I am in the process (still) of building a PTR91, and have a question regarding the front sight tower. I have the stainless heavy barrel, and the lower ring of the tower will not fit. It seems that the grenade attachment is causing interference with the fit. How do I go about removing the sleeve for the grenade adapter? I see two welds on the side of the tower; do these have to come out in order to get the attachment out? I can't find any towers without the attachment. Help!