Cartridge accuracy....

[Bart B.]

In the course of testing hundreds of different guns, all of the same make and builder, differing only in caliber, there was one thing that jumped out; size does matter. In short, the smaller the cartridge, the more accurate the long-run average of multiple guns. A 30-338 was more accurate than a 300 Win Mag, a 30-06 was more accurate than the 30-338s, and the 308 Wins were more accurate than the 30-06s. The same thing held true over a wide range of bore sizes and a large number of different cartridges.

The death knell of the 30-06 in NRA match rifle competition started at the 1964 Nationals when Mid Tompkins was the first to use the 308 Win. Over the next 3 years, all the match records were broken. They used to be held by the 30-06. Only thing that changed was the cartridge and barrel chamber. 600 yard test groups went from about 6 inches to under 4.

3 years later, scoring ring sizes through 600 yards were about halved as too many unbreakable ties were shot.

7 years later, Mid Tompkins shot some 10-shot test groups at 600 yards with his 308 that ranged from about 3/4" to 1-1/2". Then put 40 inside 1-15/16".

 

[Bart B.]

Hmmm. Long case.....short neck.....belted head......everything that's not spoze to shoot these days. Yep the 300 Winchester Magnum....Our Military's new sniper cartridge. This stuff confuses me!

Look up the accuracy specs for the MK248 300 win mag US military sniper ammo. Not impressive at all. 9 inches at 600 yards. It'll be near twice that at 1000.

That said, the US Army and Marine Corps teams won lots of matches using new 300 win mag cases. Set some records, too, as that ammo tested sub MOA @ 1000 in their match rifles.

 

[barefooter56]

Look up the accuracy specs for the MK248 300 win mag US military sniper ammo. Not impressive at all. 9 inches at 600 yards. It'll be near twice that at 1000.

That said, the US Army and Marine Corps teams won lots of matches using new 300 win mag cases. Set some records, too, as that ammo tested sub MOA @ 1000 in their match rifles.

So was it the ammo or the shooter?

 

[gunsandgunsmithing]

Look up the accuracy specs for the MK248 300 win mag US military sniper ammo. Not impressive at all. 9 inches at 600 yards. It'll be near twice that at 1000.

That said, the US Army and Marine Corps teams won lots of matches using new 300 win mag cases. Set some records, too, as that ammo tested sub MOA @ 1000 in their match rifles.

I think it's safe to say that a 300 Win Mag is better than those specs. I've had better hunting rifles.

 

[Dusty Stevens]

I think it's safe to say that a 300 Win Mag is better than those specs. I've had better hunting rifles.

This just goes to show that nobody looks to military testing for actual real accuracy... well one guy does

 

[Bart B.]

So was it the ammo or the shooter?

Phil,

Most military sniper rifles and their ammo were tested with the rifle in an accuracy cradle. Never seen any pictures of one. A review of one cradle mentioned that besides the rifle stock being clamped solid, so was its barrel at the muzzle.

300 WIN Mag target rifles and ammo in military teams were typically sand bagged to test for accuracy. A good marksman can asses their accuracy in calm winds by how far shots strike from call.

I see you're with Lapua. Mid Tompkins shot those sub 2" groups back in 1971 with Lapua D46 185 grain FMJRB match bullets. One group under an inch was pictured in a late 1971 issue of The American Rifleman magazine add for Lapua Bullets. Kevin Thomas knows about that test.

 

[270WinDude]

Is there any one place some one could turn to so as to get any wildcat testing that's been done along with notes? Or any good recommendations for reading, not talking something very specific but something that can help turn on some lightbulbs or big picture type testing. It seems like if some one wanted information like that they'd have to spend countless years in the community learning the who's-who of wildcatting from days past and current and then even more time reading their books if any. You'd think the weapon manufacturers would keep some sort of database even if proprietary and not released to the public but maybe employees could talk about.

