How accurately does your carbine shoot sub-sonic rounds?

I’m seeing 3+ inch groups at 50 yards with various commercial and hand loaded sub-sonic ammo.  I’m getting 1.5 MOA at a 100 yards with 110, 125, and 150 grain supersonic commercial rounds.  

I used the AAC  data to carefully prepare some hand loads using 220 gr SMKs and Accurate 1680.  Got a consistence ejection pattern at 3 o’clock. There was no improvement in accuracy.    

The gun is a RRA upper, lower, 2 stage trigger and chrome BCG with Wislon Combat 16 inch SS match barrel, 1 - 7 twist barrel under a Leupold Mark AR Mod 1.5-4X20mm FireDot-G SPR scope.  I’m shooting off a Lead Sled.  

I’m puzzled with the accuracy difference and I’m wondering what other folks are experiencing.

my personal opinion is remington factory subs suck . It has the worst seviation I have ever saw . my personal preference is hornady 225 match but they are like unicorns at this point in time and thats really unfortunate since they shoot great in all three of my guns . I was getting 1.5 -2.00 inch groups out of my 16 inch carbine and 1.00 inch out of my bolt gun pretty consistant . lately I have been using hornady 208 amax and they are not as accurate or I havent found the sweet spot yet I have been getting around 2 inches out of my carbine and 1.5 inches out of my bolt gun by contrast my 8.5 topped with an aimpoint pro does about 3.5 inch at 100 but I can live with that  considering the optic .
I try to make my col as long as possible to get the bullet closer to the riflings and use a lee crimp die for more consistance .

Take into consideration that you are shooting a equivalent of a pistol round when you shoot subsonic.

Don't get me wrong i love it when my 247gr cast make a 3 shot almost one hole at 50 yds out of 8.5 inch barrel.

4 inch .45 acp at 50 yds would be awesome.

What load are you using?

 

I have several loads,

11 gr 1680
10.9gr H4198
8.3gr lil gun

Usually i can keep a 1 1/2 in group at 50 yds with these but on occasion i get that beautiful 3 rounds almost touching.

Pushed OAL out to 2.255 and went to the range.  Huge improvement.  10 shot group down to 1.5 inches with 4 into a single hole and another just shy of touching it  Group could have been 1.25 inches except for a lone flyer.  Thanks for the idea.