Case Length Ignoring Science with light loads!

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  • Last Post 18 June 2012
onondaga posted this 14 June 2012

I have been watching http://www.castbulletassoc.org/view_user.php?id=6375>John Alexander's post on “Case Shortening with Light Loads", and monitoring my case length on a 100 round batch of light 3.1gr loads of H TiteGroup with a 90 gr. cast bullet in 7.62X39. I have checked every case length for 4 loading/shooting cycles with the Lee ZipTrim and with each of the 100 cases  in the collet every time and watching for case shortening from the light load.

On the 3rd cycle a few touched the gauge when checking and I thought it could have been operator error, and I trimmed them back with the Zip trim. It was less than .001” trim back that barely put a shine on the case mouths.

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Ken Campbell Iowa posted this 15 June 2012

what are your sizing and crimping dies and techniques  ?

does the lee trimmer index on the shoulder ...or on the case base  ?

how much headspace do your baseline cases have...after a few firings, the cases should have zero headspace, ....so ...geepers ....what is growing   ?

interesting.   ken

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Fg1 posted this 15 June 2012

From what I have read , although havent experienced is that the light loads shorten the case headspace length not total length . The overall length may increase but length from datum line to base will shorten resulting in incipient(sp?)case head seperation same as if one had excessive headspace issue.

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nimrod posted this 15 June 2012

Bet that it is more of a function of using the cases in a break open single shot rifle which I think you are doing? I know that in my Encore my .223 cases grow a lot but in my Savage bolt action they grow very little with the same loads.

Richard

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onondaga posted this 15 June 2012

Ken Campbell, Iowa wrote: what are your sizing and crimping dies and techniques  ?

does the lee trimmer index on the shoulder ...or on the case base  ?

how much headspace do your baseline cases have...after a few firings, the cases should have zero headspace, ....so ...geepers ....what is growing   ?

interesting.   ken Ken: Sizing is Lee Collet Neck Size Die in 7.62x39 modified with a .303 Brit Mandrel to fit my bullet size .3125” Standard die setting to instructions.Crimping Die is Lee Factory set to return case mouths .001” smaller than neutral case mouth size before case mouth flare and bullet seating. The brass ia very minimally worked. You can see the fine line the Lee FC die makes on the brass in the photo,  but it is little more than just a line from a - .001 Crimp to close case mouth flare. The rifle is a single shot, I don't need a crimp, but I don't want a flare left.  The flare is + .003” and will skid the chamber  if left there.

The Lee Zip Trim indexes with the contact of the cutter gauge pin through the flash hole and against the flat plate behind the case head that the 3 Jaw Chuck of the trimmer draws the case head too. Deformed protruding primer pocket edges or dirt can give cases a false long reading but I am not getting deformed case-heads or primer pockets . Case-heads check flat visually and are not tipsy on the case-head flats.

The cases are fully fire-formed from 5 cycles of full power loads and 4 subsequent cycles of the light loads I'm testing. Cases were checked and trimmed every cycle of full power loads also. I believe the brass is full head-space as practical  in size.

I cannot determine where the cases are lengthening other than overall length and this is only about .001” at most ... but it is happening!

If these were full power loads I would be expecting normal neck length extruding from the fire power.

There is an error somewhere, but it is only .001” at most presenting at the length overall of the brass from case head flat to case mouth  as that is all the Zip Trim monitors and trims.

I am clueless on this one.

Gary

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TRKakaCatWhisperer posted this 15 June 2012

I'll add to the ignorance (because I can't provide specific details) and say I've had cases lengthen and other cases shorten. General feeling (how's that for specifics) that the shortened cases were light loads. Lengthened cases were heavy loads, and of different caliber.

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onondaga posted this 15 June 2012

nimrod wrote: Bet that it is more of a function of using the cases in a break open single shot rifle which I think you are doing? I know that in my Encore my .223 cases grow a lot but in my Savage bolt action they grow very little with the same loads.

