Min ladder test temp for TAC/69gr

[triggerjerk]

Hope I haven't asked before and forgotten since I've loaded this combo before, but I'm fixin to do it for a 7 twist this time. So:

With TAC allegedly being so temperature sensitive, does anyone have opinions on minimum temperature for load workup when later temps could easily be upper 90s (69gr rmr, wsr primed)? Don't want to break my 16in mid AR this summer, but it's only early Spring, and I'm anxious to get started. Gonna be almost 80 (Fahrenheit!) this week....

[BobinNC]

TAC in a .223/5.56 may not be as temp sensitive as you think.

Interesting read:

https://www.handloadermagazine.com/rifle-powder-temperature-sensitivity

[1168]

How temp sensitive a powder is or isn’t can be dependent on a variety of variables beyond just the powder used. For example, you might not be able to load up 23 gr and measure the temp sensitivity, then extrapolate that to a 25.5gr load. There’s also one (fairly thorough) internet article suggesting that some of what we think of as powder temp sensitivity might actually be primer temp sensitivity.

TLDR: plan on 1-2fps/degree F for ball powders, with 1.5-2 being pretty common. So if you measure it now, you might expect to see a gain of 20-40fps midsummer. I do most load workups around 90*F to minimize risk, and do so in my “tightest” barrels.

[markm]

There’s also one (fairly thorough) internet article suggesting that some of what we think of as powder temp sensitivity might actually be primer temp sensitivity.

Word Up! Primers can completely change the pressure curve of a load with all things else held constant. I really have never had luck with the ladder test stuff.

If I were... (and I usually have to be)... worried about temp swings, I'd work a load that had 100-200 FPS upside cushion from a 5.56 load with crimped primers. For example, when I used to shoot W748 and 55 gr fmj. I'd shoot for 3100 fps out of a 20" gun to leave me some margin for error/hotter temps.

[1168]

Word Up! Primers can completely change the pressure curve of a load with all things else held constant. I really have never had luck with the ladder test stuff.

If I were... (and I usually have to be)... worried about temp swings, I'd work a load that had 100-200 FPS upside cushion from a 5.56 load with crimped primers. For example, when I used to shoot W748 and 55 gr fmj. I'd shoot for 3100 fps out of a 20" gun to leave me some margin for error/hotter temps.
Exactly.

With some manuals, there’s a bit of a cushion because the max load was worked up in a minimum dimension .223 Rem chamber, and our ARs don’t usually have those. Of course, we can’t rely on that because: a)some powders seem to get squirelley near max b) some manuals are actually quite hot, like Western’s 5.56 section* c) lot-to-lot variation and d) we don’t really know how much the pressure will change with temp, or what our average/max pressure is, as handloaders, because we can only measure pressure indirectly, and likely have not even done that.

There can be benefits to using slower or predictable powders, or just giving yourself some margin, and they don’t always show up on paper.

*I did a workup with Tac and got flat primers and spicy recoil well before book max, using Hornady 55 fmj.

[joedirt199]

I am settling around 24.2-24.3 with my 68 and 69 loads. I load them short 2.23", I was just starting to get decent ES's in the 20s around 24.2.

[223to45]

Exactly.



*I did a workup with Tac and got flat primers and spicy recoil well before book max, using Hornady 55 fmj.

Well, depending on the data source, 25gr of Tac is toward the upper range in one book, and toward the lower range in another.

Just started playing with Tac, so not sure yet which one is more correct

Sent from my SM-G991U1 using Tapatalk

[1168]

Well, depending on the data source, 25gr of Tac is toward the upper range in one book, and toward the lower range in another.

Just started playing with Tac, so not sure yet which one is more correct

Sent from my SM-G991U1 using Tapatalk The data source in this case was the powder manufacturer’s book. Western Powders max listed charge for 5.56x45 NATO and Tac is so high that I don’t even want to mention it here. 10% or more higher than multiple editions each of Hornady*, Nosler, Speer, Lyman, Berger, Hodgdon, and probably others I haven’t looked at lately.

You’ll be fine with any book but Western (or just ignore the 5.56 section if you’re using Western) using Tac. In my limited experience flirting with the upper end of Tac, it behaves more like 335 than BL-(C)2 or CFE223. I thus accept its limitations as an economic rifle powder and stick to moderate loads, and avoid letting a trend line in my workup bait me into greed.


*Hornady lists both .223 and 5.56 loads tested in separate, appropriate barrels, and their data works well.

[triggerjerk]

New component lot has always meant new workup for me. Accuracy/pressure signs, not velocity for me. That said, a season or 2 ago, I had worked up an accurate Shooters World Match Rifle/SMK load when temp in mid 70s. New load workup in mid 90s led to pressure signs maybe 1/2 grain less than previous load. Kinda woke me up.....

Guess I'll get test loads ready and just prep brass until temp closes in on 90 before I choot 'em....

Previous 69rmr loads have been 24.9 TAC with WSR and 24.2 with AR Match....

[1168]

New component lot has always meant new workup for me. Accuracy/pressure signs, not velocity for me. That said, a season or 2 ago, I had worked up an accurate Shooters World Match Rifle/SMK load when temp in mid 70s. New load workup in mid 90s led to pressure signs maybe 1/2 grain less than previous load. Kinda woke me up.....

Guess I'll get test loads ready and just prep brass until temp closes in on 90 before I choot 'em....

Previous 69rmr loads have been 24.9 TAC with WSR and 24.2 with AR Match....
No real reason not to make twice as many test loads now and shoot half at 70* and the other half at 90* or 95* later. Then you’ll know what to expect come fall. Maybe you’ll luck out and find a load that works in both conditions and/or have some data to extrapolate (weakly) to other temps.

Who am I kidding. I’m too lazy for all of that.

[triggerjerk]

Test in 70s then again in 90s? Heck, I'm already 50 rounds in for a test. Between a .3gr ladder starting a couple of gr shy of max to seating depth testing after that, I wouldn't have enough ammo left for bottles and cans! Besides, I'd just lose my records and forget what I came up with!

[markm]

Test in 70s then again in 90s? Heck, I'm already 50 rounds in for a test. Between a .3gr ladder starting a couple of gr shy of max to seating depth testing after that, I wouldn't have enough ammo left for bottles and cans! Besides, I'd just lose my records and forget what I came up with!

BINGO! We shoot too many loads in too many guns for this crap. I sometimes envy the guy who has one or two guns that he can carefully master and shoot in an organized manner.

I now have Sierra load data stickers all along the front edge of my loading bench so I can quickly refer back to a successful load. I can't tell you how many times I've tested a load, failed to log it, and had to start all over again a week or two later.

[1168]

BINGO! We shoot too many loads in too many guns for this crap. I sometimes envy the guy who has one or two guns that he can carefully master and shoot in an organized manner.

I now have Sierra load data stickers all along the front edge of my loading bench so I can quickly refer back to a successful load. I can't tell you how many times I've tested a load, failed to log it, and had to start all over again a week or two later.
I make two cards ea out of primer boxes and put them in the ziplocks inside ammo cans or buckets with the ammo. Brass goes back in the ziplocks, more or less.

Most of my loads are used across the fleet of guns, though some are made with a specific gun in mind.