RL-26 Temperature Drift Data

[WildRose]

I have a question related to this that I would like some different perspectives on. I am experimenting with RL-26 in my .260 AI, and my charges are around 49-50 grains with heavy for caliber bullets, and I am currently using CCI BR-2 primers. I have seen other people using this powder in smaller capacity (6.5 creedmore, 6.5x284 and .243) cartridges, and so what I would like to discuss is the use of magnum primers in these smaller cases with this powder and heavy bullets. What does everyone think the possible benefits/cons would be in this combo? My use ranges from around 0° up to 80°-90°.

My concern would be that going with magnum primers might cause much higher pressures by getting a much greater volume of powder firing initially particularly in the smaller and medium size cases from .308-06.

Using slow burning powders allow us to achieve higher velocities with lower pressures because it's more of a continuous relatively slow burn that just keeps pushing all the way to the end of the barrel.

Igniting a much larger portion of the powder with the bigger flash seems like a real possibility so if I were going to try it at all I'd probably back off 2-3 grains or more and then work back up slowly.

 

[codyadams]

My concern would be that going with magnum primers might cause much higher pressures by getting a much greater volume of powder firing initially particularly in the smaller and medium size cases from .308-06.

Using slow burning powders allow us to achieve higher velocities with lower pressures because it's more of a continuous relatively slow burn that just keeps pushing all the way to the end of the barrel.

Igniting a much larger portion of the powder with the bigger flash seems like a real possibility so if I were going to try it at all I'd probably back off 2-3 grains or more and then work back up slowly.

That makes sense, it may likely result in max pressure at lower velocities vs standard primers. Anytime I switch to magnum primers I back my load off about 5% from standard primers, unless my load is already right at max then I will go more.

 

[Engineering101]

Wildrose

Alliant has data for RL-23 and 140 grain class bullets on its site. Shows ~ 44 grains will get you 2,700 and change depending the particular bullet. They also have data for RL-26 in the 243 Win which would give you a ball park for the 260 Rem. Of course now that you have discovered you really can't put too much in the case with RL-26 you have better data than they do for your rifles. The burn rate on RL-26 is just about the same as Retumbo which is pretty slow so it isn't likely you could put too much of it in anything that likes H4350 such as the 260 Rem.​

 

[WildRose]

Wildrose

Alliant has data for RL-23 and 140 grain class bullets on its site. Shows ~ 44 grains will get you 2,700 and change depending the particular bullet. They also have data for RL-26 in the 243 Win which would give you a ball park for the 260 Rem. Of course now that you have discovered you really can't put too much in the case with RL-26 you have better data than they do for your rifles. The burn rate on RL-26 is just about the same as Retumbo which is pretty slow so it isn't likely you could put too much of it in anything that likes H4350 such as the 260 Rem.​

That's where I started. Unfortunately they only list one load each for four different bullets all in 140gr. I even emailed them looking for starting loads for the 125g monometals and all they could suggest is to go to the bullet manufacturers.

Compressed loads have always made me nervous to the point of shying away from them completely for many years but my little experiment has given me a lot of confidence at least with these powders.

I may try a repeat of some of the RL26 loads tomorrow and shoot them Tuesday and Wednesday since we're supposed to be having a major warm up.

We're supposed to be about 30-40 Degrees warmer than we were Saturday so it should be interesting. I haven't seen broad swings in pressures with any of the powders I've used from 20-50F but I have seen some when temps jump from the 30's and 40's to the middle or upper 80's.

I shoot pretty much year round since varmint and predator control is a daily thing here and once I settle on a load it needs to be one that is consistent in single digit temps with frequently subzero wind chills to summer highs between 95-115.

Long ago when I ran a lot of H380 and H414 in both my 220 Swift and 7mm RM I did have some problems. Occasionally we'd have slow ignition in the winter to then turn around and have the same load blowing primers out in the summer.

I had an older model Winchester that had been rechambered from .225Win to .220 Swift which just about came apart on me one day in July shooting prairie dogs and put a real scare into me. The bolt on that model had an end cap held in place by a punch pin and the firing pin shot back so hard it sheared that pin and knocked the cap off.

