The Korean-made Sumatras and Careers can be so much more than just MAXI-BLASTERS; so I sometimes lament there are no regulators available for them. That being the case, I've become pretty adept at DE-tuning them to realize their potentials as laser-accurate, mere super-magnums. Not an easy chore mind you, the results have been nothing less than startling; in fact, unbelievable to most folks.
De-"tuning" the Sumatras and Careers typically involves cutting the hammer-spring 1" to 1.5" shorter (or installing a weaker spring), 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. In my case(s) that means competition-worthy shots of no more than about 30 FPS extreme spread.
It's a time-consuming process; but by sacrificing a certain amount of their extreme power the Korean maxi-blasters can return useful power-bands of several to many shots, rather than losing velocity with every shot.
My latest 'detuning-Korean-maxi-blasters' success is a .25 Sumatra rifle that not only shoots with the finest, most expensive regulated PCPs modern manufacturing and marketing can muster, but can sometimes outshoot 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. To put the challenge into perspective, the 77 yard turkey's body is the size of a quarter.
As taken from my .25 Sumatra testing (after detuning)-
.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.
De-"tuning" the Sumatras and Careers typically involves cutting the hammer-spring 1" to 1.5" shorter (or installing a weaker spring), 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. In my case(s) that means competition-worthy shots of no more than about 30 FPS extreme spread.
It's a time-consuming process; but by sacrificing a certain amount of their extreme power the Korean maxi-blasters can return useful power-bands of several to many shots, rather than losing velocity with every shot.
My latest 'detuning-Korean-maxi-blasters' success is a .25 Sumatra rifle that not only shoots with the finest, most expensive regulated PCPs modern manufacturing and marketing can muster, but can sometimes outshoot 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. To put the challenge into perspective, the 77 yard turkey's body is the size of a quarter.
As taken from my .25 Sumatra testing (after detuning)-
.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.
Good job Ron. My .25 Taipan Veteran FX (a true mutant 
) and I look forward to meeting up with you and the Sumatra again very soon. I love heated competitions. 
