My data shows that in most cases , the 2009 import year and newer bolts, fit the pre 2009 rifles just fine and in MOST cases that I have had on my bench, tend to shrink headspace measurements by up to 5thou when these bolts are fitted to the pre 2009 barrelled receivers.
I've also, since the 2009's started arriving on the bench, found most to be 5 to 6 thou tighter than previous import years.
On average, out of 89 2009 rifles this year, average headspace measured 1.638 and I'd say this applied to 2/3 of the 89 across the bench. The remaining 1/3 varied between 1.634" and 1.636", with 2 measuring 1.632". These were ALL 2009 stamped , standard barrel.
I'd consider these chambers as just fine for a rack grade M14 of any kind and an improvement at the assembly level over in china. For interest sake, the average pre 2009 import, and of these I've handled several 100, possibly more than 500. Avverage headspace for these is/was 1.640/1.641" with the odd one over 1.644" and the odd one under 1.640"
Enough of all that mumbo jumbo.
What it basically translates to is, if I was looking or needing to replace a bolt in a pre 2009 rifle , I'd look for a 2009 or newer bolt. I would not see putting a pre 2009 bolt in a 2009 and newer as I don't think it would be advantagious as far as headspace is concerned.
Runt, I'd also suggest flipping over the receiver and very carefully inspect the under side of the left bolt lug recess as the bottom edge of the bearing surface is not supported by a whole lot of steel and if the bearing surfaces of the lug recess where to be damaged, the left underside is where I'd start my inspections.
I'd love to see the broken bolt first hand. Will also inspect and if the receiver is okay, will install your new bolt. You pay only shipping.
