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Erosion from blowback on necks

My take on the OP’s question is that the soot seen on necks is there from the very first bit of combustion products escaping upon ignition, maybe just as the bullet’s leaving the case. Pressures & temps aren’t nearly as high as a few microseconds later when the neck’s expanded enough to seal the back end.

As others suggest it’s throats that suffer, not chamber necks....
 
This is kinda a follow a follow on from the "is this case stuffed thread"

Can any of the experienced shooters here confirm that when you are getting soot on case necks due to neck not sealing properly before bullet release does those hot gases cause erosion of the chamber in the area where the neck is not sealing properly??

Thanks


I took this picture on a scanning electron microscope about 10 years ago. I was looking at bore erosion so I don't have a good pix of the neck area. 25X mag about 7000 shoots in a Douglas SS 6mm Rem barrel. There is only about a 1/4" on the left of the pix showing where the neck o.d. contacts the chamber. I don't see any obvious damage. Tony Boyers book briefly mentions the soot pattern being somewhat related to neck thickness. Sounds like soot is normal. I have had soot on the necks of about 20,000 cases.

upload_2017-12-1_17-54-32.png
 
A cross sectioned .222 chamber with a gazillion rounds down the barrel. Normal cleaning and nothing more. Bushing die..You can clearly see where the neck bushing stopped sizing the neck of the brass.The photo exaggerates it. There are no sharp edges in the chamber but it's very clear where the bushing stops. At the neck/shoulder junction is a glare. It's shiny but smooth with no burrs or sharp edges. About 1/16" from there is where I'm referring to.

I suspect the next ring up is the approximate area of the pressure ring of the bullet the owner shot mostly.
I see no parallel flame cutting or anything of the such...and never have, in several of these chamber disections that I've done over the years. I think the whole notion more unbased conjecture.

Clearly, this stub has served more than one purpose in its life. No idea what I threaded both ends for but likely setting up a cutter or testing for a thread fit..etc. It was scrap whenever I did that and it's come in handy a few times, to show customers since.
 

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My take on the OP’s question is that the soot seen on necks is there from the very first bit of combustion products escaping upon ignition, maybe just as the bullet’s leaving the case. Pressures & temps aren’t nearly as high as a few microseconds later when the neck’s expanded enough to seal the back end.

As others suggest it’s throats that suffer, not chamber necks....
Oh, but how about that abrasive powder and it's convergence point with long necks and steep shoulders. More conjecture. I'm the one mentioning the brass in this context but many are claiming it is a serious factor to barrel life. Again, IMHO...conjecture.
 
Oh, but how about that abrasive powder

A local reloader gave me 80 7mm Remington Mag cases. The carbon around the neck was packed so tight it had to be scraped off. I called him to warn him, I thought the cases were his. He said he got the cases from a neighbor that died. My concern then was focused on the rifle, if the carbon was packed on the necks the chamber neck had to be so tight the case neck could not release the bullet etc. etc.. He contacted the family, no one knew what happened to the rifle.

He reminded me the man that died was the one that had close to 200.000 pounds of machine shop equipment for sale. He was a writer for machine shop magazines and designed reloading equipment. I want my necks to expand and seal the chamber, that makes me the only reloader that understands 'time' is a factor.

F. Guffey
 
I see no parallel flame cutting or anything of the such...and never have, in several of these chamber disections that I've done over the years. I think the whole notion more unbased conjecture.
Not conjecture, just something I did not know. I am glad you could straighten it out so convincingly. Nice visual aid too!:rolleyes::D
 
Not conjecture, just something I did not know. I am glad you could straighten it out so convincingly. Nice visual aid too!:rolleyes::D
My post wasn't directly to you, since I didn't see anywhere you making suppositions about chamber erosion. But, a picture is often worth 1000 words. What does :rolleyes::D mean?
 
