how did this load go from safe to dangerous?

[dakotasin]

took the 300 wsm (win m70) out today to shake-out the new scope and mounting system. i had worked up a load for it last fall of 67.0 grains i-4350 behind a 165 grain hornady, cci mag primers, and winchester cases.

the first 12 shot fine - bullet behaved predictably and impacted the 200 yard target where expected. that was the last of that particular 'lot', so i grabbed my next box of 60. the cases had been f.l. resized, and the charges had been trickled up to 67.0 from the same lot# of i-4350, seated the same lot# hornady 165, and primed w/ cci mag primers from the same box of 1000 the previous 60 had been primed from.

the next 5 shots fired exactly as i had expected.

the next shot pierced the primer. i thought that was a little weird, but perhaps a bad primer cup or something? dunno - there had been no pressure warnings prior, and the load is slightly under hornady's listed load.

the next shot (shot 7 from my 'new lot') flattened and cratered the primer really bad. i figured that was enough playing press your luck for one day - and since i had also gone through 24 375 ruger loads, i had enough of a beating for one day.

so what happened? how did a safe and sane load suddenly become dangerously hot?

the shooting area is covered and it was cloudy and in the 50's today - so it isn't like the cases had been getting preheated by the sun.

ideas?

 

[Ridgerunner665]

Pull one apart and weight the charge.

 

[dakotasin]

ok... i just weighed the next one in line: 67.0

now what?

edit: i also just re-assembled that cartridge, and will try to fire it tomorrow to see what happens.

 

[BruM]

check bullet weight and size, check barrel,

 

[dakotasin]

no obstructions in barrel (i had been boresighting it w/ my eyeball prior to shooting) and all bullets were accounted for on target after i put the bolt in and started firing.

can't check the bullets that went downrange, but the one i just pulled was 165 grains.

 

[Fatelvis]

Were the second group of loads sitting in the sun, or in a warmer place?

 

[bobelk99]

I have loaded for 50 years, and this one has got me stumped.

If you were here and asked me an opinion, I would tell you that the powder you used for round 6 and up is not what you think it is.

If you remember, is it possible that you had to stop and restart that batch of reloads, giving the 'chance' that powder was changed?

No way is temperature change going to cause this 'mess'.

I look forward to your finding the resolution on this one.

 

[Idano]

According to my Nosler Manual you're pushing a grain over max; Nosler states 66 grs as MAX load. Unless you have reputable source that states otherwise, you should back off your load, If you do have a current published manual that shows over 67 grs or higher with IMR430 and it is not a misprint then I would tell you to look at your primer seating and make sure that all your primer are properly seated ; also look at bullet seating. A bullet against the lands or seated too deep also increases pressure. Since I don't reload for this caliber I am only covering the basics, hope it helps.

 

[Runningman]

That load sounds to kind of hot to me. Do you have any chronograph readings? If so what length barrel is your 300 WSM?

I started to get high pressure signs with 66.0 grains of IMR 4350 using a 165 grain bullet in my 300 WSM and consider 65.5 of IMR 4350 the maximum for my rifle.

 

[Remo-99]

Some variable has changed along the ways, to go from no pressure signs to flattened and cratered primers, just by changing batches which were made using the same component lots.

I'm assuming cases all trimmed to size, bullet seating depth the same, etc.

Any possiblity the first 12 were actually loaded at 66gr instead of 67gr?

 

[Fatelvis]

No way is temperature change going to cause this 'mess'.

Oh I beg to differ Bobelk.
If a load is close to max, hot weather will make it unsafe. I used a .270 Weatherby with close to max loads that were fine in cool Illinois, flew to Texas and right after getting into camp, test fired to check for zero. The bolt had to be coaxed to open, and the ejector mark was clearly seen on the case head. Surely due to the hot weather. ...I learned the hard way!

 

[dakotasin]

i checked my hornady manual and hornady has 67.6 listed as max - so i am under hornady's max using hornady's bullet by .6 grains. i also re-checked my development notes and see i tested to 67.5 grains with no ill effects.

the bullet i pulled, which would've been shot 8 had the appropriate powder in it (i load in sequence, and shoot in sequence, and fired cases from bolt guns go back into the box in sequence) so no possibility of a mix-up; besides, i never leave the bench while i have open powder out - cases have to have a bullet seated and the powder measure emptied and the working powder put back in its place with the top on before i leave the bench.

bolt lift on the 2 hot rounds was not unusual, and they chambered easily going in, too.

hot weather wasn't a culprit here - load was originally developed w/ temps in the 40's and 50's - and yesterday temps were in the 50's, clouds, and the ammo was in shade, anyway (covered firing line).

barrel length is 24" and the load chronies out at 3100 f/s when it was developed (was not shooting between the sticks yesterday so don't know what exactly yesterday's loads were).

i'm wondering if the rifle somehow is at fault here, or maybe some other method of headspace issue?

