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6mmBR AR15 is alive !!

G

Glen Seekins

Gunny Sergeant
Commercial Supporter
Full Member
Minuteman
Jan 28, 2004
1,300
115
lewiston, ID
www.seekinsprecision.com
#1
Been thinking about building a 6BRX for a few years and i just decided i didn't have time to make brass, so i did a standard 6br. Plan on running it at a few comps this year that are 600yd or less. Phoenix next weekend being the first. It shoots 95gr SMK's allot better than i can drive it. 10 shot groups are much impressive... This is with 33.5gr of superformance powder and 205m primer. I have not put it over the crono yet, but no pressure signs at all so ill probably stick more in. Anyone else play with this combo for anything? Im looking for as much velocity as i can get and i tend to be on the..hot side of things usually.

Specs case your wondering.
Our billet AR15 lower, 3gun upper/15" rail
National match trigger
Magpul PRS stock
22" Rock Barrel. 1" from upper to rifle gas block. .75 gas block and .74 to muzzle. 1" section is radial fluted. deep at the gas block and shallower as you get to the upper. Looks pretty wicked!
our adjustable gas block, Melonite gas tube
our 5/8-24 30cal comp
1.26" 34mm rings
Leupold MK6 3-18 with Horus ret.
Cant remember where R-bros got the bolt and extension from?? its BIG lol
11.5 lbs loaded..
 
#4
Re: 6mmBR AR15 is alive !!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: heatseekins</div><div class="ubbcode-body">Im looking for as much velocity as i can get and i tend to be on the..hot side of things usually.
</div></div>

I chuckled when I read this....Glen is always breaking stuff while being on the hot side of things
laugh.gif
 
#6
Re: 6mmBR AR15 is alive !!

The other one built in this group project is a 6BRX. Jesse is running 105's w/N550 at 3050 in a 22" barrel. Accuracy is 1/2moa so far with it if he does his part. Pretty much the same specs as Glen's but a Broughton barrel with a .830 muzzle. Pretty sure they will both be running them in comps this year to see how they work out.
 
#10
Re: 6mmBR AR15 is alive !!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RBros</div><div class="ubbcode-body">These are on AR-15 platforms. Using 6.8SPC mags right now with a little tweak. </div></div>

Interesting... what OAL can you use with the 105's?
 
#12
Re: 6mmBR AR15 is alive !!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sledge1</div><div class="ubbcode-body">Unless he's single feeding it, something less than 2.310. </div></div>

Thats what I was thinking... But he said 6.8 mags slightly modded but I'm looking at my AR mags and there's not much room to gain OAL there.
 
#14
Re: 6mmBR AR15 is alive !!



The company is AR15 Performance and they are located in Tennessee.

They are currently out of just about everything as you can image from all the other reports.

The 6.8 mags are used because of the diameter as the OAL is still limited by the AR15 platform at ~2.26" to 2.3" depending on the mag manufacturer.

The bolt has been named the 'Super Bolt' by the makers since it uses radius cuts instead of straight cuts for the 6mmBR bolt.

Regards.
 
#16
Re: 6mmBR AR15 is alive !!

The BRX will push 105s around 3000-3050 from a 22" barrel. 95s 3150-3200. The BR bolts and extensions are the 800 series.
.800 diameter head. He's right we can't possibly machine enough of the AR15 5.56 and 6.8 superbolts to fill the orders. Backorders add up to over a thousand in a weeks time. We only machine the 800 series about once a year, at least until we get into the larger building and add a few machines.
 
#17
Re: 6mmBR AR15 is alive !!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bustin</div><div class="ubbcode-body">The BRX will push 105s around 3000-3050 from a 22" barrel. 95s 3150-3200. The BR bolts and extensions are the 800 series.
.800 diameter head. He's right we can't possibly machine enough of the AR15 5.56 and 6.8 superbolts to fill the orders. Backorders add up to over a thousand in a weeks time. We only machine the 800 series about once a year, at least until we get into the larger building and add a few machines. </div></div>

I thought you stopped making these super bolts and the 6mm BRX? What`s the velocity difference between the BR and BRX. The BR sounds more tempting without the fireforming.
 