I think you're right though at least with moderate temp's as I don't think I could have gone more than maybe another half grain up and still get the bullets to seat well. Both RL26 and RL23 are pretty bulky powders and fill up a case pretty fast.

I wasn't particularly concerned with the 125gr Peregrines due to the reduced bearing surface and weight but I was also loading some 143gr ELD-X's and 130gr Siroccos.

Note, I'm not recommending to others they try these powders or any others in highly compressed loads, just sharing my own experience. Use your own best judgement and always load and shoot safely.

My wife has even convinced me that when I'm doing load workups to never shoot without wearing both protective tactical gloves and shooting glasses.

 

[Engineering101]

wildrose

Let me say that it is good to be conservative when dealing with any form of gun powder and that your wife is a smart women to suggest protection. However, with knowledge you can do certain things that can prove advantageous. For example, I have had QuickLoad for years and one of the things it makes you aware of is what happens when you put a powder in a case for which the powder is way too slow because it will list loads for all powders with the top performance (highest velocity) at the top of the list. Invariably the powders on top are all way slow and load densities are like 115% or more because QucikLoad assumes it still fits in the case. (You can setup QuickLoad not to show loads past a certain compression). Anyway you then pick a powder down the list where load fill percentage is closer to 100%. Just the process of picking a load makes you aware of the performance you could get if you went with a very compressed load of a really slow powder. For certain situations I've overstuffed cases with the bullet seated to just about contact the powder then remount the press upside down to do final seating. That will get you a couple of more grains in the bigger cases without compressing the powder. Very fun with a nice performance boost since the powder takes up the space surrounding the base of the bullet before the bullet is pressed home.

 

[jb1023]

For certain situations I've overstuffed cases with the bullet seated to just about contact the powder then remount the press upside down to do final seating. That will get you a couple of more grains in the bigger cases without compressing the powder. Very fun with a nice performance boost since the powder takes up the space surrounding the base of the bullet before the bullet is pressed home.

I'm sorry but how did you mount your press upside down? Like under the bench? I'm just sitting here envisioning something like a Tommy Lee drum solo.

 

[Engineering101]

jb1023

I have a wood bench with holes for the bolts that hold the press that go through the 2 inch thick wooden bench top. Just treat the bottom of the wood bench top as if it were the top of the bench and mount the press as normal to the bottom surface.

 

[jb1023]

jb1023

I have a wood bench with holes for the bolts that hold the press that go through the 2 inch thick wooden bench top. Just treat the bottom of the wood bench top as if it were the top of the bench and mount the press as normal to the bottom surface.

I have never heard of anybody doing this before. How does this method compare to using a drop tube or vibratory device on the brass? None of my loads are compressed I'm just quite curious.

 

[Engineering101]

jb1023

I don't know how my upside down press compares to a drop tube as I have never used one.

 

[Double Dropper]

I am currently loading with very favourable results RL-26. Realistically if I shoot all summer with load A, and when the weather gets cold, double check the zero ( summer 75' F and winter -25 F) and the zero is very close or almost the same, as long as I know the velocity is there really and issue? They all shoot slower when its colder, got that, highly unlikely I would shoot past 600 yards. My ballistic calculator (200 grain Horn ELD-X @ 2950 fps 75'F) is 54.7 inches low @ 600. IF it dropped to 2875 fps @ -20 degrees the bullet drop is 59.7 inches or 5 inches @ 600 yards. I understand there are many variables but for hunting ( assuming the POI is checked under cold conditions ) is this a problem?? Shoot most people cant hold 5" difference under hunting conditions.

 

[Engineering101]

Double Dropper

The problem with powder temp drift isn't just that the velocity changes from what it was running at the range when you developed and chrono'd the load but that the change in velocity knocks your carefully tuned load off the accuracy node that you found where it was putting all the bullets into one hole and all of a sudden the groups look more like they came out of a shotgun. So if you just go ahead and use your 75 degree Summer load in the -25 degrees you mention assuming all is well it will be running some velocity you don't know and the point of impact will have shifted maybe or not depending on each individual shot. If you are shooting less than 200 yards you will probably get away with it and may never know anything different was going on. it 600 yards it might be a problem or not depending on each individual shot. In the opposite case where you are going from cold to hot you may have blown primers and a bolt handle you have to hammer to get open.

