Sub Sonic .338 - Is 338 ARC better than most other sub's?

[HighDesertDrifter]

ditto. I'll most likely still be putting together my .375 raptor first, but still really interested to see where all of this goes.

[Old Bob]

Are all 338 ARC barrels gonna have carbine length gas systems? No mid-length?

[mtnlvr]

Depends on the barrel length. I've seen at least one 12" (or 12.5") call out pistol length gas system.

[LRRPF52]

Are all 338 ARC barrels gonna have carbine length gas systems? No mid-length?

Most should have pistol-length gas I think. Lots of bore volume, small propellant mass, meaning there is very little length to retain enough port pressure to feed into the gas system.

[HighDesertDrifter]

I haven't seen anyone offer anything other than pistol length gas so far including mos-tek. They're the only ones I've seen, so far, offer a variation on hornady's recommended specs. 1:5 vs 1:8 twist.

[mtnlvr]

Faxon is showing a carbine length gas systems on their 16" offering. The 14.5 goes back down to the pistol length.

[Old Bob]

The small case powder volume makes sense for short gas system lengths in the 338 ARC. Anyway, are there any 16" barrels out there? I did a search for one but came up empty. Got on some waiting lists though ...

[SDguy]

What projectiles stand out to be good performers in terms of a hunting projectile in the 338 ARC?

[HighDesertDrifter]

What projectiles stand out to be good performers in terms of a hunting projectile in the 338 ARC?

Looks like maker has offerings for subs and supers in .338 so might start there. The subs suggest a twist rate of 1:6.5 or faster though.

[GrantM]

As much as I enjoy tinkering with the 300 Blackout, I've had difficulty getting consistent subsonic performance past 100 yards. The 338 ARC intrigued me so I picked up Faxon 12" bbl (1:8).
I'm just working up sub loads right now. I started out with some 250 gr Midway soft point "seconds" To keep costs down while figuring out some powders.

Tip: The Hornady Bullet Comparator will NOT work in 338 ARC without modification. Not enough cutaway in the pushrod to accommodate a caliper. You will need to cut off the thin tip portion of the pushrod end (about 3/8"). This shouldn't affect function with any other caliber.

Anyway, a COL of 2.17" gave me .025" off the lands with those soft points. 10.7 gr Lil-Gun got me to 1055 fps SD 8.3 / ES 22.7. If I take out the first shot of each session (I'll explain) I'm at 1059 fps SD 1.3 / ES 3.2 !
The first shot in every 5 shot "session" ALL had 20-30 fps lower velocity than the next 4. I can only attribute this to Lil-Gun preferring a "hot" chamber.
For reference, 13.9 gr of I-4198 yielded 963 fps. 11 gr of I-4227 gave 724 fps,.and12 gr A1680 got 950 fps (1680 also had low 1st shot numbers)

Next I ran 300 gr Match Kings. These could be loaded to mag length which put them 0.055" off the lands.
10.5 gr Lil-Gun got 1038 fps out of a 18 shot session. SD 9.4 / ES 30.7 when "cold" shots were excluded.
300 gr Match Kings held 1 moa at 100 yds and 1.25 moa at 200 yds. That is with "cold" shots included.. Had a lot of fun ringing small steel at 200 yds Monday.
Hopefully I can work up some temp stable powders with the same results.
All of these were shot suppressed with a Hybrid 46. The 300 gr pills stabilized very well with the 1:8 twist. No indication of any bullet "wobble".

[va_connoisseur]

As much as I enjoy tinkering with the 300 Blackout, I've had difficulty getting consistent subsonic performance past 100 yards. The 338 ARC intrigued me so I picked up Faxon 12" bbl (1:8).
I'm just working up sub loads right now. I started out with some 250 gr Midway soft point "seconds" To keep costs down while figuring out some powders.

