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Conventional Wisdom: Flat base vs Boattail

This is a discussion on Conventional Wisdom: Flat base vs Boattail within the Accuracy forums, part of the M14 M1A Forum category; It's good, from time to time, to examine conventional wisdom to see if the beliefs held by the shooting community at large are based on ...


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Old May 5th, 2011, 02:57 PM   #1
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Conventional Wisdom: Flat base vs Boattail

It's good, from time to time, to examine conventional wisdom to see if the beliefs held by the shooting community at large are based on fact or myth. Anyone who has been involved in shooting sports for close to half a century, as I, has seen commonly held beliefs regarding firearms fall to the wayside. I may be an old dog but I'm not dogmatic so I'd like to use this forum occasionally to examine "Conventional Wisdom" and promote vigorous, but repectful, discussion on various matters.
Today I'd like to open a discussion regarding which base type on a bullet is, if at all, inherently more accurate. Conventional wisdom, at least in my shooting circle holds that flat base bullets are more accurate than boattail bullets. This belief is due to both subjective observations as well as empirical data. I understand boattail bullets have a better Ballistic Coefficient which, at longer distances may make it easier to hit the target due to less bullet drop, but that isn't better inherent accuracy. There was an excellent article 20 or so years ago in one of the major shooting magazines about "Which end of the bullet is the steering end?" Some of you may remember reading it. During the tests of which the author wrote, he purposely damaged the nose, then the base of several popular bullets used for reloading. the results were dramatic and counter-intuitive, at least to me. A damaged base on a bullet had a much greater effect than a damaged nose. In fact, a damaged nose had very little effect on accuracy at the ranges the bullets were tested. So the question I'm putting to everyone is this: in your experience, have you found one of the two base types to be inherently more accurate than the other? I ask this question for two reasons; one to initiate a hopefully stimulating intellectual discussion and the other is that I am planning to build an HP target rifle, most likely in .30 calibre in the reverse order. That is, instead of starting with an action and barrel type from which I try to work up an accurate load, I'm going to pick the bullet, then the case, then the rifling, then the barrel, then the action to see if I can get an ultra accurate rifle using this process.
Your thoughts gentlemen?

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Old May 5th, 2011, 03:00 PM   #2
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for inside of 300yds, hard to beat a good flat based bullet.

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Old May 5th, 2011, 04:47 PM   #3
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I don't think it's a matter of 'which design is better', but rather which design can be mass produced with more consistency.

I think that a 'flat base' is more simple to produce, and if equal care and skill goes into the mfg process then the FB bullets will be more consistent, and will be more accurate.

BT bullets have an advantage in the wind because they usually have a higher BC and are affected less by cross wind - but that does NOT mean they are more accurate. It just means that if the shooter misses a wind change, then the BT bullet would be 'off' by a smaller amount. Also at 900+ yards the BT has an advantage because it loses velocity at a slower rate which can avoid problems that happen when the bullet drops through the speed of sound.

Many (most?) competition bullets for further than 300 yards are of the BT design, and if your shooting includes distances of 600 yards and beyond, the a BT is probably the best choice. For 300 and closer, a good FB will work fine.

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Old May 5th, 2011, 05:41 PM   #4
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Let the flat base and BT fight it out for the top two spots, but may I propose another type for absolute last place: the open-base FMJ. The manufacturing process of squishing the jacket over the tip and around the base tends to leave inconsistent, lopsided blobs of lead in the open base that deflect the propellant gases and throw the bullet off balance. Look at any handful of typical 147 M80 FMJ, M193 55gr or M855 62gr bullets for examples, then look at the horrible groups.

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Old May 5th, 2011, 08:20 PM   #5
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Well sir, I'm sure there are many theories and opinions on this topic but here is my take and actual findings. I have experimented/tested/tried flat base and boat tail bullets in 4 different .22cal rifles. The higher BC of the boat tail is a no brainer for long range however the flat base might have something to offer for some shooters. A theory that I believe is this. The flat base bullets I tried measured longer to the ogive which equates to more surface area on the lands. More surface area on the lands could project a more stable bullet at the muzzle. Measuring the distance to the ogive on the boat tails were slightly shorter if I remember correctly. This could raise an issue for a guy that wanted to hang a bullet out to close the freebore. I am not sure about the larger calibers and the lengths of bullets.

In my findings, the boat tail bullets produced tighter groups in the rifles/loads I tested.

Now, If you wanted to build a rifle correctly (which you are), developing the round first with the chamber second will eliminate your length/freebore issue. With my findings and the obvious higher BC of the boat tails, I would go with the boat tail and not worry about the flat base hype. If you are going to build a .30 high power, I would go with the readily available 168/175/155 bt matches.



