Accounting for RL-15 / Temperature Swings

[Jay Christopherson]

Hey all-

Is there a rule of thumb or anything about how to dial back your loads when the temps take a big swing? I worked up a load with RL-15 in my Dasher when the temps here in the Pacific NW were about 55 - 65. No pressure issues, consistent right at around 2960 @ 34.2gr.

Then (this last week) temps swung up in to the high 80's and low 90's. I just ran out to do some bullet comparisons at my 34.2gr. load and was completely taken by surprise when my chronograph started running off readings in the 3100+ fps range. Primer's pierced, major cratering, one blown primer, all the classic signs. I ran off about 10 rounds before I stopped cause I just couldn't believe it.

I pulled the bullets on a few random rounds when I got home and double checked my measure and it came out at exactly 34.2gr as expected. Even checked it against a balance beam scale.

These loads came from the same lot of RL-15 that was producing 2966 fps when temps were around 60. So, the only factor I can find that has changed is the temp, but I'm having a hard time believing the change. 34.2gr. is definitely a little on the hotter side, but I've never seen any issues before. I ran it up to 34.5 before I backed off due to pressure in previous testing (when it was cooler). That load is a bit compressed, but not overly so.

So, I figure I just need to back off the load when it is hotter out so I was wondering if there is some sort of rule of thumb or if I just step down incrementally til I find something that works.

 

[Bobr]

Ran into the same problem with RL-15 in my .223 Ft/r gun. We shoot from Wisconsin to the Gulf Coast threw out the year, and ended up last year having 3 reduced loads on hand which got to be a pain. This years solution was to keep the larger of the loads in a small cooler with freezer packs. Maintains between 45*-50* and always gives the competition something to think about when you pull them out on the line!

 

[Jay Christopherson]

Now that's an interesting idea right there. I might have to give that a try.

 

[RonAKA]

According to Hodgdon data, you could get in excess of 1 fps per deg F. Depends on the powder and cartridge. See this link:

http://www.hodgdon.com/smokeless/extreme/page2.php#top

 

[JERRYHM]

My rule of thumb is that I do not use RL15 above 85 degrees.........Switch to Varget or H4895 depending on the cartridge.

 

[Rust]

Jerry - Could you go into a little detail on the characteristics of H4895 vs RL-15 above and below 85 degrees? What happens below 85 that you feel RL-15 is the better choice in that temperature range?

 

[savageboy]

I have wondered about the rounds in a cooler. I shoot F class in NC and it will get 100 deg and humid on an Aug. match. Any consideration on condensation (inside the case) affecting the powder when you put a cool round into a smoking hot chamber on a smoking hot day? I have heard some people talk about this consideration, however I dont know what to think. It makes sense, but wondering if there are any real world implications to doing this.

 

[RonAKA]

I have wondered about the rounds in a cooler. I shoot F class in NC and it will get 100 deg and humid on an Aug. match. Any consideration on condensation (inside the case) affecting the powder when you put a cool round into a smoking hot chamber on a smoking hot day? I have heard some people talk about this consideration, however I dont know what to think. It makes sense, but wondering if there are any real world implications to doing this.

Warm air holds more moisture than cold air, so if there was no moisture in the cool cartridge then there will be none form as it warms up. The real question would be if you loaded the cartridges on a hot humid day, and then put them in a cooler, would moisture form when they cooled off. All you really need to know is the dew point on the day you loaded them, and at that temperature water should start to form in the cartridge.

 

[necchi]

For those of us that live in humid environments, we see condensation alot, , on a soda can, a glass of ice tea..
This condensation occur's because of available moisture in the atmosphere around us, at a temprature refered to as the Dew Point. It's the specific "point" of moisture and temp.
The outside of a case is exposed to outside air and may collect moisture, the inside of a case is sealed and NOT exposed to the outside, the only moisture available is that trapped inside when we load. Yes, it can be a variable but, IMHO, a minimal one at best.
I guess what I was taught and cling too is "Don't cook'm" meaning, when the chamber/barrel get's hot, don't dally the shot once it's loaded, try to get'm off inside 5-6 seconds. It's really plenty of time if you do your prep work before hand and are in the zone.

That's my two bit's. ( ron beat me to the post whilst I was typin )

 

[Jay Christopherson]

That's interesting that you have it down so precisely (not to mention exactly what I was looking for). Mind if I ask how you came up with those numbers so I can play around?

