6mm Max in a Six8 receiver set? Yes.

vmpglenn · Nov 24, 2024

Brownells finally got some SOLGW 14.5" 6mm Max barrels in, so I picked one up with one of their coupon codes.

I paired the barrel with a Riflespeed adjustable gas block, which IMHO are simply the best for tuning unsuppressed/suppressed shooting on the fly.

I initially shot a few dozen rounds of the factory 90gr ELD-X using .350 Legend 20rd mags. Function was flawless and the barrel stacked rounds in basically one ragged hole. Recoil was minimal, and the POI shift with my legacy Surefire can was only a quarter mil straight down - probably due to the barrel being very stout. I didn't chrono the loads, but they should ballpark around 2600fps.

I've handloaded the once fired brass with 100gr Speer BTSP and definitely will chrono these.

On a whim, I decided to see if 6Max rounds would work with my Six8 receiver set and Magpul PMAGs... Yes, yes they do.

Rounds stack a bit wonky, but they fit and feed just fine. The rounds slide out of the polymer mags like butter. The Six8 PMAGs have *just* enough inside length to allow the spec'd 2.3" COAL.

Pretty dang cool. The Six8 20 rounders fit 22 6Max rounds and the 30 rounders fit 33 or so. Love it.

Edit 12/12/24:

100gr Speer handloads chrono at 2571fps, 2614fps with the Surefire can. Accuracy is 1MOA, which is just fine with me (I don't normally shoot groups). I'm using a H-buffer and I have to set the Riflespeed gas block at full open to cycle reliably, so I'll switch over to a standard CAR buffer and see what happens. I can dial the gas block down to 7 (from 12) with the can attached. Still love it.

Next up is 103 ELD-X bullets with TAC powder. Stay tuned...

TonyTheTiger · Nov 24, 2024

I've always thought those receivers would be cool to stuff all kinds of wildcat rounds in. Are they still regularly available? Or do you have to buy the whole gun?

vmpglenn · Nov 24, 2024

You can get just the receiver set; they come in and out of stock pretty regularly. I got mine at GrabAGun last year.

Ernest 5.56 · Nov 24, 2024

I'd love to see the groups

TheOE800 · Nov 25, 2024

The tragedy of the Six8 is those mags. The Saudis paid enough to get 6.8SPC in a polymer mag, then all design of that platform ended. A thinner-walled metal magazine with increased COAL would have been great.

vmpglenn · Nov 25, 2024

TheOE800 said:
The tragedy of the Six8 is those mags. The Saudis paid enough to get 6.8SPC in a polymer mag, then all design of that platform ended. A thinner-walled metal magazine with increased COAL would have been great.

I'm happy the 6mm Max rounds fit well in the available Magpul polymer mags. It's a pretty compelling combination.

LRRPF52 · Nov 26, 2024

I was wondering about the same thing, since I have an empty New Frontier Armory receiver set and some Six8 PMAGs.

I was going to bore the Six8 mags out for Grendel though of course. Has been done successfully.

Regarding the 6mm Max, since it’s a smaller case diameter than 6.8, I figured it would rattle around and the stack might not align properly.

Downside with 6mm Max is likely an inefficient propellant burn due to a longer powder column. That usually messes with SD if you don’t get full conversion inside the chamber area.

Would have made a much better SCHV cartridge in 1957 than the 222 Rem Special (aka 5.56x45mm).

vmpglenn · Nov 27, 2024

LRRPF52 said:
I was wondering about the same thing, since I have an empty New Frontier Armory receiver set and some Six8 PMAGs.

I was going to bore the Six8 mags out for Grendel though of course. Has been done successfully.

Regarding the 6mm Max, since it’s a smaller case diameter than 6.8, I figured it would rattle around and the stack might not align properly.

Downside with 6mm Max is likely an inefficient propellant burn due to a longer powder column. That usually messes with SD if you don’t get full conversion inside the chamber area.

Would have made a much better SCHV cartridge in 1957 than the 222 Rem Special (aka 5.56x45mm).

Yeah the round stacking is not perfect but it's certainly good enough to work.

knuckleballz · Nov 28, 2024

I have the frontier six8 receiver set and pmags. I had bought a lot of the 6 Hagar brass before it was discontinued. I need to get a 6 Hagar barrel ordered.

