If the lead is too soft for the pressure you may run into issues with too much obturation that could lead to leading issues. I haven't tried it with pure lead myself but with care I'm sure you'd be fine with lower pressure stuff. As I always try to remind people, it's not velocity you need to worry about, it's pressure.
If your bullets are sized properly the PC should be enough by itself. I use the LEE 55grn mold to make bullets for my .223s. I don't bother with a gas check as it seemed to reduce accuracy significantly. The PC is more than adequate if applied properly. I use a 20BHN alloy and size the bullets 0.002" (including the PC) larger than whatever barrel.
I did say I haven't used pure lead, I have used scrap from the pistol berm though. I doubt it was exceptionally hard. I wouldn't use anything too soft for that kind of loading. Considering how easy it is to get to reasonable BHN there isn't much point.
Barrel twist is one of the things you have to look at
you can push a bullet real fast, not get any leading .......... But ...... can not hit a target at any distance ..... even 50 yards could be a problem
Called Bullet RPM theory
I have powdercoated soft lead bullets for my 44 magnum. They definely lead with a medium pressure load.
PC - .223 bullets - I use wheel weight lead, cold quenched, sized, then Princess auto Blue powder coat, baked at 400F, then re-sized the powdered coated bullets. I have developed a load, that pushes them at 2500FPS with zero leading or break up, they are 4" group accurate @100M and super cheap to make. They are plinking and fun rounds.
If you only have pure lead - order some 5lbs bars from Amazon of Tin and Antimony and start adding to your lead by weight. Lots of formulas online for ratios. My sailboat lead weight haul is all pure lead, and I make 10Lbs batches of hardened "wheel weight" lead in batches.
I cast, PC, for all my .30 cal (30-30, 308, 30-06), ..23, 9mm, round balls (pure lead for black powder), "0" buckshot, and .690 round balls for 12G
Gas checked?
As I said in post #12 wood isnt solid enough to expand commercial "hard cast" but I think hard cast will expand very well when hitting solid bone in an animal at BP hunting velocity rounds (anywhere from 1100 to 1500 fps). I make this statement after observing thousands of hard cast slugs flatten out to thickness of a toony after hitting steel Cowboy Action targets at 6-700 fps.
Sounds like you want to have the bullet mushroom and still be powder coated. You can make a duplex bullet with a bit of experimenting, not hard to do just have to find the right amount of lead to add to 1/2 to 3/4 of a bullet nose. Here is what I did for my pedersoli 45-70 single shot. I filled the bottom 3/4 of the bullet with hard lead and let it setup, then with a buckshot mould I did one 00 buck pellet of pure lead and dropped it into a ladle to melt. With the ladle of soft lead I poured it into the mould on top of the 3/4 hard bullet. Then rested the whole mould on top of the molten lead in the pot until I could see that it melted both halves together. Then very carefully lifted the mould and let it air cool until it solidified and dropped the bullet onto some rags to cool.
Then I did the sizing and powder coating as usual. I shot it into a dirt pile at about 50 yards and the nose did mushroom somewhat. I would like to try and just powder coat the body of the bullet and leave the nose un coated but I would have to buy a powder coating gun of some kind to do that and I am not that curious at the moment. More important things to worry about and beside when you are working with nearly 1/2" slugs to begin with it really doesn't matter if the bullet mushrooms.