[Chopstix Kid]

You may have installed the cocking tube support at the wrong timing. On a K-gun, pointing forward, the detent should be facing the right side. If you installed the support so the detent is on the left, it can be difficult to unlock.

I have also found that if you use a standard MP5 detent spring, it can apply too much tension. If this is the case, simply cut 1-2 coils off the spring.

 

[Chopstix Kid]

Thanks Joe. I did indeed have it timed wrong. Cut 2 coils off the spring, rotated to the right, worked like a charm. I received my F1 back several weeks ago and finally had the time to send it off for engraving today.

Awesome! Put some photos up!