help! .308 load development

[SOcalsurferx]

So I am attempting to develope "the perfect load" for my freshly built .308 Win. Its a Surgeon short action with a 24" Krieger SS MTU contour - 1-11" twist, Nightforce NXS 5.5-22x glass with NF rings all sitting in a AICS 2.0 stock. So for my load development, I started with three bullets, 155 gr Lapua scenars, 168 gr Sierra Match Kings, and the 175 SMK's. I am using Lapua cases, fully prepped, all using Varget for powder. I initially loaded 15 of each bullet ( 3 different powder charge weights, 5 each) for a total of 45 rounds to test today, so it looked like this:

QTY. Bullet Powder weight
5 155 Scenar 41 grains
5 155 Scenar 43 grains
5 155 Scenar 45 grains
5 168 SMK 40 grains
5 168 SMK 43 grains
5 168 SMK 44 grains
5 175 SMK 40 grains
5 175 SMK 42 grains
5 175 SMK 44 grains - Started to see some signs of pressure here, flattened primers.

All were loaded with Varget, The SMK's were loaded to COAL of 2.800 and the Scenars were loaded to 2.795" All were shot out of new lapua brass with Wolf primers.

I shot at an indoor 100yd range so there was no wind, mirage, etc. I started with a clean barrel, fired 2 fouler shots and proceeded shoot groups for the first bullet wait (3 groups of five) after this I cleaned the barrel lightly, let it cool and repeated this process for the other two bullet weights.

I am now wondering where to go next, It seems that my rifle likes the 175's moreso than the others, the 175's showed the most consistently tight groupings, although two of them I knowingly pulled the shots, resulting in the two flyers.

I have attached the target, anyone with any advice, please feel free to chime in whether it be advice as to how I should proceed or whatever.

 

[alf]

All I see is red x's.

I do thing a little different.

In a 308 sized case, I go a grain at a time, and always shoot 3 shot groups. Still 15 rds, but say from 40-45 grains or 41-46. I think two grain increments is too much.

Also,I never do load work without a chronograph either. I'd be lost.

 

[Gearheadpyro]

I can't see any pictures, only x's.

I wrote an article on my website explaining how I do load development. (http://www.rifles-shooting-reloading.com/load-development.html) I do load development without a chronograph, but only because I don't have one. I'm sure things would be more accurate with one.

The 11 twists seem to like the 175's, not sure about the others.

 

[dreever]

Find the OAL length to engage the rifling, then compare it to your maximum magazine length which if you are using an AI mag it's 2.900. You may be able to seat bullets at, or into the lands. Scads of .308's like bullets seated right at or just before the lands. In my rifle which is similar to yours I'm using 43.0 grains of Varget Sierra 175's and CCI 250's in Lapua brass with excellent results. 2657 fps, E.S. 10, S.D. 4 seated .012 into the lands. The Sierra 175's aren't picky so in or out of the lands they should work pretty well untill you find their sweet spot for optimum accuracy.
Watch for pressure signs as seating into the lands can raise pressure. If you are seeing pressure at your 44 grain load, then you don't want to try that load in the lands. Back off and work up. Safety is ALWAYS first.
Danny

 

[SOcalsurferx]

Sorry bout the pics, they are fixed now, hopefully!

 

[Laurie]

I agree with all the suggestions you've been given - some very good avice there. Two grain steps is far larger than you should use apart from maybe initial pressure checks. As you fine-tune your loads, drop to half grain steps with 3-round groups, then if needed, do a super-refinement in 0.2gn steps with 5-round batches, around the charges that gave you the smallest groups.

You don't say what ranges you plan to shoot over. At short ranges you only need tight groups. As range increases you want the most ballistically efficient bullet that suits the rifle added to a respectable MV (to reduce wind deflection) and you also need small velocity spreads. (I assume you don't have have access to a chronograph as you haven't put MVs on your shot targets?) The reason for small MV extreme spreads at long range is to reduce vertical dispersion, that just doesn't show up at 100 yards. Ideally, you need to know what your MVs are if you shoot much beyond 300yd, so as Alf says a chronograph is a really useful bit of kit - tells you other things too such as whether your loads are mild or you're 'pushing the envelope'. You can do without and still shoot at say 600yd, but you may find that your performance then isn't as good as your 100yd groups suggest it should be, and you'll not know why.

