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Thread: Flat Base or Boat Tail

  1. #1

    Default Flat Base or Boat Tail

    For some reason or another about all my rifle loads have boat tail bullets in them. I have always liked the looks of them but now am wondering if I have missed out by not trying more flat based bullets. I have a 700 Rem. in 22-250 that will not shoot good with a boat tail bullet but will group 1/2 inch at 100 yards with a flat base bullet. Do most of you have a preference for one or the other or do you shoot both? The boat tail looks more stream lined but it make any difference?

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    Quote Originally Posted by Cast Iron View Post
    For some reason or another about all my rifle loads have boat tail bullets in them. I have always liked the looks of them but now am wondering if I have missed out by not trying more flat based bullets. I have a 700 Rem. in 22-250 that will not shoot good with a boat tail bullet but will group 1/2 inch at 100 yards with a flat base bullet. Do most of you have a preference for one or the other or do you shoot both? The boat tail looks more stream lined but it make any difference?
    This question can lead to a lengthy discussion about bullet design and how this effects ballistic coefficients…Velocity, Range..and a lot of other factors to boot….Blah Blah Blah…...

    The simple answer is this…. All rifles have their very own personality and barrel harmonics. if your rifle is shooting the best groups its ever shot, and your using flat base bullets… The proof is in the pudding.

    Trajectories and ballistic tables are all easy enough to calculate… Most of the Time a long Boat tail bullet has a higher BC then a comparable weight Flat-base bullet. This is the nature of the beast… However this does not do you any good, if you can't achieve repeatable and consistent results with a Boat-tail design. Thus IMHO this argument is irrelevant.

    I have owned rifles that shoot infinantly better groups with flat base bullets Vs Boat Tail before… sometimes 2 twin rifles with same twist rate barrel length exct…. have opposite likes and dislikes concerning ammo….. no physicists nor chart can explain it …… It is what it is.

    I like grape and you might like strawberry…...

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    I think that as a GENERAL rule of thumb the boat tail bullets really shine in long range shooting. For most 'normal' hunting/shooting ranges, flat base bullets shoot just fine. As has already been stated, find what your rifle like and use that. Boat tail bullets are easier to reload than flat base if that makes any difference to you. I use both boat tail and flat base bullets depending on what the weapon likes.

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    Not as a brag, just thought it might be helpful, but I actually do have a degree in Physics. I'm not saying that to proclaim myself some kind of perfect expert, just to show that to a certain extent, I've studied parts of this. Bullet ballistics (as mentioned before) is a very complicated subject with so many variables it's almost impossible to say X will do Y. It's more like X may do Y assuming other things remain the same and ignoring Z, Q, R, and F. Anyway, bullets traveling through air at the speeds they travel are better represented by discussing bullets traveling through water. At very high speeds, air behaves like a fluid. So aerodynamics are more critical as the speed increases. The best possible object traveling through the air would be one that splits the air cleaning at the tip and then recombines that air cleanly at the base. (of course we're ignoring surface frictions and laminar flows here...) The only real difference between the flat base and the boat tail is the amount of turbulent air that results at the base of the bullet as it travels.

    A flat base bullet will have a higher disturbed air pocket directly behind the bullet because the boundary conditions between bullet and air at the base are steeper. A boat tail will have a smaller disturbed air pocket because the air is given a shallower boundary to cross. Think of it like water. As the bullet moves through the water, the tip separates the water and it flows along the surface. When it gets the back, it HAS to come back together. The easier you make it to recombine, the less you disturb the water at the back. And disturbing the water means drag on the bullet. So as the water hits the trailing edge of the flat base, it has to make a sudden right angle turn and slams into the water coming from the other side of the bullet. Turbulence. If you can reduce that right angle, you reduce the turbulence.

    BUT, that doesn't by default equate to better or worse performance because there are too many other variables to consider. It will result in slightly less drag on the bullet (all other things being equal) which will improve the long distance performance. But if you're shooting 100 yds, you aren't reaching that distance where the difference is evident. Think shooting 1,000+ yds. So if you shoot flat base better at 100 yds, use flat base. You aren't really seeing the benefits of boat tail until you get to much longer ranges where the aerodynamics start really affecting the bullet.

    Here's a picture of the turbulent air directly behind the bullet on a boat tail:
    Click image for larger version. 

