Bolt HeadcFitting Question

[togor]

I am assembling a new bolt head of matching #0 as insurance against leaking Winchester 41 primers. The one obtained looks new of finish, and doesn't look like it will line up with the rib without some help.

I understand there was a tool for helping bolt heads fit. Have no such tool and suspect they are not common.

Asking if anyone has a preferred technique they can share for helping a new bolt head to rotate fully onto a bolt body.

[Alan de Enfield]

I am assembling a new bolt head of matching #0 as insurance against leaking Winchester 41 primers. The one obtained looks new of finish, and doesn't look like it will line up with the rib without some help.

I understand there was a tool for helping bolt heads fit. Have no such tool and suspect they are not common.

Asking if anyone has a preferred technique they can share for helping a new bolt head to rotate fully onto a bolt body.

Firstly you do realise that not all number '0' bolt heads are the same 'size', '0' is not a size it is just a number. I have seen a number zero bolt head of 0.616" and as big as 0.636" so 20 thou difference between them, the nominal 'cluster' of size zero (it is a bell-curve) is between 0.626 and 0.631, still 5 thou, which could make a big difference if your headspace is towards the top end of the spec.

How did you determine that you wantd a number 0 bolt head ?

Regarding getting it to 'clock' correctly the tool was used if it was just a few thou off being correct, some bolts / bolt heads would just not align as the start point of the threads can be 'anywhere'.

If you read Peter Laidlers notes on bolt head selection you will see that the Armourers would have trays with dozens of bolt heads and they would have to go thru them to find one that gave the correct headspace, and, the correct clocking. The chance of you buying one bolt head and it meeting all the criteria is fairly remote.

[Brian Dick]

Fitting bolt heads requires all of these things to be in spec. Guessing it's what AdE means by clocking since all of these things come into play when fitting together bolt assemblies. If your original bolt head is in spec, why change it? I wouldn't agree that "leaking primers" is a valid reason. I don't think that WRA ammo has leaking primers. I shot quite a bit of it 40 years ago, reloaded some of the brass too and never had a problem with it in rifles.

1. Bolt head overturn
2. Striker protrusion
3.Cocking piece lift
4. Bolt lift
5. Headspace

[browningautorifle]

I have seen a number zero bolt head of 0.616" and as big as 0.636" so 20 thou difference between them, the nominal 'cluster' of size zero (it is a bell-curve) is between 0.626 and 0.631

Too, you can have an overlap of size where a "0" is smaller or larger than a "1" and a "1" smaller or larger than a "2" and so on. The numbers overlap. I think there's a size list on forum here somewhere...

Too, I think a leaking primer could be construed as a pierced primer. Which is a firing pin length issue...

[Brian Dick]

Most of the bolt heads we're dealing with now have been previously fitted. The charts are nice as long as you have nos, never fitted boltheads. Once they've been fitted once, the sky becomes the limit and the only way you can start is by checking for overturn and measuring them.

[togor]

Well I intend to check the dimension between the bolt face and locking lugs to make sure. I am not stupid about such things.

Hoping the threads on these heads are at least loosely timed and not completely untimed. Garand gas cylinder locks have untimed threads but this doesn't affect headspace.

I started into milsurps years ago on M1903s. Lord knows that rifle had a long list of problems, but by the 1940's it was a perfectly good bolt action rifle. They had worked things out.

This business of the bolt head...to me it just confirms the No. 4 rifle as yet another example of needlessly peculiar British engineering. Letting the quirks become the defining attributes when they should be eliminated.

Primers sometimes leak at the edge and leave an arc of etching in the bolt face. Some brass (commercial Winchester) is known for this.

Examine enough Russian milsurps and you will see plenty of these circular scars in the bolt face.

[Brian Dick]

The dimensions you need to check are the actual length of the bolt head from the rear shoulder to the face, not the threads or distance to the locking lugs. Try and get a bolt head that has zero overturn. If they overturn more than 1/8", they are out of spec. Remember that .064 Go and .074 No-Go are the only measurements that matter.

I think you'll find the ring of erosion on just about any rifle bolt or bolt head that's seen lots of corrosive primed ammo.

[togor]

I agree that is a perfectly sensible measurement.

However,

A small amount of overturn is considered "part of it", and so the bolt locking lugs are the best reference in my situation. FWIW I measure 4.200" between lug rear and bolt face on two original bolts with original bolt heads, with the head aligned to the rib.

Looks to be roughly 5 degrees of rotation for a 0.001" change.

My new head is still under rotated, but also slightly long. Metal removal appears an option.

When I mentioned to a mechanical engineer buddy this bolt head business, how the recoil is taken on the threads (unless the head bottoms out perfectly, which I think would be rare), he found this to be a bad idea.

[Alan de Enfield]

Too, you can have an overlap of size where a "0" is smaller or larger than a "1" and a "1" smaller or larger than a "2" and so on. The numbers overlap. I think there's a size list on forum here somewhere...

Too, I think a leaking primer could be construed as a pierced primer. Which is a firing pin length issue...

I produced this list many years ago - it has been updated with more results but cannot find it at the moment.





Didn't work - formatting gone all to cock !

[Claven2]

If a bolt is clocked in spec, the threads do not bear cartridge thrust in practise. Bolts are made of hardened steel, while bolt heads are made of either wrought iron or mild steel that is hardened on the bolt face and the rail lip. The threads aren’t hardened.

So if it’s clocked in spec, the bolt head will bear on the bolt face after the first few rounds are fired, as the threads will plastically deform enough to fit itself more fully to its bolt.