Boat tail vs flat base boolits

[GregLaROCHE]

I remember reading that boat tail boolits only give you an advantage after 200 to 300yrds. And that flat bases are better for closer ranges. Something about when the hot gases are leaving the muzzle behind the boolit.

Can anyone tell me if this is true Or false?

[lightman]

My experience says that its true. I would say that its further than 2 or 300 yards though. Most short range bench rest loads use flat base bullets. My test show this too, although I shoot boat tails in my long range rifles.

[mac1911]

i think there is more to do about twist rate and such
Flatbase bullets are shorter so they can stabalize "better" in slow twist barrels. Some will say the flat base bullet design has more bearing surface, also like you say there is the existing gases some how influencing the boat tail more than a flat base?
All you can do is try some testing. i shoot some 110 grain flatbase varmint bullets out of my M1 and 1903a3 they perform no better or worse than the 155/168s out to 200 . i would not hesitate to run them out to 600.

[Lloyd Smale]

Id say over the years ive had better accuracy with flat based bullets. that said ive had some guns that shot boatails just as well. Just part of load development to me. Flatter shooting? Maybe way out there but then ive shot deer at 500 yards with flat based bullets and not a single one of them laughed at me for making the wrong choice:lol: Guess that when push comes to shove if I know im going to be faced with a 500 yard shot id rather have a rifle shooting a flat based bullet at 3/4 minute of angle then a boatail that shoots a group twice that size. I can dope for wind and elevation but I cant dope for an inaccurate load.

[Hickory]

The advantage of the boattail is most apparent beyond 400 yards, and it has to do with drag and high velocity.
The higher the velocity and the number of times the bullet exceeds the sound barrier the more drag is imparted upon the bullet, and the quicker it will slow down.

The boattail helps reduce the drag upon the bullet.
I wish I could go into more detail but I need to go to my grandson's ball game, his team is undefeated and will go into eliminations this morning before it gets hot.

[Larry Gibson]

mac1911 nails it with; "Flatbase bullets are shorter so they can stabilize "better" in slow twist barrels."

Otherwise with the quality of today's commercial bullets in non benchrest rifles both are potentially equally accurate. Over practical ranges the deciding factor in any rifle should be accuracy and terminal affect if used for hunting. At longer ranges the BT is ballistically more efficient and is the choice.

Recently, on a prairie dog shoot, I found little practical difference between a FBd 55 gr bullet and a BT 55 gr bullet out to 500 yards in the .223 Remington. The FB 55 gr Varmageddon also did as well as the BTd 55 gr Blitz King out of my 22-250 out to 500 yards.

My 30-06 M70 shoots 180/190 FB and BTd bullets with equal accuracy with the same loads. Thus I use the BTd because the are more efficient at longer ranges by retaining more velocity hence more energy. While I do try to get as close as the hunting situation allows I have, occasionally, had to make some longer range shots. Having a bullet that alllows getting the most out of it ballistically is beneficial.

[Ballistics in Scotland]

If this was about jacketed bullets the issue would be debatable. But about cast, it is undebatable. The reduction in drag shows up only at low velocity, so the range at which it does is variable, depending on such things as size of the bullet and shape at the front end. But I don't think boat-tailed bullets, comparing like with like, have ever bettered the flat-base match rifle bullets used when cast was all every target shooter had, at ranges of 1000 yards or more.

But if the bullet is under groove diameter, a heavy flat based bullet is more likely to expand under the first impulse of the powder gases. , This was well documented in the days of muzzle-loaders, when everything had to come up the way it went down, and long range demanded something else than a true minié.

Against this, what if your bullet is slightly over groove diameter, or your rifling is undesirably deep for this sort of work? There is a danger of finning at the rear of the bullet, and even worse, of its not being exactly the same all around. A gas-check can prevent this, but with a card wad or grease cookie it will be there when the thing drops off. The boat-tail (or indeed a rebated base) will have that finning flattened into the first fraction of an inch of its conical surface, instead of at the base.

[KVO]

Historically this has been more of a manufacturing tolerance issue than an aerodynamics problem with jacketed bullets. It's much easier to make a consistently flat 90 degree base from bullet to bullet than it is a boat tail as production dies wear and are adjusted. Today's run of the mill jacketed bullets are much more consistent then years' past. With FMJ it is more difficult to manufacture consistent bases due to the open base and variability as compared to soft point, HP, ballistic tip, etc. Match bullets are primarily HP for this reason, more consistent manufacturing. It's the same as us being persnickety about cast boolit bases. Stand by for onslaught of posts telling me the purpose of a JHP match bullet is to shift the center of gravity to the rear...

