Heat sesitivity of RL-15

[Ackman]

Ok, let's get REAL. A 40* temp difference isn't that much......60* is mild weather and 100* is just slightly over body temperature.

 

[bheadboy]

I have used RL15 in 7br at lower velocity, crono each loading, bullet lot etc. i find just as much variation in velocity with bullet lot, primer lot as i do with powder due to temp. All said, Rl 15 will spike with 95f temp vs 65f here in Ga at IHMSA locations. giving as much as 50pfs higher vel at 95f vs 65f. I adjust clicks in elevation to offset on hot summer days.

bheadboy

 

[Groundhogwhacka]

Saturday I got out the chrony and the rounds I had loaded for the 6.5x47 with RL-15. Had some running around to do in the morning so I sat 5 rounds out on the deck in the shade, and left 5 rounds in the cabinet in the basement. Temp in the basement is 65F and outside temp at 2:00 when I started shooting was 95F. I saw an average of 176fps difference between cool rounds and hot rounds. With noticably sticky bolt lift on the hot rounds. Plus group on hot rounds opened up to about an inch from the .410' cold group. Not saying everyone would have the same results, but its enough proof to get me looking for a different powder. Have some loaded up with VV N540 but need to get them to the range to see how they shoot. Velocity should be comparable.

 

[cliffy]

Perhaps RL-15 at 60 degrees and H4350 at 100 degrees will balance out with the correct powder grainage for each application. Just a tried load difference with 90 grain .243" fare (namely) called Swift Scirocco II attempting 3350 fps at the muzzle in a 24" barrel .243 Winchester. I prefer H4350 powder as an all-around powder regarding 90 grain fare, except in FRIGID CLIMES. Cliffy

 

[Fred Bohl]

I do not pretend to an expert on propellants. However, all the references that I can find show that "burn" (combustion) rate is proportional to the absolute temperature.

The attached chart shows the temperature scales. For absolute temperature the Rankine scale is the one in Fahrenheit degree increments.

For the values discussed in the posts above, 60 F = 519.7 R and 100 F = 559.7 R or a 7.7% increase. This is very little compared to the 3200 to 3400 F = 3659.7 to 3859.7 R during combustion or about a 700% increase.

The "burn" (combustion) rate is modified by a combination of grain shape and coatings which yield the various different types/characteristics available. I wonder if any development effort and manufacturing control is actually devoted to the extent the temperature "sensitivity" to that 7.7% change or is that a marketing "feature".

Since air density and the resultant drag force is affected by the same temperature change (also absolute temperature) how much of "on target" changes are attributable to each?

 

[Skeeter]

I agree with Ackman.

I use RL15 in my 220Swift, 22-250, 6BR and 6Dasher and have not witnessed any change in velocity or accuracy on any of my rounds based on temperature swings between 70 degrees and 95 degrees.

My usual loading,test firing and sighting in for my varmint season is in late April. Then I shoot groundhogs in late May and Prairie Dogs in June and July. When I test fire at the range a few days before my hunt neither the groups nor velocities have changed since my original sighting in done back in April.

Skeeter

 

[Benjerman08]

If r-15 IS temp sensitive, does that mean r-25 is also? I recently thought it was, but after chronying I found it is time to anneal my brass anyway so I am not sure.

 

[squirrelduster]

We have done some heat comparisons with RE17 and RE22 using a chronograph.
What we found was that the good load for the 300 win mag that we developed in the spring had over 100fps gain in the summer and it was borderline on pressure in the summer. The bolt lift was pretty hard.
The RE17 I was using in the 7-08 had the exact same issues.
Bottom line is if you are shooting deer or pigs at a reasonable range you most likely will not notice a difference. If your target is smaller such as a p. dog or ground squirrel at a longer range some of your misses will be attributed to pressure variations.
One of the bench rest guys I know had a record group in a 6mmbr using RE15 and two months later at the same range with the heat up 30 degrees he shot a really nice 7 inch group at 1000 yards. Pretty poor from sub 2 inch match winner.
The data definitely supports temperature instability and if you don't see it you are not using a chrono or shooting at long ranges. It may not affect how successful you are shooting in the dog fields but if does exist.

 

[cliffy]

Chronographs don't lie: feet-per-second at the muzzle (or within 10 feet away) give the truest indication of actual velocity available. True, also, is that chronographs are impractical while hunting. The time to use a chronograph is at a rifle range while working on developing a great load to use
afield later. Without a chronograph, my loads would be pure guesswork. I use RL-15 powder a lot, in certain select loads. Sometimes, H4350 works better with slightly heavier bullets, and, regarding 105 grain .243 bullets, RL-22 works even better yet. Cliffy