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Old January 31, 2013, 11:19 PM   #1
davery25
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K31 7.5x55 FL case sizing issue

Okay, not so much an issue as a query. I usually FL size all my rifle cases and bump the shoulder back 0.002. I use a comparator gauge to measure this.

I did the same with my once-fired 7.5x55 swiss brass except the bolt wouldn't close on it.

bumped the shoulder back to 0.004 and the bolt close but required force.

So now i have the die set up to bump the shoulder back a whopping 0.006 and they chamber fine.

Does anyone know why the shoulders need to be bumped back so much in the k-31?
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Old February 1, 2013, 08:27 AM   #2
Bart B.
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There's a dimension issue someplace.

Does a fired case rechamber easily?

Try chambering a resized fired case with its shoulder set back 2 thousandths indexing (twisting) it at different places to chamber it. If the bolt closes easy at one place but harder at all the others, your bolt face may be way out of square.

If the above test doesn't work, blacken that case all over its outside with a black marker, let it dry then try to chamber it. Remove it and see where the black ink's rubbed/scraped off and that'll show where the interference is. Then a solution can be found.
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Old February 1, 2013, 09:53 AM   #3
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Couple questions,

Did you trim the brass?

Did you compare a dummy reload with a factory shell when it comes to inserting and pulling out of your chamber?

Most military rounds are two cones and a cylinder, so the interference points are body, shoulder, or neck. Normally the neck isn't a problem unless you have a tight throat or didn't trim your brass. Bumping your shoulder back .006 sounds like the interference is elsewhere, either in the neck or in the body.

Follow Bart B.'s advice to find out where that interference is, you may need to figure out how to size the body of your brass more, or you may need to trim your brass to minimum.

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Old February 1, 2013, 09:56 AM   #4
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Unfortunately Wilson type cartridge headspace gages are not available in the US for the 7.5 Swiss. Headspace gages have not been available either until just recently. Midway had PTG made 7.5 Swiss chamber headspace gages. http://www.midwayusa.com/product/224...5x55-swiss-cip

So, I too have been using a comparator. The Swiss round has a very steep shoulder , which is an excellent design for automatic weapons as it provides a firm stopping point , however the steepness makes deciding which Stoney point gage a bit tricky. I ended up using the D4000 gage.

I like Bart’s advice about rotating the case or smoking the case, though I think rotating the case will be difficult as the Schmidt Rubin action has a unusually deep receiver ring. I can’t get my fingers on the case in my rifle. There is always the chance that your dies are insufficiently sizing the body of the case and you have an interference fit near the case head.

I set up my sizing dies with the Stoney point and the rifle chamber. I bump the shoulders back until the bolt closes, then add a little (like 0.001 to 0.003). You will just have to monitor your cases to see if you are developing case head stretch.

By the way, in my testing my 7.5 Swiss rifles liked 4350 and 175 grain bullets.
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Old February 1, 2013, 10:30 AM   #5
chiefr
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One other thing to check would be how far out are your seating your bullet.

I have a 96/11 that I have developed a load for. I cannot fire this ammo out of a K-31 because the bullet is seated too far out and bolt will not close. I have noticed some Swiss rifles are particular about bullet seating depth.
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Old February 1, 2013, 11:10 AM   #6
F. Guffey
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“bumped the shoulder back to 0.004 and the bolt close but required force.

So now i have the die set up to bump the shoulder back a whopping 0.006 and they chamber fine”

Bump? I never heard the turn ‘bump the shoulder back...” until I read ‘the forums’, I have instructions that go back to the fifties, bump had nothing to do with the shoulder and everything to do with adjustment.

Davery25, get a good start, as I have said before, “practice does not make perfect”, try this, measure the case length from the head of the case to the shoulder/datum first with new ammo, new ammo is minimum length, if the new ammo chambers save one round for reference when reloading. After firing, measure the length of the case (again) from the head of the case to its shoulder/datum, then compare the difference between the fired/new/minimum length case to the length of the fired case to determine the effect the chamber had on the case when fired.

