IMR 4955 overpressure issue

[Wapiti1]

Just got back from Montana hunting deer and elk. Had a great hunt, except for one minor issue.

Shooting reloads in a 30-06 AI loaded with 180gr Nosler AB in front of 60.0gr IMR 4955. Load work up done over the summer between 70 and 90F resulted in velocity of 2880fps average for 30 shots with a low SD. So, a grain under max for a standard 30-06 and 60 fps faster than the Hodgdon max load in a larger AI case. No pressure signs, good case life after 4 firings with R-P brass, no worries. Shot 100 rounds after that work up for practice and to get the drop data worked out. No issues or concerns came up.

Fast forward to last week. -14F and I am shooting at a great mule deer. First shot, high. Way high. Second shot, also high. WTF???? Third shot, no idea, but it didn't hit the deer. First shot was at 330 yards, last at 423. After the last shot, the bolt was locked up. I gathered the empties out of the snow and neither case had a primer in it and they were clearly blown. I smacked the bolt a couple of good whacks and it opened. Same thing, primer fell out of the case, and there is a pronounced ejector slot mark on the case head. One of the worst that I've seen.

So, good pressure at 80F. Overpressure at -14F. Never seen this one before. More pressure at low temp.

Switching to a new powder. Anyone ever see anything like that?

Jeremy

 

[Mack84]

Haven’t seen that. But threw away 49 pieces of Hornady Brass, when 7 of 7 split. Less than max charge of 4955 with a 139SST. My sizer could have been bumping the shoulder too much at .003 to .004 . For a 280 Rem I think the least amount of sizing is best. 4th firing on those cases.

 

[doverpack12]

I had something similar with 4955 in 243. Blew 3 primers and decided to pull the rest.

I was working on a load and nowhere near max charge but it was cold out. 20s I would say.

Ended up changing bullets and powder

 

[Wapiti1]

I had something similar with 4955 in 243. Blew 3 primers and decided to pull the rest.

I was working on a load and nowhere near max charge but it was cold out. 20s I would say.

Ended up changing bullets and powder

Interesting. During my hunt, I checked the zero on the rifle, and no issues. But, the rifle and ammo were at truck cab temperature, so something around 65-70, I would guess. 3 shots, nice tiny group as I expect from this rifle. Zero was right where I left it.

After a couple hour stalk in -14F air, and things went haywire.

We have swapped to 4831SC to develop a new load.

Jeremy

 

[SDHNTR]

I would call IMR. Curious to hear their explanation on this one. Please report back.

 

[Harvey_NW]

I can't find anything specific to reference at the moment, but I have read about certain powders starting to rise in pressure in extreme cold temps. I think you'll have better results with the H4831SC.

Do you use graphite or any neck lube when seating? Before using lube I experienced similar issues from bullet weld where I loaded a bunch late summer and shot some of the remaining early spring in way colder temps, zero didn't seem to have a notable shift but impacts were way high at distance and pressure signs showed up. Might be a contributing factor.

 

[Wapiti1]

I can't find anything specific to reference at the moment, but I have read about certain powders starting to rise in pressure in extreme cold temps. I think you'll have better results with the H4831SC.

Do you use graphite or any neck lube when seating? Before using lube I experienced similar issues from bullet weld where I loaded a bunch late summer and shot some of the remaining early spring in way colder temps, zero didn't seem to have a notable shift but impacts were way high at distance and pressure signs showed up. Might be a contributing factor.

The cases do get a swab of neck lube prior to loading. I use a Dillon progressive minus the auto powder measure. Each charge is weighed and dumped. The cases get one shot and a swab of lube in the neck, then they run through the loading operation.

Jeremy

 

[Wapiti1]

I would call IMR. Curious to hear their explanation on this one. Please report back.

My father is working on that through email. I'll post what he finds out.

Jeremy

 

[35WhelenAI]

Your velocity is pretty much where it should be for an AI in my experience with respect to gains over the standard cartridge when similar pressures are in play. Fwiw, a lot of the "big" gains seen from an AI based on the '06 case in general are because pressure is bumped up relative to the parent cartridge, but still within safe pressure standards. A grain under std '06 max should easily be a safe load by anyones standards and you showed that it was safe when developing the load. You did things the right way.

Sorry to hear the issue, contacting IMR is the thing to do like you are working on. Very interesting, probably not coincidental, that there was another issue shared above with respect to cold temps.