How do I accurately measure case neck length?

[Cassidy]

RVN1968 - tell me about cerrocasting the chamber; not familiar.

 

[Brians356]

RVN1968 - tell me about cerrocasting the chamber; not familiar.

Here just one online reference - many more, just Google "cerrosafe":

http://www.manthei-mess-systeme.com/gb_chamber_cast_intro.htm

 

[Cassidy]

Anyone else have experience with cerrocasting to confirm chamber dimensions; how precise for this purpose for BR rifles where close tolerances are used?

 

[spclark]

I've done it though not for BR-tolerance chambers... unless you consider any custom-chambered barrel for competition qualifies. I shoot sling & irons out to 1,000 yards.

Be very careful to read the instructions that come with the alloy; 30 minutes is the designed-in cooling time to wait before taking measurements. After that it continues to expand some which'll throw the most carefully made measurements off.

You also need to use measuring devices that are of highest quality & it stands to reason your skills in using them must be up to it.

 

[Brians356]

Years ago, way before the Neary videos, I used to trim the brass for my tight necked .222 so that it was only .005 shorter than my chamber (at the neck). I used to wonder why my fired cases showed some shiny spots on the ends of their necks, even though I knew that there was some clearance there. Today, I have a better understanding of this area of the chamber and the fit that is best. There are a number of areas where shooters' tendency to think that closer or tighter is better has been proven incorrect. I am not saying that this is always true, but we can sometimes go overboard in that direction.

Sinclair has sold a kagillion of those gauges, and I have never heard of problems with them.

[size=14pt]
"We should be careful to get out of an experience only the wisdom that is in it -- and stop there; lest we be like the cat that sits down on a hot stove-lid. She will never sit down on a hot stove-lid again -- and that is well; but also she will never sit down on a cold one anymore."

Mark Twain

 

[mikecr]

+1 LHsmith's approach
There can be advantages to tight & tightly controlled end clearance. With this, there is less sooting migrating backward(as seen right off on extracted case necks), so less carbon piling up at chamber end. Less sooting(leakby) means better ES/SD.

But you can't always get within 5thou, depending on the chamber you already have, and if your cartridge & sizing leads to frequent trimming, you might as well forget trying to manage 5thou off. I'm sure this is where most people are, and why they would run into issues(like throwing shots) with tight end clearances.
I've pulled it off with a cartridge that I do not have to FL size/trim with.

I do not agree with trimming to shortest case in a box. That makes no sense at all.
And it does take a plan to reach stable end clearances at any specific value(from new case condition). For instance, where shoulders take a higher angle on fire-forming, the mouths will pull back from your initial trim length. So for greatly improved case forming -with the intent to create tight end clearance, you would have to plan for this shortening and either leave longer than chamber end and COW FF, or FL size the case enough to re-extend the case until target clearance is reached.

 

[Cassidy]

My impression is some trim the case neck to different lengths for short range (100 yds) versus long range (600-1000 yds), but I am unsure of why these lengths should be different. Anyone know.

 

[gunsandgunsmithing]

the only tool that is made for this, I would never use, no matter what the manufacturer says. It is made by Sinclair, and if you get one, and use it, be very careful to trim the case neck as the instructions tell you to. In any case, I am never going to put a piece of steel in a case neck, run it into my chamber, and close the bolt. If I were going to do that particular chore, I would have something similar made from brass.

Boyd,

Are you aware of anyone having damaged a chamber using the Sinclair gauge (assuming the case was trimmed as short as instructed)?

I would think it prudent to make sure the edges of the slug are slightly radiused and polished; given that, I see little chance of mishap.

I know Sinclair claims their gauge won't hurt a barrel, and I never have, that I'm aware of with them, but not knowing what material they use and having brass and aluminum laying around, I simply make them out of it. The gauges Sinclair sells are too big for most tight neck chambers, with the exception of them offering one that's .262(I think) for 6mm stuff. So, I make mine a thou under chamber neck diameter and leave the edge pretty sharp so that I can get a more accurate measurement from it, due to the 45° bevel at the end of most chambers. This way, the gauge is a close fit and doesn't go up into the bevel, giving a pretty darn accurate measure for neck length.--Mike

 

[Brians356]

I know Sinclair claims their gauge won't hurt a barrel, and I never have, that I'm aware of with them, but not knowing what material they use ...

My hunch is it's a softer alloy than any barrel steel, but that's just based on the supposition the one thing Sinclair would have wanted to avoid in the design would be a reputation for damaging chambers.

In the case of Boyd's damaged chamber, if I read the post correctly, it was only a hunch that a Sinclair gauge that did that - it could have been a homebrewed gauge or lord knows what that someone jammed in there.

 

[spclark]

The Sinclair chamber length gauges I bought a few years ago came with "California-inspired" warning labels that the product contained lead - Pb, same as most of the bullets we shoot - and as such should be used with care to avoid undue risk of exposure.

They're pretty soft as alloys go, a sharp knife easily pares off a sliver yet they'll rust too under dampish conditions.

I'd have a Very Hard Time accepting that one of these things could affect modern barrel steels in some way unless I was involved in the mishap under scrutiny....

 

[spclark]

A truly accurate and scary sign-off,Mr Clark.

