Review: HK 93/33 - .22LR Conversion Kit...

[LongDuck]

Wanted to provide a thorough and detailed range report for the HK93/33 conversion kit to .22LR that I purchased recently. Knowing that there aren't many of these kits out there, I'll start off by saying that in my view it's a great investment for the collector aspects, saving some money on ammunition costs, and also remains very accurate for plinking and target shooting. What follows is a full break-down on the method of operation, performance, and other facets of the .22 conversion kit in both semi-automatic and full-automatic with a registered sear. I'll also include some pictures where they fit best to help show critical details, so... on with the review:

What's included in the kit:
Since this is a Factory HK accessory, the boxed kit has an overall fit and finish that is what you'd expect from a German company. The olive drab wooden box is built like a shipping crate, complete with indentations, padding, and cutouts for holding the components securely and without damage. The bolt carrier assembly is included at the bottom left, with the rifled chamber insert held at the bottom right corner. At the top are 2x 20-round magazines of steel construction with polymer blocks that are formed to fit the '93/33 magazine well. The magazines are solidly built and offer no play from side to side or front to back when mounted in the host weapon. They hold 20 rounds apiece, but if loaded to maximum capacity, the bolt should first be retracted in the normal fashion to allow insertion (more on that later). There is also a packing card mounted to the inside of the top lid which enumerates the contents (in English). Though the kit does not come with a fullsize '93/33 recoil rod assembly (it uses the one from the host weapon), the box is designed to accommodate a recoil rod and spring as a spare.


Design and method of operation:
This .22 conversion kit uses direct blow-back operation through a cylindrical conversion bolt which rides inside a modified full-auto capable bolt carrier. This internal .22 bolt assembly has it's own smaller and lighter recoil spring and guide rod, complete with a heavy spring buffer at it's terminal end. The steel components slide very smoothly together, and the kit that I purchased appeared to have some firing wear to the internal bolt surfaces and outside carrier. I took this as a good sign that the kit worked correctly, which I was pleasantly surprised to confirm. The machine work that went into manufacturing this assembly is typical HK with finely contoured corners and multi-axis mill work that must be seen to be appreciated:
HK-.22 bolt (foreground), compared to standard HK33 bolt carrier/head:


What's unique about this conversion kit is that it uses the Factory ejector in the trigger pack to eject the .22 casings, unlike other conversion kits which use an edge on the left side magazine feed lip to effect this function. Also, the internal bolt carrier features a white plastic sleeve to hold the .22 recoil spring, most likely to reduce internal friction and ensure reliable operation with the light powder charge typical to most .22 cartridges.

Retracting the bolt charging handle forces back the outside bolt carrier plus the internal .22 bolt, exposing the face of the smaller bolt to the top round in the magazine. Releasing the charging handle releases both bolt assemblies, being driven by the '93 recoil spring assembly, and closes bolt bolts simultaneously. This charges a round from the magazine into the chamber insert and prepares it for firing. At this point, the hammer has been cocked and is ready to fire in the usual manner. In the case of an auto-sear and trip lever, the underside of the .22 bolt contains a welded extension which forces the sear trip lever forward and down, enacting F/A operation. The back of the .22 conversion bolt carrier has an additional metal tube extension which prevents over-retraction of the bolt past the hammer. This allows the carrier to come back far enough to strip a round, but not so far as to get caught on the hammer, effectively locking up the weapon.
Bolt carriers back with retracting handle:

and bolts closed:


As a sidenote, my initial plans for purchasing this kit were to get it to work with both of my HK sear host firearms, a 1976 SACO HK93 converted to HK33E configuration, and a SACO-import Vollmer HK53 setup Factory correct with '53 parts. On inspection of the kit and test installation on the hosts, I found that it will only work on the fullsize '93, since the '53 carrier is shorter at the front. This prevents proper closure of the .22 bolt and carrier to the breech face, thereby disallowing it's use on the HK53.

Proper installation of the kit:
Installation of the conversion unit begins with removal of the 5.56mm bolt and recoil spring assembly, first clearing the weapon and making it safe. Insert the recoil spring rod into the .22 conversion bolt carrier, and set it aside. Very cautiously, the .22LR chamber insert can be slid gently into the magazine well and aligned at the trunnion and chamber with the serial number facing the magazine well. Insertion of the chamber insert must be done carefully to avoid damaging the frail bullet exit on the mouth of the insert; also, the insert must be oriented correctly to allow the bolt face to close against it and still allow operation of the charging handle. Push the chamber insert firmly forward into the trunnion until it clicks, and the spring steel C-clip on the outside edge will lock it into place against the forward edge of the side bolt carrier guide rails formed into the receiver. Once the chamber insert is properly seated, slide the conversion kit bolt carrier into the rear of the receiver and allow it to slide forward. Install the stock and rear pin as normal.

With a semi-only trigger pack, the .22LR internal bolt will close fully on the chamber face of the insert, but if a registered sear equipped trigger pack and lower is used, it's very likely that the bolt face will not make contact with the chamber due to the sear trip lever holding it back approximately 3-4mm. This is a consideration when charging and firing the kit, explained in detail later on. At this point, be sure that the charging handle is fully forward and locked, and the kit is basically ready to fire.

