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12.5" Pistol/SBR caliber choices

benson821

Gunsmith, NRL/PRS Competitor, Hunter
Full Member
Minuteman
Oct 21, 2010
117
92
Whitehall, MT
Good morning folks,

I found out a few months back my current 12.5" 5.56 barrel is toasted, can't get a group smaller than about 5-6" at 100 yards.

So to my question, do I go back to 5.56, or with another caliber with some more energy and flatter trajectory. This "pistol"/rifle will be more general purpose, it has a 2-12 optic with red dot. (currently have a 18" "SPR" and 10" AK in 5.56) So I'm thinking of changing calibers since 5.56 "roles" are filled.

My thought is to go with a 6.8 SPC in 11.5-12.5" barrel. Energy numbers are higher and a little bit flatter that a 5.56 in the same barrel length, for the research I have come across. Also I can currently get thousands of rounds of FMJ or hunting ammo for about the same as you could for equivilent 5.56/223 factory loadings, save the brass and then load specific rounds for special purposes. This will be suppressed 99% of the time, as I have a suppressor without a host on my shelf.

I don't want to do 300 Blackout. Not necessarily looking for sneaky creeper subsonic cartridge. Just a more "efficient" one over 5.56.

Any opinions and comments, let's have a "civil" discussion if possible.
Alex
 
For your intents, 6.8 SPC sounds about perfect for the intended role. I chose 6.5 Grendel for my "intermediate" AR15 cartridge, but whether you choose 6.8SPC, 6ARC, or something else altogether is mostly up to personal preference and local availability. Whatever you choose, you'll get more terminal energy on target than 5.56. While you may not necessarily see a "flatter trajectory" from short barrels, these cartridges are great for hunting, target shooting, or any other activities that call for a more energy on target than 5.56.

The 12"-14.5" length is the sweet spot for these cartridges in my eyes - you'll have a smaller package than your SPR that you can carry easily, but still hits game hard enough to ethically harvest within ~300 yards (possibly more or less depending on bullet selection). Plus, it will keep it handy with your can.

With that being said, I haven't been able to find a reliable source of Lead-Free Projectiles loaded in 6.5G ammo (I don't reload) - and since CA requires LFP for hunting, I'm planning to shift to a 14.7" 5.56 AR with 62gr and 70gr Barnes TSX (which I can find locally). My ballistic calculator shows that these should maintain enough velocity to expand past 300 yards, so I'm going to run the 14.7" as my coyote gun in 2023 and see how it fares. Based on what I've seen and read online, it should be more than suited for the task. You might be surprised at the performance of 5.56 with the right bullet selection.

When I eventually start reloading, I may get back into 6.5G for deer hunting. Since you reload, ammo and projectile selection will be much less of a concern -- but it's something to consider for people like me who aren't quite there yet.
 
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Not sure what barrel you used, but a Colt chrome-lined barrel will hold up nicely at 12.5", as will FN and Daniel Defense, all with 5.56 NATO, 55 grain or heavier. Sounds like you got a shit barrel. The barrel is the heart of the AR.
 
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Not sure what barrel you used, but a Colt chrome-lined barrel will hold up nicely at 12.5", as will FN and Daniel Defense, all with 5.56 NATO, 55 grain or heavier. Sounds like you got a shit barrel. The barrel is the heart of the AR.
It's actually a old Colt chrome lined that I have since toasted out on it. I just want some caliber with a heavier bullet in that 11.5-12.5" length. Nothing against 5.56, but I've got 2 slots filled with them and my 10" 5.56 AK is pretty good out to ~300 on humanoid targets.

For your intents, 6.8 SPC sounds about perfect for the intended role. I chose 6.5 Grendel for my "intermediate" AR15 cartridge, but whether you choose 6.8SPC, 6ARC, or something else altogether is mostly up to personal preference and local availability. Whatever you choose, you'll get more terminal energy on target than 5.56. While you may not necessarily see a "flatter trajectory" from short barrels, these cartridges are great for hunting, target shooting, or any other activities that call for a more energy on target than 5.56.

