Taming HK G3 Recoil

Heckler & Koch Gmb H Gewehr 3 pattern firearms (G3, HK-91, PTR-91), particularly those chambered in 308 Winchester or 7.62 NATO, have a widespread reputation for excessive, abrupt recoil. Excess recoil can make the gun very uncomfortable to shoot and lessen the life of the gun. This article will discuss the means of preventing or lessening excess recoil. I will assume the reader has access to one of the several HK repair or armorer’s manuals available online.

First, it is necessary to understand the mechanical principles of operation of the gun. The best article for this is a US Army study that is available online for free as BRL Memorandum Report No. 1953, A Comparative Evaluation Of The 7.62MM And 5.56MM, G-3 Assault Rifles published January 1969 by Thomas E. Carlson and David A. Golm at the U. S. Army Research and Development Center, Ballistic Research Laboratories, Aberdeen Proving Ground, Maryland (bit.ly/2Vfkr2k).

Some of the information in this article comes from that study and anyone interested in the G3 should read it. For purposes of understanding the recoil generated by the G3, the operation of the G3 action can be summarized as follows. First, the hammer falls and the firing pin strikes the primer of the cartridge, causing the powder to ignite and chamber pressure to rise.

As the chamber pressure rises, pressure is exerted on the face of the bolt which is transmitted to the locking rollers which are engaged in recesses in the trunnion and also rest on an inclined plane (the locking piece), which is connected to the more massive bolt carrier. The shallow angle of contact between the rollers and the locking piece reduces the backwards pressure on the bolt carrier to about 1/3 of that exerted on the bolt.

The bolt does not immediately open in response to the pressure on the bolt face because the locking lever latches the bolt to the bolt carrier. The grip of the locking lever is provided by the locking lever spring. Until the push exerted by the locking piece exceeds the force exerted by the locking lever and smaller forward pressure from the recoil spring, the bolt rollers cannot move from their recesses near the trunnion, and the bolt and bolt carrier cannot move backwards.

When the pressure on the locking piece is high enough, the locking lever slips over the lip on the bolt, the locking piece retracts and the rollers collapse inwards, allowing the bolt to open and the bolt carrier to be blown back by the residual chamber pressure. To repeat: when the backwards pressure on the locking piece exceeds the strength of the grip of the locking lever on the bolt and the comparatively smaller forward pressure of the recoil spring, the bolt is free to move backwards, and the action opens.

The unlocked bolt carrier moves backwards towards the shooter at approximately 25 feet per second, the fired case is stripped off the bolt face by a stationary ejector held within the trigger assembly, and the hammer is cocked for the next shot. The backwards movement of the bolt carrier is slowed by the recoil spring. The bolt carrier continues its backwards motion, usually far enough so it strikes the buffer pin protruding from the front of the buttstock.

The buffer spring is compressed, then extends, pushing the bolt carrier forward. The bolt carrier is also pushed forward by the compressed recoil spring. The forward movement of the bolt is concluded when the bolt face strikes the posterior surface of the barrel, pushing the bolt and bolt carrier together.

As the bolt and bolt carrier are pushed together, the locking piece forces the rollers outward to engage the recesses in the trunnion and the locking lever latches over the lip of the bolt, sealing the bolt and bolt carrier together, locking the bolt face against the chamber for the next shot. The engagement of the locking lever of the bolt carrier over the lip in the bolt also helps prevent bolt bounce. Within this description are some very important points.

The rollers in the bolt do not by themselves lock the action. They only help secure the bolt head against the barrel when the bolt is latched in place by the locking lever. The rollers, in conjunction with the inclined plane that they contact on the locking piece, reduce the backwards-directed force applied to the bolt carrier assembly. The angle of the locking piece (which the rollers push on) determines how much force is directed rearward onto the bolt carrier, which contains the locking lever.

The shallower the angle of the locking piece, the less force is directed rearward. The less force that is directed rearward, the longer the locking lever can hold the action closed. If there is no separation between the bolt head and the bolt carrier, the rollers and locking piece cannot play their proper role reducing the backwards thrust on the bolt carrier. The bolt carrier would be subject to

The locking lever fits over the lip of the bolt, holding the bolt and bolt carrier together. This keeps the rollers in their recesses. Above center: In middle, when a cartridge is fired, pressure builds in the chamber and presses on the bolt. Most of this pressure is diverted to the trunnion by the rollers touching the locking piece, but about 1/3 of the pressure pushes rearward on the locking lever, which pushes the locking lever and bolt carrier back away from the bolt.

