I’m thinking about converting my SMLE No 1 Mk 3* to 7.62 and I am pretty certain the receiver and barrel, along with the extractor and extractor spring are unique to 7.62. What I’m wondering however is this. Is the bolt common between the .303 rifle and the 7.62?  Same with the bolt head?

Essentially if I put a barreled receiver from a 7.62 in my stock and reused my bolt (replacing the extractor and spring with the correct 7.62 one) would I be good?

Thanks in advance!

You could, but!

you'd have to get a bolt head that would:

Headspace correctly with your bolt body.

Overclock the right amount or less with your bolt body.

Provide the correct firing pin protrusion with your bolt body.

In short it can be done, but its far from plug 'n play.

Did not not get a bolt with the 7.62 barreled action? 

I thought he was using the original bolt body?

He's thinking about converting a .303 to a 7.62, so I assume he had the original .303 bolt?

This forum contains numerous posts on this including findings from metallurgical tests by Peter Laidler showing the composition and hardness of 2A action bodies compared closely to British SMLE production.  

Please correct me if I am wrong but the bolt heads on all 762x51 Enfields in England were required to be a greater proof test than .303 ?

Yes, any "official" conversion such as the L8 and DCRA No. 4 type rifles and the later L39, L42, Envoy, Enforcer (may be a few others) would have been subject to the 7.62 NATO Proof cartridge.  Both my DCRA 7.62 conversions show Long Branch proof stamp markings on the bolt handle, barrel and action body.  

However if proofed for .308 instead of 7.62; it should be 20 tons ( in UK).

Personally, I stick with loading up to the NATO 7.62 spec'; even when using.308 components for reloading.

https://sites.google.com/site/britmilammo/home" rel="nofollow - https://sites.google.com/site/britmilammo/home

Cartridge         Mean Service Pressure       Proof Round Pressure

.303 Mk 7 Ball        19.5 tsi                                25 - 26 tsi

.303 Mk 8z Ball       20.0 - 21.0 tsi                           "

7.62 L2A1 Ball        20.5 - 21.5 tsi                      27 - 29 tsi

7.62 L2A2 Ball        22.3 tsi                                     "

Proof pressure and service cartridge pressure tests were done with the cartridge case well oiled to maximize bolt thrust loads.  

Edited to add Mk 8z ball service pressures.  

Interesting to note here that Mk 8 ammunition produced very similar service pressures as 7.62 NATO.  The Mk 8z round was permitted to be fired in the No. 4 rifles "in an emergency".  It would obviously result in a higher point of impact at the same rear sight elevation setting (probably out past 200 yards) and that may be why it was for "emergency use".  

Also note that these pressures are not directly comparable to SAAMI or CIP standards, the Brits used a completely different method of measuring chamber pressure using an oiled cartridge case that acts on an axial piston in place of the bolt in a specially made breach mechanism.   Don't try to convert these figures to psi as they are not relatable to any other standard method of pressure measurement.  

Lot acceptance testing of service ammunition is an interesting subject.  The "Mean Service Pressure" above relates to the maximum average pressure that is permitted for that specific cartridge.  It is expected that there will be a variation of this pressure in individual rounds across the lot giving rise to the muzzle velocity deviations permitted by the cartridge specification.  The proof round is set higher than this maximum average pressure of service ammunition in part to account for this but also to prove the action has a strength margin above the highest pressure expected to occur with service ammunition.  On top of this, the proof round used for proofing all rifles was oiled, which significantly increases bolt thrust loads over a dry round fired in service.  

I can't speak for the Ishapore No. 1 and 2A/2A1 rifles, but I do know that the No. 4 .303 and 7.62 conversions used the same action, just a different barrel.  The DCRA conversions only changed the barrel.  Enfield and other conversions also replaced the extractor and magazine.  The rifle was then re-proofed to the 7.62 NATO pressures.  So, other than checking for bolt locking lug bearing contact, headspace and striker protrusion, there would be no issues doing this with the No. 4 rifle.  

You might argue that the bolt in a No. 4 7.62 conversion should not be swapped for a bolt removed from a No. 4 .303 rifle, as it's not been proofed to the higher pressures that the 7.62 conversion was.