M-77 & partial case head separation

[41special]

This M-77 in .270 Winchester took an over pressure load. Of course I packed it up and put it away for the day.

Now I'm mulling on how to proceed, I guess I'll just try some Factory ammo on my next trip to the range, hopefully there was no serious damage done other than blowing out all the accumulated crap from the past 35 years out of the overpressure vents

Anyone out there dealt with the situation before?



41

 

[Big Old Boy]

I never have I for one have never loaded anything to max more or less overpressure .

 

[Alan in GA]

Not enough info on what happened, so "have a gunsmith check it" is all I could suggest.
Check with headspace gauge!

 

[DGW1949]

RE:..."Now I'm mulling on how to proceed, I guess I'll just try some Factory ammo on my next trip to the range, hopefully there was no serious damage done other than blowing out all the accumulated crap from the past 35 years out of the overpressure vents".

Dangerous thinking, that.
Me thinks that a better plan would involve the services of a qualified smith, or baring that, perhaps a trip back to Ruger.

DGW

 

[Rick Courtright]

Me thinks that a better plan would involve the services of a qualified smith, or baring that, perhaps a trip back to Ruger.

Hi,

Yup!

Since the SAAMI max for .270 Win is an already quite healthy 65kpsi, it's hard to say what it would take to do bad things like the OP experienced. So it would be good to have everything checked. By a pro. Eyeballing isn't a great idea here.

Rick C

 

[artey]

Guy I know fired a 308 factory Federal round through his 77 Mark 2 270. Sent it to Ruger with an explanation and they didn't even look at it just read the note and said it's junk and they'd send him a new gun of his choice at a discount. He declined, and believe it or not they returned it as he requested with a note saying the gun was unsafe to fire. They did remove what was left of the case for him though. He fired a round in it when he got it back and sent a 'before' case and that 'after' case to Redding and they measured them. No difference in cases so he figures it's ok...but he ain't fired it since!

 

[Rick Courtright]

No difference in cases so he figures it's ok...but he ain't fired it since!

Hi,

That's probably a wise decision. When the people who MADE the gun say it's junk, I think I'd tend to believe them over any other source. They know what they make and what it'll take. I'm surprised Ruger ever let it go back to him, though. Bet that gun's got its own dossier in some computer file, though, documenting the fact they advised the owner of their feelings on its condition.

Rick C

 

[Ol'Freak]

A full length size die if setup per the manufacturers’ instruction is likely to resize the case’s length, measured from case head to shoulder datum, nearer to SAAMI minimum. A factory chamber’s length, measured from the bolt face to the chamber’s shoulder, was likely cut nearer to SAAMI maximum though still within SAAMI specification. Factory ammo, also likely with case sized nearer SAAMI’s minimum “fits all” length, fired once in a longish but still within spec chamber isn’t a problem, not until folk repeatedly overwork the case body by sizing it to near minimum head to shoulder datum length, then again fire it in that longish factory chamber.

Nutin’s wrong with using a FL die long as it’s adjusted to give the case (for a bolt gun) a head to shoulder datum length that’s only a thousandth or so shorter than from the bolt face to chamber’s shoulder datum.

 

[41special]

A full length size die if setup per the manufacturers’ instruction is likely to resize the case’s length, measured from case head to shoulder datum, nearer to SAAMI minimum. A factory chamber’s length, measured from the bolt face to the chamber’s shoulder, was likely cut nearer to SAAMI maximum though still within SAAMI specification. Factory ammo, also likely with case sized nearer SAAMI’s minimum “fits all” length, fired once in a longish but still within spec chamber isn’t a problem, not until folk repeatedly overwork the case body by sizing it to near minimum head to shoulder datum length, then again fire it in that longish factory chamber.

Nutin’s wrong with using a FL die long as it’s adjusted to give the case (for a bolt gun) a head to shoulder datum length that’s only a thousandth or so shorter than from the bolt face to chamber’s shoulder datum.

That sir, gets to the root of the problem.

Going to readjust my FL die so my bolt closes with just a hint if resistance. Rifle worked fine with some factory loads, going to dump all my used brass & start with new.

41

 

[DGW1949]

OK...at first it was an "over pressured load" problem, but now it was an improperly sized and/or over-worked brass problem?...

Questions:...have you measured the factory ammo and compared it to one of the reloads you was using at the time, and if so, how exactly did you measure the two?...Checked the rifle's head space yet, or are we assuming that it's within spec, or are we hoping that sizing our brass long enough to create resistance while closing the bolt will make up for any excessive headspace which may be present?...

Still sayin' that you might want to get your rifle checked over by someone who knows what they're doing, that's all...no offense meant.

