Seating Depth

[mgraham112]

what seating depth is everyone using on their 300 for subsonic loads? I have been seating to the max i can with my AR platform, but not that i have an ssk encore, i can seat longer if i like. I know the risks of seating too long, but i read somewhere that with subsonic velocities, seating to the lands is not recommended. My bullet of choice is the 208 amax and i have been seating it to around 2.25. Is there any reason to try and seat it shorter with subsonics??? I also shoot 220 SMKs and 240s..

[i8asquirrel]

No need just what ever functions best in your weapon.

[Riverguide]

I just had an email thread with JD Jones last week about this very topic.

Personally am going with the theory of "as long as its not touching the lands" which for me, this means my 220 SMK;s will have a COAL of 2.235. I have done the best I can to measure where the lands would be and seems to be about 2.245 on my 300 Whisper(R).

So what about the smaller supersonic loads like the 125 balistic tips's? His answer for these were "As long as the bullet will stay in the case, more room for powder".

Both my 300 WTF's are on CZ-527 actions.

-Riverguide

[martineta]

That would be Mr. Jones.

I loaded some 125 Nos BT using his recommended loads of H110. I don't have access to my load book where I am but I think I remember 22 gr of H110 or there about. It looked like I was stressing the cases a tad plus my accuracy wasn't as good as I wanted. I backed off to 18.5 grs of H110 I think and for now thats plenty for me. I don't remember the length.

[jimpa]

I have found that with subsonics the smaller the unused volume in the case the more accurate and consistant the groupings. 3/4 inch groups or 3 and 4 inch groups out near the lands. 100 yds

[N310toN170]

I'll have to second the idea that the utilized case capacity is a major factor for accuracy, more so than any 'jump' to the lands.

To test the theory load 10 of the following:

AAC's BLK loads:~94% of case capacity

Suggested subsonic load:
• R-P 300 AAC BLACKOUT brass
• Remington 7.5 primers
• 11.2 grains of AA 1680 powder
• Case length is 1.368 +0.000 -0.020
• Sierra 220 MK loaded to 2.089 OAL
• Chamber pressure ~21,100 psi

Then, all other things being equal load 10 more extending the OAL to 2.245-2.250".

~75% of case capacity

QuickLoad indicates a drop of about 80fps, other factors to consider and watch for are cyclical function and feed reliability.