PTR91 (HK91 Clone) Part 2: Modularity And Some Accuracy Upgrades

In Part 1 I talked about my past experiences with the HK91 type rifles, it’s specs, and the accessories available and recommended. I mentioned that I had a trigger from Bill Springfield in the mail, and would give my impressions of that trigger on the accuracy of the PTR91.

THE NEW TRIGGER AND BUFFER

After zeroing the irons and scope on my most recently acquired PTR91, (same model as my other rifles, but has a Match barrel) I spoke with Bill Springfield from “Triggerwork.net” about getting one of the HK91 triggers he is justly famous for. I spoke with him on a Wednesday evening, and had the trigger pack in my hand on Monday afternoon.

HK Trigger pack with Safety

To say he is “On the ball” is an understatement, considering he advised me he’d put it (trigger pack) together the next day (Thursday) and I had it four days later. If only all business owners were so punctual. I bought one of his completed trigger packs ($189) as opposed to sending him mine and having him modify it ($75). The primary reason was to have an extra assembled trigger pack on hand in my “Spare Parts Kit”.

Location of recoil buffer in rear stock

Stock recoil buffer assembly

I also had him throw in an “Improved Recoil Buffer”  ($49) at his recommendation, because this helps with recoil reduction and more accuracy for follow up shots. Although I don’t mind the recoil of “HK91/G-3” type rifles, it wouldn’t hurt to see what the improved recoil buffer could do.

All I can say about the effect of the new trigger and buffer on the rifle was “Dramatic”. The best I have done with these types of rifles in the past was 1 MOA (1″ @ 100 meters, 2″ @ 200 meters, etc.) and this was on a very good day. The norm was 1.5 to 3 inches at 100 meters with ball, and 1.5″ with 168gr Match.

I bought some Federal 175gr Match, because the PTR91 has a 1-10″ rifling twist, as opposed to the HK91 having a 1-12″ twist ( I used 168gr Match in my original HK91). When I first tried the 175gr Match ammo (Pre-Springfield Trigger), my groups were no better than the best Ball groups (1.5 MOA).

Well I can tell you Bill Springfield’s modified HK91 trigger is worth the $189 and then some. The recoil buffer also makes a noticeable difference, primarily in the recoil impulse. This quicker recovery sets you up for a faster follow up shot.

The rifle has a Primary Arms SLx 4-14×44 FFP (First Focal Plane) scope, with an illuminated ARC-2 reticle. I wanted this optic for this rifle because it makes it easy to adjust between the zero for the 7.62N and the .22LR in the .22 Kit. I zeroed the 7.62N and put the turrets on the “0” marks, then adjusted to the zero for the .22LR kit and marked those location on the elevation and windage turrets with a silver paint pen.

Easy to read and mark for an adjustment to the .22LR setting.

That’s definitely “Minute of Squirrel”, and from a subcaliber adapter no less.

Besides the ARMS #1 scope mount with the Leupold QR rings, holding the PA 4-14 optic, the other additions made to this rifle were the cheekpiece for the fixed stock (needed for a good cheek weld for the scope), an HK polymer trigger housing with MagPul ambi safety, a wide forearm (needed to mount the HK bipod), an HK bipod, an ejection port buffer and a Smith Ent. Vortex Flash Suppressor.

First three shot group fired with 175gr Match at 100 meters. Orange dot is 1″ in diameter

First three shot group fired at 200 meters with 175gr Match.

The first two 3-shot group pictures shown, were the first rounds fired with the Federal 175gr SMK Match ammo. The first was at 100 meters and measured 1″ (1 MOA), the second was at 200 meters and was 1.75″ (0.88MOA). This is good shooting for a Match rifle that is set up with all the Match attributes, let alone a generic battle rifle with a Match grade barrel and a modified trigger. Needless to say, if you have a PTR91 or an HK91, and you want more accuracy, give Bill Springfield a call. You’ll be glad you did.

