Someone recommended that I neck turn my .38-55 brass for concentricity.  I have never heard of turning straight walled cases..the .38-55 case is tapered, unless the turning was done on a lathe with taper attatchment or compound set to proper angle, you would have a straight portion and a step where cutter stopped..I can't see where this would help unless chamber was also reamed this way.  I have inside neck reamed .38-55 case when loading groove sized+.001 bullets in order to be able to chamber in an original High Wall.  My bore slugs .375" & a .377 pin gage is a snug fit in fired brass.  I figure a .376 bullet should be a good fit.

Inside neck reaming will adjust the diameter to match the reamer DIAMETER.  Wall thickness is reduced as material is removed, but there is no control as to how uniform the thickness is that remains.

Outside neck reaming, usually done using a close fitting mandrel is to skim off a LITTLE to make the wall thickness uniform.  This has the effect of making the inside surface (a cylinder) coaxial with the outside surface (also a cylinder).

I recently acquired an H&R Buffalo Classic in 38-55 - it had the classic symptom of too tight a chamber for cast bullets.  A quick few turns with a .375Win chambering reamer took off a few thousandths and cast bullet cartridges now chamber well.

bruce moulds wrote on Jul 12^th, 2015 at 4:54am:


A friend taught me to take off just the minimum amount (6ppc) to maintain the close clearances between the neck and the chamber.

A tubing micrometer can be used to check uniformity of neck thickness.

40 rod,
you nailed that one. turning is easier, and possibly has less potential for tears.
cat whisperer,
clearance between neck and chamber is a thing to experiment with.
br guys used to use fitted cases, where a fired case had enough neck tension to seat a bullet without sizing.
this seems to have gone by the board, due to the potential for all sorts of things to go wrong.
0.002 clearance (0.001 per side) is considered minimum for consistent reliability.
fclass guys tend to run 0.004 clearance as this will generally produce better vert at longer ranges.
lead bullets introduce another variable. they can bump up.
while this is possibly not an issue with smokeless, as it burns progressively, it certainly is with  black powder.
there is no point in sizing a bullet to groove diameter or + 0.001 with black powder, because when you light the fire it will bump up to the size of the internal obturated case before it has moved 0.025".
best here is to cast bullets to be an interference fit in a fired case for best accuracy.
turning too much off your brass will mean that the bullet needs to be even bigger.
thin brass in an oversize chamber diameter will cause big bullets to be sized down in the transition/leade/throat, producing cupped bases.
custom chambering reamers are a help here.
breech seating basically eliminates all these issues.
when turning straight cases for black powder, do not forget to allow enough for the wad as well as the bullet. even allow a little more for where the step is in the brass, which goes to the inside of the case on fireforming.
keep safe,
bruce.

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Many shooters bought the H&R Target Rifle in 38-55 and opened the chamber to work with .380 bullets. 
I have never heard a single person complain that the larger chamber caused any problems.

You would think that SAAMI would update the drawing to modern standards since it is still possible to build a 38-55 with a minimum chamber that will not accept maximum ammo even though both ammo and chambers meet the SAAMI standards.