The 12"-14.5" length is the sweet spot for these cartridges in my eyes - you'll have a smaller package than your SPR that you can carry easily, but still hits game hard enough to ethically harvest within ~300 yards (possibly more or less depending on bullet selection). Plus, it will keep it handy with your can.

With that being said, I haven't been able to find a reliable source of Lead-Free Projectiles loaded in 6.5G ammo (I don't reload) - and since CA requires LFP for hunting, I'm planning to shift to a 14.7" 5.56 AR with 62gr and 70gr Barnes TSX (which I can find locally). My ballistic calculator shows that these should maintain enough velocity to expand past 300 yards, so I'm going to run the 14.7" as my coyote gun in 2023 and see how it fares. Based on what I've seen and read online, it should be more than suited for the task. You might be surprised at the performance of 5.56 with the right bullet selection.

When I eventually start reloading, I may get back into 6.5G for deer hunting. Since you reload, ammo and projectile selection will be much less of a concern -- but it's something to consider for people like me who aren't quite there yet.
My only reasons for choosing 6.8 is availability of ammo at my work, and the bullet range from small varmint bullets to heavies if I want to make some subs. Surprisingly enough through the shop I work at 270 cal bullets are pretty plentiful compared to other calibers.

As for the numbers I have read folks reporting with their 11.5-12.5" 6.8's they are still reaching mid 2500 fps which are the rough ballistics I have ran on my end with different bullets. Just a few tenth flatter than the 5.56 but 2-4 times more energy depending on bullet.

Practically hunting wise I was thinking that ~300 range like you said but for target shooting/matches stretch it out as far as I can make consistent impacts.
 
Unless you just want to maximize effective range in a 12" gun at all costs, with new brass, bullets, dies (or just different ammo), bolt, mags, then I'd stick with 5.56. 2x more energy doesn't mean 2x lethality. A couple tenths elevation at 300 yards is nothing. Steel still goes ding with a 223 at 300 yards. Pigs still die with well placed shots and a 55gr bullet. 6.8 > 5.56 in general, but the slight performance gain to me isn't worth it if you're already deep in 5.56 ammo and have other platforms that utilize the same ammo and equipment.
 
12.5" 6.8 all the way, ARP barrel of course. Mine with a 5" can is perfect for deer stand hunting. Even better if you can get ammo for the same costs as 223. If you don't decide to reload, you can sell the brass.

I run a 12.5" .223 ARP also, so I'd say build both.
 
I”ll second the above 6.8 recommendation. A suppressed 12.5” ARP sbr is my go-to hog/coyote/deer ranch rifle. Handles great getting in/out of truck and have taken critters out to 350’ish. I run mostly 120SST’s for hogs at night but bought a pile of the 90gr gold dots back when it was cheap, they work ok too (as do 95TTSX, just mo expensiver)

It’s been many years ago but seems like I was getting a bit above 2500 fps with factory loaded 120SST, albeit that was from a cheap Caldwell chronograph.
 
12.5" 6.8 all the way, ARP barrel of course. Mine with a 5" can is perfect for deer stand hunting. Even better if you can get ammo for the same costs as 223. If you don't decide to reload, you can sell the brass.

I run a 12.5" .223 ARP also, so I'd say build both.
That's a big reason right there, my price on S&B 6.8 FMJ which I would stock up on for brass and practice and some other hunting ammo ammo is quite a bit cheaper or even just a couple dollars cheaper a box than the hunting/match 5.56 and 223 loading's. But comparatively to 5.56 FMJ it's more expensive, but not by much. And I plan on loading hunting, and possibly subsonic loads, just use the cheap FMJ for practice.

I'm thinking I may build the 6.8 up get it running, grouping, load development, zeroed, etc. Then if I want, I will build up a 223 upper for it and run that. I don't "need" another 5.56 gun which is why I'm feeling this build out. My 10" 5.56 AK does what I need an sub 16" 5.56 to do, so to me why have 2....

