Establishing Combustion/ Powder Charge 308 Win.

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CKweigand

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Jan 9, 2018
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Location
Greenville, Illinois
The Setup:

RCBS Rock Chucker
Hornady FL sizing die without Expander
21st Century Expander Mandrel .306''
RCBS Chargemaster 1500
Hornady Bullet Seating Die

New Unfired PPU Brass
Federal 210 Primers
Varget Powder
Berger #30418 185 Gr. Juggernauts seated @ 2.242'' CBTO

Tikka Tac A1 308 Win.
24'' Bbl 1:11 Twist

So I'm working on a load with the above mentioned bullet. I loaded up rounds .020'' less than Max mag length. All I'm trying to do at this point is find a consistent powder charge. Not looking at groups just yet. in fact the 24 rounds that I tested I just shot in the dirt over the chrono.

I loaded 24 rounds starting at 38.2 grains of Varget and worked up to 42.8 in .2 gr increments. No pressure signs were detected.

Here are the results...

38.2 - 2314 fps
38.4 - 2349
38.6 - 2358
38.8 - 2352
39.0 - 2378
39.2 - 2373
39.4 - 2353
39.6 - 2381
40.0 - 2404
40.2 - 2462
40.4 - 2461
40.6 - 2467
40.8 - 2486
41.0 - 2501
41.2 - 2521
41.4 - 2533
41.6 - 2554
41.8 - 2615
42.0 - 2610
42.2 - 2576
42.4 - 2622
42.6 - 2591
42.8 - 2639

Looking at the above results I'm considering retesting the 40.2- 40.6 and as well the 41.8-42.4

However, If I were to settle on the data above and not retest I would probably go with a charge weight of 40.4 gr. and from there tune the load to the rifle via seating depth.

I would like to see a higher velocity though as I'm considering entering PRS and knowing that some shots would go past 800 yds I'm thinking faster velocity would help me in less mils of elevation that far out. But I wanted to open up to you guys and see what you would do with the data given or how you would interpret it. Again, I'm thinking 40.4 is the way to go as of now and then load 5 at the given seating length. and then 5 more .003" deeper in the case and so on and so on until I find a consistent node that provides the smallest group. Should I try to go faster? re-test the 41.8-42.4 group? What would you do with the data given? Thanks.

CK
 
Agreed. Next go around I think I’ll load three of each charge weight from 41.8-42.6 grains
I want to squeeze out some more FPS if I can. The 2461 at 40.4 just seems too slow for me to settle on.

CK
If your putting the rounds down range shoot a ladder test while getting the crono data... more data points for the same amount of expenditures.
 
Odd variations like that are well documented. It happens. Richard Lee discusses it in "Modern Reloading". Handloading is science, it is not an exact science.
 
***Update***

I did some more testing today before the rain settled in. The overcast was just right to take advantage of with my Caldwell Chrono.
Catridges tested were loaded from 40.2 gr. - 40.6 gr of Varget in .2 gr increments...Then the next round of cartridges were from 41.8 gr. - 43.0 gr. of Varget again in .2 gr. increments... I increased the parameter to 43.0 grains in hopes I might discover another node or see signs of one present.

This go around however, I did three rounds of each powder charge just to see maybe a correlation in groups as well, kill two birds with one stone.

FINDINGS:

40.2 gr - 2475 fps
40.2 - 2417
40.2 - 2432
40.4 - 2459
40.4 - 2457
40.4 - 2468
40.6 - 2435
40.6 - 2483
40.6 - 2472

41.8 - 2547
41.8 - 2578
41.8 - 2562
42.0 - 2560
42.0 - 2580
42.0 - 2572

42.2 - 2567
42.2 - 2570
42.2 - 2568

42.4 - 2574
42.4 - 2582
42.4 - 2578
42.6 - 2612
42.6 - 2621
42.6 - 2617
42.8 - 2582
42.8 - 2599
42.8 - 2607
43.0 - 2629
43.0 - 2612
43.0 - 2639

I think its interesting that the first range of loads (40.2 - 40.6) in my initial testing, looked very promising. However, the level of consistency I'm looking for wasn't very repeatable when I started shooting three shot groups. I wasn't heartbroken though because even if this turned out to be a consistent node it still wasn't the velocity I was looking for.

the rounds loaded with 42.2 gr seems to be the ticket. Very consistent and repeatable. This should result in very low ES/SD.

All this being said I can see a pattern in the loads from 42.0 gr - 42.6 I think I could pick a charge weight in this range and still be able to fine tune a load for my rifle very easily. It's just that 42.2 being the most consistent, why stray from it?