Tip: The Hornady Bullet Comparator will NOT work in 338 ARC without modification. Not enough cutaway in the pushrod to accommodate a caliper. You will need to cut off the thin tip portion of the pushrod end (about 3/8"). This shouldn't affect function with any other caliber.

Anyway, a COL of 2.17" gave me .025" off the lands with those soft points. 10.7 gr Lil-Gun got me to 1055 fps SD 8.3 / ES 22.7. If I take out the first shot of each session (I'll explain) I'm at 1059 fps SD 1.3 / ES 3.2 !
The first shot in every 5 shot "session" ALL had 20-30 fps lower velocity than the next 4. I can only attribute this to Lil-Gun preferring a "hot" chamber.
For reference, 13.9 gr of I-4198 yielded 963 fps. 11 gr of I-4227 gave 724 fps,.and12 gr A1680 got 950 fps (1680 also had low 1st shot numbers)

Next I ran 300 gr Match Kings. These could be loaded to mag length which put them 0.055" off the lands.
10.5 gr Lil-Gun got 1038 fps out of a 18 shot session. SD 9.4 / ES 30.7 when "cold" shots were excluded.
300 gr Match Kings held 1 moa at 100 yds and 1.25 moa at 200 yds. That is with "cold" shots included.. Had a lot of fun ringing small steel at 200 yds Monday.
Hopefully I can work up some temp stable powders with the same results.
All of these were shot suppressed with a Hybrid 46. The 300 gr pills stabilized very well with the 1:8 twist. No indication of any bullet "wobble".

How is your testing going? I am looking at getting a Mostek 1 in 5 twist for a sub only pistol.

[tdbru]

I know the focus of this thread is subs in an AR platform, but, folks have been playing with subsonic speeds out of revolver cases in lever guns for a long long time. 38 Spcl, 44 Spcl, 45 Colt, etc. with new lever guns having threaded muzzles for cans, lever carbines and subsonics should go together like PB&J. never a worry about shoulder setback with a straight wall rimmed case. Perhaps not as cool as an AR platform, but lever carbines can be fun too.
-tdbru

[HighDesertDrifter]

45-70 700gr subs are available . Havent had the opportunity but for hunting would be a slick setup in a trapper model.

For those looking for dual purpose, after running a bunch of comparisons, 45-70 is a sleeper champion imho. Tradeoff is capacity(fine for hunting), as well as recoil for supers and reload speed.

As a dedicated sub thumper in an ar-10, I'm calling it a wash between .375 raptor and 8.6 blk to 400 yards where those tools are mostly going to be utilized. 8.6 for market availabilty. 375 for diy and enhanced performance for supers.

.338 arc still has a ways to go imho to be truly useful. IMHO all it has going for it right now is plug and play on an ar 15 and support from existing parent cases and bolts. Mag capacity would change things for me. Thril has prototypes for higher capacity. There are reports of asc ar15 7.62x39 mags working for .338 arc in forums. Hopefully this will inspire others to bring higher capacity to market.

I do also love .458 socom but capacity keeps it out of my consideration but makes for a fun hunting option. Hope all this is helpful or least interesting.

[GrantM]

How is your testing going? I am looking at getting a Mostek 1 in 5 twist for a sub only pistol.

The more I shot 200 yards, the more I realized the 1:8 wasn't stabilizing as well as I thought. It wasn't glaringly obvious, but close examination of the bullet hopes showed signs of wobble and the 1.25 moa groups weren't reliable.

I picked up a Faxxon 11" 1:5 twist barrel. I have it on a BCA Bolt Action upper.
I settled back to CFE Black, 14.5.g grains gave me 1020 fps, SD of 6 and spread of 23 (10 shots) with reliable 1.5 moa using 300 gr SMK's.
13.4 gr A-1680 is running 1006 fps SD9, ES 28, with similar reliable groups..
I'm happy for the time being.
I would jump on the Mostek 1:5. The 1:5 is supposed to handle the 175 gr supers fine, but I haven't tested that yet.