243 Boattails
My Speer manual warns against using Spitzer loads for boattail bullets. No problem, I'm literate. I can follow directions and I'm meticulously cautious about working up loads from the bottom.
But I'm left wondering about the physics of this. What causes pressure spikes in boattail loads for this on particular caliber?
Thanks in advance for your learned responses.
But I'm left wondering about the physics of this. What causes pressure spikes in boattail loads for this on particular caliber?
Thanks in advance for your learned responses.
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BT's usually have a longer bearing surface than a Flat base bullet for a given weight thereby creating more friction and drag on the bullet while in the bore, raising pressures.
THIS SHOULD BE IN THE RELOADING FORUM!0 -
quote:Originally posted by bpost
BT's usually have a longer bearing surface than a Flat base bullet for a given weight thereby creating more friction and drag on the bullet while in the bore, raising pressures.
THIS SHOULD BE IN THE RELOADING FORUM!
It was in the reloading forum.
Where it languished for several hours without a look. So screw that.
The older I get, the less time I have to wait around for an answer, so I thought I'd pose it to all you know-it-alls.[:D]
Thanks for you answer, by the way. But why wouldn't every other rifle caliber also have the same admonition? Only the 243 does.0 -
quote:Originally posted by Colonel Plink
quote:Originally posted by bpost
BT's usually have a longer bearing surface than a Flat base bullet for a given weight thereby creating more friction and drag on the bullet while in the bore, raising pressures.
THIS SHOULD BE IN THE RELOADING FORUM!
It was in the reloading forum.
Where it languished for several hours without a look. So screw that.
The older I get, the less time I have to wait around for an answer, so I thought I'd pose it to all you know-it-alls.[:D]
Thanks for you answer, by the way. But why wouldn't every other rifle caliber also have the same admonition? Only the 243 does.
The 243 is one of those very sensitive cartridges we run across. It is overbore and has exhibited strange pressure issues when the slightest change is made in loads from primers to seating depths, spikes can be quite high and unexpected.
It takes very slow powders to get top performance from it. The 6BR is just as capable, burning about 10 grains less powder to do the same job. It is one of the reasons I got rid of all the 243's I had.
Sorry I did not get to your question earlier. I was out hunting the wily American White tail deer, the does walked by at 180 yards from the blind I was in, 40 -50 yards from the one I was not in. Go figure.0 -
Should have kept one .243 and loaded it with some boat tails!!![:D]
I think they can not be seated as far out so more of the powder space is taken up with bullet even though the front of the shank is just as close to the rifling.
I think Speer also does not use its "Hot-cor" process with boattails, so the jacket material may be a different hardness, thickness, or composition.0 -
quote:Originally posted by bpost
BT's usually have a longer bearing surface than a Flat base bullet for a given weight thereby creating more friction and drag on the bullet while in the bore, raising pressures.
THIS ... FORUM!
I would have to disagree with this statement. Of all the .243(6mm) bullets I reload with boat-tails I've found the bearing surface is usually smaller.
I find the problem with .243 boat-tails is boat-tails in general are not as internally ballistically efficient as flat base bullets. The easy thing to see is as pressure builds in the case during ignition, the pressures do not push at a 90* angle to the base, like a flat base. As pressures increase behind a boat-tail, because those pressures are not 90* to the base, they want to squish the guts (bearing surface) outward. But this is not a strong effect.
Anyhow, where I do find a big difference in bearing surfaces is from Spitzers to round nose bullets.
It's all academic though, if you are following good reloading practices by starting low, where you should, and working up.0 -
quote:I find the problem with .243 boat-tails is boat-tails in general are not as internally ballistically efficient as flat base bullets. The easy thing to see is as pressure builds in the case during ignition, the pressures do not push at a 90* angle to the base, like a flat base. As pressures increase behind a boat-tail, because those pressures are not 90* to the base, they want to squish the guts (bearing surface) outward. But this is not a strong effect.
Anyhow, where I do find a big difference in bearing surfaces is from Spitzers to round nose bullets.there is no effect. It exactly evens out, because the amount of area facing backward is the same as a flat base. It's a well-settled principle, even though I can't think of a clear way to put it just now.
I have looked at some round noses and put some in calipers. Their sides are not as straight as they look. They often start to taper just a bit, just ahead of the canellure. If they were really parallel right up to the round nose, then they wouldn't chamber in most rifles.0 -
quote:Originally posted by SoreShoulder
quote:I find the problem with .243 boat-tails is boat-tails in general are not as internally ballistically efficient as flat base bullets. The easy thing to see is as pressure builds in the case during ignition, the pressures do not push at a 90* angle to the base, like a flat base. As pressures increase behind a boat-tail, because those pressures are not 90* to the base, they want to squish the guts (bearing surface) outward. But this is not a strong effect.
Anyhow, where I do find a big difference in bearing surfaces is from Spitzers to round nose bullets.there is no effect. It exactly evens out, because the amount of area facing backward is the same as a flat base. It's a well-settled principle, even though I can't think of a clear way to put it just now.
I have looked at some round noses and put some in calipers. Their sides are not as straight as they look. They often start to taper just a bit, just ahead of the canellure. If they were really parallel right up to the round nose, then they wouldn't chamber in most rifles.
Would you mean to say that the total surface area of the boat-tail being pushed by an angular vector achieves the same results as a lesser surface area being pushed at a perpendicular (most efficient) is equal?
Having fired many thousands of both I would have to disagree. I have not seen anywhere where the principle is settled. Only that we who shoot long range, have accepted the loss of efficiency with a boat-tail in regards to internal ballistics to gain the external ballistic advantage.0 -
Nope, if there's a difference in muzzle velocity then it's something else.
You haven't been comparing hunting bullets to Matchkings, have you? Those have thinner jackets.0 -
YEARS AGO...I used to reload my 270 Ruger 77. I found the 150 grain flat base (pointed) much more accurate than the 150 grain Sierra Boat Tails. 0 -
quote:Originally posted by SoreShoulder
Nope, if there's a difference in muzzle velocity then it's something else.
You haven't been comparing hunting bullets to Matchkings, have you? Those have thinner jackets.
That is another issue. But, a valid one. To address it, I generally compare matchkings to A/V-max and Custom Comps and Berger and in many cases the standard what is now called Game-kings. The pro-hunter made by Sierra I understand to be of heavier construction.
In any case, there is more resistance when the bearing surface is being engraved. once that has happened the resistance is the same as any other bullet. There is a brief spike in pressure. The closer heavy jacketed bullets are to the lands the more spike you will see. Again, though, this is copper and lead with a softness to perform in this role, and the forces to overcome these factors aren't huge on the whole.
Overall, I still say you will lose some velocity with a boat-tail style bullet over a flat base bullet simply for the efficiency.
And, as I noted in my first post, how much of a factor is immaterial if you start out where you are supposed to and work up. Each rifle has a difference that bullet manufacturers can't account for. We have to be that safety margin. So, IMO, if you had two 100 gr. bullets of different styles you wanted to load, it would be safe to assume you could work ladders up with each from one starting point.0
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