School me on case design..
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Kevin Thomas
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1tonpower,
At 3100 fps with a 115 grain bullet, you're getting well into proof load territory with at least two of these cartridges, and way over it with the third. Given realistic loads that fall within SAAMI pressure limits for all three will give you a much better picture of what they're actually capable of individually.
At 3100 fps with a 115 grain bullet, you're getting well into proof load territory with at least two of these cartridges, and way over it with the third. Given realistic loads that fall within SAAMI pressure limits for all three will give you a much better picture of what they're actually capable of individually.
Mikecr
Well-Known Member
I don't see a lot of difference between the 6mm & .243 other than brass brands available.
The 6x47 departs from them, and is superior in design for both reloading precision and LR accuracy over the long run.
Do these things matter to you? Your comparison criteria seems pretty odd.
The 6x47 departs from them, and is superior in design for both reloading precision and LR accuracy over the long run.
Do these things matter to you? Your comparison criteria seems pretty odd.
In the world of super accuracy with rifled barrels at ranges up to 600 yards, the cartridges that make 'em shoot so darned accurate are typically short and fat. That is, they put as much powder as possible as close to the primer as possible. End result's a more uniform push on the bullet so they all leave at the same speed; or as close as possible.
Another very important thing is, the most accurate cartridge cases typically hold one grain of powder for each square millimeter of the bore's cross sectional area. Examples; .222 Rem. .22 PPC, .22BR, 6mmBR, 6mm PPC and 30 BR And in close second places to these are the 6XC and .308 Win. The 22 caliber ones do fine up to 300 yards but beyond that, it's best to use one of the 6mm's or the .308.
Any case that holds more powder is considered by many to be overbore. And these just don't shoot all that accurate...in general. Yes, there's exceptions. But the best odds desired means you'll pick one of the ones listed above. Of the three you mention, the .243 and 6mm Rem barrels will last about one third as long as the 6x47. And with the 6x47's lower recoil levels, it'll be easier to shoot accurately too.
Another very important thing is, the most accurate cartridge cases typically hold one grain of powder for each square millimeter of the bore's cross sectional area. Examples; .222 Rem. .22 PPC, .22BR, 6mmBR, 6mm PPC and 30 BR And in close second places to these are the 6XC and .308 Win. The 22 caliber ones do fine up to 300 yards but beyond that, it's best to use one of the 6mm's or the .308.
Any case that holds more powder is considered by many to be overbore. And these just don't shoot all that accurate...in general. Yes, there's exceptions. But the best odds desired means you'll pick one of the ones listed above. Of the three you mention, the .243 and 6mm Rem barrels will last about one third as long as the 6x47. And with the 6x47's lower recoil levels, it'll be easier to shoot accurately too.
Kevin Thomas
Well-Known Member
1tonpower,
It really depends on what you're wanting to compare here. In terms of velocity, it's really a pretty simple equation; more capacity equals more velocity, all other variables being equal. Those variables are where the rubs come in. If we assume the same barrel length and the same pressures, the larger case will deliver better velocity, although they may do so at a level of diminished efficiency. In other words, you'll start getting less energy "out" in relation to the energy you put "in" straight across the board. Can you get higher velocities out of a smaller cartridge than you do out of a bigger cartridge, all other variables remaining equal? Sure, but you have to go to higher pressures to do so. Again, it comes down to shuffling variables and changing the equation.
Accuracy is another matter, and one in which there is at least a fairly constant trend; smaller is better. Bart mentioned the short/fat concept, and this definately plays into it, but case capacity is a real indicator over long run averages. To put it bluntly, a 300 Win Mag is more accurate than a 300 RUM or 300 Wby Mag, a 30-06 is more accurate than a 300 Win Mag, and a 308 Win is more accurate than a 30-06, and a 30 BR is more accurate than a 308 Win.. Improtant to note that we're talking averages here, not inidividual rifles. The NRA HighPower series they did several years back had an excellent write-up on the average accuracy of Remington 40-Xs from their Custom Shop, with accuracy averages in a variety of chamberings. All identical guns, same make of barrel, same action, everything, and an average of hundreds of different guns over a period of several years. There was a direct (and inverse) linear relationship between case capacity and accuracy. Now, that said, you still need to match the cartridge to the job at hand. If I'm building a 30 caliber gun for 1000 yard competition, it's probably going to be a 300 Win Mag, not a 30 BR, if you get my drift.
