Brass Shrink???

[David247]

I got new Lapua 6.5 Creedmoor brass which has been cycled three times now. When first started I set my Giraud up to the trim to length (mistake) to chamfer and debur. The shooting them once, I ended with cases that very between 1.9055 and 1.907. The trim length is supposed to be 1.910.

I am using a Redding FL bushing die with no decapper or expander. I do that separately. I checked the trimmer and it is perfect. I actually reset it between max and trim to length. How does this happen?

 

[liljoe]

So you have a .0015" difference on the length?

Joe

 

[boltfluter]

Cases expand to match the chamber and the cases shrink in length. Cases are not perfect so there is a very small difference in OAL. Nothing to worry about. Carry on!

Paul

 

[Jesswil61]

Were the cases sized/should bumped and measured prior to trimming? Did you measure and verify after trimming? The .0015" though minor seems to be excessive if these things are being done, If the cases are being sized prior to trimming, and the cases shoulders are indexing off the shoulder in the case holder for the trimmer and trimmer is set up for expected OAL with equal pressure being applied to hold the case while trimming, the result should be pretty consistent. I step in here only because I have experienced a variance in the trimmed length where my cases were not indexing off the shoulder due to bottoming out on the shoulder/body junction. Your chamber dimension may vary from the case holder to some degree. I agree with boltfluter as well they could lose some length when fired due to resizing to the chamber but it should be pretty consistent.

 

[David247]

Were the cases sized/should bumped and measured prior to trimming? Did you measure and verify after trimming? The .0015" though minor seems to be excessive if these things are being done, If the cases are being sized prior to trimming, and the cases shoulders are indexing off the shoulder in the case holder for the trimmer and trimmer is set up for expected OAL with equal pressure being applied to hold the case while trimming, the result should be pretty consistent. I step in here only because I have experienced a variance in the trimmed length where my cases were not indexing off the shoulder due to bottoming out on the shoulder/body junction. Your chamber dimension may vary from the case holder to some degree. I agree with boltfluter as well they could lose some length when fired due to resizing to the chamber but it should be pretty consistent.

Yes the cases are sized before measuring and the trimmer does index off the shoulder. I am not too worried about the .0015 difference between the min and max measurements, I am more concerned that they ended up being .0045 (1.910 minus 1.9055) shorter than the trimmer was set up for. I have no idea how that could have happened.

 

[rardoin]

Keep shooting them and do not trim until they reach the set point of the trimmer.

 

[Richard Coody]

Yes the cases are sized before measuring and the trimmer does index off the shoulder. I am not too worried about the .0015 difference between the min and max measurements, I am more concerned that they ended up being .0045 (1.910 minus 1.9055) shorter than the trimmer was set up for. I have no idea how that could have happened.

simple

the case body expands to match the chamber shortening the overall length of the case.

i never trim new brass and only trim fired brass when it reaches or is over max. then i only trim .005.

i also never set up a sizing die for.a shoulder bump until that brass is a tight fit on bolt closure. until then just size the neck.

 

[dickn52]

Too much sunshine will cause them to shrink too....

 

[Jesswil61]

simple

the case body expands to match the chamber shortening the overall length of the case.

i never trim new brass and only trim fired brass when it reaches or is over max. then i only trim .005.

i also never set up a sizing die for.a shoulder bump until that brass is a tight fit on bolt closure. until then just size the neck.

Agree completely, I go one step further and determine the OAL before trimming by chambering a scrap piece of barrel with my reamer and section this to determine where the case neck will possibly jam in the chamber cut and shorten by around .005" and use this as my trim too dimension after around 4-5 firings.

 

[David247]

Too much sunshine will cause them to shrink too....

Well Damn Dick, that can't be it. We haven't seen the sun in a month.

 

[David247]

simple

the case body expands to match the chamber shortening the overall length of the case.

i never trim new brass and only trim fired brass when it reaches or is over max. then i only trim .005.

i also never set up a sizing die for.a shoulder bump until that brass is a tight fit on bolt closure. until then just size the neck.

That's what will happen from now on. Thanks

 

[dickn52]

Well Damn Dick, that can't be it. We haven't seen the sun in a month.

Move down here to Florida then. My brass is constantly shrinking on me when I put it on the patio table to dry.

 

[hambone1971]

I got new Lapua 6.5 Creedmoor brass which has been cycled three times now. When first started I set my Giraud up to the trim to length (mistake) to chamfer and debur. The shooting them once, I ended with cases that very between 1.9055 and 1.907. The trim length is supposed to be 1.910.

I am using a Redding FL bushing die with no decapper or expander. I do that separately. I checked the trimmer and it is perfect. I actually reset it between max and trim to length. How does this happen?

David you need one of these to tell you how deep the neck chamber really is. Then you can trim the brass back .020 or .030 which is probably going to be a lot longer than your book says. I use one in all my long range rifle cals... HB
https://www.sinclairintl.com/reload...s/sinclair-chamber-length-gage-prod32925.aspx

 

[dedogs]

.020 or .030

Typo? dedogs

 

[Richard Coody]

i would love for lyman to make a borescope long enough to be able to see the interface between a piece of fired and unsized and sized brass and the chamber

pics of.that would be interesting.

 

[hambone1971]

Typo? dedogs

That's .020 or .030 shorter than what the Sinclair gage says the depth is, not what the book recommends. Usually it comes out longer than what the book recommends giving more support for the bullet and more brass volume. HB

 

[dedogs]

That's .020 or .030 shorter than what the Sinclair gage says the depth is

I understand how the Sinclair gauge works. My question is why would you want to trim your brass back .020-.030 from max length? Seems like it would induce a large carbon ring. Most books recommend .010. A lot of bench shooters only trim .005. dedogs

 

[David247]

David you need one of these to tell you how deep the neck chamber really is. Then you can trim the brass back .020 or .030 which is probably going to be a lot longer than your book says. I use one in all my long range rifle cals... HB
https://www.sinclairintl.com/reload...s/sinclair-chamber-length-gage-prod32925.aspx

I will get one of them. This is a custom gun and it seems tighter and shorter than my brothers RPR chamber.

 

[hambone1971]

I understand how the Sinclair gauge works. My question is why would you want to trim your brass back .020-.030 from max length? Seems like it would induce a large carbon ring. Most books recommend .010. A lot of bench shooters only trim .005. dedogs

Well, I just took a look at my notes and your right. My Savage 12FV throat is 1.942 and my Savage Long Range Precision LRP is 1.944 to end of throat. The Hornady book suggest trimming to 1.920 or that's the number on diagram anyway. So I have .022 roughly to deal with. I'd now change my suggestion to what you mentioned at .010 or .005 if your watching it all the time. Don't want to pinch a bullet that's for sure. Thanks for catching that. HB

 

[OLEJOE]

Y'all know how cold weather will make things draw up. LOL