New 6mm AR-15 pressure tested wildcat cartridge! 6MM MAX

[BCPB6mmMAX]

Hi all,
We are New to the forum and would like to introduce ourselves and our company . I’m Brian Cook and my partner is Mike Bueschel.
We are BC Precision Ballistics and our cartridge is the 6mm MAX.
We have unlocked the code for .378 bolt head performance. After 3 years designing and testing, to include lab pressure testing at EMRTC with Dave Emary, we knew we had a winner . Paul has given us the honor to introduce our cartridge first on accurate shooters .

Why The 6mm MAX?​

The 6mm MAX is pressure tested to SAAMI standards of 55k psi. It is a brand new cartridge designed for the unmodified mil-spec .378 bolt face, and a full mass bolt carrier group. The 6mm MAX holds 35 grains of water capacity which ultimately determines the energy potential of the cartridge. In this case, 1750+Lbs of energy. Why is that so significant? The 6mm MAX can launch an 87 gr Berger VLD at 3009 fps from a 24” barrel. This produces 1749 lbs at the muzzle, 1504 lbs at 100 yards, 1093 lbs at 300 yards, 775 lbs at 500 yards, 533 lbs at 700 yards, and stays supersonic past 1000 yards. These ballistics are at standard atmospheric pressure and temperature.

Cartridge designers have struggled with 2.26 OAL, and having enough room for increased case capacity. Until recently, there hasn’t been a .378 case head cartridge available that has a 35 gr water capacity. This amount of water capacity is the engine that can power heavier, and high ballistics coefficient bullets up to 100 grs. The 6mm MAX can do this within the constraints of the AR-15, and function flawlessly. So the end result is that the 6mm MAX can push bullets 55 gr to 100 gr, and do it with the same 2.30 OAL. Some designs have emerged shorter and fatter to accommodate a bullet with better BC and enough powder for useful velocities. When comparing the water capacity of 24 Nosler (29 grs), 6.8 SPC (35 grs), 5.56 x45 NATO (28.5 grs), 6×45 (29 grs), 6 ARC (34 grs), 6.5 Grendel (35 grs), .224 Valkyrie (34.5 grs), and what do we get? For the cartridges with .378 case head, powder capacity is less than the 6mm MAX. For the cartridges with larger case heads, you get the same amount of powder or less than the 6mm MAX. The end result is that the 6mm MAX (35 grs) allows for a .378 mil-spec bolt face with full lug integrity and powder to push the heavies at useful velocities.

The 6mm MAX has unlocked the code on the .378 bolt face AR-15 cartridge. We were able to increase the OAL to 2.30 with the .350 Legend parent case, and magazine, which were originally designed for the AR-15, and function flawlessly. With the OAL set at 2.30 for all bullets 55 gr to 100 gr, we were able to keep bullet jump relatively consistent for the inherent accuracy across all bullet weights. We have been able to achieve 1 MOA accuracy with most bullet weights, and sub-MOA with premium target bullets.

BC Precision Ballistics has spent 3 years and thousands of hours in research and range time to get the 6mm MAX perfected. Our case is only slightly rebated for a well balanced cartridge maximizing capacity and 100% reliability. We designed the chamber for functionality in a repeater and for accuracy. Sometimes those two requirements conflict with each other as reliability requires loose tolerances, and accuracy requires tight tolerances. We consulted with many lifelong industry experts throughout the chamber/reamer design and listened to what they had to say. We utilize carbide reamers for our builds, and our tolerances are kept exact for predictable performance.

Wondering about accuracy? On Aug 6th, 2022, I competed with the 6mm MAX in F-Class with my local club the Central Texas Silhouette Association or CTSA. Full disclosure on me? I’m an old F-Open High Master. My normal competition gun is a .243 30” Bartlein barrel running 105 hybrids at 3050 fps with a stout load of H4831SC. The 6mm MAX is not a competitive F-Open cartridge by any stretch of the imagination, but I wanted to see an actual real world test of accuracy in the hot south Texas switching winds at 500 yards. I used a 24” Bartlein barreled hunting rig. This is the same bolt rifle pictured on this web site. It has 2600 rounds of testing down range, and is till holding sub-MOA with a load of H4895 tested to SAAMI standards of 53,000 psi. The load was 26.6 grs of H4895, and 90 gr Lapua Scenar-L at 2.30 OAL. This load was straight from our loading chart on this web site. After the 3rd relay my score was 568-6X. Nothing to write home about by F-Class standards, but in the world of hunting and rifle accuracy these rounds would have HARVESTED GAME.

