Another OCW! Advice please!

[farmer7]

Hello,

Made up some loads this afternoon to try out of my new Tikka SuperVarmint . 308 20"barrel.
Lapua Brass - Vihta Vuori N140 - CCI BR4 - 155gr AMAX

I'd appreciate it if you could have a look at the picture folks and let me know your thoughts.

Charges are:
43.5 2610 fps
43.8 2643 fps
44.1 2654 fps
44.4 2680 fps
44.7 2701 fps
45.0 2710 fps
45.3 2728 fps
45.6 2761 fps


The powder and bullet selection I'm using is maybe not ideal for a 1 in 11" twist 20" barrel but its all I lay my hands on and the velocity is better than I expected having gone from a 26" PSS to 20" Tikka. I gather from a 1 in 11" it is best with 178-190gr range???

I only loaded charges up to 45.6 but even there I had no flattened primers or sticky bolt etc. Possibly I could go a little further but would rather use something in the range above. Any and all opinions welcomed, I'd like to crank out some ammo and get shootin'! So please tell me whats my most likely OCW?!!

 

[Twoboxer]

Your rifle looks very happy at 45.0, 45.3, 45.6 . . . all nicely grouped with a common POI. The method would expect another possible OCW 3% lower, or ~ 43.8. The group at 44.1 may confirm that on its own, and may have been influenced by one less-than-perfect "high-left" shot.

I like ~45.3gr . . . JMO . . . looks like there's plenty of room for less than perfect loads and still have a common POI.

Nice shooting.

 

[Dan Newberry]

I agree with Twoboxer... clearly the 45.3 is where to be.

 

[targaflorio]

Normally I would split the difference between two tight groups at the same elevation.
45.0 and 45.3 in your case. Since 45.6 shows a worse group, I would stay between 45 and 45.3. Call it 45.2.
Well done!

 

[targaflorio]

Of course, I didn't see Dan's post in time.
Dan, you recommend splitting 45 and 45.6?

 

[farmer7]

Thanks everyone, 45.3 it is, I'll get busy tomorrow!

If I can achieve 2728 fps at 45.3 with the 155 Amax how far will I likely be able to stretch whilst maintaining stability? 700-800yards??

And special thanks to Mr Newberry for your load development method, makes things much less painless!

 

[Dan Newberry]

There is a good, stable node across the high 44's to the mid 45's... so based on POI, I would go with the 45.3 grains. I know there's also a mid 46 grain node with this bullet as well, around 46.5 grains or very close, which should give 2750 fps from most 24 to 26 inch guns.

 

[farmer7]

I didn't mention when I did this OCW my rifle was fitted with an ATEC Maxim 4 supressor. The ATEC allows you to add extra baffles for more suppression.

Mine has four baffles but I was planning on adding an extra two. So therefore adding a little extra length and weight. (About 3 oz's and 1 1/2") What I wondered was would I have to start over with another OCW if I added two extra baffles??

I did settle on 45.3 as suggested and have shot a lot in the past week and with minor tuning it is consistently shooting 3 and 5 shot groups every time in the .4's at least and some even better with that load which makes it the most accurate rifle I've owned. BUT if it meant abandoning that load and starting over I'd forget about the extra baffles and stay where I am!!! I'm very happy with that load!

Here she is :