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Topic: Annealing and velocity variance  (Read 675 times) previous topic - next topic

Re: Annealing and velocity variance

Reply #15
I was bumping the shoulders 0.002. Starting to prep 100 new pieces this morning so since I'm starting from scratch I'll only bump 0.001 or 0.0015.

Re: Annealing and velocity variance

Reply #16
I was bumping the shoulders 0.002. Starting to prep 100 new pieces this morning so since I'm starting from scratch I'll only bump 0.001 or 0.0015.

Cut one of those brass in half and see what it looks like.
When I anneal my brass, I would be able to completely flame orange on the neck and still not overheatvthe rear of the brass. I use two torch heads approx 4” apart.

Re: Annealing and velocity variance

Reply #17
I was bumping the shoulders 0.002. Starting to prep 100 new pieces this morning so since I'm starting from scratch I'll only bump 0.001 or 0.0015.

New brass is usually under sized and doesn’t need the shoulder bumped back. Use you measuring tools to verify that statement, but I bet the shoulders are already well back.

That said, the  case mouths/necks could be dinged up a little and may need attention.
RPR 6.5 Creedmoor
Bergara 6 Creedmoor

Re: Annealing and velocity variance

Reply #18
@MLN1963 I meant I would start bumping them 0.001-0.0015 after they're fire formed. I already ran them all over a Lee collet die to make sure the inside of the case necks are round and trimmed them. I did take measurements of neck wall thickness, inside and outside neck diameter, case length from the datum, as well  as body diameter just below the shoulder and at the web of ten pieces of brass that I kept separate and marked to track growth and changes on through the life of this lot of brass.
@LeadHammer so you don't think I need to worry to much about having annealed the case body to far down? With having the flame where and for the amount of time I said, the color  change only came about a quarter of an inch or maybe even a little less below the shoulder/ body junction so I couldn't imagine that I had annealed to much of the body but it still worried me since its the first time I've had that line appear from the attempted separation as well as the first time that I ever annealed.

Re: Annealing and velocity variance

Reply #19
I am far from an expert on here, but my brass look similar to those. I did not have any Templaq to use but have Tempstiks.  So with the two torch heads 4" apart, 5 sec flame exposure, I can't get 450 to melt way half way down the case, not even close.  650 will melt past the shoulder just not as far down as the 450.
If you can feel a dip with the paperclip, something else is wrong I would think. You need to cut a case in half, then you can clearly see whats up.

Re: Annealing and velocity variance

Reply #20
Here is mine after 6x fired.

Re: Annealing and velocity variance

Reply #21
dloforo

What is the measurements to the datum on your sized brass and fired brass?  The ring you feel is the result of the case stretching as you know. There will be some as it’s unavoidable for reliable clambering. Most of the time if you follow a die manufacture’s instructions the brass is going to get set to a size that is sure to work in any chamber. Their concern is your gun’s function, not brass life. Combine that with manufacturing tolerances of the gun builder and you can have a short piece of brass in a long chamber. Every firing stretches web area, every sizing pushes it back. Even quality brass can only survive a limited number of cycles of this.
RPR 6.5 Creedmoor
Bergara 6 Creedmoor

Re: Annealing and velocity variance

Reply #22
@MLN1963 I finally have some progress to report.... And of course some more questions to go with it! So my previous extreme spread was 34 and standard deviation was 9 on a 10 shot string prior to annealing. Today I shot a 20 round string with annealed cases with an

extreme spread of 24 and an SD of 5 and when seating bullets I felt much more consistent pressure and didn't have any copper shavings around the case necks from the bullets. Needless to say I was happy to cut the SD in 1/2 and 10 feet per second off my ES with twice as many rounds fired but would still like to have my ES in the teens. However each time I Chrono rounds the first round fired seems to be 15 FPS faster than the average of the string which would absolutely be the difference between teens and 20s on ES. Is this just because of a cold bore and once the barrel warms up it swells and constricts the bullet a little? Also about 1/2 of my brass showed a ring around the circumference of the case 1/2 an inch above the case head and I could clearly feel the indentation from the attempted separation with a paperclip inside the case. These are the first cases I've ever had do that and they're also the first cases that I've ever annealed. The cases showed no other  pressure signs and I have shot the same  load  a lot  with the same brass  without pressure signs. I used 750 degree Tempilaq inside the case mouths but did not have any 450 degree to run down the case body. I had my flame right at the neck/shoulder junction and the Tempilaq  inside the case mounths was melting with the cases in the flame for approximately 3.9 or 4 seconds with no change in the color of the flame of other signs of over annealing. These cases have been fired approximately 8 times prior to being annealed so I'm wondering if my case body got too hot too far down weakening the body around the web or if these cases were just at the end of their life span? Any guesses at that?
My guess is that your former bump setting worked well on the "harder" brass.  The annealed brass has less springback and therefore bumped somewhat more than your .002 target.  You should do fine with your new brass, annealing process and .001-.0015 bump setting.
Good shooting,
Randy
11X Grandfather
Part time Savagesmith

 

Re: Annealing and velocity variance

Reply #23
@MLN1963 here's the average of ten pieces of brass each of new, fired, and fired and resized bumping 0.002 with a Forster BBN: new 1.556, fired 1.560, resized 1.558. I'm thinking this lot of brass might have just been at the end of its rope. We'll see when I finally get a chance to fire this new brass. However I am sold on annealing with the drastic decrease in my numbers after annealing. Thanks again for your help.