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6BRX AR15 vel. results

B

bustin

Sergeant
Full Member
Minuteman
May 6, 2008
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I have been shooting a 6BRX AR for maybe 4-5 months, testing bolt life and accuracy etc.
These are just some random loads and velocities, the node with the 95smk seems to be 3075 and 3150fps.
6BRX rifle has a 22" 8 twist 3 groove barrel, shot at 4800ft elev temp apx 68 indoors under controlled lighting and through 2 chrongraphs.


Lapua 6BR brass, CCI BR4 primers



Vel is averaged from 10 shots

––––––––95gr Sierra Match King––––––––––-

33.5gr 4895=3170fps

33.5gr Varget=3127fps

33.5gr 4064=3156fps

34gr RE15=3142fps

37gr N550=3203fps

35.4gr RE17=3066fps



––––––-107 SMK––––––––––––

35.5gr RE17= 3042

35.5gr N550=3048

32.5gr 4895=3019fps

32.5gr Varget=3012fps



Velocities with the 95gr SMKs are very close to a .243 with 30% less powder and recoil. Feeds great from unmodified PRI 6.8 mags.
Overall pretty happy with the performance so the 6mmBR and 6.5 BR are next. We are expecting the 123gr 6.5 bullet to hit 2800+
out of a 20" barrel.
 
Re: 6BRX AR15 vel. results

Many have tried the BR case in the AR, all have had feeding/over ride problems out of the magazine due to the rebated rim.

What is your experience in mag feeding, impressive velocities aside?
 
Re: 6BRX AR15 vel. results

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hellbender</div><div class="ubbcode-body">Are you using the OLY Arms parts (upper, BCG, bbl ext.)?

</div></div>

No, we machine bolts and extensions and use DPMS slick side receivers so we can open the ejection port, receiver is stiffer also.
I have been using un modified PRI mags, with no problems, we do not rebate the 6BR rim.
Getting lots of interest from high-power shooters but, most just want a 6BR to keep from fireforming.
ETA- testing a 6.5BR today and have plans to build a 7mm on a 284/450 bushmaster case as long as the neck isn't to thick.
Quickload-says it should push a 120TSX to around 2850 from a 20" barrel so thats a decent hunting velocity.
 
Re: 6BRX AR15 vel. results

Interesting...look forward to your results.

There are a few of us who are on a quest for a competitive AR platform to be used in our Tactical LR matches. I think it will show up one day...

Respectfully,

--KJ
 
Re: 6BRX AR15 vel. results

6.5BR early test- 20" 8 twist 3 groove
32gr RE15 123gr Lapua 2.3OAL=2684fps
32gr H4895 123gr Lapua 2.3OAL=2736
32.8gr H4895 100gr Barnes TTSX=2916

Just from this quick test and no signs of pressure I believe the 6.5BR will be apx 200fps faster than the Grendel and the 6.5BRX another 100-150fps faster than the BR. 32gr of 15 is pretty much max case capacity in the BR, the BRX may allow me to get around 36gr of N540 or 550.
 
Re: 6BRX AR15 vel. results

Are you actually manufacturing your bolts and extensions, or modifying existing parts?

Does it use a standard bolt carrier?

Is your bbl. extension larger OD, requiring the upper to be opened up?

I had hoped that the new Rem. 30 AR bolt would work (308 size case head), but after seeing it, it looked very weak and potentially problematic for higher pressure rounds.

The OLY stuff is interesting, but they won't sell any component parts. I have a 243 WSSM and love it, but it has a lot of little idiosyncrasies that make it a nuisance. And OLY parts are kind of hit and miss on quality.

 
Re: 6BRX AR15 vel. results

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hellbender</div><div class="ubbcode-body">Are you actually manufacturing your bolts and extensions, or modifying existing parts?
<span style="color: #FF0000">We do make the bolt and extension, threads for the extension must be 1" in length and larger in dia than a .812 standard AR barrel.</span>

Does it use a standard bolt carrier?
<span style="color: #FF0000">It uses a standard mil spec carrier and receiver no need to open the receiver.</span>

Is your bbl. extension larger OD, requiring the upper to be opened up?

I had hoped that the new Rem. 30 AR bolt would work (308 size case head), but after seeing it, it looked very weak and potentially problematic for higher pressure rounds.

