I have a customer that want a 6.5/300 Ultra mag. He became quite excited after taking a look at the Montana LA I received last week.

This guy has been sold on STWs since there inception. Want something to equal Simpsons 6.5 STW. Though my advice regarding overbore is being ignored I have convinced him that shortening the RUM case to 3.600 is much better than trying to modify a beautiful new Montana to feed 3.850 cases.

My question:

I am going to test this on a new Winchester take-off barrel before installing a custom barrel.

Dave Kiff has already supplied me with a finish and resizing die for WSM. I've calculated that these reamers ran in the additional distance for a 3.800 OAL RUM case will result in a chamber 0.020 larger at the base than the RUM cartrige's 0.545 base.

Given that I plan to fireform with cream of wheat and fast powder will this amount of expansion result in substandard brass?

Wally

That sounds like way too much increase in diameter. We have "short chambered" barrels by a couple hundred thousandths using the .338-416 Rigby Imp to make .338 Lapua Imp. chambers. I've reduced the length of my .30-404 Jeffrey Imp by about .300, also. None of these chambers resulted in the drastic diameter change that you have calculated. Measure the dia. of an Ultra mag case right in front of the extraction groove and again about .250 ahead of that and I'll bet you don't see more than .002/.003 difference. I should go and check this but it is too early to go to the shop.

For one thing, a straight 6.5-300 RUM would hold quite a bit more powder than the STW, and at only 3.6" COL.
I don't understand why this guy wants you to go longer. From most reports at similar attempts, there is truly a point of diminishing returns, where more room just doesn't give you any more speed. NONE. I can understand the fanatic trying to squeeze the last bit of velocity out of every shot, but once you get a case this big with a bulelt this small, we just don't have the technology to make use of more.

BUT, if he insists on it, get him to blow the shoudler out (that'll give him even more useless room to be proud of) and thus decrease the taper.
Then the difference at the base will be less.

One big problem, where does he plan to get these custom lengthened RUM cases?

sounds like a can of worms to me,you're going to build it,its not going to perform like it should and he'll probably smear your name because he's being ignorant,he should listen to his smith,i have learned this the hard way. my .01 cent worth.

You do understand the nominal COL for the RUM is 3.6", right? Not to tell you how to do your work, but if he wants to seat long bullets, then he needs a custom throat, not a deeper chamber.
There's no way you'll find RUM brass that's 3" long....
Just what does he want?

Show this guy a comparison of reload data for the RUM, Dakota and Rem Mag, in say 7mm.
This will give him a good idea of what he wants.
If he wants the biggest and baddest, it is your duty to build him a 6.5-378 Weatherby with a 40" bbl, and then supply him with three extra barrels, pre-fitted, so he can get through load development and a couple hunting seasons.
160g with a 26" bbl in:
Rem = ~3050 fps
STW = ~3175
Dakota = ~3200 fps
RUM = ~3250 fps

Now, I'm not saying you won't find loads hotter than these, but this is basically what you're looking at.
Give him a crash course in expansion ratio and show him figures like these, and maybe he'll ease up to the aslightly more than moderately insane 6.5-300 RUM.
A 2.5" RUM makes a lot of sense for a really hot 6.5mm round. I'd still want a 27" bbl on it, which would mean I'd have to want a gun with a 27" bbl chambered in a 6.5....

On second thought, just make him a 24" 6.5 WSM, and tell him that's just how the reamer came out.

Wally,
I think using the WSM reamer run in deep will yield a chamber which is too large. Although it may work, the unsightly bulge at the base will be a sore point with the customer once he notices it. I think you would be better of to use a RUM reamer run in short. You may be able to rent a 6.5/300RUM reamer or let the customer buy his own. I personally think the 6.5 STW is a stupid cartridge and the only way to make it stupider is to make it bigger! But hey, it's not my money! Regards, Bill.

There comes a point where the 6.5mm bullet will actually distort from being pushed too fast. At that point he would have to lighten the load. If he goes with a 6.5 WSM he would be overbore enough and actually have a pretty fast bullet that will shoot.

I think the best thing that could possibly happen is for the customer to go ahead with his plans and to complete his big 6.5 project.

What better way to learn about the concepts of barrel-life and bore capacity than to own such a rifle, work with it, and to explore it's capabilities first-hand?

AD

okay..
first, tell him no, you don't have the reamers, dies, or load data

if he insists, and has just fistfuls of dollars, then call dave at ch4d and ask him if he knows of anything close.

