As a newbie my ability to share images is currently not allowed, but as a designer/builder for the past 10 years I can't wait to be able to start posting images and drawings of some of my more successful builds for feedback/comparisons. My avatar image features one of them...a 9mm pistol that has a muzzle energy of 100 ft/lbs but is extremely simple in design with a minimum of parts to fabricate.Normally I use LW barrels as I have no way to produce rifling, but my ancient South Bend lathe and Grizzly mini-mill plus a few basic attachments/tooling are all that is required to do the rest. I use mostly 6061 alloy, some 7075 alloy, and stainless steel/tool steel for the rest, ( plus of course a collection of files)I'm looking forward to also to getting some tips perhaps on how to do some things faster, or simpler, or with better safety margins in the finished product.
Here is a custom built, 9 mm, PCP-big-bore-hand-built-Air-Rifle, if this is your road you like to travel along. https://www.ebay.com/itm/PCP-big-bore-hand-built-Air-Rifle/323120197838?hash=item4b3b76f0ce:g:-eoAAOSwzAtadIoJTia,Don