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JP Supermatch Chamber/Throat Bore Issue

timbrline

MSgt
Full Member
Minuteman
  • Mar 8, 2010
    161
    612
    MT
    Just throwing this out there. Playing around loading up some 180g Sierra TGK's in .308 for a factory built JP (Mega receivers, 16" 1/10" Supermatch barrel, LMOS bolt/carrier, buffer, etc. the typical "JP" stuff).

    Are these know for tight throats or do they use an unforgiving reamer? Basically, seated a sample just to test jump off distance. At standard 2.800", the bolt jammed it into the lands so hard it was stuck. Seating it down eventually all the way to 2.74" OAL it still engaged the lands hard enough it stuck and scored the bullet. So, I dropped in some out of the box M118LR, which I had shot a few times with good results. While it cycled and I never realized it before, now that I check... The M118LR's when just cycled, have land scoring on them as well so its jamming them into the lands as well, just not as bad.

    So, was thinking maybe these 180 TGK's were just too much for this particular gun...but about anything should throw a M118 (within reason).

    Hence - they use a super tight match reamer or something that is going to give me fits with anything bigger than 168 or so? Just wondering if anyone had an experience similar or knew the scoop on these barrels.