Coralation of case neck length

[bench]

Has anyone ever tested case neck trim length vs chamber length for the neck.
Would their be any accuracy difference trimming the case neck closer to or farther away from the chamber max length for the neck.

 

[Immike]

Fred Sinclair wrote about this in his 10th edition of reloading and stated to measure it and bring it in to .010 for best results.

 

[spclark]

Has anyone ever tested case neck trim length vs chamber length for the neck.
Would their be any accuracy difference trimming the case neck closer to or farther away from the chamber max length for the neck.

It doesn't take much of a case neck to actually hold a bullet in place, but trimming necks back excessively when the chambers they're meant to be used with have 'normal length' neck bores will lead to problems as already noted. Too much free area to accumulate fouling, possible issues with necks sealing the chamber properly upon ignition....

Unless you're willing to pay up front for a proprietary chamber reamer, then have a barrel chambered with it & let us know what you've learn after a few hundred fired rounds, I'll with what's been proven to work well.

 

[bench]

Fellas,
Without a bore scope how would you know if you have a carbon ring buildup.
And how would you remove it or clean the neck area better.

Bench

 

[spclark]

Fellas,
Without a bore scope how would you know if you have a carbon ring buildup.
And how would you remove it or clean the neck area better.

Good questions both.

Carbon in the neck can manifest from cartridges that chamber with resistance, sometimes so much the bolt won't close. Without a borescope though this is tricky to diagnose as there are other conditions that'll have the same effect.

Same for unusual pressures with loads that have worked well before.

As for removing carbon once it's there? I've used oversize bronze or stainless steel brushes before, sometimes spun in a battery drill. Not something I'd recommend though, better to avoid the problem in the first place with case necks just short enough for safety, maybe 0.015" - 0.020" off the change in diameter where the chamber neck ends & the freebore / lead begins.

 

[mshelton]

Seen people use aluminum arrow shafts to clean out the carbon ring, find one a bit smaller than the neck diameter and make burrs on the end to scrape out the ring by hand.

 

[Laurie]

Fellas,
Without a bore scope how would you know if you have a carbon ring buildup.
And how would you remove it or clean the neck area better.

Bench

Re part 1 - this sort of issue is why a borescope is an invaluable tool. Re the second part of the question, isn't that what the Bore-O-Matic 'Hand Jobber', item 2 in yesterdays' Daily Bulletin is for? More seriously, it's a case of soaking it and scrubbing it out with the more effective carbon removers, maybe even Iosso paste or J-B if very bad, although I'm always dubious about using abrasives on barrels.

It should be noted too that in extreme cases, hard carbon rings sometimes keep a worn-out barrel performing and removing this feature can see performance collapse. This used to be an issue in GB (and I presume Canadian / Australian too) 'Target Rifle' that used 'issued' 7.62mm ball ammo with an asphalt case-mouth to bullet mouth sealant that produced noticeable hard carbon fouling just ahead of the case and in the leade area with a ring or ridge often seen after a few thousand such rounds fired. Removing it was often the death knell for the barrel!

 

[BoydAllen]

The best and most up to date information on this subject, from a member of the Benchrest Hall of Fame, is found on YouTube in one of the first two or three of six segments of a case prep and tuning lecture by Jack Neary. If you watch them all, and take notes, you will end up with a lot of information by a fellow that shoots better than you or I, unless there is another Hall of Fame shooter reading this, which I seriously doubt. Jack trims frequently, based on actual testing, and to a length that will clean up all of his necks when he does. That this is .035 under his chamber's maximum case length is is of no consequence. Based on what I know about how bore brushes interface with the front of the chamber, and what I have seen in a bore scope, I now understand that my previous practice of keeping cases fairly close to the end of tight necked chambers was incorrect from an accuracy point of view, and actually can create problems that degrade accuracy. Chambers that have typical factory clearances probably are not affected in the same way, and a more pedestrian approach may be taken to trim length.

 

[tenring]

As for removing carbon once it's there? I've used oversize bronze or stainless steel brushes before, sometimes spun in a battery drill. Not something I'd recommend though, better to avoid the problem in the first place with case necks just short enough for safety, maybe 0.015" - 0.020" off the change in diameter where the chamber neck ends & the freebore / lead begins.

