Hot temps and load reduction

This is my first summer in Central Texas. I know my winter developed loads are hot - seeing some pressure signs (difficult in extraction, but not bolt lift). To save time, is there a general rule of thumb for how much I should adjust a winter to a summer load, ceteris paribus? 5% less powder as a starting place? 10%?

 

Personally I'd start about 1.5-2 gr lower and work up in .3 increments and re shoot a
OCW test and find your sweet spot.

 

Based on what you are saying you need to find a lower node. How much you need to drop down will depend on caliber, powder, and current charge. What is your current caliber and load?

I like to operate at the lower nodes to avoid these problems.

 

I am not a precision shooter so there's that but I have seen a .6 grain difference in charge weight in my 30-06 165 grain bullet with IMR 4350. The temperature range is from 48° to 91° F.

 

My temps go from 30 below zero to the high 90s,so at least 120 degree difference . For the all-weather loads I use H4895 . I find if I develop my loads in the fall and tune with the lowest node I am safe all year round . I just shot some loads I developed in the the fall and it was 90 degrees,no signs of pressure but I am sure POI was not the same as in the fall.

 

I develop loads with ammo kept in front pants pockets. This WARMS the ammo.
When I go hunting/shooting, I keep enough ammo in my pants pocket, loading and shooting single shot.
This so far seems to take my ammo to a standard regardless of outdoor temperatures.

If I were a BR shooter, my ammo box would be controlled with heating rather than cooling.

 

I shoot benchrest 308 caliber , my shooting season temperature goes from 50° on up to the 90's . I load to the lowest node . I don't change anything my POI raises with the temperature .

 

Collected data to velocity & pressure from ladder testing will yield what the powders speed and pressure characteristics are per increment, that then can be applied to powder adjustments as need be for ambient control. Adjusting the powder to maintain one same speed is often enough.

For an example, with one of my petloads the velocity changes 6.7-fps per 1-tenth of powder on average. Can slow down or speed up the load by adjusting the powder in accordance to the rate found in a ladder (just another aspect to load development that makes ladder testing so great).

Having ladder test data from 2 different temperatures (like at say 45 and 75) is all that is needed to get a good handle on a loads sensitivity.

 

The issues I was having are with 6.5 Creedmoor. 123g A-max over 41.3g RL17.

 

I experience pressure surges in my 22 250 using H380 ball powder. I was only using 38.0 grains with a 55 grain bullet but in the summer heat of 90's I was getting hard bolt lift and ejector marks on the case rim, a sure sign of high pressure. I moved away from ball powder to Varget / IMR 4064 (stick powders) and the pressure surges disappeared.

Since I hunt all year around, varmints in the summer - predators and deer in the fall and winter I've switched to stick powders which seem more resistant to temperature changes. However my point of impact does change from winter to summer which may be more due to air density changes that powder stability.

 

External ballistics and internal ballistics are separate and different.
For internal, your load will have to be developed near conditions you shoot. There is no getting around that.
It's not just powder temps, but also barrel temps.

I warm up summer barrels to summer temps, while in the winter, before assigning credit to results.
And as mentioned I keep the powder/cases at approximately the same temps for both conditions.

 

Had the same problem with RL.17, 6.5CM and 130 gr. here in Central TX. Gets hot and so does the load. RL 17 is very temperature sensitive.

 

A lot depends on the powder you use. I'm using rl33 and seen a 100 fps increase from about a 40⁰ temp change. My barrel is almost new so it might play a part in some of the speed, I plan on testing further once the barrel has more rounds on it. Generally, I always do load development on a hot day to eliminate the issue but this is the first time doing it this way.

 

Texas10 is correct. I've had issues with RL17 once it warmed up in my .260; google it, it's not uncommon at all.

If you have it available, H4350 and H4831sc would probably be a lot more stable for your application. For example, a 6.5CM load I have only deviated 10FPS from the middle of January until now on H4350 shooting a 142 SMK (CenTex shooter as well).

I know Alliant makes good powders, but because of the weather swings we have in this area, I pretty much stick 100% to Hodgon Extreme/IMR Enduron. I've been burned too many times by Alliant. On an ironic note, it's funny how Alliant has 'Extremely Temperature Stable" printed on the outside of the keg (at least mine does).

 

Texas10 and Mike McCasland: Thank you! This is the kind of real world experience I was interested in gleaning.

I have

 

I have and regularly load H4350 but thought I'd try another powder to give me another option. I hadn't had the same heat sensitivity in RL15, but I'm going to reconsider the use of Alliant powders other than in the cooler months.

Re primers: I use cci200 primers in my centerfire rifles, using magnum primers only in my 6BR. Maybe other primers might work better, but cci200's work well for me.

 

K22
I'm using IMR 4064 only for many years , I wouldn't thing loading at the low load using any brand would cause a pressure problem . In the beginning when searching for that accurate load I tried 3 powders , Varget , RL-15 and IMR 4064 . IMR worked best for my rifle . I know your not new to reloading but are you jumping or jamming your rounds ? Temperature changes from 50 to in the 90's will cause my rounds to group still tight but raise with the rise in temp.. As the weather gets warmer the groups range 1.5" at 200 yards no big deal I don't adjust the scope , just POA . At two hundred yards it isn't much . My case Headspace is .001 - .002 no more or less with a .002 jump . Mine shoots best with alittle room .

Chris

 

CW308: I'm jumping my rounds, .010-.012 for my 6.5CM.

 

Work up a new load

 

When it gets stinking hot,have dropped powder charge 2-3 tenths of a gain,once in a while 4 tenths,Only way to tell is shoot it,look at your groups,especially at distance.If they open up,back off