Reboring 6.5x55 to 9x57 Mauser

[jackstrawIII]

Hey guys,

I have a CZ 550 in 6.5x55 that I want to convert to 9x57 Mauser. Here's the catch, I don't want to re-barrel or set the barrel back at all. Hoping to just rebore and rechamber.

Would it be as simple as:
- Have JES Rebore/rerifle the barrel to .358 (so I can use standard 35 caliber bullets)
- Reaming the chamber out with a 9x57 reamer

Is that all it would take? I realize the rim diameter for the x57 case is a just a hair smaller than the x55 case... is that a huge problem? It's hard to tell if the 9x57 reamer would "clean up" the existing x55 chamber.

I know the simple solution is to re-barrel, but I'd prefer not to do that. Want to keep the gun as unchanged as possible.

Ps. If that won't work, is there a somewhat common 35 caliber wildcat based on the x55 case that I could use? Couldn't find one... but maybe it's out there. Thanks.

[Crankylove]

Be time and money ahead to rebarrel it.

Save the old barrel if you want the option to return the gun to stock.

[Unclenick]

Getting the barrel bored and reamed for a barrel liner would likely be the more expensive option, as you'd first have to find a barrel liner with the right dimensions for your bullet. There may be one out there somewhere, but I don't know of it. Boring alone leaves the barrel smooth (no rifling), which is why you'd need a liner.

I suppose it is possible to send the barrel to a barrel maker to have it bored and cut rifled, but I don't know what the cost would be. If the barrel had any collector value, any form of reboring will put an end to it

[jackstrawIII]

UncleNick

When I say “rebored” I’m referring to the service provided by JES rebore and those guys. I’ve had them open a 243 up to 358 before and it worked great. I figure they can bring this 264 bore up to 358 no problem.

The only question is the chamber. Can we clean the 6.5x55 chamber with a 9x57 reamer? It looks like the x57 case might be a bit narrower, which wouldn’t work. But I could be wrong about that.

That’s the real question here.

[Jim Watson]

I wish there were digitized drawings we could play with on projects like this. Or at least drawings to same scale.

Ream neck and bore only for a 9x55 wildcat, maybe.
Not like you will find 9x57 at the General Store.

[Unclenick]

JackstrawIII,

I can't tell from JES's site what their process is, but they can do the bore reconfiguring you want. Your 9×57 isn't one of the chambers they list, but if you rent a reamer I don't see why they couldn't give you anything that fits. The problem will be the 6.5×55 won't be completely cleaned by the 9×57 reamer.

The fit isn't hard to determine. The CIP's drawings are the resource you want. They show minimum chamber dimensions with some things toleranced and some not, but remember that chamber tolerances are +0.05 mm and you will be good to go. What you find after making metric conversions is the 6.5×55 chamber is between 0.009"-0.011" wider at the breech end than the 9×57, and 0.0015" to 0.0035" wider at the shoulder junction with the case body than the 9×57, so, no, the 9×57 reamer won't clean the 6.5×55 chamber. Below is a thumbnail to my CAD drawing with the 6.5×55 in Blue and the overlapping 9×57 in red from the CIP drawings. The combination chamber that results is in black.

[Scorch]

Talk to JES and send them the barreled action, they will take care of how it gets done. The barrel will need to be set back one turn, but it should be invisible to the casual observer.

[old roper]

I'd want old caliber on the underside, barrel new cal on clean side no marking.

[jackstrawIII]

Unclenick,

Thanks so much for putting that image together, I really appreciate it!! And it tells me exactly what I need to know.

Scorch, setting the barrel back 1 turn could work... but it would be such a shame. The barrel/stock fit is SO nice right now. Flawless.

[jackstrawIII]

Jim,

Ream neck and bore only for a 9x55 wildcat, maybe.
Not like you will find 9x57 at the General Store.

I had thought of that, but there are a couple issues with doing that:
1. Custom reloading dies, which is a big expense and hassle.
2. How to make brass. Not sure I can neck a .264 case all the way up to .358. Even with annealing, I'm concerned that there just wouldn't be enough brass there to make it work.

[HiBC]

You get to prefer whatever you prefer,and its your rifle.

I might think a 6.5x55 is kind of a sweet spot. A keeper. Now,I might want a 9x57,too....All good! But I might let that 6.5 keep being a 6.5.

There are a whole lot of sporterized M=98 Mausers in the world. Back in the day,sure,some….many,were bubba'd

But some smiths did good work. Many of these are baby boomer rifles. Baby Boomers are getting old. A lot of younger folks don't care to hunt.

The rifle is leaning in the back of a closet...behind a wool mackinaw.

It might get chopped at a police buyback. It might get sold to pay a bill r by some pot. The Old Man had the best gunsmith he could find put the best rifle he could afford together.

You don't have to bore that CZ. Look at Lothar Walther barrels.Prethreaded,short or long chambered,reasonably priced barrels.

European sporter contours...

Browse the web site.


Or....you might find a 308 family short action 358 Win...