We are often admonished to not reverse a brush after it exits the muzzle, because the crown can become damaged over time. If that is true, would not inserting and spinning the abrasive loaded brush in the leade produce the same result?

 

[BoydAllen]

I don't know how often he cleans but your guess sounds plausible. Have you ever actually tried the larger gap?

First of all, the dominant powder in short range benchrest is still probably 133, and it is the cleanest burning rifle powder that I have ever shot. I can clean every 25-30 rounds and not have any carbon problems using Butch's, a bronze brush, and patches. This is not the case with some other powders that give accuracy in the 6PPC. The reason that I don't like a small end of neck gap is that brushes do not reach that small triangle of space that is very near where the angle at the end of the case neck part of the chamber starts. From the back edge of the freebore, to where the angle up to that point starts, to back a little ways in the neck portion of the chamber gets missed by a normal brushing, because the bristles lay back and bridge that area. For that reason powder fouling tends to escape the action of the bristles. On the other hand, it does reach the rest of the neck of the chamber behind that area, so..for me.. if necks never intrude into that area, that I have referred to as the dirty little corner, then until the fouling piles up to the point that it extends above the inside of a fired neck, it cannot touch the bullet, or the neck for that matter. On the other hand, shooting more, dirtier powder all day, without cleaning might be significantly different. That is why I asked if you have done the test. I would be curious if the targets showed a problem, and how many rounds it took to show up. Clearly, that particular situation, requiring top accuracy for a large number of rounds, is beyond my experience. I have shot a lot of rounds per day shooting ground squirrels, but as long as I kept hitting them, that was all that was required. I will say that I have heard reports of shooters who use moly coated bullets shooting an entire weekend or day (perhaps 77-80 rounds per day)without cleaning, but have never done that myself, and again, there are the differences between quantities and cleanness of powders that are factors.

 

[spclark]

We are often admonished to not reverse a brush after it exits the muzzle, because the crown can become damaged over time. If that is true, would not inserting and spinning the abrasive loaded brush in the leade produce the same result?

Certainly there's a potential to do damage by this kind of operation, so one has to evaluate the benefits vs. negative consequences beforehand.

Like I said it's better to avoid the problems of 'carbon ring' when possible.

Too, if one is cautious to insert a brush only as far as the end of the chamber neck bore - staying clear of the lead just ahead - the damage potential is avoided.

 

[BoydAllen]

Barrels can get carbon rings not matter what you do, and at some point they need to be removed. The method of removal will pretty much always involve the use of an abrasive, and abrasives have the potential to wear steel. Therefore careful selection and use is the order of the day. If you can remove it with a brush and solvent, it is powder fouling, not hard carbon, which a friend (with a bore scope) refers to as black diamond. A long time back, I was having a discussion about barrel wear, from various causes, with a friend. His reply was, "That's why they put threads on them." As to not reversing brushes once they leave the muzzle, I have never seen or heard of anyone removing one at the muzzle when cleaning between short range benchrest individual (one group) matches. This includes several world record holders that I know. If you have a lot of time to clean, and you want to, I suppose that taking the brush off would not hurt anything, but the idea that carefully pulling it back through the barrel, when stroking it both ways causes some sort of significant damage has not been my experience. I am careful when I clean, and use a bore guide of the highest quality, but I have always drawn brushes back through the bore, after only letting them exit by perhaps a quarter of an inch. I think that this whole thing is much ado about nothing, that has been given way too much credence from being written about on the internet. Let me finish with one more detail about how I clean a barrel. A long time ago, I concluded that I didn't want to run my bore brushes in a slurry that included the bits of glass that primers put in the bore, as well as unnecessary amounts of powder fouling, so I run several short stroked wet patches through a barrel before brushing with a bronze brush. That way I am only using the brush to remove what the patches will not. I think that if one starts by brushing a barrel without much patching, that there may be more potential for damage at the muzzle, than by doing as I do. My barrels' crowns look good.

 

[Citysmasher]

I think that this whole thing is much ado about nothing, that has been given way too much credence from being written about on the internet.

...and this man sums up a great many things right there...