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marine6680 · May 13, 2015, 05:43 PM

From all the reading I have done on it... I have read several reports translated from the original german...

Originally the polymer was blamed.

Further testing pointed to the ammo.

Even more testing by an independent lab found it was a combination of things.

One: the standard issue ammo used by the German military... it was not meeting the accuracy spec when the ambient temp of the rounds increased. I.E. The environmental conditions... As temps rose, average group size increased, until it eventually stopped meeting the spec. Simply exposing the rounds to sunlight was enough... Heat from firing would affect the rounds as well. So continued firing would lead to lowered accuracy.

Two: The Polymer... This one is actually a multiple issue and I will break them down. Some are material issues, and others design related.

A: The polymer can expand and contract at a different rate than the steel. This causes slight fit issues between the polymer and barrel trunnion, causing a zero shift. As temps increased, the problem grew worse.

B: The expansion affects the sight's zero, due to the fact the polymer expands, and the sights are connected directly to the polymer frame. Laying the rifle in the sun, causing uneven heating, would cause significant shifts in zero.

C: The polymer holds the heat from firing longer, and insulates the components so that they do not cool effectively. This exacerbates the above issues, and the following issue.

D: At some point without the knowledge of the Military, H&K changed the formulation of the polymer used to include a cheaper and more common Thermoplastic. (I want to say PET, but my memory could be faulty on this point) Basically the polymer was no longer a Thermoset plastic (or at least not completely) and was now able to melt slightly and soften at increased temperatures. During firing, the heat would rise above that point. This meant the plastic was soft enough to allow the barrel trunnion to shift position in the polymer frame. I seen a cross section picture of a G36, and you could readily see the evidence of melting and trunnion movement.

During the test, the lab used several other models of rifles. The list of other rifles was not made available last I looked, but was believed to include examples of other popular military rifles from other countries in 5.56... the M4 was believed to be among them.

The lab noted that several other rifles were able to meet or exceed the accuracy specs throughout testing. Though the ambient temp of the German standard issue ammo did decrease accuracy for all rifles in the test.

Using other ammo that did not show such issues with increasing temps, the G36, still could not meet accuracy specs, which pointed to problems other than simply ammo, and lead to the other findings related to the design and materials.

May 13, 2015, 05:43 PM	#4
marine6680 Senior Member Join Date: July 24, 2012 Location: Parker, CO Posts: 4,594	From all the reading I have done on it... I have read several reports translated from the original german... Originally the polymer was blamed. Further testing pointed to the ammo. Even more testing by an independent lab found it was a combination of things. One: the standard issue ammo used by the German military... it was not meeting the accuracy spec when the ambient temp of the rounds increased. I.E. The environmental conditions... As temps rose, average group size increased, until it eventually stopped meeting the spec. Simply exposing the rounds to sunlight was enough... Heat from firing would affect the rounds as well. So continued firing would lead to lowered accuracy. Two: The Polymer... This one is actually a multiple issue and I will break them down. Some are material issues, and others design related. A: The polymer can expand and contract at a different rate than the steel. This causes slight fit issues between the polymer and barrel trunnion, causing a zero shift. As temps increased, the problem grew worse. B: The expansion affects the sight's zero, due to the fact the polymer expands, and the sights are connected directly to the polymer frame. Laying the rifle in the sun, causing uneven heating, would cause significant shifts in zero. C: The polymer holds the heat from firing longer, and insulates the components so that they do not cool effectively. This exacerbates the above issues, and the following issue. D: At some point without the knowledge of the Military, H&K changed the formulation of the polymer used to include a cheaper and more common Thermoplastic. (I want to say PET, but my memory could be faulty on this point) Basically the polymer was no longer a Thermoset plastic (or at least not completely) and was now able to melt slightly and soften at increased temperatures. During firing, the heat would rise above that point. This meant the plastic was soft enough to allow the barrel trunnion to shift position in the polymer frame. I seen a cross section picture of a G36, and you could readily see the evidence of melting and trunnion movement. During the test, the lab used several other models of rifles. The list of other rifles was not made available last I looked, but was believed to include examples of other popular military rifles from other countries in 5.56... the M4 was believed to be among them. The lab noted that several other rifles were able to meet or exceed the accuracy specs throughout testing. Though the ambient temp of the German standard issue ammo did decrease accuracy for all rifles in the test. Using other ammo that did not show such issues with increasing temps, the G36, still could not meet accuracy specs, which pointed to problems other than simply ammo, and lead to the other findings related to the design and materials. Last edited by marine6680; May 13, 2015 at 05:51 PM.