1st OCW - Help Please

[sawgunner2001]

I've been trying like hell to get a GA Precision LR-308 (DPMS receivers, 20" barrel) that I bought used to shoot decent. I originally found a load with 178gr Amax's that shot *okay*, but found that the primer pockets were shot after only one or two firings. Obviously these were overpressure. I tried backing the load down and tried the 175gr SMK, but couldn't find a decent load at sane pressures. I ended up putting the rifle in the closet for a couple years. Of note, prior to today, I have only ever done ladder testing at 100, 200, or 300 yards depending upon which range I was at.

Fast forward to today. I bought some 155gr SMK's (2156) and figured I'd give them a try. I also figured I'd give this "OCW" test a try. I watched the video by 8541 Tactical on youtube and did as he said and loaded up the charges in .2gr increments up to estimated max load rather than 1% as Dan Newberry originally came up with. Ultimately I loaded charges from 44.0gr of Varget up to 46.0gr Varget in 0.2gr increments and fired them at 100 yards in round-robin fashion. If it makes any difference, I loaded the top round of the magazine and the bottom round of the magazine with a cartridge that wasn't being tested and fired it off target so that each of the rounds tested would load and eject in the same fashion and try to eliminate that variable. The velocities are:

44.0: 2661 fps
44.2: 2680 fps
44.4: 2691 fps
44.6: 2711 fps
44.8: 2722 fps
45.0: 2715 fps
45.2: 2728 fps
45.4: 2739 fps
45.6: 2752 fps
45.8: 2777 fps
46.0: 2775 fps

The 45.4gr group is all in one hole. The spot to the lower-left of the aiming point is just a discoloration in the cardboard. The question I have is, where do I go from here?

 

[scissorhands]

I think the 45.4 looks like a good load. Now move back a bit and see how she shoots. Nice shooting!

 

[sawgunner2001]

Thats definitely the tightest group of the bunch. But the preceding load of 45.2 is nasty lookin'. Maybe load up 45.4, 45.5, and 45.6 and shoot them with the hope that 45.5 is the center of that node? I'm looking at 44.6. It seems like it's smack dab in the center of an accuracy node and only sacrifices 28 fps. But that's why I asked...

 

[scudzuki]

Thats definitely the tightest group of the bunch. But the preceding load of 45.2 is nasty lookin'. Maybe load up 45.4, 45.5, and 45.6 and shoot them with the hope that 45.5 is the center of that node? I'm looking at 44.6. It seems like it's smack dab in the center of an accuracy node and only sacrifices 28 fps. But that's why I asked...

An OCW is not about the tightest group, it is about what I call "grouping of groups".

Overall there's not a lot of movement in your entire OCW but I agree that 45.4 looks to be the center of the only node I see, running from 45.2 to 45.6. It's hard to ignore the fact that it's one hole, even though it's not the point of the OCW test, it's certainly convenient that it's the center of the node. I like to go in .3 grain increments and span at least 3 grains of total charge weight on .308 size cartridges, but that's just me.

Joe

 

[shoot4fun]

Although you may have a node at 45.4 it appears to be very narrow. I would agree that 44.6 looks best. That node seems to be much broader, at least to me. I assume you are shooting from a bipod here? A mechanical rest will take a lot more of the doubt out of shot placement.

 

[sawgunner2001]

Although you may have a node at 45.4 it appears to be very narrow. I would agree that 44.6 looks best. That node seems to be much broader, at least to me. I assume you are shooting from a bipod here? A mechanical rest will take a lot more of the doubt out of shot placement.

I tend to agree with this. I'd like to go a little beyond 46.0gr, but that's a compressed charge already and I'm afraid compressing it further may damage my Redding adjustable seating die.

Keep the opinions coming folks, I'm new at this OCW testing and don't want to put this rifle back in the closet for another two years out of frustration.

 

[Rem7targetactical]

44.6 and try another 10 or so off sandbags. Same results? Then play with seating depths to see if group tightens up.

 

[Dan Newberry]

44.5 grains might be worth a second look.

I don't think 45.4 will be repeatable... the center of the 45.2 grain triangle would be around where 45.4 all hit, but that's just not a convincingly good place to be I don't think.

Something else to consider is that when your groups are forming 2 or 3 inches high of point of aim, unless you're carefully leveling the scope for each shot, there can be some arcing of the shot impacts (as you tilt the scope left or right). With a crease on the cardboard, or other such line on the target board, we can sort of unwittingly line the vertical crosshair (or horizontal) on that line... then as we move across the board, it can happen that we tilt back the other way. If your bipod doesn't have a swivel function, then this probably didn't happen from the bench. But with a swiveling bipod, it's an easy thing to let happen without a level. Not saying that happened here--just mentioning that it can be an issue when groups are forming well high of point of aim.

In the interest of not pushing it too hard, 44.5 might work out very well for you...

Dan

 

[sawgunner2001]

1st OCW - Help Please

Thanks all. I'll get some more brass prepped, zero the rifle, and take y'all's suggestions back to the range again later this week. I'll probably focus in the 44.5"ish" area, as I think that's where the most consistent load is, and maybe load a couple around 45.4"ish" and take it from there.

I forgot to add, these were fired with bipod up front and bag to the rear from the prone. The bipod used was of the swivel variety, but any cant induced due to lines in the target would have had to have been subliminal. I focused rather steadfastly in making good shots for the duration of the exercise and don't recall ever even seeing the lines.

Thanks again for the suggestions.

 

[rookie101]

my understanding of the ocw test is to find a load that has a little forgiveness, for temp, whatever other uncontrollable variables there are. Your 44.5 area is about the same above and below that charge weight, which I think is exactly what you are looking for. Plus that's what Dan said.

 

[savageshooter86]

re test and make sure all your targets are on a level line. That way POI will be easier to distinguish. Some targets are higher and some lower than others. Which makes the groups appear to be off . I would re shoot 44.0 up to 45.2

OCW gives you a "window" of charges where you have forgiveness. Whether that be to powder charge being slightly off or temp affecting it.