Straight from the Lee Web Site:
All Lee Mold Blocks are made from aluminum because of the exceptional molding qualities.
The mold cavities are lathe bored for unmatched roundness and size control.
Only Lee guarantees roundness of .001 or less.
Most bullets from Lee molds can be used as cast without sizing.
As stated above, many of the Lee Moulds state that sizing is not necessary .... If you are just the casual shooter, this may be OK. However, there are many, many varibles when talking about sizing. The very FIRST thing one needs to do is to slug their barrel. By doing so, you will learn your bore diamater and that will determine what size cast bullet you should use. You actually want your cast bullet to be .001 to .003 LARGER than you bore slugs. Cast a few bullets and measure your castings. If they are within the tollerance, you should be good to go -- of course, with the right bullet lube applied. It is important for accurancy and barrel leading prevention to shoot the oversized cast bullets. An oversized bullet "bites - in" better while traveling down the barrel and does not permit any room between the bullet and the barrel for hot gases to blow by the bullet; thus one of the major cause of barrel leading.
Example: Most 9mm are advertised with a bore diamater of .356. I have a Beretta 92 in 9mm and the barrel slugs at 357 and a S&W M&P that slugs at .356. All 9mms are not he same -- the same is true for every caliber!!
Do I shoot undersize bullets; YES!! Do I shoot bullets more the .003 over my bore diameter; NO!! -- Do not forget that you may have serious pressure build-up with a grossly oversized bullet.
Well, this may seems overly complicated, it is not ... it is actually a lot of fun. It is great to cast your own bullets and workup a load that will rivial the commercial stuff ... And to add to the pleasure, it makes it a heck of a lot cheaper to shoot -- OK, it does not make it cheaper to shot in that you find yourself shooting all the time!!
I loaded 400 9mm and 300 40S&W today with bullets I cast last October. Made a quick trip to the range and burned a couple hundred of each!! The lead I used was straight wheel weights that I paid $25 for 100#s (25cnts a lb). I was using a 120gr 9mm and 175gr 40S&W -- Let's see what it cost me -- *Note: I have am ample supply of brass!!
400 9mm 120gr = 48000grs
300 40S&W 175gr = 52500grs
Total = 100,500
100,500 divided by 7000 (grs in a lb) = 14.36#
14.36 x .25 (cost of lead per lb) = $3.59
700 primers @$35.00K = $24.50
Powder (used Bullseye in both calibers - did load some different loads so I will use the high-end load of 4grs per round - do not try that in the 9mm - maybe too hot!!) 700rds X 4gr = 2,800grs -- Bullseye by the pound sells for about $20.00 and there will be 7000grs to the pound (.003cnts per grain) -- 2,800 x .003 = $8.40 -- Of course this will be cheaper if you buy your powder in 4lb or 8lb containers.
OK -- 700 rounds using cast bullets
$3.59 for lead
$24.50 for primers
$8.40 for powder