H4350 and temp sensitivity

[DLT]

I have been keeping eye on my 6xc since I got a Garmin chrono. I shoot a load of 38.5gr H4350 107smk and 450 primer. What ever the case may be I find my batch of powder to have big swings in velocity with the temperature. While shooting in 70 degree weather she purrs along 3050 pretty religiously. Now the temps is mid 80s and my velocity has climbed to 3070 even seen couple shots at 3080. I use a beam scale and my s.d. is usually 10 or less. I do not leave one cooking in the chamber. First round yesterday with a cold barrel was 3070. Anybody else have this experience ?

I know I’m not crazy, when it was colder weather and I first used this 8lb of powder I was around 3000 fps some times in the high 29s i was afraid I had a bad slow lot of powder. Boy has that changed with the temp.

 

[rijndael]

Around me, temp changes usually mean humidity changes too. In the winter, it's 30% humidity in my basement - where I store my powder and load. In the summer, if I didn't run a dehumidifier, it'd be 55%.

 

[FeMan]

I shoot a lot of H4350 in multiple calibers. I am constantly monitoring velocity and refining temp vs velocity curves. In the 50 degree to 80 degree range 0.5 fps per degree F is what I see with H4350. In the lower temps the rate of change is a little less and in the higher temps, a little more. What you are seeing seems to be exactly what I have seen over the years.

A SD of 10 correlates to an ES of 30 or so. So make sure you are looking at enough shots to be sure a reading or two aren't in the extremes. I am not sure how many rounds on the barrel, but some of what you are seeing (3000 to 3070) could be the barrel speeding up.

As stated above, humidity conditions during loading can make a bigger difference than people realize.

 

[r bose]

I have been keeping eye on my 6xc since I got a Garmin chrono. I shoot a load of 38.5gr H4350 107smk and 450 primer. What ever the case may be I find my batch of powder to have big swings in velocity with the temperature. While shooting in 70 degree weather she purrs along 3050 pretty religiously. Now the temps is mid 80s and my velocity has climbed to 3070 even seen couple shots at 3080. I use a beam scale and my s.d. is usually 10 or less. I do not leave one cooking in the chamber. First round yesterday with a cold barrel was 3070. Anybody else have this experience ?

I know I’m not crazy, when it was colder weather and I first used this 8lb of powder I was around 3000 fps some times in the high 29s i was afraid I had a bad slow lot of powder. Boy has that changed with the temp.

Newer powders were developed to be LESS SENSITIVE to temperature. Not insensitive to temperature. You'll see a difference in velocity as temps rise. Not sure if that can be totally avoided.

Some powders (especially ball powders) are the worst. I've seem 250 FPS differences from 35 to 90 deg.

 

[Kooi]

How does humidity affect powder?

You may have heard about a relationship between humidity and bullet velocity either in a book, on a reloading forum, or from a crusty benchrest shooter right after saying they get better ES/SD&#821…

chronoplotter.com

 

[Bill Norris]

I have been keeping eye on my 6xc since I got a Garmin chrono. I shoot a load of 38.5gr H4350 107smk and 450 primer. What ever the case may be I find my batch of powder to have big swings in velocity with the temperature. While shooting in 70 degree weather she purrs along 3050 pretty religiously. Now the temps is mid 80s and my velocity has climbed to 3070 even seen couple shots at 3080. I use a beam scale and my s.d. is usually 10 or less. I do not leave one cooking in the chamber. First round yesterday with a cold barrel was 3070. Anybody else have this experience ?

I know I’m not crazy, when it was colder weather and I first used this 8lb of powder I was around 3000 fps some times in the high 29s i was afraid I had a bad slow lot of powder. Boy has that changed with the temp.

I've noticed some swing in temps with H-4350 in my 260AI as well but I contribute more of that to humidity levels as well.

 

[deertroy1]

Same here. I'm in Nova Scotia. Even with the dehumidifier I noticed larger variation due to humidity than I do temperature.
I think a humidity insensitive powder would be the ticket.
I recently got a new pound of AA2015 and identical powder chargers were over 200 fps slower than my old lot in my 45/70.
Even though I have experienced large lot to lot variations in this powder before, an email to Hodgdon revealed that this isn't that unusual in lots of powder that have been around a number of years and may have dried out!

 

[6.5 forever]

I personally do not think that is a unacceptable swing. I have seen other powders far worse than this.

 

[243winxb]

Open PDF https://apps.dtic.mil/sti/citations/ADA572333

Powder Lot Variations: A Case Study with H4831 - Hodgdon Extreme​

 

[Kracken McGraw]

All the Garmin’s on the benches now will take care of the variance pretty quickly now.

 

[Danboyd7]

I have been keeping eye on my 6xc since I got a Garmin chrono. I shoot a load of 38.5gr H4350 107smk and 450 primer. What ever the case may be I find my batch of powder to have big swings in velocity with the temperature. While shooting in 70 degree weather she purrs along 3050 pretty religiously. Now the temps is mid 80s and my velocity has climbed to 3070 even seen couple shots at 3080. I use a beam scale and my s.d. is usually 10 or less. I do not leave one cooking in the chamber. First round yesterday with a cold barrel was 3070. Anybody else have this experience ?

I know I’m not crazy, when it was colder weather and I first used this 8lb of powder I was around 3000 fps some times in the high 29s i was afraid I had a bad slow lot of powder. Boy has that changed with the temp.

Yes this normal. I use 4350 in my 260 and velocities will vary with temp changes. Velocities will gradually clime as barrel gets dirty in my rifle, maybe not yours depending on how you devolved load. I clean mine every 50 rounds or so. Hope that helps

 

[SKWERLZ]

In my 260 H4350 temp stability was quite good.
Even in eastern Washington with far greater temp swings.


Try running R17 and deal with that temp swing.