This does look interesting on first glance but raises many questions that we need more pictures to help answer. I don't see any pictures to show the muzzle end of this rifle. Can we get some nice close ups of the muzzle and front barrel band area? One picture shows that there is no front barrel band but the cut off needs to be seen. The rear sight looks like it might be an 1896 Carbine sight from the top but, as olderthansome said, it could just be the leaf. The J.F.C. is very intersting but is way too nice and not worn to be real, if indeed it is a Constabulary rifle. These are just not seen for real. The upper handguard looks to not match the stock from color and wear. The serial number and receiver is not a Model 1899 which is where we would expect the Constabulary rifle to be situated.

I don't have my references handy but these are some of the initial questions. Is the muzzle turned down to fit a bayonet?

So, thanks for showing pictures and giving us lots to consider. Please try to post more pics when you can. Always nice to have another mystery with our beloved Krags!