unexpected neck tension question

[Hengehold]

What does a fired case neck diameter measure? It should be .001-.002 greater than loaded neck. If so, you are safe. There is .0005-.001 spring back from neck chamber diameter after being fired. Occ a case mouth can "auto crimp" itself after firing making bullet insertion snug. Mid neck diameter should be .001-.002 greater than loaded neck. Spinning a nylon brush in the neck gets the particulate material out and occ a boat tail will slide in snugly.

Here are the dimensions that I am dealing with.

Chamber neck = .297
Loaded case neck = .294
Fired case neck = .296

Thanks

 

[BoydAllen]

After you have trimmed your brass to minimum length, and re-chamfered, I suggest that you turn a couple of necks to different thicknesses, fire rounds made with those cases, and check to see if your bullet will slide in with minimal finger pressure. Start with the lightest cut that will clean up the outside of the necks. That may be enough. There is a theory that has been favored by some top shooters that having a little more clearance may give a more consistent bullet release, which shows up as increased accuracy at longer ranges, not so much at 100 yards. For my 6PPC brass this has caused me to turn cases for a clearance in the .0025 to .003 range. I would think that thicker necks might have stronger snap back after firing. Mine are turned for .262 or .263 chamber necks. I have read of long range benchrest competitors using .005 clearance for .30 caliber. Basically, I do not think that additional clearance up to a reasonable limit will harm accuracy. I think that it is mostly a brass life issue, and not much of an issue there, given what I have seen in the way of brass life, with proper dies, with unturned necks and factory clearances.

 

[Hengehold]

T

After you have trimmed your brass to minimum length, and re-chamfered, I suggest that you turn a couple of necks to different thicknesses, fire rounds made with those cases, and check to see if your bullet will slide in with minimal finger pressure. Start with the lightest cut that will clean up the outside of the necks. That may be enough. There is a theory that has been favored by some top shooters that having a little more clearance may give a more consistent bullet release, which shows up as increased accuracy at longer ranges, not so much at 100 yards. For my 6PPC brass this has caused me to turn cases for a clearance in the .0025 to .003 range. I would think that thicker necks might have stronger snap back after firing. Mine are turned for .262 or .263 chamber necks. I have read of long range benchrest competitors using .005 clearance for .30 caliber. Basically, I do not think that additional clearance up to a reasonable limit will harm accuracy. I think that it is mostly a brass life issue, and not much of an issue there, given what I have seen in the way of brass life, with proper dies, with unturned necks and factory clearances.

Thanks for your thoughts. After reading all of the great comments from everyone in this thread, I concur that I am going to need to move forward with the steps you suggested.

Thanks,
Trevor

 

[Hengehold]

Thank

Cartridge dimensions posted here show 2.1701" as maximum.

Minimum's anything you think you can get away with though habitually trimming cases short can lead to problems later on if you start using longer (as in new) cases. Chamber throats get residue build-up just ahead of neck mouths; short cases leave this where longer cases then encounter it, invariably leading to pressure issues from neck clearance being reduced.

If you know what reamer was used to chamber that barrel you ought to be able to locate its dimensions. Otherwise it's fairly easy to make a casting using Cerrosafe (low MP alloy that permits taking accurate dimensions for a short period after cast is removed from chamber) that will tell you straight away what you're dealing with.

Thanks for the links.

 

[M14AMU]

I have experience with this...take your calipers and check the opening. Then slide your ID measuring side of the calipers in the mouth past the opening to where your measuring the case neck in past the very opening. My 300 ultra was the same way. The immediate opening on fired brass measured .307. In past the opening it measured .311. The brass grew forward to the edge of the chamber and was curling the mouth over enough to close the brass. My chamber was cut with a .343 neck so it had .005 clearance on a loaded round. And you could visually see it on mouth opening. If yours measures tight farther inside the mouth, then you have a tight chamber and need to turn brass if your not comfortable with it. In my case, I sent the barrel to Rayhill to rechamber

"to Rayhill"

Would that be Kevin Rayhill??

 

[Dshooter]

"to Rayhill"

Would that be Kevin Rayhill??

