chad
Well-Known Member
Can you rechamber a 7mag barrel to the 7x300?
7x300
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MudRunner2005
Well-Known Member
Yes
chad
Well-Known Member
Is it worth getting? Or is it a barrel burner?
Broz
Well-Known Member
To do it right you'd really have to spin the barrel in 2 turns to clean up the old neck on the 7rm. A factory chamber is generally pretty large in the neck dimensions and I'd want the new chamber to clean that up. If you don't you risk having a stepped neck.
upacreek
Well-Known Member
Can I ask why you pulled the barrel off? What brand, and contour?
Broz
Well-Known Member
Because my friend hunts elk mostly and he is turning it into a 338. The contour is a heavier than a Sendero but I don't have measurements right now. The barrel is a 29" too.
Jeff
MudRunner2005
Well-Known Member
You wouldn't see a huge gain, but if you want a very large jump, go to 7mm STW.
MudRunner2005
Well-Known Member
Why would you do that? The 7mm RemMag is shorter than the .300 WinMag case... Therefore, it should clean up the throat, shoulder, and neck just from a simple rechamber. And if he went 7mm STW, then he would definitely not have to set it back 2 threads, because the STW case is significantly longer than both the 7mm RM and .300 WM cases.
The middle-right is a 7mm RemMag. Next to it (right) is a .300 WinMag. Then on the far right, is a 7mm STW.
For anyone else curious, caliber list goes as follows (left to right):
.308 Win
.25-06 AI 40* Shoulder
.30-06 AI 40* Shoulder
.257 Wby
7mm RemMag
.300 WinMag
.300 Ackley Improved Magnum
7mm STW
bigngreen
Well-Known Member
He clearly explained it, just think about it!! You clearly show it in your picture!!!
MudRunner2005
Well-Known Member
I still don't see it... If you neck a .300 WM case down to 7mm, then the neck is still the same diameter as it was before (if it's larger, then the new reamer will open it up ever-so-slightly for the thicker neck walls, if that is the case), and the new case is longer, that means you will be removing MORE material to make the chamber longer for the longer case...
If he were asking about going from 7x300 down to 7mm RemMag, then yes, he would need to cut the tennon back.
Broz
Well-Known Member
Yes, one of the things we want to do would be get rid of the loose neck. So indeed set the barrel back just enough to have the new reamer 100% cutting new metal.
Expect up to 200 fps gains over a 7 Rem
Jeff
Expect up to 200 fps gains over a 7 Rem
Jeff
Like I said......most factory guns have rather large neck dimensions and the 7-300wm reamer would have to be as equally large or larger to clean it up. Most aftermarket reamers will have smaller neck dimensions unless they are specifically ordered large. You would have to cast the chamber and order a reamer .001" over the factory chamber otherwise I'd just about bet you'd have a stepped neck. My 7-300wm reamer wouldn't clean up a factory chamber from a 7RM. The neck shoulder length on a 300wm is 2.356 (a 7-300wm is slightly longer since it is a smaller caliber and the shoulder would be longer). A 7RM is 2.5" long or basically around .130" difference in 7mm. At 16tpi it's .0625" per revolution. 2 revolutions would be .125". So you'd really need to go slightly over 2 revolutions for a 16tpi barrel. I would still spin a barrel in a bit when rechambering to 7STW to try and clean up the rear of the old chamber where the belt and base of the case is. It also lets you set headspace to minimum spec. rather than relying on the factory headspace.
A 7-300wm will run at least 100-125fps faster than a 7RM.
A 7-300wm will run at least 100-125fps faster than a 7RM.
From the base to the rear of the neck on a 7-300 Win Mag, it will be about 2.390". From the base to the front of the neck on a 7mm Rem Mag is is about 2.525". That is a difference of .135". Two threads on a 16 thread pitch is .125". It will actually take more than 2 turns of set back to clean up the neck. A 7 STW is long enough to clean up the neck but if you want a nice clean chamber you should set it back some too.
