copper coated bullets

[Battis]

I've been shooting .351 180 gr copper coated bullets in my .351 Winchester. With approx. 15 grs IMR4227 in .357 cases with turned down rims, the results are impressive. I just ordered an Accurate mold for a .352 175 gr bullet without gas check.
Are copper coated bullets somewhere between jacketed and cast? Does the copper coating act as a gas check?
With that low charge of 4227, in those short cases, would a gas check (or Cream of Wheat) be needed?
Yeah, the horse is out of the barn - I should have asked this before ordering the mold. But I think it'll be fine.

[Master_Mechanic]

Plated bullets are a step between jacketed and cast. Gas checks stop bullets from skidding rifling, if you match the alloy and velocity to the twist rate of the gun properly you shouldn't need a gas check. Checks can cover up problems.

[Wayne Smith]

Alloy matters. You need to read some of the posts relating to the plastic limits of various alloys. This relates directly to the alloy's ability to maintain shape as it enters the rifling and not deform (skid). Water dropping helps, tripart alloys help, and knowing what you are doing is priceless! Fit is King, but alloy strength has to be at least a Prince.