#18
Re: 6mmBR AR15 is alive !!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sititunga1</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bustin</div><div class="ubbcode-body">The BRX will push 105s around 3000-3050 from a 22" barrel. 95s 3150-3200. The BR bolts and extensions are the 800 series.
.800 diameter head. He's right we can't possibly machine enough of the AR15 5.56 and 6.8 superbolts to fill the orders. Backorders add up to over a thousand in a weeks time. We only machine the 800 series about once a year, at least until we get into the larger building and add a few machines. </div></div>

I thought you stopped making these super bolts and the 6mm BRX? What`s the velocity difference between the BR and BRX. The BR sounds more tempting without the fireforming. </div></div>
I haven't had time in the last 2 years to do any special projects except for 1 run of bolts. Most of those will be used on some 20" 6BR varmint barrels and a run of 270 Shorts( 6.5x47 necked up to 277 and the shoulder pushed back apx .100). There is apx 150-200fps diff between the BR and BRX depending on the bullet weight. You're right the 6BR makes it easy, just drop 30gr of Varget in a case, cram a bullet in and it will shoot.
 
#19
Re: 6mmBR AR15 is alive !!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Onemoretime</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sledge1</div><div class="ubbcode-body">Unless he's single feeding it, something less than 2.310. </div></div>

Thats what I was thinking... But he said 6.8 mags slightly modded but I'm looking at my AR mags and there's not much room to gain OAL there. </div></div>
The 6.8 mags have the same oal, different followers. I figure he's had some work done to the lips. I would think that 2.300" would be plenty for such a short case.
 
#20
Re: 6mmBR AR15 is alive !!

The mags we have needed to be modded a bit for capacity reasons only, they feed just fine from an unmodified PRI 1st Gen 6.8spc mag. I run my BRX at 2.300-2.310 OAL with 105s and as noted above getting around 3000-3050fps. I'm still playing around with mine fireforming brass and finding the best 105 load, but it's shot several 1/2moa groups and definitely shows good potential. It seems that the 95smk are quite a bit less sensitive, but I'm needing a 105 load so that's where I'm focusing at the moment. The 95s will reach 3200 with N550 and shoot really good though:)
 
#22
Re: 6mmBR AR15 is alive !!

The 15 round 6.8 mags we have will only fit around 7 before bulging without modification. After some tweaking they will fit 10. Each one is a little different and it's a bit of trial and error due to slight differences/tolerances in the lowers and mags.
 
#23
Re: 6mmBR AR15 is alive !!

In my bolt gun 6BRX, I am running Varget and RL15. It is a savage w/krieger barrel. It bugholes. Would love to do a gas gun in this cartridge. Will be curious to find out more.
 
#24
Re: 6mmBR AR15 is alive !!

I'm sure that Varget would probably work out alright, I just haven't shot much of it other than in my fireform loads. I keep meaning to try some in a formed case with a 105 and see what happens. That will have to wait until my next batch of bullets shows up though!
 
#26
Re: 6mmBR AR15 is alive !!

We're running 22" barrels, but I think you'd be pretty safe with anything in the 20-24" length depending on what you're building the rifle for. I just got a new stash of N550 and Hornady 105s so I can finally get some ammo loaded up for the match this weekend. Still have a lot of work to do in the next 5 days!
 
#27
Re: 6mmBR AR15 is alive !!

I've been wanting to do a 6BR Ar15 for a while, just waiting on H to get some of the barrels in which I understand could be a long wait.

I will be running one of his .264 gARP barrels in April to see if it can run as reliable as the 6.8. If it can, I might just stick with it for 600+yd steel. With 6.5g factory ammo around $20/box, the .264 would not be a bad comp rig and would save me some reloading time.
 
#28
toyotasaurus said:
We're running 22" barrels, but I think you'd be pretty safe with anything in the 20-24" length depending on what you're building the rifle for. I just got a new stash of N550 and Hornady 105s so I can finally get some ammo loaded up for the match this weekend. Still have a lot of work to do in the next 5 days!
Click to expand...

Are the 115 gr DTACs too long to use in the BRX?
 
#29
Glenn,
Any updates from trying it out at a match?

I've been considering this route or possibly getting a 6mmART40 from Whitley. I like the idea of the compact AR15 from factor and performance that is as good or slightly better than my 155 scenar load in .308.
 
#30
sititunga said:
Are the 115 gr DTACs too long to use in the BRX?
Click to expand...

You really can't push the 115s fast enough to gain any advantage over the 105s. IIRC the 95s and 105s are near equal out to 600 then the Lapua 105 pulls away.
The 105 Amax is inexpensive but shoots as well accuracy wise as the Lapua.
 
#31
I was planning on using my BRX at the JC Steel Challenge last weekend, but ran into a little snag with the new batch of Hornady 105s I received last Monday. They were considerably different shaped and thus completely threw off my whole load I had been running. Time to start over with these new bullets and get things whipped back into shape again. The new batch of bullets have a shorter OAL and longer bearing surface so it pretty much hosed the previous month's load development.
 
