Extracts from From Any Shot You Want - pages 601-603 - to address your questions
Designed in 1977. The original design objective was to provide a .50 caliber cartridge with a maximum overall length of 3.65" so that it could be utilized as a relatively easy conversion on existing rifles.
"It is extremely efficient in terms of velocity and energy in relation to the weight of the propellant charge. It is not the maximum in .50 killing power but it certainly exceeds both the .500 Nitro Express and the .505 Gibbs. With the greater cross sectional area of the .50 caliber bullet, the .495 kills better than any .45 caliber cartridge, regardless of paper ballistics. The .495 A-Square was used on both problem animal control and elephant culls starting in 1978. During one elephant cull, when I was playing gunbearer to the center column, I nailed a stunned bull who was getting up just as we were passing him. The range was 4 or 5 feet off the muzzle and the effect of the .50 caliber bullet was tremendous. On problem animal control, using the first of what became the A-Square monolithic Solid, I took a bull elephant broadside from above (as he was preparing to charge a tracker and two skinners who had gone around the hill rather than over it) with the bullet entering high on the right side of the skull and exiting through the left jaw. The elephant dropped on the shot.Using both solid and soft point bullets, the cartridge also did well on cape buffalo.Field reports since then have been uniformly good."
"The cartridge is also notable in that it was the first one designed with the "ghost shoulder". Most cartridges that look like they have a straight taper, do, in fact, taper straight to the mouth. This includes cartridges like the .458 Winchester and the .500 Nitro Express. This actually makes handloading very difficult as the case must be sized well below bullet diameter and then have the seating fo the bullet open the case back up for a parallel neck. This never leaves a good or uniform neck tension and requires a heavy crimp. In the .495 A-Square, the taper of the body goes to a ghost point four hundred thousandths from the case mouth. From this point the case has a conventional parallel neck. This allows sizing in a two die set rather than a three die set such as the .458 Winchester which requires bell mouthing in order to get the bullet started. It also allows for a much better neck tension on the bullet and a much more consistent bullet pull and bullet torque. This, in turn, adds up to efficiency, good velocities, and an easily handloaded cartridge."
" The shooter wanting maximum power in a .50 caliber rifle will probably go up to the .500 A-Square. However, if a shooter wants maximum cross sectional area of the bullet and mximum killing power available in a reasonably compact and efficient cartridge with the lowest recoil of any cartidge in its class, then the .495 A-Square is the cartridge of choice."
.500 A-Square is same design, but 3.740" COL, so requires a longer action.
Yes, one can open up .460 Wby cases - I have some that were .460 Wby.
I also have about 60 cases (and then an additional 60 projos - I will pull them and dump the powder and deprime before shipping so I can avoid any hazmat games.) If you are interested in these, let me know - just have not gotten there yet to put them up on the sale board here.
I had not heard your bit about being under .50 caliber, but perhaps that is true.
