In past, I shot a lot of 9mm and 45 ACP handguns. Though I don't have pressure equipment, and my opinion is entirely subjective, I do believe it is quite common practice with those folks across the pond to load their ammo to higher pressures than we do here, at least according to my 1911's. It is common to find the thinking (not saddling you with it) that over pressure ammo is dangerous. The problem is that "over pressure" and "dangerous" are subjective too. In most arms, for commonly available chamberings, and especially in military chamberings, an additional 5 to 10% average pressure increase is simply not that much, is not going to burst or damage a gun, and generally will lead only to what we might call excessive wear.
The best common example is +P loadings. A good perusing through a loading manual will not only show such loadings, but the pressure and velocity increases as well.
The 38-55 has a SAAMI average pressur limit of 30,000 cup. The 375 Winchester, the modern makeover, operates at 52,000. The 30-30, the 38-55 necked down, operates at 38,000 cup. Even considering the chance of weaker brass, I wouldn't hesitate to push to 38-55 to 40,000 cup....a full 30% pressure increase. The problem is that without pressure equipment we don't know what loads are going to give that increase. We can guess, and not be too far off, certainly within the limits of the SB2, I would estimate that using 375 Win Start loads would be about as hard I would want to push it's older sibling without some data to work by. At the same time, so long as I were not surpassing 375 data I wouldn't be entirely uncomfortable. It would all depend on how the brass took the increased load. Just some thoughts, JP