You can avoid the whole problem by adding a little powder to the load, freeze it and take it to the range to see if you made the velocity the same as it was with original ammo. Then when hunting season arrives (and the cold temps) just use the load you made with more powder and all the bullets will go where they are supposed to at the velocity you expect, end of problem.

 

[Double Dropper]

Double Dropper

The problem with powder temp drift isn't just that the velocity changes from what it was running at the range when you developed and chrono'd the load but that the change in velocity knocks your carefully tuned load off the accuracy node that you found where it was putting all the bullets into one hole and all of a sudden the groups look more like they came out of a shotgun. So if you just go ahead and use your 75 degree Summer load in the -25 degrees you mention assuming all is well it will be running some velocity you don't know and the point of impact will have shifted maybe or not depending on each individual shot. If you are shooting less than 200 yards you will probably get away with it and may never know anything different was going on. it 600 yards it might be a problem or not depending on each individual shot. In the opposite case where you are going from cold to hot you may have blown primers and a bolt handle you have to hammer to get open.

You can avoid the whole problem by adding a little powder to the load, freeze it and take it to the range to see if you made the velocity the same as it was with original ammo. Then when hunting season arrives (and the cold temps) just use the load you made with more powder and all the bullets will go where they are supposed to at the velocity you expect, end of problem.

Solid advice, I will try the idea, thankslightbulb

 

[Trentcamp]

So what's the answer? I just started load development on a Kimber 280AI 24" 9 twist. After much deliberation and some fooling around I've settled on 154 gr SST and Interbond. The so called go to powder from what I've read has always been H4831 or RL22. From info on here I have been looking forward to trying RL26 but now I'm not so sure. Several threads downing it have been posted. Several singing its virtues. I just tried RL22 with the 154 SST and 162 ELD-X and it shot better than it ever has with anything I had tried before with the SST. So what is one to do.

 

[Pdvdh]

You can avoid the whole problem by adding a little powder to the load, freeze it and take it to the range to see if you made the velocity the same as it was with original ammo. Then when hunting season arrives (and the cold temps) just use the load you made with more powder and all the bullets will go where they are supposed to at the velocity you expect, end of problem.

I'm not convinced simply freezing the ammunition will provide the same MV and the same POI in 75*F air temperatures, compared to when the rifle barrel and air temperature are also -25*F. I think the cold rifle and barrel can additionally affect MV and POI.

I'm in the midst of testing the affect of cold temperatures on MVs and POIs on five separate rifles. I allow all five rifles and ammo to drop to outdoor ambient temperature for a minimum of 90 minutes. I then fire one round from each rifle, recording bullet velocity over a triplicate chronograph setup, while also recording POI on target at 300yds. These rifles are constructed properly with quality components. So far, I suspect there's more affecting my POIs than simply the temperature of the ammunition.

I haven't created a second load, as suggested, with additional gun powder to re-gain the warm weather MV in the cold temps. I'm leery of that approach. I have a hard enough time keeping track of the proper loads for the proper rifles the way it is with a single load for each rifle. The last thing I want to do is chamber a winter load in the fall and miss a game animal with an over-pressured round. But that's another matter.

My testing is really aimed at developing more complete MV versus temperature data, determining which rifle(s) are most stable across variable temperatures, which are most stable over time at the same temperature, and possibly learning something I can benefit from for future load load development and for future hunts.

I've shot 5 separate times now, in temps from -2*F to 27*F, recording the MV and POIs. So far, I'm observing some mysterious POIs causing some head scratching. I expect the cold barrels alone will affect the barrel harmonics compared to barrel temperatures which are 50-60*F warmer. There may simply be too many variables changing for me to comprehend the cause and effect on shifting POIs. But I should at least benefit from the collection of additional MV versus temperature data for my ballistics program, and learn the comparative POI stability of my rifles over time, and in variable temperatures.