Ready to pull the trigger?

[bugboy]

This was my first time putting together an upper and my first time with any AR other than 22/5.56.

I received my type 2 bolt from tactical ammunition today and everything is put together.

I've got some ammunition assembled using new Lapua brass, 123gr Amax and CFE223 powder. I started at 28gr and working up in .3 gr increments to 31.2gr and intend to shoot "ladder tests" (3 of each loaded) and checking for signs of pressure as I go. I will be looking for the smallest vertical dispersion. If there are two "nodes" I will go with the hotter load (assuming no excessive pressure signs). I don't have access to a chronograph. I've got 5 extra loaded at the low end for getting the scope on paper.

Any flaws in this plan? Inputs are appreciated.

I read conflicting info on the need to check the headspace. I've chambered some of the loaded ammo and everything seems to be in order. Is there something I need look for in regards to headspace?,,,,,, or do I just pull the trigger on the first round from an arms length away and hope for the best?

20" standard profile, machine finish, target crown, .264lbc
JP adjustable gas block
Tactical Ammunition Type II bolt
Colt bolt carrier group
Houge FF tube
Burris MTAC 4.5-14x42 mil-dot/ballistic plex
Colt lower with Accuracy Speaks trigger.

[LRRPF52]

Biggest thing that jumps out at me is no chronograph. I use the chronograph as a safety tool first to see where spikes in velocity occur, as well as where erratic velocities start showing up before relying on pressure signs on the brass, which are well into the 54,000 psi and up area if you see them.

Your barrel looks awfully like a 24" barrel to me from the angle in the picture.

If your loaded cartridges are chambering and extracting fine, you're most likely good-to-go. The main possibility after that would be excessive headspace. If your bolt is a deep-recessed .135" bolt, with a chamber cut for a .124" bolt face recess, you will have insane headspace, but it isn't likely you'll get an ignition because the firing pin will usually just push the case forward.

If you measure your bolt face recess, you either have a .135" depth, or .124" depth, +/- .001". The chamber needs to be cut for the appropriate bolt face depth.

The history behind this is that Bill A. used Colt's bolt face depth for the original 7.62x39 Colt AR15 project, which was not a half-baked program, and had a lot of industry experience behind it. They chose to use a .134"-.135" bolt face depth for the 7.62x39 Russian short cartridge for several reasons.

Bill A. used this for the Beowulf, and then the Grendel, and extensively tested this bolt design to learn its capabilities and limitations.

Meanwhile, other companies in the industry started making economy 7.62x39 AR15 upper receiver and parts kits to appeal to the customer who wanted to take advantage of cheep COMBLOC ammo, as well as hunt medium game with something with more bore diameter than a .223 Rem. What they did was instead of looking at Colt's bolt geometry and testing experience, started making bolts with a .124" depth like the 5.56 bolts.

When other shops started making offshoots of the Grendel, they of course went with a .124" bolt face depth, since these generic 7.62x39 bolts were available. This is where the confusion lies.

Anyway, here's a great video on excessive headspace from AGI:

http://www.americangunsmith.com/vidlesson/?id=37d

[RangerRick]

According to the Tactical Ammo web site the type 2 bold is recessed 0.135". Who made your barrel?

RR

[bugboy]

According to the Tactical Ammo web site the type 2 bold is recessed 0.135". Who made your barrel?

RR

Black Hole Weaponry and they specified a type 2 bolt.

I had it out and shot a "ladder test" and then work up some (3 of each) loads for further testing. Right now, the best group (.456") was with 31.8gr of CFE223 in new Lapua brass with a 123 Amax loaded to fit the magazine.
I've been informed that this load may be "on the hot side" and that I should consider backing off a couple of 1/10ths.
I think I'll load up 5 each at 31.8 and going down to check groups again.

[RangerRick]

I've used up to 32 grains of CFE223 with the 123 AMax and 31.5 with the Swift Scirocco 130 grain bullet. He found hat 31.5 was a little hot for a 130 grain bullet.

Here's a good thread of Bwild97's load tests that includes a lot of CFE loads:

http://www.65grendel.com/forum/showthread.php?2804-More-Chrony-reports!!-%28%28WARNING!%29%29-lots-of-pics.&highlight=chrono+data

RR