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Topic: Shoulder bump starting point and FL size question (Read 307 times) previous topic - next topic

Shoulder bump starting point and FL size question

I'm trying to find a starting point for managing shoulder bump by measuring the base to shoulder length using the Hornady headspace gauge. If I take 10 pieces of fired, cleaned and de-primed brass, I see about 0.001" of variation for the sample. When I mark the brass so I know who's who, I can re-visit each piece and reliably get the same measurement as last time, I think that means the tool and my technique produce repeatable results.

Given this is Hornady brass reloaded 7x and annealed after the 6th time, is 0.001 a reasonable spread for fire-formed brass?

My second question concerns my Lee FL die. When I compare, using the same Hornady gauge, some fire-formed specimens above with their FL sized counterparts where I followed Lee's recommendation for setting up the die in the press, on average I see about 0.006" of shoulder setback with the sized brass. Is it valid for me set the height of the Lee die in the press so as to reduce the amount of shoulder bump without upsetting some of it's other functions, like properly sizing the body?

I'm not opposed to a different sizing die setup but for now, the Lee is all I've got.

 
Chris

Re: Shoulder bump starting point and FL size question

Reply #1
bikemutt,
My thought would be to absolutely try to back off your FL die.  Shoot for .002 or .003.  If your brass still chambers easily at that setting your brass life should be extended.  Your 7x brass that has been sized .006 under may already show signs of some head separation so my suggestion is to check it before you shoot it too many more times.  You probably have heard of the  "paper clip" method for checking this.  I made a tool for this years ago by "heating & bending" the tip of a screw driver.  There are also some visual clues on the brass if this is happening. A search for this will better expain it.

Your brass hopefully will be fine and resetting your die will help it last a lot longer.

Good luck,
Randy
11X Grandfather
Part time Savagesmith

Re: Shoulder bump starting point and FL size question

Reply #2
BM,
Take your shortest case and check if it chambers smoothly. If so the set your neck bump to that case and stop over working your brass and extend it's useful life.
To check my cases I took and bent a piece of stainless welding wire to scrape along the inside wall.
Stop the Gun Rights Abuse @ #Me2A

Re: Shoulder bump starting point and FL size question

Reply #3
If you’re using a press that needs shell holders, I love the Redding Competition shell holder kit.  It lets you still have full contact or cam-over and reduce shoulder setback (might have used the wrong terminology...).
NRA Benefactor - Life

 

Re: Shoulder bump starting point and FL size question

Reply #4
Thanks team,

Just to clarify, this brass started life as Hornady factory ammo, 140 gr AMAX match, which was neck sized for the first 6x, then Erik Cortina called and told me to quit neck sizing  ;D . So I don't think it's been overworked yet, plus I'm mostly using this batch to practice with, and hopefully perfect, some of the brass prep techniques generously shared by others here on the forum. I have a 100 pieces of new Startline waiting for me not to trash them.

Interestingly, when I neck sized this brass, never once was the bolt hard to open or close, I think a minimum amount of bump will work just fine.

cwall64, I'm using a Forster Co-Ax press.
 
Chris

Re: Shoulder bump starting point and FL size question

Reply #5
like what has been mentioned turn your die out some to get that bump to a couple thousandths... brass will last longer and have a better fit in the chamber..
Grant

Re: Shoulder bump starting point and FL size question

Reply #6
Bike mutt

Back off that die about a 1/16 of a turn and you will be very close.

Standard dies are 14 threads (or turns) per inch. 1/14=.0714 or 71.4 thousands per turn.  1/2 turn 35 thousands. 1/4 turn 17 thousands. 1/8 turn 9 thousands. 1/16 turn 4.5 thousands.
RPR 6.5 Creedmoor
Bergara 6 Creedmoor

Re: Shoulder bump starting point and FL size question

Reply #7
OK team, here's where I'm at concerning shoulder bump with my Lee FL die in a Forster Co-Ax press.

I measured the shoulders of 10 fire-formed cases with the Hornady headspace gauge. I marked all the cases 1-10 with a sharpy.

After setting the micrometer to zero on the first case:

7 cases measured 0.000"
3 cases measured -0.001"

I measured each case 3 times round-robin, each case measured the same every time.

I lubed all 10 cases with One-Shot. Using the Lee die with round #1, I crawled the die down until the bump settled at -0.002", then I locked the die.

I sized the remaining 9 cases. All 10 cases now show -0.002" of shoulder bump. I measured all 10 cases 3 times, same answer; -0.002".

I chambered and closed the bolt on all 10 cases 3 times, perfect.

Can I safely say that, whatever the limitations of the Lee die might be, I have theses cases FL sized with 0.002" of shoulder bump?

Whew! That was a lot of work :)
Chris

Re: Shoulder bump starting point and FL size question

Reply #8
Yes....done deal.  Now start loading and shooting!

Re: Shoulder bump starting point and FL size question

Reply #9
You got it bike!

Re: Shoulder bump starting point and FL size question

Reply #10
You are on the money BM!  Houston, we have ignition! 8)
Stop the Gun Rights Abuse @ #Me2A