I picked up a nicely sporterized Mexican 7x57 a couple of years ago and it shoots very well with H4350 and the Barnes 150 TTSX. However, I have to keep the OAL to the max in the manuals and I can't get long enough to touch/backoff from the rifling due to the original magazine box length and whatever the throat is. Is there a way to lengthen the magazine box and still have proper feeding?