I do not know where you got the .004” bump? back shoulder setting? I do not know how you determined you were adjusting the die for a .004 adjustment. I start with .000, I accomplish a .000 adjustment by simply adjusting the die down to the shell holder with an additional 1/4 turn of the die, after adjusting the die for full length sizing to minimum length I size a case, then determine if the die, shell holder and press sized the case or if the case had more resistance to sizing than the presses ability to overcome the resistance. Meaning: A reloader can measure the gap between the top of the shell holder and bottom of the die, before lowering the ram, to determine if the press won or the case won. no gap, the press won, a gap, the case won.

Comparator, measure the length of the case from the head of the case to its shoulder before firing, measure again after firing, measure again after sizing. Bump and backwards. You are using a comparator to determine the effect sizing is having on the case, I start with determining the length of the chamber from the bolt face to the shoulder of the chamber/datum. My opinion, you do not have a .000 reference, I full length size to restore a case to minimum length by adjusting the die down to the shell holder with a 1/4 additional turn, I have no ideal what a reloader means when the say they adjust for .00X bump, I use the avoidance system/method, I avoid full length sizing for minimum length by adjusting my die off the shell holder with a feeler gage, the companion to the press because a feeler gage is a standard and a transfer and a means of verifying an adjustment.

Back to your question, you are bumping the shoulder back .006”? You started with .004” My opinion, you should have started with .000 by adjusting the die down to the shell holder, then to determine if the case was restored to new factory loaded length you should have compared the case with your new, never fired case. If the case chambered without resistance I would suggest you back the die out a 1/4 turn then try again. eventually you will get to the point where you started, eventual you will get to the point where a case will not chamber without resistance to bolt closing. I am the fan of cutting down on all that case travel.

There is something about the tapered sides of a round case forming cone...etc., ...etc.. One day? Then there is the diameter of the chamber, who knows? I do, but I make no excuses, I am a case former. Not starting at .000, you do not know the length of the chamber, you assume you have fire formed the case to fit the chamber from the from the bolt face to the shoulder of the chamber, again, I am not a fire former, I form first then fire, because I start with a reference of .000. I can do little with the effect the chamber has on the case body except neck size, when fired the case fills the chamber, when the chamber body allows the case body to expand the case increases in diameter, it happens, back to the tapper and cone, when the reolader insist on restoring the case to minim length/full length and takes liberties with something they do not understand (as in bump) they do not take into consideration reducing the diameter of the case increases the length of the case from the head of the case to the shoulder/datum. I start with .000, backing the die out and of off the shell holder allows the reloader to have control over the length of the case and diameter of the case body.

Then there is the part about using the comparator without knowing where you are headed, by accident you are adjusting the die to overcome resistance to sizing, all under the heading of ‘BUMP’. Bump? sounds like an accident, there is nothing I do that resembles an accident, I know, if I incorporated bump it would sound like I was going for neighbor acceptance.

“Does anyone know why the shoulders need to be bumped back so much in the k-31?” You first, explain how you determined you you were shortening the case length from the head of the case to its shoulder .004” then to .006”. Remember, full length sizing to minimum length is .000, again, I adjust the sizer die off the shell holder .014” when sizing cases for one 30/06 chamber. This method works well for the length of the chamber from the bolt face to the chamber shoulder and does the same for the tapered cone of the chamber. Starting at .000 the .014” is a plus when added to the length of the case from the head of the case to the to its shoulder, travel as in case travel? .002”

F. Guffey

Last edited by F. Guffey; February 1, 2013 at 11:18 AM. Reason: change an O to an I
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Old February 1, 2013, 09:29 PM   #7
davery25
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Thanks for the responses so far. first off, when i say bump im using lingo that i've learned on this forum. It refers to the length from the case head to a point on its shoulder. I'm going to keep using the term bump because it seems to be what everyone understands regardless of its technical accuracy.

I don't have access to factory rounds to measure because here in australia (or at least where i live) they have to be specially ordered in and cost $80 per box of 20. Hence why i had to buy Prvi brass and reload it myself.

Having no factory rounds or fire formed cases to measure off i had to follow redding's instructions on their die and screw the die till it touches the shellholder etc etc.

Using my comparator gauge that shows that this method 'bumps' (sorry f.guffey - i must give the people what they want) the shoulder back 0.009 as compared to a fire formed case. Hence i can't see how this is 0.000?

