McGowen Precision AR-15 6-ARC build

[Pig_Popper]

This build is under construction ...

The Hornady Marketing train left the station on 6.3.2020 and I’m still waiting on the platform to get on the train......

Thus far I have ordered the following:

(Ordered June 11th) 18” McGowen AR-15 mid-length gas 1-7.5 twist stainless steel 416R barrel, .750 gas journal, .078 gas port size, 5/8x24 threaded with an 11 degree target crown.

I have on hand:

100 rounds of Hornady Black to break in the barrel and use the brass to reload 

3 ASC 25 round mags - I need to tweak and tune the feedlips and mag spring -  I tested one brand new out of the package with a known good working grendel rifle and it was a jam-o-matic

Ares Armory enhanced - low friction Bolt Carrier

Bear Creak ARSEnal 6.5 Grendel bolt

AR15discounts NBS slick side billet upper and handguard

Superlative Arms adjustable gas block 

1000 cnt Speer Deep Curl 90 grain bullets

New unopened Hornady die set

An existing lower with a LaRue MBS 2 stage trigger and full length rifle stock

Will update here when I get on the train !

P.S. - I see Hornady reloading handbook and Hodgdon’s reloading tool folks standing on the platform with me ......  dang Hornady marketing team got an early jump on this one.

[BluntForceTrauma]

A good start and gonna be a good ride!

[danm]

Can't wait for range report!

[ericskennard]

forget the ASC 25 round mag. The CProducts Defense/Duramag 25 round really works. It's shape is different and the grendel/arc will feed better.

[Pig_Popper]

forget the ASC 25 round mag. The CProducts Defense/Duramag 25 round really works. It's shape is different and the grendel/arc will feed better.

As a long time Grendel user I’ve just learned to tweak every make and model of magazine - none are 100% out of the bag.

Its not a major issue - it will be a tripping point for those new to 6-ARC but we can keep an eye out for Duramag reports at that point.

if money were no issue it’d be a fun and educational post for this new forum to buy 1 new mag from every manufacture and test full mag cycling in 6mm ARC to see what works right out of the bag.

I have a few UNIMAGs which were not cheap that supposedly were designed with new patented technology to work with many calibers and there are video from folks showing they work.  All three jammed gloriously out of the bag when I first got them.  After working them in more they can almost be trusted now...

[Trashy]

That’s gonna be a great build. My barrel came in today, hoping to start putting mine together on tomorrow so I can get to the range next week. Now to get a tap to make a modified case to see how much wiggle room there is in the chamber. I’m going to start with 95 gr SST and 100 gr Sierra TGC since I have them in hand. Waiting on pics of the complete build, have fun!

Trashy

[Dino11]

Your gonna love that trigger, I have three of them in various rifles including my 6 ARC. Use the light spring it is about a 2 lb pull on the second stage

[VASCAR2]

C Products Defense/Duramag just released a new twenty round 6.5 Grendel magazine. Price is $18.95 at Aim Surplus and looks like they are still in stock. I currently don’t own any CPD/Duramags but these look pretty good.


https://aimsurplus.com/duramag-6-5-grend...-magazine/

[Pig_Popper]

McGowen has a message on their webpage that Covid is delaying barrels

Damn........

I may get impatient and have to source another barrel while I wait

[danm]

C Products Defense/Duramag just released a new twenty round 6.5 Grendel magazine.  Price is $18.95 at Aim Surplus and looks like they are still in stock.  I currently don’t own any CPD/Duramags but these look pretty good.


https://aimsurplus.com/duramag-6-5-grend...-magazine/

Just ordered 4.... Report back (with Grendel first since I'm waiting for a Proof for my 6ARC build)...

[VASCAR2]

I ordered two of the CPD 20’s today. I’ll try to test mine and get pictures once they arrive.

[Pig_Popper]

Cancelled my order for this barrel today - I’ll pay the restocking fee if it comes to it.

Aborted the mission before sending a round down range.

Reason: Hornady’s Gas Gun Load data and their proposed velocities -

https://www.hornady.com/assets/site/horn...r-data.pdf

[Trashy]

PP your not calling it quits with the ARC are you?

[Pig_Popper]

I may test a weapon system in the future in 6-ARC for a local gun manufacturer.

But in terms of spending my own money on gear / yeah I’m out.

I have a 6mm Grendel barrel in route - I’ll do this the old fashioned way and get Lapua brass, a maxim bolt, and full Grendel case capacity for powders.

