At a crossroads on new AR builds due to Black Friday sales

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boom boom

boom boom

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As usual, I saw a few things on Black Friday and Cyber Monday that were priced below my power to resist. As a result, I have two AR lowers and uppers to build out with all of the small parts on hand. I do have a pistol buffer tube kit on hand as well. One bolt carrier has the RCA adjustable gas key while the other is a bog standard nitrided one. Have spare bolt heads for 7.62x39, 5.56, and 6.5 Grendel laying around from accumulation along with necessary parts to finish them out.

Currently, I have several flavors in rifles of 7.62x39, 6.8 SPC, and 5.56 and .223 Wylde.

What I do not have at present is barrels for the build which obviously affect the cartridge?

Right now, I have several thoughts and potential builds from these but am having problems making up my mind--these are to be range toys or project guns btw.

Option A) build one as an AR pistol--possible calibers are .300 BO, 5.56/.223 Wylde, or 7.62x39
If possible, from those who have built one, what length of gas system and barrel length did you use, and what type, if any, brace did you find useful. Buffer system information would be useful too. I am most worried about the reliable functioning of this variant especially with different options on gas systems, buffers, gas blocks, etc. Primary use of this variant is for distance travel enhanced protection.

Option B) build a true range rifle in either 6.5 Grendel or .224 Valkyrie for cheaper long distance shooting. Barrel length, buffer and gas system used would be useful here.

Option C) build another 16 inch rifle in 6.5 Grendel, .300 BO, or 7.62x39. What I am unsure about is how well the Grendel does in a 16 inch barrel--flash, ballistics, etc., whether or not a BO is practical--the late rifle thread on kabooms of a .300 BO comes to mind as well as the ballistics and ammo, or the 7.62x39 which I already have one that works plus mags so relatively easy to duplicate that build.

I am going to pick two of the above options but just need some advice (other than get more parts for more builds so I have them all). Not really interested in another handloading only cartridge or proprietary type builds at the present either.
 
If it were me and I was faced with those choices I would buy an 18" 6.5 Grendel barrel. I have a 16" and they are supposed to be fine ballistically, but it was 100 bucks less than an 18 or 20" when I bought it. Some of these sales right now are only putting about $20-30 more for the longer lengths. So I would do that. Or a 10" 7.62x39 pistol with a shockwave blade brace.
 
Ended up deciding on a .300 BO 10.5" pistol build and a 6.5 Grendel 20" range build and purchased the barrels on sale. Reasons are the .300 BO performs decently from a short barrel and and the Grendel because the factory ammo online is about the same price as the Valkyrie with the option of shooting the steel cased import stuff. I also have the bolts for both of these already kitted out.

Probably start the pistol build first when the barrels arrive. Now, just have to decide what kind of pistol stabilizer to use and what type of flash devices, gas blocks, and handguards to use.
 
A & B.

A: Build a 5.56 pistol for pure enjoyment and some defensive capability. 300blk doesn’t thrill me, it doesn’t lose as much speed as a 5.56, but unless you really wanted to hunt deer with your AR pistol, I just haven’t enjoyed a 300blk pistol. X39 isn’t my cup of tea in an AR. Adjustable gas block on either length gas system. I run pistol length barrels mostly, 10.5”. H2 buffers. I don’t really like 7” barrels for balance, and 12-14” barrels may as well be a 16” rifle, so I land on the 9-10.5” stuff. Carbine gas is a nicer impulse if using lighter reciprocating mass, but I prefer to throttle my gas - and you can make a short system act long, but can’t make a long one act short. I like the KAK Shockwave brace, new gen which uses a carbine buffer tube is really stable.

B: Build a long range 6.5 Grendel. 20” barrel is great - 24” only picks up about 100-120fps. Rifle length gas, no need for extended length with these. Also full mass carriers and H2 buffers, and adjustable gas block for ultimate control, and to minimize your recoil and reset time on target. .224 Valkyrie isn’t as versatile for hunting, if you ever would, and the lighter bullets don’t hit as hard as 6.5 Grendel to give feedback at range; bullet splash off target or target response on steel. Barrel life and brass life are better for Grendel as well. I FINALLY just ordered my own 6mm Grendel variant, a 243LBC over Black Friday, something to consider if you’re interested in a different option with a really simple wildcat.

ETA: had this one loaded last night but didn’t refresh before I responded today. Looks like the decision is made. You’ll be happy with those two!
 
Varminterror said:
A & B.

