This study aimed to determine whether traditional approaches based on baseline or group-adjusted 1RM values, or velocity-based methods, provide more accurate 1RM estimations after short-term training programs. Thirty resistance-trained men were randomly assigned to either a ballistic training group (bench press [BP] throw at 40% 1RM) or a traditional strength training group (BP at 70–90% 1RM) for 4 weeks (2 sessions/week). The post-intervention BP 1RM was compared to four 1RM estimations: (i) baseline 1RM—the pre-intervention value without modification; (ii) group-adjusted 1RM—the baseline adjusted by the group-level percentage change in 1RM; (iii) load-velocity profile—estimated post-intervention as the load corresponding to a mean velocity of 0.17 m·s−1; and (iv) baseline %1RM–velocity extrapolation—estimated from a single post-intervention velocity applied to the pre-intervention individual %1RM–velocity relationship. Trivial differences (ES < 0.20) were found between actual and estimated 1RM, except for a small underestimation using baseline 1RM in both groups (ballistic: ES = −0.28; traditional: ES = −0.23). Velocity-based methods showed greater accuracy (absolute errors: 2.0–2.1 kg) compared to baseline (5.1 kg) and group-adjusted (4.4 kg) approaches. These results suggest that, after a 4-week training period, velocity-based methods provide more accurate guidance for load prescription than baseline 1RM values.