For the record, my effort with the 240 XTP Mag was done using my original Bushmaster 20", 1:24, chrome lined bore upper with a carbine gas system. I have not revisited them since I got the Bartz upper. Thought I should clear that up.
How does the feeding issue with the 275 Barnes manifest? I typically load both the 200's and 275's to a COL around 2.19, in order to drive the taper crimp down into the front driving band groove. Even though the 275 is longer, seating the bullet to the middle driving band groove IIRC, yields a COL too long to fit in the magazine. I'm at work, so the last statement is running off of recollection.
Hoot