I'm trying to figure out if my chrony is on the fritz or if the powders I am using in my 6.8mm SPC are just that sensitive to temperature change. A 40+ degree drop in temp and I'm seeing 150 fps drop with 1200R, 80 with CFE and AA2200. I know that Varget and 8208 XBR are very temperature stable but can't find data on the other powders I use (Re7, Re10x, H335, MagPro, LEVERevolution, CFE, AA2200, 1200R, TAC). I know I am getting a 40 fps drop in the .270 load with IMR 4350 so I carry my magazine in my pocket until I need it.

Doesn't do much good to develop loads over the summer and have them go flat during hunting season. I may have to do some testing on the next cold day I'm off.

Here is some data I found on the net.

Velocity spread in FPS between 0-125 degrees F:

1. H4350: 4 (FPS)
2. Varget: 8
3. H4831C: 10
4. RL 12: 26
5. AA4350: 29
6. AA2460: 36
7. IMR 4064: 46
8. VIT 550: 49
9. RL 15: 50
10. VIT N140: 50
11. AA2520: 63
12. IMR 4350: 67
13. RL22: 75
14. RL 19: 94
15. AA3100: 113
16. W 748: 114
17. VIT N560: 121
18. IMR 4831: 127
19. IMR 4895: 166

I have found both IMR and Winchester Ball powders to be temperature and humidity sensitive !!!

To what extent I can't say. (pre-chronograph days)
What I do know was loads developed in colder temps often resulted in a sticky bolt come summer. Summer loads often felt as if there was less recoil in colder weather.
When I switched to Varget I confirmed with a chronograph that temp variation wasn't really a issue.

I do believe RL powders are sensitive but I have very little experience with them.

As a side note I still do my load development in temperatures that are relative to my shooting situation.

Your findings on the CFE surprises me. It was originally advertised as being one of Hodgdon's "Extreme" powders. Guess I'll have to do some testing myself...I use a fair amount of it. More surprising was the chart's listing for IMR 4064. I have heard of fluctuations of as much as 180 fps, though I haven't experienced such an extreme spread. Good food for thought.

SingleShotLover wrote:

Your findings on the CFE surprises me. It was originally advertised as being one of Hodgdon's "Extreme" powders.

I did say I'm also trying to figure out if my chrony is not reliably providing velocity readings. It has been reliable and consistent so far, even from range session to range session. Just not the last couple of months with the temps going up and down. I don't know of another shooter locally that has a chrono I could compare to.

Slim,

My chrony has been causing me to raise my eyebrows a bit lately, albeit for different reasons. They are not infalliable and they can and do stop working, even if well cared for. I'd say they work pretty well considering what we often ask of them (sub-zero to 100+ temps throughout the year).

That being said, it could be something as mundane as the battery is nearing end-of-life and is no longer giving off consistent voltages. Cold weather can cause batteries to act wonky too. Put a $1 chemical hand warmer over the battery or take two to the range and keep one it a breast pocket and swap them out during cease fires.

With regards to which of your powders are temp. resistant you can always ask the manufacturer. Hodgdon brands their temp. resistant powders as "Extreme". As far as I know Hodgdon does not list either H335 or CFE as an "extreme" powder.

www.hodgdon.com/extreme.html

Many of the Ramshot powders have a good rep. for being fairly temp. resistant and I do believe TAC is one of them. Reloder 15 is one of the few Alliant powders I know to have that reputation. I've read that it was reformulated to be temp. resistant years back in order to make it elligible for military contract requirements.

Also, temperature sensitivity of powders is also dependent on the application. There is a "performance window" for temp. resistant powders. If that is exceeded (sometimes referred to "stressing" the powder by using it outside of it's design window) you can lose the temp. resistant property.

"A particular powder can be improved re temperature stability for certain combinations, within a certain envelope which is specific to the following three main parameters/aspects
* The caliber.
* The weight of the projectile/bullet.
* The performance level.

If any of these parameters/aspects go beyond or outside the intended ratio/s, the results will change and the performance will sometimes be different."

www.accuratepowder.com/faq/

I know that both IMR and Alliant have been getting on the "temp. resistant" powder bandwagon lately. The new IMR powders (IMR4166, IMR4451, and IMR7977) and the new Alliant powders (Reloder 23, Reloder 26) are being touted as such.