The man who won on the platform this statement formed a plank of went on to win the election. He did the best he could under extraordinarily difficult circumstances after being elected to the highest office, but didn't get a chance to run for another term.

Your comment has inspired me to quote him directly.

Election day is this Tuesday. If you haven't already voted you must vote your conscience before the opportunity is gone.

 

[snakepit]

I know Sinclair claims their gauge won't hurt a barrel, and I never have, that I'm aware of with them, but not knowing what material they use ...

My hunch is it's a softer alloy than any barrel steel, but that's just based on the supposition the one thing Sinclair would have wanted to avoid in the design would be a reputation for damaging chambers.

In the case of Boyd's damaged chamber, if I read the post correctly, it was only a hunch that a Sinclair gauge that did that - it could have been a homebrewed gauge or lord knows what that someone jammed in there.

In the Sinclair Catalog description of their Chamber Length Gauges it says "the gauge is made of 12L14 soft steel so it will not damage your chamber". I have used them with no apparent chamber damage as verified by my Hawkeye Borescope.

 

[spclark]

http://www.onealsteel.com/carbon-steel-bar-cd-12l14.html

"12L14 –12L14 bar is a standard resulfurized and rephosphorized grade carbon Steel, and a free machining steel. The added lead to the chemical composition provides improved machinability. Although the machinability is very good, the added lead content reduces the overall strength of this alloy."

 

[Hanbleceya]

To minimize carbon ring build-up, keep cases with-in 0.005" of the chamber length, which should be verified by using a gauge such as Sinclair's Chamber Length Space Gauges (just because the reamer is spec'd at a dimension does not necessarily mean that is what you have in your chamber). Forget about measuring neck length. Just adjust your sizer dies to give ~ 0.002-0.003" bolt nose clearance (headspace) and you're GTG.

The carbon ring issue is one I had to correct in my routine. .22br became significant issue

 

[Hanbleceya]

I also cut my tight neck 6mmBR to a 0.005" end clearance, and 0.0008" neck clearance (less clearance is more better, right??)

The rifle was accurate, but a real Prima Donna. After a group or two, it would throw bullets out of the group for no apparent reason.

I watched Jack's videos and he said 20 to 25 thou end clearance and 2.5 to 3 thou neck clearance, so I took a chance and recut my cases.

I cleaned the throat well and shot the newly cut cases.... that was the end of the thrown shots - the gun now is a kitten to shoot and load for.

Sinclair has sold a kagillion of those gauges, and I have never heard of problems with them.

Catshooter: got that video link handy?

 

[dedogs]

Catshooter: got that video link handy?

Catshooter is no longer a member. dedogs

 

[Hanbleceya]

Catshooter is no longer a member. dedogs

Appreciate that dedogs. After posting I notice last posting date. Something to do with my age but have not yet ascertained the exact connection. exact conn..umm

 

[Hanbleceya]

Catshooter is no longer a member. dedogs

Appreciate that dedogs. After posting I notice last posting date. Something to do with age but have not yet ascertained the direct connection.

+1 LHsmith's approach
There can be advantages to tight & tightly controlled end clearance. With this, there is less sooting migrating backward(as seen right off on extracted case necks), so less carbon piling up at chamber end. Less sooting(leakby) means better ES/SD.

But you can't always get within 5thou, depending on the chamber you already have, and if your cartridge & sizing leads to frequent trimming, you might as well forget trying to manage 5thou off. I'm sure this is where most people are, and why they would run into issues(like throwing shots) with tight end clearances.
I've pulled it off with a cartridge that I do not have to FL size/trim with.

I do not agree with trimming to shortest case in a box. That makes no sense at all.
And it does take a plan to reach stable end clearances at any specific value(from new case condition). For instance, where shoulders take a higher angle on fire-forming, the mouths will pull back from your initial trim length. So for greatly improved case forming -with the intent to create tight end clearance, you would have to plan for this shortening and either leave longer than chamber end and COW FF, or FL size the case enough to re-extend the case until target clearance is reached.

Well said dedogs. I shoot .22br and 6br with the Lapua case length issue that is inherent. Early on I would trim to shortest until I saw all the carbon and had difficulty with measurements. Now I see no need to trim at all until at least several firings because they do not arrive at the optimal distance that minimizes carbon yet allows case to move. I do not see them reaching critical before cases have reached the end of their usefulness.

 

[Mike Montgomery]

Once your brass has been fired in your chamber, the only thing that matters is the overall length of the brass.

 

[Bart B.]

Case mouth clearance to the chamber mouth for rimless bottleneck cases is primarily determined by the distance from a case shoulder reference diameter to its mouth. Case heads are a little off the bolt face and hard against the chamber shoulder when the round's fired. Measurements from case head to mouth then subtracting that from chamber length probably won't be what really happens

SAAMI specs show mouth clearance is several thousandths. Most such case shoulders are set back a little from firing pin impact and the case mouth moves forward. There needs to be a safety margin so the chamber mouth angle doesn't crimp case mouths into bullets.

As case shoulders are centered in chamber shoulders when fired, there's usually enough clearance at the neck-shoulder juncture so it won't interfere in any way.

Dies that don't size case necks all the way back to the shoulders may be a problem. The micro-shoulder at that point..........