To answer other questions - no i cannot chamber a fire formed case but this is normal for the k-31 rifle as far as everything i've read goes. neck sizing in the k-31 isnt an option. I think you can in the k-11 but dont quote me on that.

I'm hoping its not a problem with the dies. I bought redding dies because supposedly they're the only ones that make dies specifically for the k31 whereas others including lee make them for the k-11.

Im going to use bart.b's instructions and colour the case black and see where this problem is. Could well be at the case web i suppose.

To answer some other questions: chiefr - nope, this is with unloaded unprimed cases only - the k31 needs its bullets seated very deeply so this brings its own troubles into the mix.

Jimro - i did check the brass. If im not mistaken max length is 55.6mm and ive trimmed all mine to 55mm exactly. After firing they've grown to 55.06 or so but still under max. I cant get factory rounds unfortunately (mentioned above they're $80 per 20 here)
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Old February 1, 2013, 11:19 PM   #8
Jimro
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If you trimmed to min then you functionally eliminated throat interference from the list of culprits.

I wouldn't be surprised if the problem shows up at the web. The measuring tools on the market generally don't measure body taper very well.

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Old February 2, 2013, 01:10 AM   #9
F. Guffey
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"The measuring tools on the market generally don't measure body taper"

Measuring the diameter of the case, anywhere along the length of the case from the case head to its shoulder is a matter of method and technique. You say the tools don't generally, I say a reloader does not know how.

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Old February 2, 2013, 07:59 PM   #10
Bart B.
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Guffey, how about telling him how to use a micrometer and ruler to find out what the taper is?
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Old February 3, 2013, 06:28 PM   #11
davery25
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That'd be appreciated. no the reloader doesn't know how hence the reason the reloader is part of a forum that has many more experienced members.

How does one measure taper. When the die is set up to push the shoulder back only 0.002 the die does not take in all of the case. much of the web is left outside so i really wouldn't be surprised if it is the web dimensions after firing.

in fact i recall the unsized (unsized by me but sized by the factory) factory brass from prvi fitting into the chamber fine.

Now the question is - how do i deal with this assuming i only want to push the shoulder back 0.002?
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Old February 10, 2013, 12:25 PM   #12
F. Guffey
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“in fact i recall the unsized (unsized by me but sized by the factory) factory brass from prvi fitting into the chamber fine”

And I said you should have saved one of the unfired cases for reference as in for comparison.

http://www.saami.org/PubResources/CC...%20Swedish.pdf

Note: No mention of head space and case length in the same sentence, head space, as in the length of the chamber from the bolt face to the shoulder/datum applies to chamber length as in ‘measured from’.




“Now the question is - how do i deal with this assuming i only want to push the shoulder back 0.002?”

I have no ideal where the ‘push the shoulder back’ comes from, I suspect it comes from ‘fire formers, chamber a round, pull the trigger, instant gratification, and promotion to the qualification of ‘FIRE FORMER’.

Beyond ‘fire former’ there is ‘case former’ I form cases.

“Okay, not so much an issue as a query. I usually FL size all my rifle cases and bump the shoulder back 0.002. I use a comparator gauge to measure this.

I did the same with my once-fired 7.5x55 swiss brass except the bolt wouldn't close on it.

bumped the shoulder back to 0.004 and the bolt close but required force.

So now i have the die set up to bump the shoulder back a whopping 0.006 and they chamber fine”

I do not know which comparator you are using, in my opinion a bad habit starts with measuring a fired case for case length from the head of the case to the shoulder. Suggestion, before firing measure the new/unfired/minimum length case before firing, I know it is an impossible concept to understand. I measure the length of the chamber from the bolt face to the shoulder/datum first, I also measure the length of the new/unfired case from the head of the case to its shoulder. WHY?I want to know the difference in length between the chamber and case. In the perfect world the difference would be .004” to .006”. Back to some chambers, I have chambers that are longer by .016” than factory/minimum/full length sized cases, (for me?) not a problem, I form cases that are .014” longer from the head of the case to its shoulder, the perfect case for this rifle is the 280 Remington, the case body length is .051” longer than the 30/06 case body. I add .014” to the case length, I raise the die off the shell holder, I am not moving the shoulder back by adjusting the die down .037”, a reloader can not adjust the die down .037”, I raise the die .014”, WHY"? I can measure the distance the die is off the shell holder with anything that measures gaps.

