RL26 in 7mm Rem Mag Update

[MAinAR]

After testing up to 73.5 grains in 7mmRM with decent accuracy across the load weights from 70 to 73.5 with the 140AB's here are some more notes that may help anybody using it.

*Although no real visible pressure signs it was stretching primer pockets at about 72 to 72.5 grains (didn't realize until I went to decap).
*Primer pockets really loose above 72.5 grains but did not back any primers out at shot up to 73.5 grains.
*Target max velocity with 140 bullets at 3,200 to 3,250fps max and pressures should be good.
**If brass life is your game will need to back it down more.

Shot this target yesterday at 200yds with 71.5 grains (this is over book so start at about 68-69grains and be careful to watch speeds and pressure signs), this was the most accurate load tested at 100yds while checking velocities in THIS gun, which is looong throat Remington Sendero SF1, that has always been very slow!

Velocities on this load in THIS gun when checked with magnetospeed:
3216, 3202, 3198, waited 30min for cool barrel then 3206
AVG 4 shot 3205fps
SD 7.7 ES 18

Norma New Unfired Brass
140AB
71.5 grains RL 26
OAL 3.26
Fed215GM primer

There is an "imaginary" hole "penciled" on the target because I made 1 click left after shot #1, then shots 2 and 3 with no wait between. All 3 shots made in total of about a minute. I included both target measurements, the actual 3 shot and the corrected 3 shot due to the click left after first shot (yeah I know this is "hypothetical" but the process has proven in the past for me for evaluation purposes.)

Either way I am done testing this powder and will be loading some up to check temp stability now over time.....

200yd target
Actual target


"Hypothetical" target due to 1 click left after shot #1.

 

[DrMike]

Informative data set. If temperature stability meets your expectations, you're good to go.

 

[SJB358]

Seems pretty good.. I'd like to try some soon. Always been a fan of Alliant powders, pretty sure I'll like these two even more if they are temp resistant.

 

[MAinAR]

RL23 seems to live up to marketing hype of temp stability so far in what I have tested but in the 7RM the RL26 has beat its pants off on the target. Some of consistently smallest groups I have ever shot.

RL26 advertised as 0.5fps per degree of change................and may well be with heavier bullets.

BUT, with 140AB in 7RM RL26 at 71.5 grains is changing more like 1 to 1.4 fps per degree, still manageable. My testing has been from 40 to 80 degrees. Next test will come from the ice chest with cartridge temp about 25-30 degrees. Then the jury will be in.

I do temp checking with Infrared Thermometer.

 

[SJB358]

Good deal. I wonder if you'd need to make the rifle somewhat cool as well. Just thinking if the rifle is 90* and the cartridges are 30*, but the time you put the cartridge in the chamber, it would seem to heat the cartridge up fairly quick.. Maybe I am a little crazy though, I tend to overthink stuff once in awhile.. :grin:

 

[MAinAR]

Good deal. I wonder if you'd need to make the rifle somewhat cool as well. Just thinking if the rifle is 90* and the cartridges are 30*, but the time you put the cartridge in the chamber, it would seem to heat the cartridge up fairly quick.. Maybe I am a little crazy though, I tend to overthink stuff once in awhile.. :grin:

Yes I want the ambient temp AND gun temp to be below 40degrees and even then got to load and fire it quick or cartridge temp will climb due to convection from the chamber to the brass real quick.

Actually would prefer gun temp to be in low 30's........ didnt' mention this before cause lot of shooters blow it off.

i.e. have shot frozen load in warm barrel and see fps "nose dive"

but then

shoot same frozen load in real cold barrel and speeds not fall off even half of what did when frozen load shot in warm barrel.

So the plot thickens, WHY did this just occur.

We think of bore diameter as a constant its just NOT. Cold barrels contract, tighten up whatever you want to call it. ALL steel contracts and expands. Tighter the barrel faster the load when using slow burners.

So when I am testing really slow burn rate powders I often see them make as much or more speed (or at least not fall off as bad as predicted by fps/degree would indicate).

So if you want real world speed checks they have to be done in real world conditions i.e. hunting for 4 hours in below freezing temps. There is no way to truly mimic this except let gun sit loaded for adequate length of time, loaded, and then check speeds.

Barrels warm really easy and quick, just running your bare hands along the barrel can raise temp several degrees in just minutes and any sun on the barrel warms it quick regardless of ambient temp.

It is really difficult to get barrels cold, I have left them outside over night in freezing temps and them still be 5 degrees above ambient.

Put it in the truck and drive and hour to range or hunting location and barrel temp will be in the 60's at least. Lots harder to cool barrel than to warm it.

Bottom line freezing ammo and shooting in a warm barrel without the cold barrel contraction factor is just not true data. Gun ammo ALL has to be cold to get real readings.

 

[preacher]

You guys have asked/answered the question I've always had on cold barrels/hot barrels/ammo temps. I don't agonize over it but its great to know. I love to shoot, so I work up loads in all kinds of weather/temps. Because of this experimenting I have never had a problem in the field either. Its a fun hobby but one does learn a lot. Most fun I had in the Army was a stint in Fire Direction Center for an 8" howitzer unit, Germany, back in '72. I learned all kinds of neat stuff concerning the effects of spin drift, earth's rotation, weather, ambient powder temp, etc. You would think I'd really be into long range shooting, but I just never have, ha. As mentioned before I am one poor judge of the wind out past 300. A howitzer is a different critter, ha. We shot those 8 inchers in Hot summertime 90's down to minus 40...we figured data with hand held slide rules, once a grid was called in. I did everything from driving the track vehicle, to RTO to charts and computer ( manual, in your head computing!) and getting a weather update every 30 minutes in code, and every time a change in "variation from standard" you plugged in. Plus, nothing will put your war face on like witnessing a Corp size 2 minute Time on Target on a bunch of old trucks! wow! After the regular army, I was put in the Texas Nat'l Guard, a 155mm M109 Unit. I swapped back and forth from Gunner to FDC in 107 deg Ft Hood summertime, rattlesnakes and a million ticks/chiggers! wow! The best time to shoot/work up/play with loads is When You Have the Time!