What is "Spring Back"?


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BSA1
June 20, 2013, 08:05 PM
I am trying to reload some 7.62 x 54r. I am using Lee dies with .312" expander plug for a .311" gas check bullet. After I full length resize the brass the I.D. of the neck measures .305".

I called Lee and the tech I spoke with said the reason for the small I.D. was due to the brass springing back and there was no way to control it. The I.D. of the fired brass is .312" so I need to use the .311" cast lead bullet.

Suggestions?

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Twmaster
June 20, 2013, 08:19 PM
You may need to anneal your cases. I'm doing the same as you and am using a .312" expander from an Argie Mauser die set.

My brass is one time fired PRVI and expands to .311" with only .001" spring back.

Basically some brass will return to close to it's original size when you pull the expander back through. Kinda like a spring. If you anneal that may fix it.

243winxb
June 20, 2013, 08:19 PM
Buy a Lyman "M" die if they make one for 7.62 x 54r. Brass tries to return to its orginal shape. Spring back is very little, more like .001" or 2. You need to take more measurement of the expander & case mouth after sizing. Something does not sound right??

Scimmia
June 20, 2013, 08:24 PM
What you're seeing is a bit much, but remember that the neck needs to be smaller to provide neck tension to hold the bullet. If you're loading cast bullets, you usually an neck flaring die: http://leeprecision.com/universal-case-expanding-die.html

witchhunter
June 20, 2013, 09:36 PM
Don't change your bullet size because of the die, change the expander ball or have your die reamed so that you can use the bullet that fits your bore. It will work out to be more accurate if the lead bullet is the right size for the barrel. You should also get less leading if the bullet is properly sized.

243winxb
June 21, 2013, 06:41 AM
Looks like the normal diameter for a jacketed bullet is .311" or .312" Cast diameter should be larger than groove diameter by .001" to .002" The Lyman "M" die, a better choice IMO, works differently then the Lee thing.:) The M goes inside to open the neck diameter, not just the mouth of the case.

BSA1
June 21, 2013, 06:11 PM
I have not slugged the bore so I can not say for sure what it actually is. The sized brass is "springing back", if that is what is really happening, to the same neck size as new, unsized factory brass.

I am going to try to disassemble the die and measure the expander plug just to be sure it is really .312". I can barely seat the base of the gas check after I have chamfered the case mouth but I have not tried seating the bullet yet to see if I causes lead to be shaved off.

rcmodel
June 21, 2013, 08:49 PM
For .311" bullets you need a larger expander, like .313", or softer brass.

Try Twmaster's suggestion in post #2 about annealing the case necks to make it softer.

Then it won't 'spring back' anymore.

rc

Twmaster
June 21, 2013, 08:58 PM
Be aware that the Lee 7.62x54R dies come from the factory with a .308" expander pin.

BSA1
June 21, 2013, 08:59 PM
Although the Lee tech assured me that the brass will accept the .311" bullet annealing the brass seems like the next step.

I installed a .312 " expander plug some time back but have not shot the gun until recently. The larger expander did not help. Stroke the boilers and dang the torpedoes.

GLOOB
June 21, 2013, 08:59 PM
I can barely seat the base of the gas check after I have chamfered the case mouth
This sounds about right. It should be difficult if not impossible to fit the gas check in there by hand, even with a chamfer. (You might want to try flaring those case mouths; +1 on the Lyman M die).

Sounds like your expander is in the right ball park, and maybe your measuring is off. How are you measuring ID, anyways? It's very difficult to measure using calipers. Best is to measure OD, then seat a bullet and measure OD, again. You're looking for the difference to be around 1-2 thousandths of an inch. If your brass was really springing back that much, your sizing die is exceptionally small and/or the brass ridiculously thick for it to get that small to begin with. It would be springing back too big after coming out of the sizing die, no longer able to hold a bullet tight.

I have not tried seating the bullet yet to see if I causes lead to be shaved off. My guess is you'll be fine, as long as the cases are chamfered, and you can get the bullet squarely into the seater plug. One under-appreciated benefit of a gas check is that it will pretty effectively open up tight brass, protecting the base of the softer bullet from getting squished.

