To me the biggest factor would be the barrel, carrier, cocking tube/support assembly, hand guard, and rear sights of your 53. Most smiths converted the original HK93 parts to fit into a 53 size, because actual HK 53 parts were difficult to source back in the 80's. The 53 cocking tube is welded into a thicker tubing where the rear notch is on an actual 53, as that notch is over the front trunnion. The 53 has a shorter recoil spring assembly, as the recoil tubing on the carrier is shorter on a 53 carrier than a 33/93 carrier. In many of the 53 conversions, an MP5 hand guard was used. The 53 hand guard is longer because the rifle trunnion is longer than the pistol caliber trunnion.
But by far the biggest factor would be the barrel twist rate. A HK53 barrel would be 1/7 twist. The HK93 barrel is 1/12. An 8.3 inch 1/12 twist barrel would not be able to stabilize even a 55 grain bullet because the barrel is too short. So a converted 93 barrel would tend to key hole. And it is a small detail but the 53 had a long four prong flash hider. With a standard bird cage flash hider even in daylight, the fireball from such a short 8.3" 5.56X45 barrel would be big and bright, obscuring the target.
Other than the key holing issue, these are small details. But for collector value details matter. To me a 93 receiver built into a 53 using a 53 parts set by a name smith would be the high end of the market value mentioned. A chopped up 93 would be around the low end of the market value listed. So how was your 53 made? How many of the 53 details does it have? Was it made with a 53 parts set or modified 93 parts?
Scott