The 6mm MAX velocities/load chart can be found on 6mmmax.Net
We are scheduled for more lab testing in Sep. 2022 at EMRTC to expand our powders and bullets as it has been struggle to find components the last two years.

Thanks
Brian Cook
6mmMAX.net

 

[ohiofarmer]

Brian, the above looks good. Any plans for properly headstamped brass? Or just necking down .350 Legend for the time being? What’s the brass length? I see COAL above, but not the brass length. Thanks

 

[BCPB6mmMAX]

Brian, the above looks good. Any plans for properly headstamped brass? Or just necking down .350 Legend for the time being? What’s the brass length? I see COAL above, but not the brass length. Thanks

Hi Ohiofarmer,

Brass trim length is 1.715
We have 10,000 cases properly head stamped (lazer) and formed with Warner dies. We will be offering a premium upper package to include 6mm MAX upper, lee custom dies, and 100 pieces of 6mm MAX brass ready to load.
We have a PO for 100k pieces to be filled when a hole on the assembly line opens at star line brass. The last 2 years have been rough on everybody , we stayed the course and are 2-3 months from selling packages.

Brian

 

[Ledd Slinger]

Meh, ARs have been beat to death.

Being the devils advocate, I would say a 6mm Grendel would give the same performance but with the advantage of more brass down low to give a stronger case head and primer pocket. Takes mere seconds to swap out a BCG so no advantage in designing cases on the .378” face. All you are doing by making a big case on a small head is creating a weak primer pocket.

The 6mm Grendel is readily available with Lapua brass so hard to see any improvements here.
Then there is also the Grendel Improved and LBC Turbo 40 versions available. Both of which would give superior performance to this 6mm Max.

 

[BCPBMike]

We went to EMRTC to pressure test our 6mm Max. We used a Bartlein 24" Pressure test barrel. Here are a few photos from that event.

Mike Bueschel
BC Precision Ballistics

 

[BCPB6mmMAX]

Hi Ledd Slinger,
Being compared To a Grendel is a complement.
Matching the Grendel’s terminal ballistics in an AR-15 is an achievement we are proud of.
The grendel has saami spec’s of 52k psi and 2580fps with 123gr and 24” barrel. It’s a one bullet gun and a fantastic one at that.

How we differ is a 55gr bullet at 3553fps all the way to 100gr bullet at 2762fps @ 53k saami spec’d with 24” barrel all loaded to 2.300 for relative ogive to land distance. It’s one upper that can retain accuracy with a vast array of bullet selections to do many jobs.
For primer pocket life in the 6mm MAX utilizes the CCI #41 or CCI 450 small rifle primer. We have not experienced shortened primer pocket life at saami pressures . Going above these pressures in an AR platform is something I don’t endorse as there are many areas besides brass that will fatigue before the primer pocket.

Brian

 

[RickB]

Hi Ledd Slinger,
Being compared To a Grendel is a complement.
Matching the Grendel’s terminal ballistics in an AR-15 is an achievement we are proud of.
The grendel has saami spec’s of 52k psi and 2580fps with 123gr and 24” barrel. It’s a one bullet gun and a fantastic one at that.

How we differ is a 55gr bullet at 3553fps all the way to 100gr bullet at 2762fps @ 53k saami spec’d with 24” barrel all loaded to 2.300 for relative ogive to land distance. It’s one upper that can retain accuracy with a vast array of bullet selections to do many jobs.
For primer pocket life in the 6mm MAX utilizes the CCI #41 or CCI 450 small rifle primer. We have not experienced shortened primer pocket life at saami pressures . Going above these pressures in an AR platform is something I don’t endorse as there are many areas besides brass that will fatigue before the primer pocket.

