Home Forums Hunting & Shooting Ask The Gunwriters 6.5 SAUM Hype

MontanaCreekHunter... You ordered a second bolt with a mag bolt face too I hope...

Our 200 yard targets look very similar

Think how'd they look if we knew something! Grin

I'd be grinning if I could get all my sporters to shoot 9-10 shot groups that well at 1/2 the distance.

Brass - If you say that you are getting good life out of your 7saum brass - fine I will not argue that point. I am just relating my experience with rem brass.

264win vs. 6.5saum - Apples and oranges. Two different cases and can't be compared. Example, why does my 7RUM not out run my 7STW until I get to 180 gr bullets? I am using more powder?? And my stw has a 24" bbl and the rum has a 26" bbl. For whatever reason the stw is more efficient, plain and simple.

One thing to remember here is that the 6.5saum velocities are not max loads, but moderate. They will run a lot faster. I might have to dig up my Oehler 43 and see what pressures it is running just to put this to rest.

I would have to say that the entire reason is that the comparison between the two is bogus simply because the two powders being compared aren't that close in burn rate and may not act the same in the different cases. H-1000 is much slower than Magpro and Magnum. When a faster powder is used in a large case, pressure is found early.

This is easy to see during load development with different powders in the same cartridge.

I believe velocity isn't necessarily the best indication of pressure.

For example, in the .264 Winchester Magnum, just about every powder you'll find with data for the cartridge acts like pistol powder. Even some of the slowest burning powders on the chart. Velocities are anemic and pressure signs show quickly.

With extremely slow burning powders in the .264, pressure indications don't appear until well after its velocity potential is attained. I'm talking about 3250 + fps

It looks like H-1000 is just right for the 6.5 SAUM and its case capacity

Playing devils advocate. Lets say the pressure of Pats loads are 67,000 PSI. Hes getting good brass life and the gun will handle alot more than that before failure so why worry?
I have seen factory 300 WSM loads and Weatherby factory ammo show very obvious signs of pressure, so why get worked up over 2000 PSI or even 5000 PSI over 65k where traditional pressure signs show up by.
Keep in mind I am asking a question not advocating running pressures over 65k.

rifleman700,

As I mentioned in my first post, there's no ballistic evidence that any cartridge is more "efficient" at burning powder than another. All the pressure tests ever run have shown exactly the same thing: Powder capacity is the lone determinant of what velocity can be reached.

If you want examples I can provide them, but you seem to have already made up your mind.

Rick,

No, H1000 isn't "much slower" than Magpro or Magnum. You can easily check that out on any burning rate chart, or loading data where all three can be found.

Burn rate also varies somewhat due to the specific application and manufacturing lot. In my first .264 (a Westerner with 26" barrel) Magnum was slower than Magpro and Retumbo--and Retumbo is slower than H1000. I know this because it took more Magnum to reach 3200 fps with a 140 than it took Magpro or Retumbo.

And yes, velocity is a very good indication of pressure under specific circumstances. In fact without electronic pressure equipment it's the most reliable factor for handloaders--and this has been proven many times over, just like the myth that case shape can increase "efficiency" and produce more velocity with less pressure.

Again, I can provide proof of that, performed in actual professional pressure labs, not some wildcatter's mind.

You didn't answer my question.

Right from the hodgdon website, no data of mine.

7MM STW 175 GR bullet 88 grs US 869 3020 fps 62,800 psi = 34.31 fps per gr of powder

7MM RUM 175 GR bullet 102 grs US 869 3077 fps 63,000 psi = 30.16 fps per gr of powder

These were the first combos loaded so thats what I went with.

The STW case is more efficient with this powder bullet combo. Its greater with lighter gr bullets in my testing.

Now what I have found while using my Oehler 43 that I agree with you on is that velocity does equal pressure. I may not get the stated velocity - rarely with the charge that Hodgdon shows with the lot of powder they are using but if I load to their velocity I get their pressure.

Pressure is going to vary from rifle to rifle. Just because you reach 3077fps with US869 doesn't mean you're at 63,000 PSI in you rifle.

Exactly. Loading manuals give you an idea what the bulley/powder companies got on their guns/test rifles on a certain day with a certain lot of powder/primers/bullets.
Each gun is an animal unto itself IME.

Yes there are exceptions as every barrel is different but it was often enough that I only use my Oehler 35 now and not the 43 and I watch for pressure signs in load development. I very rarely chase velocity anymore anyway and look for accuracy / velocity nodes.

I have even seen bbls like pac-nor that for whatever reason have tighter tolerances and do not like higher velocity loads and show pressure signs early. So yes that is a good point and I admit the last statement was a little general in nature.

Further more I run mostly cut rifled canted lands bbls. These I have found to be more consistent - to ME.