When the pressure on the bolt carrier exceeds the grip of the locking lever on the lip of the bolt, the locking lever slips off the lip of the bolt and the bolt carrier is free to move back. This pulls the locking lever out from between the rollers, releasing the bolt from the trunnion. Once the rollers have disengaged from their recesses, the residual chamber pressure and the inertia of the two-pound bolt carrier assembly propel the bolt carrier assembly fully open.

These drawings are only intended to represent the basic principles of G3 bolt operation. the same thrust as the bolt, and bolt carrier velocity would be greatly increased. Hence the emphasis in the various G3 manuals about checking the bolt gap frequently. The locking lever spring controls the force of the locking lever. The strength of this spring is the largest determinant of when the action opens and is more important than the angle of the locking piece.

Changes in the angle of the locking piece affect the force necessary to unlock the bolt by 10% or less; a greater than 10% change in the strength of the locking lever spring has as large or larger effect than any change in the angle of locking piece. To repeat: minor changes in the strength of the locking lever spring have a larger effect on when the bolt opens than the angle of the locking piece.

Bolt carrier recoil velocity is affected by the chamber pressure at the instant the bolt unlatches, as the chamber pressure is pushing on the bolt at the moment of unlocking. Anything that slows bolt opening from the chamber pressure will slow bolt carrier velocity. Conversely, anything that prolongs a high chamber pressure, such as a longer barrel, a slower burning cartridge propellant, or (more importantly) the addition of a suppressor, will increase bolt carrier velocity.

The recoil spring helps slow the backwards movement of the bolt carrier but plays a relatively minor role in controlling when the bolt opens, as the force needed to unlock the bolt and the impulse propelling the bolt carrier backwards are much larger than the force of the recoil spring against the closed bolt. A weak recoil spring may cause faster rearward bolt carrier velocity but does not cause a faster forward bolt carrier velocity.

Provided the bolt recoils the same distance for each shot, the recoil spring releases the same energy as it extends, regardless of how quickly it was compressed. Excess bolt carrier velocity is absorbed and released by the buffer assembly. If the bolt carrier velocity is too high the bolt carrier bottoms out and strikes the buffer housing, fully compressing the buffer spring.

Unlike the recoil spring, which is substantially compressed for all but near-squib loads, variations in buffer spring compression will cause variations in forward bolt carrier velocity. Understanding Recoil Now that some principles of operation of the G3 action have been explained, let’s look at the important forces that generate recoil. The first is the forward motion of the bullet and combustion gases and their exit

Computed from data by T. E. Carlson and D. A. Golm in 1969. From Norwegian Army TM 9-1005- 25/225-14, cited at MG-42.net/G3info.htm. from the muzzle creating recoil. The backwards movement of the bolt carrier compresses the recoil spring and the impact of the bolt carrier against the buffer pin compresses the buffer spring, both of which pushes against the shoulder of the shooter. The bolt carrier is propelled forward by the buffer and recoil springs, also pushing against the shoulder of the shooter.

Finally, if the bolt carrier velocity is very high and the bolt carrier overcomes the buffer spring and strikes the buffer housing of the stock, a very abrupt and unpleasant recoil is felt, as the momentum of the bolt carrier is transferred directly and quite suddenly to the stock and thence to the user. With the exception of the forward motion of the bullet and combustion gases exiting the muzzle, recoil is worsened by high bolt carrier velocity.

Reducing the speed of the rearward movement of the bolt carrier is the single most important factor in reducing the recoil of the G3. An adequate buffer that prevents contact between the bolt carrier and the buffer housing is the second factor and should be addressed after bolt carrier recoil velocity reduction has been attempted. So, what can be done to evaluate and adjust a G3 rifle for proper recoil? Talking to the user is sometimes useful. What ammunition is used?

Different makes of ammunition may cause very different recoil. Does the gun recoil abruptly or excessively? The normal recoil of the gun I would describe as a "push" rather than an abrupt slam. With a double buffer in the buttstock assembly the recoil may have two pulses to it. Is brass thrown too far? Fifteen yards is too far. Has the user occasionally found the bolt carrier not seating fully forward with misfires (bolt bounce)? How easy is it to reassemble the bolt by hand?