Brian

CCI recommends only the #41 primer for small primer applications in the AR platform because of the floating firing pin. Federal specifically says do not use their 205 in an AR. 41s are very difficult to find. I recently scored a few and felt like it was Christmas.

While I do not doubt your thoroughness in trying to develop a SAAMI spec cartridge within acceptable pressure standards, I think there will be more than a few people comparing the performance of your cartridge to the 6mm ARC and the variety of 6mm Grendel variants including at least one Benchrest variant (the Grinch). The quality of Lapua brass is always a factor to many people.

AR bolts experience failures even in military applications although some manufacturers claim to enhance its strength by use of improved steels and heat treating.

Lastly, anyone not familiar with the CTSA range should be aware that it is one of the more challenging ranges around and the the score fired was a fine result for anything in an AR.

 

[6bra1k]

with well over 20 years invested in building and shooting ar's i will never use a cci41 in one. tried them did not like them and cold weather failures. the geometry of an ar means the bolt lugs are ENGAGED before the firing pin can touch the primer. many tend to ignore the built in safety. i tend to use 205m's most of the time, 210s in ar10's.
when the poster will produce some 1000 or even 600 yard targets, fired from an ar with the new round , i will take a look. until then he is another 224 valkyrie....factory produced and backed, all kinds of claims of a 1000 yard ar round..but they tested with 24" bbl , marketed 16" bbls and never once showed a 5 shot 1000 yard target. not interested in hot air.

 

[BCPB6mmMAX]

CCI recommends only the #41 primer for small primer applications in the AR platform because of the floating firing pin. Federal specifically says do not use their 205 in an AR. 41s are very difficult to find. I recently scored a few and felt like it was Christmas.

While I do not doubt your thoroughness in trying to develop a SAAMI spec cartridge within acceptable pressure standards, I think there will be more than a few people comparing the performance of your cartridge to the 6mm ARC and the variety of 6mm Grendel variants failures even in military applications although some manufacturers claim to enhance its strength by use of improved steels and heat treating.

Lastly, anyone not familiar with the CTSA range should be aware that it is one of the more challenging ranges around and the the score fired was a fine result for anything in an AR.

Hi Rickb,

Good points to discuss. CCI 41’s primers have been difficult to find like all primers lately. We as an industry are in an evolution that’s not pretty right now.

Bolt failures definitely happen. Utilizing the .378 bolt face maintains as much strength as possible to mitigate this occurrence to a point where the bolt is excepted as being worn out and it’s service life is over.
Comparing the 6mm MAX to all others is inevitable and part of the evolution. I will post a ballistics comparison with all applicable cartridges in AR-15 ( saami data) and we can discuss the plus and minus of each.

CTSA is indeed challenging with few cleans posted.
My F-open scores were shot with 6mm MAX 24” Bartlein barreled hunting rifle. I will be using 20” Barrett DMR suppressed , chambered in 6mm MAX For next comp and will post scores .
Attached is the load I’ll be shooting.

 

[gunsandgunsmithing]

Hi all,
We are New to the forum and would like to introduce ourselves and our company . I’m Brian Cook and my partner is Mike Bueschel.
We are BC Precision Ballistics and our cartridge is the 6mm MAX.
We have unlocked the code for .378 bolt head performance. After 3 years designing and testing, to include lab pressure testing at EMRTC with Dave Emary, we knew we had a winner . Paul has given us the honor to introduce our cartridge first on accurate shooters .

Why The 6mm MAX?​

The 6mm MAX is pressure tested to SAAMI standards of 55k psi. It is a brand new cartridge designed for the unmodified mil-spec .378 bolt face, and a full mass bolt carrier group. The 6mm MAX holds 35 grains of water capacity which ultimately determines the energy potential of the cartridge. In this case, 1750+Lbs of energy. Why is that so significant? The 6mm MAX can launch an 87 gr Berger VLD at 3009 fps from a 24” barrel. This produces 1749 lbs at the muzzle, 1504 lbs at 100 yards, 1093 lbs at 300 yards, 775 lbs at 500 yards, 533 lbs at 700 yards, and stays supersonic past 1000 yards. These ballistics are at standard atmospheric pressure and temperature.