Richard  Richard, there is a possibility with my rifle being a single shot, but I don't get why. This Russian utility rifle is built like a tank and locks up hard, tight and solid every time with a very powerfully sprung  squeeze lever and big bearing lockup surfaces. The Spartan rifle lockup is much more solid than any of my American NEF rifles.

Gary

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onondaga posted this 15 June 2012

http://www.castbulletassoc.org/view_user.php?id=97>TRK: I agree with your feelings too, Hysterically in this instance, I am getting opposite measurable results with light loads.

Gary

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onondaga posted this 15 June 2012

Fg1 wrote: From what I have read , although havent experienced is that the light loads shorten the case headspace length not total length . The overall length may increase but length from datum line to base will shorten resulting in incipient(sp?)case head seperation same as if one had excessive headspace issue. I am agreeing with incipient hysteresis of an unknown at this point . Fortunately, at this point the ~.001” is not statistically or practically significant. The gun shoots well !!!!!!

Gary

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Fg1 posted this 15 June 2012

I doubt any problems will arise as long as you dont switch to full power jacketed type loads using same cases . The cases will last a long long time at that rate ! Neck sizing only sure lengthens the life !

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joeb33050 posted this 15 June 2012

The original question was about shortening of the CASE HEADSPACE dimension. If cases get longer, then that is interesting, but doesn't have to do with the original question. That is another question. joe b.

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onondaga posted this 15 June 2012

http://www.castbulletassoc.org/view_user.php?id=3>joeb33050:

Joe , yes there is a disparity. Your new post demonstrates no length change with the Lee Collet Neck Sizing Die I am using .  The case length increase from firing that you cite is  debatable with my 3.1 gr H TiteGroup loads and a 90 grain cast SWC in the 7.62X39.

Case length shortening due to firing pin energy driving the case forward , smacking the slope/shoulder of the case into the chamber dimension with light loads sure does sound logical. I have no stats on that, just warnings from other notable shooters like http://www.castbulletassoc.org/view_user.php?id=207>Ed Harris, a member here.

Gary

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joeb33050 posted this 15 June 2012

onondaga wrote: http://www.castbulletassoc.org/view_user.php?id=3>joeb33050:

Joe , yes there is a disparity. Your new post demonstrates no length change with the Lee Collet Neck Sizing Die I am using . 

This is what I did. Measure case length. Lee Collet Die. Measure case length. No change. NOT what you found-a different procedure.

The case length increase from firing that you cite is  debatable with my 3.1 gr H TiteGroup loads and a 90 grain cast SWC in the 7.62X39.

Case length shortening due to firing pin energy driving the case forward , smacking the slope/shoulder of the case into the chamber dimension with light loads sure does sound logical. I have no stats on that, just warnings from other notable shooters like http://www.castbulletassoc.org/view_user.php?id=207>Ed Harris, a member here.

I have data that says that the firing pin fall does NOT drive the shoulder forward. If you or Ed have data, 'd like to see it. BTW Anyone can conduct a test in half an hour to find out for himself. joe b.

Gary

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onondaga posted this 16 June 2012

bump

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Pigslayer posted this 16 June 2012

joeb33050 wrote:

I have data that says that the firing pin fall does NOT drive the shoulder forward. If you or Ed have data, 'd like to see it. BTW Anyone can conduct a test in half an hour to find out for himself. joe b.

Me thinks that one should show pause before making the above statement(s).

If someone else had of done to me what I did to myself . . . I'd have killed him. Humility is an asset. Heh - heh.

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joeb33050 posted this 16 June 2012

Pigslayer wrote: joeb33050 wrote:

I have data that says that the firing pin fall does NOT drive the shoulder forward. If you or Ed have data, 'd like to see it. BTW Anyone can conduct a test in half an hour to find out for himself. joe b.

Me thinks that one should show pause before making the above statement(s).

Why? Where's the problem? joe b.

