OCW - Velocity or Powder Charge??

[farmer7]

I have always used Varget for my .223/.308 loads but over here it's nigh on impossible to get currently so I have moved over to N140.
I did an OCW development for the .308 and have a great load now but the N140 from what I've read is quite a bit more temperature sensitive.
My question is this: Is my OCW load purely based on the charge weight or will muzzle velocity drop in the winter months affect it? Do I want to tweak my load to match my summer velocity?
I know "Optimum Charge Weight" itself should answer my question but wondered about the velocity drop affecting it!
Any insight or thoughts folks?

Thank you.

P.S. The suppressor I use is an ATEC Maxim with four baffles but have ordered an extra two baffles which will add just under two inches in length and a wee bit of extra weight, maybe 1 1/2oz.
Will I have to start over with my OCW? From what research I've done some say yes some say no. The no argument backed up by the fact that FGMM shoots well out of just about anything , supressed or not. Confused!

 

[oldfatguy]

Your increased suppressor weight will change the barrel harmonics so it is best to do another OCW with the change.

OFG

 

[Dan Newberry]

You can tighten in on the best node with the suppressor change in all likelihood by a seating depth test.

It's true that FGMM shoots great in most cases, from whatever gun. But it'll shoot differently from one gun to the next, maybe 1 MOA from this one, 1/2 MOA from that one... maybe 3/4 MOA with your suppressor, maybe 1/2 MOA without it. It's all relative.

As for the velocity drop when the temperatures get cold. It will depend on how far the lower velocity moves you toward the edge of the node. If you drop 75 fps, you'll likely be off the node and accuracy will not be as good. In this case, loading winter loads toward the top of the node may be a good idea. For example, if your 70 degree Fahrenheit OCW node is 40.4 grains, then maybe your winter load should be 40.8 grains. I wouldn't do that, however, unless you test the original load to see if any tweaking is really needed.

Dan

 

[Ballistic308]

Suppressor weight didn't change my ocw,

You should not tweak your load to match summer velocity. Matching velocity from season to season isn't the same as moving from accuracy nodes.

 

[farmer7]

Thanks for the replies everyone. I'll maybe try loading another test when my two extra baffles arrive. (Wasnt happy with noise reduction compared with the old one hence the extra two!)

Just thinking about it my OCW POI was pretty stable over the test but with a few scatter nodes. The load I settled on was 45.3 which was fairly stable either side so would I be right in thinking I might be ok and not need further development? Or does that mean nothing?

Here's the test:

Sorry I cant get it upright!