Back to the big inning, you adjusted the die to move the shoulder back, I would have adjusted the die off the shell holder by raising it, to eliminate wild guestimates, I would use a feeler gage, I would adjust the die off the shell holder with a gap of .005”, if after sizing the case I could use the comparator or I could simple attempt chambering the sized case and attempt to close the bolt. If after sizing the case I found the bolt had resistance to closing I would decrease the gap by lowering .002” the die to reduce the gap, again, I would use a feeler gage to verify the adjustment. Then attempt chambering the sized case. If the case chambers without resistance to bolt closing I would know .005” was not enough and .002” would cut down on all that case travel.

Of what you are tying to accomplish is move the shoulder back? Start from the other end, start by adjusting the die off the shell holder, again (impossible concept) it is possible to adjust the die off the shell holder.

Again, I am a case former, move back is a term with an understanding know only to reloaders, I form cases, when I form cases the case shoulder does not move, it is erased, on my 30 Gibbs cases the shoulder becomes part of the case body and the part of the neck becomes part of the shoulder. To a reloader the shoulder moved .205” (forward) to a case former the shoulder did not move, the shoulder is new. Again, know only to reloaders, when does the shoulder go from bump to being erased as in forming?

When adjusting the die adjust off the shell holder, some choose to make wild guestimates, some choose to bump, I choose to adjust off the shell holder, I know the length of the chamber, I understand the dies ability to size a case back to minimum length before I start. In the big inning I scribed the shoulder/case body juncture, Hatcher? That was before me. I did have a friend that accused me of being wrong because he built some magnificent wildcats on 03 and 03A3 receivers, he had case head separation, I informed him I could have told him it was or was not going to happen, I also informed him I could have fixed ‘the problem? if I had had been at the range when he attempted to form his cases.

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Old February 10, 2013, 12:38 PM   #13
F. Guffey
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Bart B.

“Guffey, how about telling him how to use a micrometer and ruler to find out what the taper is?”

Had I said that someone would accuse me of responding in a manner rather rude.



"The measuring tools on the market generally don't measure body taper"

”Measuring the diameter of the case, anywhere along the length of the case from the case head to its shoulder is a matter of method and technique. You say the tools don't generally, I say a reloader does not know how”

“....micrometer and ruler to find out what the taper is?”

Where did the the micrometer and ruler come from?

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Old February 10, 2013, 12:59 PM   #14
F. Guffey
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“How does one measure taper. When the die is set up to push the shoulder back only 0.002 the die does not take in all of the case. much of the web is left outside so i really wouldn't be surprised if it is the web dimensions after firing.”

“i really wouldn't be surprised if it is the web dimensions after firing”

‘IT’ as being the diameter of the case head, the shell holder has a deck height of .125”, then there is the radius at the opening of the die, THEN! there is case head protrusion of the chamber, most Mausers have a case head protrusion of .110, 03 and A3s have a case head protrusion if .090 when measured from the bottom of the extractor cut. To upset the case head as in shortening the case head by would require heavy loads or case hammering as in slide and glide shooting, slide and glide is accomplished by lubing the case/chamber for what ever reason.

Not easy to measure case diameter with a ruler as Bart B. suggested, not easy to measure the diameter with a micrometer, again, as Bart B. suggested.

I have no clue as in helping, I have 6.5mm55 barrels, dies and cases and new unfired commercial ammo.

If all I had was a press, die and shell holder with fired cases I would neck the cases up with total disregard to neck splitting, annealing helps, I would neck the 6.5 cases up then size the cases with a new shoulder, I would adjust the die off the shell holder .010” to start with when sizing, then I would progressively reduce the gap between the die and shell holder while sizing, I would continue until the case chambered. Not easy to accomplish with fired cases because of the resistance to being sized, again, annealing helps.

No I do not feel compelled to use the cases for loading, I would mark the cases after determining the length of the case from the head of the case to the shoulder for future reference.

F, Guffey
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