120 fps velocity loss?

[BringBackThe80s]

In 2023, I worked up a load in my .308 Winchester Tikka T3x using 8208XBR under 130 grain TTSX in Lapua LRP cases. The charge I landed on, lit by CCI BR-2, was giving me sub-MOA 3- and 5-shot groups at 3130 fps (per Magneto Speed v3) with single-digit SDs. I was ready to start large group verification when life (a significant injury, a major illness, and job change) put shooting and reloading on hold for a year and a half.

This month I dusted off the reloading bench and loaded up a 50 rounds using all the same components. Same box of primers that have been stored in a sealed ammo can with a silica gel pack, same lot of Barnes bullets, the exact same bottle of 8208 XBR that was sitting on the shelf in my moderately temp stable workroom. Scales verified with same checkweights as in 2023. The only difference was that in 2023, the Lapua cases were on their second loading/firing, this go round is their third loading. But primers are very tight primer pockets. Temps yesterday were pretty close to my last two range trips in 2023.

Yesterday, after five foulers, and cooling barrel after every 3 rounds, the first 10 shots went into 1.27". But they left the barrel at an average of 3009 fps with a 15.5 SD per Garmin Xero. Where did the other 120 fps go?

The change from Magnetospeed to Garmin Xero could account for 3-10 fps of the change. But the only other thing I can see as a reason for the velocity loss is that the can of 8208 XBR was pretty newly opened when I loaded in 2023, but now it has sat on a shelf for 1.5-2 years.

#1 -- Could a plastic can/jar of partially used smokeless powder pick up enough humidity over 1.5-2 years to lose 120 fps out of a 3130 fps load? Even though the lid was tightly closed with the factory "gasket" foam still inside the lid?

#2 -- I live in the ultra-humid Southeast USA. How do you keep your smokeless powder moisture level stable? What moisture/humidity percent do you keep it at?

#3 -- Any other suggestions?

 

[Taudisio]

My first assumption is your barrel/chamber. Did you clean it before storing it? Scrub it out really well before shooting? A borescope would be easy to check in 30 seconds.

It could be the powder, but with your description, I doubt it. My grandfather was still loading with powder from the 70’s and 80’s 2 years ago before he passed. His shells still went bang. I don’t know the velocities, but 1.5 years is not 40/50 years.

 

[BringBackThe80s]

My first assumption is your barrel/chamber. Did you clean it before storing it? Scrub it out really well before shooting? A borescope would be easy to check in 30 seconds.

It could be the powder, but with your description, I doubt it. My grandfather was still loading with powder from the 70’s and 80’s 2 years ago before he passed. His shells still went bang. I don’t know the velocities, but 1.5 years is not 40/50 years.

I have not worried about powder declining, either. I'm still using a jar/canister of IMR 4198 that I bought in 2005. Still as potent as ever.

I didn't think about the effect of cleaning. The barrel had probably gone 100-150 rounds without a cleaning before I stopped shooting for 1.5 years. Two weeks ago, before my return to the range, I did a really thorough, multiple rounds of copper solvent soak-and-brush, down-to-bare-metal cleaning. It then had 30 shots through it before this anomalous load verification result.

Can cleaning a barrel and chamber reduce pressure and velocity that much?

Are you thinking there was a carbon ring spiking chamber pressure?

 

[Vern400]

YouTube "Winning in the wind" has a video about powder moisture levels, and actively managing it.

In short you could put a freshly recharged dessicant pack in the powder jug for a few weeks and see if the 120 fps comes back.

I keep my powder in the most stable temp room in my house. RH swings are lowest there too. And on my hunting ammo I seal the bullets and primers so they don't change.

There could be other factors as well in your case but yeah it's easy to lose 50 to 100 ft per second in extreme humidity storage.

 

[BringBackThe80s]

YouTube "Winning in the wind" has a video about powder moisture levels, and actively managing it.

In short you could put a freshly recharged dessicant pack in the powder jug for a few weeks and see if the 120 fps comes back.

I keep my powder in the most stable temp room in my house. RH swings are lowest there too. And on my hunting ammo I seal the bullets and primers so they don't change.

There could be other factors as well in your case but yeah it's easy to lose 50 to 100 ft per second in extreme humidity storage.

Ha! Yes, I doubt that I would have considered humidity as the culprit now but for having watched that video within the last few weeks.

I don't recall him specifying how many fps or percent changes were possible, and it seems wild that a plastic jar/canister would admit that much moisture with a tightly closed lid.

I have I am thinking I should pause load development for the following test:
1. Crack open new can/jug from same lot; 2. Put a humidity monitoring strip in each can/jug to see if measures different; and
3. Load & shoot 10-20 rounds from new and from old can and compare speeds.

 

[BringBackThe80s]

I just emailed Hodgdon to ask about optimal moisture level and whether it's okay to use humidity indicator strip, silica gel pack, and/or Boveda humidity controlled packet inside powder jug/can.

If anyone else knows or has experience with those in powder containers, please share.

 

[Jebel]

I’ve used the Boveda 49% packs for several years. They work fine. If you have an 8 lb jug, keep a spare 1 pounder and fill it from the 8. Keep the Boveda in the 1-pounder.