[pertnear]

I'm not sure if we're discussing cast or jacket bullets here. I have no experience with BT cast boolits so my comments only apply to jacketed bullets.

The aerodynamic advantage of the BT bullet at very long ranges is a well proven fact. But the following is IMHO so take it FWIW.

For a handloader, the BT bullet has an advantage of seating easier & with less chance of damaging the base. I realize that if cases are inside chamfered enough this is a non-issue, but I have seen tiny jacket shaving around a case mouth when seating FB bullets when the case mouth was too tight or the bullet got started in a bit crooked. On game animals, using standard cup-n-core, non-bonded bullets, the BT bullet has a better chance of shedding it's core as the bullet slows to a stop. Not a lot of significance to this because at that point your game animal is probably extra-dead!

[GregLaROCHE]

I started this thread when I started looking at the boolits from my Lee 300 230gr blackout mold. They seem to be more or less boat tailed. I may be wrong, but I don’t think this round is expected to be used at long ranges. That’s why I wonder if a flat base wouldn’t be better.

[kens]

mac1911 nails it with; "Flatbase bullets are shorter so they can stabilize "better" in slow twist barrels."

Otherwise with the quality of today's commercial bullets in non benchrest rifles both are potentially equally accurate. Over practical ranges the deciding factor in any rifle should be accuracy and terminal affect if used for hunting. At longer ranges the BT is ballistically more efficient and is the choice.

Recently, on a prairie dog shoot, I found little practical difference between a FBd 55 gr bullet and a BT 55 gr bullet out to 500 yards in the .223 Remington. The FB 55 gr Varmageddon also did as well as the BTd 55 gr Blitz King out of my 22-250 out to 500 yards.

My 30-06 M70 shoots 180/190 FB and BTd bullets with equal accuracy with the same loads. Thus I use the BTd because the are more efficient at longer ranges by retaining more velocity hence more energy. While I do try to get as close as the hunting situation allows I have, occasionally, had to make some longer range shots. Having a bullet that alllows getting the most out of it ballistically is beneficial.

Can you tell how much of a difference in velocity of the FB vs BT bullets? I mean even out there 500yd and beyond, how much difference in velocity is there, really?
Is there a means to test this?

[wmitty]

Didn't the French or Germans come up with the boat tail design for improved indirect machine gun fire at troop concentrations? Spitzer ogives and boat tails showed up around the end of the 1800's. I remember seeing Hornady , Speer and Sierra bullet charts when there were no boat tails available on their bullets.

[Ballistics in Scotland]

That would be the French Balle D of 1898, which I believe was both the first spritzer bullet and the first boat-tail, and while there were machine-guns at that time, I think an exaggerated idea of the range at which military rifles would be used was more what they had in mind. Senior commanders remembered how, insofar as France earned any credit for the Franco-Prussian War, much of it came from the superior range of the Chassepot over the Prussian needle-gun. Indirect fire was mostly used at targets such as bridges and crossroads, where the bullets arrived with no sound above the 1914-18 background noise, and men would take cover at the first shell. You can't move a crossroads.

But the Balle D was solid bronze, and I think at least finished on automatic lathes. Wear and tear on swaging tools wouldn't apply, a situation which has about been solved by tungsten carbide or nitriding.

[Larry Gibson]

Can you tell how much of a difference in velocity of the FB vs BT bullets? I mean even out there 500yd and beyond, how much difference in velocity is there, really?
Is there a means to test this?

Ballistic tables can tell us the difference. Modern ballistic formulas where we can enter a known BC, muzzle velocity and zero range are the best. They can easily provide the difference in down range ballistics (trajectory, retained velocity and energy) given an equal muzzle velocity and zero range.

[Tom W.]

I use the Jacketed BT just because they are easier to seat.....I have lost some finger skin using the FB before.
My cast boolits are seated in flared cases.

[metricmonkeywrench]

That same discussion just came up on the Midsouth Shooters blog.

http://www.mssblog.com/

[Rick Hodges]

The accuracy difference is debatable. My Heavy barrel Savage 110 will consistently shoot 5 shot groups under 9/16" @ 100 with Sierra 55 gr BTSPs (some way under). My 6mm likes 100gr. Hornady BTSP's and shoots under MOA as well. I don't know if flat base would shoot better and I really don't care. In both cases they shoot well enough for their intended purposes.

I have heard that BT's are prone to losing jackets easier than FB. On varmint bullets it is moot, and, at least on deer sized animals, I have never had a problem with the BT's. In fact the only time I had trouble with a bullet splashing on a deer and not penetrating was with a 154Horn. FB from a 7mm Rem MAG. The shot was close and the bullet was moving over 3100fps at impact and exploded on a rib. It killed the deer, but jacket and core didn't make it half way through broadside.

