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All my molds that I've bought in the past cast bullets larger than needed and I sized them down.
I have a new Lee two cavity mold that throws exactly the diameter as advertised with the alloy I'm using, but I need the bullets .002" larger diameter.
So is it better to have a mold that throws the diameter you need or larger, powder coat and size to a smaller diameter vs trying to increase the diameter by powder coating?
In short, is one better than the other as far as accuracy goes?
I have a bunch of 30 caliber molds (and more than a few 30 caliber rifles). I also own a Mauser in 7.65x53 Argentine. I can pretty much use any of the 30 caliber molds in the 7.65x53 by powder coating them to bump up the diameter. In a 30 caliber rifle I size the bullets .309". For the Argy I size the same bullets .3125" I've found that the best powders for increasing a bullet's diameter are Smoke's Signal Blue and Eastwood Ford Light Blue. I bet the same trick would work on my SKS, but I haven't tried that yet.
It does depend. :)
I size my PC bullets a bit under (.001 or .002) my desired size. After PC I size them where I want them. I have not compared accuracy with any other method lately so can't tell you if it makes a real difference. Just know that if you only need to go up .002" then a layer of PC should do the trick. Be sure to size after PC just to make sure your bullets are consistent.
I have a 30 cal mold that drops about 0.310-- I regularly PC these for my 303 British and 7.65 Argentine loads, where I use them at 0.313. Works just fine and that's at rifle velocities. In fact, in my Enfield (SMLE) that bullet shoots mire accurately than my gas checked bullets of the proper size.
The extra .001 to .0015 that powder coating gives my molds has improved performance for all my old military rifles.
Well, here is my hot take. It depends on the powder you use and your method of powder coating. Right now I'm working with a barrel that slugs out at .310" with a mold that drops right at .311". When powder coated with a 50/50 mix of Smoke's Carolina Blue and HF Matte Black using the shake 'n bake method and cured at 415F for 1hr I get bullets that measure .313". I tend to leave just a little more powder on the bullets than I normally would, but still, I usually get close to .0015" - .002" diameter increase when powder coating.
Personally I like my boolits to be about .002" over the slugged diameter if the cases and chamber allow it. It seems to be my "sweet spot" in finding a good boolit fit that doesn't lead up my bore. With that said, I also like my finished product to clean up the driving bands when I size. I don't want irregularities, if that makes any sense. So for me, I generally like to have a boolit that drops at 0.001" over, and size down to .002" over after powder coating. But if a particular powder doesn't get me there, then I would choose a boolit that drops a little larger.
So my answer is, it depends on the powder and your method of coating the boolits, specifically pertaining to their increase in size after coating. The thicker your coating ends up being the smaller I'd want the boolit. I don't want to have to size it down that I deform the boolit. But I also don't want to have to try to fatten up the boolit to the point that I'm putting on really thick or multiple coats of PC.
Thats what I do to the Lee 309 230gr. There is talk about this mold casting undersize and mine does too using an approximation of Lyman #2 alloy. 2 coats of powder brings up the diameter enough so I can size to .309 for 300 Blackout. It turns a troubled boolit into an accurate thumper at low supersonic velocities.
I appreciate the feedback as I wasn't sure.
Thanks all!