View Full Version : Setting headspace on roller locking HK style rifles
12-18-2008, 12:06 AM
With regards to setting headspace on roller locking HK style rifles, the bolt gap is supposed to be .004" to .020" but there is no reference to any use of headspace gauges in the setting of the headspace. Because of the differences in manufacturing, I would assume that the above mentioned tolerances should be used with a gauge of some kind when installing a new barrel. I used a go gauge to test tolerance when I pressed the barrel into the trunion and tested lock-up afterword with dummy rounds too.
I think I have it done correctly, or at least in the realm of safe, but I would like to double-check before I pin the barrel into the trunion. Any input on topic would be much appreciated.
12-18-2008, 05:39 AM
If I remember correctly, you use feeler gauges and measure the bolt gap when locked into the trunnion with no recoil assembly. Measure between the bolt head and carrier through the mag well. You adjust head space by changing rollers out, +2 or +4, etc. You also need to check the wedge shaped firing pin locking thing that spreads the rollers for wear it may need replaced if it is a very worn kit.
12-18-2008, 09:07 AM
That is what I am seeing everywhere, but this would only seem to be true if all barrels were chambered to the exact same depth, as without gauges, you are measuring headspace (via bolt gap) off of the breech of the barrel, and not bolt face to chamber shoulder.
12-18-2008, 02:48 PM
There is no such critter as "headspace" in a G3/Cetme roller locked rifle.
You measure "bolt gap". 4 different roller sizes are available and when these rifles come from the factory, they are all set up with the smallest size rollers (so as wear progresses, newer bigger rollers can be used to maintain an acceptable bolt gap).
After you run out of rollers that will bring your bolt gap into acceptability, you'll need to have the barrel removed and reinstalled so the smallest rollers bring the bolt gap into maximum safe tolerances.
If you're talking about a Century hack job, all bets are off, as they grind the bolts to give a false sense of "safety" when checking the bolt gap.
12-18-2008, 05:18 PM
Nalioth is correct, what bolt gap is measuring is the wear in the roller mechanism, not true headspace. No headspace guages are used, you want the bolt right up against the rear of the bbl. The wider the gap, within specs, the better as the gap closes up with wear.
The problem is the factory HK manual calls the bolt gap check a headspace check, which is incorrect. Probably just a translation problem with a translater not too familiar with technical terms.
True headspace on an HK is set by the chamber depth at manufacture, with the "floating" case due to the fluted chamber headspace is not too critical anyway. As long as the bolt closes fully and the rollers are engaged with a round in the chamber you are good to go in regards to true headspace.
12-18-2008, 05:36 PM
I was going to start another thread on HK headspacing but I'll post here since it is already going.
How can I headspace (gauge) the bolt gap with the barrel and trunion out of the gun? So I have a barrel that I want to install in the trunion headpsace it then mount it in the receiver.
How can this be accomplished.
12-18-2008, 05:44 PM
Lock your bolt and carrier assembly into the trunnion, and pull it fully rearward. Measure how deep it is in the trunnion, then press your bbl in from the rear to that depth, minus about .2" or so. Lock your bolt and carrier assembly into the trunnion, bolt gap should be way too wide. Press the bbl further in a small amount at a time until your check reveals proper bolt gap. Drill for cross pin and install.
12-19-2008, 04:06 AM
Remember that when setting gap, it will shrink .004-.005 after the first 100 rounds you put through it. I set my gap at .019 and it shrank to .014, this is common and exactly why you don't want to buy a new gun with less then .008 gap.