Dear Mr. Rawles:
In a past life I used the popular HK MP-5SD. It’s reliability prompted me to purchase one of the first PTR-91s directly from the manufacturer. (Back when that was possible–they are all now sold though distributors).
I found the PTR-91 capable of digesting a wide variety of ammunition thanks to the HK family of well designed roller delayed blowback systems. This functional reliability and availability of really cheap magazines indeed make it a popular battle rifle. What I haven’t read by those singing it’s kudos, is that the forcefulness of the extraction system throws the brass quite a distance, making policing brass difficult. The same ejection system creates dent in the brass that I believe compromises the integrity of the fired cases so as to preclude safe reloading. It also generates the tell tale HK chamber flute marks on the expended brass. This alerts anyone finding un-policed brass that someone was there with a HK family main battle rifle.
The factory PTR-91 plastic stock is overly large, clunky, and I believe fragile. I recommend replacement with much thinner and better made German military surplus furniture is often available from Cheaper than Dirt.
To someone well familiar with the 03A3 type sling system, that of the HK family rifles may present a puzzle. One should not overlook combined the weight of this rifle and a battle pack of at least 200 rounds of ammunition. Add a plate carrier, hydration system, pack, and helmet, and the load out can be tremendous.
The telescopic sight mount is also clunky and positions the sight well above the bore. The above comments notwithstanding, The PTR HK91 an effective and relatively inexpensive battle rifle. I am thinking about adding the new Ruger Gunsite Scout rifle (available in .308 Winchester) to the mix. What a shame that the Ruger Scout bolt action wasn’t designed around the HK91 magazine. Sincerely, – A Panhandle Rancher