stoph

There's also alignment issues with beefier springs. Most EAT mod kits available use a tube system that sits behind the catch, which the tail of the plunger rod passes through. It aligns the rod so that when the sear comes into play, it's at the correct height. Experiment with a range of PVC stubs to see which ones will work for you.

Do a search for Hacker spaces around your area. They're creative collectives that provide generally cheap/free manufacturing services, ie a couple dollars for a few hours on a 3D printer or laser cutter. Makes it much more accessible than paying for short runs through larger companies.

ONN made up a BB kit for the EAT, though he was having some consistency issues with his foam stock, and to my knowledge never got a full kit out (albeit perhaps in a limited release beta). He was getting BB'd Longshot ranges with it, which is huge given the difference in PT volumes between the two blasters.

Xplorer have been retrofitting large diameter PT's to the Retaliators, and given the similarities between the Rets and EATs, and with a 5-7kg spring were achieving something in the realm of 200fps with a sealed bolt. The same approach should arguably work for the EAT. If you can engineer/3D print an end cap for some suitably-sized thin wall PVC, grind down the sides to provide a flat surface, you can essentially retrofit the stock internals into it and have a larger volume to draw from. Depends how deep down the rabbit hole you'd like to go...

If you can handle losing a few KG to your desired setup, OzNerfNerd here in Australia does a great kit for the EAT. Comprises of a 7kg spring, uprated catch spring, 3D printed reinforced catch, and an alignment plate that helps keep everything square. You'll often encounter issues with higher load springs in the EAT, and the latter part should help avoid said issues. His kits are quality, and his springs are custom made. He's getting around 100fps on his chrony with AR intact (if I recall correctly). Check it!

OzNerfNerd eBay store

Is there a way to reverse the airflow so that it comes from the rear of the plunger? Perhaps a check valve? You could mount the RSCB on the grip and have the plunger move freely back and forth, while retaining a fixed barrel. Would also make for a shorter blaster and easier reloading.