Ream a 308 barrel to 300 wm

[Polinese]

Per my previous mauser thread, I have an interarms mark x action I was originally going to build into a 308. Going so far as to buy a heavy barrel from green mountain barrels.

To save myself from buying another barrel, would a gunsmith be able to ream out the chamber on that 308 barrel to a 300 wm chamber?

[Scorch]

Yes, no problem for even an amateur with a little bit of skill. The bolt face is going to need to be opened up as well. The 300 WinMag chamber is much larger than 308. The Green Mountain barrels are very nice to work with. 4D Reamer Rentals can get you a reamer. Cut it to length as a blank, face off the cut side, thread the breach (marked) end of the barrel to fit the action, chamber/headspace the barrel, crown the barrel, profile the barrel. Very simple if you have the proper tools.

[Polinese]

Awesome I figured it would work, randomly occurred to me the other day it might be a possibility and puts me a lot closer to actually having this project worked on. Need a trigger, and the ptg bottom metal and I'll have all the pieces.

The barrel is already threaded, crowned etc just need to recut the chamber on it.

[tangolima]

Chamber is bigger. Does the chamber wall still have enough meat left to hold the higher pressure?

-TL

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[Polinese]

It's a heavy barrel so I was thinking yes, but that's why I asked here. I know there's been plenty of mauser 98 actions in 300 with sporter barrels

[Jim Watson]

The bolt face is going to need to be opened up as well.

Won't it also need modification of the magazine and action rails for the bigger cartridge?

[Polinese]

I'm planning on using some PTG bottom metal for aics mags, from what others have said that'll eliminate most if not all of the feed rail issues.

[44 AMP]

The feed rails on a Mauser 98 action are part of the action itself, not the bottom metal. Typically the "bottom metal" only includes the trigger guard and magazine BOX, not the feed lips and may not include the magazine spring and follower.

[tangolima]

I think the op is trying to replace the Mauser action feed lips with the ones on aics magazine. It is single stack mag if I understand it correctly.

-TL

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[Polinese]

Correct. My understanding was the feed rails would become mostly irrelevant when feeding from the aics mag.

[44 AMP]

If one is installing a single stack magazine inside the Mauser box then the existing feed rails of the action should not matter as the single stack magazine will be narrower than the existing opening.

[Clemson]

I would not recommend this conversion. There are a couple of reasons:
Yes, theoretically you could ream the chamber to .300 Win Mag. This photo shows a .300 Win Mag reamer with a .308 Winchester cartridge. As you may be able to tell, the reamer will begin cutting way before the pilot engages the bore of the barrel. That means that the reamer will be unsupported. That could cause a chamber that is not concentric with the bore or which may be too large at the rear, etc.
.300 Reamer by jakefromclemson, on Flickr

This photo shows a .300 Win Mag cartridge feeding into the throat of an unmodified Model 98 Mauser receiver. it hangs up with a couple of inches left to go. That is because you MUST open the feed rails to feed magnum cartridges so that the cartridge will feed up throught the bottom of the receiver. This is true whether you are using the original staggared box or an after-market single stack box. If the rifle is a controlled round feed action, the cartridge has to ride up under the extractor.
.300 FeedRails by jakefromclemson, on Flickr

Bill Jacobs

[Polinese]

Ah thanks for the input!

[Scorch]

Won't it also need modification of the magazine and action rails for the bigger cartridge?

Maybe.

Not trying to sound elusive, but I've built a few rifles over the years, and people think they are much more precisely made than they actually are. I have opened up 98 Mausers that required feed lip modification and others that did not. Remember, a lot of people's favorite rifles were made before micrometers.

[tangolima]

Things will become easier if you have access to a lathe. It would be a good idea to pre-drill the chamber to rough enlarged size before reaming.

-TL

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[Polinese]

I was just going to give it over to a gunsmith.

[Unclenick]

Originally Posted by Scorch

Remember, a lot of people's favorite rifles were made before micrometers.

A little older than you might think. Brown & Sharpe started marketing the first mass-produced micrometer about six years before the trapdoor Springfield was adopted by the U.S. Army.