I suggest trying a different powder if you are consistently getting slower results from the 7 PRC than the 7 SAUM. The PRC is a considerably more potent cartridge according to all published load data I can access freely on the internet. It has 4 grains (5%) more case capacity after all.
Here's a direct comparison of Nosler's load data for the 7 SAUM vs Hodgdon's load data for the 7 PRC. With identical powders, bullets, and barrel lengths, the PRC outruns the SAUM by over 100 fps, and when optimized, over 200 fps.
Cartridge | Powder | Charge | Velocity | FPS/Gr | FPS Difference |
7 PRC | H1000 | 67.2 | 2968 | 44.2 | |
7 SAUM | H1000 | 61.5 | 2836 | 46.1 | 132 |
| | | | | |
7 PRC | Retumbo | 70.0 | 2985 | 42.6 | |
7 SAUM | Retumbo | 63.5 | 2879 | 45.3 | 106 |
| | | | | |
7 PRC | Magnum | 70.4 | 2946 | 41.8 | |
7 SAUM | Magnum | 65.0 | 2832 | 43.6 | 114 |
Max Published Load | | | | | |
7 PRC | LRT | 79 | 3106 | 39.3 | |
7 SAUM | RL22 | 59 | 2882 | 48.8 | 224 |
I understand that individual rifles vary, but even if one compared the slowest 7 PRC barrel to the fastest 7 SAUM barrel, it is unlikely that the 7 SAUM would ever outrun the 7 PRC with properly developed hand loads.
Based on published data (and physics), there are only two "common" cartridges that match or exceed the 7 PRC, while staying within reason of SAAMI specs. 28 Nosler and 7 Rem Mag.