There are gonna be 2 options when it comes to high quality prints. Out of darts or silverfox industries. Both are pacific northwest based, both have fantastic customer service and both have awesome print quality. Both also have a great selection of colors, although technically silverfox has a few more options.

As far as upgrades go, I do generally recommend the aluminum “vanguard” ramrod and even injection molded rambase, plunger and sear upgrades. I believe out of darts and possibly silverfox both sell those upgrades, although I’m not certain of their compatibility with the caliburn 4 specifically. If I’m not mistaken the ones offered by are made of either acetal or delrin. Generally going to give you a better seal due to high quality tolerances, and last longer as they’re more durable than their 3d printed counterparts.

As far as barrel upgrades go, I recommend getting a 13mm ID barrel. I’m not 100% sure of the optimal length for a caliburn barrel, but with my 40cm long 13mm ID barrel paired with a k25 caliburn length spring I generally get in the 210-230 fps range, with a very manageable prime. I believe out of darts has the 13mm ID barrels on their website organized by what blaster it’s recommended to be paired with.

As far as a foregrip goes, not that you asked, It’s mostly a preference thing, although some folks find priming with an angled grip easier on the arm because of the muscle group it engages, while some folks find a vertical grip is more comfortable. It may wear on your elbow more than an angled grip, however. I personally recommend a k25 spring as long as you’re not trying to break 250 fps, as I find any heavier spring is generally uncomfortable to prime. Lot’s of folks may go with a k26 and while it’s manageable I don’t feel the additional weight justifies the FPS gain.

As far as a scar or bcar goes, I believe you can choose to include one of Sillybutts’ printed spigot scars with both silverfox and OOD, which offers printed rifling(which has decent accuracy but tends to affect FPS more drastically) and the ability to shoot mega XL darts by fitting them over the end of the pcar. Beyond that, I’m not terribly familiar with the popular BCAR or SCAR options out there as I generally use a printed version by old fusion designs that’s very easy to string yourself, and my only experience with BCARs is an integrated one on my lynx blaster, so hopefully another commenter can offer their advice if you’re looking to get the best of the best. Hopefully that answers most of your questions!