WindstormSCR · Nov 29, 2024

@vmpglenn mind checking something for me since you have 6Max brass on hand? how do they fit in M27 links?

I had the wild hair of an idea to rebarrel one of the Fightlite MCR uppers into a 6 Max, it should work since the case head is the same, but the body taper was the question

LRRPF52 · Nov 29, 2024

knuckleballz said:
I have the frontier six8 receiver set and pmags. I had bought a lot of the 6 Hagar brass before it was discontinued. I need to get a 6 Hagar barrel ordered.

I would neck that up to .257” I think. Problem with 6mm HAGAR is case length basically sets it up to be limited to short bullets, unless you want to jam the projectile down into the propellant column. It would be kinda fun for varmints within 350-400yds maybe. I think the HAGAR case really needs a 2.500” COL action and magazine to be useful with the heavier bullets.

It has a 1.775” case length.

knuckleballz · Nov 29, 2024

I like the hagar case necked down to 22(220 thunderbolt). im running 77grain bullets at 3100 fps with a mild load of RL15.5 in an ar15. Problem is getting another barrel chambered. Keystone made the one I have, but doesnt seem interested in chambering another barrel. I have 6 hagar dies and a lot of 87vmax, 95gr berger, and 100gr sierra bullets on the shelf. It seems like I should be able to find one of those bullets that will fit in the magazine and give me good velocity. I can get a barrel chambered in 6 hagar at white oak.

vmpglenn · Dec 1, 2024

WindstormSCR said:
@vmpglenn mind checking something for me since you have 6Max brass on hand? how do they fit in M27 links?

I had the wild hair of an idea to rebarrel one of the Fightlite MCR uppers into a 6 Max, it should work since the case head is the same, but the body taper was the question

I would for sure if I had any M27 links...

WindstormSCR · Dec 1, 2024

vmpglenn said:
I would for sure if I had any M27 links...

I’d mail you some, but if you want to get any yourself for a talking point or curiosity, this is a decent option: https://tribetacticalsupply.com/5-5...bw0OKJHEn3GF2EbmTCTV9vX5sRDV6azVM7MXquXaAFCKI

They never go for too much, military generates a crazy amount of used surplus

LRRPF52 · Dec 2, 2024

If anyone is looking to dip their toes into a Six8 dimension receiver set, New Frontier Armory has blem lowers for $43.

ETA: They’re out.

WindstormSCR · Dec 2, 2024

LRRPF52 said:
If anyone is looking to dip their toes into a Six8 dimension receiver set, New Frontier Armory has blem lowers for $43.

the draw for these is just using 6.8SPC mags? how do you think they'd do for .350 legend since that's the aforementioned 6Max parent case?

Ernest 5.56 · Dec 3, 2024

WindstormSCR said:
the draw for these is just using 6.8SPC mags? how do you think they'd do for .350 legend since that's the aforementioned 6Max parent case?

The special mags that go with that receiver set

Magpul PMAG 30 Round 6.8 SPC Magazine

reelserious · Dec 3, 2024

TheOE800 said:
The tragedy of the Six8 is those mags. The Saudis paid enough to get 6.8SPC in a polymer mag, then all design of that platform ended. A thinner-walled metal magazine with increased COAL would have been great.

amen to that

LRRPF52 · Dec 3, 2024

WindstormSCR said:
the draw for these is just using 6.8SPC mags? how do you think they'd do for .350 legend since that's the aforementioned 6Max parent case?

The two SAAMI cartridges with factory ammo support that work with the Six8 receiver sets and Six8 PMAGs are:

6.8 SPC
224 Valkyrie

You can also do 338 Spectre, though you might need mods to the front guide ribs.

You can also modify the mags to fit and feed 6.5 Grendel. The guide ribs inside the mag bodies need to be sanded/filed down, and the follower modified.

WindstormSCR · Dec 3, 2024

LRRPF52 said:
You can also modify the mags to fit and feed 6.5 Grendel. The guide ribs inside the mag bodies need to be sanded/filed down, and the follower modified.

That’s neat, mind dropping that info into a DM? Since I don’t want to off topic clutter the thread up any further.

vmpglenn · Dec 12, 2024

Updates in OP.

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6mm Max in a Six8 receiver set? Yes.

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