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What causes sooty necks on the cases?
I thought it was something to do with not enough pressure sealing the neck in the chamber on firing?
I did a ladder test the other day and the necks were all quite dirty after firing. Some of the loads were over book max as I had found no pressure in the previous ladder test.
On the last load I had a bit of trouble opening the bolt and had a flat'ish primer, so know thats over loaded for me. But it was still sooty.
Powder is AR2217 in a 270wsm.
Thoughts...
Dirty chamber from the initial low loads?
Suppressor pushing dirty gas back after case has shrunk back?
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is it a problem?
I get it on my cases too but it dosent faze me,
I get it with all my hand loads
If your getting residue on your neck with your max load, it can just the diff between chamber and case neck dimentions. The case neck is not obturating or it is returning to size as the gasses settle. Usually shows around a 5 thou difference. You can get it with or without a suppressor.
I dont think it is a problem if you are near max powder load as long as it shows no further than the necks.
I get it in varing degrees throughout several cals and the only major difference is neck clearance. Worse in lots of clearance, less in little.
A sooty inside color can indicate an inefficient burn of the powder. BUT, that could be for several reasons. It could be from a powder that burns too slowly, a very light powder load of the correct powder, or other causes. IMHO, the root cause is low chamber pressure.
However, you should be aware that sooty cases ranks right up there with fired primers as being no more than "a general indicator". It is NOT exact in any manner, shape, or form. Nor should you use it as a reliable reference in place of chrono data.
Having said that, let me say also that I'm not aware of any fuel (wood, coal, kerosine, nat gas, gasoline, or smokeless powder) that is sooty when it's burning efficiently.
A sooty exterior can indicate not enough chamber pressure to properly expand the brass.
Cam, No suppressor so can't be that. Also if I chamber a loaded case and extract it there is no sooty marks
I was under the impression that having sooty necks was one of the signs of low chamber pressuresQuote:
Originally Posted by Bill999
Can't be if my over max loads do it too
Ok so my neck clearance in the chamber might be quite high. I think I can live with that, Something to do with being a Tikka I suppose. I was just wondering if there was something I was doing wrong perhaps.Quote:
Originally Posted by R93
The fact it doesn't go up the shoulder is comforting, as I'm not real keen on a face lift with hot gasses.
Sakkaranz,
The soot is around the outside of the necks and a dark black colour.
Not high, puku just not as tight as some custom chambers as far as neck clearance goes. Pretty sure I get it on all my reloads. I can wipe it off with a rag easy enough and never really addressed or worried about it.
I get it on my .260 imp cases but in saying that, it has a very low ES and I get 9-10 uses of a case before I consider forming a new one. So it cant be anything to be concerned about.
Could be other things as well. I notice a change using different powders and even in a change in primer, maybe leading on to what sakkaranz says about efficiency.
For anyone interested this how the ladder test went.
Attachment 13393
Aiming point was the top right corner of the box. First shot 1/4" right, Second shot 1/4" low, Third shot 1/3" high and left. Forth shot out right, then fifth shot low 1" and right 1 1/2".
The two other shots were from some other shooting.
Slight pressure signs were in shot four. And I had trouble opening the bolt on final load.
Fuck how the hell did that turn around. Fucking stupid computer
It won't be soot, just the same carbon you scrub out of the barrel.Quote:
Originally Posted by sakkaranz
What range was the ladder test shot at - I do mine at 300 or so and the holes are never that close together (crappy old Mauser's - ya all can say it!).
It was a shade under 300m, a bit closer to 100m to tell you the truth.
Once I pick out a weight ill play at longer distance when changing OAL
I dont if that helps with a data point, and i get sooty necks
where as winny factory dosent seem to get the soot like i do
I haven't seen you explain what your ladder test is for (so I might be wide of the mark so to speak) but as I understand, ladder tests are only effective beyond 200 yards, inside that the vertical separation of rounds at different velocities or vibration nodes hasn't happened yet . . as I mentioned I shoot mine at about 320 metres.
There is a method for achieving a similar result at 100, its called "Optimal charge weight" or OCW, but I have never really been able to get my head around it.
Yep, I normally rub off the lube. Or else put it through the tumbler after sizing (I don't always tumble).
Technically it's probably not a 'ladder test' but that's what I call it anyway.
During the process of testing my heavy 338edge at 1500yrds i prepped some brass to very minimal neck clearances, an interesting side effect after firing that special brass was very clean case necks.
Not a lot of sooty
(pic of a pic hence poor quality)
http://i254.photobucket.com/albums/h...psfc33af55.jpg
http://i254.photobucket.com/albums/h...ps8f4866e3.jpg
I had sooty necks on a 243Rem until I annealed the necks and the sooty effect did not happen again.
I owned a T3 270WSM, amongst other brands, some time ago. It was also inclined to blow soot back over neck, sometimes shoulder. Agree that lowish pressure is a factor, also neck-clearance and throat length. My T3 had a long throat(non-SAAMI spec?) compared to some other makes, as did a Sako 75 I checked. Typically, I would need 3gns more powder to bring velocities up to that clocked by standard throat rifles. It seemed that guide max. loads were a reasonable starting load in my T3.
The cartridge is also prone to neck-splitting and formation of 'dough-nuts' at neck/shoulder joint. I eventually dealt to these issues with the use of a Redding Type S Full-length Bushing Die, adjusted to leave the lower half of neck blown out. A .305 bushing worked well.
Tried 2217, but found I was burning about 5gns more powder than say, N165, for no better performance.
