.308 OCW Interpretation Help

[DFenn]

This was my first go at performing an OCW test. In the past I've always loaded up charges at different intervals and picked the load with the smallest group.

The load: .308, 165 grain Hornady SST, Varget, Federal Brass, CCI 200 Primer, seated to 2.805 OAL

The rifle: Remington 700 SPS in an HS Precision stock with a Vortex Viper PST 2.5-10

I shot the rifle prone with a bipod and a rear bag, and the rounds were fired round robin.

It looks like there may be a node between 44.9 and 45.2, but I'm not sure. I don't know if I'm reading the results properly. Any help in interpreting this is greatly appreciated!

 

[Dan Newberry]

There is too much dispersion here to get much out of, probably owing to the Federal brass, which is not well suited to repeated reloading. If you anneal the brass, it's much easier to work with and gives better neck tension uniformity.

In spite of that it seems likely that there's a useful node at mid 44's... maybe try 44.5 grains (with the FC brass)... but anneal before your next loading session. Even though FC cases may be once fired, they seem to benefit from a light annealing, possibly because the factory annealing is not as thorough as it ought to be.

Dan

 

[DFenn]

I was afraid that it might be inconclusive. I thought maybe I was missing something. I have some once fired Lake City brass prepped up, and I'm going to try and run the test again tomorrow. It looks like I will be relegating my FC brass to plinking loads.

Thanks for your help Dan.

 

[Dan Newberry]

The LC brass should behave a lot like the Federal, as to where the nodes are... the capacity is very similar (though the LC is a little heavier).

Check the vicinity of 44.0 to 44.2 grains for a good, workable node with the LC.

Dan

 

[DanSavage]

One thing I do when I get results similar to yours is make a seating depth adjustment, then test again.

 

[DFenn]

I didn't have time yesterday to load up and shoot a full test again with the LC, but I did have time to get out and try and shoot some quick groups. I loaded up 4 rounds at 44 and 4 rounds at 44.2 with LC brass and an OAL of 2.805" just to see if anything was there. Both groups shot similar to the test target. For giggles, I loaded up a few rounds with 42.8 grains of IMR 4064 with both LC and FC brass. Both shot poorly. Just to be sure it wasn't me or the rifle I shot three rounds of 168 grain FGMM and they cloverleafed.

One thing I do when I get results similar to yours is make a seating depth adjustment, then test again.

I think you might be right and a seating depth adjustment is in order. I've shot these 165 grain SST's over 45 grains of Varget at the same OAL through my Mega Ma-Ten with an 18" Black Hole Weaponry barrel and they shot just as well as 168 grain A-max's, easily sub-MOA.

 

[jdgray]

I would shit can the bipod, re test off a sandbag or front rest.....

 

[DFenn]

I decided to take the 45 grain load and see what difference, if any, adjusting the seating depth made. I loaded in once fired LC brass and seated groups at 2.83", 2.80" and 2.78" OAL. The target can be seen below. The further I seated, the tighter the groups got.

 

[shell_guy]

I would redo the OCW test completely at 2.78 OAL (are you measuring from Ogive or from the tip?)

 

[Jhnmdahl]

Looks a little scattered to be of a great deal of use, but best guess from what I can see is that something around 44.5 grains should give you the least charge weight sensitivity.

 

[DFenn]

I would redo the OCW test completely at 2.78 OAL (are you measuring from Ogive or from the tip?)

I am measuring from the tip. It is 2.78" OAL. The Hornady Comparator is on my short list of things to buy.

I want to run the full test again, but I don't have a very large supply of these bullets and I can't find them anywhere to replenish my stock. This load is for our whitetail season, which is a month away.