Home Forums Hunting & Shooting Custom Rifles & Wildcats 6mm Mach IV

I was wondering if anyone has ever played with the 6mm Mach IV? I have the article written by Ross Seyfried about and there is something I like about the cartridge.

For those that don't know its a 7mm Remington Mag necked down to 6mm.

In the article Seyfried stated that he could get 4205 fps with IMR 7828 and 70 grain nosler BT and 4150 fps with 75 grain x bullet and ww 860 (25 inch tube).

I keep thinking that a 80 grain ttsx at about 4100 fps would be great fun...

Anyone have one?

Dink

sounds like a 243 catbird - 270 necked down to 6mm. supposedly 4100 with a 70gr bullet.

i'm running 80gr ttsx out of my 257 roy around 3800fps - can't wait to see what it does to a deer this fall

I do not think you would shoot it long before it is burnt out.
plus a lot more powder with little gain.
I have 70gr sierra hp that will do 4000+ in my 6mm rem ackley imp
my load i use is 3990 but they will go faster but they are HOT.
this is from a 26" 14 twist tube.
I would think you could match or be very close with a 6mm-06 or
6mm-06imp with less powder and cheaper brass of course just my 2 cents

Seyfried states that the barrel will last about a 1000 shots.

I know that he 6-06 or the 6-06AI make alot more sense and will be easier to form with cheap brass but they are not the fastest 6mm...grin.

I was thinking (which is very very dangerous) that with today's new powders such as RL 25 and Retumbo that the 6mm Mach IV would be that much better.

Dink

In 1995 a friend and I necked a 7mm Rem Mag to 6mm and blew the case out to a 40 degree shoulder. Chambered a 8 twist HV barrel and shot the 107 Sierras at 3600 fps. We killed prairie dogs at 800+ meters (Barr & Stroud range finder) with boring regularity. Barrel was toast at 750 rounds.

Dink, I had a 6mm AI with a 26" Shilen Barrel, 14 twist, minimum spec chamber with zero freebore that fire formed the brass with the 70's at 4050 fps and a formed load with 51.5g of Win 760 shooting groups in the low .300's at 4150, neck sized the brass. Same gun shoots the 80g Sierra Blitz BT at 3800+ into a single ragged hole.

I had another 6mm AI. 26" Douglas SS Match with a 10 twist and 3850 was the accuracy load with the 70's.

I have a 30" 243 Ai, 12 twist Hart and with 50.5g of Win 760, Win Mag primer shoots the 70's in the High .200's at 4030 fps. I throttled the load back to 3850 to avoid rapid copper build up, at which load I have never used the full length sizer.

DocEd that is exactly the cartridge I am talking about. Do think the cartridge would make a good antelope/deer round? Is more trouble than its worth?

Keith I had no idea that a 6mm AI could drive a 70 grain bullet that fast...hmmm...something to think about.

Thanks for the information everyone.

Dink

"Is it more trouble than it's worth?"
I think so. Giving up barrel life to fireform can only be offset by having a dedicated fireform barrel. Short barrel life and cost of custom dies also a drawback. An 8 twist 6mmAI or, an 8 twist 6x47 Lapua makes more sense.

Thanks Doc.

Dink

You don't have to loose any barrel life to fireformming. Just use the old trick for fireforming. Small charge of blue dot i.e. 10 grains, tissue paper for an over powder wad, and fill the remainder of the case with cream of wheat. No bullet needed. It will form cases perfectly.
Folks have done that very thing for ages without effecting barrel wear or using up bullets that cost.

Have you ever blown a Magnum case out to a minimum taper, 40 degree shoulder, using the fast powder/case filler method, and ended up with good cases? I tried but the shoulders never formed well resulting in having to fireform a second time.

I have done it forming for a buddies 6.5mm wildcat based on .300 Win Mag., ended up using a blue dot charge of around 15 grains IIRC. Even if you end up doing it twice its quick, easy, and doesn't eat up throats.

I learned the method as told me by Ken Howell, discussing how to form cases for his .444 Rimless Howell. That is blowing out annealed .35 Whelen cases to straight cylinder and trimming back to length.

No doubt that would be a scorcher but I think Seyfried him self said it was right up there with the 585 Nyati as far as practicality. He regretted altering the shoulder and taper if I remember correctly.

The gains above 6mm AI to the Weatherby & 6-284 and beyond get pretty slim. Always wanted a 244 H&H magnum for no good reason but the only practical thing about it is to lower pressure and velocity to the 6/06 range and the barrel will last a long time for hunting use only.

So it's "damn the mines and full speed ahead" if you want to go for it.

As far as the Cream of wheat thing not harming a barrel I don't know about that. I almost melted a Tupper wear stock by not resting the rifle between forming loads, can't be good for the barrel.

Tejano I know there is no practicality to it but I like things that are different.

I will probaly never get around to building one and if I build a fast 6mm it will probaly be a 6-06.

The 244 H&H is also a round I like. Its the 375 H&H necked down right?

Dink

Keep parts of the statement I reckon.
Nothing personal but if you use sensible approach it shouldn't be an issue.

I also remember Ross's article. He talked about it being the closest thing to a death ray he had ever used. He had an issue with a hard carbon like substance building up on the first barrel due to not cleaning it every dozen rounds or so. IIRC he had to throw away that first barrel.

Sounds like a great test for Ultra Bore Coat!

Azshooter that is the article. I was thinking that with todays slower burning powders it would be a barn burner with a 80 gr ttsx.

Dink

Dink,

Resurrected this after the gunwriter thread made me remember the Seyfried article. Googled the cartridge and found your thread.

Here's a thought/question: how about a chrome-lined bore to extend bbl life like the military uses?

I've always experienced 1 MOA or less with scoped military 1-7 barrels in .223. I know much better accuracy is obtained with SS bbls, but what if chrome-lined doubled the life to 2,000 rounds?

Since the Mach IV would be a game rifle, does it absolutely need to be south of .5 MOA in order to kill coyotes, antelope and deer with an 80 TTSX?

Contrary-wise, if you chambered a standard SS bbl for it and fire 7 out of every 10 rounds at animals, that would theoretically be looking at 700 dead critters. Not too bad.

Wow. Bored loony. Need to just try burning out the barrel of my .243 I've had since the early '70s first...