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Old March 9, 2019, 10:31 PM   #1
5whiskey
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K31 7.5 Swiss HELP!!

Ok. Not your normal question, I’m aware of the short lead in the throat and have planned accordingly. My problem is light primer strikes. I have 80 once fired PRVI cases that were fired from this rifle. All loaded PRVI ammo fired fine, with no issues, and was reasonably accurate.

So I make 4 different loadings to work up and I head to the range. Powder was h414, hornaday 168gn projectile, PRVI brass, and Winchester LR primers. I go to shoot, and “click.” I try like 15 rounds, and only 1 fires. I’ve never had this happen before. I know I seated the primers properly such that the anvil was contacting.

This was over a month ago. I’ve loaded over 10k rounds and never experienced this problem. I measured the depth of the primer from the case head, and some seemed quite deeper than is normal. While most were seated from .011 to .015 below flush (from what I’ve read this is on the edge between too deep and the ragged edge of acceptable), a few were as much as .019 below flush.

Today on a whim, I picked up some federal LR primers. I primed quite a few cases and finally got about the last 30 to all touch off reliably. From best I can tell I have to use the perfect touch seating the primers to get it just right.

A friend who has been loading at least as long as I have advised to replace the striker spring in the k31. I am not inclined to believe this is an issue as I had zero issues from 80 rounds of factory PRVI ammo. But then again, switching to federal primers, along with perfect priming form, seems to have corrected the issue. I know federal has a softer primer cup, so maybe there is something to the striker spring thing... in that maybe it somewhat compounds the problem.

So a few questions.
1. What on earth is going on, I’m inclined to believe this is a brass out of spec issue, but loaded ammo shot fine... what say you?

2. Would you see if you could order a striker spring, just to at least try it?

3. I have debated honing the head of the cases to take a few thousandths off so that the primer is closer to flush. I have resisted this urge because I’m concerned about going off-square and the head having adequate strength. Do you think honing a few thousandths from the head/base is safe, and a likely solution.

4. Or just run it as is, ensuring that I wait for the moon and stars to align while I stand on one foot holding my tongue out to ensure reliable primer seating?
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Old March 10, 2019, 01:58 PM   #2
RC20
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I shoot all PPU ala NNY in 3 guns (1911/K31 and a home built Savage 7.5 Loather Walther barrel)

What I can tell you is that there is chamber shape differences in all 3.

Also note there is variance in what the COAL case (no bullet) should be.

While this is some hearsay (by some) , I think you may be setting your shoulder back to far.

What die are you using (RCBS is a good go to for working with the 7.5 cases and I think Redding is the other one recommended)

Also, are you doing the 1/8 to 1/4 turn after contact the shell holder (and what press?)

If you don't have the Horandy comparative tool, to do the minimum shoulder bump back thingy, crank you die back 1/4 turn from contact. Size one case, try in the chamber. In very small increment (1/16th) turn it down until the case fits in the gun and cycles right.

At that point put a primer in and fire it off! If success try 10.

I thought I could at least get the PPU to work in the K31 and my Savage, no matter how much fiddling (where is Mr G when you need him) I could not get it to work and each one now has its own designated cases.
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Old March 10, 2019, 02:03 PM   #3
reddog81
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Could some large pistol primers snuck into the rounds? They’re the same diameter but not as tall. I’d guess they could cause the issues you’re seeing.
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Old March 10, 2019, 02:51 PM   #4
5whiskey
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RC20 I had thought of the same thing. Maybe headspace is loose and the extractor is loose enough that it won’t hold in place for a good firing pin strike. But... that’s not the case. I got the hornaday k31 dies, which I am not super impressed with as they do oversized the body some. I am not pushing the shoulder back too far though. As a matter of fact I set the die to not move the shoulder back at all for this first resizing.

Another interesting tidbit. I’ve now discovered if I slammed the bolt home with authority, every round fires fine. When I was having misfires the rounds were extracting, so I know the extractor was engaging. The bolt also locks without “force” so the rounds aren’t too tight in the chamber. This one has gotten me. I don’t know what’s going on...
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Old March 10, 2019, 03:32 PM   #5
Dufus
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The normal primer seating is 0.003-0.005" below flush.

Short primers or too deep primer pockets on the brass?
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Old March 10, 2019, 05:29 PM   #6
RC20
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I saw that and forgot to comment. Those reading can't be right, tight pocket yes but not depth issues.

