The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

K31 in 7.5x55
A=1.55mm
B=12.69mm
C=21.81mm

Howa1500 in.308
A=3.15mm
B=11.77mm
C=17.27mm

ovenpaa wrote:Either is good John, the important one to me is the depth of the seat for the case head in the bolt face however that is also going to be the hardest to measure accurately. Right now I am not unduly fussed by a couple of thou either way. I have a depth DTI I used for checking my own bolts however I would like to get another half a dozen or so checked as well.

If what I am trying to achieve is proved to work then no doubt I will be pouncing on people at the range over the next few weeks and asking them if I can measure their bolts

Ovenpaa;
I enjoy the rearguard battle of the "Imperialists" when UK have gone ISO and metric since deades....
You buy your petrol by the litre, but accept the robbery of the .473 litre imperial pint for beer at a price much, much over the metric pint (.5 litre) elsewhere..... LOL!!.

Bolt head recess depth usually vary from 2,50mm (Mauser) to 3,5mm ( Grunig-Elmiger), with most around 3mm. (for nstance, Swings to RPA are 2,9mm), and this depends mostly on the extractor form than anything else, although, ideally, the smaller the better for good case surrounding and support in chamber.

Bolt head recess diameter is for match actions normally 0,05mm over rear chanber diameter (.308 is normally at 12,05mm for a 12mm chamber), but this can go upe to 0,2mm oversize on commercial repeaters.

.223 is normally 9,65mm.

As the position of the extraction groove can vary form calibre or base diameter (.223 base is 1,4mm while .308 base is 1,60mm) recess depth or extractor location can vary accordingly.

Hope this help...pr may be cofiuse!!!!.

R.G.C

Thank you Robert

David
Accuracy International AW .308 win

A = 3.08
B = 12.08
C = 16.52 ??? Difficult its a 3 lug bolt But if I add the 2 wall thickness's to B it is 16.48