PowderMonkey --

In my experience, to maintain your 2960-fps and pressure level from 34.1gr at 55-F to a new temperature of 90-F, you would need to drop the charge down to 32.4gr.
At 80-F = 33.2
At 70-F = 33.6
At 40-F = 34.4

Happy Shooting
Donovan Moran

 

[Bobr]

Have shoot out of the cooler in 98* 90% humidity without an issue. You will have some exterior condensation by the time you get to the last few rounds, but I only remove the rounds needed for that string from the cooler. Also do not use anything other than cooler packs, dry ice lowered the temp to low and it showed up on the chrony, regular ice did create a moisture issue.

 

[boltman13]

Here in western CO it is hot and dry. Mt HP load in 223 of 25.0 gr Re-15, Win cases, and Rem 7 1/2 primers, and Sierra 69 gr MK, does not show signs of excessive pressure when it gets hot in the summer. That load is 0.5 gr below max. I do keep the loads out of direct sunlight at all times. Some people here do use a cooler and blue ice to keep their rounds cooler. I don't know if they are using Re-15 or running hotter loads, however.

 

[savageboy]

Here in Humid North Carolina, I have shot F class matches in August where it is 98-101 deg. and humid. If I hear what you are all saying:
1. Try to load them on a less humid day- its the inside air that matters
2. Take out only what you need- 2 sighters and 20 for record in my case for 600yd F Open
3. Try to shoot quickly- a little difficult in F class depending on how good your target puller is.

If I do these things, it sounds like I shouldn't have any problems?

Did I miss anything?

 

[Bobr]

Shop where we reload has AC so 35%- 45% humidity is about average, but thats about it. Did have to use the full 20min. in the heat(poor pit service) and did find the primers to start crattering on the last 3 rounds. Next string had cooler on the line and only removed 5 at a time.

 

[kentuckytroutbum]

Shop where we reload has AC so 35%- 45% humidity is about average, but thats about it. Did have to use the full 20min. in the heat(poor pit service) and did find the primers to start crattering on the last 3 rounds. Next string had cooler on the line and only removed 5 at a time.

The cooler is the way to go on hot days. I have a small "soft" cooler that I take to the 600 yd line, and remove each round as I need it. Also, keep the ammo out of the sun while on the line will help also. The blue freezer packs are the way to go.
I've noticed that all powders have some form of sensitivity to temperature, some more than others. Even Win 748 and Accurate 2520, which I consider to be stable powders will show some temp issues on very hot days.

 

[JERRYHM]

Rust,

I'm shooting a 6mmAR Turbo 40, it like 6BR performance out of a AR.
In cool weather 60 degrees my load of RL15 gets me 2896 fps where the 4895 load runs at 2808 fps, both using the Berger 108s.

Comparing the 600 yard scores in across the course:
Feb. --- 600/RL-15 = 200-10X -- about 65 degrees
Apr. --- 600/Rl-15 = 197-08X --- about 70 degrees
June 12 600/RL-15 = 197-08X --- about 80 degrees
June 13 600/RL-15 = 197-07X --- 90 degrees, several pierced primers
July 11 600/4895 = 199-15X ---- over 100 degrees , NO problems

Maybe I could have reduced the load on the RL-15 powder, I guess it is a lack of trust with the RL in hot weather...

Yea I could have cooled the RL-15 rounds, but I did not expect the hot day.

Talk about cold rounds, I did a test where I put rounds (308s) in a freezer for a day and took them the range in a cooler, they shot smaller groups than the warm rounds. The cold rounds only lost 10 fps over the warm rounds. I did have to wipe the condensation off them before firing.

Jerry

 

[Rust]

Jerry - Exactly the sort of information I was looking for. It looks as if the increased temperatures raised pressures and pushed velocities a little past the center of the barrel node. So it looks as if for both the new .223 and .308 I'll be adjusting charge to suit temperature a little bit.

Between work and waiting on stocks, this is taking a bit longer than I was hoping for, and leaves me asking for rather than being able to hit the range and generate some of my own.

 

[RonAKA]

Is there a reason for using a temperature sensitive powder, considering the issues it causes?

 

[Rust]

Accuracy. All powders are temperature sensitive to varying degrees. If a particular powder that is a little more temperature sensitive produces the best results, some prefer to adjust the load to suit conditions provided the load is still accurate at a lower or higher charge weight. Other folks prefer to change over to a different powder.

 

[Alaska Bush Man]

Temp swings is the reason Military replaced contractor for M118LR to ATK and IMR 4064