Reumbo pressure spike below freezing!

[tbrice23]

Someone tell me I'm crazy.
I have worked up a load for 264wm with140vld and Retumbo up to 71.5 gr in 65° with mild pressure signs, so I backed down to 69.0 grains at 3250 fps average.

Today 30°F I shot some of the same ammo loaded 3 weeks ago and the velocity spiked to 3340fps and blown primers. This barrel is completely cleaned, no copper or carbon with a dry chamber verified with my bore scope.
Same lot of brass, primers, bullet and powder.

The only thing that changed is last week I did a several groups of RL 25, but I always clean to bare metal when I change to a different powder.

*** !! Help!

 

[J E Custom]

Retumbo is one of those powders that can go critical with just .02 tenths of a grain increase.

There are a few more powders that have that characteristic and even though you have a good load any change can put you over the top.

Some powders are very linear and each increase will produce a linear increase in velocity. Retumbo is a great powder and seems to produce the best velocity, but that comes with a price and you have to watch the pressures closely.

I am surprised that the pressure went up in very cold weather, but stranger things have happened
with this small group of powders.

If you want to use Retumbo, you may have to back off a little more or back off the lands a little more. (If you are shooting against the lands pressure will be erratic with some powders).

J E CUSTOM

 

[RockyMtnMT]

I'll add a question here. We have had the same things happen every now and then with various powders. I think there is a correlation with higher humidity or heavier air. This would make sense with the colder air?

Any thoughts?


Steve

 

[Greyfox]

It is strange. If any change in pressure was expected at all, one would expect it to be lower. Question: Any evidence of bullet setback in the case, or variation in the bullet ogive or diameter?. I have been using Retumbo in my 6.5x284 and 300WM at max case capacity(I can hear the light crunch) for several years in sub zero through 85+ degree temperatures and have not experienced evidence of pressure spikes or variations in velocity. Hope you figure it out.....keep us informed.

 

[6point5x284]

Tagging in. Curious as well.

 

[tbrice23]

I'm clueless,
I've used Retumbo in 6.5 284 also with no problems and in both chambers I'm loading vlds .01" jump. I've been checking for throat erosion every 50 rounds with not even .001" loss in approximately 350 rounds fired.
I'm going to back off to 68.0 gr and give it another try.

This is not a tight neck chamber and my fired cases fit over a bullet easily, but does anyone think that I should do a JB Bore scrub in the throat , or will it complicate things? (I try to stay away from any abrasives)

 

[Steelflight]

Thinking out side te box and any one can call me crazy. but here is an experiment for you.

Tkae your Calipers or you mic. out to the shoot range on the next cold wheather day. measure your brass diameter before leaving the house and do it again out side at the range. Then shoot.

it will be ridiculously small but you brass should shrunk in the cold. With this powder if your using a constant measuring system. But have seen the increase in pressure something has indeed changed. under any other circumstances i would not even think of this. if retumbo is as volatile as has been suggested. then perhaps even a slightly smaller case in cold air can cause this change.

but like i said maybe i over thought it. lightbulb

 

[tbrice23]

Will do.

 

[MagnumManiac]

Someone tell me I'm crazy.
I have worked up a load for 264wm with140vld and Retumbo up to 71.5 gr in 65° with mild pressure signs, so I backed down to 69.0 grains at 3250 fps average.

Today 30°F I shot some of the same ammo loaded 3 weeks ago and the velocity spiked to 3340fps and blown primers. This barrel is completely cleaned, no copper or carbon with a dry chamber verified with my bore scope.
Same lot of brass, primers, bullet and powder.

The only thing that changed is last week I did a several groups of RL 25, but I always clean to bare metal when I change to a different powder.

*** !! Help!

Were the loads you shot 3 weeks ago loaded and fired within a short period or straight from the bench to your gun and tested, and were the the more recent loads transported any distance before being shot?

I had an instance with a powder here that was similar to Retumbo, made by Thales, that would get temperamental after being transported in a vehicle. If I shot them just after loading, which I often do, then there was no problem.
Transporting changed how the powder sat in the case, causing a pressure spike.
I was able to repeat this at will. I would load up 10, put 5 aside, and the other 5 I would hold each cartridge to my tumbler for a few minutes, and shoot them, the same result everytime. The 5 that were held against the tumbler would blow primers. This powder was eventually pulled from manufacture, H1000 was it's replacement.
The solution was to 'swirl charge' each load and settle the powder and work back up, I found that the velocity dropped and the max charge weight was reduced by 2 grains.
It took me a while to figure all this out, an etched boltface was the last thing I wanted, and that's what I got.

