fmjcafe,
I just got my first Ishapore Enfield in 7.62 nato this last week. A really fun rifle and with cheap ammo, what's not to like. Sure it's ugly as sin, but it shoots fairly accurately and functions reliably.
fmj..... the friend I got this rifle from has had 9 Ishy .308's in the last year. He has kept the best 3 and selling the rest. He tells me that I got the best of his "rejects".
He did tell me of one rifle that was, according to him, a real beauty with all matching serials and nice wood. It practically broke his heart when he began firing it though. He was experiencing the same problems you were, VERY hard extractions. What he found was that there was a bulged "ring" in the chamber that the case was expanding into on firing, and then being virtually locked into the chamber. This one is now a "parts gun".
He has no idea how this ring was made, but was most likely made by an overpressure round.
Look over some of the brass from your rifle.... Is there a shiny ring made by a bulge being swaged out as you pull it from the chamber??? Can you get a bore light and see into the chamber area?? Look for anything suspicious.
Just my .02,
Swampy