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New 6mm Advanced Rifle Cartridge

are y'all seeing around 19 for the standard deviation also?

i just thought it might be a little more consistent than that?

for the factory 108 eld m loads from hornady?

i'm stocked up on sierra 110 smk's and tubb 115 dtacs anyway, might as well start working up loads
 
The lot I got last month of 108 ammo was at 2650fps and the the SDs were about the same as the others. Not near 20 let alone 30.
 
are y'all seeing around 19 for the standard deviation also?

i just thought it might be a little more consistent than that?

for the factory 108 eld m loads from hornady?

i'm stocked up on sierra 110 smk's and tubb 115 dtacs anyway, might as well start working up loads
SD 12.5-18.5 in similar weather 1 month apart this fall. 64-72 F.
Garmin Xero 18” Proof CF AR

This was all one box. Not sure if the 12.5 I posted previously was a different lot or same honestly.

72F 40% 30.36in
Hornady 108 ELDM Factory
2504, 2506, 2480, 2472, 2445
2505, 2492, 2488, 2480, 2463
2498, 2517, 2511, 2513, 2510
2479, 2511, 2487, 2508, 2494
SD 18.5 ES 72 2”

My Shaw SS 1:7.5 liked 105 Black factory ammo. 0.75 five shot group and 1” ten shot. 2550 fps SD 13.9
Proof similar but 1.2” group. Different lot too so…

108 ELD-M
IMG_2176.jpeg
 
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I get 2650-2680 with my 20" Proof and the factory 108. SD has been around 13.

What length gas system you have on your rifle? I wonder if a longer system will allow for longer time under pressure and more velocity. Not a lot but just some smaller differences we are seeing.
 
What length gas system you have on your rifle? I wonder if a longer system will allow for longer time under pressure and more velocity. Not a lot but just some smaller differences we are seeing.
Rifle +1. Its just a regular carbon Proof. It sped up some once I got around 75-100 rounds through it. They were jumping about .030". I need to check it again soon to see if it has changed any.

This lot is from early last year or late 2022. I tossed the boxes and have them in my MTM cases now so I have no lot #. These have the brass colored primers. They had a mix going on because of supply issues around that time. My buddy has basically an identical build and a lot from mid of last year with the nickel primers. He he getting the same speed and SD as I am. I have been very impressed with the groups close and at distance with this factory stuff. I hope when I start loading for it I can match it.
 
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It’s been so long since I’ve used factory ammo between working insane hours the past few years and hand loading for the few years prior to that …

What is a reasonable expectation for factory match ammo as far as sd?
 
I would expect a SD of 15 or less from match grade factory loaded ammo. Most of the time Hornady delivers but recent lots of ELD-M are all over the place in my experience.
 
What length gas system you have on your rifle? I wonder if a longer system will allow for longer time under pressure and more velocity. Not a lot but just some smaller differences we are seeing.
In fleet testing, there have been no noticeable differences in muzzle velocity between gas system lengths, or even gas guns vs bolt guns from what I recall. The conflagration wave of gas left over from propellant conversion in the chamber only has such a tiny fraction of time to act on the projectile.

Bigger factors are rifling profile, bore diameter adherence to spec, chamber spec, etc..

I had a 16” Grendel that’s faster than any of my 18” Grendels, maybe because it uses Enfield rifling vs 5R or 3 Groove? Not really sure, just that it consistently shot the same ammo at faster speeds.

I sent it to my brother.
 
It’s so painful watching Henry shoot that course every time when he has a capable rifle that he could really hammer the close range targets and move on quickly.

The first 3 targets can be cleared in seconds by a low-mid level competitive shooter.

Those guys should have had a Grendel on that course years ago. Every time I see them messing around with anything in 5.56, I think about how they don’t realize what they’re missing out on.

You could shoot the first 2 targets on a cadence with tight splits.
 
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I'm sure Josh could double the close range stuff, oh well.
Other than JP, who makes a top tier complete Grendel rifle? They don't seem interested in home brew guns on 9 Hole. The JP Grendel I've shot would do well though.
 
In fleet testing, there have been no noticeable differences in muzzle velocity between gas system lengths, or even gas guns vs bolt guns from what I recall. The conflagration wave of gas left over from propellant conversion in the chamber only has such a tiny fraction of time to act on the projectile.

Bigger factors are rifling profile, bore diameter adherence to spec, chamber spec, etc..

I had a 16” Grendel that’s faster than any of my 18” Grendels, maybe because it uses Enfield rifling vs 5R or 3 Groove? Not really sure, just that it consistently shot the same ammo at faster speeds.

I sent it to my brother.

Was just wondering as the bulletin is only in the bore for a tiny fraction of time it wouldn’t take much to change the small amount of differences but being around this sport long enough it definitely can be a bucket load of other things making it happen also.
 
