swd
Member
Just curious, what would you gain by doing that?
Chamber length question
- Thread starter Russ661
- Start date
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elkaholic
Well-Known Member
By setting it back and running a chamber reamer in it with the proper spec, it would put the neck length where it needs to be. It will be a continual battle otherwise and jumping . 030" of space doesn't do anything for accuracy besides the carbon issue.
Mikecr
Well-Known Member
I don't understand myself how it could be chambered with a neck 40thou longer than cartridge design. That's why I assumed initially that the necks had been trimmed back that much.
There are many occasions where forum members suggest trimming necks to shortest in batch. This is always bad advice, but people do it.
Look at what's happening here:
On firing the case body/shoulder/neck expands just a bit, very early on. Any amount of neck expansion freely releases a bullet, and some of the gases behind it. While the charge is still igniting gas goes around the bullet and also into the space provided by chamber end clearance(far larger space). With excess space at chamber end, some gas will whip around backwards (blow-back) into the neck & shoulder clearance areas. This, delaying or preventing good neck sealing. It may also have messed with good unfettered neck expansion.
The borescope image here is showing that the case neck is eventually reaching chamber neck, stopping the mass within blow-back (carbon) at the case mouth. The carbon builds right there as it has flow momentum to the timing/location of barrier.
What & where that matters is another thread, but I can tell you it's all different with tight chamber end clearances. With 5thou clearance there is no blow-back, and carbon ring development, if allowed, takes 1,000 or more rounds to build. That's just gas (with carbon in it) condensing at chamber end. It's normal & not a problem.
Neck sealing with tight chamber end and tight neck clearance is near instant. No sooting on extracted case necks.
Of course you have to manage running with tight chamber end clearances. This is measuring chamber end and allowing necks to reach inside that clearance, and THEN trim to that standard. Eventually, all cases in batch are there.
While close you watch it. I look for any shiny spot at case mouths, every single one by habit, as I extract them. This can be from impact with carbon ring or chamber end. When I see it, it's time to borescope and possibly trim. With my chosen cartridges and sizing, it's rare that I have to re-trim.
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Russ661
Well-Known Member
Excellent explanation, Mike. Thank you, that answers a lot of questions.
Russ661
Well-Known Member
As promised, a picture of the cleaned chamber mouth. I do NOT look forward to doing that again, especially when it is 90*F out in the garage where I do all this stuff! Chamber OAL from cartridge base to chamber mouth still measures 2.658 inches so that is where I am at.
elkaholic
Well-Known Member
squeaky clean!
Mikecr
Well-Known Member
You deserve an indoor reloading bench!
