A fun day almost turn into a disaster.

[Mountain Goat]

It's possible that it wasn't an over or under-charge situation, but perhaps some tumbling media was stuck in the case. Case polish can sometimes make the media lumpy, and the bottleneck case doesn't allow for it to "dry" and therefor stays inside the case. Just a thought.

I like your idea of pulling all the bullets, even if you find nothing conclusive with the loads. That is a good safe practice and reminds us all that what we do can be very dangerous at times.

 

[Desert Fox]

Bolt ring looks like it may have failed in column compression bending?

You're looking at the bolt bushing. The bolt is fine. Broke the bolt handle trying to removed the stuck case.

My guy at work bolted it together today and he did a pretty good job. He doesn't even know anything about guns. He does have a lot of experience working with metal. He told me that bolting the handle will be much stronger than silver solder or welding it for that matter. I respect his opinion, so I had him do it.

The bolt timing was slightly off after he finish it, so I have to do a little filing and grinding. All it need now is a little more polishing and then I will re-blue the bolt handle.

Here's how it look so far.

 

[Desert Fox]

Initial investigation so far revealed a likely culprit. I had about 30 cartridge left in a box of fifty that I brought to the range Sunday. I started weighing each one and the pattern began to emerged. Twenty of the cartridges weigh an average of 390.9 grains. Ten of them weigh 392.5 for a difference of 1.6 grain. I pulled bullet from each sample and weigh them. Both cartridge had 50.5 grain each so there's no issue with powder charge here. I had so much faith on Lapua's quality that I did not bothered to weight sort the brass. I'm mistaken.

When I developed this load using IMR 4831, I can't find any data anywhere. Almost every 6.5-284 shooters use H4831. The only thing I found where IMR is being use was with 6.5x55 Swede and 6.5-06. What I did was split the difference between the two and start from there. I started developing this load towards the end of October and finalized it around November. I maxed the charge of IMR 4831 to 51 grain with resulting velocity close to 3000 fps. I could see telltale sign that I'm really close or right at maximum, so I reduced the load by a half a grain and dropped the velocity to around 2975 fps.

The temperature Sunday was around 80 degrees. I fired my first 5 shot as soon as I got to the range. The cartridge was probably still cool coming out from an air conditioned car. The next time I fired the rifle was probably about an hour later, so the cartridge had already acclimated to the ambient temperature. Guess which cartridge I plucked when I made that faithful shot. You guess it the one that weigh 392.5.

I had this same scenario happened with my 308 a couple of years ago. I developed load around wintertime and shot the cartridge during summer, where temperature was in the triple digit. The result was the same. I did not connect the two at first because I never suspected that there were correlation. Looking back at it, I believed the exact same thing happened here with heat as the common denominator.

 

[SJB358]

Thanks for the heads up DF. Makes a bunch of sense to me. Scotty

 

[Oldtrader3]

That was a nasty looking case. Glad that you weren't hurt.

 

[Desert Fox]

Took the 6.5-284 to the range yesterday to chrono the two segregated groups of loaded round and see what kind of velocity spread I'm gonna get. As predicted the rounds that weigh 392.5 grains averages 2960.5 fps, while the 390.9 averages 2937.3 fps. The temperature was around 67 degrees early in the morning just before sunrise. No sign of pressure whatsoever. I waited another hour when the sun was up and warmed the range to shoot another 3 shot each of the segregated rounds. I recorded the temperature at 78 degrees. The round that weigh 392.5 grains averages 2988.4 fps while the rounds that weigh 390.9 averages 2957.5. The fired case showed no sign of pressure and the extraction was normal but, the increase velocity obviously tells me that I'm right at or close to maximum. I have no problem using this load for winter but for summer load, I will definitely reduced it by a grain.

 

[Too Tall]

I'd change powder.

 

[Elkman]

DF

So you are thinking that the 10 degree temp change made the difference. Is there a case brand difference in the weight?

Then in my circumstance the temp change was probably closer to +30 degrees because of my body heat. Interesting

 

[efw]

Glad you're ok. Bolt can be replaced.

+1!

That kind of stuff scares the crap out of me... glad you're well.

 

[Desert Fox]

DF

So you are thinking that the 10 degree temp change made the difference. Is there a case brand difference in the weight?

Then in my circumstance the temp change was probably closer to +30 degrees because of my body heat. Interesting

The most common powder reloader use for 6.5-284 is H4831. The max load using this powder is 51 grain. I'm using IMR 4831, which is tad faster than Hodgdon, so on average, the charge should be less. I was able to work up a max load with my rifle to 51 grain with resultant velocity close to 3000 fps. I noticed telltale sign of high pressure so I dropped my load half a grain. I developed this load around November when the temperature was a lot cooler so I have no way of knowing if the load will be safe to shoot during summer time when the temperature here in Cali is in triple digit. Looking back at it, I should have dropped the powder charge another half a grain.

 

[Desert Fox]

I'd change powder.

TT, That should be the prudent things to do but when your getting groups like the one below, You'll be hard pressed to walk away from it.

 

[Too Tall]

I hear that. I'll bet you can get her to group with Extreme powder too. Better than getting yourself hurt, or tearing up your equipment.

 

[Desert Fox]

I hear that. I'll bet you can get her to group with Extreme powder too. Better than getting yourself hurt, or tearing up your equipment.

I think I got it figured out. I had been using IMR powder in majority of my reloading for a long time. This was my first mishap and hopefully my last. IMR 4831 is my powder of choice for my 280 Remington and been reloading with it close to twenty years by now. The load that i developed for my 280 was above SAAMI spec (55.5 grain with 150 grain Nosler Ballistic Tip) but not once I experienced any pressure issue.

I think I slacked off on this one by not sorting the brass in the first place. I then compounded it by loading them at probably over max load. In doing so, I've left no cushion for any changes in temperature.

 

[JD338]

DF

Your explanation make sense to me.
That is why I like to do my load development in the summer months.

JD338

 

[DrMike]

I appreciate your analytical approach to resolving the problem, Rommel. Your conclusion sounds solid.