I’m loading some 230 grain cast lead bullets for my s&w 625. Brass is full length sized, and checked in a Hornady headspace/case length gauge. Sized brass plunks right into the gauge with no problem. Seat a bullet, check in the gauge and no go. Seat bullet a little deeper, and the cartridge goes in the gauge a little further. I have to seat them what seems to be pretty deep to get them to plunk into the gauge. I understand that seating depth with increase pressure, these things seem pretty short to me. Can anyone explain to me what’s going on here?

Plunk the rounds to the revolver and say bye bye to the gauge. IMO

Get a Lee Carbide crimp die. I had the same headache with some ammo. The Lee Carbide Crimp dies fixed the problem.

^This^

They are gonna be fired in the revolver, not that that gauge.

Did that, the ones that are seated long only go half way into the cylinder.

1.275 max length with 230 ball. Your revolver is telling you they are too damn long.

If your Cast Bullets are a bit oversize they will in some cases expand the case making them difficult to chamber. I size to .452 /.453 diameter and Load to recommended OAL.
At .454 I had the same problem with a 625 Revolver, and a tight chambered Colt 1911 Match gun.

That was the problem right there. These were purchased from a commercial caster. And I checked them this morning and they are .454. Ran them through a Lee sizing die and now they are good to go.

Years ago I switched to .45 auto rim cases for my 45acp revolvers. For me it made things a lot easier.