Cartridge designers have struggled with 2.26 OAL, and having enough room for increased case capacity. Until recently, there hasn’t been a .378 case head cartridge available that has a 35 gr water capacity. This amount of water capacity is the engine that can power heavier, and high ballistics coefficient bullets up to 100 grs. The 6mm MAX can do this within the constraints of the AR-15, and function flawlessly. So the end result is that the 6mm MAX can push bullets 55 gr to 100 gr, and do it with the same 2.30 OAL. Some designs have emerged shorter and fatter to accommodate a bullet with better BC and enough powder for useful velocities. When comparing the water capacity of 24 Nosler (29 grs), 6.8 SPC (35 grs), 5.56 x45 NATO (28.5 grs), 6×45 (29 grs), 6 ARC (34 grs), 6.5 Grendel (35 grs), .224 Valkyrie (34.5 grs), and what do we get? For the cartridges with .378 case head, powder capacity is less than the 6mm MAX. For the cartridges with larger case heads, you get the same amount of powder or less than the 6mm MAX. The end result is that the 6mm MAX (35 grs) allows for a .378 mil-spec bolt face with full lug integrity and powder to push the heavies at useful velocities.

The 6mm MAX has unlocked the code on the .378 bolt face AR-15 cartridge. We were able to increase the OAL to 2.30 with the .350 Legend parent case, and magazine, which were originally designed for the AR-15, and function flawlessly. With the OAL set at 2.30 for all bullets 55 gr to 100 gr, we were able to keep bullet jump relatively consistent for the inherent accuracy across all bullet weights. We have been able to achieve 1 MOA accuracy with most bullet weights, and sub-MOA with premium target bullets.

BC Precision Ballistics has spent 3 years and thousands of hours in research and range time to get the 6mm MAX perfected. Our case is only slightly rebated for a well balanced cartridge maximizing capacity and 100% reliability. We designed the chamber for functionality in a repeater and for accuracy. Sometimes those two requirements conflict with each other as reliability requires loose tolerances, and accuracy requires tight tolerances. We consulted with many lifelong industry experts throughout the chamber/reamer design and listened to what they had to say. We utilize carbide reamers for our builds, and our tolerances are kept exact for predictable performance.

Wondering about accuracy? On Aug 6th, 2022, I competed with the 6mm MAX in F-Class with my local club the Central Texas Silhouette Association or CTSA. Full disclosure on me? I’m an old F-Open High Master. My normal competition gun is a .243 30” Bartlein barrel running 105 hybrids at 3050 fps with a stout load of H4831SC. The 6mm MAX is not a competitive F-Open cartridge by any stretch of the imagination, but I wanted to see an actual real world test of accuracy in the hot south Texas switching winds at 500 yards. I used a 24” Bartlein barreled hunting rig. This is the same bolt rifle pictured on this web site. It has 2600 rounds of testing down range, and is till holding sub-MOA with a load of H4895 tested to SAAMI standards of 53,000 psi. The load was 26.6 grs of H4895, and 90 gr Lapua Scenar-L at 2.30 OAL. This load was straight from our loading chart on this web site. After the 3rd relay my score was 568-6X. Nothing to write home about by F-Class standards, but in the world of hunting and rifle accuracy these rounds would have HARVESTED GAME.

The 6mm MAX velocities/load chart can be found on 6mmmax.Net
We are scheduled for more lab testing in Sep. 2022 at EMRTC to expand our powders and bullets as it has been struggle to find components the last two years.

Thanks
Brian Cook
6mmMAX.net

I hope you do realize that rebating the rim does not reduce bolt thrust. Granted, you probably have a small margin due to 5.56 vs the 223 saami 55000 psi max on the same platform, but it's hard to compare the two.
Here's a good article on bolt thrust, the real issue with AR15 bolt failures.

A Look at Bolt Lug Strength - Lilja

All action designers are concerned primarily with producing a safe and functional product. All other considerations such as weight, finish, eye appeal and other cosmetics are secondary. From a safety standpoint, the strength of the bolt lugs is of prime concern. Bolt lug shear strength depends...

riflebarrels.com

 

[No manches"]

Picture's of case,cartridge and Sammi specs diagram needed.
To known what we are dealing with.