I”ll second the above 6.8 recommendation. A suppressed 12.5” ARP sbr is my go-to hog/coyote/deer ranch rifle. Handles great getting in/out of truck and have taken critters out to 350’ish. I run mostly 120SST’s for hogs at night but bought a pile of the 90gr gold dots back when it was cheap, they work ok too (as do 95TTSX, just mo expensiver)

It’s been many years ago but seems like I was getting a bit above 2500 fps with factory loaded 120SST, albeit that was from a cheap Caldwell chronograph.
I was initially looking at the ARP 12.5" barrels but they are running a 11T and after doing some research I was leaning more towards the Bison Armory 11.5" with the 7T just in case I wanted to run the 150+ bullets subsonic. Some folks say they will stabilize but running stability calculators the 7T just seems a better way to go. Also I will be running a Rex Silentium ModX 308 on this in probably long configuration so that 11.5" barrel will keep the overall just around 16".
 
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I was able to get 150s stable subsonic from my ARP barreled bolt gun, just for shits and grins, but wouldn't go heavier. My stuff is pretty much all ARP but not a thing wrong with Bison.
 
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Shot my 12” 6mm arc. Factory Hornady black gets 2320, and I was able to reach 2519 with handloads, but got pressure signs at that charge. Going to back it down to 2450-2475. I’m impressed with that speed from a 105 out of a tiny case and 12” barrel
 
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Old thread but...Only problem with 7 twist or enfield (square) rifling is you leave velocity on the table. The 16" 5R and 3R barrels are capable of pushing 110gr bullets to 2750fps loaded with H335. The 12.5s(really 13") will go to 2650 and that is as fast as a 16" Wilson or Bison. Barrels with 5R or 3R rifling are consistently 60-90fps faster than the old enfield type.
 
I made this chart back in Oct 2017:

Cartridge20Utility20Comparison_zpsvckmugph.jpg


If we add 6mm ARC to it, I would rate it thusly:

Hunting legal - Yes
HD/ Vehicle Defense - Good choice
Affordability - Mid-High cost (currently $1.30 to $2.80/rd)
Practical Long Range - Yes
Effective Pistol/PDW - Yes
Factory Ammo - Limited support with Hornady and Black Hills

Prices have of course increased into stupid territory.
 
Late reply to the thread I started but ended up getting a great deal on the 11.5" bison armory 6.8 barrel. Built it up, put a 2-12 athlon helos on and its fairly impressive. About 200 rounds of S&B fmj hrough it and I've made first round impacts out to 600ish and walked it out to 1k just to see what happens. I think with a tuned reload it will be a great intermediate gun bridging my 5.56 to 308
 
Late reply to the thread I started but ended up getting a great deal on the 11.5" bison armory 6.8 barrel. Built it up, put a 2-12 athlon helos on and its fairly impressive. About 200 rounds of S&B fmj hrough it and I've made first round impacts out to 600ish and walked it out to 1k just to see what happens. I think with a tuned reload it will be a great intermediate gun bridging my 5.56 to 308
1/7 twist will help it with the bullets that are more suitable for intermediate/long range.

Are you shooting suppressed?
 
Late reply to the thread I started but ended up getting a great deal on the 11.5" bison armory 6.8 barrel. Built it up, put a 2-12 athlon helos on and its fairly impressive. About 200 rounds of S&B fmj hrough it and I've made first round impacts out to 600ish and walked it out to 1k just to see what happens. I think with a tuned reload it will be a great intermediate gun bridging my 5.56 to 308
Try 29.2gr RE7 with 85 and 90 gr bullets, that was one of the first universally accurate loads we found in 2008. Other powders work fine for accur acy but to get top velocity powder in that burn range needs to be used RE-7 to 10X. The bad part is Alliant powders are now running about $50/lb. Norma 200 will also work with those 85-90gr bullets.
110gr-120gr works with AA2200 or H335
 
Try 29.2gr RE7 with 85 and 90 gr bullets, that was one of the first universally accurate loads we found in 2008. Other powders work fine for accur acy but to get top velocity powder in that burn range needs to be used RE-7 to 10X. The bad part is Alliant powders are now running about $50/lb. Norma 200 will also work with those 85-90gr bullets.
110gr-120gr works with AA2200 or H335
I've got a jug of AA2200 and H335 sitting here as well as a case of 3k Hornady 110gr BTHP. I plan on building up a load for it here soon, but time is against me.
 