[jackstrawIII]

What about this:

- Keep the x55 chamber as is.
- Have JES rebore the barrel to 358 caliber
- Shoot some 7.5x55 PPU ammo in there to fireform the brass
- Send those fireformed cases to Hornady to make a set of 358x55 dies based off the fireformed brass.

Would that work?

[HiBC]

I'm not personally a fan of necking up. Some folks do use a standard die set,decapping spindle .expander ball to neck up. I tried that,making 35 Whelens from 30-06.

No doubt someone will comment they have been doing it for 20 years. I believe them.

But it makes lousy brass.The brass of the neck won't stretch ina uniform,concentric way. There will be a weaker side,and that's where the brass will stretch.Two things then happen.That side of the neck gets thin.You have an eccentric neck.The other problem is the spindle will deflect to the weaker,thinner side.You get a weird eccentric shoulder. Some folks shoot them,thy "fireform" and they use them. The neck wall thickness will not be uniform.

I'm not going to tell you it can't be done.I think somebody necks 284 Win brass up to 375.

It all depends on how you like to spend your time and money,I guess.

You might call Redding and ask for advice and price true case forming dies

[DockRock]

Jesse can do it but he will need to rent a chamber reamer for 9x57, so it will take longer than his usual rapid turn around and cost more, but I like the idea floated above of a .358x 55. That would be cool!

[Scorch]

Jesse can do it but he will need to rent a chamber reamer for 9x57

Renting a reamer is about $75-$80 including shipping.

What about this:
- Keep the x55 chamber as is.
- Have JES rebore the barrel to 358 caliber
- Shoot some 7.5x55 PPU ammo in there to fireform the brass
- Send those fireformed cases to Hornady to make a set of 358x55 dies based off the fireformed brass.

You don't just rebore the barrel and go, you would still need to ream the neck for the chamber. A custom reamer will run you about $400 and about 6 months to get.
A set of custom dies will run you about $350 and 6 months to get.
All that will work, but you will end up tripling the cost of the job.

I know you didn't ask, but from my point of view, the easiest thing to do is buy a barrel blank ($130-$400) and have the barrel profile matched($100), thread/chamber/crown for 358 Winchester ($300), and go shooting. Ammo is available, dies are available, the 51mm case will likely fit the action better than a 57mm case, and you will still have your 6.5 barrel if you change your mind later.

[HiBC]

I suggest people consult the drawings if they believe any of the "x57mm" reamers will clean a "x55mm" chamber.

While the diameter at the shoulder is .435 for both,the diameter at the 6.5x55 rim and case head is .479 .The 57mm length mauser carridgesand the 30-06 and 308 families all have .473 dia case heads.

The 6.5x55 cartridge case and chamber are larger diameter than the 9x57 cartridge and chamber.

Once again,I'd leave your 6.5x55 as it is. If you must have a 9mm or 358 bore,thats OK. How many nice commercial 98 type Mauser rifles...like FN Supreme,Mark 10,BSA, JC Higgins,etc are out there? Some will be the 30-06 family..you can build a 35 Whelen. Some will be originally a 7x57,6mm,257 Roberts,etc. All made fore the 57 mm Mauser cartridge family. No feeding issues to work out.
Or any of the 308 family are a drop in for a 358 Win.

Pick a barrelmaker. Any of them can probably set you up with a short or long chambered pre-threaded Mauser barrel. You might go to Lothar Walther's website.

Going from a 6.5 bore to a .358 bore,one step up in contour might not be a bad idea. Wall thickness and all..

So you have wood in the donor rifles barrel channel to fit,or glass bed,or bed and free float.

Scorch is right,going full custom on reamers and dies costs money.

Rebore/rerifle...How much $ ?? Chamber work? Full custom die set? reamer? Another cost is the original rifle.

A $400 donor rifle, I'd think you could get a rebarrel done for $ 350 in a reasonably standard cartridge,even 9x57.

No blowing a 6.5 neck out to 358. Normal price dies. A rentable reamer,if you smith doesn't have one

For essentially the same total cash outlay,you get to keep a perfectly wonderful 6.555 and get a nice 9x57 or 35 Whelen,or .358.

Here is another silly idea...find an old Husqvarna sporter in 8x57.

What does a 9x57 do that an 8x57 won't do?

[44 AMP]

What does a 9x57 do that an 8x57 won't do?

Shoot 9mm bullets??

The OP commented on not wanting to change the barrel, or set it back because the stock fit is so nice, wants to keep it as original as possible, so, why the desire to rebore it at all?

I didn't see mention of the 6.5 bore being shot out or throat worn or any reason there was a need to rebore it. So if it was just a project you were considering, that's cool, too. That's the point of asking the questions, to find out what you don't know and if what looks like it might work, actually will.

Seems like it won't work out perfectly. So, you still could do it, as a complete wildcat, but other than "can it do it"? I don't see a point.

It looks like you could do a wildcat 9mm based on the x55 Swede case, having the rifle bored for that wouldn't change the appearance or barrel/stock fit. You'd need custom dies and have to form the brass but it seems possible. Just a thought.