Both of the throating reamers I've rented from 4D were solid pilot and were used by hand, all three 45-70s and the 35 Remington are very accurate, so I guess it just depends on how well the reamer pilot fits the bore and how careful you are doing the work.
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Since you're ordering the reamer, you may be able to specify the pilot size to fit your bore.
FWIW, I've rented a few chamber reamers, all reamed by hand, all but one had solid pilots, all barrels, except the 460S&W which has only been to the range once, shoot good to excellent, the one reamer that had a floating pilot, a 270 Improved, is just as accurate as any of the others, specially considering the bore is .2795" and I shoot .284" bullets in it which is the only load I've worked up so far.
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The 357Max reamer that has done
49 90 rechambers so far has a solid pilot, not one member has complained about accuracy yet.
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Tim