Hallo good people.

I'm sorry if I ask a stupid question now...,
but can I expect a UNIFORM diameter of the die after lapping ?!

-I coat the sizing-stem with LBT lapping compound, and push the coated stem back and forth by hand ?

Chr.

Welcome aboard chr.

I wouldn't do it that way for two reasons. You will lapp the stem down as much as open up the die and it may not lap even done that way. I split a bolt lengthways so a piece of fine wet and dry (about 400grt) will wrap the bolt to just fit in the die and put the bolt in a battery drill. Put a bit of laping paste on the papper and with the drill on slow let the die turn slowly as well so any inadvertant sideways pressure is directed evenly round the die. Stop and check often by cleaning and sizing a couple of bullets till you get to the size you need. There is only a short portion of the die that sizes so do check often.

Von Gruff.

The split rod wrapped with 400 wet or dry or fine emery cloth is best. No compound needed. Make the wrap a tight fit going into the die and SPIN IT FAST. That allows self centering and will round out an oblong hole. Do a little and size a boolit at each stage. Clean the die before sizing a boolit and lube the boolit.
Takes about 5 minutes to do a Lee die.

brf shooter, as you say I spin the lap fast but because the lap is a tight fit it also allows the die to turn slowly. For me it gave a perfect bullet fit when finished,

Von Gruff.

I have done jit to several lee sizing dies to get the dia bullets I needed work well chucked it my lathe spin them fairly fast use real fine emery cloth. test often untill one gets the dia that you want.

I know this will be a dumb question, but here it is.
What lap the die at all?

I am thinking of getting into bullet casting so I've never done it.(trying to learn some stuff here)

You lap the sizers when you need a bullet to be a little larger. There are a few reasons you might need to do this, making an oversized bullet fit a worn bore, for example.

I see, but say for a newer bore, you wouldn't need to do this?

It depends on the size of your bore - grooves compared to the size of your die.Not all barrels are produced with the same dimensions and all sizing dies may also vary a bit from what is marked on them. You will need to measure a barrel slug and a bullet from your sizing die. Ideally the die should be .001 - .0015 larger than the slug. There are some variables as it also depends on the alloy you are casting with as well.You can get away with a slightly smaller sized bullet with harder alloy and - or a GC but with a softer or a plain base bullet you may need to lap a die to get sufficient size to stop blow-by which can be a cause of leading and poor accuracy. Having said that, sometimes a soft alloy will bump up but we may be getting ahead of your requirements just yet.If you post your data we may have a better understanding of your needs.
Be aware that this is an adiction that has no known cure.
Von Gruff.

Ok, so I need to make a barrel slug for each gun I plan on shooting the cast bullets in? Then measure that vs the bullet after sizing?

Ok. one other dumb question (well it probable won't be my last) Why is it I can buy cast bullets from a suppliers (have been using Tennessee Vally Bullets for 45 acp and 38 spcl)and shoot them in several different guns?

James the question you asked first was why lap a sizing die and the answer is to get a larger sized bullet for a particular need. This dose not necessarily mean that every die needs laped but in certain situations may improve the results gained. A barrel will except most bullets meant for that caliber but SOMETIMES with experience some gains can be made with a bit of tinkering, whether it be in alloy, velocity, sizing or any one of the many variables inherent in chasing beterment (is that a word)in cast bullet shooting.

No question is dumb if it leads to a better understanding, besides how do you think the rest of us learned.

Happy new year to you all

Von Gruff.

I agree with Von Gruff. Fit is king! Slug your bore on any/all firerms in which you will shoot cast! That is the starting point. Ideally you want your bullet to be one to three thousandths over the GROVE size of your firearm. You may be able to use your castings "as cast" without sizing them at all,, but you won't know until you have slugged and measured your firear's internal dimensions. There is a wealth of information/instruction on all aspects of bullet casting on the "net" if you Google "Cast Boolits". Welcome to the addiction!!!

Here are a couple of dedicated casting sites with very clued up casters.

http://www.castbulletassoc.org/forum/

http://castboolits.gunloads.com/forumdisplay.php?f=8

Von Gruff.