I think they probably are close to the same as JSB, I've never bought any FX pellets so I couldn't say about them.
I measured the head and I'm seeing right around .250 at 4 different points, so it seems just the skirts are out of spec. I guess this deserves a little more inspection to figure out what is happening and why.
well sounds like it is probably not a leade prob... but would check on a few with expanded skirts also just to see what I get...I think would chuck up a piece of .25 dowel in the drill press and then angle the end slightly greater angle than skirt to try expanding skirts consistently that way..?
I just chambered a a couple and pushed them back out. They chambered easily and of the process left any marks at all, I can't see it.
If the 249-39 was a .250 or larger(so could size down) would be all over it... if it was available when $ match wants.. on that style of round my more tightly choked .25 rod likes the H&N Grizzly... they seem to be .0002 under land size .2495"...that barrel is choked to about .2487 ish the looser choke mrod is about .2493 ...pic of loosly shot groups below... Kings shot highest... Jumbo 34g to the left and best... Grizzly hit lowest and the one to the right is not a flier ... aim point for it was even with horiz bar of cross under K in word kings... do not know if it was luck... but that is where I though it would... without lube the griz do bad... have to head out for a while to deliver bed frame to son... back in a while...
I was casting at around 800 degrees so that may not help.