HK/ PTR-91 head space, when new. Just picked up yesterday.

[Ignition Override]

Being brand-new with these, I picked up the nib PTR-91 yesterday (just bought on GB).
The seller stated that he bought the gun from the PTR factory last month, for what it's worth. (fwiw).

The young shop "gunsmith" had never used Feeler Gauges or dealt with such HK rifles, and I had only observed a few people use them on Youtube.

No luck using " HKPro" boards: my membership is too new or has too few attempted posts.

Being a little subjective, it's hard to know the ideal pressure to use between the bolt and carrier.
The safe range is .010" - .020 ". The bolt gap is reported to change slowly over time.

My gauges are brand new, and .018 can be inserted with 'slight pressure', but the .019 is difficult....and the .017 seems to be -missing; .016 goes in pretty easily.

Assuming that my use of the .018 is correct, and OK for a while (?), would the bolt's present bolt gap allow -- over much more time --
A) smaller numbers/thinner gauges
B) a thicker gauge to insert-closer to the max. limit? If an extra set of rollers should be ordered...don't know which size.

Maybe this bolt gap reading is normal in a brand-new PTR-91------------------

 

[Holescreek]

The spec for the bolt gap is .004" to .020". If you're sitting at .018" make a note of it then check it again after 200 rounds. Barrel movement of around .002" is considered acceptable on a brand new rifle.

A caveat to this is that you (we) are assuming that the rifle arrived with "zero" sized rollers in the bolt head. Zero sized rollers will each measure 8.0 mm. +1 rollers will measure 8.01 mm and increases .01mm with each increment. There are also "minus" sized rollers, -1, -2, etc. All are used to keep the bolt gap in the .004"~.020" range.

The reason why the range is so important is the amount of contact that the bolt locking lever (attached to the left side of the carrier body) has on the ramp on the rear of the bolt head. The locking lever and it's spring are what actually "locks" the rollers out while inside the trunnion and in when the action is open.

 

[Ignition Override]

Holescreek: Will keep every used ammo box in a baggy, and do so after 200 rds.

Already doing this in marked large baggies just to show people how reliable my Czechpoint and ZPAP are.

 

[Slamfire]

When I purchased a new PTR91 I was worried about all the numbers for the bolt head gap, etc. Mine was within what I read on the web. Worries all went away when I shot the thing. It went bang each and every time and the round was knocked a country mile.

If your gauges read 0.018 to 0.019 don't worry about it. After all, when was the last time you took your gauges to a calibration lab to determine if they are still within limits? Manufacturer's often have their own calibration labs, or hire itinerate calibration contractors to regularly come in and check their gauges. I think @Holescreek has it right, go out and shoot the thing.

By the way, these roller bolts are "grease guns". Use grease to lubricate the locking piece and the rollers. I have a Swiss service rifle cleaning kit and they used a black grease, which I suspect was grease with molybdenum disulfide Molybdenum disulfide is a dry lubricant, no reason why it would not be added to grease.

I wiped the grease off for pictures, but you can still see it inside the bolt head.





I think LSA would work wonderfully too, I love these semi fluid greases.

 

[Holescreek]

These blowback guns are very dirty and it's a whole lot easier for me to flush (dirty) light oil out of the bolt head after a range day. I have been known to smear lubriplate on the side grooves of the carrier though. Everybody has their favorite lubes though, I don't think there is any one good way to run them as long as they aren't dry.

 

[Ignition Override]

So much residue on Friday after the 40 rds. in this new PTR!
And this was US-made ammo.

Dirtier than a hardcore Biker Chick on a desert road.

Makes the same consumption with Wolf/Tula in my AKMs and VZ-58 seem almost as clean as .22LR.

 

[Holescreek]

There is a fellow in Las Vegas with a FA Cetme who hasn't cleaned the rifle in over 5k rounds. It was interesting to look into the chamber ta say the least.