It’s so painful watching Henry shoot that course every time when he has a capable rifle that he could really hammer the close range targets and move on quickly.

The first 3 targets can be cleared in seconds by a low-mid level competitive shooter.

Those guys should have had a Grendel on that course years ago. Every time I see them messing around with anything in 5.56, I think about how they don’t realize what they’re missing out on.

You could shoot the first 2 targets on a cadence with tight splits.

That's my home range. It's a known distance setup save for a few pieces on the left side that they move around from time to time. He really shouldn't even bother with any of the targets until 400-500 yards IMHO. There's a gnarly vortex at the 600-800 mark with a crosswind (north or south winds) that comes into play if shooting beyond 800 with a cartridge that has a lot of drop (308).

From the looks of it that day the wind wasn't as big of a factor as it can be a lot of the time. I have yet to take my 14.5" 6 ARC out to the 1000 yard line but when I was running it with the 18" barrel it cleaned the course from 100 out to 1000 in a similar fashion. It's a touch difficult at times to visually see those hits at 1000 without an audial report if you're not shooting with a spotter. Large pieces of steel that don't want to move much with a little old 108 grain projectile.
 
That's my home range. It's a known distance setup save for a few pieces on the left side that they move around from time to time. He really shouldn't even bother with any of the targets until 400-500 yards IMHO. There's a gnarly vortex at the 600-800 mark with a crosswind (north or south winds) that comes into play if shooting beyond 800 with a cartridge that has a lot of drop (308).

From the looks of it that day the wind wasn't as big of a factor as it can be a lot of the time. I have yet to take my 14.5" 6 ARC out to the 1000 yard line but when I was running it with the 18" barrel it cleaned the course from 100 out to 1000 in a similar fashion. It's a touch difficult at times to visually see those hits at 1000 without an audial report if you're not shooting with a spotter. Large pieces of steel that don't want to move much with a little old 108 grain projectile.
I wanted to say, “Welcome to 2003-2009."

You start to see why I prefer the Grendel. It’s very easy to hit with 6mm for sure, but I personally can’t hear or see bullet splash that well even when we start getting out to 700yds.

I don’t even waste my time shooting 200yd TGTs unless I just want to confirm zero, and that’s with my 12” Grendel.

My shortest TGTs I’ll engage are 300-400yds, but I often just immediately start at 760yds with it. It’s not hard to hit for me even with an LPVO. I actually preferred my 1-4x LPVOs vs 1-8 because of FoV.

The main range complex I use had flat ranges with steel every 50yds from 200-1000, then another next to it that goes to 600, then multiple field ranges over and up into canyons. You have to drive to each one, that’s how big the place is.

I prefer the canyon ranges because they’re UKD.

When a 123gr hits steel, you know you hit.

I need to take out these Fort Scott 123gr TUIs, which have a really high BC. They look like missiles.
 
I wanted to say, “Welcome to 2003-2009."

You start to see why I prefer the Grendel. It’s very easy to hit with 6mm for sure, but I personally can’t hear or see bullet splash that well even when we start getting out to 700yds.

I don’t even waste my time shooting 200yd TGTs unless I just want to confirm zero, and that’s with my 12” Grendel.

My shortest TGTs I’ll engage are 300-400yds, but I often just immediately start at 760yds with it. It’s not hard to hit for me even with an LPVO. I actually preferred my 1-4x LPVOs vs 1-8 because of FoV.

The main range complex I use had flat ranges with steel every 50yds from 200-1000, then another next to it that goes to 600, then multiple field ranges over and up into canyons. You have to drive to each one, that’s how big the place is.

I prefer the canyon ranges because they’re UKD.

When a 123gr hits steel, you know you hit.

I need to take out these Fort Scott 123gr TUIs, which have a really high BC. They look like missiles.

The 108's are a little light when compared to the 130/140/147's of the 6.5 and up from there for any of the larger calibers but I love the cartridge and it's here to stay. I have plenty of other rifles and calibers/cartridges if I want to hit with authority at distance on the regular.

In regards to the range, It's nice to be able to shoot to 1000 without having to setup your own steel/range but there isn't a lot of variance out there and it gets rather predictable after a while. That said, I am grateful to have it, the days of me having to setup my own steel, my hide, range it all and then tear it back down and put it away again are gone.
 
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Thinking of swapping barrels and bolts on an existing 5.56 to create (another) 6mm ARC.

Which barrel and bolt to use?

Targets and hunting. Targets to 1K hunting to 700? for deer sized game.
Im still trying to figure out which barrel to get but for bolts most people seem to recommend the following (try to get one headspaced to your barrel):

Bolts (6 ARC is the same as Grendel type 2 bolts):
 
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Thinking of swapping barrels and bolts on an existing 5.56 to create (another) 6mm ARC.

Which barrel and bolt to use?