I've got a jug of AA2200 and H335 sitting here as well as a case of 3k Hornady 110gr BTHP. I plan on building up a load for it here soon, but time is against me.
Try 28.4gr 2200 with the 110s, some load them to factory length of 2.26 others load as long as possible 2.295" It's posted as a favorite load over on 68forums.
 
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I recently shot a 6.8 SPC and was amazed. It was a nice shooting rifle. I'm considering doing a 6 ARC 12.5" build at some point. I saw a video regarding one and it looks impressive.
 
I recently shot a 6.8 SPC and was amazed. It was a nice shooting rifle. I'm considering doing a 6 ARC 12.5" build at some point. I saw a video regarding one and it looks impressive.
The main choices with some factory ammo and brass support really narrow down to:

6.5 Grendel
6mm ARC
6.8 SPC
.224 Valkyrie

6.5 Grendel has the most factory ammo support and brass availability, followed by 6.8 SPC, which used to have a lot more support.
Grendel had at least 94 factory loads pre-Wuhanflu ranging from 90gr TNT from Federal up to 130gr VLD. Most Grendel ammo is 120-123gr.

6mm ARC has Hornady factory ammo, HSM, and now Black Hills. It’s all 103gr to 108gr so far.

Biggest thing from a cost perspective is the Wolf Steel case for Grendel, which has risen to 79 cents/round now. Used to be around 20 cents. PSA said they’ll be making 6.5 Grendel under the AAC brand.
Grendel also has PPU and S&B for affordable brass options, in addition to all the US brass-cased ammo from the alphabet of companies.

.224 Valkyrie is basically limited to Federal for the most part. Not sure they ever worked out the chamber design for AR-15s to get them to shoot sub-MOA consistently. Valkyrie can be found pretty cheap right now, as it didn’t really catch on and projectile mass is pretty small. Factory loads range from 75gr to 90gr. Valkyrie makes for a great yote and P-dog cartridge, as do 6mm AR and lighter load 6.5 Grendel like the 90gr TNT from Federal. You have to hand-load the 6mm ARC for varmint loads like the 87gr V-MAX.

6.8 factory ammo ranges from 90gr Federal Fusion to 120gr Hornady SST. Most 6.8 SPC ammo is 110gr or 115gr, all of which have pretty low BCs but a lot of frontal area for impact on hogs and deer. Hits hard within 200-300yds depending on barrel length and conditions.

All of them have noticeable performance increases over 5.56 for energy on-target, with certain compromises, the main one being magazine capacity of 24-26rds vs 30 for the same size/profile magazines. 3 of the 4 do really well for target shooting and hunting, whereas 6.8 SPC has been more of a hunting application cartridge due to the BC and slower twist rates. If you shoot the 1/7 twist from Bison Armory with 130gr Bergers, it will behave very similar to a 120gr from a shorter barrel Grendel and do well on-target, hit with a lot of momentum compared to other 6.8 loads.

I think the totality of the data still favors Grendel mainly due to ammunition availability and versatility. It will do most or all of what the others do, while each of them has a relatively niche performance envelope specific to their diameter and bullet weight availability, along with the constraints of their case lengths. In the case of 6mm ARC, it was optimized for longer TGT bullets but not varmint bullets. Valkyrie was really made with the 90gr .224” SMK in-mind since you can’t mag-feed the longer VLD or heavier TGT bullets in .223 through AR-15s. Valkyrie and 6.8 share bolts and magazines. Grendel and 6mm ARC share bolts and magazines.
 
I've got a jug of AA2200 and H335 sitting here as well as a case of 3k Hornady 110gr BTHP. I plan on building up a load for it here soon, but time is against me
Since you reload you can really squeeze some extra performance out of the 6.8. Getting 2.295 COAL is no problem with most 6.8 mags (PRI, ASC, CPD(or duramag) for sure). As constructor said there's a pile of data over at 68forums.
 
