Reumbo pressure spike below freezing!

[tbrice23]

Being a Retumbo user in many different cartridges over the years this thread has my interest. After reading almost all the post completely I believe is is the answer, if not it's a dang go suspect.


Don Dunlap

I'll say this one more time.

A dozen rifles I shoot regularly show no discrepancy, loaded on the same day with the same equipment!

I'll be willing to blame the barrel metal way before my reloading QC.

 

[tbrice23]

Throw your scale away! It's drifting as you load. 0.8g less powder shouldn't produce higher velocity, especially when it's colder.

You mean throw both scales away. I weigh each and every charge twice.

 

[tbrice23]

No offense taken.
I drop charges with a Hornady Chargemaster then I double check EVERY dropped charge on a Gempro.
I calibrate both scales before each use and both are turned on to warmed up an hour before use. I keep a 20g weight beside the Gempro to verify calibration during its use.
Nothing has changed in my electrical layout. My outlets are about 6 feet away. I bring 2 rifles to the range always for a couple of reasons. The 300wm I shot the same day had rounds that were loaded with the same equipment on the same day. Other rifles loaded with the same equipment recently with other powders show no change.
When I dumped these rounds I re-weighed the charges, they all weighed good.

They are both calibrated before each session , my drift is never more than .02 gr on the Gempro. When I see the drift I check the 20g tare weight.

I'm now going after the actual barrel instead of Retumbo. I wish I was loading Retumbo in a different rifle or cartridge to confirm/ compare.

 

[Trnelson]

You mean throw both scales away. I weigh each and every charge twice.

Certainly that choice is yours alone to make. I'm not at all calling to question your diligence or your attention to detail, obviously something outside of your normal QC protocols has changed. You have the advantage of keeping detailed records of what you are doing and how it is affecting your results.
I tend to be most suspicious of the most simple things that I know can lead to tollerence stacking and an insidious deviation. You are dancing pretty lose to the upper limits, a small change, even unperceived will push you past the safety cushion you've built into your load. At the simplest level, less powder should never make more velocity, as you've reported and confirmed, unless you are experiencing powder bridging, carbon ring or a simple deviation of a scaler type. It's the most likely source.
I don't trust electronic scales. I have several, they all have quirks. I use them, but I still utilize my beam scale, at least every third powder charge. You'd be surprised just how often I go back and dump the last three and re-check the fourth.
I went out and bought three different electronic scales, I was TOTALLY convinced the problem was the scale and I needed redundancy to be able to check one against the other and that would clear up my issues. It actually made them worse, they would register three different weights with the same check-weight. That was a rough couple months, let me tell you.
I leave mine plugged in and on all the time, Warm-up drift still shows up after a half hour in mine, sometimes longer and I don't know why that is so now they just stay on. I re-zero at least every five charges. I control temperature, humidity and air flow. I've documented how a change in each effects my individual electronic scales. For example, the furnace blower kicking on will cause one scale to drift up to 0.3g. It just gets erratic and I have shut off the airflow so the scale can settle, it takes about ten minutes. If I accidentally forget to re-open the air duct vent and the tempurature in my loading room falls just 3• my other reads 0.2g lighter than the charge actually weighs. If I let the humidity get above 50% it tends to read heavier that it actually weighs.
Best of luck, it's likely there someplace,and I'm sure you are persistent enough to find it. Merry Christmas to you and yours.

 

[Dgd6mm]

I may have been premature on my posting, but your situation has me stumped. With your diligence of keeping up with your scale readings you would think it would produce consistent results. I'm going to keep quiet and see how this unfolds while learning something in the process.


Don Dunlap

 

[Pdvdh]

I've completed some extensive testing on the temperature sensitivity of Retumbo, H-1000, and IMR 7828 5-7 years ago.

Retumbo and H-1000 didn't return reduced velocity as temperatures fell down into the 0*F range. Retumbo MV increased a little from 32*F down to 14*F and 5*F. http://www.longrangehunting.com/forums/f28/retumbo-temperature-73877/#post516193

The increase in MV with declining temperatures was greater with H-1000 than Retumbo, but both powders actually produced increases in MV. Nothing like your experience. So this information isn't an effort to claim my MV measurements versus temperature for Retumbo explains your experience. But if you were expecting reduced MV with decreasing temperatures, then this information should remove 1/2 of your surprise, contrasting with the more normal expectation of lowered MVs with lowered temperatures.

I shared some more powder temperature versus MV information in this thread:
http://www.longrangehunting.com/for...ons-due-temperature-changes-62036/index4.html

PS: I collect my MVs over duplicate and triplicate chronographs. If I don't obtain good correlation of recorded velocities, I discard the data. So my data is much better quality than MV data collected over a single chronograph, IMO.

 

[benchracer]

I seem to remember reading a warning in the Vihtavuori manual some years back, regarding their slower double base powders and pressure spikes in cold temps. IIRC, it had something to do with the way nitroglycerine behaves. I find myself wondering if this issue with Retumbo involves the same phenomenon.

I can't find my copy of the manual right now, so I am not completely sure if I am remembering right. I have had that thought in the back of my mind since this thread started.

 

[Greyfox]

Checking my records for my load development and shooting sessions for my rifles I might have discovered a possible cause. For several years I have recorded temperature, wind, velocity, etc. After checking my records I wonder if primer choice/ignition could be playing a role with the problems some are experiencing. With my 6.5x284's that use 58gr of Retumbo I found about five years ago that when using Fed215M's, groups were still excellent and I would get velocities which were generally higher by 30-50FPS compared to Fed210M's, but, would increase another 30-50FPS with higher ES in colder temperatures. For that reason I settled on Fed210M's. This has not occured at all with the Fed210M's which have proven to produce consistent velocities and low ES over a wide temperature range since.

 

[tbrice23]

I am using BR2 primers.

 

[Pdvdh]

Have you taken room temp rifle/ammo out of the house since original incident and fired with no pressure? Repeated the high pressure in below freezing temps yet?

 

[tbrice23]

No sir. I've backed my load down to 68.2gr. I'm afraid to shoot the 69.0 gr again.

 

[tbrice23]

I honestly have not blown a primer in 10 years (since back before I knew about rl22 and pressure/temp swings).

This has me gun shy.

 

[Greyfox]

I am using BR2 primers.

Understood. But not all primers types are created equal, and given your jump in velocity remains remains somewhat of a mystery, I was just thinking priming/ignition may be a relevant variable.

 

[Timber338]

I've read most of this thread, but missed if you are using the same jug of Retumbo or if the pressure is spiking with different jugs/lots of Retumbo?

This reloading game that we play is always such a huge experiment, and there are so many variables. Seems like you have narrowed down just about everything, so just maybe it's just a bad jug if powder that maybe got mishandled during shipping and got crushed (you would probably see that) or extremely shaken or exposed to moisture or just something weird that changed something?

At first I got to thinking that your barrel could have some odd internal inclusion near the chamber/throat that would only show up with a die pen test or X-ray and it was changing to an oval shape at cold temps. But that would shoot all powders funny and you are not experiencing that.