I hate the fold down charging handle on the G3/PTR-91/HK91.  It would be so much better if it was stationary like the MP5 or FAL.  Does anyone make the option I am looking for?

Reminds me of my Kriss Vector, it's designed to make it easier to rack the bolt. You could probably have something made that you could experiment with, spare charging handles are
pretty cheap.

As Osprey said, the camming action of the folding handle is need to unlock the rollers from the trunnion. The HK21 style long handle is easier to pry up and give a much larger handle to retract the carrier.

I use the larger rubber coated handle for the HK21 series on my G3 sized receiver guns.  It provides for a much larger purchase area (two or three fingers) vs. the normal 1 finger grab area on the standard handle.  The larger HK21 handle is overmolded with a softer rubber and is more ergonomic vs. the all square all metal design or the metal with hard plastic overmold.

https://www.hkparts.net/shop/pc/HK21-Extended-Style-Cocking-Handle-US-Made-267p363.htm




As others have mentioned, you would need gorilla strength to do a straight pull back handle as the folding design is set up specifically to give you mechanical leverage to pull the bolt head away from the carrier and break the release on the bolt head lock.

The bolt head lock is the spring loaded arm on the carrier that grabs and locks over the bolt head when closed to the carrier.  This  little arm  will  permanently lock the bolt head to the carrier if you accidentally push the bolt head toward the carrier when you have the BCG assembly out of the gun, and necesstating the "rotate/twist and pull" operation to free the bolt head from the carrier locks "death grip".

Its not infrequent to see folks with complaints about how hard their HK rollerlocks are to charge when they were not built right and there is too much of a gap between the charging handle and bolt carrier tube and they lose a significant portion of the mechanical leverage the charging handle provides to unlock the bolt head from the carrier.

The reason the MP5 has a straight pull arrangement is because there is no bolt head locking arm on the MP5 series carrier, so you can just pull it straight back and only have to overcome the recoil spring pressure.