Another Noob question, bolts: No.1 vs. No.4

[finloq]

Here's a beginner's question: are the No.1 and No. 4 bolt bodies and/or cocking pieces compatible?



Scenario:

My No.1 Mk. III is missing the striker screw. I order one from a parts warehouse, it is too small (diameter). I assume that they sent the wrong screw (although for the life of me, I can't figure out where this screw goes). I order another one from another parts warehouse; same thing.

I go down to my local Lowes and pick up a machine screw (#6-32 x 1/4"), which fits perfectly (but kills me to have a non-reg. part).

I then get the brilliant idea () to pull the screw from my No. 4 Mk. I* and try it, perfect fit.

Wait a minute, are they not different bolt bodies and/or cocking pieces?

Apologies, if this is the epitomy of ignorance.

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[jmoore]

It's possible that you have a No.4 cocking piece on the SMLE bolt.

The firing pins usually don't interchange, but w/ a bit of effort, it's possible to get them to go together and function.

Is the cocking piece on your SMLE the flat sided type? Markings on it ought to reveal its origins.

(I've even found that SMLE bolts can be made to work in No.4 bodies, but I don't recommend it.)

[Mk VII]

BA screws (which constitute most No.4 ones) are the closest to Sht L.E. types and will sometimes work provided the length of thread engagement is not too long.

[finloq]

It's possible that you have a No.4 cocking piece on the SMLE bolt.

The firing pins usually don't interchange, but w/ a bit of effort, it's possible to get them to go together and function.

Is the cocking piece on your SMLE the flat sided type? Markings on it ought to reveal its origins.

(I've even found that SMLE bolts can be made to work in No.4 bodies, but I don't recommend it.)

Slab style cocking piece.
Marked on right side:
RFI
162

[Mk VII]

So, it's Indian. It's possible they may have changed the thread. Or 'somebody' has opened it up with a Unified tap "cause everybody uses American screwthreads, right?"

[finloq]

Well, I am glad that I now have 2-$3 screws in my parts kit. Now, I get to buy another.

[jmoore]

Being Indian, as stated above by MkVII, means it ought to be SMLE rather than No.4 compatible.

However, gotta make do w/ what works, I reckon...

[Peter Laidler]

The No4 bolt assembly thread form is 1/4" Unified and BA while the SMLE is is the strange Enfield thread.

I understand that you can use a No1 cocking piece in a No4 bolt but only if you use a No1 striker. And vice verca, a No 4 striker and cocking piece in an SMLE bolt. But I'd prefer the old maxim of KISS - keeping it all simple stupid

[Bruce_in_Oz]

Peter is spot on as usual.

SMLEs are full of "Enfield Special" threads. My favourite is the thread on the fixing screw for the dial sight plate: 26 1/3 TPI! This is also used on the catch on the bayonet. The closest to a "Standard" thread in a SMLE is the stock bolt, which is notionally 7/16 BSW, but the thread form appears to be slightly different. This was about the only thread size carried over to the production No.4 series. That is why all the early "trials" No4s were identified as a separate breed in the system, even when "upgraded" to notional full spec.

SMLE striker thread is 1/4" x 33TPI, Enfield form.

No4 is 1/4" BSF (26TPI, Whitworth form)

The one that causes a lot of grief, especially in Bubba Land, is the breech thread.

SMLE and No4 are both 14TPI but are NOT the same form.

Breech thread on a SMLE barrel has a 49deg, 60min included angle and radiused roots and crests. Different radii, as well).

On a No4, the thread is essentially Whitworth form but with crest flattening allowed. Winding a new No4 barrel into a good SMLE receiver WILL cause damage. Vice versa is not too nice, either. And never mind about the thread indexing / extractor slot alignment / headspace issues.

Apparently, in later years, standards were relaxed on things like swivel screws. I understand there was an instruction in the system allowing these to be changed to 2BA as per No4 spec. A quick run through with the tap and away you went.

[finloq]

Peter is spot on as usual.

SMLEs are full of "Enfield Special" threads. My favourite is the thread on the fixing screw for the dial sight plate: 26 1/3 TPI! This is also used on the catch on the bayonet. The closest to a "Standard" thread in a SMLE is the stock bolt, which is notionally 7/16 BSW, but the thread form appears to be slightly different. This was about the only thread size carried over to the production No.4 series. That is why all the early "trials" No4s were identified as a separate breed in the system, even when "upgraded" to notional full spec.

SMLE striker thread is 1/4" x 33TPI, Enfield form.

No4 is 1/4" BSF (26TPI, Whitworth form)

The one that causes a lot of grief, especially in Bubba Land, is the breech thread.

SMLE and No4 are both 14TPI but are NOT the same form.

Breech thread on a SMLE barrel has a 49deg, 60min included angle and radiused roots and crests. Different radii, as well).

On a No4, the thread is essentially Whitworth form but with crest flattening allowed. Winding a new No4 barrel into a good SMLE receiver WILL cause damage. Vice versa is not too nice, either. And never mind about the thread indexing / extractor slot alignment / headspace issues.

Apparently, in later years, standards were relaxed on things like swivel screws. I understand there was an instruction in the system allowing these to be changed to 2BA as per No4 spec. A quick run through with the tap and away you went.

Oh, I have a headache. I think that I will just replace the cocking piece - striker & spring.