Don't let these design features or attributes blind you to what the ultimate purpose of the gun is to be. They all have their place, and they're all something of a trade-off between positives and negatives.
It really depends on what you're wanting to compare here. In terms of velocity, it's really a pretty simple equation; more capacity equals more velocity, all other variables being equal. Those variables are where the rubs come in. If we assume the same barrel length and the same pressures, the larger case will deliver better velocity, although they may do so at a level of diminished efficiency. In other words, you'll start getting less energy "out" in relation to the energy you put "in" straight across the board. Can you get higher velocities out of a smaller cartridge than you do out of a bigger cartridge, all other variables remaining equal? Sure, but you have to go to higher pressures to do so. Again, it comes down to shuffling variables and changing the equation.
Accuracy is another matter, and one in which there is at least a fairly constant trend; smaller is better. Bart mentioned the short/fat concept, and this definately plays into it, but case capacity is a real indicator over long run averages. To put it bluntly, a 300 Win Mag is more accurate than a 300 RUM or 300 Wby Mag, a 30-06 is more accurate than a 300 Win Mag, and a 308 Win is more accurate than a 30-06, and a 30 BR is more accurate than a 308 Win.. Improtant to note that we're talking averages here, not inidividual rifles. The NRA HighPower series they did several years back had an excellent write-up on the average accuracy of Remington 40-Xs from their Custom Shop, with accuracy averages in a variety of chamberings. All identical guns, same make of barrel, same action, everything, and an average of hundreds of different guns over a period of several years. There was a direct (and inverse) linear relationship between case capacity and accuracy. Now, that said, you still need to match the cartridge to the job at hand. If I'm building a 30 caliber gun for 1000 yard competition, it's probably going to be a 300 Win Mag, not a 30 BR, if you get my drift.
Don't let these design features or attributes blind you to what the ultimate purpose of the gun is to be. They all have their place, and they're all something of a trade-off between positives and negatives.
Thanks for the thoughts.. Now Ill let it soak in for a bit. Some of what was said I have read before some is new info. I don't have any plains on shooting rifle comp at this point in time. I'm more interested in long range hunting and shooing for funn..
You make sense-I didn't know any of that. What causes a barrel to shoot out? How can the recoil vary much between the 3? (energy out equals energy back)
By your estimate, then, a .270 should have an accuracy advantage over a 30.06, but not much bullet availability on the higher side. Why is that? Seems like a very long .270 bullet in the 180-200 gr range would have a great BC. Some bullet manufacturers make 150 gr max.
Are you talking about water capacity or the actual powder weight?
If actual powder weight would you search for a powders bulk density ( within the appropriate burn rate ) to maximize this relationship?
Interesting concept that I never considered before.
edge.
Jim asks me:
Burning powder escaping around the bullet as it enters the rifling acts like a cutting torch. It removes metal at the origin of the rifling. When that gets eroded away too much, the first thing noticed is a drop in muzzle velocity, then accuracy goes bad.[/QUOTE]
Two of 'em burn much more powder pushing out heavier bullets. And those two move the rifle around more while the bullet's going down the barrel. It's the recoil you don't feel while this happens that moves the barrel axis around a little bit.
As the .270 is a little more overbore than the .30-06, it has a slight accuracy disadvantage.
Bart, thanks for the education. How about the .308 Palma Lapua, with the small primer. What physical effects would improve the accuracy by changing to the smaller primer? Intuitively, it would seem to slow the powder burn. Also, there apparently is a tradeoff between barrel length and accuracy. Some of the bullet stabilization problems would seemingly be enhanced with longer barrels, say 34",
but they would have to be extremely heavy. Seems like a long barrel, slower burning powder, and progressive twist would be a solution for stabilization and improved velocity. The new bullet designs by Berger are bumping up against this problem.
but they would have to be extremely heavy. Seems like a long barrel, slower burning powder, and progressive twist would be a solution for stabilization and improved velocity. The new bullet designs by Berger are bumping up against this problem.