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    Some of this can relate to how gas acts on the base of the bullet as it leaves the barrel. If the base is being kicked slightly to one side as it leaves the barrel it can have a dramatic effect on accuracy. I suspect that there is less probability for the base to be affected on a flat base vs a boat tail. But that is just a guess from one that has no degrees in anything.

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    Quote Originally Posted by rbuck351 View Post
    Some of this can relate to how gas acts on the base of the bullet as it leaves the barrel. If the base is being kicked slightly to one side as it leaves the barrel it can have a dramatic effect on accuracy. I suspect that there is less probability for the base to be affected on a flat base vs a boat tail. But that is just a guess from one that has no degrees in anything.
    That's a good point. The gas seal location is different for boat tail versus flat base and different crowns may affect the transition differently. I know there's a new style trying to make noise called the rebated boat tail. It's kind of a best of both worlds approach. The initial edge is flat like a flat base, but transitions to a boat tail with a smaller diameter than the bullet itself. Supposedly it avoids the gas seal issues of the boat tail and provides a reduced back pressure over a flat base. Again, does it really matter for 100 yds? I'm skeptical.

    BTW, I hope bringing up my degree wasn't seen as an insult or a "na, na, I'm better." I wasn't trying to be "smarter than thou." I was just saying that because it explains where I'm coming from in these kinds of discussions. If I insulted I'm sorry.

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    Yes, no and maybe. Now that I have that out of the way,,,. First of all rebated boatails have been around a very long time and are not the new kid on the block. MOst of your shots with that are probably going to be under 300 yards, correct me if I'm wrong.
    In my quest's for bullet selection I first decided on what animal I was intending on shooting with it and then picking a appropriately constructed bullet. All 22-250's I have shot are accurate enough for what I needed them to do and as a hunting gun I always shot flat based bullets and they were at about 1" at 100 yards. If you want to shoot a boatail look at Berger Bullets but you really don't need to go the extra expense.

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    My AR shoots 69gr HPBT fantastic (.4MOA) and 55gr FMJ-BT terrible (1.5MOA), it also shoots Noslers bonded flat base well (.75 MOA), don't know why. I would much rather hand load boat tails, but I just shoot what works and I don't worry about it.

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    [QUOTE=Mobius;1342208]Not as a brag, just thought it might be helpful, but I actually do have a degree in Physics. I'm not saying that to proclaim myself some kind of perfect expert, just to show that to a certain extent, I've studied parts of this. Bullet ballistics (as mentioned before) is a very complicated subject with so many variables it's almost impossible to say X will do Y. It's more like X may do Y assuming other things remain the same and ignoring Z, Q, R, and F. Anyway, bullets traveling through air at the speeds they travel are better represented by discussing bullets traveling through water. At very high speeds, air behaves like a fluid. So aerodynamics are more critical as the speed increases. The best possible object traveling through the air would be one that splits the air cleaning at the tip and then recombines that air cleanly at the base. (of course we're ignoring surface frictions and laminar flows here...) The only real difference between the flat base and the boat tail is the amount of turbulent air that results at the base of the bullet as it travels.

    A flat base bullet will have a higher disturbed air pocket directly behind the bullet because the boundary conditions between bullet and air at the base are steeper. A boat tail will have a smaller disturbed air pocket because the air is given a shallower boundary to cross. Think of it like water. As the bullet moves through the water, the tip separates the water and it flows along the surface. When it gets the back, it HAS to come back together. The easier you make it to recombine, the less you disturb the water at the back. And disturbing the water means drag on the bullet. So as the water hits the trailing edge of the flat base, it has to make a sudden right angle turn and slams into the water coming from the other side of the bullet. Turbulence. If you can reduce that right angle, you reduce the turbulence.

    BUT, that doesn't by default equate to better or worse performance because there are too many other variables to consider. It will result in slightly less drag on the bullet (all other things being equal) which will improve the long distance performance. But if you're shooting 100 yds, you aren't reaching that distance where the difference is evident. Think shooting 1,000+ yds. So if you shoot flat base better at 100 yds, use flat base. You aren't really seeing the benefits of boat tail until you get to much longer ranges where the aerodynamics start really affecting the bullet.

    That is an excellent Description……. I think you made my point however when you admitted that there are so many Variables that its near impossible to understand why X affects Y.