It should outpace the 6-ARC load data velocities by 200 FPS

[Troy fairweather]

Cancelled my order for this barrel today - I’ll pay the restocking fee if it comes to it.

Aborted the mission before sending a round down range.

Reason: Hornady’s Gas Gun Load data and their proposed velocities -

https://www.hornady.com/assets/site/horn...r-data.pdf

The odin works barrels use mcgowen blanks, I have. 21" on its way

[AM4966]

The factory ammo in a 18” barrel is faster than the reloading data, from what I’ve seen out of other videos.

By there speeds, you might as well just use a Grendel with a 123gr bullet since your getting comparable speeds. Something doesn’t seem right.

[StoneHendge]

I may test a weapon system in the future in 6-ARC for a local gun manufacturer.

But in terms of spending my own money on gear / yeah I’m out.

I have a 6mm Grendel barrel in route - I’ll do this the old fashioned way and get Lapua brass, a maxim bolt, and full Grendel case capacity for powders.

It should outpace the 6-ARC load data velocities by 200 FPS

The only way you're going to get another 200 fps out of ~3.2% more case capacity in a 6mm Grendel is by exceeding Hornady's pressures. The Hornady data does indeed seem anemic and is likely conservative. It would be nice if they listed pressures.  And us wildcatters have probably been running over pressure. 
Anyone using charges in the range of Whitley's data certainly has. His starting points are around Hornady's maxes.

[grayfox]

In my view it is not a case of exceeding hornady's pressures, since we don't know them. It is a case of exceeding hornady's MVs. I've done a graph of load vs MV for a few 6Arc loads now, for the data presented on here, and they all have shown, for a given powder charge, 140-180 ft/s faster MV than hornady's barrel at a given grs of powder, and that is taking into account the differing barrel lengths. This would not indicate to me higher pressures, however I can't totally explain it either.
If hornady, and I say, IF, they would publish their pressures, maybe we could figure it out better. For now I'm ok with the case fill, MVs and data I've been seeing in our 18-20" barrels.
For some reason these barrels in hand are showing to be faster than whatever hornady is shooting.

---

Another thought, for a suitable powder speed/burn rate, there is no reason (that I know of) not to expect a 100-gr bullet to get somewhere in vicinity of 2700 ft/s, since in the 6.5 you can do that -- I have done it with the 100 Nosler and 100 ttsx and 100 eldm in my 20" Grendel Lilja and in the Grendel-BA barrel I have. I know the 6 is slimmer, and the case a bit shorter, but in terms of energy imparted from a powder burn and acceleration, the two calibers should be "close" together for similar -mass bullets. To me that is just a physics thing.
Hornady doesn't show anything like 2700 for 100 gr class bullets, 20" barrel.
Call me a Columbo-style ballistics guy......

[StoneHendge]

GF, so you think they have a slow barrel? Or maybe a cheap made in China Chronograph?

If you look at Hodgdon data for 107s in both 6 CM and 6.5 CM,  without making a spreadsheet, it looks like about 3000 or so should be expected with 107s in 6 CM and  3100 with 6.5 CM. Makes sense since the narrower caliber will have a bit more bearing surface.  70s in .223 vs 6x45 are a little closer in the Hodgdon data, but it does look like they run a little faster in the 6x45.  In my experience I am running 70s just shy of 3k with a very mild load in a 24" 6x45 while I ran 69s just over 2900 out of an old 24" 5.56. A large portion of the difference could be due to The 6x45s BHW-ness, though.

I've got 3 of the powders Hornady lists for 105s in the ARC. I might load up some 105 RDFs that are useless for me in a 1:8 twist at the midpoints and see how the velocity matches up in my 243 LBC. A given charge should run a little slower with the slightly larger case, right?  (Offset by BHW-ness).

I'll add, it seems that Hornady pretty much flubbed this rollout. Not criticizing the caliber, but how they've rolled it out.

[grayfox]

Honestly don't know. I'd be pretty sure it's an ok chrony, my guess (and it is a guess) would be the barrel, somehow. If they are running enfield rifling or even the Proof barrel (which as I understand is a 4-groove thing -- - weird) when they developed the charts? Or maybe (and this is a possibility) they used software. One thing that makes me think it's software is the plot of their MVs are an exactly straight line -- trendline r^2 of 1.00 correlation to linear. I have seen 0000000 barrels that have that type of MV performance!!!
Anyway I could understand 40-50 ft/s or so deviations all else being equal, but to have several barrels track so much higher than their data.... well it puzzles me.