I never lapped a mold, but, as Jess mentioned, I tried that beagling on an old Winchester mold for my trials of bullets. It was just a little undersized for my rifle's preferences, so what the heck.
I had aluminum tape and the mold was actually out of round anyhow. On the sides of the partings it was bigger than the across way. So, the 'beagling' actually improved the overall roundness- but it didn't shoot worth a hoot in my rifle that way either. Worth the try to find out, though.

I could see how a cherried mould might be out of round, but the way Accurate and NOE do it, in a CNC lathe, I can't see how the mould could be anything BUT round.  I'll have to dig out one of my father's old Lyman moulds and do a trial.  Of late I've only been casting in new CNC cut moulds.

I also can't see how lapping wouldn't improve a mould that started out seriously out of round.  The lap just has to bear more heavily on the small diameter and if anything not cut at all on the big diameter.  'Course if you're starting out with an out-of-round bullet cast in that mould, you'll never get it started unless you start with the mould not fully closed. 

So maybe the best practice would be to size the lap to maybe .001" over the smaller diameter, to make it round before you start lapping with it.

JLouis wrote on Jun 17^th, 2019 at 3:14pm:


Machinists have known for 200 years that it's the other way 'round.  The abrasive embeds in the softer material, and proceeds to cut the harder one.  When lapping steel, cast iron is commonly used.  When lapping small holes, brass "split laps" are common.  They look like an oversized needle - a wedge is used in the eye to expand them as needed.  

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Just one of hundreds of hits I got from searching >lapping small holes<

Quote:


When I was in the machine tool industry, I watched a man improving the accuracy of a long Acme-thread leadscrew by lapping it with a bronze lap. This bit of magic goes way back to Jos. Whitworth. We also lapped the hardened steel sleeve bushings in deVlieg spindles, using a complex cast iron lap.  The bars were also lapped to size and cylindricity, but we had deVlieg do that.   

Why it didn't occur to me until now I can't fathom.

Ordinary Lead is too soft for lapping cast iron.  Cast your laps from Cerrosafe, or at least monotype.

Hope I remember this when next I need to lap out a mould.

I agree that, given that the mould was already so bad,you had a tough row to hoe.  Sizing the lap as I suggested might have helped, but it's water under the bridge now. 

I'm still curious to know whether the bore in your Stevens is really that big!

Yeah, you don't hear about so much anymore, since the Bubbas are all off playing with their plastic pistols and AR/AK whatchamacallits.  But it used to be pretty common.  One thing I admit to having done a couple of times is to lap the bearing surfaces of bolt lugs.  Equalizing the bearing did help a Rem 700 that I was enamored of some decades ago.  Getting all the compound out is a real problem, though. I don't positively KNOW that I ever got it all.

I have a very nice all original 44.5 with a butiful looking bore ,
My father just got a all original 52 with all original numbers matching perfect bore also.
I've slugged both barrels with a .321 sized bullet and we get
Vary little riffling grooves on the slug, ( 2 slight taps with a small plastic hammer and it's all the way in ).both rifles are 32-40
Personally I have never had this many problems loading all my big 
Cartridge Guns as these little ones. . I have shot only the 44.5 so far with a sized.321 bullet and could not get any better groops 
Than 4-5" at 100 yards. I think it needs a bigger dia. Bullet. Oh yea fixed amo, not breach seated.niether riffle will be used for compitition but it should shoot better than that.

Doug