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What does it indicate about a load if lube is deposited on the case mouth upon firing?Two otherwise identically loaded rounds whose only difference is powder type. One will have lube attached to the very edge of the case mouth and the other will have nothing. This isn't just random either. It's consistent and repeatable. Also happens with different bullets and more than just one powder.
I'm not alarmed or anything but very curious what this might indicate about a load and/or powder.
Thoughts?
Not enough initial pressure at firing. The lube is slightly blown back before the case mouth has sealed the chamber. Just a little more powder should prevent it, if it's a bother
Im not so sure about this. It happens with known high pressure loads and fast powders. Slow too.
To be clear about what I'm describing, NOTHING is on outside of the case. It doesn't present in the same way as soot when the cartridge doesn't seal the chamber right away. This is a very defined ring of lube that hangs onto the very end of the case mouth. It LOOKS like it could be the exact image of the space between the case mouth and the end of the chamber. It's very consistent in size and is never bigger.
It sounds to me like your chamber is a little long or the case is a bit short and the space is filling with lube blown off the bottom portion of the boolit. The heat burns the lube a little bit and causes it to stick in the space that is available. It just happens to be sticking to the case sometimes.
I think one of the powders is burning hotter in the chamber than the other.
You didn't mention what gun you were having this issue with but I am not sure it really matters.
As long as the cases don't jam up when going into the chamber, I don't know if this is a problem.
Not an issue per se. Just something I saw that made me curious. This was my hypothesis as well but I wasn't sure why one powder would do it and not another.
Quote:
Originally Posted by tazman
Just looked through fired brass. Two separate Unique loads in 357 magnum. One heavy, one light. Higher pressure load has the lube rings. Lower pressure load has nothing.
Are the higher pressure loads blowing lube into that gap between case mouth and end of chamber?
Perfect seal of chamber! We like it when this happens as it indicates lube is being dispersed immediately and I bet your brass is clean because it seals to the chamber. Lower pressure loads aren't upsetting lube groove enough to eject lube.
Interesting!
This make sense to me.Quote:
It LOOKS like it could be the exact image of the space between the case mouth and the end of the chamber. It's very consistent in size and is never bigger.
I seen it sometimes in 357 mag or 38 special. Forget what one.
It seemed the brass that retained the most crimp on firing, did it?
The heat is not applied long enough during ignition to "burn" or melt anything.
The bullet is in the barrel for just a few milliseconds.
High pressure loads bump up the boolit causing some lube to be scraped off into the gap between the case mouth and the chamber end. My 303 Brit does it sometimes. With paper patching it will sometimes leave a small paper ring on the case mouth or just inside the mouth. That ring was the small overhang on the boolit base. These were rifle loads so not mild.
A low pressure load will normally heat the boolit base and lube more than a high pressure load due to the time duration as mentioned by edp2k. Unless one is using a compressed charge of Lil'Gun in a hornet - that will heat the barrel as much a full power 308! Just a little more powder and the barrel stays cool. Go figure!
303Guy and Messybear explained it the way I would. You get the same thing when using fillers that prevent any gas leaks around the bullet body inside the neck, leading me to conclude that the powder pressure and alloy happen to be working together to bump the bullet base up in the neck, creating a tight seal. Lube is extruded into the void in front of the case mouth as the bullet compresses. This actually is a good thing, unless the lube fouling stays in the chamber and causes problems chambering the next round. One thing is for sure, if you're seeing that lube ring on the case mouth, you aren't getting any blowby around the bullet nose, and that's a good thing.
Gear
Good to know. I have seen this time and again in my Savage 340 in 30-30Quote:
Originally Posted by geargnasher
Thanks guys!
Found this photo of a paper ring still on the case mouth.
https://s19.postimg.org/p06jgkz2r/19..._PATCH_047.jpg
I've had lube doing the same thing.
VERY similar!