Gummed Up Cylinder

[TwoPoundPull]

My steel plate gun is a mooned 627, used to shoot 158gn Laser Cast over 231 in 38spl...
Now I'm casting 158gn RN Saeco #390, range scrap-10% w/w, thru a Star sizer with Magma Red, and 7.5gn 2400 38+P...
The issue is after 4-5 cylinder refills the moon clips do not wish to play nice and drop in and out, they need to be pushed...
It is not a leading problem, I have no more 231 or Laser Cast...
How might I know if it's the lube or the powder that's gumming up,

[Outpost75]

My steel plate gun is a mooned 627, used to shoot 158gn Laser Cast over 231 in 38spl...
Now I'm casting 158gn RN Saeco #390, range scrap-10% w/w, thru a Star sizer with Magma Red, and 7.5gn 2400 38+P...
The issue is after 4-5 cylinder refills the moon clips do not wish to play nice and drop in and out, they need to be pushed...
It is not a leading problem, I have no more 231 or Laser Cast...
How might I know if it's the lube or the powder that's gumming up,

It sounds to me like the #2400 powder is leaving unburned granules under the extractor when you eject the empties. Try brushing the underside of the extractor star and its recess in the cylinder. Hold the muzzle vertical when you eject the empties so any unburned powder fall out with the brass, instead if being deposited under the extractor.

Also #2400 is not the best choice for. 38 Special +P as it doesn't burn well below about 20,000 psia. I load 9 grains with Saeco #348 DEWC for use in my. 357s, which is accurate, but it exceeds +P pressure in .38 brass.

[Artful]

Push a paper towel thru the cylinder if it comes out greased it's the lube coming back around your cases.
If there is still a coating of grey it's the powder. It sounds like the cases are not expanding enough to keep all the contaminants from blowing back into the extractor and chambers.

[bhn22]

Most of the pin shooters I used to hang around with used Allison Tool Speed Brushes after each relay to keep the cylinder clean. The carbon ring situation has been around since the 357 was originally developed, you could simply try using 357 brass, or try a different powder than 2400. Anyway, your load doesn't burn efficiently as mentioned before, and you need to change something somewhere. Accurate Solo 1000 is very popular since it burns really cleanly and efficiently, but most fast powders should work fine if you can get the velocity you need for your class. As you discovered, 231/HP38 are in kind of a sweet spot for your application. Titegroup might work for you, but it makes the guns really hot during any extended strings of fire. Oh, and I never was a fan of Magmas bullet lube, it always seemed a bit "dirty" burning to me.

[runfiverun]

it's micro-paraffin with a titch of carnuba added in.

[bhn22]

Paraffin. My favorite.