adding choke to a barrel--success!

[mackeral5]

I've read Motorhead reference adding choke to a barrel by heating then quenching in oil.  I had an old .177 QB78 barrel that exhibited shotgun type performance even after cutting and recrowning.  It was very loose and once you pushed a pellet 3/4 down the barrel you could practically shake it out the rest of the way.  50 yard groups were hard to even call groups at 5-6".

I heated the last inch to cherry red with my map gas torch and quenched it in vegetable oil.  once it cooled down I pushed  a pellet through and to my amazement there was now a nice choke at the end of the barrel! 

After cleaning, reassembling and shooting a few dozen shots my groups went from 5-6" down to 1.5" at 50 yards.  I haven't shot .177 in quite some time so all I had was some older oxidized crosman 10.5 domes.  I placed a quick order for some fresh H&N's which hopefully should be here Saturday so I can see if a better pellet will shrink the groups down a bit more. 

I do realize that 1.5" at 50 yards isn't the best, but compared to the 5-6" starting point it is an awesome improvement.  I basically saved a trash barrel  by trying out the DIY choke method shared by Scott. 

It did discolor the end of the barrel, but this one has a slip-on TKO LDC so you don't see it. 

[FuzzyGrub]

I remember reading that quite some time ago.  I never had the "guts" to try it.  I might give a try to some of those old crosman "bad" barrels relegated to the shelf.

[KnifeMaker]

Anyone trying this, just be careful not to go above low cherry red. Any higher and carbides will migrate to the surface and ruin the bore. Under 1400 deg, safe, above 1450, very bad. 


this is not taking into account what oxygen in the atmosphere does to steel at high heats. There are coatings that cam be applied to help here. Mostly a ceramic. I use Titanium/stainless steel sheet rap. (Professional heat treating foil). Keeps the oxy. away.


Heat as fast as possible. Quench faster! Longer in atmosphere, more the damage. always quench straight in. No angle what so ever. Any angle, and the steel will want to warp toward the top of the angle or surface of the quench bath. (this is exactly how the curve is produced in a sword blade).


Knife

[BackStop]

Anyone trying this, just be careful not to go above low cherry red. Any higher and carbides will migrate to the surface and ruin the bore. Under 1400 deg, safe, above 1450, very bad. 


this is not taking into account what oxygen in the atmosphere does to steel at high heats. There are coatings that cam be applied to help here. Mostly a ceramic. I use Titanium/stainless steel sheet rap. (Professional heat treating foil). Keeps the oxy. away.


Heat as fast as possible. Quench faster! Longer in atmosphere, more the damage. always quench straight in. No angle what so ever. Any angle, and the steel will want to warp toward the top of the angle or surface of the quench bath. (this is exactly how the curve is produced in a sword blade).


Knife

Thanks Mike!   I don't plan on doing this any time soon, but I appreciate your knowledge and advice!

It's a good thing that this knowledge is posted here because I can't remember squat!  (grin)

[lennyk]

What type of torch did you use to heat ?
I have an old loose barrel to try.

I've read Motorhead reference adding choke to a barrel by heating then quenching in oil.  I had an old .177 QB78 barrel that exhibited shotgun type performance even after cutting and recrowning.  It was very loose and once you pushed a pellet 3/4 down the barrel you could practically shake it out the rest of the way.  50 yard groups were hard to even call groups at 5-6".

I heated the last inch to cherry red with my map gas torch and quenched it in vegetable oil.  once it cooled down I pushed  a pellet through and to my amazement there was now a nice choke at the end of the barrel! 

After cleaning, reassembling and shooting a few dozen shots my groups went from 5-6" down to 1.5" at 50 yards.  I haven't shot .177 in quite some time so all I had was some older oxidized crosman 10.5 domes.  I placed a quick order for some fresh H&N's which hopefully should be here Saturday so I can see if a better pellet will shrink the groups down a bit more. 

I do realize that 1.5" at 50 yards isn't the best, but compared to the 5-6" starting point it is an awesome improvement.  I basically saved a trash barrel  by trying out the DIY choke method shared by Scott. 

It did discolor the end of the barrel, but this one has a slip-on TKO LDC so you don't see it.

[BackStop]

What type of torch did you use to heat ?
I have an old loose barrel to try.

I've read Motorhead reference adding choke to a barrel by heating then quenching in oil.  I had an old .177 QB78 barrel that exhibited shotgun type performance even after cutting and recrowning.  It was very loose and once you pushed a pellet 3/4 down the barrel you could practically shake it out the rest of the way.  50 yard groups were hard to even call groups at 5-6".

