Seating Depth Analysis--My Assessment Meter is Pegged Out.

[TF160 Guy]

I have maxed out my assessment meter for this load development and am not sure which combination I should pursue.

Equipment:

.308 Peterson Brass, CCI SRP. 231 Total Rounds. New barrel old action.​

24” Kreiger #8 Standard Match Target, 5R, 1:10 R twist, Obermeyer Chamber​

BAT VR Action.​

185 gr Berger Hybrid.​

Varget Powder​

Course of fire for OCW and seating depth at 100 yards.

10 fouling rounds. Cool 5 minutes.​

5 total rounds for each target, round robin sequential string.​

String 1: Shoot 1, 2, 3, 4, 5​

Cool 2 minutes​

String 2: Shoot 2, 3, 4, 5, 1​

Cool 2 minute​

Continue sequential string.​

Shot from a bench
LabRadar with recoil trigger.

The picture.
A, B, and C are 1 ½ inch targets for OCW shot at 100 yards seated 0.020 off the LANS.

A is 43.0 Varget;​

B is 43.2 Varget;​

C is 43.4 Varget​

From what I see the OCW is between B and C so I went with 43.3 gr Varget.

Next the seating test. Dots are 1 inch. 5 depths: -0.020, -0.030, -0.040, -0.050, -0.060. 43.3 gr Varget. On target 1 the second round went 2703. I attribute this to my loading. There was a problem in the amount thrown. Mag length limit me to no longer than -0.020 off.

My take.
Good correlation for ES and velocity for all 5. Numbers for the OCW are not far off either. The differences are in the grouping and the SD.
Targets 3 and 4 indicate to me that a seating depth of -0.045 may be the answer. However, target 5 POA and POI are good and the SD says -0.060

Your comments would be appreciated. The end state for this rifle is PRS.

 

[acourvil]

If the end state for the rifle is PRS and the mag length limit is .020, why aren’t you focusing on optimizing .020 and less?

 

[Buzzinga]

Load 43 grains of varget, set the COAL to whatever the Berger manual says, the go shoot. Forget the rest, it's a waste of time.

 

[pabrousseau]

Not what you asked but from what I have seen with the 308 rifles I've worked with before I went to far with the one bullet and powder I would try 8208 and 4895 and a sierra bullet .

 

[TF160 Guy]

If the end state for the rifle is PRS and the mag length limit is .020, why aren’t you focusing on optimizing .020 and less?

Cannot jump less than -0.0200. COAL becomes too long for magazine.

 

[TF160 Guy]

Not what you asked but from what I have seen with the 308 rifles I've worked with before I went to far with the one bullet and powder I would try 8208 and 4895 and a sierra bullet .

Already committed to Varget and Berger. This is a rebarrel so my shelf is stocked.
Thanks

 

[acourvil]

Cannot jump less than -0.0200. COAL becomes too long for magazine.

Ah, sorry, I was thinking about it backwards. Have you tried longer jumps? I had a rifle that shot best with a .120 jump. Not sure how deep that puts the bullet; the 185g bullet is probably pretty long for the .308 case (I’m guessing, sold my last 308 in favor of a 6.5 a while back). Otherwise, your results all look close enough that I don’t see any clear advantages.

 

[ShtrRdy]

Is there a reason you limited the range of powder charge weights tested?

 

[OREGUN]

First, .2 grains is half a percent of total charge weight. That’s a tiny little bit to be looking at. So saying there’s a difference between a, b, and c is a stretch. Maybe, but how did you get there and why not look for a bigger range that groups well than .4 grains. It’s not my method but I would be looking for at least .5 grains to fall into an “acceptable range”. To say it another way, if any of those loads are giving you the speed you want and aren’t close to overpressure, pick any of them and go nuts.

Regarding seating depth, exactly the opposite of the above…i think you have sliced that too thickly. Pick one you like, it sounds like you are excited about the 4-5 spots. Reshoot that range say 4 groups of three for 12 total. Look for two depths that seem to group ok, pick the longer length and be done with this.

At this rate, you are going to use up your barrel looking for a load, give yourself a stroke, and none of this will make you a better PRS shooter.

 

[OREGUN]

BTW, es/sd have more to do with your reloading technique than your seating depth so trying to correlate seating depth and chrono stats is a fools errand. Throw accurate charges and deal with your neck tension and your es/SD will drop. YMMV. Don’t blow your face off.

 

[TF160 Guy]

First, .2 grains is half a percent of total charge weight.

Agree. .2 gr was the second step. First pass was .4 gr. Didn't show it as it was not relevant to my current question.

Regarding seating depth, exactly the opposite of the above…i think you have sliced that too thickly.

I tried Berger's recommendation for a seating depth test.

How to Load a Hybrid Bullet

Berger Hybrid Bullets were designed to be easy to load and tune to your rifle. Follow these simple steps to get started.

bergerbullets.com

Reshoot that range say 4 groups of three for 12 total. Look for two depths that seem to group ok, pick the longer length and be done with this.

And this may be the solution. Thank you

 

[Doom]

Let me make some comments that may go against the grain. For the most part your SD numbers aren't telling you much other than you are loading very consistent ammunition and I would not make any decisions on which loading is better. Just not enough data and the numbers are so low they challenge the resolution/accuracy of the chronograph.

Looking at the targets I don't see anything conclusive and it's puzzling to me. Your POI group to group seems very consistent and I would say you seem to be shooting very well but the groups aren't as small as I would expect. Could be that you are getting off and getting back on for each shot or possibly the scope crosshair thickness or too much magnification. Don't take this wrong but I think this rifle is much more accurate than the shooter. Anyway, I 'd pick a load and seating depth and shoot it at 200 or 300 yds and see how it does. If it holds up then go with it until it doesn't.

Just for grins and giggles if it were me I would load a few rounds at 2.800" or 2.820" COAL and see what happens.

 

[MarkyMark007]

your groups are ALL the same. just pick any your load; they all shot the SAME.

if you test for powder charge and seating depth, take LARGE steps. like at least 1gr of powder and 0.050'' jump.