You're correct.

They're all very close to one another

I guess what I'm saying is consider loading the .264 win with IMR 4350 and Retumbo both with a 140 grain bullet.

When 70,000 psi is reached in each load, the IMR 4350 load's velocity will be nowhere close to Retumbo's

Correct?

Lost in the gack, is brass life (pockets) is increased with a good chamber with a reamer that matches the brass in the web area, without getting dimensions too tight. That'll open up another can of worms.

Some prefer to shoot their brass a time or two to work harden it, and claim better primer pocket life as well.

There's more to this than meets the eye.....

Rick,

Yep, that's correct.

Now, the .264 will get some more velocity with even slower-burning powders. I've got a bunch of US869 and H50BMG on hand, partly because I'm going to be handloading the .26 Nosler in the next couple of months, but I'm also going to try them in the .264.

But one basic formula for internal ballistics is that when using the optimum powders for any cartridge, any increase or decrease in powder capacity for that caliber is going to result in 1/4 that amount in potential velocity--AT THE SAME PRESSURE.

Even if we can get another 100 fps out of the .264 in a 24" barrel at 63K psi with slower powders, the 6.5 SAUM is going to be around 4% behind (15% less case capacity = 3.75% less velocity). So if the .264 is capable of 3200 with a 140 at 63K, the 6.5 SAUM is capable of about 3070 with a 140 at 63,000. (Remember, this is using the optimum powders, not the same powders).

Another basic rule of interior ballistics is that with single-based powders like H1000, pressure increases at twice the rate of velocity. Another rule is that velocity with single-based powders increases at the same rate as the powder charge.

If we apply those formulas to the 6.5 SAUM, a 140 at 3100 will be producing around 64K psi. Of course, this will vary some with the bullet, but I am willing to bet that the loads being discussed produce over 60K psi, probably around 65K and maybe even more.

One classic example of how poorly tight primer pockets indicate actual pressure is the 7mm STW. When Layne Simpson developed the round, he used all the standard pressure "indicators", ahd reported 3600+ fps with 140-grain bullets in 26" barrels with no problems. A bunch of other people built rifles and reported the same basic velocity level.

When Remington decided to make the 7mm STW a factory round, they pressure-tested Layne's loads, along with some others. ALL were at least in the 70,000 psi range, and some were around 75,000. That's why no factory 7mm STW load is listed at more tan 3400 fps.

This has little to do with whether or not such pressures are "safe." Obviously Layne and others shot such loads a lot (with the dreaded Remington brass) and never had a problem. Similarly, a lot of people who're loading and shooting the 6.5mm SAUM haven't had any problems.

But tight primer pockets prove exactly one thing: The primer pockets are still tight. They're not even an approximate indication of actual pressure.

This is exactly why I believe velocity is not the best indicator of pressure.

You have stated that slower burning powders are able to produce more velocity at the same pressure as faster burning powders, and that's what I'm getting at.

On the Hodgdon site, data for the .264 win with a 140 partition shows this:

Retumbo at 2900 fps and pressure of 57k+

IMR 4350 at 2900 fps and pressure of 61k+


Also in my Creedmoor with an old lot of faster burning H4350, I hit traditional pressure signs of sticky bolt and ejector marks at 42.5 grains and velocity below 2800

With a new, slower burning lot of H4350, pressure signs were not noticed until 45.3 grains with a velocity of well over 2900 fps

If pressure is directly tied to velocity and can be predicted by velocity, how can the above happen?

Rick,

Obviously different powders are going to result in different velocities at the same pressure.

But the formula for predicting how much velocity a case with a certain capacity is capable of uses OPTIMUM powders, meaning the powders that get the maximum velocity out of any given case--not the same powder in different cases.

We have enough powders today that optimum powders for any case size, bullet and velocity are easy to find. If some case is producing more velocity than the formula predicts, pressures are higher.

Velocity is also a very good indication of pressure in different barrels chambered for the same cartridge. For instance, if we have a .270 Winchester with a 22" barrel that gets 3200 fps with a typical cup-and-core 130-grain bullet and 60 grains of H4381, we can be very sure that the pressure is higher than the "normal" 62-64K psi. Similarly, if velocity is only 2850 with the same load, we can be sure the pressure is lower.

All of this has been proven on modern pressure equipment. The top techie in a major pressure lab says that pressure will vary about 800-1000 psi with each 1/10,000ths of an inch variation in bullet OR bore diameter. He's proven this by years of experimentation.

So yes, velocity is an indication of pressure, but we have to know how to apply it.

Thank you for your time here; I'm sorry to "hijack". LOL

But...




"Optimum" powders in each case change as technology changes.

IE, RL-33 in the .264 Win Mag.

If you don't test it in the 26 Nosler you'll be missin' the Boat!