Yes, the steel will contract, the wood does not. That pulls the metal from the
bedding. I came up with that idea years ago.
I change allot of roller bearings working on locomotives & locomotive parts. I
shrink & expand bearings on shafts & housing all the time to make them go on
easier, & not pull metal on the shafts & housings.
On day I walked pass the deep freeze with one & it hit me, same thing. Shrink the
metal from the wood & bedding. It worked.
But again, Preperation is MOST important. Taper that breechplug & tang. Fill the
holes if there is any. I fill the rear of the barrel flush with modeling clay. Those few
threads on that barrel even with breechplug in ?

Will lock that barrel IN.
Fill it even with modeling clay & scrap it flush with a razor blade.