Just looking at my 270win, it's design for modern bullets is strange to me. I'm seating bullets past the neck area into the case body, creating more area and angles of the bullet exposed to the charge and other variables for non uniformity, for non compressed charges, not perfect chambers, not perfectly concentric brass, it just adds to all the existing variables for precision. The alternate would be seating a flat base bullet perfectly aligned with the brass' case and back of neck. I've never seen a highly accurate PPC, BR, ETC in person but I'm curious as to bullet seating depth in relation to the case and neck, I doubt it has any significant role but I'd like to look for patterns there. The example of how the 30-06 was literally swept away in precision by the 308 without conclusive reasoning really blows my mind. I'm certain quality of equipment has risen at a rate correlated with the rise of 308win vs 30-06 but just not exactly.

P.S. Has anyone built and shot the 270-300Win Mag from Pac Nor??? I'm curious the accuracy, I assume not precision level but still curious.

 

[270WinDude]

The brass condition / management factor seems to be as important as the short fat case factor, and maybe the 6PPC just has the perfect case capacity / powder charge weight to bore ratio. (But if so, then why would the .22PPC also be a super performer with a much different case capacity to bore ratio, likewise the .30BR vs 6mm BR?)....

I had that same question. Some like the BR chamberings are very accurate even when bore size changes. I suspect that the charge to bore ratio plays a role but bore size as a direct variable in the equation, pertaining to precision, is probably not that sensitive in tolerance, as seen in the PPC and BR examples, and possibly even the creedmoor example. (although, at least with the 6mm creedmoor, I'm not certain it's more precise of a cartridge then a well built 243win which has a similar capacity but pretty different design..) Again, I'd like to see in person where the bullets are seated to in the 22-30brs. After re-reading this thread, lots of good info. I might make a list of all the variables talked about then start an argument on order of importance of them.

 

[gunsandgunsmithing]

I had that same question. Some like the BR chamberings are very accurate even when bore size changes. I suspect that the charge to bore ratio plays a role but bore size as a direct variable in the equation, pertaining to precision, is probably not that sensitive in tolerance, as seen in the PPC and BR examples, and possibly even the creedmoor example. (although, at least with the 6mm creedmoor, I'm not certain it's more precise of a cartridge then a well built 243win which has a similar capacity but pretty different design..) Again, I'd like to see in person where the bullets are seated to in the 22-30brs. After re-reading this thread, lots of good info. I might make a list of all the variables talked about then start an argument on order of importance of them.

No need to argue. Just try some Varget in a 30BR and report back. Lol!

 

[Bart B.]

The example of how the 30-06 was literally swept away in precision by the 308 without conclusive reasoning really blows my mind. I'm certain quality of equipment has risen at a rate correlated with the rise of 308win vs 30-06 but just not exactly.

The 308's big advantage back then was its shorter, fatter powder charge space. Next was a sharper case shoulder angle. And its chamber throat was 1.5 degrees instead of 2.5 like the 30-06 was back then. Milder recoil during barrel time was a smaller advantage for 308's making it a little easier to shoot rifles precisely hand held to the shoulder.

The only things that's significantly improved since then, in my opinion, are bullets and sights. Sierra's switch from FMJBT 30 caliber heavy match bullets to HPBT design was a major breakthrough in the early 60's.

P.S.
I remember Sierra's ballistic tech saying the 300 Savage was a more accurate cartridge than the 30-06. No wonder Frankfort Arsenal got several thousand 300 Savage cases from Winchester to develop the military cartridge that replaced the 30-06. They also got better accuracy with all the military bullets with 1:12 twists in spite of shooting them 100 fps slower in the new cartridge.

How 'bout the even smaller 30 BR cartridge shooting 115 to 125 grain bullets in 1:17 or 1:18 twists bringing home most of the marbles in short range score matches?

 

[Bart B.]

I suspect that the charge to bore ratio plays a role but bore size as a direct variable in the equation, pertaining to precision, is probably not that sensitive in tolerance, as seen in the PPC and BR examples, and possibly even the creedmoor example.

