Do I need to modify my Howa 223? Yes, on all our chassis and any Howa 223 that is converting to an AICS mag, you will need to shorten the bolt stop. The Howa action was designed to have the mags further forward than on an AICS style magazines. All Howa 223 actions will be affected. The AICS pattern magazines locate the rear of the cartridge further back than the factory magazine, therefore a modification to the bolt stop is needed in order to allow the bolt extra rearward travel.
You will need to remove the bolt stop from the receiver and shorten it with a file or grinder in order to allow the bolt face to come back far enough to pick up the cartridge.
Here are the steps.
Pic 1: This is the bolt stop. You remove the screw and it comes out. Don't lose the spring.
Pic 2: This shows the part of the bolt stop that stops the bolt. This face is what needs to be filed back.
The basic rule of thumb is that it needs to be taken down 4 - 6 mm. I would say to start with 4mm using a file or grinder or vice with a small bladed hack saw. Continue to remove more if required.
The easiest way to see if you need to take off more material is to assemble the rifle and insert a magazine (using dummies or empty cases for safety reasons). Then draw the bolt back to the stop and observe/measure how much more the bolt stop needs to be shortened.
Click this link to view or YouTube Video of the bolt modificationhttps://www.youtube.com/watch?v=sR3aNUSqQrw&feature=youtu.be
Here is a video for the hearing impaired. https://www.youtube.com/watch?v=pu396y6AllM