 

[BCPB6mmMAX]

with well over 20 years invested in building and shooting ar's i will never use a cci41 in one. tried them did not like them and cold weather failures. the geometry of an ar means the bolt lugs are ENGAGED before the firing pin can touch the primer. many tend to ignore the built in safety. i tend to use 205m's most of the time, 210s in ar10's.
when the poster will produce some 1000 or even 600 yard targets, fired from an ar with the new round , i will take a look. until then he is another 224 valkyrie....factory produced and backed, all kinds of claims of a 1000 yard ar round..but they tested with 24" bbl , marketed 16" bbls and never once showed a 5 shot 1000 yard target. not interested in hot air.

Hi 6bra1k,

The CCI 41 and Winchester#41 are the two mil-spec primers that are approved and were available for our cartridge testing in AR-15’s. These two both mitigate slam fire through thicker cups and moving the anvil slightly forward. I believe these are the only two primers that are specifically designed this way for AR’s.
If you release the bolt and chamber a round , then un-chamber said round, you will find a slight primer indentation from firing pin. The firing pin is free floating and strikes the primer every time a round is chambered.
Full bolt lug engagement allows the hammer to be cycled due to correct bolt carrier position, which is a built in safety, but I believe this has no interaction with slam fire.

The 6mmMAX cartridge was designed to increase the effect range of the M16/AR-15 its variants. The same as every cartridge that has preceded us.
We differ in having achieved this on the mil-spec .378 bolt head for lug integrity.
I will continue to post scores from F-Class open at 500yards. I will try and make a video at 550yards shooting clays. This is currently the farthest distance I have without travel.
They will be fired from AR-15 platform although this is not a legal F-Class gun with brake and suppressor it’s fun as all get out.

Brian

 

[gunsandgunsmithing]

We differ in having achieved this on the mil-spec .378 bolt head for lug integrity.

Again, bolt head has nothing to do with bolt thrust. It's the "piston" area that works on the case head that generates thrust on the bolt. That area being, the internal diameter of the case itself. Since you failed or ignored replying to my post in regard to this, I'm left to think it has NOT been considered. Fair enough or not? I even posted a link to Dan Lilja, an engineer and bbl maker's web site, offering the formula for calculating thrust. Still, no reply. This does worry me, regardless of what others might or might not think. You seem to be ignoring the physics involved in bolt thrust. If facts bother you, I'll stop offering them and we can go our separate ways. But there are plenty of people that do in fact appreciate facts when they involve a 55,000psi bomb inches from their face that has potentially not been properly accounted.
I applaud you for your work. Just finish it before touting it, please and thank you.---Mike Ezell

 

[BCPB6mmMAX]

I hope you do realize that rebating the rim does not reduce bolt thrust. Granted, you probably have a small margin due to 5.56 vs the 223 saami 55000 psi max on the same platform, but it's hard to compare the two.
Here's a good article on bolt thrust, the real issue with AR15 bolt failures.

A Look at Bolt Lug Strength - Lilja

All action designers are concerned primarily with producing a safe and functional product. All other considerations such as weight, finish, eye appeal and other cosmetics are secondary. From a safety standpoint, the strength of the bolt lugs is of prime concern. Bolt lug shear strength depends...

riflebarrels.com

Excellent point and that’s a fantastic article.
The 6mm MAX is based off the .350 legend parent
Case SAAMI certified to 55k max nominal PSI or 53.5psi spec load. We choose to except the engineering as fact and designed and pressure tested to the same.

The 5.56x45 NATO has a press cap at 57,500psi.
The M855A1 EPR went to 63,500psi and experienced fatigue and failures at severely reduced round count than mil-spec. The Marines were the only branch that had the courage to through to BS flag in testing.
We have lab tested to NATO pressure and achieved 3180fps with a 77gr MTH solid copper bullet with a .370BC.
The civilian load on our loading chart is 3100fps @ 53.5k psi with max nominal 55k.