A locking lever that does not put up a bit of a fight when reassembling the bolt on the bolt carrier is a sign of a weak locking lever spring. Commonly, anew or even somewhat experienced user may not know the answers to these questions. Even if the gun was working properly years ago, there may have been a gradual change in functioning and the user has become accustomed to it. Finally, is a suppressor used?

Adding a suppressor will lessen the thrust created by the combustion gases, but at the expense of prolonged chamber/barrel pressure, which causes higher bolt carrier velocity and more violent recoil. Examination The gun should be examined for barrel length. Guns with barrels longer than the standard 18" or guns used with suppressors will maintain a high chamber pressure for longer and will produce higher bolt velocity.

These guns may need a shallowerangle locking piece and anew G3 or even an upgraded version such as the PSG-1 (Präzisionsschützengewehr or "precision shooting rifle") locking piece spring. Anew locking lever spring may also help prevent bolt bounce on suppressed guns. Next, the bolt gap should be measured, even if the shooter has no complaints about excessive recoil.

The bolt gap is the distance between the bolt and bolt carrier in an assembled, unloaded gun when the bolt slams home on an empty chamber as measured with a feeler gauge. If the gap is less than 0.1 mm, there is a higher chance the pressure on the bolt face may be directly transmitted to the bolt carrier, causing premature unlocking with high bolt velocity. If the bolt gap is too large the locking lever may not be properly engaged on the bolt lip.

When a standard 45 degree locking piece is used, the suggested gap is 0.1 to 0.5 mm. It is not clear to me that different angle locking pieces require a different bolt gap in a G3. A different bolt gap is recommended in a PSG-1 and HK-21 but the roller geometry is different in those guns. The proper bolt gap can be obtained by adjusting roller sizes or (less often) replacing a worn locking piece with a newer one. A 0.1 mm change in gap will occur for each step up or down in roller size.

Rollers are sized in even numbers. For instance, going from a +2 (8.02 mm diameter) roller up to the next size roller (+4 – 8.04 mm diameter) will increase the bolt gap by 0.1 mm.

The firing pin recess is aligned with the firing pin, while the buffer pin only contacts a hemispherical region of the lower bolt carrier (buffer strike zone). HK recommends regularly checking the bolt gap, so even if a gun is apparently functioning normally, this should be done as a good gunsmithing practice. There is a huge fascination with bolt gap in the HK community, far out of proportion to its importance, and many an online argument has been spawned over a disagreement of less than 0.2 mm.

I suspect this is because factory manuals insist on measuring the bolt gap, stating that it is a safety issue, but hardly ever discuss spring strength. Very useful clues about excess bolt carrier velocity can be obtained by inspection of the receiver and buffer housing. The buffer pin does not strike the center of mass of the rear of the bolt carrier, but only touches the lower edge of the carrier.

This concentration of force on the lower rear of the bolt carrier tilts the front of the bolt carrier up so the upper front of the bolt carrier strikes the inside of the upper receiver. The abrupt strike can be so forceful that an impression is made on the receiver by the machined grooves on the head of the bolt carrier tube.

While some wear in this area is inevitable, if there is widespread gouging of the upper receiver this is evidence of repeated forceful impact with the buffer pin from excessive bolt carrier velocity. The buffer housing should be checked for signs of bolt carrier impact, which is a sign of excess bolt carrier velocity or weak recoil or buffer springs.

There is a hole in the buffer housing to accommodate the firing pin, so the flat back surface of the bolt carrier can come to within 1 to 0.5 mm without the firing pin bottoming out in this hole. As the bolt carrier comes closer to the housing the firing pin will strike the bottom of the hole, marring the finish of the housing at the bottom of this hole or even creating an indentation.

I have not seen a firing pin relief hole in a housing that would permit the bolt carrier to strike the housing without the firing pin touching first. Hence, the firing pin relief hole in the buffer housing should be the first point to inspect when looking for contact between the bolt carrier assembly and the housing. When the buffer spring is completely overpowered by a too-fast bolt carrier, the back surface of the bolt carrier will stamp an impression of itself on the housing.

