need some help from the X spurts

[singleshotbuff]

Gentlemen,

Just had something happen at my front yard range that scared the hell out of me! Scared me enough to stop shooting for the day.

I was shooting my K-31 Swiss 7.5X55mm. I was shooting a load that I had worked up when it was 20 degrees or so. I had previously fired this load when it was about 65 degrees and the velocity had went up a little, but nothing alarming. Today it was about 80 degrees. The reason for the weather report is that I have heard of a great deal of temperature sensitivity with IMR-7383.

The load used was;

Prvi Partizan case
WLR primer
48.0gr IMR-7383
150gr FMJ BT surplus pulldown bullet

Shots 1 through 6 had slightly sticky extraction, which I didn't recall getting the last time I shot this load. Round #7 locked the action up solidly!! I had to tap it open with a rubber mallet!! when I got it open, the fired case came out, WITHOUT THE PRIMER!! The primer was laying lose in the action. There were no other signs of pressure on the case, such as burnished brass etc, and I didn't see any gas escape from the action when I fired the shot.

What the hell happened?? I've NEVER had anything like this happen before, I've been reloading for 15+ years.

I have read all the warnings etc about 7383 being spikey/quirky/ temperature sensitive, but I worked up to this load using due diligence and a chronograph. As noted it was worked up in the cold, but was fired a couple months ago in decent weather.

One other piece of the puzzle. In looking at my notes, I see that this lot of brass had been fired several times and was recently annealed. Could I have possibly softened the head of this case? I normally anneal all my milsurp brass every 4 or 5 firings to make it last longer as I normally only buy it a gun shows which only come around once a month. When I anneal, I hold the case in the flame of a propane torch until it turns color, then drop it in water. I know entire threads can be (and have been) written on the pros, cons and how to's of annealing, I'm not saying my method is the best, but I've never had problems with it before.

So, care to take a guess what I screwed up?

Was it the 7383?
Was it the cases?
Was it ?????

Thank God and the Swiss for the strength and gas handling of the K-31 action. I love this rifle more now than ever!

Thanks for any help.

SSB

[Ricochet]

That sounds like a near full capacity load. Was it compressed? My eye-opening experiences with 7383 have been with compressed loads. Pressures can go up VERY suddenly when it's crushed. Add in temperature sensitivity, and there could be a problem. I got some sticky-case pressure levels in my K-31 with cast boolits with a combination that included a long heavy boolit that mildy compressed the powder, a boolit starting against the throat of the chamber, and a Lee Factory Crimp on the case.

Did you check the case length? There is NO tapered throat ahead of the chamber in these rifles. If the case lengthens so the case mouth interferes with the bullet entering the bore-diameter tube starting right ahead of the chamber, you'll have pressure problems.

Check the other cases from that batch closely for signs of pressure problems, and measure their lengths.

[felix]

The best rule is to anneal only when you get splits in the neck. Actually, ideally, anneal before you get a split, but who knows when that will occur without getting one or two or three per outing. Yes, the bottom of the case could have gotten too hot for too long. Remember, it takes temp and time to anneal. From now on out, just do the neck area only with a very fine jewler's nozzle on that torch, and count the rotations, and don't wait for a hot bottom. You only need intense heat for a second or two, say one complete, at most two, rotation(s) hand held.

Also, any fat grained powder should never be compressed. Why? Because where did the grains break? At the top next to the bullet, or in the primer area. All big grained powder should be jingled a little on the table top before seating the boolit, to avoid all possible chances of any compression. Any difference at the primer area will surely alter ignition, as well as a hotter chamber, even on a cold day.

Also, the chamber area could have been clogged somewhat by the soot of that powder, adding to the bullet static friction as seen by the ignition.

Any of these combinations could have caused an erratic ignition, and taken together, well, you know what can happen by your experience.

A SEE condition was not involved as far as I can tell by your circumstance.

... felix

[singleshotbuff]

Ricochet,

It was a full load to the base of the bullet, but not compressed, everything I have read about 7383 keeps me from compressing it.

I'll double check case lengths after I steady my nerves with a beer or 2.

Felix,

I'll do some more research and probably change my annealing procedure in the future.

Thanks for the input so far gentlemen.

SSB

[Ricochet]

Also, the chamber area could have been clogged somewhat by the soot of that powder, adding to the bullet static friction as seen by the ignition.
Ah! There's a problem I HAVE encountered with 7383 more than with other powders I've used, a very hard carbon buildup in the throat of the bore just in front of the chamber that constricts the bullet and seriously degrades accuracy after a while if not cleaned out. It's not easily cleaned out, either.

[versifier]

I have had Privi Partisan Swiss cases spit out primers (CCI) with no signs of pressure once each with both WC860 (2nd firing) and IMR 3031 (third firing). Same lot of brass. Neither were hot loads, there was no difficulty with extraction, no flattening/cupping on the other primers. I just tossed the offending cases. I have fired the remaining cases five times more since with no other problems. I'm not saying you didn't have a pressure spike - you obviously did - but I have had problems with those cases unrelated to pressure. (Never any trouble with Norma at all in 7.5Swiss.) I still have no idea what caused them, but I speculate the heads may have been too soft in just those two cases.

[Ricochet]

That's certainly quite possible. I've got a recovered boolit from the abovementioned Swiss load that went too hot indicating that it did indeed generate too much pressure in that particular instance as the very hard quenched wheelweight metal slumped on acceleration, greatly shortening the long ogive of the HBC boolit with rifling engraved well ahead of what was originally the beginning of the ogive. My Prvi cases haven't shown signs of being soft. But that's a small sample.

[singleshotbuff]

Measured the case length on that lot of brass this evening, after my nerves calmed down.

2.185"

Which, according to my sources, is under maximum.

Not sure what to do here, don't know with 100% certainy if this was a soft case from annealing or if the load is too hot for warm weather. I'd hate to lose my nerve for using 7383, it's SO cheap and available locally.

I think I may get a new lot of brass and re-work this load while it's warm.

SSB

[Ricochet]

Sounds like a good plan to me.

Remember that Dan at Hi Tech originally said that 7383 was equivalent to 4320 or 4064. I don't know what he based that on, and my initial results looked more like 4350 charge weight/velocity equivalency where the maximum amounts I could get into cases were about the same as starting loads of 4350. But in cases where more can be gotten in, the pressure and apparent burning rate seems to climb steeply. If you don't have pressure measuring equipment, caution is definitely in order.

[tom barthel]

I rarely anneal. When I do, I put the cases in a pan pf water with the shoulder and neck exposed. This prevents me from over annealing. Oh, I shake the pan and the cases fall over in the water. I'm not very brave. I would alter everything and just start over. I know this doesn't answer any of your questions about what happened. I'm just thankful you and your rifle escaped injury. Good luck figuring it out.
Tom

[Baron von Trollwhack]

How are the primer pockets on the "sticky cases?, What about case headspace? BvT