Lapping a barrel

[rob4586]

Hi Gents,

Interested to hear your opinion on getting a rifle barrel lapped? I've got a new rifle and I've heard it can improve accuracy, but as always, experience counts for a lot.

What are your experiences of lapping a new rifle barrel? Worth while or stay away? Obviously I'd get a gunsmith to do the work.

 

[Steff]

On hammer forged barrels, which prevail with the majority of production rifles, the surface is what it is. No lapping will change that.
Lapping is done on button cut barrels, but this is part of the manufacturing process anyway. As a consumer you should not have the need to do it again.

 

[ashray]

good afternoon,i take it this is on a sako you had replaced recently by gmk? if so leave it alone and go shooting ,rifles are tool to be used not admired.

 

[Uncas]

good afternoon,i take it this is on a sako you had replaced recently by gmk? if so leave it alone and go shooting ,rifles are tool to be used not admired.

Obviously you don't have a classic with lovely wood

 

[enfieldspares]

A question. Or three. What size group does it currently shoot? What do you use it for? Do you think a smaller group will give any advantage to you in what you currently use it for?

 

[ejg]

Of course one can lapp any barrel with constant twist. Why should one not be able to lapp a hammer forged barrel? I have done it in the past. Shot great. Guy who bought it from me put his custom in the corner.
More important is, what does one want to achieve with the lapping? Just making the hole bigger...?
edi

 

[Steff]

Of course one can lapp any barrel with constant twist. Why should one not be able to lapp a hammer forged barrel? I have done it in the past. Shot great. Guy who bought it from me put his custom in the corner.
More important is, what does one want to achieve with the lapping? Just making the hole bigger...?
edi

Certainly you can work the surface of a hammer forged barrel with the appropriate abrasive. But due to the hardness of such barrels this would not be lapping but rather filing or, as you said yourself, making the hole bigger.
Classical lapping will add a finishing touch to the surface by smoothing out burrs from the cutting process on button cut barrels. And this is only possible because the surface is not as compacted as on a hammered barrel. On a hammered barrel such burrs don‘t even exist.

 

[Smokedude]

Um wow can of worms. But ok I’ll bite
Nathan Foster from terminal ballistic studies. Had a very good series of books on rifle Maintence and setting them up to shoot.
All areas are covered from bedding to rifle barrel lapping. As well as general up keep and Maintence.
Well worth the investment.
I’ve learn a lot and his reloading book had actually saved me money

 

[ejg]

Certainly you can work the surface of a hammer forged barrel with the appropriate abrasive. But due to the hardness of such barrels this would not be lapping but rather filing or, as you said yourself, making the hole bigger.
Classical lapping will add a finishing touch to the surface by smoothing out burrs from the cutting process on button cut barrels. And this is only possible because the surface is not as compacted as on a hammered barrel. On a hammered barrel such burrs don‘t even exist.

You don't know much about lapping do you? In terms of hardness a hammer forged barrel is still very soft. I am used to working materials harder than carbide via lapping.
As I mentioned, it depends what you want to achieve with lapping. Lapping can do more to a barrel than smoothing or removing burrs etc.

edi

 

[rob4586]

Mornings Gents,

Well this appears to be more of a black art, rather than anything scientific. I have wondered whether the process of lapping removes material and hence reduces the barrel life? I which case, I will be steering clear of it!

I would only opt is there was a significant accuracy increase, but it appears that's unlikely.

 

[Steff]

You don't know much about lapping do you? In terms of hardness a hammer forged barrel is still very soft. I am used to working materials harder than carbide via lapping.
As I mentioned, it depends what you want to achieve with lapping. Lapping can do more to a barrel than smoothing or removing burrs etc.

edi

Edi, you are of course absolutely right; I don't know much about lapping.
But then what IS the purpose of lapping a hammer forged barrel?

 

[ejg]

Firstly the hardness of a hammer forged barrel is not much over a normal barrel, one cannot compress steel. Hammer forging of a bore is only a very small amount of metal movement, not huge amount of work hardening. Button pulling also moves/displaces metal. The lapping process is done via two different metals and an abrasive media. The abrasive media beds mainly into the softer of the two metals and then works like a file to remove metal from the harder metal. So in the case of a barrel which is very soft in terms of lapping, much softer lead is mostly used as far as I understand. (Lapping an advanced ceramic or even diamond one often uses copper) Lap media can be anything hard, Aluoxide, SIC, ZrO2, Diamond etc. in varying "grit" sizes.
Lapping any barrel can possibly make a bore more even, you might have a rougher section or a tighter section due to hammer forging not being 100% consistent. One can also lap a bit of a "choke" into the barrel. Many match barrels have slightly tightening bore towards the muzzle that's why some manufacturers like Hawk Hill will prefer to manufacture a near finished length blank. (Cut barrel).
Another nice thing about lapping is that one get's a feeling for the barrel, one will notice tight or loose areas.
edi

 

[dodgyrog]

I have to say that back in the pistol shooting days I was competing at a high level. (Police and service pistol and 1500). I had custom revolvers with special barrels fitted. I always used Gold Medallion on a new barrel to polish it before the first firing. This became Remington Gold Medallion and I have the remains of one bottle still. I don't know if this is still available. I would have thought it would be beneficial for and rifle with a cut barrel. Anyway, that's my 4 pennyworth!

 

[Ronin]

You can usually tell how good a barrel bore is by passing a patch through it on an appropriately sized jag

One can feel tight or rough areas within the bore easily

Lapping is done with a steel rod inserted in the bore which has a slug of molten lead poured into the bore - the slug is removed and then re inserted once abrasive compound has been applied to the bore and exterior of the lapping slug

A time consuming process usually done by a bank of lapping machines working on several barrels at once

Hand polishing - something I do with barrels I’ve used for my own and customers rifles - I always polish the throat area after chambering to make the bullet transition to the bore a smooth and uneventful process (for the bullet)

By polishing the bore in this area aids cleaning and also seems to aid accuracy as the bullet is not swaged with imperfections left over from machining in this area

Works for me anyway

 

[8x57]

Does anybody remember the fad for fire lapping that was for a time in the mid 80s advocated in some U.S. shooting magazines?

Basically the process involved applying a coat of grinding paste to a number of jacketed bullets and shooting them down the barrel of the rifle. I haven't heard about anyone using this method for many years presumably because it never caught on when it was realised that perhaps it wasn't such a good idea and liable to cause all sorts of problems, including ring bulging if it hadn't already have burst the barrel.
I don't know where the idea originated from but I think I recall Ross Seyfried writing about it in Guns & Ammo. The notion of it probably originated from the days of the first .30-03 jacketed bullet competitions at camp Perry where they hadn't got the make up of bullet jackets perfected at that time and it was necessary to coat bullet jackets with a lubricating oil before shooting.

 

[Ronin]

Superior Shooting Systems (David Tubb) sell a similar bullet lapping system

Great for rifle smiths ,,,,,,

 

[ejg]

PRS shooter from Luxembourg I know used the Tubb bullets to get his barrel in a new rifle to improve. After the results of a comp he sold the rifle. I told him not to use them.
edi

 

[Bavarianbrit]

Chatted with border barrels at the IWA show in March and he said that they lap all their barrels.

 

[palmer_mike]

Chatted with border barrels at the IWA show in March and he said that they lap all their barrels.

Really? I’m surprised to hear that

 

[palmer_mike]

Chatted with border barrels at the IWA show in March and he said that they lap all their barrels.

Really? I’m surprised to hear that