The OLY stuff is interesting, but they won't sell any component parts. I have a 243 WSSM and love it, but it has a lot of little idiosyncrasies that make it a nuisance. And OLY parts are kind of hit and miss on quality.

</div></div>
This is a raw machined 9310 alloy bolt, we have some parkerized and some are being Titanium Nitrate coated this week, TI is 86 rockwell. The radius at the root of the lugs increases attachment of the lugs 40% and thickens the wall around the bolt face.
I fireformed the first 100 pieces of Lapua and flattened every primer, probably shot over 2000 rounds through the test barrel, I'm in the 3rd box of 107s and 1 box of 95s.

PA150023_ezr.JPG
 
Re: 6BRX AR15 vel. results

I had seen this over on AR15.com some time ago, looked interesting and has potential.

Could you get a face-on pic of the extension so we could see the size of the lugs? Maybe a comparison pic to a standard bolt and extension?
 
Re: 6BRX AR15 vel. results

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hellbender</div><div class="ubbcode-body">I had seen this over on AR15.com some time ago, looked interesting and has potential.

Could you get a face-on pic of the extension so we could see the size of the lugs? Maybe a comparison pic to a standard bolt and extension? </div></div>

Standard CMT 6.8 bolt in the middle, our 6.8 on the left and 6BR on the right.
boltlineup.jpg
 
Re: 6BRX AR15 vel. results

Looks pretty interesting, you have changed the lug contact area from rectangular to an oval.

By increasing the ID of the bbl extension (w/ same OD) what wall thickness are you left with behind the lugs in the extension?

Would you have a comparison pic of the stock vs. new extension?

What pressures are you running (from QL) to get the velocities quoted above?

Would be interesting to see what total bolt thrust is compared to stock.
 
Re: 6BRX AR15 vel. results

Damn, looks cool. Will be interested to see the longevity stats.
 
Re: 6BRX AR15 vel. results

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hellbender</div><div class="ubbcode-body">Looks pretty interesting, you have changed the lug contact area from rectangular to an oval.

By increasing the ID of the bbl extension (w/ same OD) what wall thickness are you left with behind the lugs in the extension? <span style="color: #FF0000">.082</span>

Would you have a comparison pic of the stock vs. new extension?

What pressures are you running (from QL) to get the velocities quoted above? <span style="color: #FF0000">60K No swipes or flat primers</span>

Would be interesting to see what total bolt thrust is compared to stock.

</div></div>
I'll try to get a photo up shortly.
I have had a few Oly's and made a 6.5ARSM(wssm) and 338 ARSM(wssm) from them but, I really don't like the idea of a .555 dia case at 65000psi in that small of a barrel. The 6BRX is pretty flat, it would take stepping up to a 243 or 7mm mag to find better ballistics.
 
Re: 6BRX AR15 vel. results

Hey Bustin,
Looks interesting, do you have a web page we can look at? I searched for "6mmBRX ARs" from your sig line but did not find anything directly related to what you are working on. Are you familiar with what the guys at BR Armament Technologies are doing?

Thanks,
Erik
 
Re: 6BRX AR15 vel. results

Are you affiliated with AR Performance? The picture of the bolt is the same as on their website.

If so, ARP is good to go, bought an 6.8 SPC upper from them and am very satisfied.
 
Re: 6BRX AR15 vel. results

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: nhm16</div><div class="ubbcode-body">Are you affiliated with AR Performance? The picture of the bolt is the same as on their website.

If so, ARP is good to go, bought an 6.8 SPC upper from them and am very satisfied. </div></div>

Thanks.
We have a bunch of new projects, 6BR, 6BRX, 6.5BR, 6.5BRX, 5.56x42(SPC), 6x42(SPC) 338RCM on the AR10 platform. A AR12 sized in between the AR15 and AR10. The 6.5BR with 123gr Lapuas will hit 2840 from a 20" barrel, about 200fps faster than the Grendel.
ETA- New results for the 6.5BR from a different powder-31.2gr RE10X with CCI41 primers pushed the Barnes 100gr TTSX to an average of 3009fps from a 20" barrel, thats decent for a deer and hog hunting round.
 
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