PPU is the same as PVRI, I have yet to get a batch that was no fine. Just got another 100.
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Old March 10, 2019, 07:00 PM   #7
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5Whiskey,

I had the same thought Reddog81 did. LP primers are the same height as SP and SR primers; about 0.009" shorter than LR primers. That would sure go a long way toward explaining you having below-flush numbers around 0.009" below normal (normal is 0.003"-0.005" below flush with the case head).
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Old March 10, 2019, 07:20 PM   #8
lonniemike
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your light strikes could be explained by slightly undersized cases. when you ram the tight carts home the serial numbers will be straight up on top and fire. when carts are limp wristed-non slammed home the serial number may be off centered and not on top. when the trigger is pulled the energy/mass in the firing mechanism forces the bolt into the last bit off battery with the firing pin not having enough force to make a robust strike.
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Old March 10, 2019, 07:25 PM   #9
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primer depth is not your problem. you should not have to slam your 31 closed.
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Old March 10, 2019, 08:00 PM   #10
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"as a matter of fact, I did set the die not to push the shoulders back at all". I'll say check your locked bolt before you pull the trigger and your serial number will not be locked up at the 12 o'clock position.RC20 gave you excellent advise. push the shoulders back. Best
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Old March 10, 2019, 10:10 PM   #11
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Ok, Thats the mystery. S/N is always straight up before I fire, I check based on reading I’ve done of a very few k31 failures. The lugs lock, the s/n is straight up, but then it feels like I can give it another shove and it gives a little more. Then it will fire. I’m at a loss, other than I will size differently after this firing of the cases I think.

Pistol primers sneaking in was the first thought I had the day I had the problem at the range. I came home and confirmed that wasn’t the case. Also tried other primers now. Which seems to help some, but doesn’t seem to be the golden fix. And no matter what, primers are still seated a good bit below flush. The federal primers average a measurement of .008-.012 in most cases. Better than Winchester. I think slightly out of spec brass adds to some other problem that I’m having... a problem that I’m now thinking may be my sizing process. Gonna bump the shoulder back a touch more next time I size.
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Old March 25, 2019, 07:55 PM   #12
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I loaded my first ever 7.5x55 rounds a month or two back, and had the same issue. First few rounds didn’t go bang. Probably used Winchester primers, but might have been CCI, I’d have to go look. PPU once-fired brass. Lee dies. Worked better when I closed the bolt with more authority.
I did notice the short throat, and even though it was below what my manual said, I seated the bullets just until they plunked. I’ll try seating a smidge deeper next time.
Let us know if bumping the shoulder back made any difference.
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Old March 25, 2019, 10:50 PM   #13
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Close the action with empty chamber. Mark bolt position with sharpie. Chamber a round normally (like you were to have a click instead of a bang). Is the bolt position same as with empty chamber? Repeat with closing the action smartly.

I guess your brass wasn't sized quite to length, so that the rifle was slightly out of battery. I would suggest progressively turn down the sizing die (l like 1/24 of a turn each time) till the bolt can be fully closed with no felt resistance.

K31 tends to have short chamber. Following the normally die setting procedure, friend of mine couldn't even close the action. He finally solved the problem by summoning the courage to turn down the sizing die.

-TL

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Old March 26, 2019, 10:27 AM   #14
RC20
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I am going to go with tangolima on this.

It sound like you are slighly out of battery and not fully locked up. Its an aspect of the straight pull bolts, the extra push seems to confimr that.

Get the Hornady comparator to measure you shoulder and then bump it back .003 - .005 and see what happens.

You can work with just sized and primered cases and see what results are.

You do want a fairly aggressive forward motion regardless. These Swiss 7.5's are not intended as delicate - they are full fledged combat rifles.
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Old April 11, 2019, 03:46 PM   #15
5whiskey
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Thanks everyone for the response. Still haven't really solved the mystery but closing the bolt with authority clears it right up. I will play around with my sizing some with my now-twice fired brass.

On another note I'm almost afraid to change a darn thing. I loaded 10 cases each at 3 different charge weights, and found 43.4 gns of H414 gives me nice groups that are better than I should be able to shoot with iron sights given the astigmatism in my dominant eye. 1" at a 100 yards all day. Easiest load work-up I've ever done.
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Old April 11, 2019, 05:28 PM   #16
gwpercle
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I don't care what you read...the proper depth for primers is all the way in...to the bottom of the primer cup...no measurements required.

The reason being , if not seated to the bottom of the pocket the first strike moves the primer deeper but the blow is cushioned, a second strike will fire the now seated primer.
I've been reloading for over 50 years....trust me, seat the primers to the bottom of the pocket .
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