This is the best method to tweak your A-Bolt 243 WSSM magazine so that it feeds reliably.
For my two A-Bolt 243 WSSM rifles I took an old credit card and cut a couple of strips that I then slid between the plastic insert and the outer metal wall of the magazine.
A good friend of mine Rick Camuglia is an avid long range target shooter. He has a 243 WSSM and recently had some issues with is Browning A-Bolt feeding a new load with Berger VLDs that he was working up. He tried bending the magazine shell holding lips on the top of the magazine and he still could not get his rifle to feed reliably. Rick found the following simple solution that I have tried and it works really well. Thanks for passing this along Rick.
Here are some of his comments: "...the ENTIRE problem with the feeding in these WSSMs is that “shoulder bump” thing in the magazine. This is what I saw you call it on your site when referring to the X-Bolt's magazine design... Simply shim the plastic shoulder bump portion away from the side metal and closer to the front portion of the follower with something as simple as folded paper. The plastic insert in the magazine for the WSSM’s that is the “shoulder bump” portion does not ‘hug’ the front portion of the follower. It needs to so that the shoulder is actually bumped, forcing the case upward and toward the center of the chamber for a perfect feed."
This is my old method. It works well until you switch to a different load then it might not feed well and require tweaking again.
I had to ever so slightly bend, probably only 1/32nd of an inch (originally I bent them slightly down which worked. I have now found that bending them slightly upward feeds even smoother), the top shell holding arms (see red circled areas in the photo above) on my A-Bolt's magazines to get shells to feed smoothly. This tips the cartridge tips upward slightly and I have never had a feeding problem since.
I have also heard that a gunsmith can polishing areas of the magazine and action that can help shells feed reliably.
Using the methods I describe on my 243 WSSM vs 243 Win. page I have noticed that different bullets that I have shot have required slightly different angles on the shell holding arms on the top of the magazine to get the cartridge to feed reliably. Rick's solution is easier and I believe offers a better overall solution that should work with any load/bullet. Another thing I also like with this solution is that the "Shoulder Bumpers" now hold the cartridges better assuring that the tips of the bullet do not get damaged from recoil.