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@strikeeagle1 Thats a sweet ride! Several years ago when I had access to a private 500yd KD I took my 12.5arp 6.8 to 500 with S&B 110fmj. PA 1-6x on 6x got me a ~5x7" grouping. Still my first "we gotta leave right now" rifle to grab from the safe (though now it has a prism sight on it).
 
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@strikeeagle1 Thats a sweet ride! Several years ago when I had access to a private 500yd KD I took my 12.5arp 6.8 to 500 with S&B 110fmj. PA 1-6x on 6x got me a ~5x7" grouping. Still my first "we gotta leave right now" rifle to grab from the safe (though now it has a prism sight on it).
I'm waiting on Blackstone Arms to get some 14.5" 6.8s in now.
 
@strikeeagle1 - congrats sir, that’s a sweet rig you’ve “cobbled” up.

Curious how the Remington factory ammo groups at 100, and if you’ve tried any other loadings. Maybe they’ve sorted some things out but seems like it had a not so good reputation 10-12 years ago when I began my 6.8 journey.
 
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I only these target results archived I could access easily. 100 (tripod)-150-250-300-400 Meters. All 115 gr Remington FMJ for consistency.
IMG_2330 copyCracker Swamp 06.02.19WILSON COMBAT 6.8 SPC 2 copy.JPG
IMG_2328 copyCracker Swamp 06.02.19WILSON COMBAT 6.8 SPC 2 copy.JPG
IMG_5792Wilson Combat 6.8 SPC Cracker Swamp 300 Meters 01.27.23 copy.jpg
IMG_6660WILSON COMBAT 6.8 SPC CRACKER SWAMP 400 METERS 03.10.23.jpg
 
@strikeeagle1 - congrats sir, that’s a sweet rig you’ve “cobbled” up.

Curious how the Remington factory ammo groups at 100, and if you’ve tried any other loadings. Maybe they’ve sorted some things out but seems like it had a not so good reputation 10-12 years ago when I began my 6.8 journey.
I think Hornady 110 HPBT, 115 Federal Fusion, S&B 110 PTS is better ammo. Pretty easy to get 1" at 100yds with those.
 
The WC should shoot better than that. Definitely try some better ammo, Remington would be my last choice for accuracy testing.

I don't have any targets saved but my 12.5" ARP can easily do 1" groups at 100yds with factory 120gr SST's and a tbac 30PSS hanging off the end. My 18" wasn't any more accurate so sold it as the 12.5" is my main deer rifle. I have found the same with accuracy results with ARP's 12.5" and 18" .223 barrels.
 
The WC should shoot better than that. Definitely try some better ammo, Remington would be my last choice for accuracy testing.
^^ Thanks for your thoughts, that's my next Plan. I used the Rem 115 as I had a lot of it to step it out to 500 meters. I have LR data on Hornady 120 SST and HSM 115 SMK; all three are within a few fps @ 2300. Found my WC test target which is ~ 1 MOA and noticed they used 110 gr HPBT, so I am going to source some and re-zero. Any recommenations as to which brand? I have some S&B 110 but it's not HP.
Wilson Combat 6.8 SPC II 11.3 Complete Upper Test Target copy.JPG
IMG_7748.jpg
IMG_7747.jpg
Screen Shot 2023-07-14 at 11.41.52 AM.png
Screen Shot 2023-07-14 at 11.42.24 AM.png
 
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@strikeeagle1 Thats a sweet ride! Several years ago when I had access to a private 500yd KD I took my 12.5arp 6.8 to 500 with S&B 110fmj. PA 1-6x on 6x got me a ~5x7" grouping. Still my first "we gotta leave right now" rifle to grab from the safe (though now it has a prism sight on it).
A cut-n-paste of my post on another forum in 2014

"5x7" 5-shot group at 500yds mag-supported, 6x Primary arms scope, 12.5ARP, with S&B ammo (chrono'd at 2500fps on a humid, 95*) up hill, both ways in the snow."
20140815_145218_resized.jpg


All true except for last couple comments. There's no hills here and it really hasn't snowed since 1996 lol. Somewhat bigger than 5x7 I guess but not bad for a 12.5"bbl, factory ammo, a 6x scope, and a shooter of questionable worth.
 
