Long necked 7mm mag.

[pig ranch deadeye]

I have a Remington 700 with long magazine box in 7 mm Rem Mag. I was thinking of necking down some 300 win mag brass to 7mm mag, using the 7 mag sizing die, and leaving the neck long. 300 mag brass is about 2.6 inches long but 7mm rem mag is only 2.5 inches. So this approach would give me an extra tenth of an inch or so neck length. That way I could seat the bullet further out and still use the crimping ring. The bullet being further out would free up more space for powder, maybe 2 o 3 grains more.
Would I have to modify the chamber? Would I have to have the gunsmith ream out the neck in the chamber to make a longer neck space? I was thinking of using this approach with the 175 grain bullet and Ramshot Magnum powder. As an alternative I could re-chamber to the 7mm Mashburn Magnum, but I could no longer use 7 mag factory ammo. What do you guys think?

 

[JJMoody]

Look at the 7 practical or 7-300 win mag. Simple , effective.

 

[sedancowboy]

So what you are wanting to do is create more case volume. Just rechamber it to a 28 Nosler and be done. To modify your current chamber would require a new chamber reamer be made so just go with a new design.

 

[pig ranch deadeye]

What if I simply had the gunsmith use a 7 STW reamer to give me more neck and more freebore? I would still have a 7 rem mag, only with a slight modification...

 

[jasonco]

 

[JMW67]

I would shoot it till the barrel was shot out then rebarrel to what ever i wanted I wont spend money doing anything to a factory barrel but thats just me

 

[ntsqd]

The right sized std. chucking reamer would easily increase the length of the neck in the chamber, but that doesn't solve the need to move the throat too.

As noted above, I also wouldn't spend the time & money to do this to a factory barrel. I'd have a barrel made for the rifle with your proposed changes made to it. Then you can select the twist that works the best with your proposed bullet and you can have it throated for that bullet as well. Likely the place to start is to make up a couple dummies of your proposed cartridges complete with bullets seated at the desired depth.

 

[pig ranch deadeye]

Good advice. If I put on a new barrel I would go with the 7mm Mashburn. I have wanted one since 1963!

 

[DUSTY NOGGIN]

new barrel

 

[Gater]

I would shoot it till the barrel was shot out then rebarrel to what ever i wanted I wont spend money doing anything to a factory barrel but thats just me

I had a 7mm mag did exactly that shot the barrel out now it's a rem 700 BDL in .338 win mag

 

[pig ranch deadeye]

The right sized std. chucking reamer would easily increase the length of the neck in the chamber, but that doesn't solve the need to move the throat too.

As noted above, I also wouldn't spend the time & money to do this to a factory barrel. I'd have a barrel made for the rifle with your proposed changes made to it. Then you can select the twist that works the best with your proposed bullet and you can have it throated for that bullet as well. Likely the place to start is to make up a couple dummies of your proposed cartridges complete with bullets seated at the desired depth.

What does "cross threaded" mean?

 

[Dirtrax]

It's completely practical to have your barrel throat cut to accomplish much of what I think you're after. It's inexpensive and quick. It can be done by you or a 'smith. You can gain some capacity and freshen up the lands. Two caveats, will the extended OAL still fit in you magazine, and will it limit bullet selection.
After you shoot this barrel out I highly recommend the 7mm-300 type cartridges. With a simple neck down one can preclude buying new equipment.

 

[Rhovee]

Necked down 300 PRC to 7MM would be the winner.

 

[ntsqd]

What does "cross threaded" mean?

Cross-threaded is when a bolt doesn't engage the threads in the hole correctly and mangles the threads on one, the other, or both.