GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: oldpro on August 14, 2017, 12:17:48 PM
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I want to choke a barrel that doesnt shoot well to see how it will perform is there any way I can do it at home?
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I don't remember the details, but I remember reading a post about using a pipe cutter with the blade removed.
Here it is - https://www.gatewaytoairguns.org/GTA/index.php?topic=117625.msg1139906#msg1139906 (https://www.gatewaytoairguns.org/GTA/index.php?topic=117625.msg1139906#msg1139906)
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Hammer and torch should work.... ;D
If you made a flat wheel to replace the blade on the pipe cutter, it might work. I think it would take a lot more pressure than you could achieve though. Maybe one of the really big pipe cutters with the T handle would work?
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Large pipe-cutter with the blade replaced by a wheel is the method most commonly used.... It takes a lot of pressure, but you have good control over the process, and can check the muzzle diameter with pin gauges, or adjustable gauges, as you proceed.... I have never done it, BTW....
Bob
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Forget it. You will never do it with pipe cutters of any kind except hydraulic. Unless your barrell is made of aluminium.
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Large pipe-cutter with the blade replaced by a wheel is the method most commonly used.... It takes a lot of pressure, but you have good control over the process, and can check the muzzle diameter with pin gauges, or adjustable gauges, as you proceed.... I have never done it, BTW....
Bob
And it takes a lot of time!! You are compressing steel, not cutting thin-wall copper.
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And it takes a lot of time!! You are compressing steel, not cutting thin-wall copper.
Done it sometimes? I once tried with a lathe, chome moly barrell, thin one. I broke the study lever tightening it too much and rolled long time, just nothing else happened.
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I know for a fact it can be done, Sean Pero in Ontario, Canada did it all the time.... It was a heavy-duty pipe cutter, however.... We were using TJ's barrels at the time, which are CrMoly.... I have one which is .30 cal and a 1/2" OD that he choked....
Bob
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I cant imagine a pipe cutter having enough pressure to compress a hardened barrel but I do have one and I will try it and report back Wish me luck!
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It is not hardened, CrMo-barrells are in their soft state although they can be hardened as well. It is through hardening steel. Well I wish you good luck.
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I recall on another forum a fellow airgunner known for his experience and love of the R9 with a user name of nced used a modified higher grade nut cut in half and compressed it in a healthy vice to get his barrel choked to what he wanted. You might be able to find it in a google search to find it but I didn't keep any links.
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I use a semi split die made for the purpose, a heavy 6" vise (mine is a Record from England) and a 18" snipe. Have done 7/16" Crosman and 14mm qb barrels (.177and.22) and .25 Tj's liners without breaking anything. Don't have pin gauges, I push pellets through. When rifling marks on the head are about what I'm looking for, I stop.
Die is 1"od x 1.5" long 1045 bored to fit barrel, then split lengthwise to within 1/8" of being two pieces. Not hardened, but leave it with a good surface finish at final id.
The split end goes in the vise with the split vertical, solid end toward the breech end, muzzle flush with the end of the die.
Squeeze, rotate barrel 30 degrees, repeat until all the way around. Check with a pellet. Repeat till you think you're where you want to be. Start out slow until you get a feel for it.
Then measure the muzzle in several places...it will be out of round. Find the high spot and squeeze it down. Repeat until muzzle is within .001" of round. Push a pellet through to verify and done.
Will need to re-do the crown afterwards.
Al
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I did the wedding band method on my 22 synrod. Worked perfect the first time after messing around with soda straw .177 barrel first.
I did not even have to heat it up.
I turned down the barrel a bit, made a steel sleeve a thousandth smaller or so, broke the edge on one side of the sleeve, highly polished barrel side and ID of sleeve, and wacked that sucker on. I held the barrel by hand and wacked the sleeve on.
Re-chucked the barrel back in the lathe, turned the sleeve down to match barrel diameter, faced off, and re-crowned. Interesting part is if you choked too much, you can turn the sleeve down further (right on the barrel) and the chock will open up slightly.
Worked for me on the 22 synrod and FD-pcp in .177.
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I did the wedding band method on my 22 synrod. Worked perfect the first time after messing around with soda straw .177 barrel first.
I did not even have to heat it up.
I turned down the barrel a bit, made a steel sleeve a thousandth smaller or so, broke the edge on one side of the sleeve, highly polished barrel side and ID of sleeve, and wacked that sucker on. I held the barrel by hand and wacked the sleeve on.
Re-chucked the barrel back in the lathe, turned the sleeve down to match barrel diameter, faced off, and re-crowned. Interesting part is if you choked too much, you can turn the sleeve down further (right on the barrel) and the chock will open up slightly.
Worked for me on the 22 synrod and FD-pcp in .177.
Thanks Tim sounds like more of how I was thinking on the approach but ill give it a try first with the pipe cutter method and get back.
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Just quite successfully did a QB 79 barrel ....
Oxy Acetylene torch taking the last inch of barrel to Red / Straw color and quenching into a quart or so of Hydraulic oil ( Dextron II used )
Did 3 cycles of this .. then a good brush scrub to remove burnt oil residue ... MUCH more accurate !!
