OCW Test Question

[Infinity]

Hi All,

I am getting ready to develop a load for my new hunting rifle. I just got 100 pieces of new Lapua brass (my first Lapua brass). Will my OCW test results with the new brass (prepped with Sinclair expander mandrel/die) be the same as when I load up the once-fired brass (after Lee collet neck sizing)? How much might I expect group sizes to shrink when I use fire-formed vs new Lapua brass? If this has been answered before, please excuse my weak google-fu. As always, thanks,

Adam

 

[Dan Newberry]

If you properly identify the OCW, then you'll see little to no difference from virgin to once fired brass. After the brass has been fired about 3 times, it may start showing some signs of accuracy loss, which will mean you need to anneal it. With many rifles, folks get several firings off Lapua cases and they don't end up needing to anneal.

Dan

 

[Infinity]

Dan, thanks for the "right from the source" answer.

 

[Dacam]

Im actually up to 7 firings on Lapua 308 cases and have no accuracy loss. I will anneal the cases on the next round though.

 

[Infinity]

Good info. I don't plan on pushing it to that point but good to know. Thanks,
Adam

 

[Infinity]

Dan, or anyone else who knows the answer,

I am going to initially do this OCW test with 178 Amax bullets to see what my new hunting build can do. After that, I am going to develop a load for, and primarily shoot, 180 Gamekings out of this rifle. Will it be necessary for me to run pressure tests again for the 180s, then run another OCW test, or is it safe (and does it make a difference node-wise?) to cheat this with only a 2 grain (1.1%) bullet weight difference. What would you do? How much, if at all, would you drop the charge weight if you "cheated"?

Thanks,

Adam

 

[Infinity]

Any takers?

 

[Dan Newberry]

Adam,

You'd most likely find that .1 or .2 grains less powder will work for the 180's. I've done nearly exactly what you're planning, except with a 30-06, and I developed initially with 180 GK's, and wanted to see how 178 AMAX's did, so I bumped the powder charge .2 grains and all went well.

As a caveat, you'd want to shoot a couple pressure check shots at 1 grain, then a half grain under... then test for group at the suspected OCW level with the new bullet.

Dan

 

[Infinity]

Dan,

Thank you very much...saves me time and components.

Adam

 

[Infinity]

Dan's advice was spot on. My rifle loves the Sierra Game Kings. This picture is my ocw test group. 44.9 grains is perfect...



Did I break it? Mongo happy...