One thing I've noticed over the years is cartridges favored for best accuracy tend to burn powder charges whose charge weight numbers in grains are about the same as the bore cross section area in square millimeters.

That's my definition of bore capacity. 30 caliber bore's number is 46. 308 Win charge weights average 46 grains. Bore cross section area for 30 caliber (7.62mm) is about 46 square millimeters.

 

[M14AMU]

I won lots of junk shooting a 300 Win Mag in 1000 yard prone matches back in the day. There were a couple things I did to enhance that situation! The main thing was not relying upon the belt to establish correct headspacing from cartridge to cartridge!

 

[Dusty Stevens]

Is there any one place some one could turn to so as to get any wildcat testing that's been done along with notes? Or any good recommendations for reading, not talking something very specific but something that can help turn on some lightbulbs or big picture type testing. It seems like if some one wanted information like that they'd have to spend countless years in the community learning the who's-who of wildcatting from days past and current and then even more time reading their books if any. You'd think the weapon manufacturers would keep some sort of database even if proprietary and not released to the public but maybe employees could talk about.

Just looking at my 270win, it's design for modern bullets is strange to me. I'm seating bullets past the neck area into the case body, creating more area and angles of the bullet exposed to the charge and other variables for non uniformity, for non compressed charges, not perfect chambers, not perfectly concentric brass, it just adds to all the existing variables for precision. The alternate would be seating a flat base bullet perfectly aligned with the brass' case and back of neck. I've never seen a highly accurate PPC, BR, ETC in person but I'm curious as to bullet seating depth in relation to the case and neck, I doubt it has any significant role but I'd like to look for patterns there. The example of how the 30-06 was literally swept away in precision by the 308 without conclusive reasoning really blows my mind. I'm certain quality of equipment has risen at a rate correlated with the rise of 308win vs 30-06 but just not exactly.

P.S. Has anyone built and shot the 270-300Win Mag from Pac Nor??? I'm curious the accuracy, I assume not precision level but still curious.

Not many people that win many matches on a regular basis seats the pressure ring of the bullet past the neck/ shoulder junction. If youre seating the pressure ring past the neck you need to throat it out so the bullet sits right- a throating reamer will do this nicely. But at the end of the day if youre looking for pure accuracy youll have to give up on the 270. I know you like it and its a decent hunting caliber but like the 25 cal it just aint going anywhere in the accuracy world.

 

[Bart B.]

I won lots of junk shooting a 300 Win Mag in 1000 yard prone matches back in the day. There were a couple things I did to enhance that situation! The main thing was not relying upon the belt to establish correct headspacing from cartridge to cartridge!

Some belted case chambers were short shouldered so new cases would headspace there instead of the belt.

 

[270WinDude]

Not many people that win many matches on a regular basis seats the pressure ring of the bullet past the neck/ shoulder junction. If youre seating the pressure ring past the neck you need to throat it out so the bullet sits right- a throating reamer will do this nicely. But at the end of the day if youre looking for pure accuracy youll have to give up on the 270. I know you like it and its a decent hunting caliber but like the 25 cal it just aint going anywhere in the accuracy world.

Good info, I will have to look into getting that done. Plus it answers my question on the matter. I'd have to double check but almost certain a lot of my bullets like the VLD 140s are seated past what I think you're calling a pressure ring. Something to look into for me any way, thanks.

 

[Dusty Stevens]

Good info, I will have to look into getting that done. Plus it answers my question on the matter. I'd have to double check but almost certain a lot of my bullets like the VLD 140s are seated past what I think you're calling a pressure ring. Something to look into for me any way, thanks.

The pressure ring is either the base of a flat base bullet or the last part before the bt. It measures bigger so if you have a mic you can see the exact spot i mean. Here is a quick pic- you can see the fattest part (right above the bt) is in the neck