Looking at the reamer print they sent with my shilen barrel in 260 rem It shows the neck is .298" diameter. Fired brass from 2 different brands all measure .295" on the outside of the neck. I assume the chamber is cut with a .295" neck and not a .298" neck? I assume there is a little spring back after firing but i dont think its going to spring back .003". Am i correct?
True chamber size vs fired brass.
- Thread starter Mtstalker
- Start date
On a much smaller caliber - a 20 VarTarg - fired case necks of two brands of brass measure 1.8 mils and 2.1 mils smaller than the chamber neck. So I'm not really surprised by your results.
Remember yield strength is not zero. There will always be spring-back. In fact, yield strength is strain-rate dependent, so there will be more spring-back due to firing than due to sizing.
Remember yield strength is not zero. There will always be spring-back. In fact, yield strength is strain-rate dependent, so there will be more spring-back due to firing than due to sizing.
Alex Wheeler
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Totally dependent on the brass. I have seen less than .001" to .003" spring back after firing.
Someoldguy
If you want to know the precise diameter of your chamber neck, you'll have to make a chamber casting or a 'pound cast'.
Fireformed brass will only get you close. Not precise.
Trust the blue print. You don't have a problem.
I have fired cases in chambers that had no memory of what they were before I pulled the trigger. The case gets hammered from the inside out when fired, I would suggest you measure the outside diameter of the case neck before firing, I would suggest you stick the bullet of the eext case into the neck of the fired case after firing. If there is any truth to the neck not expanding the neck should have bullet hold, if the neck did expand the bullet will not touch the neck of the fired case.
F. Guffey
Take several junk cases and anneal the necks well.
Take a long tapered punch like a center punch or even a spire point bullet and expand the case mouths into a funnel shape so the out side of the funnel is about .320 to .330. You only need to expand them about .020 to .030 over size.
Then slowly chamber the big mouth cases. This will squeeze the brass back down to the chamber neck size.
Carefully pull the brass out of the chamber and measure the brass at the mouth with a mike. You can repeat with several pieces of brass until you are satisfied that you are getting accurate results.
I use this method on old military rifles a lot. It agrees with Cerrosafe casts and pin gauges and is quicker and easier than Cerrosafe.
Take a long tapered punch like a center punch or even a spire point bullet and expand the case mouths into a funnel shape so the out side of the funnel is about .320 to .330. You only need to expand them about .020 to .030 over size.
Then slowly chamber the big mouth cases. This will squeeze the brass back down to the chamber neck size.
Carefully pull the brass out of the chamber and measure the brass at the mouth with a mike. You can repeat with several pieces of brass until you are satisfied that you are getting accurate results.
I use this method on old military rifles a lot. It agrees with Cerrosafe casts and pin gauges and is quicker and easier than Cerrosafe.
I should have been more clear. A loaded round with .0015" neck tension measures .291". Fired .295" i will trust the print. I have lapua brass on the way so i wanted to make sure i would have enough clearance because i heard the necks are thicker. Does any one have a idea of lapua neck thickness in the 260 rem.
carlsbad
Lions don't lose sleep over the opinions of sheep.
I've never seen one this small. Do you have one? --Jerry
The drawing is nothing but a piece of paper.
There is a reamer and a chamber that exists and both are real. Both can be different than the drawing if a mistake was made and reamer makers do make mistakes. It costs nothing and takes little time to check the neck diameter using a case with a flared open case mouth. I have used that method dozens of times with no problems. You do need a micrometer though.
There is a reamer and a chamber that exists and both are real. Both can be different than the drawing if a mistake was made and reamer makers do make mistakes. It costs nothing and takes little time to check the neck diameter using a case with a flared open case mouth. I have used that method dozens of times with no problems. You do need a micrometer though.
Most hole gages and Intramikes are not long enough to reach through a bolt gun receiver and into the neck of chamber.
You are better off using a .001 increment pin gage set to gage the case neck. You can carefully let the pins slide into the neck under their own weight and then tip the rifle the opposite way to get them to slide out.
I like using an old case with an expanded mouth a lot better.
You are better off using a .001 increment pin gage set to gage the case neck. You can carefully let the pins slide into the neck under their own weight and then tip the rifle the opposite way to get them to slide out.
I like using an old case with an expanded mouth a lot better.
There is nothing wrong with your chamber or brass. If your chamber is .298 when the cartridge is fired it expand to .298 touch the chamber wall then spring back smaller. Why would you think .003" is abnormal.
I don't have any as fired cases on hand. They are all loaded or sized. Maybe a few guys out there can submit their numbers? I have been involved with metallurgical failure analysis all my life but certainly not expert on everything. I believe the amount of spring back wouldn't be a constant number for all situations. You should be OK just reloading and shooting.
Several variables:
chamber clearance
neck thickness
neck hardness
Someoldguy
carlsbad
Lions don't lose sleep over the opinions of sheep.
OK. I just happen to have some fired brass sitting around. Brass is annealed every firing and has been vibrated, annealed but not sized as it currently sits.
6xc norma brass measures .276. But I don't have a print handy. I was thinking the neck is .276.
6.5 SAUM . Hornady brass. Measures .2955. print shows neck as .298.
--Jerry
6xc norma brass measures .276. But I don't have a print handy. I was thinking the neck is .276.
6.5 SAUM . Hornady brass. Measures .2955. print shows neck as .298.
--Jerry
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