Thanks for reviving this one. I would like to add another detailed source of information on this subject, from the Springfield Armory Museum:
http://ww2.rediscov.com/spring/VFPC...g/DETAILS.IDC,SPECIFIC=10839,DATABASE=objects
I have been trying to resolve a question about the ammunition used for some time. and in particular the ballistics; there is some confusion because two different guns were developed, the T250X-1 and T250-X2. Also, two cartridges were developed, a "long" and a "short" one (37 x 255 and 37 x 217), both firing the same projectile. I have examples of both in my collection, as shown below:
Interestingly, the information in this Springfield document states that in July-Dec 1957 consideration was given to "shortening the ammunition case 1 1/2 inches" for the model X-2. That implies pretty clearly that the long round came in the X-1, the short one in the X-2.
However, the document posted by Tround in May 2013 includes a data sheet which quotes the muzzle velocities as 3,000 fps standard (I can't quite make out the designation - is it T423E-22?), or 3,600 fps for the "improved" version. This implies that the short round came before the long one, since the long one will obviously be associated with the higher muzzle velocity. Yet another oddity is the photo of the ammo in this report seems to be of the long-cased one.
I am inclined to believe the Springfield report, because my two examples are headstamped 1957 (long) and 1960 (short).
I understand that only two actual gun systems were built: one on a towed mounting, the other one on the tracked SPAAG mounting. I wonder if they both fired the 37 x 217 ammo or if one came in 37 x 255?