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Well, saw this and had to chuckle a little smile

6mm max



What ya think?

Last edited by lanenebraska; 09/24/23.
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Bless their hearts. Hint.

The ARC is nothing shy of being absolutely fhuqking SENSATIONAL. Bullets matter wayyyyyyyy more than headstamps. Hint................


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I watched it Lane. Instead of the 6 x 45, what I gather is that the case is NOT a 223 necked up...

its the 350 Legend case, necked down to 6mm, which has a rebated base, so yeah it may hold another 2 grains or so of powder.. beyond that its nothing special...

Since they are using ARs, they are restricted by the magazine in the AR Mag well, vs running this in a bolt action instead.

The 6 x 45 is more than capable of reaching out to 1000 yds, just figure out the elevation and especially when running like 87 grain or heavier match bullets. In the bolt 6 x 45, that I have ( two barrels on two different actions), with 1 in 7 twists, I've used bullets as heavy as 105 and 107 grains. I have not used the 108 ELD Match, but I have a couple of boxes available, to whenever I get around to it.

I don't know why I never built one of these 40 years ago. If I have done so, I'd have less 223s in the gun cabinet. I also don't know why the Military didn't use the 6mm round vs the 22 caliber round in Vietnam.
it would have been much more lethal on the VC and NVA. As a trained combat corpsman, I know we would have had a lot less wounded enemy soldiers to take care of in 'Nam.

If the military adopts this round and keeps with the AR, I hope they lengthen the action and mag, to an intermediate length.. shorter than a 308 length mag and action. but longer than the 223. A little fatter case of the 350 Legend, might also be an improvement, but I think with 105 , 107 and 108 grain bullets, the ability to be lethal to our enemy's soldiers, would be a big plus. I think it might be a better choice than the 6.8 SPC...We'll see where it goes... I'll be watching where this goes.


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Seafire: thanks for you service!

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Originally Posted by Seafire
I watched it Lane. Instead of the 6 x 45, what I gather is that the case is NOT a 223 necked up...

its the 350 Legend case, necked down to 6mm, which has a rebated base, so yeah it may hold another 2 grains or so of powder.. beyond that its nothing special...

Since they are using ARs, they are restricted by the magazine in the AR Mag well, vs running this in a bolt action instead.

The 6 x 45 is more than capable of reaching out to 1000 yds, just figure out the elevation and especially when running like 87 grain or heavier match bullets. In the bolt 6 x 45, that I have ( two barrels on two different actions), with 1 in 7 twists, I've used bullets as heavy as 105 and 107 grains. I have not used the 108 ELD Match, but I have a couple of boxes available, to whenever I get around to it.

I don't know why I never built one of these 40 years ago. If I have done so, I'd have less 223s in the gun cabinet. I also don't know why the Military didn't use the 6mm round vs the 22 caliber round in Vietnam.
it would have been much more lethal on the VC and NVA. As a trained combat corpsman, I know we would have had a lot less wounded enemy soldiers to take care of in 'Nam.

If the military adopts this round and keeps with the AR, I hope they lengthen the action and mag, to an intermediate length.. shorter than a 308 length mag and action. but longer than the 223. A little fatter case of the 350 Legend, might also be an improvement, but I think with 105 , 107 and 108 grain bullets, the ability to be lethal to our enemy's soldiers, would be a big plus. I think it might be a better choice than the 6.8 SPC...We'll see where it goes... I'll be watching where this goes.

My sentiments exactly. It would only take a barrel change on the gun and probably a powder change in the cartridge and this would be the right round for the future and for the tax payers. Pretty much everything else would be the same.

kwg


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FWIW, here's the post by the designers from another forum from last year.

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 .

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


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Compared with the load data for the 6 x 45, and a 90 grain Speer SP

Load data is only 0.6 of a grain using H 4895, different between the 6 x 45 and the 6mm Max...
it results in only another 75 or so fps...

Difference in the load data on the 6mm Max web site and several sources of the 6 x 45, you get a little more out of the 6mm Max...but then you are necking down 350 Legend cases down to 6mm.. which has to be a multitude of steps, and 350 Legend brass is not readily available like used 223 brass...

on the other end, it is relatively simple one step procedure to neck up shot 223 brass to 6 x 45...
and the brass is much more plentiful, cheaper and available about on any gun range, just laying on the ground to be picked up....

another good reason I see for the 6 x 45, over say the 6 ARC....what less velocity you give up ( for the availability of free brass), you can eliminate the difference by a couple of clicks up on your scopes elevation knob.

with a one in 7 twist on my two 6 x 45 barrels, I have worked with where they will stabilize the 105 HP and 107 Sierra HP bullets just fine...

always love another tool in the tool box... for myself, reading on the 6mm Max, it just solidifies to me that the 6 x 45 is still the right choice base on ease of loading and the economy of cost on reloading for it.

but each one of them seem like a lot of fun to play with...


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I hope they come off with some new load data for modern powders of today. 6x45/6TCU load data is dated. Nothing new since the mid 80’s.
I have been a fan for many years, 6x45 XP and built a 6TCU rifle a few years ago. H335 is my go to powder for 55-80 grain bullets.
They get this legitimized, would save me a lot of load work.
You will never see me neck down the 350 legend, to much work with little gain.

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Well let the boys play. Me I am sticking with the 6 Grendel. Have two of them now.

Last edited by rickt300; 09/29/23.

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I don’t see much need in experimenting with this round for over the 6 ARC. There is a local guy building 6 GT AR15 running up to around 80 gr bullets using a 450 BM bolt and upper. It’s pretty impressive as a hunting rifle. I wonder about shortening a BM case and necking to .257” or .264” for 130s. That may be worth doing, but I’m not doing the work. I’d rather shoot and hunt than tinker.


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Actually the 6mm version on the 223 case that can use 110-115s, in the AR-15 platform already exists.
Go to Mad Dog Weapons Systems and then go to the forums and look for the 6mm Mongoose. You will find load data and performance listings It is a 6mm TCU or improved 6x45 that has been shortened .050, with the shoulder blown out to 40 degrees and body taper reduced by blowing the body out to give it 31 grans water capacity. It works in a standard AR-15 length and with a standard AR mag, with heavy bullets using H-335/844 poweder, amongst others. Uses Lake City brass, by specific design. A neat concept that addresses many points and it duplicates the 6x45 with lighter bullets but can work well with heavier bullets in the AR mag length, plus is intended to be used with shortened 223 military brass. The 6x45 is a very good cartridge but the Mongoose is an improvement in the search to make the AR-15 platform more useful. The 24 Varmint (recently renamed after two years testing by Varmit Magazine) is one step by MDWS above the Mongoose, based on the 6.8 SPC case shortened and formed to the 24 GPC.

This is what the Mongoose looks like, fire formed with 80s It shoots 3/10ths with a 1-8 barrel 18" long. It will do 3,000 fps with the 80 grain. Shot a cayote at 75 off hand with the 80, it did not fully penetrate, exploded in the yote, DRT. A good thing if livestock is near by.

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