True chamber size vs fired brass.

[Mtstalker]

Well print shows .298 lapua brass measured .295 with bullet seated. They assured me its a .298 and thats what the print shows. I now have a ruined firing pin and had hot gas blow in my face on the first round fired at starting load with lapua brass. Lapua neck after firing .295 cant even get a bullet started in a fired case. So now i need to call them monday and neck turn all the brass.

 

[mikecr]

I was told by a shooter i trust that .001" was normal.

This is correct. Nobody's necks are springing back 3thou..
Unless your starting load is stupid low, you likely have a .296 chamber neck.

Is your Lapua 260 neck thickness 15.5thou? (.295loaded -.264cal)/2
If so, I wouldn't personally run with that, regardless of the chamber. Too thick.

 

[Mtstalker]

It is .015" thick. Im contacting shilen on monday to tell them the print they sent is more than likely the wrong one. Im fine with it i will just turn the brass. The barrel is a shooter, with other brass loaded with 130 and 140's its consitansty shooting. 250" groups at 100. I would hate to replace it with one that doesn't shoot as good. Maybe they will replace the firing pin. I havent been able to find a savage SA firing pin.

 

[Webster]

I was told by a shooter i trust that .001" was normal.

I have a 6BR Norma chambered by Kelbly Inc. No turn .272" chamber neck. My Lapua cases are turned to 0.0125. Just measured the neck O.D. on 10 fired cases that were not annealed for about 3 firings. They average 0.0269" O.D. When people tell you that they think 0.003" is too much it's a personal opinion. Back it up with real numbers. The cases have about 20 firings on them.

 

[mikecr]

That's one person who thinks he has 3thou of neck spring back, and one person who thinks that brass doesn't spring back that much.
Anyone else?

 

[Alex Wheeler]

That's one person who thinks he has 3thou of neck spring back, and one person who thinks that brass doesn't spring back that much.
Anyone else?

My 284 necks come of of a .313 chamber measuring .310. I own and know how to use tools capable of measuring. These are un annealed cases necked up from 6.5x284 lapua.

 

[mikecr]

In discussion is determining chamber size from fired brass. Prerequisite to this determination is knowing that your necks at least expanded to and sprung back from chamber.
I'm suggesting that brass reaching chamber neck dimension will not spring back 3thou from it -because our brass does not spring back that much.

You can manually size (up/down) necks anyway you like and they will never spring back 3thou from it. Maybe half that.
Even near web brass, very thick & well supported, does not spring back 3thou. If it did, there could never be popping extraction, because guns would fail before reaching it.
The reasoning behind standard bushing choice of 2thou under loaded neck diameter, is that necks spring back from this sizing(which is yielding) by as much as ~1thou, leaving ~1thou of interference fit.

I have my own experiences & testing, but I'm confident 'Googling' would lead to conclusions backing mine.
Quick example from Varmint Al's; http://www.varmintal.com/arelo.htm
"The difference between the barrel's chamber neck diameter and this fire-formed case neck's "spring back" diameter is usually about 0.0013 inch to 0.0015 inch. This spring back is for the .224 to .243 calibers.".

But like you say; You just don't know what you don't know.
Can't argue with that

 

[Alex Wheeler]

These are straight out of a chamber with a .313 neck

 

[CaptainMal]

FYI... Bostrom tells me his Dasher reamer cuts a .2705 neck. Just measured some cases I shot yesterday after annealing and tumbling. All are right at .2695" with that Norma Dasher brass.

Just one rifle and one set of 42 pieces of brass. FYI.

 

[Mtstalker]

I took a piece and over annealed it and then slowly chambered it after expanding it to .305" outside. I got .298" at the base of the neck and .2975 at the mouth. Im still confused, why would the lapua brass thats .294-.295 loaded not let a bullet in the neck after firing?

 

[mikecr]

Like Alex, you're running high clearance and never reaching chamber with necks.
On firing your necks expand to release the bullet & a bit more, and with this, pressure is either equalizing around the necks, or dropping off enough otherwise to prevent further neck expansion all the way to chamber. Then it springs back the pretty much the same as with everyone else (~1thou).
Maybe you have a good bit of neck sooting?

