Lapping Size

[ColColt]

I know I've seen this before but couldn't recall the specifics. Lapping a mold with #320 Clover-what size increase can you expect....001" or greater? It's for a Lyman 358421 mold.

[mooman76]

You can keep going quite abit. I have heard of some going as much as .005 but the more you go, the more distorted it will get depending on the care you use when lapping also. best to cast a new bullet to lap with after each .001 you go.

[ColColt]

A couple thousands would be good. Lyman was suppose to have reworked or replaced the one I sent them and they sent a new one. It's still not right. It mikes out at .356-.3575". The one I sent them was worse.

[RobS]

I've run a mold out .003 before but a person should expect it to take time to do a good job. I like to use air cooled WW boolits that are aged for the lap and I not only turn the boolit clockwise but will then also come back with a small easy-out so I can spin counter clockwise.

The big thing I've learned to keeping the cavities round is remembering that less is more. I roll the lapping boolit between two metal plates and work the compound into the boolit real well and then wipe most of it off. The compound that is embedded into the boolit will do the work, the cutting. When the boolit becomes easy to turn simply add more compound by rolling it between the metal plates that have the compound on them.

I start by turning the lapping boolit in the cavities very slowly while gently closing in on the blocks. I'll stop after about 10-15 revolutions the first go and then wipe the excess lapping compound that builds up on the mold block face near the edges of the cavity. This build up will keep the mold blocks for fully closing when the mold halves do finally come together which makes for an un-round cavity.

[blackthorn]

Do a search for posts by "longbow". Some time ago IIRC he did a post explaining how he lapped out a significant amount.

[geargnasher]

Just send it to Erik Ohlen with some castings of known alloy and tell him how big you want the bands to cast. He'll enlarge the driving bands and you won't risk ruining the mould. I will also be ROUND when he's done. Even if you do get it lapped evenly, it's difficult to keep the edges of the bands sharp.

Gear

[ColColt]

Erik is tops in what he does. He recently did a Lyman 429421 mold for me and I've been most pleased with the results...no more beagling that one. I had thought of him yet again but thought I'd give lapping a try but since I'm in no hurry I may send this one to his as well. It's the only permanent fix for an undersized mould and you'll be happy about it.

[GaryN]

I tried the lapping thing. It took way longer than I thought. I really don't think it is worth the time on an iron mold. It is also hard to keep the cavities perfectly round. I have another one that is under size and I think I am going to send it to Erik. I'm just trying to decide whether to have it hollow pointed while it is there.