Brian

 

[Rocketvapor]

I'm going to follow your development as 6mm is the new cat's meow. Legal hunting in more states than a 5.56 round.
The base/rim of 0.390"/0.378" are not as "rebated" as the 22 Nosler @ 0.420/0.378 and we all know how well the idea of rebated rim went over with that round. One reason some (me included) started necking down 6mm Hagar cases. When talking lug strength It seems obvious that the larger rim diameters have less lug strength and that the larger case diameters produce higher bolt thrusts (at the same pressures).
When you get to Grendel sized rims this starts to show up as higher failure rates.
Recommending the 41 over the 450 primer, whether needed or not is a lawyer feature for a manufacturer.
A reloaded can opt to use either, and pick their max pressure (safe or not).
Making a higher powered AR-15 round and still being able to load at mag length was the attraction that propelled the .224 Valkyrie.

I know your testing will be primarily on AR 6mm rounds, but don't forget about us F-Open shooters with a 22 Nosler/NOSGAR We have some heavies (loaded long) that have decent ballistics down range.
Best to you and I will follow.

 

[expiper]

i will take the grendell with lapua brass any ole day---if you want to hunt with a rattle gun you gotta try a 450 Bushmaster -i have one it is capable of 1" groups at 100yds and 2200 fps with a 250 gr bullet !!!!!--it is fun to shoot and is no fun to shoot if that makes any sense--Roger

 

[BCPB6mmMAX]

Picture's of case,cartridge and Sammi specs diagram needed.
To known what we are dealing with.

Hi No manches,
I can post pics of case and cartridge. THE 6MM MAX Is trademarked and reamer drawings our still in house.

 

[gunsandgunsmithing]

The 5.56x45 NATO has a press cap at 57,500psi.
The M855A1 EPR went to 63,500psi and experienced fatigue and failures at severely reduced round count than mil-spec.

Where did that data come from? It's pretty near impossible to relate cup and psi. If the testing came from actual pressure testing, that's great but it's still above saami established pressures and you can't compare 556 vs 223 chambers due to differences in shape and design...ie, longer and bigger freebores on 556 than saami 223.
FWIW, saami recognized the difference in bolt thrust for the 6.5 Grendel and reduced max psi ACCORDINGLY to bolt thrust. You can reverse engineer the math and see yourself. They did NOT adjust it down due to thinner lugs but by an amount equal to the additional bolt thrust generated by the larger case ID of the grendel. fwiw.

 

[BCPB6mmMAX]

I'm going to follow your development as 6mm is the new cat's meow. Legal hunting in more states than a 5.56 round.
The base/rim of 0.390"/0.378" are not as "rebated" as the 22 Nosler @ 0.420/0.378 and we all know how well the idea of rebated rim went over with that round. One reason some (me included) started necking down 6mm Hagar cases. When talking lug strength It seems obvious that the larger rim diameters have less lug strength and that the larger case diameters produce higher bolt thrusts (at the same pressures).
When you get to Grendel sized rims this starts to show up as higher failure rates.
Recommending the 41 over the 450 primer, whether needed or not is a lawyer feature for a manufacturer.
A reloaded can opt to use either, and pick their max pressure (safe or not).
Making a higher powered AR-15 round and still being able to load at mag length was the attraction that propelled the .224 Valkyrie.

I know your testing will be primarily on AR 6mm rounds, but don't forget about us F-Open shooters with a 22 Nosler/NOSGAR We have some heavies (loaded long) that have decent ballistics down range.
Best to you and I will follow.

Thanks for the support , I have a load for bolt guns in the works with the 105 hybrid. It does 2750fps with varget. I’m lab testing this load in September then I will release the data.

 

[BCPB6mmMAX]

Where did that data come from? It's pretty near impossible to relate cup and psi. If the testing came from actual pressure testing, that's great but it's still above saami established pressures and you can't compare 556 vs 223 chambers due to differences in shape and design...ie, longer and bigger freebores on 556 than saami 223.
FWIW, saami recognized the difference in bolt thrust for the 6.5 Grendel and reduced max psi ACCORDINGLY to bolt thrust. You can reverse engineer the math and see yourself. They did NOT adjust it down due to thinner lugs but by an amount equal to the additional bolt thrust generated by the larger case ID of the grendel. fwiw.

There is a good article published about the EPR round. I’ll try to find and post