Who is the best place to send a forend to have a Remington 1100 crack fixed...Its a hairline crack following the upper edge of the inside fiberglass

That’s not hard to fix. I’d use my Dremel to cut a “V” on the back side of the crack.

I’d mix up some Acraglas with brown dye. Fill the crack from the back side, working it into the crack. I’d gently compress the forearm in a padded vice, wipe off any excess.

That would hold. A layer of fiberglass cloth on the back side would make it even better.

If that’s not your thing, most gunsmiths could fix it.

DF

That - plus, a thin pin can be drilled/epoxied in, entering from the thickest portion of the back end, and at an angle so as to be mostly unnoticeable.. A bit tricky, but I've done several over the years with good success.