I heated the last inch to cherry red with my map gas torch and quenched it in vegetable oil.  once it cooled down I pushed  a pellet through and to my amazement there was now a nice choke at the end of the barrel! 

After cleaning, reassembling and shooting a few dozen shots my groups went from 5-6" down to 1.5" at 50 yards.  I haven't shot .177 in quite some time so all I had was some older oxidized crosman 10.5 domes.  I placed a quick order for some fresh H&N's which hopefully should be here Saturday so I can see if a better pellet will shrink the groups down a bit more. 

I do realize that 1.5" at 50 yards isn't the best, but compared to the 5-6" starting point it is an awesome improvement.  I basically saved a trash barrel  by trying out the DIY choke method shared by Scott. 

It did discolor the end of the barrel, but this one has a slip-on TKO LDC so you don't see it.

He meant Mapp Gas torch...  I think...

https://en.wikipedia.org/wiki/MAPP_gas


 

[mackeral5]

In this instance I think I got lucky in getting it right on the first try.  Hopefully next time will go as smoothly thanks to your arming us with additional knowledge around the process.

I was surprised at how fast the mapp gas torch turned the muzzle cherry red.  I've seen it take much longer when heating smaller parts....

Yes MAPP gas torch....dam autocorrect!

[bear air]

Shrinking a 50 yard group 3.5-4.5 inches is huge! Great work.

[FuzzyGrub]

Michael,

Thx for the additional information. I'll have to look for some Professional heat treating foil. 


Question?  Is this a one time event, or would repeated treating's make an even tighter choke?

[lennyk]

ok, those are the torchs aircon guys use.

[FuzzyGrub]

ok, those are the torchs aircon guys use.

You can get it in the disposable cylinders the same size as the propane ones.   Much better for soldering 3/4" copper pipe. 

[Xraycer]

Very cool info to keep in the back of the mind!

Thank you, Mike D and Knife Mike for sharing!

[Springrrrr]

Very cool HOT info to keep in the back of the mind!

Thank you, Mike D and Knife Mike for sharing!

Fixed it   

[Xraycer]

Very cool HOT info to keep in the back of the mind!

Thank you, Mike D and Knife Mike for sharing!

Fixed it   

Haha
Thanks, Bob!

[subscriber]

Anti-scale clay that could be used to prevent scaling in the bore.  This product flakes off on quenching, although some residue may remain:  https://www.brownells.com/aspx/search/productdetail.aspx?sid=49084&pid=23076

Liquid anti-scale compound can be sprayed, flow coated, brushed or dipped onto parts to minimize the formation of oxide scale and drastically reduce pitting, decarb loss, cuts down on rework time, too. Has a hot working range of 1000° to 2300° Fahrenheit, crumbles on cooling, and parts rinse clean in hot water.

Anyone trying this, just be careful not to go above low cherry red. Any higher and carbides will migrate to the surface and ruin the bore. Under 1400 deg, safe, above 1450, very bad. 


this is not taking into account what oxygen in the atmosphere does to steel at high heats. There are coatings that cam be applied to help here. Mostly a ceramic. I use Titanium/stainless steel sheet rap. (Professional heat treating foil). Keeps the oxy. away.


Heat as fast as possible. Quench faster! Longer in atmosphere, more the damage. always quench straight in. No angle what so ever. Any angle, and the steel will want to warp toward the top of the angle or surface of the quench bath. (this is exactly how the curve is produced in a sword blade).


Knife

[happymecanic]

I remember reading that quite some time ago.  I never had the "guts" to try it.  I might give a try to some of those old crosman "bad" barrels relegated to the shelf.

I did that to a cut Crosman Phantom .22 barrel, and it definitely improved the accuracy. Groups @ 10 meters improved from 7/8''-1'' to 3/8''. I think the muzzle end shrank about 0.001''. I didn't quench the barrel, I let cool down slowly. I didn't feel too concerned about carbide precipitation, since airgun barrels are typically made from low-carbon (0.18-0.2 %) steel. There was a little scaling inside the bore, but a lapping job made that go away, and a pellet pushed through by hand feels smooth all the way out. Will def re-do that to any other ''bad'' barrel I may get, especially the ''pellet-picky'' ones.

[SilentMatt]

We tried this and a few other "easy" methods of barrel choking in the shop, and none of them worked. The quenching method felt like it did something pushing a pellet through it, but once any scale was removed, the pin qauges always fit the same.

[randy_68]

Years ago I had a B50 .22 that didn't shoot very good and I used the hyd hose machine at work to squeeze a choke at the end. It worked out good. But it would be easy to overdo though as its hard to judge. Our machine has a micro adjust so I just went slow and kept pushing pellets through to check it as I went.