sierra 220gr rn subsonic 308 load

[rjacobs]

Well I loaded up 30 more to try next week. 13.9 to 14.5 in .1 increments at the 3.745 coal. Then 3 more at 14.3 (which was the ideal about 1050 fps) at the coals 3.705,3.645,3.920

That covers everything from a little shorter, to about as short as I can go before compressing powder, to as long as I can do for mag length.

Should those 3's be 2's?

 

[rjacobs]

I also run 208 amax with trailboss in my 1in 10 twist barrel with great results. It stabilizes good. I have not experimented with anything heavier because I was told the 10 twist may have a hard time stabilizing.

Although it is considered a match bullet it is very effective on hogs!

I personally wont shoot 208g AMAX out of my 10 twist 308 because the stability calculator says its not stable. I just dont want to take the chance I guess.

 

[timelinex]

I'm going to the range today to test the new loads.

i bought some 208 AMAX's to try out as well, if these 220gr RN don't work out.

I looked up the stability factor and at 1000fps, in 30 degree weather of 29.92 pressure they are at around a 1.250, which is most likely stable. Anyone ever have any stability issues with them? They seem to be an extremely popular choice for subsonic 308(probably only less popular than the 180gr RN bullets), and I havent seen one thread yet saying they weren't stable.

 

[timelinex]

So I finally got out to the range and did some testing.

Here are my results:

The first 3 pictures show load development between 13.9 and 14.5 gr of trailboss, with a COAL of 2.745 and then 3 COAL variations of 43gr to see if seating would make a big difference. The last picture are my two groups right after, with my regular load, just for good measure. I'm surprised that my groups for my load stayed just as tight, if not tighter, when I put something as big as a 338 suppressor on the end of the barrel.


So what do you guys think? It looks like somewhere between 14.1 and 14.2 is the winner? They are just a smidge over 1moa, which from my understanding is as good as subsonics get right?

 

[Gottschalk]

Tag. Good stuff.

 

[Kymoonshiner]

Tagged as well, I stocked up on 220g SMK a while back in anticipation of developing a sub load but didn't consider stability issues, will I be looking at problems out of a 22" 11.25 twist? I'm looking into other projectiles just in case... my 1:7 300blk should handle those 220smks if I can't use them for subs in a 308 or I could just use them as supersonic loads.

 

[MaxVasc]

I spent weeks trying to get an idea of where to start for subsonic .308. After having developed a consistent load, I want to post it to make it a little easier on the next guy.

My subsonic load below:

Case: Lake City 7.62x51 once fired in my rifle. Full length size.
Bullet: 220gr Sierra Pro Hunter RN (MFG Part #2180)
Powder: Trail Boss
Charge Weight: 13.7 grains
Primer: Federal 210
COAL: 2.775" In my investigation, this is just about touching the powder without actually compressing it at all. This is about .096" jump in my chamber.
Medium Crimp (through initial load development, my SDs were lower with a crimp as opposed to without)
Rifle: Bolt action, 20" barrel, 1:10 twist

In my rifle, this produces a MV of 1,074 fps (magnetospeed) with a SD in the single digits and about 1 MOA accuracy.

 

[RTH1800]

I did not read all the post. There is some good info here and some bad.
The only way to truly know if your rifle will stabilize bullet X at SS velocity is to shoot bullet X at SS velocity. Too many variables. One of the big ones is that not all barrels are twisted as they are marked or marketed as. The 220 RN is a good SS bullet. I used many of them prior to getting the Lapua 200 grain which is also good.