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onondaga posted this 16 June 2012

http://www.castbulletassoc.org/view_user.php?id=3>joeb33050 :

Here is the problem Joe. Your data and my 100 cases are in agreement so far. However Deductive logic disagrees with both sets and reports from other shooters like Harris reporting case shortening with light loads.

I actually agree with Harris and not you, due to the deductive logic . The cases are slammed forward by firing pin energy;  bumping the case into the chamber limits. There is no high energy to push them back and fire-form them with light propellant charges. Logic says , they will eventually get shorter, regardless of your data or my 100 latest measurements that agree with you. I have only 4 cycles of light loads  on the brass thet was previously fire formed with heavy loads. 

Harris warned that “many” cycles with light loads will shorten the brass. I don't believe my 4 cycles has yet met the “many” cycles term in the Harris warning.

You have got your data and you are sticking to it with your tiny sample compared to my 100 cases fired fired for 9 cycles for a sample size of 900 measurements so far.  Well Bravo, I am not closing the door on this. I disagree with you, so what!

Gary

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pat i. posted this 16 June 2012

onondaga wrote:  Richard, there is a possibility with my rifle being a single shot, but I don't get why. Gary

I'm kindathinkin the shoulder gets pushed back with lite loads in bolt guns because the momentum of the bolt moving forward, after the firing pin shoulder hits it's stop, hammers the case into the chamber. This wouldn't happen with single shot rifles or rimmed cases which would explain why Gary doesn't have the problem. There's a gap between the front of the bolt and the rear of the barrel tenon and if the pressure in the fired case wasn't strong enough to hammer back something has to give, which in this instance would be the shoulder of the case. I'm not a big fan of the firing pin hitting the primer driving the case forward because in my experience the primer was sticking out of the case on lightly loaded rounds.  

Joe, Try the same experiment you tried before with the paper shims on the bolt face except this time use a fully formed case and leave the primer pocket empty. I'm sure how work hardened the case is is going to effect the results with a once fired case showing a lot more set back than a 10 times reloaded case. 

 

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nimrod posted this 16 June 2012

I'm kindathinkin that since we are talking about a swing open single shot that rotates around a pin that there is enough give in the area of the pin and surrounding action and barrel lug that may have some bearing on the case length and light loads. Don't know just guessing, I do know that this a crtical area in the Encores and causes a lot of vertical stringing issues. I also blame the same for my cases growing more than normal.

Richard

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onondaga posted this 16 June 2012

http://www.castbulletassoc.org/view_user.php?id=5498>pat i.:

You make a lot of sense.  I have been curious about the Harris warning only from a practical standpoint, wondering if I will have to change my loading procedure to segregate  my brass that has been lightly loaded and switch it to heavy loadings to re-form the brass as Harris recommends. I've also been wondering how many cycles will it take to show a significant change to warrant change to heavy loadings again.

In actuality, so far, with my brass through 10 cycles, nothing is really going on to cause concern about my brass. I have been doing more than my fair share of shooting and may surpass my average 100 pounds of cast bullets per year. That is not a bad thing either....I have been having fun!

Gary

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joeb33050 posted this 16 June 2012

My tests showed that cases fired with a dead-but-new primer did NOT have the shoulder moved back, did NOT decrease case headspace.

My test showed very quickly that cases fired with a primer only moved the case shoulder back, decreasing case headspace.

Either of these tests is easily repeated.

I have NO data showing that either: A Case headspace changes with low velocity loads. or B Case length changes with low velocity loads.

Thus, I am NOT disagreeing with Gary or Ed or Pat.

You 3 are talking about cartridges loaded with primer and powder and bullet. I have NO data.

Pat; Maybe the extractor-snapping-force would set the shoulder back, I don't know. And, I don't think that that has anything to do with the question. How about going back to the question. Do LV loads set the shoulder back, decreasing case headspace? Mine didn't, John's didn't. A test would take a short bit of time. I have the tools to measure the cases.

Or, we could continue to argue whether it's raining out, without looking out the window. joe b.

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