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6Willbird, new wildcat large frame AR project ctg


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My first fit and chamber of a rifle barrel was a wildcat 6-284 with 1/8 twist. Built up on a remington 40XC action. I have shot it a lot and have really liked it. Also built a 22-250AI which I really like. The 6-284 as is really qualifies as an "improved" ctg for the most part.


Recently I got an itch to build a light to medium bullet 6mm on the AR308 platform. Looked at some off the shelf options including plain Jane 243, 6mm competition match, and some other similar variants. Or just a 6mm creedmore. The current vogue of making up ctg to use really high BC bullets is interesting, but the same rounds when loaded with lighter more explosive on impact bullets end up being really short, lots of magazine space left. We also hear a lot of "ackley cased do not feed well in semi auto". Well Hmm the 6.5 creedmore pretty much IS a 30 degree shoulder "improved" case, and the 6mm creedmore is too.

Something caught my eye and I did a bit of autocad work and came up with this. Naysayers need not apply, it is happening, parts and tools on the way.

Basics are just run a 6mm creedmore reamer in about .149" deeper, then use 243 win brass or 260 brass necked to 6mm. Case capacity will be more than 6mm creedmore, more than 243, a touch less that 243AI 40 degree. One downside to off the shelf reamer is that the necks of the 243 brass are about .025" too short, but I'm not losing sleep over that. if it works as well as I hope I will send the reamer to have the neck shortened and the throat altered. 6Willbird on left, standard 243 in middle, 6 creedmore on right.


Edited by willbird
left out description for the picture.
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Will use a Green Mountian 1/10 chrome moly barrel. Build 1.2" and 24" long to begin with....no gas port.

A 243 AI 40 degree more less is a 6mm remington as far as case capacity goes. This case will be a touch smaller. Most data I am seeing for 6mm says they used 24" barrel. We should be able to use 243 win maximum loads as a starting point, and work up towards 6mm data, if we reach the quoted 6mm velocity for a given powder we should be near maximum even if we have not seen any pressure signs yet.

Final plan is 18" pencil with either rifle gas or rifle minus 1". Goal is a light, short and handy 6mm varmint rifle :-). Focus will be on 75 and 87 Hornady Vmax bullets.



Edited by willbird
forgot something :-)
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Made a shoulder bump gauge and a headspace gauge .005 shorter than the ctg case in the gauge



Use the 6 creedmore full lengthg size die to do a crude hydraulic shoulder bump. Set the die up .005 longer than the headsapce gauge, filled it with marvel mystery oil (it was handy hehe) and put a gage pin inside the case mouth, hit the gage pin with a big ass dead blow hammer :-). This gave me headspace of about +.005 from the gauge, bumped that back with the die.


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Maybe should explain the .005 shorter than the brass for a headspace gauge. This is an Ackley thing, the parent ctg head spaces on the corner of the new shoulder angle, so .005 shorter helps ensure that the ctg fits tight while fire forming. There is a bit of give to that fit so it is nothing like a round with equal shoulder angle to the chamber being .005 long on headspace.

some folks neck up then back down to get a small false shoulder. In this case we could just neck down 260 brass maybe. The hydraulic pre form also works, Hornady makes dies for $180 or so. Honestly just firing live rounds as PO Ackley intended works great in my experience.


where there is no parent  ctg to begin with I like to set things up about .002 shorter than the brass, then use Redding competition shell holders. In the case of the 6 Willbird I'm using the 6 creedmore dies to begin with so the shell holder is .150 or so from the bottom of the die. That perhaps will not work for successive reloadings (we will see) and I may need to have a die made.



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Fedex brought me a package with an empty reamer tube. Package had a hole where the tool escaped. Fedex taped over the hole after the tool escaped. Creedmore sports said they would ship replacement today. Lesson there is to wrap stuff up so it cannot punch a hole through all of the packing materials.



Edited by willbird
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  • 2 weeks later...
  • 2 weeks later...

Building a pile of parts. Bought a 308 faxon 18" pencil so that I can document the barrel contour. Here is where things are headed


Aero M5 lower

Aero M5 upper

Faxon Pencil 18" (just for measurements and weight)

Aero LPK minus FCG

Brownells BCG...

PSA nickle boron 2 stage trigger

Magpull MOE grip

BATTLELINK Minimalist Stock

AR-10® 6 POSITION RECEIVER EXTENSION KIT (NO STOCK) – AR10REKIT01..includes spring and buffer.

White oak precision gas tube rifle minus 1"

That totals up to 6lbs 7oz

Coming in mail....


This is specified as 10oz complete which is fairly light...not many other fairly light M-Lok options that are not $300-$400

Surefire PROCOMP 762

So that supports 7lbs 8oz or lighter...which makes me smile :-).


Not ordered yet

gas block, probably going to be


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GunTec is doing some good rails, man. I have one of those on the 12.5" Grendel.  I like where this whole build is going.  :thumbup:

I think all their rails are DPMS Low Profile - and the Aero M5 set is DPMS High Profile.  If that doesn't bug you, it'll be a great setup.

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29 minutes ago, 98Z5V said:

GunTec is doing some good rails, man. I have one of those on the 12.5" Grendel.  I like where this whole build is going.  :thumbup:

I think all their rails are DPMS Low Profile - and the Aero M5 set is DPMS High Profile.  If that doesn't bug you, it'll be a great setup.

Yea the profile thing will be fine :-). So far I have never set anything up where half of it was on the rail and half was on the upper. I was just spinning it and seeing that shaving 2 oz from the rail was going to cost $200 more or less, $100 an ounce is usery hehe.



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OK here we are mocked up with Faxon pencil 18" 308. Lacking a gas block. 


The rules say for total weight it needs sights or scope and a magazine...but without those.

Lower 2lb 6.6oz

Upper 5lb 3.9oz

Total 7lb 10.5oz.  So 2.5 oz heavier than projected, 6mm bore will add a litle weight unless I pare it off in the lathe :-).

The rail and nut actually weighed in at 13oz, guntec claims 10oz :-(. (Total Weight Including Barrel Nut Is 10 Oz!!). A smoke composite would 8.53 total...not gonna go nuts over a few oz :-).


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  • 3 months later...

Brownells had these hard chrome BCG on sale, Brownells brand, I am a sucker for a half off sale any day :-).


Weight is 477G vs the 503G for the either Toolcraft or Brownells.

I REALLY like the ejector a lot better.


No concerns with plating thickness because I am making my own barrel. 

Here is what Brownells calls it. BROWNELLS - AR 308 BOLT CARRIER GROUP CHROME

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2 hours ago, willbird said:

Snagged one for $119 last year, they came up with these for their retro series, not sure if they changed their minds or are still using them in that rifle but I sure like the fit and finish on mine.

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7 hours ago, willbird said:

Here's what came up when I did a search for AR 30 cal. BCG's;


Those people need to do some work on their website search feature apparently!


So, I went back and found that if you scroll down there's another option for 308 BCG's! Why would there be a need for two different categories with two different results? I still think they need work on their website!

Edited by 392heminut
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