 

[Old Shooter]

Is it possible that particular load is borderline overmax for your particular rifle?

I know it has shot well for you in the past and your reloading practices seem very good but mayby you're just tip-toeing on the edge of maximum with your rifle.

I don't know. It just seems there should be little, if any, variance in the load to explain the situation so mayby the rifle/load combo is the reason.

 

[Old Shooter]

Just thinking about it some more. How many times had those cases been loaded?

I wonder if the results would be the same using virgin brass?

Mayby a difference in brass expansion and flow in the chamber?

 

[steve4102]

Hornady #7, 67.6gr Max


Nosler #6, 66gr Max


Lyman 48, 65.5gr Max


Sierra #5, 66gr max

 

[Old Shooter]

Thats a pretty healthy step up to that Hornady load listing, definitly food for thought.

 

[Innovative]

dakotasin .......

The 300 wsm is an extreme high pressure round. It might help to see a picture of your fired primers.

- Innovative

 

[Sport45]

Where did the hot rounds impact on the target?

 

[MMCSRET]

Check your bore for jacket fouling. When you are loading on the "edge", it won't take much of an accumulation of copper fouling to slightly increase pressures.
Just thinking out loud!!!

 

[Remo-99]

The 300 wsm is an extreme high pressure round. It might help to see a picture of your fired primers.

yes, the pressures of WSM's are over and above those expected from most other calibres, the CCI primer cups are the hardest of the bunch, though.
And did I read somewhere that the ejector imprinted on the caseheads, which is a sign of excessive pressure in any calibre, even for a WSM.

 

[NCsmitty]

MMCSRET's analysis makes sense to me. Gilding metal can accumulate in the throat of the lands quickly, with high intensity rounds. Running an on-the-edge loading can conceivably turn on you, if the throat has rough tooling marks that loads up with copper.



NCsmitty

 

[243winxb]

What is "i" 4350, you mean IMR 4350? How far are you seating bullets off the lands? If your only off by .005" with a clean barrel, a dirty barrel can raise pressure. Not all rounds produce the exact same velocity and pressure, some high, some low.

flattened and cratered the primer really bad

I suggest you reduce your load.

 

[Slamfire]

Cut your load. The instant you blow a primer or pierce a primer, and you are at the top of the recommended load levels, cut your load.

Overpressure indications are not always telegraphed ahead of time. Primers can look good, bolt lift easy, and then you blow a primer.

I have developed ammunition during load testing, everything looked good. Then took the stuff out to a match and then, before 88 rounds are done, I have had pierced or leaking primers. Not on all, on a few. So why did it not show up on the bench? Heck if I know. But there is one thing I have learned, if you have leaking primers, pierced primers, blown primers, your load is too hot.

Cut your load.

 

[dakotasin]

ok, pics uploading... post 'em in a minute. meanwhile:
old shooter - the brass issue came to my mind as well. unfortunately i do not have any virgin cases to compare to, yet. may have to give graf's a call...? the cases have 3 full power loads fired, and 1 or 2 very mild reduced loads (110 grain bullet at 2400 f/s).

innovative - pics coming...

sport - rounds impacted within the group on the target.

mmc - that may be a possibility. however, before we go very far down that road, the bore was sparkly clean when i first started out (i stripped all copper), and i have taken this bore into the many dozen rounds before cleaning in the past. i don't think it is likely a culprit here, since i wasn't even at the 2-dozen mark.

remo - no ejector imprinting, so if you read it, you didn't read it from me.

243 - yes, i-4350 is my shorthand for imr-4350. not necessarily looking for ideas to reduce the load. looking for reasons why a load that has fired dozens, possibly 100's of rounds safely and without incident suddenly went from normal to pierced primer.

slamfire - i don't think barrel heat was a contributor. the barrel wasn't cool, but i've definitely had hot barrels before, and this one wasn't one...









i shoot my cases in vertical order starting on the left. so what you see in the pics on the left side are the first cases fired. row 1 is 5 cases. then, row 2 (shot 6) is where the blown primer was, and shot 7 is the cratered primer.

as you can see, i was 5 rounds into this 'lot' with no apparent problems.

thanks for your help guys.

 

[Runningman]

But there is one thing I have learned, if you have leaking primers, pierced primers, blown primers, your load is too hot.

Cut your load.

+1000.... Load is to HOT that is the bottom line here.

Pressure can vary many thousands of pounds in a 10 shot group. Let alone a 30 shot string. My best guess is you just found the "one" with top pressure.

The WSM cases are very tough in my experience, pressure signs are not always obvious all the time.