Extended magazine box for browning A=bolt


Well-Known Member
Jan 31, 2009
Libby, MT
Does anyone know of a replacement or modification on an a-bolt magazine as to get a longer seated cartridge. I have done a search using different wording and have come up empty handed. My buddy has an A-bolt in 300 win mag and the bullets have to be seated way into the case to get them into his mag, so much that they look funny. any help would be greatly appreciated. Thanks. Jeff
I know the browning uses a removable box but maybe a remington spring and follower could be modified. to work in the browning...? just an idea I didnt know browning did that. I have an a-bolt stainless stalker in 7 mag and its not like that. at all but its a shorter cartrige in the same action...
You can buy a 375 H&H clip or take the rivet out of the front of the box grind that dohickey down replace the rivet and you are good to go.
What it, keep in mind.. what if you cut some of the metal out so the tips extend beyond?

I would also check the inletting to see how much of an air gap there is between the stock and magazine.

If you only cut a U out be sure to leave some metal attached at the bottom so it doesn't cave in.

I do have an A Bolt and I feel it could be done.
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How short does he have to seat them? SAAMI spec is 3.340, are they shorter than that? I am not sure if they ever chambered that in 300 Wthby, but if they did, he may be able to get a replacement mag in that caliber. I would think the mag would handle the case, and the OAL is a bit longer.
Easy as pie, just take a chainsaw file and file in two grooves down the front aluminum spacer, don't forget to taper the land at the top between the grooves so feeding is clear. Be sure to test the bullet feeding to look for and clear obstructions.

I did this in about an hour or so years ago. I load my rounds out to 3.525" which gives me .050 clearance to the front of the mag.

Afterwards I spray painted it with flat black paint to give it that aesthetic professional look.


Always willing to help!

This magazine is for my 300 Win Mag Stainless Stalker Abolt, same caliber as your friends. It's the standard mag that comes with the rifle. I originally looked at other mags but the aluminum shoulder stop in the mag didn't line up properly with the 300 WM shoulder, and I wanted it to work the way it was designed - to protect the bullet tips from recoil damage. So this came to mind. I took out the floor plate and spring assembly, filed it, painted it and re-assembled it.

I've put hundreds of rounds through with no problem whatsoever.

The only prerequsite - you need to be handy with a file.

thanks again, may try a die grinder with a cylindrical flute if not the file or both should do the trick. I appreciate the help. Jeff
Just googled this problem and here's the solution. Thought I would get this up again as it is a very helpful solution to this problem for Browning A bolt owners who reload for the .300 WM. Excellent idea, about to start filing on mine now. Thanks Jay Kyle
or you could just shoot them at factory oal.. My browning a-bolt stainless stalker lh boss has a standard mag and it's fine. My hornady bullets are set to 3.34" and they are twenty thou. off the lands. I really see no reason to fiddle with this one; it's fixing something that isn't broke.
Does anyone have a picture of the bottom of the mag that would show how thick the base is? Are the base and the top the same thickness in the area that was filed off?