Home Forums Hunting & Shooting Ask The Gunwriters 6.5 SAUM Hype

Rick,

Yes, they do--and they change in all cartridges. But the formula still provides a very good idea of the differences in potential between cartridges.

I've been trying to get some RL-33 for over a year now! I'd like to try it in several rounds--but Nosler's testing doesn't have it among the front-runners in the 26.

I have plenty to send to you.

Thanks very much for the offer! Let me try a contact at ATK first and see what happens.

It appears to me that the closest pressure-tested comparison we have to the 6.5SAUM is the commercial 7SAUM. Looking at that chambering with a 140 grain bullet, all the best loads run 3100-3150 at 62-64k psi. The 6.5 cannot ran at any less pressure than that to accomplish the same thing, and due to being a smaller bore diameter would have to have the pressure a bit higher. I think that it will test out at right around 65k psi in the end.

John,

Lots of good thoughts here.

Thanks for taking the time.

The last time I was in Cliff's Reloading in Boise they had a lot of RL-33 in stock. (there is a reason they have a good supply on hand. I paid $33 for a can of 4756 which I felt I absolutely could not live without.) I really need to grab a can of RL-33 and do some more experimentation with my 27 inch Pac-Nor 264.

DakotaDeer,

There's even an approximate formula for the same case but different calibers: Divide the cross-sectional area of one cartridge's bullet by the area of the other cartridge's bullet, then divide the difference by 4.

Here it would be .0633 (7mm) divided by .0547 (6.5mm):

.0633 divided by .0547 = 1.157
.157 divided by 4 = .0392

Then subtract .0392 from 1, and multiply the result times the velocity of the larger-bored cartridge:

1-.0392 = .9608
.9608 x 3175 (velocity of 140 in 7mm SAUM) = 3050 fps

This would be the approximate potential velocity of a 140 in the 6.5mm SAUM at the same pressure as a 140 from a 7mm SAUM, at around 62,000-63,000 psi.

Just checked the Hodgdon site, and the top velocity with a 140 in the SAUM is 3217 (with H100V). That would change the calculated maximum velocity with a 140 in the 6.5mm to 3088 fps--again, at right around 62-63K psi.

Just to keep this little diversion going a bit longer...
One thing that's easy to forget as a handloader (but I'm sure most know) is that the pressures quoted in a reloading manual and elsewhere correspond to the peak pressure experienced while the bullets moved down the barrel. The pressure however is not constant. Speed is maximized by choosing the powder that will give the highest average pressure without exceeding your maximum pressure criteria. With the big magnums, a faster burning powder may hit the same peak pressure as a slower burning powder but its average pressure as defined by the pressure curve will be lower for a given max value.

All gack. Just build the damn thing and choot the hell out of it.

That's what I'm talking about!^^^^^

I mentioned something similar a couple months back based on Hodgdon data and the 264W vs 6.5 SAUM. Was told the bullets being used in the 6.5 SAUM were lower friction due to lower bearing surface compared to the hunting bullets I was referring to. This was given as the explanation to the low pressure and high velocity. I could see 1k psi or so, but didn't think it would make that much diff (i.e. 62-63k vs 58k for 6.5SAUM).

At that time I went back and reviewed a bunch of posts at the other site and from what I gathered, it seemed like GAP was using low pressure (58k) and getting great barrel life. Then pressure went up and I don't think GAP was claiming great life anymore (although that might have still been true). BUT, it seems that the casual observers were still mentioning the great life even though George set-back 1x in 3000 rounds. Seems to me that once the idea of low pressure got into people's minds it stuck. And barrel life. But, I don't doubt Pat's claim on barrel life either.

The pressures are more interesting to me and would be easy to measure. I'd like to see the max pressure, but also the area under the curve compared to some other carts like the 7SAUM and 264W.

Jason

Karnis and Pat are on the right track......

John, you obviously have a handle on this. If you have a quick way to estimate, and could hazard a guess on the pressure generated by a 6.5-06 AI pushing a 140 grain VLD out of a 24' barrel at 3050 with 60 grains H-1000, I'd be much obliged.

If not, no worries.

Karnis and Pat on the right track? Who'd have tthink it.

4th_Point,

That's interesting about the bullets, because of the four bullets listed in the Ramshot/Accurate data, three are the 140 Berger VLD, the 140 Hornady A-Max and the 142 Sierra MatchKing, hardly a selection of typical "hunting" bullets.

The fourth bullet is the 140 Nosler Partition, a bullet noted for producing more pressure 9and velocity) than others with the same powder charges. Interestingly, the Sierra MK requires the least powder to reach 63K psi, whether using Magpro or Magnum, indicating it creates even more pressure than the Partition. The A-Max requires the most powder to get to 63K, with the Berger VLD right behind.

smokepole,

Hodgdon's 6.5-06 data lists 55.0 grains of H1000 as maximum with the 142 SMK, for a little over 63K psi and 2800 fps from a 24" barrel. In my own 6.5-06 I used 56.0 grains with the 140 VLD for 2950 from a 26" barrel. Don't the pressure but guess it would be about like the Hodgdon load, given that the 142 SMK produces a little more pressure than the VLD.

The 6.5-06 AI has just about the same case capacity as the 6.5 SAUM. Given that, and the data from Hodgdon I'd guess you're getting similar pressures, somewhere in the 63K range. But I emphasize GUESS.

I never could figure out why the 7mm SAUM wasn't more popular, because it's basically a short .280 Ackley, and allows enough room in a .28" magazine box for really long bullets. It's also very accurate and kills stuff!

Gack is Good. Keep fanning the flames.

At one time I think the 6.5 bore had more variation in bullet bearing surface than any other caliber. With all the two diameter "bore rider" bullets that came out with the .264 WM and now three diameter if you count the driving band on some target bullets.

Sometimes these were changed by the manufacturer with no notice.

I think this is why results vary so much even with the same weight bullet. The difference between a sticky hunting bullet and a soft two diameter target bullet could easily be 3,000 PSI or more.

Thanks John.

Mule Deer,

I find this formula very interesting. I would have guessed that with the only difference being the diameter that the 7mm would have had more pressure and less velocity due to the increased surface area / friction / force?

This is a good thread and has certainly cut into my work performance the last couple days...:)

What's the fun in that--gack makes the world go 'round!