1) Where was the HK91 designed?
A: The HK91 was designed after WWII by German and Spanish engineers at Spain’s CETME arms plant. The original rifle was called the CETME rifle and was chambered in the 7.62×51 CETME cartridge. This round was identical to the 7.62×51 NATO cartridge, but was loaded to a lower pressure and velocity. The German firm Heckler & Koch eventually obtained all rights to build the rifle and, with updates, it became the G3 rifle which fired the NATO round. The G3 is a selective-fire assault rifle and the semiautomatic only version is the HK91.
2) When did the HK91/G3 first see military service?
A: The selective-fire G3 was officially adopted by the West German Border Guard in 1959. It remains in service today in many countries around the world.
4) Was the HK91 offered in any other calibers?
A: A 5.56 NATO version is produced and designated the HK33 (selective fire) and the HK93 (semiautomatic).
5) What is the capacity of the standard HK91 magazine?
A: Standard HK91 magazines have a 20-round capacity. There are also 30-round magazines available.
6) Are the CETME and the HK91 the same rifle?
A: Essentially, yes. The CETME is the predecessor to the HKG3/91 rifle.
7) Will stocks interchange between the CETME and the HK91?
A: In most cases, yes. There will be manufacturing tolerance differences between rifles that may cause stock fitment issues. In some cases, minor fitting may be required.
8) How can I mount a scope on my CETME or HK91?
A: The most common method is the claw mount. The top of the receiver has indexing points for the mount to attach to. The mount clamps to the receiver and, in theory, can be removed and reinstalled without loss of zero. Several companies manufacture claw mounts for the HK91/CETME and most have rails that will accept Picatinny or Weaver style rings. Original H&K claw mounts and scopes can also be found, but at a significantly higher cost. Some models will have a rail that is welded to the top of the receiver to accept Picatinny or Weaver style rings.
9) Are there alternative stock styles for my HK91 other than the original fixed stock?
A: There are several styles including the original H&K collapsible stock, AR-15-style collapsible stock, sniper and side folding stocks.
10) Original HK91s are very expensive. Are there other companies that manufacture this model?
A: There have been many companies that have produced HK91 clones over the years including Century Arms and PTR. The PTR 91 is considered by many to be the best clone available at this time.
11) Will HK91 magazines work in my CETME and vice versa?
A: Some HK91 magazines will work in some CETMEs and some will require minor filing to work. This is an easy modification that can be done with a hand file. CETME magazines should work in HK91s and clones.
12) My CETME does some serious damage to brass during ejection. Is there anything I can do about this?
A: Unfortunately, no. This is a design characteristic of the firearm that doesn’t lend itself to reloading. The delayed roller blow-back system provides positive extraction of the fired case, but is also very violent when compared to other systems.
13) The trigger in my HK91 is very heavy. Can this be improved?
A: You can replace the hammer spring with an MP5 trigger spring, but misfires may occur with military surplus ammunition. Light stoning of the trigger and hammer surfaces can also be done, but you don’t want to stone too much. These engagement surfaces are only surface hardened and if you break through this hardening, the part will be ruined. Bill Springfield of Colorado Springs, CO does some very good trigger work on the HK91/CETME including a set trigger.
HK 91/G3 and CETME Parts Compatibility Guide
The following HK 91/G3 parts are interchangeable with the older CETME rifle:
- Backplate or Complete recoil Assembly (minor fitting to the plastic sleeve at the end of the spring guide rod is required)
- Barrel Retainer Pins
- Blank Firing Adapter
- Buttstock- with minor fitting (buffer hole must be matched in order to use the cetme buffer)
- Carry handle and Port Buffer (requires modification to CETME handguard)
- Claw, Stanag Scope Mount
- Collapsible Stock (minor fitting to the plastic sleeve at the end of the spring guide rod required)
- Complete Stock set (fitting to the plastic sleeve at the end of the spring guide rod required)
- Complete Trigger Pack (as a set but not individual parts)
- End Cap/Dust Cover (CETME end cap/dust cover will not fit g3)
- Eyeloop for triple frame
- Flash Hider
- Grip Frames
- Handguards, Slim
- Handguards Wide (fitting is required, CETME has a bipod retaining ring that prevents the wide handguards from being installed)
- Mag Catch parts
- Paddle mag release
- Pistol Grip
- Pivot Pin for cocking handle
- Rear Sight (but only if entire sight base is swapped)
- Retainer Plate and Roll Pin Retainer for Rollers
- +2, +4 Rollers
- Triple Frames
The following HK 91/G3 parts are recommended upgrades to the CETME rifle:
- Bayonet (only when using adapter)
- Bayonet Adapter
- Cocking Handle
- Cocking Handle Spring
- Extractor Spring
- Firing Pin
- Firing Pin Spring
- Recoil Spring
- Retainer Pins
The following parts are NOT interchangeable between the HK 91/G3 and the CETME:
- Bolt Carriers
- Bolt Head
- Cocking Tube
- Individual fire control group parts like trigger, sear, hammer (can be swapped out as a set)
- Locking Lever for bolt carrier
- Locking Piece
- Recoil Buffer (Unless using HK buttstock)
- Support for Cocking Handle