New partial AR-15 build ... not sure where it's heading

I woulda chose Grendel...

I love Montana more than my own mother but you should consider Compass Lake Engineering for your barrel and/or complete upper. Not saying that Proof or any of the other Kalispell area manufacturers would steer you wrong.

Falkor makes top quality stuff. I have a Falkor Omega which has one of their Dracos 6.5 Creedmoor barrels and it is a legit 1/4 MOA rifle. I like it so much that I bought another Dracos barrel for my 6.5 G build and I’m pleased with it. Heavier than the Proof for sure, but these barrels just do not get hot. When I bought my 6.5 G barrel they were on sale for 50% off which took them from $800 (Proof price range) down to $400. I couldn’t pass that up. Good luck with your build and I would definitely go 6.5 G or 6mm ARC if I was in your shoes. I love my 6.8 SPC, but I feel like it may be a dying cartridge.

6arc in an 18" barrel.
Maybe
A 6arc in Carbine length would be cool, but what you have argues for more of a rifle length build.
At least for my 2¢

Ok, I typed this yesterday, but the Forum glitch ate it. Still my answer, though.

MCMXI said:

I've been doing some research on the 6mm ARC and it seems that magazines are an issue, specifically in terms of reliable feeding. Supposedly the 6.5 Grendel magazines don't work that well for 6mm ARC. Does anyone have any insight?

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No, but that surprises me since they are so close in shape to each other. What is the issue with it?

I'd sell it and put the money towards a TP9

yes, that was a joke

Ironically, the only eight boxes of ammunition left at the local outside store is Hornady 6ARC. I was almost entertaining the thought, but you bring up a very good question, not that I will need a project anyway.

I am at a loss as to why they wouldn’t work, for reasons Bigblue suggests. I haven’t heard of rampant magazine problems with the Grendel or 6.8 cartridges. I found no issues with my Valkyrie and its long bullets. They, like my Bushmaster, take different magazines. I don’t find this to be a problem. I even have separate one for my Blackout, for safety.

I wouldn’t let some nay saying sway me.

MCMXI said:

I've been doing some research on the 6mm ARC and it seems that magazines are an issue, specifically in terms of reliable feeding. Supposedly the 6.5 Grendel magazines don't work that well for 6mm ARC. Does anyone have any insight?

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Are they using regular .223 AR mags? I don’t have any experience w 6mm ARC, but plenty w 7.62 x39 and 6.5 Grendel in ARs. As long as you get the highly curved mags (I like c products) they work interchangeably after you fill and empty them a few times. In a pinch 2-3 Grendel rounds might feed in a regular .223 AR mag, but reliability gets really spotty beyond that. Nevertheless I constantly see people trying to use them - unsuccessfully, and swearing that regular AR mags will work.

However, I recognize getting the mag curve angle aligned w the bullet taper is key. So there might be something too the issue you describe. Maybe line up 25 Grendel bullets and 25 6mm arc and see if the resulting curve is noticeably different? If it is, I doubt the same mag bodies would work. Also I wonder if oddball handloaded bullets throw off the taper angle - especially if you are using long high BC bullets.

The greatest ability is availability, so I’ll always go with reliability. You may want to consider something more developed, like Grendel, if the mags won’t work.

I worked up a load for my 6BRA using those 109s. Be advised, they are LOOOoooonng

MCMXI said:

@Nature Boy, probably shooting myself in the foot already!

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Somebody's got to pioneer this stuff! Great thread MCMXI.

You opposed to loaded rounds to get your brass?

It’s not ideal when used to starting with virgin Lapua but times are different.

In stock

https://www.freedommunitions.com/hornady-6mm-arc-108-gr-eld-match.html

If that doesn’t work out let me know. I’ll check a place local to me. I saw some on the shelf, it caught my attention because it was the only thing left. Not surprising due to its newness. I don’t mind buying it and shipping it to you if it comes to it.