with the muzzys all you have to do is ad 5gr brass washer be hind the head to keep from spliting the shaft... The Perfect Arrow thread is the ticket with the carbon insert, i`ll be trying it really soon... it sounds like exactly what swampbucks looking for high foc an strength. I`m going to try it with the axis shafts gotta love that small dia. it blows through every thing i shoot if i can get the internal footing to work it will be one hell of shaft strong, thin, i guess in the upper 25-30% foc... check it out