Why grips converted for MP5Ks have a weirdly shaped rear pin hole

Grips for the MP5/HK33 and HK91/G3 rifles can be converted for use on MP5K-type weapons. As you can see in the photo above, a small circle appears at about 2:30 position on the larger hole for the pin when this is done. I used to wonder why and since I started offering converted grips for sale, I’ve had a few guys also ask me why this is the case.

Well, the short answer is that the steel reinforcing that is cast into the rear of the grip has different holes when an MP5K grip is made vs. the others. This allows the hole for the pin and the countersink for the head to not encounter another hole.

This is a real German H&K MP5K grip. The top rear hole doesn’t have that telltale circle of conversion because it was purpose built to be mounted on a MP5K.

Not one of my better photos but you can see the pin hole on the far side. The anchor holes to secure the metal strap are to the left and right of it are filled in with plastic during injection molding. Notably at the rear right there are two anchor holes to help compensate and secure the strap.

With the MP5/HK33 and HK91/G3 grips, the designers never planned for a hole to be made in that location and as a result, the newly drilled hole runs right into an anchor hole they have in the metal to allow the injection molding to adequate bond to it.

If you try to drill into one of these grips, the smaller hole will get cut open and then ride the flute of the drill upwards and make a mess. To compensate for this, an end mill must be used to do a plunge cut straight down. There must be careful workholding fixtures to keep the grip from moving. Trust me, I’ve trashed a bunch of grips by not making sure the grip was completely secure.

This HK33 contract grip has anchor holes that go evenly across. There isn’t enough spacing between those holes for a new 6mm pin hole and 9.5mm countersink to be milled without hitting the rear anchor hole.

This is a Malaysian contract grip has the rear steel “tail” has been cut off. Both pin holes and countersinks have been drilled. Look at the hole on the right. The pin hole ran right into the anchor hole and tore out the plastic that would have filled it. By the way, the orange paint was from me tracking early prototypes. It’s not something someone would normally see.

Despite those rear anchor holes being removed, the steel reinforcing is still held in place. While theoretically weaker, I have not heard of any real world cases where the the steel (it’s folded sheet metal really) has come lose due to separation from the surrounding polymer.

For people using converted grips, just insert your rear pin such that the retaining wire is on the shoulder and not in the hole. That’s really the only difference. Of course, like most grips, some final fitting may be required – by using a circular file to adjust the rear hole, filing the front locking plate or removing a bit of material off the back with a file or by sanding.

Summary

In short, purpose built MP5K grips have enough spacing between the rear metal strap’s anchor holes for the 6mm pin hole and 9.5mm countersink to be drilled. Other HK models do not use that same spacing so the tell tale partial hole appears at the 2:30 position. It’s purely cosmetic and just requires the user to insert the rear pin such that the locking wire rests on the normal shoulder of the hole and not the newly formed void.

I hope this helps you out.

If you are interested, our online store has a number of HK grips available – both converted and not. Click here.

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