Barrel slug bigger than barrel?

[Hobbyman2007]

Looking for a bit of clarity. I've slugged my barrel numerous times now using a three decimal point outside micrometer and it always came out to .254" just like the barrel specs ( Lothar Walther) states. Yesterday I was confirming measurements with a newly aquired four decimal mic. This time I pushed in the slug (51gr BBT ) that measured .2550"before . Once pushed trough the bore it came out bigger .2553" . I repeated the process several times to confirm my measuring . Has anyone seen this before ? Does it make sense that the lead would expand /swell once out of the bore ? Thanks

[rkr]

I would say that the bullet bands expand a bit as rifling lands bite in to it. The lead has to go somewhere so it expands to the grooves.

[rsterne]

Yes, entirely possible for the OD of the bullet to increase slightly if the rifling lands displace lead and it flows outwards into the area in the grooves.... This can only happen if the original bullet is smaller than the groove diameter of the barrel, of course.... Otherwise the groove portion of the barrel will "resize" the OD to a smaller diameter to match the groove diameter.... In that case you nearly always will see marks on the portion of the bullet between the rifling grooves, where the OD is scoured by the grooves....

With an LW barrel, you will most likely get a different diameter at the muzzle than at the breech, because they are usually choked slightly....

Bob