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That wedding band method is the only thing I have seen that seems plausible.
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Just quite successfully did a QB 79 barrel ....
Oxy Acetylene torch taking the last inch of barrel to Red / Straw color and quenching into a quart or so of Hydraulic oil ( Dextron II used )
Did 3 cycles of this .. then a good brush scrub to remove burnt oil residue ... MUCH more accurate !!
Scott
Did you allow the barrel to cool slowly and completely between each heating and quinching?
Or did you reheat immediately?
And just exactly what is "straw" colored
Thanks
Ray
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Travis,
Send the barrel over to Jim WAR. He does great work..
Just giving you a bad time buddy.
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Just quite successfully did a QB 79 barrel ....
Oxy Acetylene torch taking the last inch of barrel to Red / Straw color and quenching into a quart or so of Hydraulic oil ( Dextron II used )
Did 3 cycles of this .. then a good brush scrub to remove burnt oil residue ... MUCH more accurate !!
Scott
Did you allow the barrel to cool slowly and completely between each heating and quinching?
Or did you reheat immediately?
And just exactly what is "straw" colored
Thanks
Ray
Cool down ... test shoot and redo within @ 30-40 min between heat & cool cycles.
Fresh cool oil too ... one quench makes a quart of oil too hot to handle !!!
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Sure fire... they all sound like a bit of a gamble till you get the method down.. ;)
I accidentally choked a Crosman 2100 straw barrel with a to tight nylon barrel stabilizer I made and then cracked trying to force it on... was a laser with 7.4 pointed afterwards... Big Bore Bart then used it on a 2100 pcp and reported very good results with the Winchester pellets...
I would imagine choking a hammer forged barrel is going to take more pressure than most button rifled barrels...
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Interesting to me, Scott, since I am an old retired toolmaker.
I am wondering though how this works, not that I question the results but can you at offer an opinion about what happens during this process?
Also, how much smaller it the barrel diameter than what it was originally?
Again, I am curious about this and anything you would like to add would be appreciated.
Regards.
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Travis,
So did you try any of the methods mentioned ? If so, what happen ?
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Have used the "wedding band"menthod, and it did put a choke in the barrel. Turned out to not really help accuracy enough to matter, but it certainly chganged what pellets shot well and which didn't.
If a barrel is going to have a tight spot, best it be at the muzzle. Have "saved" barrels that showed a slight tight spot 3 or 4 inches below the muzzle by cutting them off at the tight spot (if you can deal with a carbine barrel).
However, If a barrel is slickly uniform in diameter, choke doesn't seem to matter (although non-choked barrels can certainly be more picky...there is usually a pellet that shoots great....it just might not be the pellet you WANT to shoot great).
Anyway, if I had to do it today, I'd likely go back to what worked before.
If I knew the exact alloy of the barrels and the band materials and could work them straight and smooth to the 10/1000th, could probley calculate the exact diameters....fat chance of that, so it's more hit-or-miss.
Lathe a "step" on the muzzle for about 1" (can be a bit shorter or longer). This likely expands the barrel a little (which is the reverse ow what you want), but the next step will cure that.
Ream/bore a hollow steel tube, a little bit longer than the stepped section, SMOOTH inside, but just a bit too small to fit on the step down section. Be nice if it was 16mm on the ouside to give a smooth transition to the outside of the barrel.
IDea is to get the tube (the "wedding band" to just barely NOT FIT. With the band a touch too small, need to shrink the barrel and expand the band.
Deep-freezer cool the barrel and heat the "band" (one shrinks a little in the freezer, the expands a lot when heated) and QUICKLY put the band on firmly to the barrel.
YEah...can get it wrong. Not enough choke or too much choke. But rather than cutting the barrel off for another try, can just lahte the band off and try a new one (thicker band for more choke...or a deeper barrel step for more choke).
The other bad news is that if the barrel still has a tight spot somewhere down the barrel (especially close to the breech end), are still not likely to find a drastic improvement.
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Travis,
So did you try any of the methods mentioned ? If so, what happen ?
I tried the tubing cutter method and it just didnt work well enough for me to call it a solution. I only have a propane torch currently so I cant get the barrel hot enough for Scotts method the band Idea works well but hard to control how much choke it will apply and if you stick a pin gauge in and put the band on you cant get the pin gauge out without loosing choke. Im curious how well Scotts method will work and will find out as soon as my torch set gets here.
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Welding a bead around it should tighten it up I would think . I know welding bearing races makes them shrink . It would be hard to know how much to weld though and I don't know if a barrel would react the same way
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have to weld that bead real quick
I've welded pieces of pipe to join many times and very hard to get it straight as it shrinks.
Might be better to use a mig welder and do some spot tacks around the barrel at 180 quickly.
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This thread kind of piqued my interest, so I had a close look at a few of my choked LW blanks.
I first pushed a few pellets thru the bore with a wooden dowel.
The choke starts at about the last 1-1/8" of the barrel.
The resistance (felt) from the swage is very uniform throughout the last 1-1/8".
I believe that the choke is tapered (like a funnel) and has a uniform taper.