DGW

 

[robertkirksey]

P. O. Ackley squeezed a lot of oversized bullets through Jap rifles experimenting. It took a LOT of pressure to damage them and I would bet that a 77 is quite a bit stronger. With the .308 in the 270, the bullet had a good running start before it was swayed down .031". I would not be afraid of that rifle.

 

[41special]

DGW, to be honest it was both problems in one. And I compounded it with a third issue.

The overpressure load was one I had worked up safely in this same rifle but with the original Ruger 22" barrel in place. I had that old worn-out 1982 barrel replaced with a new Benchmark 25" stainless steel barrel. I'd only fired 50 or so Factory rounds of ammunition in the new barrel and was testing a new load I was working up using the Nosler 150 LRAB. As I was down in my my reloading room I found at that box of reloaded elk hunting .270 ammunition from 2004, remembered it as a nice combanation and thought I'd try it that old trusty load over the chronograph & see what the 160 Partition over 52.0 grains of IMR 4831 would clock.

I honestly didn't even think about the "new Barrel equals a new rifle" scenario.

The the first two rounds worked fine though from the looks of the primers the pressure was on the high side, the extraction was nice and easy and I didn't think too much of it because it was a Nosler book maximum load. Then the #3 round let go.

Ok, that was all dumb enough in itself. Then after the fact I was looking at the ammunition and & my recorded data, to my amazement I found that I had I had changed up the primer!

I went from a CCI 250 to the Federal 215.

So there you have it that's my full confession, a series of mistakes on my part that led to that partial case head separation.


I guess the moral of the story is if a guy reloads long enough and does so with no issues for darn near 40 years, he thinks it can never turn around and bite him.

Well, it can.


41

 

[Ol'Freak]

SAAMI headspace technically still “within tolerance” covers .010”, ranging from 2.0487” minimum to 2.0587” maximum measuring from the case head to the .375” datum diameter on the case’s shoulder.

The firing pin smacks the primer, first shoving the round until its forward progress is stopped by the meeting of the case’s and chamber’s shoulders, and then the pin’s remaining energy gets spent lighting off the primer. “Headspace” with that round inside this chamber would’ve been whatever the space left betwixt the bolt face and that case’s head after the case’s forward progress was stopped by the meeting of the two shoulders.

 

[NEMThunter]

The the first two rounds worked fine though from the looks of the primers the pressure was on the high side, the extraction was nice and easy and I didn't think too much of it because it was a Nosler book maximum load. Then the #3 round let go.



41

I think you answered the question right here. If the first two worked fine. (with a small sign that you were close to max pressure) Then the third one was the problem like you state. That might be the key. How long did you let the third round sit in the warm chamber before shooting it? what powder was used in that load? Some powders are very heat sensitive and getting it hot from the first two shots fired could had put it over the edge pressure wise. OR the third one some how got a little more powder doring reloading.

Or it could be as simple as a cracked or lightly fractured (same thing to a point) case that when it was fired it went to peaces and did not grip the chamber right thous causing the "over pressure" problem.

If its a recommended load from a load book it should have been fine even in the different barrel even with a different the wrong primer. the loads in the book should be safe. They do cover themselves. Another thing to think about is to have a case split or have separate like you said would take a BIG pressure jump over the limit of 65,000 PSI.

After that shot how hard did the bolt pick up and pull back?

Do you have a picture of the case? I would lean more to the fact you had a weakened case. Especially with how and were it separated.

Just my thoughts . There are other things that could have caused it to. I would not be so quick to say the load was to hot for the new barrel.

 

[Coyote Hunter]

This M-77 in .270 Winchester took an over pressure load. Of course I packed it up and put it away for the day.

Now I'm mulling on how to proceed, I guess I'll just try some Factory ammo on my next trip to the range, hopefully there was no serious damage done other than blowing out all the accumulated crap from the past 35 years out of the overpressure vents

Anyone out there dealt with the situation before?

41

Case head separation, yes, on more than one occasion. It is NOT necessarily an overpressure situation.

In my M77 7mm RM the problem was I full-length size all my brass. After 4-5 sizings I would get a case-head separation. Reduced the load a bit and now get many more loadings but if I try for too many I still get a case-head separation.

Had a Remington M700 in .308 Win that had a similar problem but more so. 2-3 firings and a case was done, even with below max loads. Sold that one.

What I would do is pull some of the reloads and check the inside of the case for incipient separation. I now do this with EVERY rifle case I reload. My tool is a large paper clip, straightened out enough to reach the primer pocket with slight bend a quarter inch from the end. Use it as a feeler gage to fine rings where the case is thinning just above the bottom of the powder space. Good cases are smooth as butter, cases ready to fail will let you know with a faint 'bump' as you drag the tip in and out. I turn the case and check 2-3 different spots. Takes a couple seconds per case.