In extreme cases, the abrupt stop of bolt carrier at its most rearward travel may attempt to force the bolt head into a locked position, which will push the rollers out against the stamped guide rails of the receiver, leaving marks or even indentations on the rails. A toofast recoil velocity may even damage the cross-pin holes that secure the buttstock. One trick to look for how close the bolt carrier comes to the buffer housing is to put a thin strip of modeling clay on the front of the housing.

In theory, it would be best if the buffer contributed to the forward bolt carrier movement as little as possible, and the recoil spring did almost all of the work returning the bolt carrier to the forward position. Indeed, the contribution of the buffer is totally unnecessary for

The wear on the finish of the buffer pin is evident as well. On the right is the buffer housing from a moderately used gun. The bolt carrier has not marred the housing. There is a subtle impression from the firing pin (inset), which shows the bolt carrier is beginning to overpower the recoil spring and/or buffer, permitting the firing pin to touch the bottom if its hole in the housing. This is an early sign that the gun needs attention.

There is also less wear on the finish of buffer pin than on the buffer on the left. Buffer pins are the among last parts to show finish wear from excess recoil. chambering of rounds. In Carlson and Golm’s Army Memorandum Report mentioned above it was demonstrated that full compression of the recoil spring was not needed for reliable operation of the gun. In many well-maintained guns the face of the buffer pin has little or no wear.

However, all of HK’s technical literature states that the buffer helps propel the bolt carrier forward. Sufficient bolt carrier velocity with the ensuing bolt carrier-to-buffer contact is necessary for reliability in the varying conditions in which the gun was intended to be used. Addressing Recoil If it is believed that the recoil is excessive for the shooter or ammunition used, or the examination of the gun reveals signs of excessive bolt carrier velocity, then the following steps should be performed.

First, inspect the locking lever and locking lever spring. If the tip of the locking lever is worn, it may slip over the bolt lip too early in the firing cycle. A worn locking lever would be a rare occurrence in civilian guns. The locking lever spring is far more likely to be weak. If it is easy to reassemble the bolt to the bolt carrier by hand, or if the back of the locking lever can be pushed down even a small amount by strong finger pressure, the locking lever spring should be replaced.

Most of the time, simply replacing the locking lever spring is all that is necessary to greatly improve the recoil. In exceptional circumstances, such as when along barrel is present or a suppressor used, a stronger locking lever spring (made for the longer-barreled PSG-1 precision shooting rifles) can be used and will provide even more delay on bolt opening and a slower bolt carrier recoil velocity. The stronger locking lever spring will also lessen the occurrence of bolt bounce.

If the locking lever spring is in good condition and excess recoil is present, the locking piece can be changed to one with a shallower angle. This will reduce backwards force on the bolt carrier and is very helpful if the gun is to be shot suppressed, or if the barrel is longer than 18". After changing the locking piece the bolt gap should be remeasured. Sometimes it will be necessary to replace the rollers to adjust the bolt gap to the recommended range.

Bear in mind that changing the locking piece angle is not a substitute for a fresh locking lever spring, as the locking lever spring has just as much or more influence on bolt velocity as the locking piece angle. Once the bolt unlocks the recoil spring provides the principal resistance to bolt recoil and helps return the bolt forward.

However, based on Carlson and Golm’s report on the G3, the components of the bolt carrier assembly (i.e., the rollers, locking piece, locking lever and locking lever spring) have much more influence on bolt carrier velocity than the recoil spring. Nonetheless, if the recoil spring is weak a fresh recoil spring may further reduce the bolt velocity so the contact between the bolt carrier and the buffer pin is a gentle "kiss".

The recoil spring can be tested by using a scale with a hook attached to the bolt carrier retracting handle to measure the force necessary to keep the bolt carrier fully retracted. Changes in opening bolt carrier velocity caused by the above alterations to the gun (or simply changes in ammunition) can be shown by where and how far brass is thrown by ejection. Of course, it is necessary to use the same ammunition in monitoring for changes in the ejection pattern.

A grossly excessive bolt carrier velocity may throw brass to the four o’clock direction while an excessive velocity may throw brass to two o’clock 15 yards or more away from the gun. In many cases, this distance can be reduced by a third by changing the locking piece angle from 45 degrees to 36 degrees. The angle the brass is thrown will not change, as the two o’clock direction is the normal direction for ejection.