Kevin, that's the best statement I've come across for case size vs. long range accuracy. Very well stated.
I've oft times suggested folks wanting good long range accuracy for shoulder fired rifles is to pick the one with the least recoil that delivers acceptable down range ballistics. My reasoning has been based on their being easier to shoot accurate more consistantly. The rifle shooting them moves less while the bullet's going down the barrel. Without perfect follow through, the muzzle will be pointing a bit off from where it should be to put the bullet exactly on the aiming point.
While there's always great accuracy claims for really big cases, they're typically the very best a case has done. The worst, or what accuracy they produce and therefore count on all the time, is rarely, if ever mentioned.
I've had excellent results using Remington .308 Win. cases with small primer pockets. had to use Rem. 7.5 primers and they did very well. I watched the guy shooting Sierra 200 HPMK's from his .308 full of IMR4350 using these cases and primers set a 600 yard prone record at the Nationals in the late 90's. He put 20 shots inside 4 inches....with aperture sights.
Mild primers were found to work very well in the .308 Win. from an interesting test. A .17 Rem. barrel was shortened then some cases' primer pockets reamed out to hold large rifle primers. Those cases were primed then a BB put in the case mouth. BB's were shot through a chronograph and velocity noted. Some primers produced very uniform average velocities, some very fast but inconsistant and some low velocities that weren't always too consistant. When the primer lots were sorted as to the BB test performance, the mildest ones produced the best down range accurace from a .308 rifle clamped in a machine rest. Even better than match primers producing very consistant medium velocity with those BB's. After learning this, I switched to RWS5341 primers, the mildest large rifle primer made at the time. Even with my .30-.338 Mag, best accuracy at 1000 yards was attained with these very mild primers burning about 65 grains of IMR4350 under 190 and 200 gr. HPMK's; in both hot and cold weather. My last barrel put 30 consecutive shots in about 5 inches when I tested it with those mild primers.
Another "ignition" device was tried by a couple of high power competitors that also worked well. The flash hole in a regular .308 Win. case was drilled out then threaded for a brass tube over an inch long. The tube's hole was about .060" and carried the primer flash up close to the shoulder so the powder would burn from the front to the back inside the case. This also worked very well, but the work required to drill and thread the flash hole, make, thread then install the flash tubes, and finally have to use a 2 inch long decapping pin to push the fired primer out was just too much. Using a good lot of primers did just as good.
From the accuracy levels I've observed with both long and short barrels for a given cartridge, barrel length isn't an issue. If it was, then 30 to 32 inch whippy Palma rifle barrels would never shoot 1/2 MOA at 800 to 1000 yards with good bullets, which they do. They're just as accurate as a stiff 22 inch .308 Win. barrel in a rail gun testing those same 30 caliber bullets at 100 or 200 yards shooting groups with the best bullets in the 1/10th to 2/10ths MOA range that open up to 1/2 MOA at long range.
Virtually all cases shoot bullets the most accurate when a medium speed powder's used for its case size. For example, folks using the .308 Win. to do best use Varget and IMR4895 speed powders for light bullets, IMR 4064 speed for medium and IMR 4350 speed for the heavies. These seem to produce the best push of the bullet into the rifling and velocity control as they leave. While slower powders for a give case can produce higher velocities with heavier bullets, they typically do so at the expense of low velocity spreads. I'll gladly give up 50 to 100 fps in muzzle velocity for a 20% gain in accuracy at long range.
Bullet stabilization levels happen when the bullets are perfectly balanced when they leave the barrel and are spinning at the rpm needed to keep their long axis parallel to the trajectory. Which means the bullets have to be perfect in shape, mass and center of gravity on the center of form....and none of that's disturbed when it's fired. So the barrel's got to be perfect, too. There's all sorts of things that can distort and unbalance bullets; some when made, others when fired.
I don't think progressive, or gain twist barrels are a good idea. A century ago, they worked well for lead bullets, but these days I dont' believe they'll consistantly do well. Comments from top match rifle barrel makers reflect their knowledge that the biggest single flaw in barrels that causes accuracy is an inconsistant twist rate. When the twist rate changes, it moves jacket material around on the bullet and can easily upset its balance. Unbalanced bullets just don't shoot accurate.
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