[Ballistics in Scotland]

The accuracy difference is debatable.

Boat-tails giving superior accuracy is, although people as knowledgeable as Sierra use them almost universally for bullets in the style of he MatchKings. But boat-tails giving inferior accuracy is a theory which doesn't get a look-in.

What the really dedicated benchresters do with rifles and cases is often of very limited relevance to what the rest of us need. Not so, however, what they do with bullets. The improvement in accuracy from the old "2moa? What are you complaining about?" days is mostly down to them, for some barrels and rifles have always been made as well as the best of the present day. Unless they have changed of late, they seem pretty sold on boat-tails.

[Lloyd Smale]

I don't understand how a bullet can break the sound barrier more then once.
The advantage of the boattail is most apparent beyond 400 yards, and it has to do with drag and high velocity.
The higher the velocity and the number of times the bullet exceeds the sound barrier the more drag is imparted upon the bullet, and the quicker it will slow down.

The boattail helps reduce the drag upon the bullet.
I wish I could go into more detail but I need to go to my grandson's ball game, his team is undefeated and will go into eliminations this morning before it gets hot.

[Larry Gibson]

I don't understand how a bullet can break the sound barrier more then once.

Lloyd

Bullets, airplanes, rockets and other projectiles can "break the sound barrier" (which is simply a term for speed)/velocity) several times. It's called MACH I, MACH II, MACH III, etc.

[popper]

Well, once in the barrel and once on the way to the target. General bullet design is to reduce air friction and turbulence that reduce velocity and interfere with gyro stability. The turbulence range (~speed of sound) is actually a 'range' of velocity that changes with atmospheric conditions.

[Lloyd Smale]

I thought mach 2 mach 3 ect were just a speed. Once a bullet breaks the sound barrier there is only one speed of sound and that's where the air disturbance is and it doesn't break it again and cause another sonic boom again when it goes twice the speed of sound. Either way its irrelevant in bullets because I don't know of a single one of them that does mach 2. Ive never heard of a plane or anything else that does it more then once unless you slow to slower then the speed of sound and accelerate through it again which no bullet can do. Going past the speed of sound Mach I causes a disturbance in the air and mach 2 mach 3 ect are just a speed based on the speed of sound
Lloyd

Bullets, airplanes, rockets and other projectiles can "break the sound barrier" (which is simply a term for speed)/velocity) several times. It's called MACH I, MACH II, MACH III, etc.

[Larry Gibson]

Lloyd

Yes, Mach I and Mach II are speeds but there is a shock wave that forms as the bullet/aircraft, etc. passes through Mach I. The shock wave changes in force, intensity and location created on the bullet/aircraft, etc. as additional Mach levels are passed. However you hear only one sonic boom, crack or whatever you call it when the shock wave reaches you. The shock wave follows behind and outwardly from the path of the bullet/aircraft, etc. You hear only one "boom/crack" regardless of whether additional Mach levels are reached later because the shock wave/boom is already past you. If it's going Mach I, II or III you will hear only one boom/crack because there is usually only one shock wave created regardless of the mach level or if more they are so close together you can't distinguish between them.

"Either way its irrelevant in bullets because I don't know of a single one of them that does mach 2."

Uh, Lloyd, lots of bullets travel faster than Mach II.......any over 2200 - 2400 fps are traveling Mach II or greater. You only hear one "crack" (if the muzzle blast is suppressed) because if the muzzle velocity is above Mach I, II or III it is already that Mach level speed on exit from the muzzle. There is no "crack" of the bullet while it is still inside the restriction of the barrel reaching whatever Mach level+ it exits the muzzle at.

Since the bullet is at max velocity on muzzle exit it will not increase in velocity and go "through" another Mach level (perhaps this is what you meant?).

[Ballistics in Scotland]

I don't understand how a bullet can break the sound barrier more then once.


Strictly speaking no bullet or aeroplane ever breaks through a barrier. of sound waves. What happens is that the velocity of sound in a medium varies with its density, being greater as the density of air increases. A tiny cushion of highly compressed air builds up in front of the bullet's nose, and in it the speed of sound increases, so that the bullet never quite catches up.


223084

This picture, illuminated by the quite incredible brevity of an electric spark, was taken by a Professor Boys of Imperial College in the 1890s, and is much better that Dr. Mach was taking at the time. The shock-wave in uncompressed air, non-existent or very slight when the bullet is subsonic, becomes sharp and rather percussive on the eardrum. This is the sonic crack or boom. The nature of this wave structure explains some important facts.