If the buffer itself is weak and strikes of the buffer housing continue to occur after bolt recoil velocity has been reduced, the buffer spring

or even the entire buffer assembly can be replaced. The latter course of action is usually faster and replaces all the vulnerable parts. There is a good demand for enhanced buffers and I suspect they are overly used as a panacea for excess bolt velocity.

It is simpler and better for the gun and shooter to keep the bolt velocity down by replacing the locking lever spring, adjusting the angle of the locking piece or replacing the recoil spring, rather than trying to mask the symptom of high bolt velocity with a stronger buffer.

Further, if upper receiver scarring is occurring because of bolt carrier tilt, a so-called double buffer does not solve this problem because this buffer strikes the bolt carrier in the same region as the original G3 buffer pin, tilting the front of the bolt carrier up in the same manner. Also, with an enhanced buffer, an excessively fast bolt carrier may be propelled forward so efficiently Quick guide to fixing G3 excess recoil I. Assess for excess recoil A. Ask shooter regarding – 1. Abrupt recoil 2.

Excessively forceful ejection 3. Easy assembly of bolt carrier 4. Bolt bounce 5. Suppressor use B. Examine gun for – 1. Barrel length 2. Bolt gap 3. Scoring on upper receiver 4. Damage to receiver/buffer housing II. Minimize recoil A. Reduce bolt carrier velocity 1. Adjust bolt gap 2. Assess/replace locking lever 3. Assess/replace locking lever spring 4. Reduce locking piece angle 5. Assess/replace recoil spring B. Assure adequate buffer 1. Replace buffer or buffer spring 2. Change type of buffer C.

Address other factors 1. Change brand of ammunition 2. Add buttpad 3. Change model of stock 4. Use reduced-power ammunition 5. Muzzle brake that the gun shudders obnoxiously. At very high bolt velocity speeds, an enhanced or double buffer may make bolt bounce more frequent. Hence, an enhanced buffer should be one of the last steps in moderating recoil.

If bolt bounce remains a problem in a 308 Winchester or 7.62 NATO G3, a tungsten-buffered bolt carrier (now uncommon and available at a premium cost) might help lessen it. Bolt bounce is a known problem in 223 Remington or 5.56 NATO versions of the G3 and all of these bolt carriers are buffered. After any adjustments/repairs are made to the bolt carrier or buffer I touch up the paint on the buffer housing so future strikes can be detected.

Finally, if the G3’s recoil is still excessive for the user, different brands of ammunition should be tried. The normal buttpad can be replaced with a thicker and wider HK-21 buttpad. This will increase the length of pull and may prevent the shooter from seeing the "ring within a ring" sight picture that these guns are famous for. A slip-on recoil pad can be added.

Smaller recoil pads sized for the AK-47 stock fit well, however, they interfere with the normal sling attachment points, increase the length of pull, and may also interfere with the sight picture. The buttstock can be changed to a Spuhr G3 Stock Assembly (SpuhrWebshop.com) also sold through Mile High Shooting Accessories (MileHighShooting.com, but this will require that optical sights be mounted to the gun, adding more weight. Reduced power ammunition can be obtained or handloaded.

The G3 was originally designed for a less powerful cartridge than current NATO cartridges so using reduced loads is one way of returning the gun to the roots of its design. A muzzle break can be substituted for the flash hider, though I wonder if this might not prolong a high chamber pressure. G3s are so rugged, reliable, and long-lasting that they have been called the "AK-47 of .308’s".

Part of the reason for this is that the soul of the gun is a well-built, large bolt carrier assembly which is made of wear-resistant parts. The gun remains reliable over wide variations in bolt carrier velocity—and the neglect that caused it. With long-term use the bolt carrier velocity gradually increases until the bolt carrier strikes the buffer pin at high velocity or even contacts the buffer housing, abruptly increasing the felt recoil.

This pattern of slow change in the recoil may prevent the gun’s user from identifying increased recoil until it reaches absurd levels, disillusioning the shooter and damaging the gun. The maintenance and/or repairs to keep the gun more comfortable to shoot are easily done. When a customer complains about the recoil of this gun, now you know how to evaluate and fix it. AG