Modifying a .30 FX Crown MK1

Very nice. I'd ran some numbers prior, and reconed with a larger valve, and an additional plenum I could hit 93fpe with a 600mm barrel (at 150bar). Seems I just need a MKII, lol. Temping, but no budget for it right now. Thanks for sharing the data, though!

I do have a spare bottle which is actually on this gun (480cc fx bottle is taken off), and I have a spare stock. As well as several .22 barrels. Maybe I can convince FX to sell me a receiver block some day, lol.

@knifemaker It actually is polished. I find if I make them nice and smooth I actually loose some velocity. A rough surface actually creates a buffer for flow. Where a smooth surface would create more tumbling... pretty crazy, but I've seen it in MY test data.

I did put my custom 7mm valve and 6.5mm seat in, and picked up another 4fpe for 85 total (925fps) @ 150 bar. I thought about turning it up more, but I am happy with that for now.

@Vetmx LOL that is the one. Don't worry, I havn't done anything that hasnt been done to it prior. I've used the same 7gm hammer weight for two years off and on shooting slugs. (65fpe with 700mm .22 cal, 150 bar)

I've never touched the hammer preset since I originally tuned the gun in early 2019. I actually have another preset block and pin, so I'll never be tempted to change the original, lol.

I have a lot of spare parts for this gun. If I modify a part, I don't modify the original, I modify a new spare. Save for barrel ports and probes. 

I don't have any plans of big power. I just wanted to see what the gun was comfortable with. 925fps is quite a bit. Might even be too much. I don't have any real practical use for the .30 either, and had just planned to shoot standard 44.75gr pellets.


The barrel on it is an older STX with extendable shroud. I had origianlly wanted a superlight, but I've been thinking otherwise... This one feels sturdier. Not sure if it is, lol... But, it's surprisingly quiet extended. Meaning I have no real use for a moderator, and get to save the extra length. And I like that it has a pin/notch lock so that the index of the shroud is always repeated when extended. 

Oh, in other news.... the MKII valve appears to be identical to the MKI other than being made for use with a 6.5mm valve seat.... which should also drop in.

If my 7mm valve fails, I may have to put forward the effort to aquire one. 

Apparently the valve return spring is lighter on the MKII as well... And I am also wondering if the forward valve pin seal retainer is improved?





Here is my custom 7mm valve. Nothing special to look at.... The seal it's-self is .2mm larger in width. and slightly longer than the original.... idea being that more material behind the seal edges will provide a little more support and make it less likely to fail? I scoured the surfaces on the seal front, rear, bore, pin shaft, collar bore, and retainer back. Then epoxied them all. With the expoxy specifications, I should be WELL below failure threshold. Question will be if the seal extrudes or not, lol. Normally the metal cone makes contact with the seat so the seal doesnt get stripped off the shaft... The new MKII valve has a much larger cone that still makes contact with a 6.5mm seat. Mine does not, lol. (and I am using a custom 6.5mm seat)