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Originally Posted by 2336USMC View Post
Let the flat base and BT fight it out for the top two spots, but may I propose another type for absolute last place: the open-base FMJ. The manufacturing process of squishing the jacket over the tip and around the base tends to leave inconsistent, lopsided blobs of lead in the open base that deflect the propellant gases and throw the bullet off balance. Look at any handful of typical 147 M80 FMJ, M193 55gr or M855 62gr bullets for examples, then look at the horrible groups.


I do agree with you that the open base bullets might not be as concentric nor accurate as a match bullet. I currently run a bulk Montana Gold (golden west) 55gn FMJ open base through my 16" Bull barreled AR and get 1/2" 3 shot groups with 25gns of H335, LC brass, CCI primer. Depending on how much you shoot, 1/5" sacrifice in accuracy might work as it does for me.

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Old May 6th, 2011, 12:25 AM   #6
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I would like too sound edumaketed on this subject, I know that flat based pills make for less T/E than boat tailled pills for the same number of rounds fired, the flame and blow torch effect is much kinder to the throat area with a F/B. Barrels are not getting any cheaper and with 50% of the rounds fired on the short line 200yds I will stick with F/B pills, 300yds the 168's and 600yds 175's.

I also remember a old rifle magizine article about military rifle/ammo test done at ether Frankfort or Rock Island Arsonal, the rifle used was a 03 Springfield (unnamed rifle so it could have been RI or SA rifle) the then current service rifle, firing M1 ammo that used the then standard M1 load(170gr flat base) the projected barrel life was 10,000rds before it would need a new tube.


So thats my story and I'm stickin' too it.

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Old May 6th, 2011, 01:06 AM   #7
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Some of the best groups and scores I shot in a match either with AR or M1A were shot wtih FB. Shot the 64 grain Berger's FB in my AR service rifle, shot the 135 grains Berger's FB in my M1A. I've even shot 171 grains FB BIB bullets @ 600 and tied my best score shot with 175 BT.

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Old May 6th, 2011, 02:47 AM   #8
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Many years ago when I could regularly shoot longer ranges my reloads were "built" around .30 boat tail match bullets and for me/my rifles they were more accurate than anything else. They were Sierra bullets.

When I started shooting my .223 varmint rifle I bought more Sierra hollow point match bullets but I soon found out that at the ranges I shot those (under 300 yds) the flat based lighter bullets (45 grain thin jacketed bullets became my favorite) gave me the best groups.

It might not be a good idea to categorize bullets into types alone as in my rifles the brand of bullet made a difference as well. There may have been improvements over the years but in my rifles the most accurate boat tails were Sierra, Hornady in the middle and Speer at the bottom. That was the .30 caliber bullets. With the .223 bullets it was different. The Speer and Hornaday bullets were more accurate than the Sierra bullets (in the 45 grain thin jacketed type of bullets).

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Old May 6th, 2011, 12:05 PM   #9
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Don't forget that the 168 grain Sierra Match King, a boat tailed bullet, held the .30 caliber bench rest record for many years. It may still.
There are lots of great bullet choices and very accurate rifles out there. None of them shoot worth a darn without a high degree of skill from the operator.
Accuracy is almost a mute point without the skills to bring it all together.

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Old May 6th, 2011, 02:34 PM   #10
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I personally don't have enough personal experience to make any kind of call here. I tend to stick with a certain configuration bullet such as the 168 HPBT in .308 Winchester pretty much because I believe it is the optimal all around bullet for that caliber for what *I* want to do.

If you are just sticking to .30 Caliber without a specific cartridge, you might want to talk to your local Benchrest competition shooters and find out what calibers win the matches at each distance. If you aren't stuck on .30 caliber, I would say that 6 mm PPC with flat base bullets is the way to go up to about 200 yards.

When shooting this class of rifle, the skill comes in judging the wind. The rifle typically sits on a front and rear adjustable rest and the "Shooter" hardly even touches the rifle when firing it. They are allowed to free recoil which works when the rifles are very heavy for a light recoiling cartridge.

You might want to consider what level of accuracy will meet your requirements because with this many options, getting a gun under 1/4 MOA should not be all that difficult.

- Ivan.

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Old May 6th, 2011, 03:21 PM   #11
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http://www.tobystactical.com/2007/11...r-milspec.html

read the subpage in there also

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Old May 6th, 2011, 03:46 PM   #12
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Here is some food for thought. I have an older book entitled "Principles and Practice of Loading Ammunition" by Earl Naramore. Col. Naramore spent his entire life working with ammunition. He worked for Lyman and as an Ordnance officer in the Army reserves he worked at several proving grounds with his last assignment being the Chief Proof Officer, Chief of the Inspection Division, Operations Officer, and Executive Officer at the Erie Proving Ground.

