How to measure neck diameter in chamber.

[Ryeguy]

140gn Berger elite hunter. -20 off lands. Shoulder bump 2-3thou. Whidden dies, co-ax press, flame anneal every time, V4 auto Trickler A&D scale.
I do have bore scope.
I was using rubbing alcohol in chamber thinking maybe I had oil residue left over from cleaning barrel, not using it to clean barrel. Cleaning barrel now after every outing
Using wipe out and accelerator for cleaning, or Iosso bore past. Everything is squeaky clean..
I did hammer some of that brass pretty good, also did a powder test/work up before fire forming/virgin brass cause I just didn’t know that’s not the right way. I still have 50 pieces unfired so maybe I’ll start over the right way and see what happens.

 

[SSgt G Cody]

You misunderstand; clearance is not measured from diameter, but rather is measured as headspace (how far bullet is backed-off from firm contact with the lands), which is usually .020-.080”. Any less can cause dangerous high-pressure spikes. This usually means that total diameter clearance is AT LEAST .005”, depending on shape of bullet nose.

 

[milo-2]

Shot a few today here’s the necks..
To me it looks like it’s sealing at neck/shoulder junction? Again loaded rd = .2935.. Directly after shooting = .2960.. 5 hrs after .2950.. So I’d say I have .0035 clearance? If it sprung back 1thou from exiting chamber.

Are you cleaning this brass before firing a 2nd time. Reason I ask, your whole cases look dirty, like a lot of gas is coming back at you.
Here is a Quickload model, w/o your exact parameters, I lowered the total case capacity by 1gr, and the OAL in my model is relatively short. Seat The important number here is highlighted in your yellow. Seat bullet out farther, pressure will drop more in this program.
I personally think all your issues are caused by low pressure rds.
This sounds like bad advice, but I would clean the gun up, chamber-barrel, and just load 5 charges at around 61gr of H1K and fire them, inspecting each case as you fire. My advice is free, and one opinion, take at your own risk!

 

[milo-2]

You misunderstand; clearance is not measured from diameter, but rather is measured as headspace (how far bullet is backed-off from firm contact with the lands), which is usually .020-.080”. Any less can cause dangerous high-pressure spikes. This usually means that total diameter clearance is AT LEAST .005”, depending on shape of bullet nose.

What are you talking about?

 

[Mikecr]

Nothing about that is right...

 

[Ryeguy]

Are you cleaning this brass before firing a 2nd time. Reason I ask, your whole cases look dirty, like a lot of gas is coming back at you.

Yes I dry tumble after sizing, 20-30 min

Here is a Quickload model, w/o your exact parameters, I lowered the total case capacity by 1gr, and the OAL in my model is relatively short. Seat The important number here is highlighted in your yellow. Seat bullet out farther, pressure will drop more in this program.
I personally think all your issues are caused by low pressure rds.
This sounds like bad advice, but I would clean the gun up, chamber-barrel, and just load 5 charges at around 61gr of H1K and fire them, inspecting each case as you fire. My advice is free, and one opinion, take at your own risk!

Here my latest MV W/ Lab radar, maybe something jumps out to you? Pretty sure my pressures higher than that quick load data due to actual MV.
With COAL of 2.910 (-20thou off hard jam)
58.8gn= 3026
59.1= 3057
59.5gn H1k= 3100 @ 80* Stopped here due to heavy bolt, tried the below to see if pressure dropped w/ less COAL. All had heavy bolt.
2.888 COAL (-42thou) 59.5gn= 3074, 3110, 3082, 3087
(-47) @ 59.5gn = 3107, 3106
New brass will be here Sat. I will FF W/ moderate load, Clean chamber/barrel, and redo coarse powder test and get back to. Thanks all that reply, its nice to have somewhere to go and ask questions. You input/help is appreciated.

 

[milo-2]

Yes I dry tumble after sizing, 20-30 min

Here my latest MV W/ Lab radar, maybe something jumps out to you? Pretty sure my pressures higher than that quick load data due to actual MV.
With COAL of 2.910 (-20thou off hard jam)
58.8gn= 3026
59.1= 3057
59.5gn H1k= 3100 @ 80* Stopped here due to heavy bolt, tried the below to see if pressure dropped w/ less COAL. All had heavy bolt.
2.888 COAL (-42thou) 59.5gn= 3074, 3110, 3082, 3087
(-47) @ 59.5gn = 3107, 3106
New brass will be here Sat. I will FF W/ moderate load, Clean chamber/barrel, and redo coarse powder test and get back to. Thanks all that reply, its nice to have somewhere to go and ask questions. You input/help is appreciated.

Don't add powder, bad advice on my end, 3100 fps no joke 22" barrel!

 

[tim_w]

You misunderstand; clearance is not measured from diameter, but rather is measured as headspace (how far bullet is backed-off from firm contact with the lands), which is usually .020-.080”. Any less can cause dangerous high-pressure spikes. This usually means that total diameter clearance is AT LEAST .005”, depending on shape of bullet nose.

I think its quite clear who is having trouble with understanding.