Quick search here:

bench: I buy my own chambering reamers (PTG) and have the reamer drawings. What I see consistantly is .001" of springback in the case neck. .269" chamber neck walls will equal .268" as fired diameter.

http://forum.accurateshooter.com/threads/brass-spring-back.3802676/

Both of my Grendels spring back .001" on Lapua cases...

http://forum.accurateshooter.com/threads/tight-neck-advice.3821827/#post-36265115

I measure a fired round and add about .001 for spring back to guesstimate my chamber dimension and go from there

http://forum.accurateshooter.com/threads/neck-tension-plug-gauges.3768281/#post-35969624

 

[Alex Wheeler]

Like Alex, you're running high clearance and never reaching chamber with necks.
On firing your necks expand to release the bullet & a bit more, and with this, pressure is either equalizing around the necks, or dropping off enough otherwise to prevent further neck expansion all the way to chamber. Then it springs back the pretty much the same as with everyone else (~1thou).
Maybe you have a good bit of neck sooting?

Quick search here:
http://forum.accurateshooter.com/threads/brass-spring-back.3802676/


http://forum.accurateshooter.com/threads/tight-neck-advice.3821827/#post-36265115

\
http://forum.accurateshooter.com/threads/neck-tension-plug-gauges.3768281/#post-35969624

My loaded round measures .310, so if the bullet was slipping out and neck not expanding the necks would be closer to .309. 60k psi is expanding my necks just fine. .003" is not high clearance.

 

[mikecr]

I never said the necks did not expand..
I said that necks do not spring back 3thou.

The highest spring back I've ever seen, or credibly heard of, is with 25WSSM necks that I expanded to 26cal. After expansion these necks were still 19.5thou thick!
This, leading to an extreme spring back of ~1.5thou, causing tight fit on a Sinclair turning mandrel. So I had to expand/turn at 25cal, before necking up(trial & error).
It's not normal for necks to spring back that much, but then it isn't normal for necks to be so thick..

I know of no process that could cause necks to spring back more. If I did, I'm thinking there is potential to make money with that, helping those needing extreme tension to get it with partial neck sizing.

 

[Alex Wheeler]

I took a piece and over annealed it and then slowly chambered it after expanding it to .305" outside. I got .298" at the base of the neck and .2975 at the mouth. Im still confused, why would the lapua brass thats .294-.295 loaded not let a bullet in the neck after firing?

Will it slip in point first? Some bullets have a rather large pressure ring. Don't pull your hair out over this. Its simple, you have a lot of neck clearance. 291 expanding to 298 is going to spring back more than if you only had .002" clearance. You dont have a problem.

 

[Webster]

That's one person who thinks he has 3thou of neck spring back, and one person who thinks that brass doesn't spring back that much.
Anyone else?

I don't think I have 0.003", I know it's real.

 

[Someoldguy]

I still do not understand what is wrong with making a chamber cast or pound cast and THEN measuring the fireformed brass/loaded round?

Am I obtuse? I don't understand the problem?

 

[Shynloco]

....... Does any one have a idea of lapua neck thickness in the 260 rem.

Unturned/unfired new Lapua Brass comes in at .014 thickness in the neck.

 

[Mtstalker]

My lapua is coming in at .0155" . No biggy i have neck turned it all to .0135" and yes if i flip the berger vld around it slides in up to the very base. I feel like a complete idiot now. But it still doesnt explain the pierced primers. And no neck sooting with lapua but a little with hornady or remington.

 

[Mtstalker]

I still do not understand what is wrong with making a chamber cast or pound cast and THEN measuring the fireformed brass/loaded round?

Am I obtuse? I don't understand the problem?

I would but i have to order everything to do that. And where i live it would take a week or more to show up. Overnight shipping takes 2 or 3 days to arrive. . I dont have that kind of time right now.

 

[Someoldguy]

Pardon me for being Captain Obvious, but you started this thread on the 9th, and I suggested a chamber cast on the 9th, and today is the 16th.

You've had time to order chamber casting materials, it seems. (?)