Subs/Supers POI Question

[VariousCheeses]

I recently built a 8.5" 300blk upper for my AR, using a Saker762 on the trifecta flash hider. All ammo was Gemtech brand (110gr Barnes, 125gr Nosler, 187gr, and 220gr SMK). I got an ACOG with a 300blk reticle, which has a BDC calibrated for supers and subs - the idea being you can switch between ammo types without re-zeroing.

Here's where things went a little wrong: I was dialing in the gas block at 25 yards, but when I shot a group of 110gr, they grouped left. I rezeroed for the supers, put it back to 50 yards, and still had a tight group with the 125gr rounds, but the subs were really loosely grouped to the right about 6" or so. Both 187s and 220s had the same general POI, but the groupings sucked. Is my barrel just having issues stabilizing the rounds? No signs of a baffle strike or anything unusual.

The 110s and 125s grouped about 1" across. The subs seemed nice and tight at 25 yards, I could cover 3 shots with my thumb, but out to 50 yards it spread to 3" and just kind of felt all over the place.

It's an 8.5" Rainier Arms Select. Maybe I should've gone for the 10.5".

[Jbhurley]

1.) Anytime there is a concern with the accuracy of a suppressed gun I would shoot without the can just to make sure. You really don't want to make an expensive mistake until you have this sorted out.

2.) As far as the accuracy goes with the subs several factors can come into play: The twist rate of your barrel, the weight of the bullet and the speed it is moving all play a role. Several people here can Help here much better than I.

My suggestion is to try shooting with a variety of subs of different brands and weights and see if you can't get some better results. Check them for bullet stabilization before you use your muffler again.

Good luck to you!

[68Guy]

I recently built a 8.5" 300blk upper for my AR, using a Saker762 on the trifecta flash hider. All ammo was Gemtech brand (110gr Barnes, 125gr Nosler, 187gr, and 220gr SMK). I got an ACOG with a 300blk reticle, which has a BDC calibrated for supers and subs - the idea being you can switch between ammo types without re-zeroing.

Here's where things went a little wrong: I was dialing in the gas block at 25 yards, but when I shot a group of 110gr, they grouped left. I rezeroed for the supers, put it back to 50 yards, and still had a tight group with the 125gr rounds, but the subs were really loosely grouped to the right about 6" or so. Both 187s and 220s had the same general POI, but the groupings sucked. Is my barrel just having issues stabilizing the rounds? No signs of a baffle strike or anything unusual.

The 110s and 125s grouped about 1" across. The subs seemed nice and tight at 25 yards, I could cover 3 shots with my thumb, but out to 50 yards it spread to 3" and just kind of felt all over the place.

It's an 8.5" Rainier Arms Select. Maybe I should've gone for the 10.5".

Barrel length does not affect accuracy, it affects velocity. I run the Rainer Arms match 8.5 and it is very accurate. That vendor did choose to use a 1:8 twist instead of the 1:7 that AAC standardized on. Longer heavier subs "should" actually benefit from that twist rate. Again mine running 208 A-MAX and 200 SMK subs run great. I assume you have read that some of the Remington factory sub loads using the 220gr SMK have terrible accuracy and consistency. Specifically the yellow/green box so try some other source.

[rb288]

I shoot a Remington 700 sps tactical with my specwar 762.

Without the specwar, I zero the scope shooting supers, 110gr, 120gr, etc, they all group @ 1 moa @ 100 yds.
With the specwar, with subs, mostly 220gr, but some 208gr, they group 1.5-2 moa, @ 50 yds, about 4 inches right and 6 inches low.

Obviously, lower velocity and greater weight will effect POI.
But, the offsets are consistent and repeatable

I have marked the scope "dope" for each round so that when I shoot a different round, I just adjust the scope and it works every time.

[VariousCheeses]

Thanks for the replies everyone. I guess I just figured there would be more drop than drift. I'll need to shoot some more and keep some dope for different rounds.

This is my first experience with the cartridge btw, and I can see why it's so popular. The subs were quieter than my suppressed 10/22. Taking the supersonic crack away makes a huge difference.

[jwb47]

take the can off and shoot for groups . check for bullets key holing before you put the can on . one more thing try some different ammo I have tried gemtech in three different guns an 8.5 inch , 16 inch carbine and remington 700 . it is ok for plinking but not up to what I would call the best avalible . what I saw over my chronograph was extreme spread in velocity . I wouldnt expect any better than 1.5 - 3 inches at 50 yds .

[RDA]

Barrel length does not affect accuracy, it affects velocity. I run the Rainer Arms match 8.5 and it is very accurate. That vendor did choose to use a 1:8 twist instead of the 1:7 that AAC standardized on. Longer heavier subs "should" actually benefit from that twist rate.

I think you have that backwards, longer subs would benefit typically by the faster twist rate (i.e., 1:7).