Denton<

grass pants, I can see you have been to the local area here.

As I always say to people who are from out of town, when they spell it, is to not forget the letter P in Grants Pass.,

Ol Denton, must be in the business of some sort with all of that loading equipment and testing equipment.

However, several cartridges I have been able to get quite a bit velocity out of them, compared to what is listed. Just an educated guess, and working up.

Seating depth can have a lot to do with it also. I usually seat the bullets as long as I can get them. Often I have the chamber reamed out to be able to seat bullets to the length of the magazine.

My Remington 260 VLS actually was reamed out a fair amount.

Still once again, pay attention to ballistic charts, or trajectory charts. In a 6.5 mm bullet, based on their High BC and aerodynamic capabilities, a hundred or 200 fps is not going to really dramatically increase the flatness of the trajectory at 300 or 400 yds. Why try to plaY with higher pressures in that instance? Or more recoil.

Once gets to the point of diminishing returns. Like in the 25 caliber bore, what does a 25/06 do that is all that more improvement on a 257 AI or even a handloaded 257 Roberts?

Powder companies, and Rifle Companies and barrel makers do want you to shoot bigger cased cartridges/ It is good for their sales. Burn more powder, burn out barrels faster, and supports the economy.

Like when I use to live in Wisconsin. What was called an alcoholic in Minnesota, was called a Patriot in Wisconsin. Drinking all that beer he was supporting all those breweries, and the economy of Wisconsin.

Drink UP!

How i can calculate efficency in a cartridge? for see if it is overbore or not? Is there formula? thanx

Here's the best info I have on that. It comes from P O Ackley, vol 1, paraphrased:

Increase the powder charge, grain by grain, watching both muzzle velocity and chamber pressure.

Graph chamber pressure and muzzle velocity on the same graph, using separate scales for each.

As you increase charge, pressure will go up. Actually, pressure isn't linear, but increases in a fairly gentle exponential fashion.

As you increase charge, muzzle velocity will go up linearly for a while, and then the curve will start to flatten out. You'll be getting 50 fps per grain for a while, then 35, then 20, and finally none.

The place that the exponential nature of the pressure curve starts to make it climb steeply, and the muzzle velocity curve starts to flatten is called the "delta".

Above the delta, you're overbore, and your efficiency is falling as you increase charge.

"Overbore" is a term that really has no definition. It should be avoided. It's been most generally used to mean a case big enough relative to the bore that no powder available can be used in a full capacity load without exceeding safe pressure limits, but it's often used much more loosely. There's no usable general formula for the efficiency of cartridges, as the optimum powder types change with the relationship of the case volume, bore diameter and bullet sectional density. But it's a general rule that as the case capacity goes up, the velocity gain goes up far more slowly. It's related mainly to the expansion ratio, the ratio of the total volume of the whole chamber and bore together to the initial powder space in the case under the bullet, higher ratios being more efficient. But since in rifles the powder doesn't burn all at once in a constant volume, the actual peak pressure is developed when the bullet's moved some variable distance down the bore, throwing those calculations off. What's actually used are empirical relationships with built in "fudge factors." A good introduction to internal ballistics is available at: http://www.fabriquescientific.com/

Ummm.... I guess Ricochet and I amicably disagree.

It is true that there is not bright line that tells exactly where overbore begins. Overweight isn't precisely defined either, but it's a useful concept.

I find it a lot simpler to say "The cartridge is overbore" than to say "There has been so much powder added to the cartridge, that efficiency is dropping".

The consideration that seems to have been left out of this discussion of ballistics so far is "time".



Bullet velocity is roughly a product of base area of the bullet (what the gas pushes against), inertia & friction (directly related to how much force is necessary to to overcome the innate tendency of the bullet to not move, which is related to mass), pressure (the force available...a varying product of primer & powder burning), and the time the pressure is applied.



Bullets of the identical size and composition, operating in cartridges at identical peak pressure, can have very different velocities when using different powders.



For instance, the 350 gr. bullet of the .416 WSM (a wildcat called the 416 Ridgerunner, developed by K. Ewing of Bonner's Ferry, ID) travels approximately 1.1" in the bore while the powder gases stay at peak pressure, if using VV-N135. With every other powder appropriate to the capacity of that case, the bullet travels from slightly less than 1.1" to less than 1.0" while the pressure remains at maximum.