That would be correct

 

[M14AMU]

That would be correct

I've got a 7MM WSM he made for me years back and it's STILL A HAMMER!!

 

[Dshooter]

I've got a 7MM WSM he made for me years back and it's STILL A HAMMER!!

He built me my Savage that is a laser to this day so he'll straighten out my Ultra and he's building my 7 saum.

 

[Hengehold]

I have noticed that in one of my rifles my fired case necks are not large enough to allow a bullet to slide freely through the case mouth. In other words, if I hold a bullet above the case mouth of a fired case and drop it, it will not pass through the case mouth opening and fall through to the bottom of the case. All of my other rifles allow a bullet to pass freely through a fired case mouth.

- I am reloading for a 6.5x284 with Lapua brass.
- brand new reamer used marked as .297 neck diameter.
- loaded round diameter is .294 which gives a total of 3 thousandths clearance in the neck or 1.5 thousandths clearance on each side of the case neck.

My initial conclusion is that my chamber neck is about 1-2 thousandths too tight and I will need to trim the necks on my brass. Has anyone else had this experience with an overall neck clearance of .003?

Thanks,

Trevor

I turned the neck on a piece of brass from a loaded OD of .294 down to .292 which changed my overall neck clearance from .003 to .005. The results is that now my necks open up enough to allow a bullet to drop through the neck opening.

Conclusion: .003 neck clearance may not be a safe amount of room for neck expansion and bullet release.

I should note that I have fired around 300 rds out of the barrel with virgin brass and even though necks are not fully expanding, the performance on target was as good as any other barrel I have had. This lead me to wonder, am I trying to fix something that is not broken? I was unsure if carbon buildup in the chamber could quickly escalate into unsafe pressure conditions so I elected to Create more space by turning the necks.
Thanks for everyone's help, input, and comments

-Trevor

 

[Dusty Stevens]

Like i said way back i like to turn em just enough that the bullet drops in. With that you have the perfect amount of clearance.

 

[Rtheurer]

Trevor
Is this from My Reamer?
Russel

 

[dkhunt14]

Did you measure loaded rounds with a micrometer and at a couple of places around the neck? Sometimes calipers are not accurate, easy to be off .001 to .002. Did you measure neck walls with a neck mike? It sounds like your rounds are a little too tight. Matt

 

[Hengehold]

Trevor
Is this from My Reamer?
Russel

It was a reamer from PTG designed for use with lapua brass (.297 neck). Not sure of the model or name of the reamer.
-Trevor

 

[fguffey]

I have noticed that in one of my rifles my fired case necks are not large enough to allow a bullet to slide freely through the case mouth. In other words, if I hold a bullet above the case mouth of a fired case and drop it, it will not pass through the case mouth opening and fall through to the bottom of the case. All of my other rifles allow a bullet to pass freely through a fired case mouth.

Not sure how someone makes the same mistake over and over etc.. When I fire a round at the range the first case I fire is ejected and the bullet in the next round to be fired is placed into the neck of the fired case. I want clearance, if the bullet does not have clearance I do not shoot the next round.


F. Guffey

 

[Brians356]

2. You need one of these. Along with a sacrificial case into which one is inserted, it helps you measure where your chamber neck ends and the freebore begins.

I use those. But someone mentioned build-up in the chamber neck, and the Sinclair chamber gauge can get hung up on on that, so one should make sure the chamber neck is really clean if the rifle as been in use for some time.

You can also make your own chamber length gauge for 22-cal and 6mm using fired 22 LR or 22 WMR cases respectively, for use with the Hornady L&L OAL tool. I posted a write-up w/ pictures here in another thread last year, however for 6.5 mm there is no fired case I know of which is the right size.

Here 'tis, end of this thread:

http://forum.accurateshooter.com/threads/headspace-gauge.3875237/#post-36585857

 

[Rtheurer]

It was a reamer from PTG designed for use with lapua brass (.297 neck). Not sure of the model or name of the reamer.
-Trevor

OK
Eric told me he barrowed my reamer for you to use. Was wondering if this is the same one.

Hope all is well.
Russel.