Targets and hunting. Targets to 1K hunting to 700? for deer sized game.
Rexus Ultra Bolt. This seems to be the most improved Grendel bolt on the market using standard materials. The extractor is for sure better than anything else I've seen and takes a lot less dressing to the corners than other bolts.

 
The 108's are a little light when compared to the 130/140/147's of the 6.5 and up from there for any of the larger calibers but I love the cartridge and it's here to stay. I have plenty of other rifles and calibers/cartridges if I want to hit with authority at distance on the regular.

In regards to the range, It's nice to be able to shoot to 1000 without having to setup your own steel/range but there isn't a lot of variance out there and it gets rather predictable after a while. That said, I am grateful to have it, the days of me having to setup my own steel, my hide, range it all and then tear it back down and put it away again are gone.
Yeah, If I lived near that range in Texas, I’d be there all the time too. I’d shoot it on a shot timer though with different target array runs. That would make it fun. Shoot it from positions too.

In courses, I use the 1000yd flat range as the classroom, then the canyon ranges as Practical Field Exercises where you really have to work in different positions, shooting off the tripod, and solving problems using the flat range work as building blocks.

The flat ranges became fun for me again once we started shooting them at night with NV Devices. I’m able to hammer 2-round and 3-round rapid strings at 700yds from seated position through NV, which sounds really cool at night suppressed.

That range sure beats lugging around and setting up/breaking down all my steel TGTs.

I would live down there if it wasn’t for the nearby town. It’s a place to be from, not move to.
 
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Yeah, If I lived near that range in Texas, I’d be there all the time too. I’d shoot it on a shot timer though with different target array runs. That would make it fun. Shoot it from positions too.

In courses, I use the 1000yd flat range as the classroom, then the canyon ranges as Practical Field Exercises where you really have to work in different positions, shooting off the tripod, and solving problems using the flat range work as building blocks.

The flat ranges became fun for me again once we started shooting them at night with NV Devices. I’m able to hammer 2-round and 3-round rapid strings at 700yds from seated position through NV, which sounds really cool at night suppressed.

That range sure beats lugging around and setting up/breaking down all my steel TGTs.

I would live down there if it wasn’t for the nearby town. It’s a place to be from, not move to.

I joined because I got tired of setting up and breaking down my range every time I wanted to go shoot. It’s a solid hour drive from the house but so is our property so it’s a wash and I have the ranch house rooms to use for when we duck hunt in that area as well.

Shooting at night and positional shooting definitely change things up and break up the mundane flat range drills. The Ranch is a 24 hour facility so after you check out for night qual the opportunities to train under nods and with thermal abound.
 
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Yep. I think he was shooting a geissele GFR gun so it would be a geissele barrel. Not sure if its CHF or cut rifled.
It was a 16” CHF chrome-lined.

It’s so painful watching Henry shoot that course every time when he has a capable rifle that he could really hammer the close range targets and move on quickly.

The first 3 targets can be cleared in seconds by a low-mid level competitive shooter.

Those guys should have had a Grendel on that course years ago. Every time I see them messing around with anything in 5.56, I think about how they don’t realize what they’re missing out on.

You could shoot the first 2 targets on a cadence with tight splits.
They move slow on that particular show because it’s what they call a Practical Accuracy episode.

If you want speed, check out their Speedway episodes here:


They’ve defined their Practical Accuracy shows as measured shooting to see how well the shooter and rifle can hit stuff. Sorta like 100yd paper target shooting except at steel and at increasing distances. Speed has no part in it except for some bonus round stuff.

They have a newish format called Sniper Course / 60sec COUNTDOWN that has a randomized time (aka “target exposure“), distance, shooter position, and shots needed to clear.
1739069698334.png


I think they have to make it harder, but I like the idea.
 
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I posted this in an unpinned thread so I figured I'd share it here as well. I have purchased all the below parts just need to wait for them to arrive then assemble!
Mainly a BCM and Geissele build with an FN stripped lower and Magpul Furniture.

6mm ARC build:
 
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Looks great! Besides the Proof barrel is that a mostly Geissele build (MK16 rail, lower, etc.)?
Yea it's all Geissele except for barrel, gas block, bolt, bolt carrier. It's the mk18 rail with integrated arca. I have some brass weights and a PRS lite stock coming to get it balanced out
 
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What setting did you end up using with the Bootleg?

I love my Bootleg carriers.
So I left it on fully suppressed and then tuned the AGB so it would lock back on an empty mag and then 2 clicks out. This should keep reliability with the can while keeping recoil down. As the gun gets dirty I can then just open the gas carrier up to give it more gas without having to get under handguards with a tool. I figure for a match gun it will be much easier to increase gas quickly that way.
 
There's another lengthy thread in the reloading forum with significant white-knighting and pearl clutching. This one is more results oriented.

 
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