APE is short for antipreengagement and it's a feature of bolts/bolt carriers not a specific component. Anti preengagement features essentially prevent the bolt itself from trying to rotate/unlock up until the point in the firing cycle where it's time to commence the unlocking cycle. 

As an example, the AK has an antipreengagement feature in it's cam track that requires a solid whack to get past and start the bolt rotating. The israeli bullpup uses a system quite similar to the desert eagle pistols to handle this 

The vanilla AR15 doesn't have a whole bunch In the way of antipreengagement features which results in the steel cam pin putting pretty serious sliding force pressure on the inside wall of the upper receiver.

In a bunch of Sig's guns like virtus mcx et Al they've compensated for this by implementing changeable steel raceways in this part of the upper. Caracal/haenel also do a version of this (same designers).

The 416 does not have any version of this implemented though. In vanilla AR15's it's not all that much of a big deal either because, frankly, stripped uppers cost less to replace than the pair of shoes you're probably wearing now.

Ideally though antipreengagement features are like sufficient underslide and extra run-out distance for the bolt carrier in that they can and do improve efficiency and functionality while dirty/at high round counts.

The 416 does not have an insert.

Yes, the upper of an AR-15 outlasts the barrel, and is cheap to replace. However, it's even cheaper just to replace a tiny piece of metal, and that piece of metal can be steel instead of aluminum (and therefore last even longer) and it can be replaced without pulling the barrel. If the cam track and the barrel are out of sync, you might need to disassemble the upper to save the barrel and replace the receiver itself. With an insert, you just unscrew the insert and move on with your life. The downsides are added cost and complexity.

Of course, that's if you're using an AR-15 type design with no APE. My designs have APE, so they don't need any surface in the receiver to accomplish this. The bolt group rides in the receiver on rails, with no additional contact. Smooth and reliable, like an AK (or Garand, or AUG, for that matter).

This video gives you a good look at how worn out my AR-15 is hahaha:

https://www.youtube.com/watch?v=B3-vEiMeYlM

More info on the acquisition process (and some doubts about the outcome) from TFB.

It looks like this might not be a 100% money in the bank  done deal , between politics and performance of the 390 test guns in the first year, things could go sideways like its often the case with military procurement 

''The current schedule is that the German Parliament is to consider the project at the end of 2020. No delivery contract can be signed with Haenel (or anyone else) before then. Currently the procurement plan is for a total of 118,718 assault rifles, in the period from 2023 to 2026 and onwards. The procurement of the Bundeswehr assault rifle system is planned to be done in four separate lots. a) Basic weapon with accessories. b) Optics for proficiency levels 1-2. c) Optics for proficiency levels 3. d) Laser Light Module.

The supply of weapons is planned as follows :

2021 390 Test samples.

2022 0

2023 13,300

2024 20,000

2025 20,000

2026 65.028''

The German Ministry of Defence has published the process followed in this assault rifle competition.

According to press reports published in Germany today, the Haenel offer costs 152 million Euros, compared to 179 millions offered by HK.

Or perhaps not?   https://www.overtdefense.com/2020/10/09/breaking-bundeswehr-withdraw-order-for-haenel-mk556/

A patent blitzkrieg is being developed right now.

Over a basic 60 years old design. Even SIG could participate in it ROFL

It seems the case is not as clear cut as it seemed, I am sure H&K put all its lobying might behind this but,in addtion to the patent stuff ,some of the results of the testing just don't add up, like Haenel having 7% better penetration than HK using the same barrel length and ammo.?