powder temp sensitivity question(s)

[Thelaststraw]

From digging around on 6.5Grendel and a few others it appears Leverevolution is in the same ballpark as CFE223. Is 1.6 per degree a decent estimate? Also, does the velocity loss start and progress in a linear manner from a certain point, 70 degrees perhaps? And finally does this diminish at any particular temperature? 

  I've had good results with LVR so far but it's getting to that time in the Gulf South where 20-30 degree swings can make a big difference in ballistics. Wouldn't be a big deal for me normally but I'm going to a class in Nov and don't want to have to deal with any more variables than I have to. The only temp stable powder I have currently is H4895 and I think it may be a little fast for 105VLDs. Found lots of data on everything but LVR and I don't know if it's as big a deal as the napkin math says it could be. Thank you in advance.

[grayfox]

what barrel length?
The Hdy gas gun data has H4895, TAC, and Varget, for a workup they should all get you to about 2500 max ft/s in a 20" barrel for a comparable 105 bullet.
My compiled data for powder sensitivities shows CFE to be about 1ft/s per degree.
But as an editorial comment, IMO the powder-temp studies were probably done for a common cartridge like the 308, so for that capacity size maybe the numbers are right... but, my opinion, it would be difficult to just simply go 1 for 1 down to a smaller and more efficient cartridge like the grendel, or 6 Arc. Just my 2 cents, but the sensitivity in these smaller cases, anybody's guess. Probably in a similar ratio among the powders however.

CFE has been known to spike in really hot temps, IIRC perhaps 90*+, something like that.

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Edit to add: depending on what distance you're going to, might consider some of those berger 95's, currently available on ammoseek. You can get some more speed, and XBR is in there too.... for my 20" barrels they shoot about ~120-150 faster than the hdy data for a given load and pill. Just luck of the draw I guess.

[Thelaststraw]

Sorry, I neglected barrel length. Currently a 20" monster but have a a 24" barrel coming soon from CLE. I didn't take into account cartridge size/efficiency and that makes total sense now that I read it. My question on the H4895 was in regards to it's functionality, since I assume the max published load is due to case fill mainly. In comparison to LVR in a 6ARC I take it my best chance of getting solid data for my case is the old fashioned way of chrono during some colder temps and see for myself. I'm hoping it proves usable since I've got pretty comfortable with it so far and I have no experience with extruded powders yet. Thank you sir, very helpful as always.

I had thought about 95s also, the course is out to 1000+ and group depending they will go farther. All I aim for is to keep up reasonably as most will have custom bolt rigs. The instructors welcome gas guns as all three are ex army/marine snipers so they have a certain love for gassers.

[grayfox]

A 20" monster barrel should get about the same +MV from the hdy tables (120-150) as I'm getting, with both a faxon and a monster. Give or take.
As a single data point, the "data" on RE-17 is 1.42 ft/s per * so I did my own test, bringing a cooler packed with ice and did it in summer when temps were in 80's (I think)... anyway over the range 40-80 the MV loss that I saw was more like 1 ft/s per *, from my mgtospd data. That was with 6.5 CM in my rifle. So yeah, my feeling is the speed losses may not be exact altho similar in ratio or in magnitude-order...
My simple ballistics app says a 105 BTHP hornady would start transonic at about 900 yds when initial MV is ~2500... ~1240 at a grand. yours could be similar.

[Thelaststraw]

I appreciate the information. My load development has been done in 88 - 95 degree Louisiana heat so I'm safe there. If I won't be looking at too much more than 1 fps per degree at say 50 degrees it may be tolerable. I'll do more load development during some cooler weather coming up and give the H4895 a shot and see what it gives me.

I've heard it said that temp sensitivity is cartridge dependent but never understood how or why. Thank you for the help.

[StoneHendge]

I used CFE 223 extensively in 6.5G for several years. I loaded 30.8 gr with 123 gr Scenars and that was right near the limit for my somewhat tight chamber (22" JP). I used 2560 in my ballistics app. I was in the mountains of CO and had about a 7 month shooting season and would shoot from temps of about 50 to 90. Ammo storage temp was relatively stable at 65-75 degrees and I was generally able to keep it out of the sun at the range. It ran around 2640 or a little slower on the cool days and up around 2580/2590 on the warm ones. If I was on one end of the temp spectrum it would take a few shots to adjust the dope at 1k (which is a lot closer at 7k ASL than it is at sea level). 

When I moved to Arizona, I knew that load wouldn't work and would need adjustment, especially since I was about to start competing. I ended up deciding upon 30.4 gr which ran 2600 at 95°. I shot just one of the old 30.8 that day and it ran 2660 with a seriously flattened primer. I loaded 100 up for my first match expecting an average temp of 95, and it ended up being a day that was actually cloudy with a temp of around 80. I was all over the place. Best estimate is that I was running 40 fps slow, but the worst part was that my zero shifted and accuracy blew out to about 2 MOA.

The moral is that it gets extremely sensitive and the curve steepens once you get above 90 degrees. It's hearsay, but I've heard similar reports of a steepening curve down around freezing. I personally have sworn off all ball powders, but recognize that I do live in an extreme climate with a 12 month shooting season.

Is the course your taking a practical shooting type course? I don't want to assume so, but have some insight that would make you comfortable with H4895 velocities if it is.

[Thelaststraw]

Is the course your taking a practical shooting type course? I don't want to assume so, but have some insight that would make you comfortable with H4895 velocities if it is.

