Remixed Caliburn backbutt (with lengthened guide rod)

A quick experimental remix of the Caliburn back butt piece -- the only change is a lengthened guide rod, which is now almost twice as tall as the original.

[UPDATE] 24 April 2018: after lots of testing, it seems that having a longer guide rod does not make the prime any easier, nor does it change the performance of the spring (fps). So consider this purely an aesthetic option, if you prefer seeing your spring straight instead of flexed/bent.

WARNING: Print and use this at your own risk, an