I have the Impulse Big Game rifle in 6.5 CM.
This is the 4-round magazine that I got.
This is the 10-round magazine but it only holds nine rounds.
I will do my best to describe the modification. The procedure is the same for both 4 and 10 round magazines except that it takes a little longer to get the 10 round magazine filed down to the correct dimensions.
1 - Before you take the magazine apart and start filing, see if the 110 magazine will work without any modification. I say this because I have a Boyd's stock on my rifle. If you still have the OEM stock, you might get lucky without modifying the additional magazine. I use the A-zoom snap caps to check for correct feeding so I don't have to use live ammunition.
2 - Assuming the 110 magazine needs modification, compare it with the one that came with the rifle. You should see a discernable difference in the height of the box of the magazine. Note the differences on the top edges forward of the feed lips. The feed lips may be modified but more on that later.
3 - Remove the box from the bottom of the magazine by squeezing the sides at the bottom so the tabs slip out of the holes in the bottom. This takes a little finesse.
4 - You may also want to disassemble the magazine that came with the rifle if your additional magazine is the 4-round version. If the addition magazine is the 10-round version, leave the original magazine assembled.
5 - If both magazines are 4-round versions, measure the height of the box at various points forward of the feed lips. Do this so you know how much to file on the additional magazine. Record your measurements. This will give you a good starting point. Nevertheless, you are still going to do a lot of measuring by eye.
6 - If your additional magazine is the 10-round version you are going to have to eyeball the desired height that you want it to be at the end of the process. Try to match the way the top edges are sloped and shaped on the original magazine. You will have to assemble the magazine and use dummy rounds periodically to do a function check. If you run into feeding problems, disassemble again and do some more filing.
7 - Use the same filing method as you did with the 10-round magazine except that you will need to check your progress with reassembling the magazine and performing function checks with dummy rounds.
8 - You might think that an empty magazine that fits inside the rifle will work the same as a loaded one. Not true. I found this out the hard way. I would chamber a loaded round in the rifle at the range. When it's fired, the recoil combined with the weight of the remaining rounds in the magazine would cause the latch to pop loose dropping the magazine.
9 - I got good at using a file on the magazines but resorted to a Dremel tool on the last few. I would not recommend this for your first time. The bottom line is that the magazines need to be hand-fitted.
10 - Let's address the feed lips. You might have to file a little off the top of the feed lips. Don't do this with a Dremel tool! Only file a little at a time then smooth any rough edges with emery cloth. Insert the reassembled magazine with dummy rounds and perform a function check. Listen a feel for any dragging and roughness of the bolt moving over the magazine. Also check for roughness or dragging on an empty magazine. Be careful not to take too much off of the feed lips as it may not hold the loaded rounds. I don't know why the 10 round magazine will on hold 9 of the 6.5CM cartridge.
11 - You might think that a tight magazine fit will be necessary. Not so. I discovered that a little looseness with the loaded and unloaded magazine prevents the latch from popping loose under recoil and dropping it from the rifle. You will want a little play with the final product.
12 - Take your time and don't hurry. I only had two failures during the modification process of the 4-round magazines. The first one was when I tired to bend the hooked tab at the back of the magazine and broke it. There is no need to mess with that tab. The second failure was with a used magazine that I got off of gun broker. The darn thing would not work. I compared the bottom to the other magazines that did work. The used magazine bottom was thicker than the other ones. So I took the bottom of the magazine with the broken hooked tab and put it on the box of the used magazine. It worked!
13 - One thing to look for on the function check is how it works when upward pressure is exerted on the magazine. With the way the Boyd's stock is made along with my form when shooting, I find it better for me to place my support hand under the magazine. Make sure that you get proper feeding with upward pressure on the magazine. Even though you may not shoot that way you should still check for it. You never know if you are going to be prone, in the dirt, and the ground is putting pressure on a 10-round magazine.
14 - I like the 4-round magazines for my hand placement under the receiver when shooting prone. This rifle with the Boyd's stock hates bipod. So I shoot over a bag or backpack. With that said, the light 4-round magazine doesn't drop as freely as the heavier 10-round magazine. So take note of how well the loaded and empty magazine drops from your rifle.
15 - I bought this magazine pouch from Midway to store my 4-round magazines.
The MidwayUSA 6 Magazine Pouch holds 6 double stack pistol magazines or 12 single stack magazines. It has 2 rows of webbing along the back for easy...
www.midwayusa.com
Hope this helps.