In my experience with the cartridge, the 175gn Sierra MK is a very good all-rounder for short to medium ranges ballistically, and is usually an easy bullet to get good groups with. If you're not shooting beyond 600yd, it may well be worth concentrating on it. If you want to shoot at longer ranges, I'd suggest having a go with the 185gn Berger Match BT Long-Range (not the VLD). Assuming pricing is similar where you are to here (the UK), this is a more expensive bullet than the Sierra, but it does perform very well indeed and is very efficient ballistically with an exceptionally high BC. As it retains a tangent ogive form nose/shoulder, it is easier to tune loads and less sensitive to bullet seating positions than equivalent (secant ogive) VLDs.

Laurie,
York, England

 

[Mikem]

All above are great suggestions.
And if this will help, I have a 26" 1 in 12 twist barrel, and when shooting 168g SMK, Lapua brass, Fed GM 210M primers, and using 44.0g of Varget, I get 2680 fps MV. 44.5g gives me 2710 fps, I consider this my max for this bullet and powder, and its my most accurate load, .2 to .3 @100, when im having a good day.
Mike.

 

[SOcalsurferx]

Thanks for the help. I was leaning towards using the 175 SMK's for the high BC (.505) as I do plan on doing some distance shooting. I have access to a chronigraph but I didnt even think about what Laurie said in regards to the ES and vertical dispersion at distance, makes perfect sense! I did some more searching and decided I need to stop and focus on one bullet for now, that being the 175 SMK and develope the load for this. I will go back and use the OCW method starting at 8% under max charge weight and work my way up in 1% increments till I get upto max and look for the signs, groups, placement etc. I am trying to stick to doing my load development at 100yards becuase the 100yd range I go to is completely enclosed, eliminating enviro factors. After I find the sweet spot for the powder, I will experiment with seating depths, etc. I just purchased a bullet comparator and the Sinclair seating depth gauge to help me out a bit. Also, as someone mentioned, as now my New Lapua brass is fire formed, I will neck size it and hopefully that will help out a bit as well!


One last question, is there any need to neck turn Lapua brass? and also, I have a bunch of once fired Winchester brass that I have prepped, should I stick to one brand of brass only for my load development or is it ok to switch and load a batch with the Winchester brass?

 

[alf]

I turn my Lapua brass. How much depends on your chamber/ loaded round dimension.

Do all your load work with the Lapua for now. After that you can see how the Win stuff compares.

Good move on limiting the variables for now, but don't discount the 155. That's the bullet I chose in a set up that's a twin, almost, to yours. Mine run 2930 and stay super to beyond 1000. Not that I'm gonna play that far.....

 

[SOcalsurferx]

Thats also part of the reason I am looking into the 175, I believe they are supposed to stay super beyond 1K as well, correct?

I am going to focus on the 155's next. I think part of my problem is I dove in too deep at first. too much to factor at one time.

Thanks!

I turn my Lapua brass. How much depends on your chamber/ loaded round dimension.

Do all your load work with the Lapua for now. After that you can see how the Win stuff compares.

Good move on limiting the variables for now, but don't discount the 155. That's the bullet I chose in a set up that's a twin, almost, to yours. Mine run 2930 and stay super to beyond 1000. Not that I'm gonna play that far.....

 

[Laurie]

Forget the 0.505 BC value for 1,000yd shooting - that's based on the G1 drag curve model and the results it produces are overly dependent on what speed the bullet is travelling at. Results aren't too far out for shooting at up to 600yd, but will be over-optimistic for the 1,000yd range.

G7 curve based BCs are much better. Bryan Litz's book Applied Ballistics for Long Range Shooting explains all this and has the various bits of data for around 175 long-range match and sporting bullets, all obtained by measuring velocities in flight over long ranges. He also includes a G7 based PC ballistics program, to input the data into.

the 175gn SMK needs 2,700 fps MV to remain reliably supersonic at 1,000yd in 'standard environmental conditions' 59-degrees F; 29.92" mercury air pressure - so more velocity needed on a cold winter's day; less shooting at Raton 6,000 odd ft altitude at 80 degrees in high summer. You really want more than just enough to stay supersonic though as bullets suffer from buffeting as they drop into speeds just above the sound barrier (1,122 fps at 59 degrees etc) and that often increases the drag to cause them to be braked substantially after hitting 1,200 fps or maybe even a bit more.

The 175 SMK is a very well designed bullet and does perform well. It is not outstanding BC-wise however. That's why I suggested the 185gn Berger Match BT Long-Range if you're considering 1,000yd shooting. At 2,625 fps MV which is the equivalent of the 175's aforementioned 2,700 fps, the 185gn Berger is claculated to still be travelling at 1,286 fps at 1,000yd, 142 fps more than the 175/2,700 combination. It also sees an 18% reduction in wind deflection at this range again using these two MV values.

Both will stabilise in 1-13" twist rate barrels, although 1-12" is a slightly better bet for the 185gn Berger.

Laurie