#32
JLR said:
I was planning on using my BRX at the JC Steel Challenge last weekend, but ran into a little snag with the new batch of Hornady 105s I received last Monday. They were considerably different shaped and thus completely threw off my whole load I had been running. Time to start over with these new bullets and get things whipped back into shape again. The new batch of bullets have a shorter OAL and longer bearing surface so it pretty much hosed the previous month's load development.
Click to expand...

Do you think they are changing the design? New dies? or just messed up?
 
#33
I don't know wtf is going on with them, but I know they are a bunch different than the ones I did load development with. I sent off a message to Hornady so I'll see what they have to say. They have to be seated about .070 deeper than the 95smk to get the same OAL to the ogive per my comparator.
 
#34
JLR said:
I don't know wtf is going on with them, but I know they are a bunch different than the ones I did load development with. I sent off a message to Hornady so I'll see what they have to say. They have to be seated about .070 deeper than the 95smk to get the same OAL to the ogive per my comparator.
Click to expand...

How old were the bullets? I spent a bit of time last summer shooting a 6mmAR and I found that the 105 BTHPs I bought in early 2012 were differently shaped from the same bullets bought in June. I sent Hornady a message asking if they changed the bullet's design but I never heard back from them.
 
#35
UA_Flyfisher said:
Glenn,
Any updates from trying it out at a match?

I've been considering this route or possibly getting a 6mmART40 from Whitley. I like the idea of the compact AR15 from factor and performance that is as good or slightly better than my 155 scenar load in .308.
Click to expand...

I've been looking at the Turbo 40 also, but I always come back to the hassle of fire-forming. His 224AR shoots a 90 grain bullet pretty flat, no fire-forming required with this wildcat. I'm giving this a hard look now. But the BRX is still tempting.
 
#40
And here is another one from keystone, the .240 Tomahawk. No fireforming and also based on the hagar. Making 6 hagar brass is described as a bear, but now that it is available, some of these hagar based cartridges are more viable. I think a heavy bullet setup for the .220 Thunderbolt would be good for a lot of things. You can do a lot with a 80-90gr .224 pill running around 3K fps.
 
Last edited:
#41
thorbird said:
And here is another one from keystone, the .240 Tomahawk. No fireforming and also based on the hagar. Making 6 hagar brass is described as a bear, but now that it is available, some of these hagar based cartridges are more viable. I think a heavy bullet setup for the .220 Thunderbolt would be good for a lot of things. You can do a lot with a 80-90gr .224 pill running around 3K fps.
Click to expand...
To run the 75 amax or a 80-90gr 224 bullet at mag length(2.3" in PRI mags) the case must be 42mm or shorter to keep the ogive out of the case neck. A plain 6.8 case can be shortened. That is why I made the 5.56x42 about 5 years ago.
To shoot 95smks at mag length the case must be 41mm or shorter, again a plain 6.8 case can be used (my 6x41).
A 22PPC works fine, a Grendel necked down to .224 is only about 75fps faster than the PPC and dies are available for the 22PPC. Some things just aren't worth the hassle of fireforming but I do have a 6 and 6.5BRX. We've been trying to talk Lapua into making 6 or 6.5BRX brass, until then I've started using 6.5x47 brass just to get around the time consuming fireforming process.
My next one is a hunting round. It's a 6.5x47 necked up to .277 with the shoulder pushed back .100 and overall case shortened to the same as the 6.8 so it will work in the 6.8 PRI mags. It will push a 110gr Nosler to 3000fps out of a 20" barrel. With 10 rounds in a mag it should be one heck of a hog stopper.
 
#42
Wow, factory 6brx brass. I would love not to fireform for it. Love that little round. Then I could just neck down for my 22brx. Love the 6.5x47 to .277 hunting round idea for 6.8 mags. Got to be a winner.
 
#43
If you want factory Lapua BRX brass please email Lapua. I told them I would order 10,000 to start but they aren't biting yet. Two guys that shoot silhouette at a national level are trying to get them to make it too.
 
#45
Market_Garden said:
How old were the bullets? I spent a bit of time last summer shooting a 6mmAR and I found that the 105 BTHPs I bought in early 2012 were differently shaped from the same bullets bought in June. I sent Hornady a message asking if they changed the bullet's design but I never heard back from them.
Click to expand...


I'm not sure what vintage the tester box I had was. It was purchased around the first of the year, but could have been some old stock. I think I may try some 105 Amax next or just open up the chamber with a little more freebore.
 
#46
Beautiful Rig. Yes, I will email lapua. I had heard some talk floating around that lapua were thinking of introducing their own improved 6br. I wonder if they are in the works on something similar to the brx or dasher?
 
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