H4350 Lot to Lot Consistency

[BrianTom]

I've spent the last few months working up a load for a 284 Winchester with H4350. I am shooting 150 grain Sierra TGK with Peterson brass and Federal 210M primers. I recently finished off a pound of H4350 and opened a new 8lb container. I was fine tuning 3 well known loads at 53.5, 53.6, and 53.7 grains which should have produced rough average velocities of 2890, 2900, and 2910 FPS per my extensive previous testing. Instead what I recorded was 53.5 grains pushing close to 3000+ FPS. After I shot 2 rounds of the 53.6 grain load and recorded over 3000 FPS I quit. The cases and gun were both showing signs of pressure which is expected when running at those velocities. First thing when I got home I checked my scale. The test weights proved true so I loaded 2 more rounds at 53.5 grains and headed back to the range (conveniently 2 minutes from home) and recorded the same results; velocities near or above 3000 FPS. I then loaded up 20 rounds, 2 at each charge, working in 0.1 grain increments starting at 51.4 grains and ending at 52.3 grains. The velocities for 51.9, 52, and 52.1 grains (2885, 2913, 2923; 2 shot avg FPS) were close to what I was expecting with the previous lot of powder using 53.5, 53.6, and 53.7 grains. Nothing else except the new powder lot and outside temperature (it is cooler now than when I first started testing) has changed in my reloading process. This amount of variation seems insane to me. Has anyone else experienced anything like this, particularly with H4350? I normally use VV and am considering switching back to N160 if I can find some.

 

[A382DWDZQ]

Do you live somewhere with high humidity?

 

[BrianTom]

I live in Pennsylvania. I keep the powders not in use in a storage container sealed with an o ring (not in a basement). I purchased the 8lb H4350 from Brownells sometime within the last 6 months. I thought I was lucky at the time to find it. Maybe not so much now. I just opened the new powder this week.

 

[Travis Bertrand]

Brian. Powder Humidity plays a large role in velocity. Whenever I get a new can of powder, I open it and throw a few desiccant packs in it. That way it’s consistent and not at the humidity from the factory.


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[Lawnboi]

When I open a new jug, I leave it open to acclimate to the humidity in my reloading room, which varies from a controlled 50% in the summer to dry as hell in the winter.

I have shot 10 plus lots of h4350 in the last couple years, and doing the above they have all been close enough, I also don’t run on the ragged edge of pressure, partially for this very reason. Being within a fraction of a grain of pressure is what ends up screwing shooters a lot. Carbon build up, subsequent brass firings, and inconsistent reloading practices add up.

 

[doverpack12]

I’ve had to adjust a little (less than 0.5gr) in the past but will try the desiccant packs or just opening up the life since I have lower humidity.

 

[A382DWDZQ]

The variance you encountered is about 3%. While not common, I don't think it would be insane. Underscores the manufacturers' warnings to work up from a starting load whenever changing lot numbers of any components. I saw someone's method that I like, which was to load 5 rounds of starting load before the bottle is empty, and then load 5 with the new one and compare those, then you safely have an idea of where they stack up to each other. Quickload has their 10% warning, and if you added 10% to that max load of 53.7, I think it would be getting pretty close to a proof load.

 

[BrianTom]

Thanks to everybody above for their insight and information.

The humidity factor was not on my radar at all. But since you guys brought it up I started looking into it. I found this article: https://chronoplotter.com/2021/08/19/how-does-humidity-affect-powder/

My situation makes sense if the data from that article is accurate. My several year old H4350 1 lb lot likely contained much more humidity than the new 8lb container resulting in the much higher velocities.

My max load with the initial 1lb H4350 was 54.6 gr producing an average velocity of 2996 FPS so I assumed (incorrectly) that I wouldn't have any major issues testing at 53.5-53.7 gr with a new lot of the same powder. For me, 1.7 gr of powder is a significant number when I am expecting a particular velocity at 53.7 gr but getting that expected velocity with only 52 gr of the new powder lot. It is especially frustrating when I am to the point of fine tuning the charge in increments of 0.1 gr.