View Full Version : need help with heavy hk91 build

January 04, 2009, 10:35
ok i am in the middle of a custom build. long range coyote gun thinking 500 or 600 yards

Has anyone here fit a heavier barrel to their g3?

i was thinking of machining down a remmy 700 hb or browning bbr hb down to fit. max dia about 2 inches from chamber to absorb heat and ease installion by having a step machined in to ease the pressing of the trunion on. then reduced down to about .850 at the step til the front sight post then what ever max dia is past that.

1. the hole in the trunion is .875 correct? i havent checked. so a bbr or remmy barrel with threads over an inch should have enough meat to be turned down to fit?

2. what is the barrel hole dia in the triple frame?

3. is a triple frame aviable with a larger diameter barrel hole

4. i know ptr made a heavier barrel and custom triple frame. any one know where to get these and what there dia was.

5. is a fluted chamber required? i find it hard to believe that a different barrel wouldnt work

6. the barrels range from 22 to 24 inches should i keep the length or cut down to 20

January 04, 2009, 10:42
You need a fluted barrel. It will not eject without it.

Fr. Vince

January 04, 2009, 12:51
Yeah, you have to have the flutes in the chamber. The gases escaping through the flutes push the bolt back to load the next round. Without the flutes you won't have an autoloading action.

January 04, 2009, 16:30
The HK has no primary extraction. Without the flutes, it'll just yank caseheads off if it tries to function at all. The whole HK system just sucks,.........designed by people who have no idea what makes a gun function. It's fundamentally wrong.

USMC 0341
January 05, 2009, 20:05
Actually, gas in the flutes float the front of the case while the rear (in the un-fluted area) slides in the chamber.

In this design primary extraction occurs while the chamber is under full pressure. The case starts extraction from the chamber as soon as the bullet leaves the case mouth - pressure inside and outside the case in the fluted area is equal at that point. The case does not erupt because the bolt does not move much more than a millimeter or two before the bullet leaves the muzzle and the chamber pressure drops.

January 05, 2009, 21:28
if you use a PSG handguard you dont need the triple frame. but you will need a trunion extension for the handguard. if i was home in washington i could take a picture of all the parts laid out to explain it better. i think my PSG barrel is 25.6" or something like that. i havent looked at it in a about 10 months.

i do know for sure my psg bolt head has an extractor and the PSG barrel is cut for it.

where my urbach barrel does not have the extractor cut and i can use any G3 bolt head. but either way both barrels are fluted.

i am sure gunplumber will come along and explain it a whole lot better.

January 08, 2009, 03:45
Had a buddy do a HK91 clone heavy barrel build... he was very happy with the results...

Yes, as stated, you MUST have a fluted chamber. Gun will not extract consitantly without, if at all.

My friend left off a front sight, going with straight optics. He welded a steel pic rail on top for a scope mount.

Good luck with your build,


January 16, 2009, 09:29
that was my plan weld 1913 steel rail to the top. reinforcing t rails to the side, probably keep the irons as back ups.
heavy barrel straight profile and custom make the handguard hanger piece and other bits to run a thicker barrel.