first carbine unboxing

[Matt_X]

Here's what I did to resolve the FTF. Maybe it will help.
First I knew the FTFs were only from the Korean made mags that I had brought to the range.
I didn''t know if it was both or just one of them.
As mentioned above I had already examined the mag catch and observed a little bit of vertical play on the right and recalled the FTs were always on the right, at least sometimes the second to last round.

Second I checked the mag fit into the assembly with the stock off. Then loaded each of the magazines with 15 dummy rounds and cycled them. I did this with all four mags that I had brought to the range. I did this mostly to be sure I wasn't throwing the results by hand cycling at different rates or short cycling.

After getting a FTF from one of the korean made mags on the second to last round, I repeated the test with just 5 rounds in both. This time checked using different cartridges.
So this got me to another FTF from the 2nd to last round.

Then I measured the nib to top hieghts a couple differnt ways on all 4 mags. I also measured the lip openings, and dissassembled all four to compare followers and springs.
In my case I found the magazine had a shortest nib to top height (1.455"), and the narrowest lip opening of the four magazines. The straight section of the nib opening also bowed or bent downward. That could explain why the bolt usually caught the cartridge but then over rode it as it continued further.

To increase the hieght over 1.5" and increase the feed opening required a little bit of sheet metal shaping. After doing this, retested by manually cycling the dummy rounds again.
Ran perfectly!

At this point I should mention something I've observed about cycling rounds through the carbine. When the round is chambered, the bullet bites into the rifling just a little. After cycling it may get pulled out a little. I know changing the seat has effects on the pressure development, so if you are cycling live rounds, check that the round is still within spec before using.

I'm using dummy rounds. I have 10 that are made up with rubber primers to cushion the firing pin and recently got some 1943 and 1944 dummy rounds with no primers. I thought the bullets older dummy rounds might not pull out when cycled, but after enough cycles, they did.

Since I do alot of dry firing, I made a little gage to check the overall length. When dummy cartridge is too long, I gently squeeze it back to spec in the bench vise. Obviously don't want to do that with a live round! My rule is no live rounds in the workshop where I'm working on or dry firing a firearm.