Bolt HeadcFitting Question

[Alan de Enfield]

The bolt head chart that was on here a few years ago think ADe was updating it (Think he was the OP of it).

Yes it was mine.

As you can see you can have a number '0' that is larger than a number '3' so specifying I want a 'number 3' is pointless, it is important to specify the actual measurement you need.

This was part of the original post I made :

Very few of us will have a bucket-full of bolt heads to work with so we need to have an idea of what bolt head size we need to overcome the headspace problem, headspace gauges will tell us it fails but not by how much.
A simple way, that gives a close approximation is by using a case and a primer :
Since the 303 headspaces on the rim, its headspace is the distance from the front of the rim of a seated case to the face of the bolt. To determine that distance we:
• Measure the rim thickness of a new case. A fired case will have expanded and closed the headspace. You must use a new, i.e., unfired case. Measure around the rim and use the highest value obtained. For an example, we'll say it measures .062".
• Take a fired primer and start it into the unfired case's primer pocket. Seat it just enough that it doesn't fall out.
• Hand chamber the new case, and slam home the bolt, seating the fired primer with the bolt.
• Remove the case from the rifle's chamber, and measure the distance the primer protrudes from the case head. For an example, we'll say it protrudes .014".
• Add the rim thickness measurement to the primer protrusion measurement and you have your rifle's headspace, at least you have a close approximation of its headspace.
In our example, 0.062" + 0.014" = 0.076"


Thus if your headspace comes out at 0.076” and your bolt head is currently 0.630” then you’ll need a bolt head a minimum of 0.002” (two thou) longer but ideally somewhere between 0.002” (to give the 0.074” max) and 0.012” (to give the 0.064” min).
Instead of specifying “I want a number 3 bolt head” you can now look for a bolt head between 0.632” and 0.642”