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6BR Powder Temperature-Velocity Responses

BillC79

Gold $$ Contributor
I am posting some of my data that may be of interest to others.

It is time for me to work up a match load for my re-barreled 6BR rifle. I want to use a powder other than Varget and screened several powders for velocity responses across the temperature range I normally shoot in North Central and Central Florida (40F to 95F). Temperatures during a match can easily vary 30 to 35 degrees F.

I selected among powders I had on hand as well as Reloader 15 which is a favorite among other 6BR shooters.

I used methods from my other powder temperature sensitivity studies with .308 Win (link) and 223 Remington loads (link) as well as other 6BR tests (link).

Results are summarized below. ARComp gave the flattest temperature-velocity response across my normal shooting temperatures. Lovex S062 (Shooters World Precision Rifle Powder) gave the second best response, although shot to shot variability was higher than that for other powders.

fig1.jpg
table1.jpg


Comments/suggestions are appreciated. Thank you for looking.

Addendum: March 30, 2022 @ 6PM EDT
Specific Methods for the above data were posted HERE.
 
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I feel vindicated.

AR COMP is essentially flat and R15 is crazy as a March hare... Wait until you get that R15 over 100 degrees... Zoom!!

Ummm... Yup.

Which agrees with the chart I posted here about 4 years ago... The one you linked too here.

Awesome test, btw. One test ends a lot of speculation. Why these tests do not seem to interest anyone is quite odd to me...
 
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Are these the same lots of powder you used in previous testing?
The Varget powder is a newer lot than I used in the 223 Remington cartridge tests. ARComp and S062 tests used the same lot of powder. The RL 15 is a new purchase lot. I’ll write up the methods in more detail with lot numbers of powders used.

I almost didn’t do these tests since I assumed that temperature-velocity relationships for the powders would be very similar between the 223 cartridge and the 6BR. The slopes of the temperature-velocity relationship appear to differ slightly between powder fired in the long and narrow 223 Remington case and that in the short and fat 6BR case. Part of this apparent difference in slope may also be because I tested a more narrow temperature range with the powders in the 6BR tests (3C to 36C) than in the 223 tests (0C to 55C).
 
I am posting some of my data that may be of interest to others.

It is time for me to work up a match load for my re-barreled 6BR rifle. I want to use a powder other than Varget and screened several powders for velocity responses across the temperature range I normally shoot in North Central and Central Florida (40F to 95F). Temperatures during a match can easily vary 30 to 35 degrees F.

I selected among powders I had on hand as well as Reloader 15 which is a favorite among other 6BR shooters.

I used methods from my other powder temperature sensitivity studies with .308 Win (link) and 223 Remington loads (link) as well as other 6BR tests (link).

Results are summarized below. ARComp gave the flattest temperature-velocity response across my normal shooting temperatures. Lovex S062 (Shooters World Precision Rifle Powder) gave the second best response, although shot to shot variability was higher than that for other powders.

View attachment 1329107
View attachment 1329108


Comments/suggestions are appreciated. Thank you for
How did you conduct your test? Was the powder heated and cooled then shot? Or did you conduct the test with actual ambient temperature changes?
Bart
 
How did you conduct your test?
I’m writing up the methods for a full report that I’ll post on my website and reference here in the near future. I used methods similar to those for the powder temperature sensitivity tests that I ran with 223 cartridges. I posted the link to the study in my first post. A link to the specific methods in that 223 test are HERE.

Briefly, I put the cartridges in water-tight 50ml centrifuge tubes and hold the tubes in water in Yeti Rambler 36oz vacuum insulated bottles at the desired temperature for 2-2.5 hours before loading and firing the cartridges over a chronograph.
 
It is a powder temperature test...

What would be very cool is to do the ambient temperature test after. Isolating those two viarables.

Because they are separate variables. Not one variable. As many people mistakenly think.

Obviously, changing the range temp 60 degrees is much harder proposition. However, now that you have established that AR COMP is essentially totally insensitive you could test over a period of time.

Cold air is thicker and slower. Hot air is thinner and faster. Then there is the pressure too. These are all SEPERATE variables.

But eliminating the powder variation would be step one, and would immediately offer a competitive advantage.
 
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I’m writing up the methods for a full report that I’ll post on my website and reference here in the near future. I used methods similar to those for the powder temperature sensitivity tests that I ran with 223 cartridges. I posted the link to the study in my first post. A link to the specific methods in that 223 test are HERE.

Briefly, I put the cartridges in water-tight 50ml centrifuge tubes and hold the tubes in water in Yeti Rambler 36oz vacuum insulated bottles at the desired temperature for 2-2.5 hours before loading and firing the cartridges over a chronograph.
That’s what I thought. If you re-shoot the test in the actual ambient temperature as it increases you’ll see a lot larger changes in velocity. For example I’ve watched Varget increase 40 to 50 foot over a 20 degree increase in Temperature.

Temperature isn’t the only variable that effects burn rates but it is a main culprit.

Bart
 
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The Varget powder is a newer lot than I used in the 223 Remington cartridge tests. ARComp and S062 tests used the same lot of powder. The RL 15 is a new purchase lot. I’ll write up the methods in more detail with lot numbers of powders used.

I almost didn’t do these tests since I assumed that temperature-velocity relationships for the powders would be very similar between the 223 cartridge and the 6BR. The slopes of the temperature-velocity relationship appear to differ slightly between powder fired in the long and narrow 223 Remington case and that in the short and fat 6BR case. Part of this apparent difference in slope may also be because I tested a more narrow temperature range with the powders in the 6BR tests (3C to 36C) than in the 223 tests (0C to 55C).
Interesting to see a negative velocity correlation with your 223 tests with comp and 4166 and with the same lot (of comp at least) positive trends in 308 and 6br.
 
Interesting to see a negative velocity correlation with your 223 tests with comp and 4166 and with the same lot (of comp at least) positive trends in 308 and 6br.
AR-Comp is made by Eurenco Bofors AB and is the rebranded, packaged version of RP-34TZ. RP-34TZ induces increased velocity at lower temperatures in .308 Win as shown in the attached Bofors catalog data. I found that AR-Comp induces higher velocity in 223 Rem at 0C than at 20C.

I ran my tests with 6BR in a temperature range that I shoot in Florida (no lower than 3C) to see if this cold-induced increased velocity would be a problem for me shooting in Florida. It isn’t a problem with 6BR cartridges based on my data. I have shot AR-Comp with 80 gr 223 match rounds that performed well at 20C, but showed pressure signs at 4C. I am guessing that the difference is based on how AR-Comp performs in a narrow, long 223 cartridge case compared to a short, fat 6BR case. Perhaps others can explain the difference in behavior of explosives packed differently.

RP34TZ.jpg
 
it also gave the lowest velocity.
if you shoot is stable temps, rl15 is ok....i have a national championship with barts bullets to prove it.
low velocity maybe ok in prs but not in long range be
look at the right side of middle and three are about the same..but still too low
 
nice test, but for those reading this is , it is not a bible, maybe not even a tool.
unless you are shooting the same the info may not relate to your ammo and rifle.
what pressures were seen in the test ? powders vary in burn characteristics based on pressure.
different pressures,, different results are POSSIBLE.
my 105s at 3025 with rl15 at 75 to 85 so well but in a dasher not a 6br
the details count
 
Thank you for posting this. The timing is perfect as I am trying to build a load for my 2022 F--class load with AR-Comp. It just helps to boost my confidence.
 

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