264 vs 7mm clear as mud
Why can't you use the same charge with the same bullet weight if the cases are almost exactly the same size if you don't count the case neck?
I tried to offer some thoughts on the comparison on another thread, then found my answer was clear as mud because I didn't proofread it. The thread is now locked so I can't even edit or delete my reply. I didn't wind up selecting either caliber but I think I've got a pretty good lock on how it works.
There are a few different things going on which keep you from being able to use the same powder charge even if the bullets weigh the same and the rounds were loaded to the same pressure.
The pressure limit difference is probably just because two different companies designed the rounds in two different decades. I.e. a matter of taste and preference on the part of the designer. The 7mm and 264 have the same base diameter so they put about the same stress on the action for a given amount of PSI.
Even if they used the same max pressure and bullet weight, though, the 7mm makes space for the burning powder faster.
*The bullet has more area so it would get a harder push from the same PSI.
*The bigger bore means it makes space faster even if it wasn't going faster.
If they had the same max psi and bullet weight, the only way they'd have roughly the same powder charge size is if the 264 used a slower burning grade.
The same grain weight will be a bit slower but will be more ballistically efficient from the 264. It would also penetrate better.
The 264 should also have a milder kick.
I tried to offer some thoughts on the comparison on another thread, then found my answer was clear as mud because I didn't proofread it. The thread is now locked so I can't even edit or delete my reply. I didn't wind up selecting either caliber but I think I've got a pretty good lock on how it works.
There are a few different things going on which keep you from being able to use the same powder charge even if the bullets weigh the same and the rounds were loaded to the same pressure.
The pressure limit difference is probably just because two different companies designed the rounds in two different decades. I.e. a matter of taste and preference on the part of the designer. The 7mm and 264 have the same base diameter so they put about the same stress on the action for a given amount of PSI.
Even if they used the same max pressure and bullet weight, though, the 7mm makes space for the burning powder faster.
*The bullet has more area so it would get a harder push from the same PSI.
*The bigger bore means it makes space faster even if it wasn't going faster.
If they had the same max psi and bullet weight, the only way they'd have roughly the same powder charge size is if the 264 used a slower burning grade.
The same grain weight will be a bit slower but will be more ballistically efficient from the 264. It would also penetrate better.
The 264 should also have a milder kick.
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I've never owned either of the two caliber rifles you mention so I have no knowledge of the ballistics. I do remember a question submitted to the American Rifleman, an old one in my collection, think was 50's, which went like this, "The .303 British and the .30-40 Krag cases are virtually identical. Which is the more powerful round?" I think either General Hatcher or Townsend Whelen answered the question thusly, "The .303 British rifle is proofed at 45,000 cup's and the .30-40 Krag is proofed at 42,000 cup's, making the .303 British the more powerful round. Whether this factor would influence the loadings I have no idea. Just throwing it out for comments. 0 -
A specific rifle powder possesses a finite amount of theoretical energy. All else being equal, I cannot see the .020" difference in bore diameter in having any real impact on the potential energy levels.
These 2 cartridges, properly loaded in a modern rifle, accomplish the exact same task.0 -
With regards to the .303 vs .30-40; the .308 vs .311 diameters are a wash, as are the virtual tie in max PSI... COTW has 180 gr loads within a few FPS and FtLbs of each other (.303 about 60 FtLbs more) I doubt anything hit with either one would tell the difference between the two rounds, which are darn fine short to mid range deer/elk loads...and would dispatch a moose or two as well if called upon.
COTW has 160 gr loads for both the .264 Win and the 7mm rem, the Rem has a slightly larger powder charge, with slightly more velocity and energy cited...so the explanations above make sense regarding the larger max limits of the 7mm Rem load over the .264 Win.
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Have both rounds and have taken deer with both. All that I can say is that with either one if you do your part you better have a sharp knife. 0 -
quote:Originally posted by MG1890
A specific rifle powder possesses a finite amount of theoretical energy. All else being equal, I cannot see the .020" difference in bore diameter in having any real impact on the potential energy levels.
These 2 cartridges, properly loaded in a modern rifle, accomplish the exact same task.
