So I have completed converting my MKE AT94A2 into a 922(r) compliant, semi-automatic only MP5 ( I think this nomeclature is appropriate since HK sells semi-only MP5s, and it isnt' exactly like an HK94). For those who are not familiar with the MKE guns, MKE is a contract manufacture that makes roller-lock guns in Turkey under license from HK. I bought my MKE online for $899 plus shipping. I have about $400 in conversion parts. I will be mailing my Form 1 tomorrow, and when I get it back I will have someone with a lathe cut the barrel and thread it so I can attach a tri-lug adapter and thread protector, MP5-N style. I already have several 9mm suppressors that will work well with this gun.
First, here is the rifle as it came out of the box. Note that it is sporterized for import purposes. The stock and lower are welded together, and there are bars welded into the magazine well, so it will only work with the special 10 round magazine that comes with the rifle.
In order to de-sporterize the rifle and install normal MP5 mags, stock, and lower on it, I needed to use enought US-made parts to avoid running afoul of 922(r). It is unlawful to assemble an MP5-type rifle using more than ten foreign made parts from the ATF's list. In order to achieve this, I used the following US-made parts: hammer, trigger, sear, trigger box, cocking handle, and forend. I bought the parts from HK Parts and RTG, except the used Surefire forend which was off the for sale forum on another board for $80.
First, the most difficult part of the job was to carefully remove the bars from the mag well. This was not really hard, but it took patience and some skill with a Dremel tool. If you screw it up, you could seriously mess up your gun by cutting a hole in the mag well. I spent about 2.5 hours carefully grinding out the bars with a small, diamond cutter. I feld stripped the rifle, chucked it in a padded vise, wore safety glasses, and slowly worked at it, test fitting both a curved and straight mag as I went. There was a point as which the mags would go all the way into the receiver, but wouldn't lock in. I just kept working at it, and everything turned out fine.
My plan had been to mask the mag well off after I got the bars out and spray paint the inside with Krylon to protect the steel of the receiver where the finish was now gone. While browsing through Bass Pro, I saw a paint pen made by Birchwood Casey intended for touching up the finish on painted guns. It was just the ticket. At some point after I get the barrel cut and threaded, I might bead blast, re-parkerize, and re-paint the whole gun, but for now, this is the perfect solution. It's inside the mag well anyway. The paint dried very fast.
With that done, I installed a US-made cocking handle. This is just a matter of removing the bolt assembly, lining up the roll pin with the holes in the cocking tube, driving it out, switching handles, and driving it back in. It is way easier than on a G3.
Next came the trigger pack. I had some spare trigger pack parts laying around from a G3 build I did last year, so I assembled a complete new pack using the US made trigger housing, hammer, trigger, and sear, along with German axles, springs, hammer spring, and hammer strut. Here is a picture of the new pack (bottom) with the MKE factory pack (top right) and the G3 pack I converted to semi-auto for my G3 build last year (top left).
Once it was together and function tested, I swapped the hammer spring and ejector out of the MKE pack. I didn't care to trying using the .308 ejector and spring in a 9mm gun, although I have read a few accounts where people have said it works. Here is the completed pack that went in the gun.
Finally, I had to fit the lower to the receiver. The MKE shelf is much smaller than on an HK94 or US made clones. I did some test fitting, and a clipped lower set up for a 94-type gun will work fine, but you don't need to remove nearly that much material. I used a Dremel to remove just a very small amount of material from the inside of the ears on the front of the lower, and it fits like a glove.
That just left putting it all together. I took it to the range and put 100 rounds through it. It ran like a top with the curved MKE mag I had using Winchester White Box 115 grain. It failed to feed almost every time with the surplus German straight mag I have. Lesson learned, no more straight mags. I might try some bigger bullets in the straight mag though. I think the narrow profile of the 115 grain bullets is causing the problem. Either way, thats why I just bought one of each to start, and based on online accounts, plenty of HK factory guns don't work well with straight mags. I'll order some HK factory curved mags soon.
Here are pics of the semi-finished product. The OD POF A2 stock was cheap and available. At some point while waiting for my tax stamp, I'll replace it with a nice black, Geman one.
And finally, here it is with the barrel draped off about where it will be cut once it is an SBR: