People keep mentioning wood. I didn't use it but I see a few issues. 1 wood will scratch if you drop it, put it against the paint, and IMO just awkward (lots of stopping power tho) and for the end holes the gap gets more narrow and the wood may not fit.

Just shove a bunch of shop towels behind there. They catch the bit as its coming thru and fit as the handle narrows at the ends.

Really pretty simple once u get first hole drilled and know what's coming.

 

Not a problem!! Glad to help! Told you it was easy

 

Agreed. Easier to just use a towel or rag behind the handle.

 

and you then have a cartridge holder might just cut the cartridge and leave them for accent on mine