Bolt HeadcFitting Question

[CINDERS]

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

[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”

[Surpmil]

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.

Just to clarify slightly Togor, if that's needed: the reason bolt heads can be found with such widely varying or inconsistent measurements relative to their marked lengths is mostly due to previous grinding and lapping by owners or armourers, rather than poor QC in manufacture.

Generally speaking you can be pretty confident that the 0,1,2,3 size marking does indeed reflect a longer bolthead, but by exactly how much? The original size difference was 0.003" between each number.

Civilian owners including myself, tend to want the bolt to just close over the "0.064" GO gauge, but anything between 0.064" and 0.074" was considered acceptable so there was little need to grind boltheads unless as the manual says, the bolt would not close over the 0.064" GO gauge.

There's really no substitute for the correct gauges.

[Alan de Enfield]

Just to clarify slightly Togor, if that's needed: the reason bolt heads can be found with such widely varying or inconsistent measurements relative to their marked lengths is mostly due to previous grinding and lapping by owners or armourers, rather than poor QC in manufacture.

That would certainly account for 'undersize' bolt heads but not 'oversize' (outside of the expected) bolt heads.



What Size Should The Bolt Heads Be ?

It seems to be generally accepted that No4 / No5 bolt heads should fall in the following range :
Size 0 = 0.620” – 0.625”
Size 1 = 0.625” – 0.630”
Size 2 = 0.630” – 0.635”
Size 3 = 0.635” – 0.640”

Whilst I don’t question that this information is printed somewhere, I have not been able to find the original source, the information I have found does not actually state the ‘starting’ dimension, only that the sizes are incrementally larger :

a) From “Parts Identification List Rifle No4 Mk1 and Mk1*” dated 1945
Bolt head 0 part number BB8584
Bolt head 1 part number BB8585
Bolt head 2 part number BB8586
Bolt head 3 part number BB8587

“Number 0 to 3 increase in length by increments of 0.003 inch”

b) From Canadian National Defence Manual “First Line Maintenance Instructions Rifle No4, all marks” dated 28th June 2002

Bolt head size 0 NSN = 1005-21-103-1143
Bolt head size 1 NSN = 1005-21-103-1144
Bolt head size 2 NSN = 1005-21-103-1145
Bolt head size 3 NSN = 1005-21-103-1146

“…….. the sizes being progressively larger in increments of 0.08mm (0.003”)


What I cannot find in any document is the 'starting size' of the #0 bolt head such that the 0.003" incremental increase per number can be referenced.

[browningautorifle]

The bolt head chart

That was the one I was referring to. I've used it myself in past. The information is very clear.