I was looking at some load data today, and noticed something. All the former military rounds, 6.5x55, 7x57, 8x57 etc., all had max pressure limits 7-12,000cup lower than other rounds such as 7mm-08, 270 and so on. Is this just because of the caution factor of people putting hot rounds in old guns?

If so, is it safe to load a round in these calibers higher than these limits for use in a modern rifle? A 6.5x55 looks like a good choice for my next deer rifle if so.

Lower pressure limits for older rounds are generally predicated on the idea that they will be used in older, weaker actions (93 & 96 Mausers, remington Rolling Blocks, etc.) When used in strong actions they can be loaded to higher pressures.

Pressures were also moderate because suitable rifle powders of that gas lit era tended to build pressure faster than velocity.

Most vintage military cartridges, when chambered in modern firearms, can safely be stepped up a notch by the prudent handloader. The 6.5X55 is a classic in its own right, and with modern slow-burning powders, it can be stepped up a notch or two.
The 6.5X55 & M96

In Scandinavia 6.5x55 is loaded to normal pressures for modern guns.

Check out load data from Norma and Vihtavouri:

http://www.norma.cc/sortimentladd.asp?Kaliber=6,5x55%20Swedish%20Mauser&Lang=2

http://www.lapua.com/uploads/media/InternationalReloguide2008.pdf

quote:

If so, is it safe to load a round in these calibers higher than these limits for use in a modern rifle? A 6.5x55 looks like a good choice for my next deer rifle if so.

Given excellent brass yes. But the ammo you load may not be safe in a rusty battered 100+ year old Mauser.