HK SYSTEM MODULARITY

The HK system of rifles are the most modular rifles in the world. This is a bold statement, but I will give a brief description of why I believe this. HK created a series of rifles starting with the G-3, which was based off of the Spanish CETME Model 58.

HK Rifles started with the G-3, a 7.62x51N chambered rifle, but later expanded to include a 5.56x45N model, the HK33, and a 9mm submachine gun, which is the MP-5. In semi-auto form, this translated to a 7.62x51N HK91, a 5.56x45N version called the HK93, and a semi-auto 9mm rifle called the HK94. HK even had a prototype version, chambered in 7.62x39S called the HK32, and fortunately, this is manufactured by PTR as the Model 32.

Easily switches from a DMR type rifle to a compact (33″ with stock collapsed), fighting rifle in about a minute.

PTR manufactures three of the four caliber rifles listed above. The PTR91 in 7.62x51N, the PTR32 in 7.62x39S, and the PTR608 in 9mm (I own one of these as well). I don’t know if they have plans for making an HK93 clone in 5.56x45N at this time, but I bet they would have pretty good sales if they did.

OK, on to the modularity of these systems. The main difference that is apparent when you look at an HK rifle, is the number of pins holding the stock to the rear of the receiver. The larger 7.62N and 7.62S (Model 32) are a two pin attachment, and the 5.56N and 9mm are a one pin affair.

Generally, when it comes to stocks, as long as the stock has the correct matching number of corresponding holes on the receiver, it will fit, and replacement takes about 30 seconds. The handguards are organized according to length, and all use a one pin attachment point.

To disassemble the lower receiver trigger pack housing, start with releasing the hammer and rotating the safety to the “12” O’clock position. NOTE: The HK  polymer lower receiver housing on the left and the original steel housing on the right. They are interchangeable in use, but the polymer housing allows use of an ambidextrous safety.

Pull the safety straight out of the lower receiver housing

The trigger pack will slide straight up out of the lower receiver housing.

For instance, the HK93 (5.56N) handguard will fit the G3K (7.62N w/ 12″ barrel), and the MP5 handguard will fit the HK51 (7.62N w/ 8 3/8″ barrel). The handguard also takes about 30 seconds to change. On semi-auto rifles, the lower receiver trigger pack housing will come off when you remove the stock pins, and the trigger pack inside it can be swapped out with another trigger pack (like I did with the earlier mentioned Bill Springfield trigger pack) in about……thirty seconds.

The HK or ARMS #1 scope mount will fit all of the HK type receivers, unless they already have a welded rail in place. Many items, like the carrying handle, can fit the rifle caliber firearms (example, PTR91, HK93, PTR32). The front sight assembly is interchangeable on all the original HK rifles and subguns, but specific diopter drums (rear sights) are made for each caliber based on their cartridge’s ballistic drop.

Last group of the day after removing and reinstalling the ARMS #1 scope mount. I forgot to shoot a confirmation group till after I packed up and was almost ready to leave the range. I threw in two rounds of Match ammo, deployed the bipod and quickly (was on a time hack) fired two from the prone. Two in the head (bracketing the aim point) fired quickly at 200meters tells me the zero is still fine.

No other firearm system that I have seen has this “whole weapon” type of modularity across a family of weapons. Being able to quickly change out a trigger pack in your rifle, could be a very important consideration in a non-permissive environment, and it’s easy enough to keep that and some spare bolt parts in a very small space.

Well that’s it for “Part 2”. The HK91 rifle system as manufactured by PTR as the PTR91 is a modular and inherently accurate rifle. If you invest some time and money into it, it can be even more accurate than you would have thought, while still maintaining it’s robust and durable attributes.

To give you an idea of how impressed I am with the versatility of the set-up shown in this post, I will be hunting both deer (Bought some Black Hills 175gr TMK’s (polymer tipped Match Kings that are loaded to the same specs as the 175gr SMK’s I used at the range) and squirrel (.22LR Kit) with it this coming Fall. PTR makes quality firearms, and I’ll be doing a post on the PTR 608 carbine (HK94) soon.

JCD,

The Bushbastard