Moderator rear bush

[kingsy18]

Need to machine out a bigger diameter on rear moderator bush,can it be done by yourself or do you need specialist tools,or is it best not to fit at all.

[Dougy]

How much do you need to open it up by ? you could use sand paper on a dowel or similar. 

The only reason for the bushing is to prevent excessive pressure on the thread if knocked and to guide onto the thread, and if your concerned about rub marks on the barrel wrap a layer of insulation tape round the barrel where it rubs. 

[London Best]

15 hours ago, Dougy said:

How much do you need to open it up by ? you could use sand paper on a dowel or similar. 

 

Nooo! 
It needs to be a close fit and perfectly true to the barrel.

[Dougy]

1 hour ago, London Best said:

Nooo! 
It needs to be a close fit and perfectly true to the barrel.

I beg to differ.

They should be perfectly functional without the rear bush, This is all of course dependant on how true the screw cutting is. 

If the bushing is tight to the barrel and not concentric with the bore you risk clipping the mod with bullets by pushing the mod off center, basically saying the cheap piece of plastic kind of overrules the very close tolerance of the smith's work when cutting the thread for the mod. 

The bush is simply there to prevent damage to the internal thread in the mod if knocked and the thread on the barrel. 0.025" clearance 

 

@kingsy18

seek advice from a decent rifle-smith, but dont buy into its a precision lathe job that will cost you silly money. 

[London Best]

2 minutes ago, Dougy said:

. 

The bush is simply there to prevent damage to the internal thread in the mod if knocked and the thread on the barrel. 0.025" clearance 

 

@kingsy18

seek advice from a decent rifle-smith, but dont buy into its a precision lathe job that will cost you silly money. 

The nationally famous rifle smith and bench rest shooter (now deceased) who fitted mine told me the exact opposite. When I suggested that the bush might need .002” clearance he insisted that .0005” was preferable.

Of course it’s a precision lathe job. If not concentric it is no use at all.

[Dougy]

2 minutes ago, London Best said:

The nationally famous rifle smith and bench rest shooter (now deceased) who fitted mine told me the exact opposite. When I suggested that the bush might need .002” clearance he insisted that .0005” was preferable.

Of course it’s a precision lathe job. If not concentric it is no use at all.

Not sure who your referring to but B Harvey, D Wild, S Kershaw, C Ferguson, N Clarke (M Norris 😬) Ronin all say the same, and none agree that it should be a tight fit, and all for the same reason i mentioned. 

 

 

 

[London Best]

2 minutes ago, Dougy said:

Not sure who your referring to but B Harvey, D Wild, S Kershaw, C Ferguson, N Clarke (M Norris 😬) Ronin all say the same, and none agree that it should be a tight fit, and all for the same reason i mentioned. 

 

 

 

Dunno then?? Maybe it doesn’t matter either way?

25 minutes ago, Dougy said:

This is all of course dependant on how true the screw cutting is

If the screw cutting is not perfect the job is no good at all.

[Rim Fire]

My mate done all  mine the bush is only for protection i know a chap who had his done and it was rubbing the barrel it did take the bluing off the barrel but never affected the zero 

Edited November 10, 2023 by Rim Fire

[miki]

On 05/11/2023 at 11:45, London Best said:

Nooo! 
It needs to be a close fit and perfectly true to the barrel.

No it doesn't.
I dosent do anything other than help the careless guide the barrel thread into the moderators bridge and wear the blue off the barrel.

It does stop bits of pine needle, grass and other vegetation getting in between the vertex chamber wall and the barrel for those who carry muzzle down.
I take mine out.
Carry muzzel up and take the moderator off after every outing.
These bushes have no effect whatsoever on the position of the moderator relative to the bore of the barrel.

Edited November 10, 2023 by miki

[miki]

On 05/11/2023 at 13:37, London Best said:

The nationally famous rifle smith and bench rest shooter (now deceased) who fitted mine told me the exact opposite. When I suggested that the bush might need .002” clearance he insisted that .0005” was preferable.

Of course it’s a precision lathe job. If not concentric it is no use at all.

 

He was confused (or you were), what he was talking about was the backcut barrel thread and face onto which the moderators bridge is threaded, relative to the bore.

The nominal tollerance is 2thou, in bench rest that large an offset can cause drift as the bullet, when exiting the moderator, could be (depending how long the baffle stack is) 1thou closer to one side than the other resulting in a disruption to the poa/poi.

Many bench rest shooters don't use moderators for that reason.
 

[London Best]

1 hour ago, miki said:

 

He was confused (or you were), what he was talking about was the backcut barrel thread and face onto which the moderators bridge is threaded, relative to the bore.

The nominal tollerance is 2thou, in bench rest that large an offset can cause drift as the bullet, when exiting the moderator, could be (depending how long the baffle stack is) 1thou closer to one side than the other resulting in a disruption to the poa/poi.

Many bench rest shooters don't use moderators for that reason.
 

I understand what you are saying about the thread and face, but to me 2 thou concentricity is no good for a thread except for nuts and bolts. 
I was an apprentice trained toolmaker and worked as a toolmaker for 51 years, specialising in threads.
 

[miki]

28 minutes ago, London Best said:

I understand what you are saying about the thread and face, but to me 2 thou concentricity is no good for a thread except for nuts and bolts. 
I was an apprentice trained toolmaker and worked as a toolmaker for 51 years, specialising in threads.
 

 

Your right.
The face is the key, the threads merely bring/hold the faces together.
You need a bit of 'slack' in the thread, I think most are around 4H and 4/5G in the case of UTS probably Class 3

[keeper96]

For what it’s worth I’ve got on old ase utra mod that was on my .22-250 and now on my .243 that’s never had a bush in it and both rifles shot 1 hole groups at 100yds

they also had a hard life in and out of land rovers, Argos and quads, up and down rock faces getting knocked about and abused when I was keepering and never had an issue with accuracy or the bullets clipping the mod. 
 

i wouldn’t worry too much about it if I was you