Starburst on cylinder face...what can it be?

[Pigshooter]

Details:

Taurus Raging Bull, 454 Casull, Stainless (Matte).

250gr hard cast (BHN 18-ish), powders used = Unique (1100fps), 2400 (1450fps), H110 (1700??fps). Small Rifle Magnums in all except Unique, which got small rifle primers. The hot one I have never chronoed but it is pretty swift.

All shots single action, standing, slow and steady. Each cylinder of 5 shot in a 2 minute spread, always starting with the same cylinder. The reason for the different loads IHMSA competition at different ranges.

The problem: On inspection, I noticed a starburst pattern on the front of one of the cylinder faces around the chamber mouth. It does not seem to be leading, and yet it does not look like gas cutting either. I can find no brass that looks bad, although it is getting pretty old. I am starting into my 4th box of primers, and most brass came from loaded shells, so this has well over 3000 rounds through it.

What do you think? What can this be? It has never occurred before.

 

[riddleofsteel]

hard powder residue

it can be more of a pain to remove than copper in a rifle bore

you do not see it in revolvers or pistols much until you get to the high pressure "magnum" rounds

actually the discharge from the cylinder gap is part lead or copper, escaping gases and unburned/partially burned powder

most modern gunpowder is a close cousin of plastic or celluloid

the starburst you speak of can be a bear to remove

try a Rigs Lead Removing cloth on stainless cylinders

if that does not work try a pencil eraser

 

[Radicalcleric]

I suggest trying standard large pistol primers. I have never needed magnum primers in any caliber I have loaded, including the .375 H&H or the .460 G&A which uses well over 100 grains in many loadings. In my experience the hot primers increase pressure very quickly and way out of proportion to any velocity increase they generate. I have never had any trouble getting standard ones to fire the biggest powder charges effectively.

 

[AC]

My take on this, unless I'm misunderstanding the initial posting is that the starburst is not around every cylinder throat.

If that is indeed the case I think one of the chambers is not aligned with the barrel very well and you are getting some lead and powder vapor splashed back on the cylinder face at that chamber.