I was curious if anyone has ever put together a 6MM rifle based on the Remington Ultra Mag or STW case size?

I know it would be overbore in the extreme, but, would it be any more overbore than a .257 STW or one of z-hat's Ultracats?

What velocities do you think would be possible with a 28-30 inch barrel and 100-105 grain bullets? 4,000fps?

Also, what would likely be the barrel life (1,000-1,500 rounds?)?
Thanks for the input

I built a high-velocity wildcat back in 1990.....much like Ross Seyfried's 6mm Mach IV which came along three years later, mine was a .264 Win Mag necked down to .243 (45 degree shoulder). I called the round the .240 Incinerator. With a 70 Ballistic Tip, I could get 4,400 fps out of a 28.5" barrel (much faster than I expected). In 1994 I did the same with a 7mm STW necked to 6mm and again used a 45 degree shoulder.....the velocity gains were extremely marginal and the case proved overly inefficient. Personally, I think an improved 6mm on the standard magnum case is plenty.

Lee Martin
www.singleactions.com

I built Ross a 6mm Mach IV years ago and have built several others. Trust me, it is the max usable case capacity in a 6mm. You mentioned the 257 STW. It is also way beyond usable case capacity for the bore size. There does come a point where you have to ask if coming up with a new cartridge idea is worth doing or just a waste of time.

6 mm max cas is the 7 rem fmily I agrre with the others because if you go over you

get erious to find slower powder ( 30 mm powder canon ) BUT this type of powder burn not very well in a small pipe as 6 mm and you get gunk inside the barel when you shootthe next bulet you smash gunk in thebarrel and get a very bad carbon fouling which is a nightmare to remove and a nightmare for accuracy

max of the max capacity seem to be
06 case in 224
7 REM case in 6 mm
300 Wea in 257 and 6.5
300 ULtra in 7 mm
378 we or 416 rigby in 30 cal

but if you use several wilcats in same caliber with increase ofwater capacity you can check for example in 6 mm that with a 06 case max capacity you reach the mach IV velovity but with the 7 REM you just win only few fps with lot of more powder lot of less barrel life and only group of 3 shots because your barrel became too hot and too durty .

6/284 , 6/06 are ok for max velocity but perhaps the RSUM case can make a real nice hot rod with a long neck .

and don t forget o shoot solid bullet as for example GScustom made to avoid burst bullet at the muzzle

good shooting

DAN TEC

i have a 6mm on 7mmrsum case. case cap on fired round is near 73 grains h2o. i think an stw would be near 100 grains h2o. i haven't reached 100% load density with re25 or hod retumbo so powder selection would be limmited. 87v-max at 3700fps, 95 berger at 3540, 105 a-max at 3300 is as far as i have gone. think a 6-284 will do about the same but this fits a short action better.