Based on the picture your headspace is about approximately 1.625-1.626 if you only applied light pressure to close it.
I went back and closed the bolts again after reading this, and yes it's with light pressure. My Clymer gauge doesn't seem to flex. Once it stops with light pressure, that's where it will be even after increasing pressure. I didn't take a punch and try to cam it further shut with the extractor hole or anything to force it.
You can lap that in, but unless you have a low grit compound it might take a while.
You may want to start with a 300 grit and get it to close before you move to a finishing grit of 600 and then 800.
I have some Permatex Grease Mix Valve Grinding Compound which lists silicon carbide on the can. It doesn't have a number rating on it but I would guess it's 200-300 grit. Can I start with that?
Use an unfired case and hammer spring with 4-5 coils cut off for pressure. If you have extra hammer springs you can cut one longer than the other and start with more pressure for a more rapid process.
I have a cut case, polished down, with a hamerspring in it using a nylon flathead countersunk head type screw. The head matches the 308win/762nato head size perfectly.
I don't have any extra hammersprings. I could order some, but, do you see any issues with me just backing out the barrel to decrease the pressure as needed, using the full size spring?
You may also bear in mind that some receivers are tight and the fact that the bolt will not close could be due to other factors not related to headspace. You should always try to pre-lap a bolt before installing the barrel to rule out those other factors. You can also close the bolt on an empty chamber and see if there is any wiggle room front to back and side to side. It could be binding on the sides and even on the front left lug (as viewing from the top of the bolt) as the front left lug could bind on the barrel face or the receiver.
I want my builds to have chrome-lined barrels. So I figured instead of lapping the bolt to receiver first, I would install the barrels I have and see if the HS could be lapped in. That way if it looked like one of my receivers would not HS with any of the chrome lined barrels I have, I could resell the receiver. I guess it doesn't really matter as once lapped I could just sell the bolt with the receiver as a matted pair.
On the Fulton/chicom, once the barrel was indexed the bolt would not close on an empty chamber because of the barrel face. I used Blue Dykem (you can probably see some in the photo) in an attempt to find the offending areas, and carefully and slowly, used a Dremel with a right angle attachment and a couple different grinding/sanding attachments to relieve the offending areas. Now the bolt closes in that one. I may have to relieve just a bit more once the bolt is assembled as I think the extractor will stick forward a bit more than the front ring of the bolt itself.
On the Fulton/chicom combo I have good wiggle left-right and up-down at the rear. I do not have forward-rearward wiggle, which I thought you don't want much of anyway. I would expect that you'd get the little bit of forward-rearward travel you're looking for once the bolt/receiver recesses are lapped in.
On the LRB/Criterion combo I have some (not much though) wiggle left-right at the rear. It has good wiggle up-down at the rear.
This LRB/Criterion also has no forward-rearward wiggle which I think will change once lapped.
To check whether the left lug is binding at all on the receiver or barrel face I've been using a really thin sheet of receipt paper that I cut down to a wide strip, sort of like what a shredder kicks out, so I can stick it where I want, close the bolt and see if it binds the paper. On the Fulton/Chicom it just slides out without much feel. On the LRB/Criterion it will bind the paper in the full closed position, but if I open the bolt at all, I mean any percievable amount, the paper slides out easily. So, I think the LRB will be fine once I start lapping and both future rifles are ok as far as bolt fit at this stage. Do correct me as necessary.
What I would do at this point is put an unfired round in the chamber and see how far the bolt will close. If you have a precision mic gauge you can better estimate your actual headspace. Most commercial rounds have a length from the face to the datum of 1.627-1.628.
Here's a photo of the Fulton/chicom with a Winchester round in it.
And the LRB/Criterion with the same Winchester round:
I bought the RCBS Precision Mic for 308win a few weeks back. Measuring a couple of loaded rounds and using the "0" on the RCBS gauge as the reference point I get -0.0015" from Winchester SP and a DAG mil-surp. I get -0.0035" from another Hornady hunting load.
Now, my Clymer 1.630" gauge reads -0.0015" also. I can get different readings +/- a thousandths or so with the Precision Mic depending on amount pressure, direction of gauge when using, etc. But these readings are all done the same way, gauge upright, spinning the head with light pressure until it stops, each round done multiple times to get a consitant repeatable measurement.
When I put my 1.632" (Manson 762NATO GO) gauge in the Precision Mic it reads about "0", and so on as I try different length gauges, so I think the index marks on the RCBS gauge itself is just a bit off and the HS gauges I have are fine as the increase in gauge lengths seem to be what they should be.
If you don't have this tool, you can lap the rib cage of the bolt; the area right behind the lugs and the left front lug to make sure it's not binding in the receiver. After this you can get a better feel for actual headspace if the bolt was binding. If it's not binding, your picture indicates the headspace is still very short and will need lapping to bring it in to a safe tolerance. The picture indicates you have quite a bit of lapping in front of you and if I had one that tight, I probably would try lapping but if it doesn't move much after your first round (10 minutes) I might look at other options.
I presume that you lap the "rib cage" and "left front lug" areas with the bolt in the receiver just like you do with the rear of the lugs? Not that I think these need it, but I'm trying to learn everything I can, saving what mistakes I can by picking others' brains.
So, basically it's "happy lapping", eh? As long as it will be safe to do so I don't mind taking the time to lap enough to make it work.
Talking with a buddy, we thought of other things that might help reach headspace, too.
I could polish the bolt face itself. Jerry's book says you can do this once, removing as much as 0.002" in material. I would just polish smooth to take the high spots of the parkerizing off. I have Dremel felt polishing wheels that are the perfect size to do this. Also thought polishing the chamber might help also. It shouldn't hurt reliability of the rifle, that's for certain. These two items may give me 1-2 thousandths right there.
Another thing I was wondering about. Does anyone ever shim the barrel? The LRB took much less torque to index than the Fulton. Could you put a thousandths or two shim on the barrel shoulder to increase draw and HS length? Seems like the threads are heavy enough that you could add a thousandths or two.
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SS