That 0.020" of diameter, provides 21% more surface area for the same amount of pressure to push on, therefor making more energy, providing the bullet weights are the same.
Think of it like this...you have a 1 1/2" open pipe, and a 2" open pipe, both with 100psig of water on them. which is it harder to hold your hand over and stop the water flow?
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The point was why you couldn't use the same charge with the same bullet weight.
The 7mm makes volume faster two different ways. One, the bullet gets a harder push because its base is bigger so it moves further down the barrel than the 264 does in the same amount of time. Two, the bore is bigger.
So you need either a smaller charge or a slower powder for the 264 to keep the pressure safe. both of those things would also help keep it at a lower max pressure.0 -
TSR, that is an interesting point, the water pipe analogy. In the context of burning powder, In my mind I am still holding that a given amount of powder will yield a specific level of energy, and gas volume will remain constant regardless of bore volume. The water pipes are assuming unlimited water volume. All else being equal, the 7mm will have a lower gas pressure at the muzzle than a .264, thus, equal thrust is applied to either diameter.
But, I did not stay at a Holiday Inn last night, and have an open mind to be educated.
Interesting discussion.0 -
quote:Originally posted by MG1890
TSR, that is an interesting point, the water pipe analogy. In the context of burning powder, In my mind I am still holding that a given amount of powder will yield a specific level of energy, and gas volume will remain constant regardless of bore volume. The water pipes are assuming unlimited water volume. All else being equal, the 7mm will have a lower gas pressure at the muzzle than a .264, thus, equal thrust is applied to either diameter.
But, I did not stay at a Holiday Inn last night, and have an open mind to be educated.
Interesting discussion.
That simply is not true, because all of the powder is not burnt inside the barrel. The larger bore will burn more powder, and create more plasma, with all else being equal. The water pipe analogy, does assume that the pressures are constant, and equal, with no shortage of water volume.
There some dynamics of the burning powder, and its behavior, that does factor into this. If you are able to burn more powder at any given time, it creates more plasma, to enhance the dwell time of the pressure applied to the base of the bullet. If you need some of case capacity being the same, but charge weight differ, look at the cartridges based on the 308 Winchester...243 Win, 260 Remington, 7mm-08 Remington, 308 Win, 338 Federal, and 358 Winchester. Albeit small differences, you will notice that going from smallest to largest the powder charge grows too.
Keep in mind, that the pressure created by the burning powder, creating gas and plasma, is static. Being static, it cannot be measured with force measurements. When that static acts on an object, and sets it in motion, then force is created. How much force that is created, is determined by how much of the object(surface area, in this case) is acted upon by the static counterpart(pressure).
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quote:the difference is in the eye of the beholder. ammo for the 7 mag is more available and cheaper but neither really out shines the 270 or 06 on deer and elk
Fortunately, or unfortunately, which ever way, that you wish to behold it, that is simply not true. I do have experience with the 30-06, 260 Remington, 264 win, 7mm Rem Mag, 7mm RUM, 300 Win, and 300 RUM. Of course, the most spectacular performer's are the RUM's.
I can tell you that the 260, will outperform the 270, and depending on if it is dangerous game, the 30-06. The other's on that list will do what the 270, and 30-06 will do, but at 100-200 yards further out. That is fact from experience. But dead, is dead, no matter how you look at it, and shot placement is the most important factor, when harvesting game, next to selecting the proper bullet, for the task at hand.
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the difference is in the eye of the beholder.ammo for the 7 mag is more available and cheaper but neither really out shines the 270 or 06 on deer and elk 0 -
MG1890, the smaller caliber does have more pressure at the muzzle but it doesn't even out. The pressure is higher because the powder did less work.
The work done on the bullet and the volume change are directly proportional.
So the 264, if it had the same bullet weight and same max pressure as a 7mm, would be going the same speed if its barrel was enough longer than the 7mm to make the muzzle pressure equal.
Roughly speaking, of course. there would be a difference in friction, backpressure, and the 7mm would need better progressivity in its powder for best results. Or in other words, there's differences that don't depend on geometry. The smaller caliber needs a less progressive powder because the volume doesn't change as fast.
However, to give it an optimum powder charge, you would have to use slower burning powder in the 264.0
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