Rifle cartridge "headspace" on case mouth

[Bravo 4]

I have been looking at rebarreling my Savage long action to a 50 Razorback (.300 ultra mag cut off at the shoulder 2.375" and loaded with .510 cal bullets). I'm having trouble getting any info for the build so I have some questions I'm sure somebody can answer.
This cartridge headspaces on the case mouth. How big a problem would this be?
The only person I know of that has a rifle in this caliber is apparently really hard to get ahold of, been trying for a couple months to get some info.
How could I go about getting a barrel chambered in such an odd ball chambering? Have a reamer made by PM&G?
Could a reamer be made by altering an existing .300 ultra mag reamer?
I have been told that 50 Alaskan dies could be used, and are being used successfully.

All you wildcatters, how do you get started with something new?

I have a smith willing to do all the work but the though of paying $1200 for a savage drop in barrel an dies he would make just puts a sour taste in my mouth.
Not knocking him at all, lots of machining on his part. However, the knowledge is out there and could save me some money and possibly heartache.
My other option is to buy a TC Encore and have a 50 Alaskan barrel built for it. I would rather use what I got, plus I already have a crap load of ultra mag brass.

Thanks for any help.

 

[TikkaShooters]

Headspacing is the easiest part of your project here. There are many cartridges that headspace off the case mouth. Any rebated rimmed straight walled cartridge such as the 45 acp uses the mouth to headspace.

Forming brass sounds easy enough. You may need to inside neck ream if the internal diameter is too small. No belling of the case should be necessary since .510 bullets have a boat tail.

Dave at PTG may already have a reamer print for this. You should give him a call.

Your next challenge will be getting a barrel cut with a .510 bore in a diameter suitable for the Savage action.

I looked into building a .510 whisper a couple years ago on a Savage action and I believe Pac-Nor was the only company making something that would fit.

You could probably send them the reamer and they could get everything set up for you to screw on yourself.

Good luck! It sounds like a fun project. What type of ballistics are you expecting?

 

[Bravo 4]

Thanks for the reply.
I want to have the capability of sending a 750 Amax at subsonic velocities and also be able to push it out around 1600fps or faster if wanted. It will be getting a can as well, if the build even works out.

 

[TikkaShooters]

I like the concept. It's much like the .510 whisper with more capabilities.

Keep us posted on your progress.

 

[ROBSTER]

I have the 50 sidewinder basicly the same thing only uses .500 bullets if you have any problems with head spacing in the long run you just leave the case mouth open a little.Was told the main problem with these cartridges is that with hot loads they will eroad the throat where the case head spaces off of.
Robster

 

[Bravo 4]

I spoke with Dave at PTG and he has done one. That's in the works, should be done in a few weeks.
Ordered a 20" 1-9 twist Kreiger. 3-4 months on that.
The suppressor paperwork will be turned in by the end of the week. 4-6-8 months on that?! The can should be done in a week or so, just gotta play the waiting game.

 

[375rifleman]

Has no one necked up a 300 Winchester, 300 Weatherby, or 338 Winchester to .510 ?

 

[Bravo 4]

The 375 H&H based cases cannot support such a fat bullet, I wouldn't even load a .500 diameter bullet in one.
One pic is a loaded round with a .510 cal 750 Amax, the other is the base of a 7mm mag case just above the belt.

 

[Bravo 4]

Sorry, it didn't load one of the pics:

 

[J E Custom]

I have been looking at rebarreling my Savage long action to a 50 Razorback (.300 ultra mag cut off at the shoulder 2.375" and loaded with .510 cal bullets). I'm having trouble getting any info for the build so I have some questions I'm sure somebody can answer.
This cartridge headspaces on the case mouth. How big a problem would this be?
The only person I know of that has a rifle in this caliber is apparently really hard to get ahold of, been trying for a couple months to get some info.
How could I go about getting a barrel chambered in such an odd ball chambering? Have a reamer made by PM&G?
Could a reamer be made by altering an existing .300 ultra mag reamer?
I have been told that 50 Alaskan dies could be used, and are being used successfully.

All you wildcatters, how do you get started with something new?

I have a smith willing to do all the work but the though of paying $1200 for a savage drop in barrel an dies he would make just puts a sour taste in my mouth.
Not knocking him at all, lots of machining on his part. However, the knowledge is out there and could save me some money and possibly heartache.
My other option is to buy a TC Encore and have a 50 Alaskan barrel built for it. I would rather use what I got, plus I already have a crap load of ultra mag brass.

Thanks for any help.

A rimless cartridge is very possible and there are quite a few people doing this.

There are however some problems with then especially one that long. Most of the successful rimless cartridges are for pistols and considered short compared to what you want to build.

Head space is very critical and the longer the case the more care that has to be taken to trim often.
(The longer a case the more it grows when fired and that growth changes the head space.

If the powder charge is low this problem will be minimized, but the higher pressure loads will have to be trimmed often, if not every time to maintain headspace. High pressure pistol cartridges normally have rims to head space and sometimes they have to be trimmed to chamber easy after several firings.

I would recommend something like the 50/140 caliber brass because it can be trimmed to whatever length you want and it has a rim for head spacing (Plus you can buy dies for it).

Also the 458 Lott would do what you want if you trimmed the brass and it has a belt to headspace on
there are dies for it also. it is a 45 cal but with 500 grain bullets it could be awesome sub sonic or super sonic.

Just a heads up from someone that has built rifles like this and found them to be problematic.

J E CUSTOM

 

[Bravo 4]

Thanks for the info JE. However, this thread is several years old and just revised. The rifle has been built for about two years now.
I wanted a .510 caliber because of the ability to shoot a 750 Amax with it's 1.+ BC and the several hundred pulled BMG projectiles I have.