But without a flare, you will probably get a few bullets that "crunch" to get started, which might be damaging the gas check a little. And some of your bullets might tip over a little and catch the seater plug offcenter. Those bullets will shave and/or seat awful crooked. This is why the Lyman M die is the bees knees for cast rifle reloading.

BSA1
June 21, 2013, 09:45 PM
Lee dies do not flair the case mouth hence I chamfered them inside and out.

I have never worked with this cartridge and gun. After the set of reloads years ago I found out the dies had a .308" expander ball. I am pretty certain I replaced it with a .312" plug. This is my first set of reloads since then with the same poor results.

Measuring is a fair question. Using calipers I got .312" on the fired brass which seems right for a military rifle.

Since annealing doesn't cause any harm I give it a try.

Jesse Heywood
June 21, 2013, 10:17 PM
Since annealing doesn't cause any harm I give it a try.

If you get the brass too hot it can hurt the case. Follow the instructions in other posts using a torch and pan, which keeps the base cool.

Twmaster
June 22, 2013, 06:32 AM
I should have added that I use a Lee case mouth expander die to load my 7.62x54R cases. I've been using 200 grain .312" gas checked hard cast with a Gopher Fart load.

GP100man
June 22, 2013, 06:53 AM
Seat it ,flare it ,expand it it all does`nt mean squat !!

Seat a boolit ,then pull it, if it`s smaller than when it went in ,then ya need to address the expanding issue .

& yes brass does have springback , that`s what allows us to extract a fired case from a chamber.

Different "lots"can sometimes vary as to the elasticity.

I prep my 54r brass by sizing ,trimming,priming & the last step is to flare the mouth with lees universal flaring die & yes I have the larger expander .

I cast a fairly soft (11 bhn) Lyman 314299, lubesize it in a 314 die & seat it with a very slight roll to make sure I have no flare left .

This set up has not resized any of my cast down any.

http://i746.photobucket.com/albums/xx110/GP100man/102_0310.jpg (http://s746.photobucket.com/user/GP100man/media/102_0310.jpg.html)

stubbicatt
June 25, 2013, 07:44 PM
If you are determining inside diameter with a calipers, you will likely obtain inaccurate measurements. If you want to get a little bit closer, get a ball mic, measure the neck walls in 4 or 5 places to get an average neck wall thickness, and then do the same with a standard micrometer on the outsides of your case necks. You can average these numbers out, subtract neck wall thickness from outside diameter and get a little bit closer on your inside diameter.

There are manufacturers who will produce an expander plug or mandrel for you so that you can expand your case mouths to whatever diameter you desire. They aren't terribly expensive, but it might save you a headache when trying to load cast bullets.

Walkalong
June 25, 2013, 07:51 PM
Seat a boolit ,then pull it, if it`s smaller than when it went in ,then ya need to address the expanding issue .

& yes brass does have springback , that`s what allows us to extract a fired case from a chamber.

Different "lots"can sometimes vary as to the elasticity.This is it in a nutshell, unless you are playing with neck tension on jacketed bullets, but the OP is using lead.

GP100man
June 25, 2013, 08:03 PM
Me to , as you see in the pic ,those boolits are 11-12bhn & have no down sizing from the case mouth .

They mic .3135" & do purty good with 12gr. of 2400 pushing em .

Walkalong
June 25, 2013, 08:13 PM
There are manufacturers who will produce an expander plug or mandrel for you so that you can expand your case mouths to whatever diameter you desire. They aren't terribly expensive, but it might save you a headache when trying to load cast bullets.

Expander body (http://www.sinclairintl.com/reloading-equipment/case-preparation/neck-turning/turning-expander-mandrels/sinclair-generation-ii-expander-dies-prod38807.aspx)

Mandrels (http://www.sinclairintl.com/search/index.htm?k=expander+mandrel&ksubmit=y)

These are intended for jacketed though. The Lyman M die will expand the neck and give its unique straight "flare". good stuff.

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