My post wasn't directly to you, since I didn't see anywhere you making suppositions about chamber erosion. But, a picture is often worth 1000 words. What does :rolleyes::D mean?
I think Pigdog started this thread based on something I said in another thread. The faces are just that most people will give a long winded explaination that may be hard to follow, whereas you had just the right item to definitively show the answer to his exact question.
 
thanks mike this is the sort of knowledge I'm looking for.

Guys can we keep the topic on hand if possible I'm not sure what is going on between fguffey and the others but I'm more interested in if anyone can offer practical advice on where I go to from here I'm thinking of the possible following scenarios.

1.) increase loads so that I'm running at absolute max pressure of 63kpsi (not real keen on this)
2.)Size necks with a bushing down to .279 thoughts on this?
3.)don't worry about it continue shooting and get a chamber cleaning kit and clean regularly
4.)put the gun in the safe until I can afford new lapua brass, neck turning gear and a new full length sizing die as recommended in the article on this site about neck turning before getting started he said you need to full length size with a non bushing die which I don't have.
5.) other?

thanks for keeping on topic
+1 on number 3 here.. You may just need to clean it really well or step up the charge a little bit... I get some soot on necks even when useing factory ammo or reloads in every rifle I shoot.. seems pretty normal on the necks , not so much all the way back to the shoulders... Are you just shooting underpowered reloads..???
 
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This is kinda a follow a follow on from the "is this case stuffed thread"

Can any of the experienced shooters here confirm that when you are getting soot on case necks due to neck not sealing properly before bullet release does those hot gases cause erosion of the chamber in the area where the neck is not sealing properly??

My 6.5x47l has a .286 neck. Necks have been turned by previous owner to 8.5 thou thick. This gives a loaded round diameter of .281 after sizing through a .281 bushing. Load used is 40g H4350 with 139 scenars at 2.840coal 10 thou off lands. All cases have just been annealed and had 5-6 firings estimated pressure from quickload 58k psi.

A clever gentleman from the other thread worked out why I'm getting soot on necks (zero neck tension and 5 thou of neck to chamber clearance. He suggested maybe trying a .279 bushing to give some more neck tension. I don't want to have to buy new lapua cases and neck turning gear as that is gunna set me back several hundred and my wife is already pissed I'm getting another gun Saturday. My main concern is if this soot and gas escaping is damaging the gun causing more erosion?? I have contacted Sinclair to see what attachment I need to clean my chamber as i already have their recoil lug cleaning tool. If the soot is not doing any damage I'm very happy with how the gun shoots and would be ok with simply cleaning the chamber to keep on top of the soot.

Can any experts help a mug out

Thanks

I think soot on the necks is normal. There may be a few things that determine how much soot you see. Quit worrying about it. Doesn't make sense to adjust neck thickness, neck tension and powder charge bases on soot and ignore the target. No-one ever thru a barrel away because they thought there was erosion next to the neck in the chamber. Make your adjustments based on target results forget about soot. My photo and gunsandgunsmithing photo show no damage. gunsandgunsmithing photo clearly shows the neck area of the chamber is bright, shiny, smooth and free of damage.
 
thanks guys going to try going up to around 41-42g estimated around 63kpsi and see what happens otherwise I'm going to order the Sinclair chamber cleaning tool and a 7mm bronze brush and just keep the chamber clean. thanks
 
thanks guys going to try going up to around 41-42g estimated around 63kpsi and see what happens otherwise I'm going to order the Sinclair chamber cleaning tool and a 7mm bronze brush and just keep the chamber clean. thanks

Why are you obsessed with soot on the case neck? You adjust your loads for accuracy not to remove soot. 63 PSI is way excessive for a factory action and pushing the limits on a custom action. Don't assume Quick Load is giving you accurate PSI for your loads. My Berger manual gives a max load of 38.3 grains of 4350 with a 140 gr bullet. A standard bronze brush and patches are oversize enough to clean the neck area of the chamber. Why would increasing neck tension reduce soot? You adjust tension to improve accuracy not to remove soot. Sounds like your doing everything backwards.
 

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