Home Forums Hunting & Shooting Ask The Gunwriters Powder Temperature sensitivity, again? With a meander on seating depth free bored rifles.

Being a shut in has increased my anal gun loonyism to the next level. I am getting ready to work up some 257 Weatherby loads and want to do it as efficiently as possible to save on barrel wear. First is there a reliable chart for velocity and temperature change? I have seen some that may have come from quick load not sure. I do realize it is relative to application. Here are the candidates how would these be ranked for stability and are there any I should just skip trying? : H1000,7828, VV165, MRP, R26, R22, R25,AA8700, H870. This is my ranking but not sure about a couple of these? Are there others I should look at? Magnum for sure if I can find some locally. R33, Retumbo, 8133, Mag Pro, any others? I know the 8700 series can have wide swings but may try it anyway since I have 4-5 lbs of each that needs to be shot up. I am betting that after all the mental gyrations the first load I try might be the winner, it has happened before. Any advice appreciated. Any other tips for the 257? This is in a Ruger No. 1 so I will have a wide range of seating possibilities, from almost no freebore to the full .386" jump. I will start with factory or whatever the load manual recommends and then go back with the longest seating and seating deeper in pretty large increments.

There isn't a reliable way the predict temperature sensitivity.

It's not the ambient temperature that matters. It's the temperature of the barrel (especially near the chamber) and secondarily the temperature of the brass and lead in the ammunition.

In the powders I have tested, good temperature compensation depends on cartridge geometry. For example, I found Varget to be very well compensated in 308, not well compensated in 7.62x54R, and poorly compensated in 223/5.56.

All of what Denton said, plus Hodgdon states the primer makes a difference as well, along with powder compression--both of which I have seen in my tests as well.

Thanks, I knew most of this but looking for easy answers that don't exist while waiting for all of the components to be shipped.

John,

What effect have you observed with powder compression on temp stability? Thanks

Compression generally helps. A good example is listed in my chapter on temp-resistance in GUN GACK III, where I listed a bunch of tests, mostly in cold (zero F.) but also some in heat. Good old IMR4350 isn't supposed to be as good as H4350, but in the only rifle I still use IMR4350 much, my Whitworth .375 H&H (mostly because I've never bettered the original load worked up for 300-grain bullets almost 30 years ago), the difference in velocity between 70 F. and zero averages 25-30 fps--which is right in there with many loads with H4350, and newer temp-resistant powders. The charge is 81.0 grains, which is heavily compressed (but not "crunched") with 300-grain lead-core bullets. The groups also land right in the same place at 100 yards/

I also used a lot of IMR4350 in the .30-06 with 165-grain bullets for many years, usually 58.5 grains. In my NULA Model 24 .30-06 this charge with 165-grain Partitions averaged a difference of around 75 fps slower at zero than 70. That actually isn't bad, but while the load fills a typical case up to the shoulder, it isn't compressed. And at zero it groups two inches higher at 100 yards than at 70 degrees.

No, that's not a typo. It shoots HIGHER, not lower, in the cold, even though NULAs tend to group most loads in the same place, due to their bedding system. This isn't unusual for loads in colder weather, when most hunters expected the POI would be lower at 100, if anything. (As I also point out in the chapter, if there's much difference in velocity between 70 and zero, POI in cold can change in ANY direction, not just up and down. In one load .270 (which lost saw it shift three inches to the right--but with that load the velocity loss was around 120 fps.

Thanks!

H1000 would be my first pick because it's one of Hodgdon's extreme powders, meaning it's temp stable. Dunno about RL26 in your case, but it's touted to be temp stable, and in alot of apps it'll give more velocity.

grovey,

RL-26 wasn't designed to be temp-resistant--but turned out to be at least OK. In my cold-temperature tests using the .270 Winchester (one of the cartridges where 26 works really well) it actually GAINED around 50 fps at zero F., compared to the results at 70. This is unusual but not unknown.

I load RL26 in only one cartridge presently due to lack of availability these days. It seems to work fine in all temps in the .300 Weatherby. It went to the same poi at 11 F as it did at 45 - 50 F last year. Happy Trails

I just don't see a downside with RL 26, other than availability- great through the powder measure and the trickler, Rocket fuel for my .270 wcf's

Hard to beat, 7RM with 160's. 3K fps with stellar accuracy...

DF

With R26 the 0-70 degree range is very good, it is the 70-100 temperature range you have to watch out for. Somewhere in the 80-100 degree range I saw a 100 fps increase with the 6.5x55. Strangely no traditional pressure signs other than slightly flatter primers. I dropped back a grain and a half and my hot weather velocity was the same as I was getting with the heavier load in cooler weather, have not gone back to see if I loose any fps in cool weather but I suspect or am hoping for an anomaly where I don't loose much.

In this situation it may be worthwhile for me to switch to R23 which can come close velocity wise but with much less temperature sensitivity.

How significant are primers and does the general rule of thumb to use magnum primers for cold weather hold any merit?

Is that true if you do load workup at 75* ?

I only did hot weather work up on that load, 6.5x55. Another load I kept it about a grain under max and it was fine in the 70-80 degree range, in 25-06, I have not tried it when it is hotter or by cooking the cases in the sun but hope to before next deer season. I also worked up loads with the 270 and no drama at all but 80-85 degrees may be the hottest I tested those so far. Need to shoot all of them at 90+ degrees to see if it is just certain combinations or an across the board increase, and to see if the 1-1.5 grain reduction changes it or just lower pressure enough but with the velocity shift still occurring?

Tejano, I guess if you worked up loads in 90* weather, I don't understand the temp sensitivity issues in 70-100*?

I'm starting to work up loads for a 300 PRC. First time out was 90 degrees. With RL26 215 grain bullets I was getting about 2970 fps with very good consistency. Came back a few days later with temp at 64 degrees and was getting an average of about 2945 fps and the consistency had gone way south. Went from extreme spreads of 13 and standard deviation of 4.7 to ES of 60 and SD of 26.1. Its not unusual to get over 90F during the summer in this area so I'm going to try some H1000 and hope for better luck. I expected velocity loss but was surprised at the drop in consistency.

ETA: The velocities etc were from 5 shot groups.

Alliant original stated Reloder 26 was not developed as a temp-resistant powder, but turned out to be. Their recent website profile says, "Controlled temperature stability." I don't know whether they actually changed the formula to be more stable or not, but in my tests at 70 degrees and zero with the .270 Winchester, it actually GAINED about 50 fps at zero.

Should add that I probably should test some newer lots of 26. My present supply is around 4 pounds, purchased when it was pretty new.

Based on a sample of only 5, that much change in SD may or may not represent real change.