The Sumatras and Careers can be so much more than just maxi-blasters; so I lament there are no regulators available for them. But that being the case, I've become pretty adept at
DE-tuning them to realize their potentials as
mere super-magnums. Not an easy chore mind you, the results have been nothing less than startling; in fact, unbelievable to most folks.
My latest 'detuning-Korean-maxi-blasters-to-mere-super-magnums' success is my .25 Sumatra rifle that not only shoots with the finest,
most expensive regulated PCPs modern manufacturing and marketing can muster, but in fact outshoots them! In its last Bench-rest Silhouette competition The Beast prevailed over such heady competition as .30 Uragans and FX Impacts; that competition featuring 1/10 scale silhouettes shot at 40 to 100 yards from bench-rest
in real-world wind conditions.
De-"tuning" the Sumatras and Careers typically involves cutting the hammer-spring 1" to 1.5" shorter, reassembling and chronograph testing (usually several times) until you find the maximum power level desired, and the sweet-spot charge pressure required to return a bell-curve power-band of (in my case)
competition-worthy shots of no more than about 30 FPS extreme spread. It's a time-consuming process, but literally transforms a one-trick pony into a quarter-horse! As taken from my testing results-
.25 Sam Yang Sumatra lever-action PCP repeater 33.95gr JSB, 2450 PSI, 26 shot powerband- Low= 893, Hi= 925, ES= 32,
SD= 5, Average= 910 FPS/63.1 FP
These excellent numbers came after shortening and moly-lubing the hammer-spring. 7/17/2019- 12 consecutive six-shot groups with 33.95 JSBs averaged 1.26” c-t-c at 100 yards. The best group measured .6o” c-t-c; the second best 100 yard group I've ever achieved with an airgun. 6/6/2020- Won the second Ranchito Robinson Airgun BRS match with a 34/40, including ten-in-a-row turkeys and pigs. 
