BR cased AR 15 wildcats??

steve garrett

Active member
I know this has been done before. but how viable is a BR case in an ar 15? I am wondering how a 6mm br would be with medium and light bullets say 55-90 grain bullets. or punch the case out to a full blown dasher. There seems to be stuff on the WSSM's and several PPC based wildcats. What are the challenges with a BR case in an ar 15??
 
Originally Posted By: steve garrettI know this has been done before. but how viable is a BR case in an ar 15? I am wondering how a 6mm br would be with medium and light bullets say 55-90 grain bullets. or punch the case out to a full blown dasher. There seems to be stuff on the WSSM's and several PPC based wildcats. What are the challenges with a BR case in an ar 15??

Bolt heads are a problem as is incresed bolt thrust and hoop strength. Fire forming is usally needed. Hoop strength rears sit head because of case size. Performance wise there is little to be gained over a 243LBC or the 6X6.8.

Greg
 
what is hoop strength??? someone just posted about a 257 bobcat they made which got me to thinking wouldn't the BR case have been better?? The wssm cases have been successfully adapted to the ar 15 platform and they use yet an even bigger bolt face. When I look at the LBC or grendel wildcats the problem everyone says you have to run them at 52kspi. That really restricts the capability of the case with that much lower pressure. When I look at the 6.8 case I see only about 150 fps a most over a 223 case if loaded to EQUAL pressures. The BR case would be step up from all those. It could also run longer bullets which is where the 6.8 case has a weakness. You get the advantage of a shorter case like the grendel but with more horsepower.
 
Hoop strength is the basic burst level around the barrel tennon. You need XX metal around the chamber to bold the pressure. An AR15 is limited in size of the pressure it can hold safely.

The WSSM uses AR10 sized extensions and bolts. They need a special upper to handle that. Essentially a cross between the 10 & the 15.. The 6.8 throws a much heavier bullet at higher velocities than any 223 can hope to do. Expansion ratios and plain old case capacites are the key.

A 6 BR variant is easier to make than the Bobcat. They require a special bolt and extension to be used and these are not readily available.

The LBC is easy to load and will handle long bullets.The 6X6.8 will shoot the weight bullets you want at magazine lenght. The 646 yard antelope shot by Ritch's boy was a 90 grain Berger at magazine lenght.

These are all wildcats. None of them run at the same pressures. The 6.8 variants can handle more bolt thrust. The LBC less pressure because of bolt thrust and the BR even less. We load the 243LBC midway between the 6PPC and the BR because of this. Remember the AR is not a bolt gun and we have to hold pressures down to some extent and are limited in powder choices because of the gas system.

Greg
 
thanks for the explanation of hoop strength. basically there really isn't a good way to run a standard bolt face case like the BR very well unless your making a purpose built upper or have access to one. a plain ar 10 bolt head at least should work. What did they do in the olympic arms umar?? are they just dealing with the less material in and around the barrel extension??
 
arperformance made some 6br, 6brx, 6.5 br and 6.5 brx, he is bringing back the 6.5 brx shortly, you may want to ask him about the 6br.
 
on hoop strength, that is the famous argument a few people bring up everytime someone wants to build a rifle in a caliber that they don't make and that will out perform what they make.

a 308 case in an ar15 still has a safety factor of 2 in hoop strength so it isn't a problem. there have been many many br,brx ar's running with out any problem what so ever.

show me proof of a tenon exploding on a normal charged 60,000 psi load -- there is none.

if you want a br based cat you can build one pm me if you want info.
 
Originally Posted By: steve garrettthanks for the explanation of hoop strength. basically there really isn't a good way to run a standard bolt face case like the BR very well unless your making a purpose built upper or have access to one. a plain ar 10 bolt head at least should work. What did they do in the olympic arms umar?? are they just dealing with the less material in and around the barrel extension??

They basically just increased the hole for the extension to slide into. Bigger bolt. I really should measure mine and see what the difference is but ut is noticeable. Thd proprietary approach is what keeps this one down besides lack of brass and choice of magazines.

Greg
 
big dawg what all is different about your bobcat, can you post some pics of the bolt carrier, maybe alongside a standard bolt carrier. is your bolt adapted from an AR 10?? how was the barrel extension addressed. what kind of magazine setup are you using.

if hoop strength indeed isn't an issue a 6mm BRX in my mind would make the ultimate AR 15 variant. I hope one day parts to make a conversion like this will be plug and play.
 
Originally Posted By: steve garrettbig dawg what all is different about your bobcat, can you post some pics of the bolt carrier, maybe alongside a standard bolt carrier. is your bolt adapted from an AR 10?? how was the barrel extension addressed. what kind of magazine setup are you using.

if hoop strength indeed isn't an issue a 6mm BRX in my mind would make the ultimate AR 15 variant. I hope one day parts to make a conversion like this will be plug and play.

the only thing different on my build than a standard build is the bolt and barrel extension.

I am using ARP 800 series bolt with extension. I am using pri 6.8 mags and a 10 round mag i can get 7 rounds in and they let me load to 2.295

here is a picture of a standard bolt on the right and an 800 series on the left
 
so is the bolt carrier just opened up to allow the larger bolt?? in your own mind what do you feel is better about your bobcat wildcat over one in a BR case? I suppose yours has slightly more case compacity. in my mind if this could be perfected it really makes the ar 10 just a big clumsy rifle
 
Originally Posted By: steve garrettso is the bolt carrier just opened up to allow the larger bolt?? in your own mind what do you feel is better about your bobcat wildcat over one in a BR case? I suppose yours has slightly more case compacity. in my mind if this could be perfected it really makes the ar 10 just a big clumsy rifle

you don't have to do anything to the carrier, the bolt on the back half is the same as a standard bolt it goes right in to a standard carrier






i did mine because it has more case capacity, there is no fire forming, can be made from any 308 based case -- but 6.5x47 lapua lasts the longest. and i already had the 270AR so i had dies and everything i needed to make the brass.

i also did it because i wanted to do my own wildcat i have bought many wildcat chambered barrels and i wanted to do my own. there wasn't a 25 on the br case that i knew of so i did it.

now i am going to make a 7mm version so i will have 25,270, and 7mm all on the same case.

draw backs yes there are draw backs you have to neck turn and ream to make the cases but that just makes it more accurate in the end. it isn't that bad making the brass, i have made a few video's to help guys with their 270AR's and i made one for my bobcat all the steps are the same except one you size up the other size down.

there are several guys now offering brass conversion including myself for those that want to get in on the 270ar we will convert the brass to help out then it is just loading like any other round.
 
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that is freaking cool. a 6mm one should be next. what is the advantage to making the bolt lugs rounded over the squared lugs of the 223 type bolt

that bolt and barrel extension setup should work great for a BR or BRX based setup like I am suggesting
 
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yes that is what harrison designed the bolt for. I think the rounded lugs add strength and aid in locking, you would have to ask him. i didn't design it he did.

I have thought about a 6 too to replace my 6mm grendel so maybe when i get the others done.

like i said you can contact ar15performance he may have a 6 br left i just don't know. i do know he is bringing back the 6.5 brx -- i am getting one when he does.
 
That is my barrel and bolt for sale. PM me and I can tell you about it. You should read in the vendor section on 68forums under AR15Performance. The super bolt shown above and his 800 series extensions debunk the hoop strength argument. Everyone on here is bonkers about the 243lbc, 6x6.8, and 6DTI. The performance you get out of those is impressive. You can get the same performance out of the 6BR without all the reloading backflips. Check out 6mmbr.com for more information as well.
 
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