blastar (./16) :
for most games accurate collision is not needed, I use a simple and fast box-collide routine with variable box-sizes, no optimizations yet - works great. I check all collisions every frame, no problems so far - there are more critical parts than this, moving 100 enemy-bullets takes more raster-time than 100 checks vs. player!
test for slower objects (most enemy-bullets or upgrades) you can split onto 2 frames

I can understand that. VRAM access does seem quite slow on Neo Geo. You might have trouble if you have a lot of enemies on screen at the same time as a lot of player bullets. E.g. 40 player bullets x 80 enemies = 3200 collision checks. Then you would probably need collision zones to reduce the checks

I didn't know about that method Razoola. I suppose you have to take into account that the player's speed too since they may move also towards the bullets.