Not hard at all. If you have the cheek rest up, you might need to lower it to get the hex screw in; but that's it. No need to take it out of the stock.
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All I did with my Crosman Challenger is added a wider .150 transfer port. I lengthened the hammer throw fully...striker flush to the hammer, hammer spring at it's factory setting, and that is all. My Challenger now shoots a 45 shot string with a 842 fps average @ nearly 17fpe with 10.54gr. Crosman Premiers. Dime size groups @ 50 yds. You need less power for field target?; I simply dial out the hammer striker 6 full counter-clockwise turns, and I am @ 690fps for about 11.7fpe. This tune will have you prepared to compete in both the low power and higher power field target classes. You need to get the fpe even lower for 10 meter?; from this tune, I dial back the hammer spring adjuster 5 full turns, go down to a lighter pellet like the 7.3gr Crosman Premiers...and I am @ 610fps at just about 6fpe.
All I did with my Crosman Challenger is added a wider .150 transfer port. I lengthened the hammer throw fully...striker flush to the hammer, hammer spring at it's factory setting, and that is all. My Challenger now shoots a 45 shot string with a 842 fps average @ nearly 17fpe with 10.54gr. Crosman Premiers. Dime size groups @ 50 yds. You need less power for field target?; I simply dial out the hammer striker 6 full counter-clockwise turns, and I am @ 690fps for about 11.7fpe. This tune will have you prepared to compete in both the low power and higher power field target classes. You need to get the fpe even lower for 10 meter?; from this tune, I dial back the hammer spring adjuster 5 full turns, go down to a lighter pellet like the 7.3gr Crosman Premiers...and I am @ 610fps at just about 6fpe.
I got the .150 tp from Magnum AirPower. The Challenger will physically take up to a .160 transfer port without any drilling.; but I think the .150 is just right without overkill.
Oh yea...the ONLY thing the Challenger is lacking from being a true utility gun, is a multi shot breech. The Lothar Walther barrel is insanely accurate. Have any of you seen the new 2021 Crosman Challenger?