Cheers.
lightbulb

 

[tbrice23]

Were the loads you shot 3 weeks ago loaded and fired within a short period or straight from the bench to your gun and tested, and were the the more recent loads transported any distance before being shot?

I had an instance with a powder here that was similar to Retumbo, made by Thales, that would get temperamental after being transported in a vehicle. If I shot them just after loading, which I often do, then there was no problem.
Transporting changed how the powder sat in the case, causing a pressure spike.
I was able to repeat this at will. I would load up 10, put 5 aside, and the other 5 I would hold each cartridge to my tumbler for a few minutes, and shoot them, the same result everytime. The 5 that were held against the tumbler would blow primers. This powder was eventually pulled from manufacture, H1000 was it's replacement.
The solution was to 'swirl charge' each load and settle the powder and work back up, I found that the velocity dropped and the max charge weight was reduced by 2 grains.
It took me a while to figure all this out, an etched boltface was the last thing I wanted, and that's what I got.

Cheers.
lightbulb

Negative.
Im relentless about a cold barrel. I wait 5 min between rounds.
My ammo is loaded into my truck outside overnight ,so it's ambient temperature when shot.
I'll try shaking a few next time.

 

[RockyMtnMT]

Were the loads you shot 3 weeks ago loaded and fired within a short period or straight from the bench to your gun and tested, and were the the more recent loads transported any distance before being shot?

I had an instance with a powder here that was similar to Retumbo, made by Thales, that would get temperamental after being transported in a vehicle. If I shot them just after loading, which I often do, then there was no problem.
Transporting changed how the powder sat in the case, causing a pressure spike.
I was able to repeat this at will. I would load up 10, put 5 aside, and the other 5 I would hold each cartridge to my tumbler for a few minutes, and shoot them, the same result everytime. The 5 that were held against the tumbler would blow primers. This powder was eventually pulled from manufacture, H1000 was it's replacement.
The solution was to 'swirl charge' each load and settle the powder and work back up, I found that the velocity dropped and the max charge weight was reduced by 2 grains.
It took me a while to figure all this out, an etched boltface was the last thing I wanted, and that's what I got.

Cheers.
lightbulb

This is very interesting. Could be the answer to some mysteries. Every load shakes in transportation so it seems the solution would be pre settle the loads during load development if you are not transporting to the range.

Any thoughts on ball vs stick?

Steve

 

[tbrice23]

Were the loads you shot 3 weeks ago loaded and fired within a short period or straight from the bench to your gun and tested, and were the the more recent loads transported any distance before being shot?

I had an instance with a powder here that was similar to Retumbo, made by Thales, that would get temperamental after being transported in a vehicle. If I shot them just after loading, which I often do, then there was no problem.
Transporting changed how the powder sat in the case, causing a pressure spike.
I was able to repeat this at will. I would load up 10, put 5 aside, and the other 5 I would hold each cartridge to my tumbler for a few minutes, and shoot them, the same result everytime. The 5 that were held against the tumbler would blow primers. This powder was eventually pulled from manufacture, H1000 was it's replacement.
The solution was to 'swirl charge' each load and settle the powder and work back up, I found that the velocity dropped and the max charge weight was reduced by 2 grains.
It took me a while to figure all this out, an etched boltface was the last thing I wanted, and that's what I got.

Cheers.
lightbulb

All the other times they've been transported the same. Nothing changed except the temp.

 

[Greyfox]

Just thinking of all the possibilities. You mention that you are loading .01" off the lands. It doesn't take much for the bulleti to end up to far into the lands. This would cause an increase in pressure. It's a long shot but I'd check your bullets ogives and/or diameters, as well as the consistency of your seating depths. Were the bullets you tested fed from the magazine, or, were they ever in the magazine when the rifle was shot when huntiing, then removed?

 

[tbrice23]

Just thinking of all the possibilities. You mention that you are loading .01" off the lands. It doesn't take much for the bulleti to end up to far into the lands. This would cause an increase in pressure. It's a long shot but I'd check your bullets ogives and/or diameters, as well as the consistency of your seating depths. Were the bullets you tested fed from the magazine, or, were they ever in the magazine when the rifle was shot when huntiing, then removed?

All were single feed.
I check every round for CBTO, believe me I double checked length and when I dumped the rounds I re-weighed them.