A: Build a 5.56 pistol for pure enjoyment and some defensive capability. 300blk doesn’t thrill me, it doesn’t lose as much speed as a 5.56, but unless you really wanted to hunt deer with your AR pistol, I just haven’t enjoyed a 300blk pistol. X39 isn’t my cup of tea in an AR. Adjustable gas block on either length gas system. I run pistol length barrels mostly, 10.5”. H2 buffers. I don’t really like 7” barrels for balance, and 12-14” barrels may as well be a 16” rifle, so I land on the 9-10.5” stuff. Carbine gas is a nicer impulse if using lighter reciprocating mass, but I prefer to throttle my gas - and you can make a short system act long, but can’t make a long one act short. I like the KAK Shockwave brace, new gen which uses a carbine buffer tube is really stable.

B: Build a long range 6.5 Grendel. 20” barrel is great - 24” only picks up about 100-120fps. Rifle length gas, no need for extended length with these. Also full mass carriers and H2 buffers, and adjustable gas block for ultimate control, and to minimize your recoil and reset time on target. .224 Valkyrie isn’t as versatile for hunting, if you ever would, and the lighter bullets don’t hit as hard as 6.5 Grendel to give feedback at range; bullet splash off target or target response on steel. Barrel life and brass life are better for Grendel as well. I FINALLY just ordered my own 6mm Grendel variant, a 243LBC over Black Friday, something to consider if you’re interested in a different option with a really simple wildcat.

ETA: had this one loaded last night but didn’t refresh before I responded today. Looks like the decision is made. You’ll be happy with those two!
Click to expand...

Thanks, I really appreciate the information because you've been there and done that.

At the price that I got the .300 BO barrel, I can probably sell it as is without building it out. Went back and forth on the 5.56 versus the Blackout on the pistol build so what you said makes sense and of course the factory ammo is much cheaper and I am set up the reload it. To me, the .300 BO is kinda like a M1 Carbine or a 7.62x39 as an intermediate round.

Just did not see that much recent information about 5.56 pistols and I know that you have built more than a few AR rifles and some AR pistols so I appreciate your input. Nice to know that an adjustable gas block benefits the Grendel as does the M16 carrier. I do have an H2 buffer laying around so that is good too. I guess I will do the Grendel build first then and look for a 5.56 short barrel.

I have a dirt cheap 7.62x39 16" upper simply to keep shooting if others aren't available and I was already set up to reload it for other rifles plus I have a couple of extra bolts for it but I wasn't as sure if it would function as it should in a pistol.
 
I’ll acknowledge I’m pretty hard on the 300blk, but I am so, only because it objectively doesn’t stand out. I fall into the same logic loop every time...

Me talking to me:

I want a blasting pistol or carbine. Maybe I should build another 300 instead of a 5.56. Bigger bores do get more energy out of shorter barrels than small bores, and less wasted blast. 5.56 is enough for occasional hunting or home defense though and has better range capabilities than the 300, in case I want to do something silly on a Sunday like shoot a 10.5” pistol at 500yrds. And 5.56/223 ammo is cheaper and more readily available. And I wouldn’t have to worry as much about policing brass - and 5.56 brass is easier to find than 300, and making 300 brass from 5.56 just to blast and then lose sucks... ok, let’s just build another 5.56 with a big smile on our face....

I do have a 10.5” 6.8spc which I built as a PDW. My logic was: I won’t shoot it too terribly much, so I don’t need the world’s cheapest ammo. I will need/want more bullet weight and punch than 5.56. I don’t necessarily wanna be handcuffed to reloading. I should probably pick between 6.8 and 6.5G. Eh, Flip a coin, head’s it’s a Grendel. Tails... guess I’ll build another 6.8... (today, the ammo and brass availability has tipped to favor the Grendel, so I’d probably go that way today, vs. what I did a few years ago before the 6.5 craze brought the Grendel to the front).

Lots of right answers, some just more right than others for their applications.
 
Varminterror said:
I’ll acknowledge I’m pretty hard on the 300blk, but I am so, only because it objectively doesn’t stand out. I fall into the same logic loop every time...

Me talking to me:

I want a blasting pistol or carbine. Maybe I should build another 300 instead of a 5.56. Bigger bores do get more energy out of shorter barrels than small bores, and less wasted blast. 5.56 is enough for occasional hunting or home defense though and has better range capabilities than the 300, in case I want to do something silly on a Sunday like shoot a 10.5” pistol at 500yrds. And 5.56/223 ammo is cheaper and more readily available. And I wouldn’t have to worry as much about policing brass - and 5.56 brass is easier to find than 300, and making 300 brass from 5.56 just to blast and then lose sucks... ok, let’s just build another 5.56 with a big smile on our face....

