Sorry to res a bit of an old thread but it seems to be a great source of knowledge for the 249.
I've just bought mine, put in the HPA conversion V2 from AirTac, an A&K Sound wound box mag which feeds perfectly, and so far performance has been pretty good.
I did try to fit a 430mm Mapleleaf crazy jet barrel with a 4uantum gbb bucking but the mapleleaf barrel just wouldn't sit comfortably and the hop unit refuses to close properly (which is a git to get out anyway!) so putting it back was just a no go. Any tips appreciated there!
Also, has anyone improved the nozzle seal - that O-Ring basically is zero resistence - and the return spring sucks its so weak. I've replaced the spring plug with a Waldo Designs replacement which is a nicer little mod that has a 0.5mm allen screw instead of a raul pin. Handy.
I've also installed a Jaeger recoil weight - went in easy and added some solid recoil weight - very novel! I can't get that open again now though lol it's solid at least!
Any tips on any of the above - please shout me!
Thanks 249'ers!