Seeing 80fps difference in new pound of powder??

[coast range]

So loaded up some more 7mm08 rounds with big game and accubonds.

I used up the last of my pound last time I shot. So cracked open a new bottle and loaded up the best load from a week ago 47.5 grains. They were 80 fps slower. Obviously not the same lot. If I had gotten a change I would have figured it would have been more speed.

The only thing else different was the first batch was loaded to mag length (tikka) and this batch was loaded to .003 off the lands. Other than that it was all same, virgin peterson brass and mag primers.

Have you guys seen it that bad before?

 

[KyleR1985]

What is the overall length difference between the two loads?

It probably accounts for a lot of the velocity spread.

Increasing case capacity by increasing OAL, and holding powder charge constant, will decrease pressure, and velocity.

Jamming lands counters this to some degree.

Do you mean .030, or .003?

 

[Jebel]

Powder lot, powder humidity, and seating depth can all affect velocity. 80 fps is a lot, but possible. Are there any other changes, particularly in brass brand, lot, resizing methods, or iterations of reloads (new, FF1, FF2+)?

Edit add that a recent lot change of H4350 for me resulted in a 65 fps change in a 6 Creedmoor with no other changes in methods.

 

[coast range]

What is the overall length difference between the two loads?

It probably accounts for a lot of the velocity spread.

Increasing case capacity by increasing OAL, and holding powder charge constant, will decrease pressure, and velocity.

Jamming lands counters this to some degree.

Do you mean .030, or .003?

Yeah typo .03. Everything else identical. New brass so everything was just chamfered and deburred

 

[KyleR1985]

Yeah typo .03. Everything else identical. New brass so everything was just chamfered and deburred

What COAL did you load to for “mag length”?

What COAL did you load to for .030 off lands?

 

[coast range]

So just got home from work and looked at my notes. I originally loaded 2.820” for mag length on my first work up. The second time I loaded up 2.899” with my best powder charge.

That is .0500” off the lands. Sorry I said .0300” before I was going off of memory and I am working on 2 rifles right now.

 

[coyotekilla]

Temp sensitive powder? Clean rifle?

 

[greyghostnw]

Its a thing. My new lot h1000 is 65 fps faster. Humidity in container deviates weight as well

 

[KyleR1985]

The difference in oal alone would explain whole difference in a .223. Different powder lots, different temperature on ignition could explain the rest for bigger cartridge.

 

[TaperPin]

It doesn’t happen very often, but I had a pound of a different powder that was slow like that.

 

[Taudisio]

Seat some down to exactly the same as you had before the jug change and verify that the lot is slower. Eliminate that as a factor before changing anything else. Both things are possible for a slower velocity.

 

[coast range]

Seat some down to exactly the same as you had before the jug change and verify that the lot is slower. Eliminate that as a factor before changing anything else. Both things are possible for a slower velocity.

That’s what I am going to do hopefully this weekend.
Powder is Big game, Peterson brass, wlrm, and 140 accubonds

Rifle has maybe 150 rounds through it, and I think I mentioned it is a tikka

 

[Tahoe1305]

I have had same with RL26 different lots. Typically you can add a smidge more and get the same pressure=velocity without overpressure. But kinda sucks to have to test loads again.

 

[HuntHarder]

I have a thread on here I started a month or 2 ago about the same thing. My new 8lb'r of H4350 is considerably slower than my last 8lb'r.

 

[Ryan Avery]

I see this a lot with powders; the worst is Retumbo.

 

[Ckat]

I make my own “lots” by batch mixing all of each specific powder to avoid pound to pound variations. It also allows me to save some space in my cabinet by filling each container versus having a bunch of 2/3-3/4 full “sealed” jugs.