Also,

A good sanity check for a chronograph is to bring along a .22 LR rifle. Modern .22's and ammo are very consistent. Barrel lengths are pretty standardized as well.

Most .22 LR ammo will clock very close to advertized velocity. Just this last Saturday I brought along my Marlin 70HC and some CCI standard velocity (1070 fps) and some Winchester high velocity (1280 fps) as a sanity check. The readings were pretty close, but varied more than I wanted to see. It was an overcast day and I had put the diffusers on anyway. My first 4 shots from my 6.5x55 didn't get any readings at all. Once the diffusers were removed, I got readings that appeared to be right in-line with what I expected (I didn't re-chrono the .22 LR after removing the diffusers, but I should have).

Just a thought.

Most electronics are sensitive to temperature changes, some less than others. Chronographs that use ambient lighting are also sensitive to light levels. The newer IR lighted chronographs are almost free from lighting sensitivity but do require more power to operate the built in lighting. chronographs use a very high frequency oscillator and clock to measure the pass time of the bullets and those devices rely on acurate power supplies. I modified my chronograph to use a larger battery that could maintain power levels in all but the coldest temperatures and that really helped to stabilize my cold temperature readings.
I have had my chronograph for long enough that there is no support for it and am considering getting a new one with IR lighting. There are a few that employ the IR technology and some are, quite frankly, out of my price range, but others that are affordable. I do know that I won't be going with the "Big O" because it uses the lowest frequency clock on the market. It is ancient technology and not worth the money they are asking.
Irregularities in any of your components, changes in light levels or position, and temperature changes can add up to big variations when using a chronograph.

SSL, When I was using the IMR powders I came to believe the larger case capacity the more sensitivity !!! What cartridge are you loading it in ???


Slim, Arguing with a chronograph .....my bet is the chrono is gonna win !!!
I feel your pain.... BTDT
Mine was sent back twice and compared to 3 others.....it won !!!

I also use a .22RF to set mine up and verify readings, light diffusion can be a real PIA at the range I go to.
Should I ever replace mine it will definitely be with the IR unit.

good comments and gives me more to think about. I've already bought new batteries to use but will get heat packs. Use 22 LR for verification. Will use .223, 6.8, and .270 and have some common powders to spread between them to see how quanity is affected. At least 2 weeks or more from doing this. I found another chrono to borrow and will mount mine and his in-line on the same board.

Just a thought but the most consistent rifle I have with respect to velocity is my Dianna air rifle. I wonder if it would work to check a chronographs consistency?

I haven't been able to get my chrony to read the air rifle which was strange because it reads rubber bands.

chambered221 wrote:

SSL, When I was using the IMR powders I came to believe the larger case capacity the more sensitivity !!! What cartridge are you loading it in ??

I used to use 3031 and 4895, but that was before I had a chronograph so I can't comment on them. I currently use IMR 4064 in .22/250, .280 Remington, .30/06 and occasionally .35 Remington. I use it because it has always performed well for me and, because of a rare smart move on my part, I acquired a considerable quantity of it at a very low price some years ago. I honestly haven't notice a great difference in performance tied to temperature, but then again I haven't done any specific testing either.

My experience with RL15 (a great powder) mirrors slimjim's.

I got a 54 fps increase when the temperature went to the 90+ region.

The load I use is the same one that Alliant used for the M118LR - 175gr SMK, it was published on their web site, but removed it when the US Army started damaging M14's in Iraq. The velocity is 2700fps.

I use it in a PGWDTI Coyote, a very strong action, but I'm leary about using it in my M700, even though it didn't damage the Army's Remington's, but they may have used the long action .308's.

FYI the M118LR is a very accurate round.

MAC- Yes, - I check my Chrono with an air rifle and it works well.

slimjim wrote:

I haven't been able to get my chrony to read the air rifle which was strange because it reads rubber bands.

Try painting the projectile with a Sharpie !!!
I've ran into the same issue with lead pistol bullets.