Range Report:
On my HK33E, I used both a 0-1-25 C/P lower with semi-only triggerpack, and a Qualified H-series sear mounted by Urbach in a Picto-Ambi-Burst (3RB) lower which was C/P to fit the '53 mentioned before. Both of these packs functioned perfectly with the .22 conversion kit. The only problem that I noticed was with the registered sear pack in which the hammer was not being retracted far enough to operate the 3RB cam, resulting in F/A fire in the 3RB position. That single point aside, the F/A operation of this kit fired the .22 Remington 'Golden Bullets' like clockwork at a fast ROF of approximately 900-1000 rpm. While fast, it will dump the 20 round magazine in about 1-1/2 seconds, though the HK33E is adequately heavy that there is very little recoil noticeable to the shooter. Accuracy reflects this as well with the pictures here showing first the semi-automatic shot grouping at 15 yards, followed by the F/A shot grouping at 15 yards (Will post target pictures later).

As a tip to other shooters, if you attempt to ride the charging handle forward when chambering a round, it will undoubtedly create a misfeed. This is due to the feed angle from the magazine to the chamber insert, and I found that by performing the 'HK Slap' on the retracted charging handle, it chambered and fired the first round without incident. Trying to lower the bolt carefully always resulted in a misfeed, which then required removal of the magazine and retraction of the bolt to drop out the doublefeed. Also, when retracting the bolt carrier on a round that didn't fire, do so quickly and with authority to ensure that the ejected round clears the ejection port - otherwise, it will fall back down into the action and lodge in the triggerpack.

Ejection pattern is between 2 O'clock and 3 O'clock and at a distance of about 3 feet and HIGH - these cases rocket out of the ejection port and fly right out to the firing range.

Comparison to other .22 machinegun conversion kits:
As an accessory for a registered sear owner, this kit compares very favorably to my Vector UZI .22LR conversion kit, and appears to use an identical ejector mechanism (thin metal plate) including method of attachment to the bolt. In fact, the parts look to be interchangeable.

The UZI .22 kit fires at about the same rate (900-1000rpm), but due to the lighter weight of that weapon, accuracy is not nearly as good, even with a dedicated .22LR barrel with the correct twist rate of 1-16". The HK33E and conversion kit exhibited better accuracy and about the same reliability as the .22 kit on the UZI. I was pleased that both guns fire the Golden Bullets reliably and accurately, and since these rounds are copper jacketed, exhibit far less carbon build-up and barrel leading than unjacketed rounds. Cleanup of the rifle and receiver was actually easier than cleaning after firing 5.56mm. The sole exception is cleaning of the chamber insert, which appeared to pick up lead and carbon build-up extensively in the voids where the chamber flutes are located. This was scrubbed off with a brass-bristle brush, and I recommend cleaning the flutes in your rifle after extensive firing.

I hope you guys enjoyed this review,

[edman99]

Thanks for the review. Your attention to detail doesn't leave many questions to be asked. It seems that maybe this kit is a little more "tempermental" than the G3 kit. I say this because I don't have to perform the "slap" to get mine to chamber a round properly.

Thanks again.

[SudS]

LongDuck,

I really liked your write-up on the kit. I also have a kit but haven't tried it out yet. One question I have is, I've not seen a 93 kit that had the card in the lid. I've seen plenty of 91 kits that had the card, but not a 93 kit. Is your card original or a copy of the 91 card? If it's original, I'd be happy to pay you to do a real good photocopy of it so I can reproduce it on heavy stock. Thanks.

SudS

PS I tried to send a PM but we both cannot receive or send PMs because we've exceeded or storage limit. I have no clue how to creat more storage space.

[CZ-75]

Excellent review!

Thanks!

[hkpete]

That was a very enjoyable and interesting read! Nicely done.

[LongDuck]

On the kit 'card', after inspecting mine, it does appear to reference the G3 .22 kit contents, as the location of the internal parts and diagrams does not accurately portray the 93/33 kit. So, to answer your question, this looks to be the standard G3 kit contents listing, and not specific to the '93 kit, though it does list the correct parts, and a reference to 5.56mm at the top line (not visible in the pictures).

If you're still interested in a copy of the card, I'd be happy to make one for you.

Also, as promised, here are the pictures of accuracy on this kit which were referenced in my prior Range Report (limit of 4 images, apparently);

Slow fire, 20 rounds, .22LR Golden Bullets at 15yds:


Cyclic, 1000rpm, many rounds, same ammo at 15yds:


As you can see in the above picture, the F/A kit really tears a hole in that target and extended ranges seem to offer better than expected accuracy, likely due to the long barrel and slow (1-12") twist rate of this early HK import. By the way, these shot groups are using the settings in place for 25m Point Blank when firing 55gr 5.56x45 in this rifle - I didn't want to have to adjust the sights when using the .22 kit, so just shot it with the fixed settings to see where they'd hit. It turned out to be close enough for most plinking.

Thanks for the comments, guys. I figured as enthusiasts, you'd enjoy hearing about how the kit runs.

[SturmgewehrXXX]

Great report! Thank you!

[edman99]

As rare as those kits are most of us will never own one. Another board member bought one but had to return it when it arrived without the chamber insert!

Thanks again.

[LongDuck]

I'd buy that kit just to get some spare parts and the magazines!

The chamber insert is obviously a critical component in the design, however.

[SudS]

Many thanks for the offer. I have the 91 kit with the card. Still looking for the HK factory 94 kit. Perhaps some day I'll find one at a reasonable price (and yes, I know they don't work all that well).