    In ballistics, the ballistic coefficient (BC) of a body is a measure of its ability to overcome air resistance in flight.[1] It is inversely proportional to the negative acceleration — a high number indicates a low negative acceleration. This is roughly the same as saying that the projectile in question possesses low drag, although some meaning is lost in the generalization. BC is a function of mass, diameter, and drag coefficient. It is given by the mass of the object divided by the diametersquared that it presents to the airflow divided by a dimensionless constant i that relates to the aerodynamics of its shape. Ballistic coefficient has units of lb/in² or kg/m². BCs for bullets are normally stated in lb/in² by their manufacturers without referring to this unit.

    Even though I copied and pasted that from wiki……I believe it gives an accurate description. its much the same definition you are giving however for me it puts numerical values to work…..Thus its easier for me to understand then theory.

    This explains exactly why boat tail bullets (have a higher BC) and therefore at least mathematically or better for long range then Flat base…..However forgetting the (many other Factors) ... if he's shooting boat tails 2 MOA at 100 yards then in theory this is going to = roughly 20 inches at 1000 yds. and he might very well be better off with what his rifle likes…..regardless of some formula.

    I understand that sometimes a load shoots much better at 300 yards then it does at 100….however if I don't get results I like at normal distances 100-400 yards…. I rarely try them at the longer ranges….more often then not, in my personal experience I have found this largely a waste of time.

    Ultimately with the ranges a 22-250 are effective for,,,, Load it with flat base bullets and call it a day….Just MHO

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    Nope, no insult, just wanted folks to know that my speculation is just that and I have no sientific proof to back it up. Over the years I have read from many different gun rag writers many of which believe the flat base is generally more accurate but I think it really depends on the rifle and the exact bullet you are using. On the other hand, Sierra's Match Kings tend to be very accurate and they are boat tails. I tend to go with what ever works.

  11. #11

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    Quote Originally Posted by Cast Iron View Post
    For some reason or another about all my rifle loads have boat tail bullets in them. I have always liked the looks of them but now am wondering if I have missed out by not trying more flat based bullets. I have a 700 Rem. in 22-250 that will not shoot good with a boat tail bullet but will group 1/2 inch at 100 yards with a flat base bullet. Do most of you have a preference for one or the other or do you shoot both? The boat tail looks more stream lined but it make any difference?
    In your 22-250 the boat tailed bullet may be too long for your rifling and may not be stabilizing. A 50 grain boat tailed bullet can be too long for the rifling yet the same weight bullet in a flat based bullet will stabilize. This could require that you shoot a lighter weight boat tailed bullet to acheive the same degree of stabilization that you are currently seeing with your flat based bullets; lightning the bullet weight shortens the overall bullet length. Also if the bullets get really long even out of rifles with bullets matched to the barrel twist it may require 200 yards for the bullet to go "to sleep" and produce it's best groups; common in long for caliber boat tailed bullets. The boat tailed bullets do load easier do to the tapered base and the cool factor is there, however for the first 150-200 yards the difference in velocity isn't nearly as important as the difference in accuracy. A bullet that's moving a little faster and misses doesn't do nearly as much damage as much as one that connects with it's target in the proper zone.
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  12. #12

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    Just for the record the 53 gr. Sierra #1400 is the bullet my gun likes the best at around 1/2 inch groups at 100 yards. The best I can do with boat tails is around 1 inch at 100 yards. I have tried Hornady, Sierra, and a few others as well. The 52 gr. Sierra #1410 was about 1 and 1/4 inch at 100. I had several of the boat tail bullets in several brands and only a few of the 53 gr. flat base that my gun likes on hand. I did find 200 more of these bullets yesterday but can not find H 380 powder now.

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    Quote Originally Posted by AlaskanTides View Post
    That is an excellent Description……. I think you made my point however when you admitted that there are so many Variables that its near impossible to understand why X affects Y.
    That's cause I agree with you! LOL! I was ignoring all other factors (including the effects of the crown itself) and focusing on only what the difference between the 2 bullets does in flight.

    I guess to me, I feel people can spend a lot of unnecessary time over thinking things instead of just using their gut. Like you said, if you shoot X better, why change unless Y is better than X? If Y is not better, don't try to over think the problem and try to make Y work because some marketing guy said you needed that new product. If you got your caribou with X for the last 10 years, are we suddenly not going to get him this year with the same set up? This is not directed at Cast Iron, don't take it that way. Sometimes it's good to try Y to see if it's better. And if it is, great. If not, no biggie. Unless of course you haven't gotten your game (or your bullseye if you're talking sport) with X for the last 10 years and are trying to fix that. That's different.

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