THEN
make the customer buy the reamers, rough and finish, and buy the dies.

however, anything bigger than a 6.5x06 is overbore, the 264 is known for burning barrels, and I doubt Mr Hotrod's barrel lasts 500 rounds.

itnerest him in something that you might can sell another one later... say a 6.5xwsm.

.020 is CRAZY, btw. that's like the height of a belt mag's belt.

jeffe

Bill Leeper said, "I personally think the 6.5 STW is a stupid cartridge and the only way to make it stupider is to make it bigger! But hey, it's not my money! Regards, Bill."
Bill,
Another way is to build it with a slow twist so you can REALLY make light bullets go fast. And then question why you see pressure signs way before you get close to filling the case with powder. A friend has a whole safe full of slow twist, overbore custom rifles. Now he knows that it was not the right way to go.

I know several have said it, in so many words, but I would strongly suggest your client reconsider and think of a more reasonable cartridge. I wish someone had given me a good shaking when I was obviously delerious . . .

I have a 6.5-300 Weatherby/Wright/Hoyer, a .300 Wby case necked to 6.5. It burns 84 grains of H-870 (until it's gone?!), and pushes a 140 at 3,400 +/-.

The high velocity is great. I love that aspect of it. Bullets carry 1,000 FPE to 1,000 yards. I don't shoot game that far, but the point is the ballistic efficiency. Shoots flatter than my .22-250 at any range and way flatter farther out. Wind drift resistance is quite good as well. It really lands with authority and kills small and mid-size game dramatically. Very cool.

Barrel life is/was/has been OK, all things considered. It is a Hart 30" heavy barrel, tapered to .950 at the muzzle, 9" twist. My gunsmith promised me 500 rounds or less, but I am over 600 and it will still shoot 3/8" groups. It started out with many groups at 1/4" or less. Needless to say, the throat is moving - in 600 rounds, about .075", best I can tell.

I doubt I could be competitive in a match (as if), but I shoot deer out to 4 or 500 and kill groundhogs as far as I can set up a shot, 725 to date and it works great. I very much doubt that I could get through a ten shot match with this cartridge, though. By the time I shoot a few zero/foulers, then a few sighters, then a ten round group, my primers would probably be falling out.

Overbore? Some . . . Hahahahaha (insert maniacal laughter) I must have really been mad with myself when I made this decision. Too much idle time with ballistic software, I suspect. Powder selections are limited to about two (surplus) powders - good luck. Regarding lighter bullets, Sierra 85's pattern like a .410 at fifteen yards, I really don't think they took a spin at all, just skipped and blew, judging by the copper in the grooves. I suppose 4,200 fps exceeds their design parameters. Lightest I shot that held together to the target were Nosler 100 BT's and accuracy was quite unimpressive. Best groups were with Nosler 120 BT's, then Berger 140 VLD's, then 140 SMK's.

Fouling is very, very bad. I cannot believe what a high-maintenence rifle this thing is. Fouling has always been UGLY. With throat wear and the associated roughness increasing, fouling is getting so bad I am ready to rebarrel now, even while accuracy is quite good. I am considering a 6.5-06, a more sane selection.

As an average, throughout the use of the rifle to date, it must be cleaned every 5 or 8 shots for absolute best accuracy. It MUST be cleaned before about 20 shots are fired, or pressures JUMP. I cannot go on a weekend trip without the full cleaning gear, vise, solvents, JB, the whole deal.

In spite of a very careful break-in, where I fired one and cleaned, etc., cleaning is still a nightmare. First, a powder solvent, then a copper solvent, then a powder solvent, then more copper . . . . Add in a bunch of JB throughout the process. Powder fouling was so difficult to remove, a bronze brush wouldn't scratch it. I finally got to the point of using Bon Ami in it to get back to bare metal.

I understand your client isn't concerned about spending a buck a shot in barrel wear, I'm not either. I'm not concerned that I can't load a hundred rounds out of a pound of powder. Buying (quality) brass for a buck apiece, then spending hours case forming doesn't bother me either.

What IS killing me is the constant, difficult, time-consuming cleaning regimen that could have been avoided by letting 150 FPS go by. Even a .264 allows use of different powders, powders well-known to foul less than the MG and 20mm stuff you'll be stuck with. I very easily spend more time cleaning than I do shooting, perhaps by a factor of two.

When I pull this rifle out of the box, I don't think about how much better is is than any of it's neighbors, or than a .264 or 6.5-284, but about how long I'll be cleaning it afterward. I look at it with the same contempt I have for my blackpowder arms. That is not how it should be. Other than that, I love it.

[ 10-22-2003, 18:36: Message edited by: eshell ]