Airgun barrel choke

[lensman57]

Does anyone know where I could find some information on how much tighter a choke should be from the nominal size of the barrel?
Any help would be appreciated.

Regards,

A.G

[Shed tuner]

... as little as possible - just enough to ensure that it's tighter than any other spot of the bore.

I guess you already know this, but I think it really is the answer. Too tight a choke wastes power, and causes fouling and reduces accuracy.

[lensman57]

... as little as possible - just enough to ensure that it's tighter than any other spot of the bore.

I guess you already know this, but I think it really is the answer. Too tight a choke wastes power, and causes fouling and reduces accuracy.

Thank you sir for your reply. I was thinking of a figure of about 0.02 mm, would you say that this is about right?
I have one of those faulty HW barrels. It groups reasonably well with 4.53 but with anything else it is shotgun. I was thinking of getting rid of the choke that appears to be the fault with these barrels and machine a brass collar and heat it up to put on the end of the barrel, probably about 30 mm long. Once it cools it should choke the barrel evenly. The dimensions will need some research but that was the plan.
I'd be grateful for any advice.

Regards,

A.G

[TonyL]

Our JB started a thread on here a while ago, A.G., detailing his diy choking method.

Maybe he'll post a little linky up.

[thisisdonald]

I think its possible to use a big pipe cutter with the blade replaced with a hardened steel washer. you can buy these for next to nothing and is definitely worth a shot before going to all the trouble of machining and blowtorching and pressing

[lensman57]

I think its possible to use a big pipe cutter with the blade replaced with a hardened steel washer. you can buy these for next to nothing and is definitely worth a shot before going to all the trouble of machining and blowtorching and pressing

Thanks, I am considering all possibilities at the moment so this one sounds good too. So far it appears that freezing the barrel to -25C is preferable to heating the collar as the transfer of heat may alter the charactristics of barrel.

If so the contraction in diameter is about 0.03mm. I have no idea what grade of steel HW have used in the construction of the barrel but apparently the most popular steel for none military use is 4140 ( not hammer forged barrels ) which is known as ordenance steel.

A.G

[Shed tuner]

Thanks, I am considering all possibilities at the moment so this one sounds good too. So far it appears that freezing the barrel to -25C is preferable to heating the collar as the transfer of heat may alter the charactristics of barrel.

If so the contraction in diameter is about 0.03mm. I have no idea what grade of steel HW have used in the construction of the barrel but apparently the most popular steel for none military use is 4140 ( not hammer forged barrels ) which is known as ordenance steel.

A.G

I think doing that, plus have a "gentle hammer" fit bushing, is the way to go. Then machine the OD of the choke bush down to suit.

I'm planning exactly this as per the "bucketboy" method quoted on that thread a few months ago, for my "not-bad-but-not-brilliant" HW barrel, funnily enough...

[bighit]

Thanks, I am considering all possibilities at the moment so this one sounds good too. So far it appears that freezing the barrel to -25C is preferable to heating the collar as the transfer of heat may alter the charactristics of barrel.

If so the contraction in diameter is about 0.03mm. I have no idea what grade of steel HW have used in the construction of the barrel but apparently the most popular steel for none military use is 4140 ( not hammer forged barrels ) which is known as ordenance steel.

A.G

Used to put valve guides in the freezer at work for replacing worn or broken guides in heads off engines.

[buttloaves]

Used to put valve guides in the freezer at work for replacing worn or broken guides in heads off engines.

Could the choke be polished out?

[lensman57]

Used to put valve guides in the freezer at work for replacing worn or broken guides in heads off engines.

That is why I changed my mind about heating the collar and thought of putting the barrel in my brothers freezer. He has a restaurant and one of his freezers go down to -30C. If I machined a brass collar to the nominal diameter of the barrel -0.02 mm it should exert enough force on the barrel to just tighten it.

I can then test the barrel and see how the choke preforms, if not enough then the operation can be repeated with the a new collar machined to -0.04 mm and so on. I have taken the advice of Jon and the less is the way to go here.
The other indication of final size could be taken from the breech end " choke ", so the muzzel end should perhaps be at most 0.01~0.02 mm smaller.
It is all experimenting I guess.

A.G

[lensman57]

Could the choke be polished out?

I haven't thought of that TBH. There maybe a possibility of altering the rifling if the choke is lapped or polished out.

A.G

[lensman57]

I think doing that, plus have a "gentle hammer" fit bushing, is the way to go. Then machine the OD of the choke bush down to suit.

I'm planning exactly this as per the "bucketboy" method quoted on that thread a few months ago, for my "not-bad-but-not-brilliant" HW barrel, funnily enough...

Thanks for the advice Jon. What would we do without the thrills of the HW barrels? Exhilirating when they work and very often they do and frustrating on the odd occasion that something is not right.

A.G

[bighit]

That is why I changed my mind about heating the collar and thought of putting the barrel in my brothers freezer. He has a restaurant and one of his freezers go down to -30C. If I machined a brass collar to the nominal diameter of the barrel -0.02 mm it should exert enough force on the barrel to just tighten it.

I can then test the barrel and see how the choke preforms, if not enough then the operation can be repeated with the a new collar machined to -0.04 mm and so on. I have taken the advice of Jon and the less is the way to go here.
The other indication of final size could be taken from the breech end " choke ", so the muzzel end should perhaps be at most 0.01~0.02 mm smaller.
It is all experimenting I guess.

A.G

I'm not sure if this makes a difference .some guides were bronze or cast iron. It may mean different metals have different contraction when cold.

Take a measurement room temp then when frozen. Use a mike and not a verynear.

I cant remember what the size differences were frozen and room temp. Stopped doing that job 3years ago.

I do remember heating some heads (Vauxhall) and freezing the guide. We used a drift to install them. So a frozen barrel and hot band would work. Maybe constrict it too much though.
http://www.gatewaytoairguns.org/GTA/...?topic=43105.0 ideas there.

[bighit]

Some barrel info

http://www.pyramydair.com/blog/2015/...ifling-part-3/

[bighit]

He goes on to say this

But spring guns don’t need a choke, since the act of firing swells the pellet skirts. However, some spring guns do have the same resistance near the muzzle that is felt in better pneumatics. This is an accident of swaging-in the dovetails for the front sight attachment. Weihrauch guns that have front dovetails all have this and we have called it a choked bore. It’s really just an accident of the manufacturing process and is as random as can be. But it’s there and some shooters feel it helps accuracy. Even though the choke doesn’t wrap all the way around the bore, they feel that it still provides the same stability that an intentionally-choked bore does.


Mmmmmm so what is right?