The wave doesn't shoot out like growing whiskers. It travels at right angles to its front, so that the part of it behind the rear of the bullet was created in about the spot where the contact wire changes from thick to thin. As it is travelling in ordinary air, we could calculate bullet velocity from its angle, sharper as bullet velocity increases.

The rounding of the apex of the bow-wave is due to the compression of the air near the bullet. Greater roundness tells us that it was disturbing the air more. If the bullet was invisible, we could tell from the extent of that rounding how well shaped it was, to minimise disturbance of the air.

Like a seagull bobbing up and down as the waves of the sea pass under him, the air molecules oscillate but do not travel with the wave. (If you want to detect the first trace of an unhealthy noisez in your car engine, press a screwdriver against it and put your ear to the other end, as sound travels extremely well in the virtually immovable molecules of steel.) This is why only metal makes a clean hole in a target card, sometimes "pencilled" with lead, rather than the zone of elevated pressure.

As the wave can only travel at Mach 1, a bullet travelling at Mach 3 or more, with a more sharply angled bow-wave than Professor Boys's Lee-Metford bullet, can.t make the sound any greater. With a larger bullet, however, it does increase. A supersonic aircraft at close range can damage ears and break windows, but a bullet which doesn't hit them can't.

The bullet has hurled away a little cloud of pulverised contact wire, which (I think due to the elasticity of the metal) has acquired a higher velocity than the bullet that did it. This may be very important for wounding effect. General Hatcher tells of an experiment with a terminally sick mule, wearing a GI helmet. (It may have inspired the understandably worried one in the cartoon "The Old Western Scrounger" used to have in their catalogue.) Not only did a solid copper .220 Swift bullet penetrate it, but fragment of skull did on the way out.

Note that there is an extra wave originating at the rear of the bullet, and very slight ones from cannelures etc. So there is indeed a double sonic boom. I remember it well at a range of many miles, when they were testing the airliner Concorde in the North Channel between Scotland and Ireland. Due to its very great size, he sound carried very far. Being about 200 feet long, the booms should in theory have been around a sixth of a second apart. In fact they are both slightly drawn-out by distance, and sound more separate. But with a bullet, they can't be distinguished by the ear.

The same object can emit a sound fairly describable as a sonic crack or sonic crack, as the sound of a bullet is altered in pitch by the Doppler shift. The sound vibrations a the front are compressed by the movement of their source, and in a rearward direction stretched further apart. Think of a machine-gun in an aeroplane, and streams of bullet fired to front or rear. So the bullet passing close by you makes a vicious crack, as if it was carrying its own health warning, while from your own departing bullet the same sound may be heart as a low rumble.

The Doppler shift is why we hear a quick deepening of the bullet’s note as it passes, like a faster version of a passing car. Civil War veterans described the voice of a Minié bullet, from a direction range officers don't allow, as a chirp. A Union private at the all-American version of the battle of Yorktown observed a soldier named Spinney showing an unbecoming concern for his health. He afterwards explained that every bullet which passed said ‘Spinney’, which appeared just a little too personal for comfort.

[Lloyd Smale]

your right larry I don't know what I was thinking. I was mixing up a 1000fps with a 1000 mph.
Lloyd

Yes, Mach I and Mach II are speeds but there is a shock wave that forms as the bullet/aircraft, etc. passes through Mach I. The shock wave changes in force, intensity and location created on the bullet/aircraft, etc. as additional Mach levels are passed. However you hear only one sonic boom, crack or whatever you call it when the shock wave reaches you. The shock wave follows behind and outwardly from the path of the bullet/aircraft, etc. You hear only one "boom/crack" regardless of whether additional Mach levels are reached later because the shock wave/boom is already past you. If it's going Mach I, II or III you will hear only one boom/crack because there is usually only one shock wave created regardless of the mach level or if more they are so close together you can't distinguish between them.

"Either way its irrelevant in bullets because I don't know of a single one of them that does mach 2."

Uh, Lloyd, lots of bullets travel faster than Mach II.......any over 2200 - 2400 fps are traveling Mach II or greater. You only hear one "crack" (if the muzzle blast is suppressed) because if the muzzle velocity is above Mach I, II or III it is already that Mach level speed on exit from the muzzle. There is no "crack" of the bullet while it is still inside the restriction of the barrel reaching whatever Mach level+ it exits the muzzle at.

Since the bullet is at max velocity on muzzle exit it will not increase in velocity and go "through" another Mach level (perhaps this is what you meant?).