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If having something on hand with more power for medium game such as deer/hogs….I have a Bison Armory 10.5” 6.8 upper on a sbr lower I run suppressed for night time hunting these days….I am well pleased and it is my goto pig popper.

Also have a POF Revolution 12.5” .308 sbr with a 1-6 lvpo I keep on hand as a truck/buggy rifle…..great for the task and very accurate, but suppressed is required for it to be pleasant to shoot…..unless you enjoy feeling the sound wave permeate your inner core when you shoot😁
 
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I don't have any pictures of my groups but with S&B 110gr FMJ I had about 1" groups at 100. It shoots surprisingly well like I had said before out to 5-600 for what I remember which was staying 2moa sized steel. I plan on this fall/winter to get the gun room squared away and work up a load for it using 110-135gr bullets.

Very happy with the cartridge for the playing I've done with it. Plus the shop I work at has been able to get S&B ammo for around $1 a round so it's good practice to stock up on brass.
 
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I don't have any pictures of my groups but with S&B 110gr FMJ I had about 1" groups at 100. It shoots surprisingly well like I had said before out to 5-600 for what I remember which was staying 2moa sized steel. I plan on this fall/winter to get the gun room squared away and work up a load for it using 110-135gr bullets.

Very happy with the cartridge for the playing I've done with it. Plus the shop I work at has been able to get S&B ammo for around $1 a round so it's good practice to stock up on brass.
Missed the post above mine where you landed with a BA 11.5”….glad to hear it is working out for you. I use the S&B PTS for pig hunting….it is a nasty round for that purpose. Not quite as hot as the Hornady VMAX, but I think the same bullet. My only regret is not stocking up on more of it a few months back when it was $1 a round.
 
Missed the post above mine where you landed with a BA 11.5”….glad to hear it is working out for you. I use the S&B PTS for pig hunting….it is a nasty round for that purpose. Not quite as hot as the Hornady VMAX, but I think the same bullet. My only regret is not stocking up on more of it a few months back when it was $1 a round.
I've got it on a stock list at work to get a pile of it. Looks like an awesome round. Plus reasonably priced comparatively
 
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Thanks for the link! Will read thru it…..fwiw my tips are red and not green. Was expecting green but got red in 2 different batches🤷🏼‍♂️
I think the newer ones are red. Now that I think about it, I think there was some dissatisfaction with the new ones... you may have to dig around over there to find the thread.
 
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My 12.5 core is pushing north of 2630 fps without the can, and north of 2650 with it. That's good enough for me to not look at other calibers.
 
My bad! @lou400a guess i missed some important piece of information
Black hills 77gr smk 556 (red box)
There isn’t anything you can do to a 77gr SMK to make it move my meter on steel even at 400yds, let alone any distances farther than that, even if you cook it from a .22-250. BC is too low, not enough projectile weight, bleeds energy really fast.

It’s one of the main things you notice with SPRs (Mk.12 Mod 0/Mod 1). You go through so much effort on the gun end to get it all right, then spit out a tiny little bullet that barely dings the steel, oftentimes unable to be heard with even light winds at full value.

Bring a 24” bolt gun chambered in .223 Rem and shoot steel next to a 12” Grendel at 700-1000yds and see what I’m talking about. 5.56 hits hard at 200yds and is very respectable there, but really starts to run out of gas after that. If it’s a clear, windless day or night, it sounds fine on steel with heavier bullets at distance, as long as your have good electronic ear pro.

I can make hits with it at distance, but they just aren’t impressive in terms of energy on-target.
 
Idk I can hear and see the steel swinging when I ring my clubs 400y plates. I've had no problem with hits at 600 either.

I'm not claiming it to put out the energy that Grendel does.