I do have a 10.5” 6.8spc which I built as a PDW. My logic was: I won’t shoot it too terribly much, so I don’t need the world’s cheapest ammo. I will need/want more bullet weight and punch than 5.56. I don’t necessarily wanna be handcuffed to reloading. I should probably pick between 6.8 and 6.5G. Eh, Flip a coin, head’s it’s a Grendel. Tails... guess I’ll build another 6.8... (today, the ammo and brass availability has tipped to favor the Grendel, so I’d probably go that way today, vs. what I did a few years ago before the 6.5 craze brought the Grendel to the front).

Lots of right answers, some just more right than others for their applications.
Click to expand...
I thought about a 6.8 spc pistol build but the barrels have dried up and I would have to cut a carbine length barrel to do so. As you say, the winds are blowing toward the grendel but it doesn't shine quite as well in a short barrel compared with the 6.8 spc.
 
boom boom said:
I thought about a 6.8 spc pistol build but the barrels have dried up and I would have to cut a carbine length barrel to do so. As you say, the winds are blowing toward the grendel but it doesn't shine quite as well in a short barrel compared with the 6.8 spc.
Click to expand...

That difference is HUGELY exaggerated. I put together a 12.5” Grendel pistol upper for an ex co-worker a while back, I’d be lying if I said I could really tell any performance advantage for the short 6.8’s vs. short 6.5’s - and I held lower SD’s and smaller groups with the Grendel. I used to sell that same advice online when I was shooting a 16” SPC to outrun an 18” Grendel, and drinking all of the forum koolaid (and spewing it myself). Can’t say the difference was substantial, but the SPC was a bit faster, and I then my next 6.8 barrel was 40fps slower with the same load as the old one, and the few FPS it outran the Grendel evaporated. Then came the pistol/SBR uppers... poof, that legendary short barreled advantage manifests itself as about 30fps, with larger groups, more vertical dispersion, and narrower nodes.

I’m drooling over a CZ mini action in 6.5 Grendel, barreled at 14” and dropped into a specialty pistol stock.
 
Varminterror said:
That difference is HUGELY exaggerated. I put together a 12.5” Grendel pistol upper for an ex co-worker a while back, I’d be lying if I said I could really tell any performance advantage for the short 6.8’s vs. short 6.5’s - and I held lower SD’s and smaller groups with the Grendel. I used to sell that same advice online when I was shooting a 16” SPC to outrun an 18” Grendel, and drinking all of the forum koolaid (and spewing it myself). Can’t say the difference was substantial, but the SPC was a bit faster, and I then my next 6.8 barrel was 40fps slower with the same load as the old one, and the few FPS it outran the Grendel evaporated. Then came the pistol/SBR uppers... poof, that legendary short barreled advantage manifests itself as about 30fps, with larger groups, more vertical dispersion, and narrower nodes.

I’m drooling over a CZ mini action in 6.5 Grendel, barreled at 14” and dropped into a specialty pistol stock.
Click to expand...

Interesting because the 6.8 was supposedly designed for short barrels while the grendel wasn't. Does Thompson Center make one of their pistols in a 6.5 Grendel.
Mauser?
 
We hear stuff about rounds being “optimized” for certain barrel lengths all of the time, but saying something like that is very short-sighted. What does “optimized” even mean? It certainly doesn’t mean they’ve reached maximum velocity - only the 22LR is documented to LOSE velocity due to standard length barrels being overly long for the case. Every bottleneck centerfire case on the market is large enough to keep gaining past 26” unless you feed it some super silly powder in reduced loads - so what is “optimized”? A guy can talk about powder burn percentage, as if that meant anything at all, or complain about muzzle flash and blast as if a small ball of fire is really better than a SLIGHTLY larger one... Powder choice for either will affect flash a LOT more than SPC vs. Grendel, and I personally don’t shoot in the dark often enough to be terribly concerned about the same blindness I might experience when my wife accidentally flips on the light for a split second instead of the ceiling fan in our bedroom at night...

The SPC and Grendel operate close enough in pressure, have similar enough bore cross-section, have similar enough case capacities, and run similar enough bullet weights to intuitively get the same work done in roughly the same barrel lengths. I’m not sweating over 50fps for either of them.

The difference is largely marketing hype and gossip.

MGM makes TC barrels for the Grendel. PURELY subjectively, I greatly prefer bolt action specialty pistols, especially repeaters, just for the novelty, over Encore/Contenders, so I’d waste the money myself on a Howa or CZ mini instead of getting another barrel for my Encore.
 
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