The load data tables do not show performance for these two cartridges at 'modern' pressures. (308 levels). Does anyone have any data for them at higher load intensities? This is just out of interest - it's a topic that comes up from time to time over a beer.

I have got 3900 fps with 75 gr bullets in a 257RAI, but brass life is too short.
3600 fps is more sustainable.

So I work up to short brass life and back off a safety margin ala Vernon Speer 1956.
I like to measure the extractor groove of the case before and after firing with dial calipers. I can see a 0.0002" change on dial calipers. One only need to be able to resolve a 0.0010" change, which requires less skill. Typically in a work up at maybe 5 grains more than max book load, the groove change is .0000", but at 6 grains it is 0.0010" and 0.0020" growth at 7 grains over par. The correct max load for my rifle is then 4 or 5 grains over max book load.

The 6.5 Swede is not a normal .470" Mauser case head, but .480".

The European manufactures make it .480", but the US manufacturers just use standard Mauser case head tooling and sell .470" case head 6.5x55mm brass.

It does not matter much.
The weak spot is still the large Boxer primer pocket growth.... unless you are Denton Bramwell, and then the weak spot is in your brain.

Thanks. Hodgdon gives a velocity of around 3550fps for the 75gr at around 45500 CUP for the standard Roberts. Looking at the 25-06 and comparing 100gr velocities, the 25-06 has around 100fps edge but with 5,000 CUP more pressure! In the case of the 6.5 Swede, the smaller cased 260 Rem has the same velocity but at 5,000 CUP higher pressure (they give different units of measure so I can't really tell how much higher).

quote:

It does not matter much.
The weak spot is still the large Boxer primer pocket growth....

It matters a lot if you have a maximum chamber used with some of that undersize brass. A case failure at the junction of the solid head is serious if your face is behind the action. I have witnessed a .243 letting go in a 98 Mauser. The escaping gas did a number on the guy's face.
This same situation has been SOP for decades with .250 Savage and .22-250 brass. Chambers are sized for .473 cases but both cases are a good bit smaller around .464. Not a good deal for high pressure loads but it was needed for chambering in the 99 Savage with the .250. The .22-250 has been hosed for being derived from the .250.

This is me overloading a 243 in an 98 Mauser.

No gas for me.

I have not overloaded 6.5x55 chambers with .470 brass, but I have bought some 6.5x55 rifles just for overloading, maybe I should do that.

The difference in Swede brass everyone seems to believe exists isn`t really notable IMO. I posted these once before somewhere, I can`t recall where though. I`m sorry if it was here.

Federal


Norma


PMC


Speer and Nosler offer data up to 51K psi and the Bob with similar pressures.

quote:

Originally posted by Ol` Joe:
The difference in Swede brass everyone seems to believe exists isn`t really notable IMO. I posted these once before somewhere, I can`t recall where though. I`m sorry if it was here.

Federal


Norma


PMC


Speer and Nosler offer data up to 51K psi and the Bob with similar pressures.

Joe
You need to measure WW and RP brass and then compare it and the other to 6.5X55 arsenal brass. My Swedish Kongsberg 1944 brass measures .482. WW and RP brass measure about .467 to .468 or about .010 smaller than the brass you show and .015 smaller than 6.5X55 arsenal brass. The results of the under size are much more notable when you examine the pressure ring of fired cases.

303 Guy, the latest Handloader has hit the shelves here in Nelson with a 257 Robts article in it. I don't have it but the loads seemed to be a mixture of old cautious & some getting up there. A ring around might find you a copy.
Steve

Thanks, Shinzo.
Looking at one of ADI's data sheets, it gives the 260 as slightly faster than the 6.5 - curious. But they don't give pressure. It seems that the 260 is a more efficient cartridge in that it uses less powder to achieve similar results.

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260 is a more efficient cartridge in that it uses less powder to achieve similar results.

That is translated into higher pressure.

quote:

That is translated into higher pressure.

Is it necessarily? I was checking Hodgdon's data for the 250 Savage, 257 Roberts and the 25-06. The amount of powder, velocity and pressure seem to indicate a 'saturation point' - deminishing returns. With 100gr bullets and H4350, the 25-06 uses more powder than the 257 Roberts, generates more pressure but doesn't get that much more velocity! Have a look and check out the starting loads for the 25-06.

25-06
100 GR. NOS PART Hodgdon H4350 .257" 3.200" 47.0 3038 47,800 CUP 50.0 3155 51,500 CUP

257 Roberts
100 GR. SPR SPBT Hodgdon H4350 .257" 2.770" 43.0 2833 34,200 CUP 45.0 2970 45,400 CUP

Mmmmm.... different bullets, so the comparison is not necessarily valid!

With a little caution you can use Quickload for that kind of load, just increase the powder weight until you reach the required pressure. Since we do not talk big increases here, in my experience this was pretty reliable.

deleted

303Guy, what SR4759 said was based on common sense. Your response was based on published load data. At some point, you want to throw away the cook books.

quote:

303Guy, what SR4759 said was based on common sense. Your response was based on published load data. At some point, you want to throw away the cook books.

True! I was selective in that comparison. Another consideration (apart from a different bullet) is that it is the energy we should be looking at, not the velocity (from an efficiency point of view). I've noticed that velocity gain does not seem to be proportional to pressure increase (also energy versus velocity?)