Home Forums Hunting & Shooting Ask The Gunwriters 6.5 Creedmoor Inherently Accurate?

More than one of the pressure labs I deal with has noted larger pressure variations in the .243 Winchester and 7mm Remington Magnum than most cartridges--not just "spikes" but lower variations as well. In the .243 its apparently most common with heavier bullets; dunno about the 7mm RM.

Have also read and been told that's why the SAAMI maximum average pressure level (MAP) of both cartridges was reduced after after electronic pressure-testing equipment became common, because it could detect those pressure variations, which weren't apparent with copper-crusher equipment.

No doubt somebody will soon post that they've never "seen" this when handloading for either cartridge.

RE: Pressure spikes - 7RM & 243 I think it could have been due to non canister grade 7828 when it was used in factory loads before it came on the market. MD wrote that it was also possibly due to the wide variation in throat dimensions especially if you factor in European rifles. SAAMI may have done these cartridges a disservice as 7828 and many other powders function best at near maximum pressure. Lower pressures could actually increase pressure fluctuations.. I would like to see these tests run again with a test barrel with a good throat. No idea what factory cartridges are loaded with now but probably some at least are not 7828 or if they are it is newly manufactured.

But if David Tubb says he is seeing the pressure excursions I would believe it.

Inherently inaccurate cartridges? 25 ACP is worthless in my hands. Could be the light short barreled pistols but who knows?

Tejano,

I've seen those "spikes" myself in a 7mm Remington when visiting a pressure lab, with more than one powder in a new pressure barrel. Was also told about the problem with the .243 by a major ammunition company, when visiting the plant (and pressure lab). The problems are well-known in the business, and do NOT just occur with 7828, or any other specific powder, in pressure barrels with worn throats.

MD - Thanks for the clarification. I am having a hard time figuring out what is responsible for this? The 7RM with a 25 degree shoulder should be a good case design in spite of the shorter neck. If case design then why hasn't the 264 WM shown the same excursions? I have heard people say this about the 264 but no lab data to back it up.

The 243 if it is the case them the 260, 7mm-08 and 308 should show it too, but they don't. Case bore ratio?

One reason for setting the MAP's a little lower for some cartridges is because they do show greater pressure variations, NOT "excursions." When this subject has come up before, many people keep saying "excursions," as if the pressure only jumps higher, and jumps a LOT.

Which is why some object when they hear, saying they've never seen "evidence" of high pressures in their handloads. It's not something you're going to generally "see" with traditional pressure signs, or even much on a chronograph, especially typical light-screen chrono with a 1-foot spacing.

Instead it's just a wider range of pressures than many other cartridges exhibit. SAAMI's MAP isn't right at the top end of acceptable pressures for a given round. Instead it involves the possible pressure-spread for a cartridge. If SOME of the cartridges in a test-string go over a certain pressure level, then the MAP is set a little lower, so none of the rounds will exceed a certain upper level.

The maximum MAP, however, that SAAMI allows for any cartridge is 65,000 PSI. A lower level can be set for any number of reasons, including typical actions, or wider pressure variations, or more esoteric reasons.

As far as I've been able to discover (and I've asked a lot of pressure people about it) there of isn't any reason they can figure out for such wider variations. Instead the variations are simply observed during testing.

Here are the SAAMI MAP's for the cartridges you mention. Please note the .260, 7mm-08 and .308 also have MAP's lower than 65,000 PSI, in fact in the same range as the .243 and 7mm Remington Magnum. The .264's is a little higher:

.243--60,000
.260--60,000
.264 WM--64,000
7mm-08--61,000
7mm RM--61,000
.308--62,000

Even some of the Weatherby rounds have different MAPs. Most are 65,000, but the .270 Weatherby's is 62,500.

Your out of touch. Your ignorance of innovation in cartridge design and its effects on accuracy is readily apparent. We are learning to taylor the burning characteristics of a powder column to the utmost efficiency by how we shape the combustion chamber it is burned in, in an effort to produce a bullet that comes out of the barrel with the least amount of harmonic disturbance to the shooting platform it is being fired from.

One reason some powders max published charge is lower than others is a wider range of pressures measured for a given charge.

Don't have one! I have never seen a cartridge that has been given so much hype in such a short time. Reminds me of all the schills found down in the classifieds. May have to get me one if ya'll don't
quit!

Yep, the Creedmoor's gotten an incredible amount of publicity in the 11 short years since it appeared....

Crap.

I forgot that I was going to buy one to support Hornady for thumbing their nose at New York.


Maybe I could just buy some ammo and donate it to a needy farm kid.

Hardly. I first mentioned improvements to brass when they stopped using the older, BP case designs (droopy shoulders and long necks) as smokeless took over. I also said, repeatedly, improvements are ongoing.

https://www.24hourcampfire.com/ubbt...eedmoor-inherently-accurate#Post12888573

Many of you fail to understand that virtually every improvement comes from analyzing and changing existing designs. But developments are also happening with firearms, metals, optics, propellant chemistry, etc. They all combine to improve accuracy.

I wonder if military snipers of the past and present chose " inherently accurate cartridges," or just highly acurate rifles? How about the Russian male and female snipers of WWII, or the Germans, or Americans, or British snipers, and so on...

I just don't understand how a cartridge can be "inherently accurate."
.

I was wondering if Hornady earns any royalties for each rifle chambered in 6.5CM or brass producers in 6.5CM , because they ( copied the 6.5x47L ) "invented" the 6.5 CM?

Northman,

Actually, the 6.5x47 Lapua pretty much copied the 6.5/.250 Savage RCBS Improved. None of these cartridges are as new and startling as their "inventors" would like other people to believe.

The major difference between the 6.5 Creedmoor and 6.5x47 Lapua, as I have pointed out before, is the 6.5 Creedmoor provided far more "affordable" ammunition and components, and was chambered in far more affordable and available rifles. So yes, it became more popular.

The other difference is the size of the primer pocket. The 6.5x47 was designed with a small-primer pocket, for the supposed ultimate in target accuracy. David Tubb disagrees with that theory, but aside from that, many hunters prefer large-rifle primers for cold-weather performance. That's yet another reason the 6.5 Creedmoor became far more popular than the 6.5x47 Lapua. (Of course, if anybody disagrees with Tubb and quite a few hunters, they can buy 6.5 Creedmoor brass with small-rifle primer pockets--made by Lapua.)

But the big reason the 6.5 Creedmoor became far more popular than the 6.5x47 it "copied" is far more widely available and affordable ammunition, brass and rifles. Which is also, of course, the reason the 6.5 Creedmoor became far more popular than the 6.5/.250 Savage RCBS Improved.

And Starline.

Word is they can get 6 XC brass with the same "afflictions" from Peterson, maybe Alpha, I don't recall.


Cartridges with small rifle primer pockets AND smaller flash holes are inherently more accurate than those that use LR priming; the testing of PPC cartridges and later the Remington BR cartridges proved this.....

Tubb says any cartridge with a powder capacity of over 35 grains is more consistently accurate with various powders, in varying conditions, using LR primers. Which is why he designed the 6XC with LR primers.

Totally contradictory to Lapua; who's telling the truth?

The capacities of the PPC and 6 BR cases are well under 35 grains.

So what is considered the absolutely most consistently accurate rifle cartridge case in the world at 100m? The 6mm PPC?