The result is that VV-N135 gives the highest velocity with that bullet in that case. That's because the chosen peak pressure (and the area under the curve in a pressure graph) is/are applied for more time than powders of other burning rates.



Put it a different way, the 416 WSM is slightly overbore capacity for most fast/medium burning rate powders, but it is close to the ideally correct powder capacity for the VV-N135 at the chosen max pressure of 54,000 psi.



Similarly, one reason a .264 Win Mag can get more velocity than a 6.5x55 is because one can use more of a slower burning powder at the same pressure, and apply the force (max pressure) longer. The velocity produced would be even greater than it is, if longer barrels were practical. Even when pressure has dropped to about 6,000 psi, as it may at the muzzle, it is still boosting acceleration of the bullet.



When one says a case is "overbore capacity", they really are saying its capacity is too big to hold the optimum amount of powder that will burn in that barrel at a designated acceptable peak pressure (bore diameter & length determine bore capacity).



AC

I think you're exactly right, right up to the point that you picked your example of the 264 Mag vs. the 6.5x55. They both thrive on exactly the same slow powders, which is not the usual case.



I truly do not understand how Sven and Ole did it, but the 6.5x55 is the the most forgiving cartridge I've ever shot. Feed it RL22, or H4350, or H4831 or anything in that ballpark, and it will always do well. I routinely get single digit MV SD's without any extra effort at all. Somehow, my Swede just seems to always want to delight me. I have others that seem to want to fight with me.

What that indicates to me is that the correct powder is not being used in the .264...maybe because no powder of exactly the correct burning rate is available to use in it.

There is no magical "design" way to get around physics, but we may not be able to apply physics at its optimum performance if we don't have the ingredients to do so.

Best wishes,

AC

H-870 is the perfect .264 win powder

Getlemen

It seems that RL 22, Norma MRP 2 and Vitavouri N-165 and N-170 would be best powders. We have not tried any US. made powders.

/ JOHAN

I'm in the middle of reading "Rifle Accuracy Facts" by Harold Vaughn. Some of the guys on the board had recommended it, and it turns out to be a very interesting, useful book.



One of the problems he laments is that most bullets do not have a long enough cylindrical rear section. That causes the bullet to cant in the bore, and when it exits, that causes inaccuracy.



The 6.5mm bullet is exceptionally long and skinny, and probably does not have that problem. It sounds like that contributes to its characteristic accuracy. I wonder if the Swedes got that right by accident, or if they were just the best ballisticians of their time?? Just one more reason to love the Swede.



BTW, Harold is an aerodynamics guy, and he looks to be well into retirement. This guy is doing his research by hauling an old Tektronix 555 oscilloscope, about 60 pounds, and full of vacuum tubes, around in the back of his pickup, with a generator to run it. Now that is a guy dedicated to making his decisions based on data.



He also makes a really good case for a different barrel-receiver joint. I'll have to go read Savage's web page, but I think it is the lock nut system that they are now using. (Edit: Nope. The Savage system is different.)

Denton, or anyone else.

Would you please comment on thbe 6.5 x 55 Improved? I am very intrigued by this cartridge and its apparent potential. I have a Swedish Mauser which has been sporterized and with a "cock-on-opening" kit installed. I am toying with the idea of punching it out to 6.5 x 55 Improved, just for fun. Can this twin lugged milsurp action handle this "improvement" and the resultant pressure? I've seen some numbers indicating that 3050 fps is reasonable with a 140 grain bullet. It seems to me that this could be excellent
mule deer and elk medicine.


Jordan

The Swede's didn't invent the 6.5x55, Paul Mauser did!

Maybe someone with one of the load estimation programs can run the numbers on a 6.5x55 AI. My guess is that it won't make much difference, since the cartridge is already a little overbore.

Mauser invented the 6.5x55? I didn't know that. So the Swedes just adopted a done design?

Denton

When Sweden bought the 1896 rifle they wanted a cartridge for it. I guess mauser designed one in co-operation with some technical staff from the buyers (Sweden in this case). When the nowegians bought a their rifles they made a slight modification in the cartridge design soo that norwegian ammo would not work in a Swedish rifle(hope I remeber correctly). To my knowledge there has never been any other army that have adopted 6,5X55 cartridge.

Now, "overbore" or not is for each to decide. Some say that 6,5BR is the most well balanced

/ JOHAN