from a velocity standpoint. Same for the effort of tweaking and tuning for tight-group accuracy. "It's an edge thing."

Art

[Gewehr98]

Particularly the popular 168gr HPBTM variety seen so often in competition. The hollow point is merely a byproduct of the jacket being swaged from the bullet base forward. Speer/Sierra/Hornady/Berger/Lapua all put emphasis on jacket uniformity, particularly on the bullet base, which must be consistent for each and every bullet as it departs the muzzle crown. The tiny air pocket and hollowpoint in that type of bullet was never designed to produce terminal upset, fragmentation, or expansion. It's simply *there*, as an effect from the jacket swaging. The concept of the hollowpoint producing additional wounding effects was brought front and center not too long ago (12 October 1990) by military judge advocate group efforts, weighing in on the suitability of the 168gr and 175gr Sierra hollowpoint boattail match bullets for sniper use under the Hague Convention.

http://www.thegunzone.com/hague.html

Now, if you want to really throw a wrench in the boattail accuracy/barrel wear/wind drift discussion, I shoot Lapua D46 rebated boattail bullets from my .30 caliber long-range precision rifles. Chew on that!

[Jimro]

Jimro, what I meant was (here we go), since a boattail seals the bore further up on the bullet than a flatbase, gas is in contact with the barrel over a greater surface area. Therefore, more of the barrel is exposed to the heat and pressure at any given moment in the bullet's travel down the bore.

This is a physical fact beyond dispute.

Well it is obviously not beyond dispute since we are disputing it.

The bullet has to travel down the bore yes? There is only so much of bore? The flat based bulled and the boattail bullet have to travel the same distance?

Imagine the "ring" of gas pushing the projectile. The ring coincides with the base of the flat base, and slightly forward for the boat tail. Both projectile butts start way back inside the cartrige and the first time that "ring" gets exposed to the bore is when it passes into the throat.

Now imagine the "ring" extending from the throat to the muzzle. The ring would then map the bore exactly. Once the sealing portion of the bullet passes the crown the pressure drops, no matter the bullet shape.

If we could get both types of bullets and magivally give them the same friction coefficient then using the same powder charge they would have the same muzzle velocity (within standard deviation of each other in real life, the exact same in a physicists wet dream).

PV=nRt. Pressure times volume equals the number of mols of gas times the ideal gas constant time temperature in Kelvin. This shows that for the same volume (cartrige and bore) that the same pressure will be developed for any bullets of the same friction coefficient, regardless of shape.

Wait, let me ask one question. If a flat base bullet exposes 100% of the bore to the gasses, how can a boat tail expose MORE than that?

Jimro

[Ruger4570]

I guess I better give up my Sierrs and Nosler 225 gr. 35 cal bullets and go to flat base bullets to save my bore. What a bummer as I get anywhere fron 1/2" to 3/4" groups at 100 yards and generally 1 1/4 to 1 3/8 at 200 yards. It is good to know flat bases will be more accurate,, have less wear on my barrel and in general kill game better.

[Art Eatman]

Personal opinion, but from what little I know about physics and of heat transfer, worrying about enhanced erosion of the leade from the use of boattail bullets is picking flypoop out of pepper.

I've played with quite a few varieties of the Sierra .30 bullets. We even had a Sierra person enter into a discussion about them, here at TFL.

The gist: The jackets of the 150-grain boattails are thinner than for the flat-base, which is why I had a blowup on a mule deer's neck at 30 yards. I ws pushing it too fast.

In my experience, the same, apparently, is true for Sierra's 165-grain HPBT hunting bullet. I hit bone on a doe at some 40 or 50 yards and had a fist-sized glob blow out the off side.

Odds are that the target 165-grain boattail has a thicker jacket.

Based on the relative depth of the dings or craters on steel at 500 yards, their 180-grain SPBT would be excellent for penetration on something like elk.

All their hunting bullets have provided five-shot groups inside one MOA, since back around 1970-something when I first went to using them.

All three weights of boattails seem to have pretty much the same trajectory to 500 yards. Or, better said, AT 500 yards. The shape of the curve might be somewhat different; the only other distance at which I've shot is 100 yards. At any rate, any differences are trivial.

Art