On page 419 of his book he talks about the deformation of flat based (FB) bullets vs. boat tailed (BT) bullets. Here is a picture of the test results

He states that the deformation is due to the mass of the bullet taking time to start moving. The gas pressure pushes on the base of the bullet but the nose of the bullet resists movement for a short period of time. During that time the base is squashed in to the barrel walls and actually deforms. On the other hand, a BT bullet doesn't experience this deformation because the shape of the base allows gases to go around the bullet and surround it, the BT bullet's shape allows the gas pressure to press it around it's entire outside circumference rather than just pushing against the base. This leaves the BT bullet closer to it's original shape.

My assumption is that this would explain why a FB bullet does not perform as well at longer distances. The deformation would cause it to start yawing right out of the muzzle and it would also tend to slow down quicker. So like others have said, at shorter ranges there is very little difference between the performance of the two types of bullet but at longer ranges the BT will show better accuracy and velocity retention. So I've come to the conclusion that if money is an issue and you don't intend to shoot beyond 200 or 300 yards then buy the cheapest flat base bullet that will suite your needs, there is no advantage to using a more expensive boat tail design.

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Old May 6th, 2011, 03:48 PM   #13
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In my limited experiecne I find that out to 300 yards with most cal. of bullets that it's a near toss up between boat tail and flat base bullets with the boat tail a bit better. For anything past 300 or 400 yards the boat tails outshine by perverbial miles the flat base bullets. I will only use boat tail bullets in my loads for all ranges for target shooting. I strive to shoot for score points.

Here's the 100 yard zero for the 300 Win. Mag. target rifle using 190 gr. SMK boat tails.

100 yard zero 1017.2010 001.jpg

This rifle can do this holes in holes thing @ 100 yards all day long. I shoot fairly regularly 1000 yard target.

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Old May 6th, 2011, 04:00 PM   #14
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From my rocking chair....

Had this very chat with Phil Berger at the SHOT show about 12 years ago. He contended then that the micro-moment of muzzle escape by the two types of bullet were significantly different, or so Berger's experiments and über-high-speed filming showed. They showed that the escaping gas jets around a BT bullet base are less "regular" than those escaping around the FB. Think of it: the BT allows some early release, more so on one side than on the other, and so on, while a FB immediately opens the muzzle portal when the tail end of that type of bullet slips out of the muzzle. Of course, this assumes a good/pefect muzzle crown, but you can imagine the theoretical difference.

This is also the theory behind the (relatively) new 11˚ crown on target rifle muzzle crowns, versus the older stepped design, which was good at protecting the crown, but not so good in terms of reflected pressure waves as the outbound radially directed high pressure wave, independent of the escaping gas front, hit that 90˚ machined ridge and then bounced back (all of this @ about 1100 fps wave-front velocity, BTW...), richocheting off the now-departing bullet's butt-end. Ouch! Problem was that the various grooves and lands created different wave fronts depending on different radial index positions around that crown.

But with the, for instance, Krieger concave/11˚ degree muzzle crown, it's smooth, and allows both the emerging pressure wave and the hot gas jet to escape without having any deleterious effects ( I wanted to use that word all week! Hurrah!) on the now-departing bullet.

And so, this also affects the departure moment's dynamics with flash hiders and muzzle brakes, as you can imagine. In my experience, the addition of even a good design muzzle brake will have either no effect, or a slight worsening, of rifle accuracy overall. [The bad designs? They not only might actually increase flash and blast, but they can also destroy accuracy. There's a lot more to it than creating a pretty machining pattern. Just check out Ron Smith's Vortex flash hiders. Excellent!]

It may only be a reduction on group size of, oh.... 0.010 ", but it's measurable on a good BR rifle in, let's say, 6BR. This is why you don't see muzzle brakes on too many BR rifle,s even on the vaunted .338 Lapua (hey; my .340 Wby has near-identical ballistics to the Lapua!! WTH?). With ultra-fast videography of the muzzle of a .378 Wby, with and without a factory MB you get to see some astounding events! Quite the turmoil with that muzzle brake; lots of gases going every which way! Of course, you're not necessarily going for sub 0.3" MoA with that cruisin' bruiser, eh? Yah just want some relief from that self-induced headache generator!

But Wait! There's more! The BT may be better at re-stabilizing a de-stabilized bullet downstream, even as close in as 100 - 150 m out from the muzzle termoil, where a test group size measurement @, let's say, 70 - 90 yds is worse, in terms of MoA, than it becomes at, say, 200 m!

We know this happens in many bullet types, and certainly in the BPCR rifles I also shoot, that huck big-'ol oil-barrel shaped 550 gr .458 diam. bullets with truly miserable BCs and aerodynamics. As well, when they drop through the supersonic velocities, the bullet literally shudders for a brief micro-second, which may or may not destabilize it. Reasonably, it probably does. Some sort of slippery BT shape might, in theory, re-stabilize such a bullet and ensure it's more "true" adherence to the shooter's intended path.

