I use Lee Dies and have no problems with both resizing the 284 brass and reloading it for the 7.5x55. If there is a difference it must very little as I can not see any problems with it. Also the Swiss cartridge has not changed since the 1911 rifle so I think this die controversy is a bunch of Internet Bullcrap. Lots of guys are using Lee dies and have no problems with them myself one of them.
The GP11 was load with a 174 grain spitzer bullet. The round could travel at 2640 fps. The diameter of the bullet was increase, and the length of the case was increased to 55m. The GP11 generates around 45,500 psi of pressure. Most older Schmidt-Rubins were converted to fire the GP11, and the round saw service with the 1911 series, the K31 series, and the Stgw 57 series, remaining in service until the mid-1980s. Due to the greater pressures produced by the GP11 round, it is not safe to fire GP11 rounds in Model 1889 Schmidt-Rubins!!!
In addition to the standard FMJ GP11 rounds, specialty rounds were produced as well. Armor-piercing Steel-cored rounds can be identified by their violet bases. These rounds can easily pierce .2" of steel plate at 550 yards. Tracer rounds burn out to 880 yards, and can be identified by their red bases. However, most Swiss match shooters use standard GP11 ammunition, a testament to the accuracy of the GP11 round.
The headstamps on GP11 rounds can be read as thus; The numbers at the top and bottom of the case represents the month and year of manufacture, respectively. The letter to the left of the headstamp represents where the case was manufactured, while the letter to the right represent the finally assembly point of the cartridge. Letters used include D=Dornach, A=Altdorf, and T=Thun.
As a curious side note: according to an article on Cruffler.com. The Swiss GP11 bullet strongly influenced the design of the M1 .30-06 round. For more information, click here.
Today, 7.5 ammo is finally becoming fairly easy to find. Several companies, are now importing GP11 ammunition. GP11 ammuntion is Berdan primed, and not easily reloadable. In addition, there are other alternatives. The first, was from INDEP of Portugal. The INDEP round is a 180gr round, traveling at around 1950fps. INEP ammuntion is no longer available, but Prvi Partisan is similar, and available from various sources.
Swiss GP11
INDEP 7.5x55
Norma 7.5x55
Norma is the second company to produce loads the for the 7.5 Swiss round. They have a 190 gr. hollowpoint round with a velocity of 2592 fps. A 200 gr hollowpoint round with a velocity of 2493 fps. And a 180 gr soft-point round with a velocity of 2651 fps. Norma tends to be much more expensive, currently street prices range from $27 to $35, but it is also more accurate.
The Norma loads offer performance similar to the 7.62 NATO round, and at least one source reports the hollowpoint round performs well as a hunting round.
Finally, Ruag, the manufacturer of Swiss ammunition, also produces a line of Match grade ammunition. It is believed a lot SM Match Grade is about to be imported into the US.
Imported GP11 ammunition is sold as either 480 round cases or 10 round boxes.