I was shooting all the above rounds at 200 yards. It was interesting to see the groups go from 3-4'' groups to 3/4'' group and back to 2'' groups. Its nice to see a correlation with the velocity because at 42.2 gr I achieved my smallest group. Something to be said about consistency = accuracy. I feel pretty spoiled in receiving these results, it came easily, and now with some fine tuning and small changes in seating depth I think I can get amazing results. Though I know this was pretty lucky it was nice to gain some confidence in my load development methods and practices. Thank you everyone for the input and suggestions. It worked out very well.


Next step:

Shoot out to 300-400 yards and start changing seating depths in .003'' increments.
Starting with 5 rounds seated at 2.242'' (CBTO)
Then another 5 seated at 2.239"
Another 5 at 2.236'' and so on.
hoping to stay sub 1/2 MOA and establish a seating node.
 
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I was trying to quickly review your numbers prior to reading your review and came up in the same ball park. I would move to seating depth tests at 42.4. Or you could run a primer test at the same point.
I would graph the numbers because a visual works better for me for deep analysis
 
Shoot a couple five shot groups over the chrono with both 42.2 & 42.6

20 more rounds.

Try to find a calm evening and be consistent shooting from group to group. Inconsistent shoulder pressure can not only cause vertical in groups, it can affect ES/SD numbers.
 
Considering( Barrel life matters) and now that you have determined your charge window would you say a lesser amount of components are in order as you move towards seating depth testing.
 
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Considering( Barrel life matters) and now that you have determined your charge window would you say a lesser amount of components are in order as you move towards seating depth testing.

this is just my two cents. Take it with a grain of salt. This is what works for me...


I definately want to make my steps count for sure. I can see me loading another thirty rounds and having a “standard load” to go by afterwards. In less than a hundred rounds I’m confident I’ll have the result im looking for. Ladder tests can definitely rack up round count. But even as unorthodox it may seem I’m looking in hindsight now, the first 24 rounds that I’ve shot out of this barrel were probably the most important. Someone might say I wasted them by shooting in dirt or you could say I didn’t shoot enough in each weight. However, by shooting them in the dirt and only one per charge weight. I’m keeping myself from having any false inclinations or biases as to what might shoot well or be a good group and then I find myself going down a rabbit hole chasing a load that just isn’t there. By getting a broad idea at first and then finding my plateaus in velocity. I can expand on this and open up my parameters to a specific range/ranges of charge weights. And if I see repeated results I know they must be accurate. (Accurate as in reliable data)

Anyone can take a measurement. But simply taking a measurement by itself means nothing. We have to be able to repeat the said measurement in order to have an accurate measurement

That’s why I’m not scared of racking up round count. If sending more rounds down range means I can have better data that in the end allows me to have repeatable results and a load I can tune with along my barrel life via seating depth. Then that’s what I’ll do.

that being said it was a virgin 308 barrel when I purchased it and I have plenty of components stockpiled to last from over the years. And after all I expect I’ll be able to put thousands of rounds down it before I have to worry about barrel life.

Jim, I hope that somewhat answered your question. If not let me know. I might have just rambled on for nothing lol.

CK
 
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Thx ' much appreciated response, the virgin barrel probably needs a few rounds and maybe a hundred before you see it speed up and stabilize or perhaps it already has, plus your brass is still expanding.
Hope ya don't mind me trolling a bit I'm taking mental notes on your load work up. Yeah I agree the repeatability is definitely vital I know I wouldn't get far without it.
Thx again
J
 
In a 308 I believe worries about barrel life to be a minimal consern. If we were talking about a barrel burner like 243 or 22-250 maybe. In our current environment maybe component availability being a primary consern. If this is the first barrel used in an effort to learn it's never a loss. Opinions vary widely and just enjoying the adventure is the real goal of life and shooting for me.
 
They all burn up , I have a dollar that says the Op has done this before and not speaking for the PRS guys but I venture to say they go through a lot of barrels despite caliber. For myself there's always a balance between testing a few components then developing the load and barrel life.
I don't want to de rail the thread so apology to the op
 
No worries Jim. I’m working an outage all this month at a power plant, working 6/12’s. When I can get back to shooting I’ll give another update. Thanks everyone for being supportive and very helpful. I appreciate it whole heartedly.
 
It is not just velocity that counts. Got to take into account standard deviation and extreme spread, especially for the long shots... Then find the sweet spot the barrel likes .
You can't miss'em fast enough to kill'em :rofl:
 
Also it’s not the trajectory that demands velocity.
Elevation is easily repeatable, and readily calculated.

It’s time of flight as it relates to windage that’s significant. The longer the time of flight, the greater the wind deflection.
Based on what I see from your limited data, I’d just go with 42.6 and try different primers and seating dept to optimize, then go practice!
 
Totally understandable. And also trying to take in account what kind of kinetic energy such velocities bring to the table is also being considered in this.
 
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