Does this happen with modern, BT or FB bullets. You bet; just ask the developers of the original AK rifles. They wanted them to be inherently unstable, as was also purposefully designed into the early .223s: when they hit, they go all Koo-Koo and rip the "target material" () apart!

V. interesting thread! Kudos. (PS: how do you "rep point" a poster on this forum?)

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Old May 8th, 2011, 11:30 AM   #15
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Bullet yaw

Quote:
Originally Posted by MesaRifle View Post
Had this very chat with Phil Berger at the SHOT show about 12 years ago. He contended then that the micro-moment of muzzle escape by the two types of bullet were significantly different, or so Berger's experiments and über-high-speed filming showed. They showed that the escaping gas jets around a BT bullet base are less "regular" than those escaping around the FB. Think of it: the BT allows some early release, more so on one side than on the other, and so on, while a FB immediately opens the muzzle portal when the tail end of that type of bullet slips out of the muzzle. Of course, this assumes a good/pefect muzzle crown, but you can imagine the theoretical difference.

This is also the theory behind the (relatively) new 11˚ crown on target rifle muzzle crowns, versus the older stepped design, which was good at protecting the crown, but not so good in terms of reflected pressure waves as the outbound radially directed high pressure wave, independent of the escaping gas front, hit that 90˚ machined ridge and then bounced back (all of this @ about 1100 fps wave-front velocity, BTW...), richocheting off the now-departing bullet's butt-end. Ouch! Problem was that the various grooves and lands created different wave fronts depending on different radial index positions around that crown.

But with the, for instance, Krieger concave/11˚ degree muzzle crown, it's smooth, and allows both the emerging pressure wave and the hot gas jet to escape without having any deleterious effects ( I wanted to use that word all week! Hurrah!) on the now-departing bullet.

And so, this also affects the departure moment's dynamics with flash hiders and muzzle brakes, as you can imagine. In my experience, the addition of even a good design muzzle brake will have either no effect, or a slight worsening, of rifle accuracy overall. [The bad designs? They not only might actually increase flash and blast, but they can also destroy accuracy. There's a lot more to it than creating a pretty machining pattern. Just check out Ron Smith's Vortex flash hiders. Excellent!]

It may only be a reduction on group size of, oh.... 0.010 ", but it's measurable on a good BR rifle in, let's say, 6BR. This is why you don't see muzzle brakes on too many BR rifle,s even on the vaunted .338 Lapua (hey; my .340 Wby has near-identical ballistics to the Lapua!! WTH?). With ultra-fast videography of the muzzle of a .378 Wby, with and without a factory MB you get to see some astounding events! Quite the turmoil with that muzzle brake; lots of gases going every which way! Of course, you're not necessarily going for sub 0.3" MoA with that cruisin' bruiser, eh? Yah just want some relief from that self-induced headache generator!

But Wait! There's more! The BT may be better at re-stabilizing a de-stabilized bullet downstream, even as close in as 100 - 150 m out from the muzzle termoil, where a test group size measurement @, let's say, 70 - 90 yds is worse, in terms of MoA, than it becomes at, say, 200 m!

We know this happens in many bullet types, and certainly in the BPCR rifles I also shoot, that huck big-'ol oil-barrel shaped 550 gr .458 diam. bullets with truly miserable BCs and aerodynamics. As well, when they drop through the supersonic velocities, the bullet literally shudders for a brief micro-second, which may or may not destabilize it. Reasonably, it probably does. Some sort of slippery BT shape might, in theory, re-stabilize such a bullet and ensure it's more "true" adherence to the shooter's intended path.

Does this happen with modern, BT or FB bullets. You bet; just ask the developers of the original AK rifles. They wanted them to be inherently unstable, as was also purposefully designed into the early .223s: when they hit, they go all Koo-Koo and rip the "target material" () apart!

V. interesting thread! Kudos. (PS: how do you "rep point" a poster on this forum?)

Interesting post! The effect of the escaping gas on the base of the bullet at the point of departure from the barrel may explain why some rifles shooter better, in regards to MOA, at longer distances. The bullet needs to "settle down" if it's yawing slightly after leaving the barrel. This "yaw" can be caused by the bullet being upset as it leaves the barrel or also by it's jump in the chamber from the case mouth to where it engages the lands on the rifling. I assume most handloaders seat the bullet out so that it engages the rifling in the chamber, if magazine length allows, or is that another case of Conventional Wisdom gone wrong. I may not have stated this before, but all my target shooting was done some twenty years ago!
Another point made by some BT handloaders which may have merit is that you are less likely to scratch the base of a BT bullet during the reloading process. I'd like to pull a selection of BT and FB bullets from handloaded ammunition to see if there is any discernible scratches. I think it unlikely, as the jacket on the bullet is harder than the brass case although there can be some work hardening on a case that has been resized muitiple times.

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