Screw cutting a rimfire barrel

[Jimiles]

I am going to take my Remington 597 to a local machine shop and ask them to shorten the barrel to about 14"and then re-cut the thread. They've not done this before but they're quite happy to simply replicate the original pattern. Before they do this can anybody explain why there is such a wide & deep groove as arrowed between the thread and the machined face? Why can't the thread simply continue up to the face?  I am concerned that this groove looks to be quite deep but surely removing so much metal here is creating an unnecessarily weak point in the barrel. 

My other concern is the crown of which I've got no understanding at all. Looking at my rifle it appears to be a simple rounding of the muzzle area with a slight chamfer cut inside the bore. Is that all that is required or should I use this opportunity to get a more elaborate crown machined?

 

[walshie]

I don't know why the arrowed bit is there, but I'd think twice about letting someone who hasn't done it before screwcut my rifle. The thread has to be concentric with the bore, not the outside of the barrel and the slightest deviation from that will make your gun unusable with the mod on.  

[Jimiles]

Thanks Walshie, I have explained the importance of the thread being central to the bore and NOT to the outside diameter of the barrel and they do understand this. Apparently they can centre it on the bore so I'm happy in that aspect.

[TIGHTCHOKE]

Why not get the work carried out by a firm that do this work regularly, are you hoping to save a few pounds?

[Bazooka Joe]

Its common when butting up to a solid face to take the last of the thread off and square the face, looks and is a lot neater. If the depth of the groove is a couple of thou under the depth of the bottom of the thread it wont weaken the barrel. Good machine practise, you stop the cut in that area, saves running the tool into the face. 

Others may do it different... 

[Jimiles]

27 minutes ago, TIGHTCHOKE said:

Why not get the work carried out by a firm that do this work regularly, are you hoping to save a few pounds?

Basically yes, I don't want to put a lot of money into what is basically a second hand ratting rifle. A modern machine shop seems a good compromise for me. I'm in Snowdonia and the nearest professional facility offering this type of work are north of Shrewsbury, about two hours away. They also insist on getting the rifle proofed after the work which, for my purposes, I do not think I need.

[TIGHTCHOKE]

That makes good sense.

[Scully]

Makes sense to allow a bit of leeway ( which you have done ) in length of chopping just in case they get it wrong; gives you a second bite of the cherry.

Mine cost about 35 quid to have it done around 10 years ago. 

[Jimiles]

12 minutes ago, Scully said:

Mine cost about 35 quid to have it done around 10 years ago. 

Those were the days...they haven't quoted a price yet but I reckon it will have gone up by at least a hundred!

[walshie]

5 minutes ago, Jimiles said:

Those were the days...they haven't quoted a price yet but I reckon it will have gone up by at least a hundred!

I had a r/f done about 3 years ago by a guy who specialises in guns. Think it was £65. 

[Jimiles]

Where were they Walshie?

[walshie]

Too far for me now which is a shame as he does excellent work. He is near Reading.

[bruno22rf]

It's simply undercut - fairly routine practice.

[Flyboy1950]

2 hours ago, Jimiles said:

 They also insist on getting the rifle proofed after the work which, for my purposes, I do not think I need.

Quite right you don`t need it reproofing as you are the owner. When you come to sell it however, you will have to have it reproofed.

FB

[Scully]

53 minutes ago, Flyboy1950 said:

Quite right you don`t need it reproofing as you are the owner. When you come to sell it however, you will have to have it reproofed.

FB

Or you can enter it as 'gifted or 'given' on the buyers ticket, which means no 'proof' is necessary.

[Big Mat]

The groove that you arrow points to is an undercut, standard practice when threading up to a shoulder. 

 

It is there to allowed the moderator to screw all the way to the shoulder. If it wasn't there, chances are the moderator would stop short of the shoulder as you can't get the threading tool all the way to the shoulder. 

 

Oh and take the rifle to a gunsmith who does threading all the time,  chances are the barrel is tapered and he'll have the right jig to hold it in the lathe,  if the machine shop has to make one, it won't be a cheap job

[Dibble]

My explanation is that the tool used to cut the thread is a similar shape to your Arrow (but a 60degree angle).You can see you can't cut a thread right to the shoulder without the edge of the tool hitting it first.

Your undercut is deeper than you strictly need it only really needs to be a fraction deeper than the thread depth (minor diameter).

I've threaded a Chinese CO2 rifle which was easy but I wouldn't dare doing something more expensive.

Are Rifle barrels choked like Air Rifle Barrels?

[A bolt 22.250]

Would it not have to have the barrel reproofed if you cut it or machine it I thought that any work carried out on the barrel of a firearm ment a trip to the proof house??

[TIGHTCHOKE]

Just now, A bolt 22.250 said:

Would it not have to have the barrel reproofed if you cut it or machine it I thought that any work carried out on the barrel of a firearm ment a trip to the proof house??

Only if you wish to sell it!

[Scully]

24 minutes ago, TIGHTCHOKE said:

Only if you wish to sell it!

This.

[welshwarrior]

1 hour ago, A bolt 22.250 said:

Would it not have to have the barrel reproofed if you cut it or machine it I thought that any work carried out on the barrel of a firearm ment a trip to the proof house??

Only if it materially weakens the barrel this not a high pressure area and there has been legal opion (not law but proof house have not challenged it either) that screwcutting does not materially weaken the barrel. 

[Jimiles]

As the barrel is already screwcut - and proof marked accordingly - all I am doing is re-machining exactly the same feature five inches nearer to the breach. I do appreciate that its a legal requirement if/when I come to sell the rifle but logically I don't see that I am weakening the barrel in any way. I actually wouldn't take the undercut quite as deep as shown in the photograph so if anything the new work should be stronger than the original.

[eddoakley]

12 hours ago, Jimiles said:

As the barrel is already screwcut - and proof marked accordingly - all I am doing is re-machining exactly the same feature five inches nearer to the breach. I do appreciate that its a legal requirement if/when I come to sell the rifle but logically I don't see that I am weakening the barrel in any way. I actually wouldn't take the undercut quite as deep as shown in the photograph so if anything the new work should be stronger than the original.

It's not a legal requirement.

As has been said above reproofing is only required if the barrel is materially weakened (or similar wording)

I wouldn't want to be the test case but I'm pretty sure that nobody has every been to court to have to justify that threading does not weaken the barrel, therefore it is not a requirement.

I've done dozens of threads over the years and apart from machining errors resulting in cutting off and starring again I have never had any problem afterwards. 

As long as the thread is concentric with the barrel there really shouldn't be a problem. Any decent machinist should be able to do this.

 

Edd

[geordieh]

Cost me £40 to have a 243 threaded a few weeks ago at a gunsmiths is it worth risking your gun at a machine shop

[Jimiles]

13 minutes ago, geordieh said:

is it worth risking your gun at a machine shop

It is if I can't find a gunsmith who wants the work. To date I have contacted five gunsmiths within striking distance and I have only had one response - and the price quoted is £145.