I really hope this is possibly a sauce induced inebriated post of nonsensical info. A retraction or rewrite when everything stops spinning might be in order. As all ^ THIS ^........ It's all wrong , so very very wrong.

 

[tim_w]

@Ryeguy

Your neck clearance is fine by the info you have posted.

I tend to do the same moderate load to fire form as part of case prep. I do find a nice accurate forming load and use it for practice.

Your orginal concern is a high SD/ES. Your focus was on a tight neck being the issue which does not seem to be the case. I do not recalling seeing ES/SD numbers did you post them? If not please do.

Lots of things can cause higher ES/SD that have nothing to do with case neck to chamber clearance. Certain powder to cartridges have higher ES, retumbo has a rep for this, as example.

I only change one thing at a time when working up a load.

Your accuracy of weighing powder charge will effect this.
Based on your pressure ladder test find a accuracy node @ or below 58.5 gr. Do not get hung up on trying to get every last fps out of it. Running near the limit is only gonna cost you brass and powder and the animals are not gonna know the difference.

The primer your using can affect this. In short mag cases I usually get best results with std primers not magnum. I tend to use CCI and Fed. for large primer cases. Still have a huge supply of Wolf for SRP.

Neck tension or more correctly interference fit is another thing that can cause vel spread. I usually start with a neck tension of 0.002 as most seem to work well there and it's usually enough to keep bullets from moving. It's also my minimum for hunting.

If you bullets seating length puts its ogive very close to touching the lands (kissing) can create erratic vel as some touch others do not. I stay either fully into the lands or a min of 0.005 jump. 0 - 0.005 is a no go area for me. In a hunting rifle as a general rule I use a jump, which means 0.005+.

I, personally, do not like using a hard jam to establish the actual land touch location as its base of "hard" jam is subjective. You could possibly actually be 0.020 into the land. It does not take much force to go 0.010 in with these long neck bullets and shallow throat leades.

I like to use a way I learned from @Alex Wheeler which was slightly different than I knew. Before that I used the hornady tool. Take your bolt with firing pin and ejector removed and slowly seat the bullet deeper until close then by a thou until the bolt has no resistance click on the uplift after close and drops closed freely. It put you +/- 0.001 at most and not nearly as subjective. Then I use a minimum jump of 0.005 otherwise I seat into the lands. That way there is a gap tolerance range of 5 thou so I can be sure I am into or not near touching.

I do something similar with case sizing after the fireform load. Deprime the case. Pull the FP and ejector from the bolt. Check fired case. Then size a minimal amount. Try again. Get it where the bolt closes with a tiny bit resistance at the bottom. Then size it 0.002. Bolt should then drop freely closed. Take your case measurement and record it. Then use those cases to do your bullet seating to land measurement.

@Alex Wheeler has a few videos on his site that demonstrates these things. They do a far better job than my description. IIRC, I first saw his video when they were on YouTube and learned his land measuring technique.

Keep all your cases together in lots for the loads and annealing necks if your doing that. This way they yield, work harden, and size the same. Infind it helpful to record the number of firings and the loads used....their general history. I keep track of things like case head measurement etc.. as well

 

[Bang4theBuck]

One thing I've done to help me verify that there is clearance is to use a small strip of scotch tape one side of the case, and attempt to chamber the round (slowly and with a lot of feel). If that goes in (generally accepted at .002" thick, then I try a complete wrap (generally accepted as .004") if it chambers with a full wrap, even with a very small amount of resistance, I consider that good enough.

Conversely, I used to neck turn all of my brass to 'true it up', and once I got some lapua brass that was only .011" neck thickness. by the time I trued it up, it was down to .010" thick, and my SDs were terrible. I used the same method to determine just how much excess expansion there was in the neck area. That brass had to be trashed. Don't just turn it for the heck of it, unless you are prepared to throw it away.

None of the above were precision measurements, but rather a test to determine if I was in the ball park or had a serious chamber problem.

 

[ncwg2boatguy]

So your necking down 6.5 Lapua to 6x47 Lapua correct? What kind of SD/ES are we talking about when you say "high"? Ive shot 6.5 Lapua 15 yrs and sorriest SD ever during load development was a 12 . And I was suprised because it normally under 8 worst case and avg 2

 

[hunter0528]

Nice to have a cast of chamber. So simple.

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I agree this is the simple way and a way to check over time.

Chamber Casting Alloy Ingot aka low 158-190F

[email protected]

www.rotometals.com

has it for less money than Brownells

13.99 for a 1 lb block

 

[Kivaari]

Benchrest guys "true up" case necks immediately after neck sizing...no springback or very little but consistent.
They also attest to oal trim frequently...consistent volumn of brass affecting the bullet.

 

[Rflshootr]

Shot a few today here’s the necks..
To me it looks like it’s sealing at neck/shoulder junction? Again loaded rd = .2935.. Directly after shooting = .2960.. 5 hrs after .2950.. So I’d say I have .0035 clearance? If it sprung back 1thou from exiting chamber.

You're fine. Keep an eye on the trim length.