I gots to wade in here as there sure is a lot of bogus remarks regarding accuracy and this headspace discussion need some commenting on
there's not much wrong with most Chinese barrels, sure guys get rifles that won't group to their satisfaction but there are a lot of factors at play and in the crap loads of these rifles I've tuned or full blown customized...... the barrels were seldom the main culprit in a bad shooting rifle. for those new around here , and with no intent of braggery, I've worked on and fired a few hundred of these rifles, with no exaggeration.
now as for headspace...... here's the deal, directly from my personal notes I've been keeping since about the beginning of 2007 when I hosted my first m14 clinic.
early norinco and polytech rifles tended to have measured headspace on average 1.640" to 1.646" ...... the long side of the 7.62 nato range. this trended until 2007 when the rifles we were measuring were pretty damn consistant around 1.640" or for the layman, the middle range of 7.62 nato
these rifles, the ones 1.640" and over, really let the brass stretch when using Federal commercial power shok .308 , an ammunition I've been using religiously in these rifles due to it's performance and reliability I've come to expect due to my own use for well over a decade in these rifles particularly.
so, in 2009 we started to see improvements in headspace values, both on my rifle smithing bench (m14doc) and at the many clinics I was doing back then. In my logbook , 1.636" to 1.638" are headspace values that started to become pretty standard right up to recent imports I've measured.
These values are hardly of any concern to the shooter and in my own findings, having safely fired a few thousand rounds of federal powershok .308 commercial ammo thru Chinese m305/m14s rifles , regularly since the late 90's , I'll wade in and state as I've stated before, that these rifles, with a chamber measuring 1.640" and under , are generally safe to shoot factory .308 and properly tailored reloads.
if the rifle measures over 1.640...... well, me personally, I'd only fire nato brassed 7.62x51 or reloads using same brass.
the only way to truly measure headspace correctly is to strip the bolt and use the correct gauges. Brownells sells Clymer headspace gauges in singles or as a set. I believe you can also place an order directly with Clymer. These are the only gauges I personally use. although I do have the US Military 7.62 Nato set as well....... good luck finding those
I'll add that 100's of CGN members alone have purchased these rifles over the last bunch of years, and for the most part, our dicks are still attached...... sh*t mine might have even grown a little bit bigger HAHAHA