 Yes sir, it is a PR1 course with CR2 and Frank Galli. I suspected that any velocity loss was strongly offset by the consistency. I may use the 95s with the H4895 and not have to constantly be checking DA/temp on top of wind. 

 Not sure how accurate this is but I've heard single base powders tend to burn a little slower than burn charts may lead people to believe...is there any merit to that? I would like to learn the why's of powder selection for given cartridges.

[grayfox]

Charts are not really much good for anything IMO than somewhat relatives among the various powders. And I have not heard of single base burning "slower than the chart"... however, I have seen MV differences, thus burning difference of some kind, from equal loads of same powder but 2 different lots. Ex, for 123 sst and 1 lot of AR comp, 28.2 will give me 2510 fps. A separate lot of AR comp will give me 27.4 and 2520 fps - in that lot a 28.2 gave me 2580 and flattened primers. 0.8 grain delta means ~2-2.5% burning difference. Other powders, with 2 lots, might be much the same (I have a couple of H4831sc's like that). I don't know a rhyme or reason, you just have to do the chrony's yourself and see what they do in your rifle.

[Thelaststraw]

Gotcha, still learning what are hear-say myths and factual stuff. I have seen differences in lots before and always buy a bunch each time, bullets, powder etc to hopefully eliminate that kind of thing. I appreciate ya'lls patience and help when asked such elementary questions, not all forums have that kind of atmosphere.

  I'll be keeping the LVR for the summer months since it's always stupid hot down here and its pretty reliable in my experience. In the meantime I'll be milking the little H4895 I have until I can find more or other viable substitute single base powders for the off season where we get 20-30* temp swings.

[grayfox]

Yeah the real problem with h4895 is it’s only made in Aussie and right now, zero output, I mean zero.

[StoneHendge]

TLS, you'll be absolutely fine in the 2450-2500 range. If it's like other courses, you'll spend most of your time in the 400 to 800 range. They always advertise the 1k since it's a milepost and you will get it, but I doubt it will be the focus. I did the JP PR1 with an 18" Grendel and factory Amax with a BC of 2.3 something at 2450 and got plenty out of it - and I did get the 1k. Don't go crazy on worrying about equipment - you need to be prepared, but the one thing you really learn is what you really need. Don't worry about the bolt gun guys with their bolt thingies either. You'll have an advantage in some ways by having less recoil, but you'll never have their velocity or trigger lock time - and they don't have to deal with a bolt slamming back into the battery as your trying to spot your shot and maintain your position. (I personally enjoy that additional challenge).

With respect to single base powders, I hate to let out my secret, but I am now firmly in the crowd that believes Shooters World Precision is BETTER than Varget (which they unabashedly state that it is a clone of). I don't have any loads that would be apples to apples comparisons in terms of accuracy and SDs, but I give a small edge to Precision and it is also as temp insensitive and meters better. Plus it's made in a country (Czech Republic) that isn't under a seemingly permanent lockdown like Australia. With my H4350 jug getting a little light, I tried it with 123 grain Scenars in my 6.5 CM PRS match rifle and got this with 3 shots per charge (top is velocity, middle is SD and bottom is ES). 
   

All groups were a little under MOA with Magneto strapped on. They were also done with a Chargemaster drop only - I've been struggling to get an SD of 10 with my latest keg of H4350 when I trickle onto a balance beam.  I worked up more in the middle range and did this with 37.9

   

It was off a slick cement bench and the first group was with the big aiming point (I used that since the rifle is zero'd to my current (now former) 130 load. The big aiming point is harder and some of the vertical dispersion was me, but it's still about 0.75 MOA. The big ragged hole is 5 shots and measures about 0.4 MOA, and if it was juxtaposed on the other, they'd be right on top of other. The main point is that Shooters World Precision rocks! Just don't tell anyone else - let them keep fighting over the dribs and drabs of Varget that make it to our shores. I'll note that I didn't even bother with the other charges I dropped - at 2870, that's flatter than the Berger Hybrid 130s I was doing at 2740 and has no practical difference in wind drift out to 1k. I'll use them for practice.

I also saw Alliant Reloder 15.5 on the shelf of my local supply store, so it's finally hit the market. It's also the same burn rate as Varget and has a special coating to reduce temp sensitivity. I have no idea as to bulk, but it has to be similar since they use Varget as a reference point. It's made in Sweden. I contemplated grabbing a pound, but decided against it since I'm more than happy with what I have in that class.

[Thelaststraw]

Wow, thank you. That's a ton of information and I really appreciate it. I had talked to one of the instructors over the phone for a bit a month or 2 back but we didn't get into too many specifics. I'm pretty comfortable out to 800 but have no dope past that so it's all new ground for me. I appreciate the reassuring of the velocities since I figured needing about 150-200 more for a safety net. I know that I don't know much, hence the class and goofy questions here. 

  I'll look into the powder and get some chrono numbers myself as suggested. Thank you for all the help.

[Thelaststraw]

Just an update since I go5 my new upper going.
24" compass Lake Criterion +2 gas
SA gas block
H4895
Berger 105VLD
26gr 0.030 jump
Temps were 46F
10 shot string unsuppressed
2626 fps
6. SD
16 ES

Tightest group I ever shot. That varmint contour is heavy! Rifle didn't budge. The rest were hovering under and over 1" groups. All prone which I'm not set up good for. LOP and scope height set for positional mainly. I'll get some pics up when I get home.

Thank you Stonehenge and Grayfox.