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H4350 temp sensitive?






#1
Weird day at the range. I loaded up 50 rounds to test/ confirm/zero etc. Standard load developed in cooler months.

Then
41.2 H4350
Lapua brass
CCI 450 primer
140 ELDM seated at 2.238
Velocity 2735-2750

Today
2812

Wut?
 
#3
today was 50 rounds through the chrono. Same one as before. Only difference is I initially tested with new unfired lapua and the loads are now fire formed brass bumped 2 thou. I remeasured CBTO and there appears to be some throat erosion but a bigger jump isn’t going to change the velocity.
 

LongRange

Obsessed Member
Forum Supporter
#4
ill ask the normal questions just to get it outta the way...
was this done with the same lots of powder and primers?
what was the temp when you put this load together?
what was the temp yesterday? looks like it was over 100.
did you leave the ammo laying in the sun?


that said ALL powder is temp sensitive...to a point...some powders just handle the temp swings a bit better than others heres a few examples...
hodgdon varget...the current lot im running now....32deg 2956 95deg 2998
hodgdon H4895...a lot a was testing over the winter....from my pack outta my truck so id say about 70deg to 32deg was 40fps slower
Reloader 17 i tested in my 260 years ago was the worst powder i ever tested....from 32 to about 90 was 115fps
ive also tested H4350 and from 32 to about 85 was 40fps

so if you run these numbers its pretty safe to say that most powders are from 1/2fps to 1fps per degree of temp change with the exception of the double base powders like alliant....Vihtavuori and a few others.

i know everyone thinks hodgdon extreme powders are not temp sensitive but they are and its easy enough to test yourself....take 2 rounds and put them in a plastic bag and put them in the freezer over night and transport them to the range in a cooler on ice.
take one at a time and fire them over the chrony...do not let them set out...straight from cooler to fired.

take 2 rounds and if its hot out let them set in the sun for 20mins if not turn you heater on in you car on defrost and set them on the defroster for 20-30mins and again straight from heater to fired.

i test this every time i tap a new jug of powder because some lots are faster or slow and also because of the big temp swings we have from morning to afternoon...if your trying to hit small-er targets out past 600-700yds a 30fps change in velocity can/will cause a miss.
 
#5
Same lot of everything. Load developed in August last year, not exactly cool.

loaded up some more backing down the charge and playing with seating depth.
 
#6
I bet the chronograph is lying to you ....mine does all the time depending on the lighting , gotta get me a Labradar or magneto speed
 
#7
Bring your Coleman cooler or even a wide mouth thermos to the next range session.

Use ice packs or frozen water bottles or something similar for cooling. Slender ballons, tied and filled with frozen water can be used for the thermos.

Transport some of the ammunition in the cold packaging.
Shoot some of the cartridges at ambient temperature, and some of the chilled cartridges. Don't let the cold ammunition stay in the chamber or magazine long enough to heat them up to ambient temperature, just chamber and shoot.

Compare the chronograph data.

I have a non-contact IR thermometer.
It's good for reading the temperature of the ammunition.
Record the temperature vs speed data and adjust accordingly in your ballistics solution calculator.
 

LongRange

Obsessed Member
Forum Supporter
#8
Same lot of everything. Load developed in August last year, not exactly cool.

loaded up some more backing down the charge and playing with seating depth.
was this a new barrel when you made the load in august? how many rounds through the barrel now?
 
#9
was this a new barrel when you made the load in august? how many rounds through the barrel now?
1500

I loaded up some rounds to test adjusting seating depth. Velocity generally goes down with erosion not up, so it has to be a combo of powder / chronograph. I need one of those magentospeed or whatever they're called.
 

42tula

uber Member
#10
I never had good luck with CCI primers, and the deviation was all over the place. I switched to federal 205m and the deviation was in single digits. Any signs of over pressure issues?
 
#11
I never had good luck with CCI primers, and the deviation was all over the place. I switched to federal 205m and the deviation was in single digits. Any signs of over pressure issues?
a little flatter, but nothing too crazy. I Have a lot of 210Ms but couldn't find any small rifle last time I looked. I was using the 210s until I switched brass to lapua small primer. Let me know if you want to swap 1000. All the same lot
 

LongRange

Obsessed Member
Forum Supporter
#12
1500

I loaded up some rounds to test adjusting seating depth. Velocity generally goes down with erosion not up, so it has to be a combo of powder / chronograph. I need one of those magentospeed or whatever they're called.
That’s why I asked about round count...new barrels speed up.

Other than possibly carbon build up in the throat I’m at a loss....also like 42tula said I’d swap primers...I to run and have had the best luck with 205Ms.
 
#13
That’s why I asked about round count...new barrels speed up.

Other than possibly carbon build up in the throat I’m at a loss....also like 42tula said I’d swap primers...I to run and have had the best luck with 205Ms.
I had just done a deep cleaning 100 rounds ago. Obv I’m perplexed I’ll definitely try switching primers