The o.d. of the barrel also follows this taper (somewhat) and is about .002" smaller in diameter at the very end.
So the pro's must swage the choke with a taper built into the rollers (jaws?). Whatever they do, it leaves no visible markings on the outside.
I also share Robert's observation, that if the bore is uniform and the pellets fit, you don't need a choke. But not all of the pellets fit when pulling directly from the tin. My choked barrels have less "flyers". Interesting stuff...
Wyo
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I've shrunk metal tubing before using the steps Scott outlined: heat to cherry-red then quench. It took a number of times, but I was modifying a freebie CJ roll cage for use in a baja bug after cutting everything and welding tabs for bolting. I had to heat and swage some tubing, shrink others... (took them down about .0015 inch- just enough for a deadblow hammer to encourage things to fit).
I would think a greater wall thickness will be easier to shrink/choke because of the internal stresses involved. I could be very wrong and haven't played with the math involving thermal expansion rates in steel since 1991. Hardest part would be cleaning all the coked oil out. Also knew some body-shop guys back in San Jose in the old VW club that could shrink kinked metal back using a torch and dry ice. But those guys were reaaaaallly good at welding too. Saw one weld two aluminum cans together with his TIG set-up- I lost $100 on that bet.
I may have to try this on one of my QB barrels just for giggles, though I also have a spare MK-177 barrel I can try it with first.
And FWIW, I believe I've read in a number of spots here that choked barrels tend to be less pellet-picky.
Travis- if yours is just a little torch, try MAPP gas; it burns considerably hotter. I'll be trying it later today provided I can find a steel can large enough.
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The only method I have used successfully is to poke a pellet down the bore and hope there is a deformity/ restriction near where you want the choke to be. Cut the barrel there and re-crown. Oxy acetylene on a barrel-- bit risky for me.
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help an inaccurate barrel thinking a choke will help... hmmm...
well maybe it should not be choked but smoothed and slightly tapered...
https://www.midwayusa.com/product/1006412014/wheeler-engineering-bore-lapping-kit (https://www.midwayusa.com/product/1006412014/wheeler-engineering-bore-lapping-kit)
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The only method I have used successfully is to poke a pellet down the bore and hope there is a deformity/ restriction near where you want the choke to be. Cut the barrel there and re-crown. Oxy acetylene on a barrel-- bit risky for me.
I did this with one of my QB's barrels. Resulted in a somewhat picky barrel but gracious is it accurate with the right pellet. I wanted a barrel that was not 20 1/2 inches long, so I pushed a CP brown box dome from the breech and measured where it got snug, cut it right as it started to loosen, then filed it flat by hand and recrowned. Mind you, my crowning tool usually is a deburring bit and I leave the pellet in the barrel until done.
End result at 15 yards was a barrel that was pretty picky until I used H&N Barracudas- 10 shots, same hole in .177 and a .22 pellet wouldn't drop through the hole. Even my PP700 can't do that. So despite the barrel being picky, those Barracudas are a good all-around plinking, pesting, and paper-punching pellet. If I ever get around to redoing the Ninja's regulator for more power, preference may chance.
Kirby, that lapping kit is pretty slick. I think I'm going to get it for my buddy with a hex-receiver Mosin. He was quote some ugly figures by a local "gunsmith" for lapping the bore of his. I don't know how it would work with a pellet rifle, but the reviews for use with powderburners look promising.
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Peter that kit is way to coarse for the softer barrels but I might try it with a hammer forged barrel which to me would be work hardened... For my Crosman Barrels I use JB Bore Paste, auto, rubbing compound, and some toothpaste... Below was a Dianna barrel that looked to have grooves left from the boring/reaming stage...
https://www.gatewaytoairguns.org/GTA/index.php?topic=77016.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=77016.0)
There is also pouring a lead lapp and hand lapping... So yeah depends on what you have decided what it is your barrel needs as to how and how much you do with what method...
I know I would not try to shrink a hammer forged barrel with heat and quench to many unpredictable stresses...
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I know I would not try to shrink a hammer forged barrel with heat and quench to many unpredictable stresses...
Leaves out BSA/Gamo and Cometa. I'm not sure who else hammer-forges, but IIRC, CZ barrels are hammer forged. And I could be very wrong. Anything work-hardened would respond unpredictably to heating/quenching.
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A 16 ton hand operated hydraulic cable crimp tool is what i use. It comes in a yellow carry case with 11 dies and is available at jet.com. I just take my time and work the last 1-1.5" of the barrel at the muzzle with more squeeze at the end. I just push a new pellet through to check progress. I use nuts cut in half to fit in the jaws provided with the tool. Also, I grind out the threads a little and use a copper sleeve over the barrel to minimize marking.
Hope that helps
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A 16 ton hand operated hydraulic cable crimp tool is what i use.
That sounds like the best method yet! Only 50 bucks on Amazon: https://www.amazon.com/Best-Choice-Products-Hydraulic-Crimping/dp/B00EA6GU9U (https://www.amazon.com/Best-Choice-Products-Hydraulic-Crimping/dp/B00EA6GU9U)