Opening up a TIGHT choke?

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Franklink

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Sep 3, 2017
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Anybody have first-hand experience of opening up a really tight choke? (without chopping the barrel)

Bought a Vet Long a while back, really hoping it would like the JSB 25.4gr Monster Redesign. Well, it doesn't. It'll throw 2 or 3 flyers out of 10 shots with them. Bad flyers, can see them dodging and diving (curveball, screwball, etc).

I pulled the barrel and pushed some pellets through. VERY tight choke. Measured pellets after being pushed all the way through the barrel and choke and they're at 0.211inches (in the grooves). Pellets feel quite fine up to the point of the choke- nice consistent and minimal resistance and no loosy goosy spots like I've seen with other traditionally rifled LW barrels. Pellets pushed up to the choke and then back out the breech end are measuring the 0.214-0.215 or so that seems typical.

Accuracy with 18.1gr JSB is phenomenal with the barrel as-is. It suprisingly even shoots them quite fast @ 940-950fps without seeming to have detrimental effects. That puts me in the 35fpe realm. I've been making some crazy long shots on pdogs with it and even some really good long range groups on paper.

The reg pressure won't let me come back off the hammer tension without the ES going up. So, it's a one-trick pony right now. Too much fps for any lighter weight pellets. No good accuracy with the better BC 25.4grainers. Also tried some low weight slugs (17.5 and 20.2) at various speeds. Same problem as the 25.4s, 70-80% good shots, the rest really bad flyers.

I bought this gun specifically to be used as a higher fpe gun. It'll push the JSB 25.4s up to right under 47fpe, but not accurately. I was hoping for around 45fpe and it'll do that just fine, but that's pointless if it won't hit what I'm aiming at.

So, I'm considering scary things like sandpaper on a flapper dowel or coarse steel wool on an old cleaning brush, focused on the last bout 3/4inch of the barrel. And then polishing it back nice and smooth once I've opened it up some.

Horrible idea? Anybody done it without ruining a barrel?
 
Alright, looks like Motorhead answered my question in a different discussion



"YOU ABSOLUTELY DO NOT want to spin any polish, abrasive or lapping compounds ACROSS the rifling !!!!!!!!

Lapping and polishing is done having the process FOLLOWING the helix of rifling's twist and NEVER ACROSS IT !!!!



Drill spinning, lathe spinning is Wrong wrong wrong !!!!"

Answered it in no uncertain terms he did. lol
 
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The trick with opening up a constriction (choke) is to do it without significantly altering the geometry of the rifling. Therefore you do not want to use a compressible material like you might use to polish a barrel. This is a job better suited for a poured lead lap. It's a somewhat advanced procedure. Sean Pero made an excellent how-to here
https://www.youtube.com/watch?v=WM8xaaUaTTY
https://www.youtube.com/watch?v=IXzmlDT-yxE


 
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I would never ever mess with a phenomenal shooting long range shooting barrel and tinker with the gun in any way shape or form period. I leave well enough alone. Perfect is enough for me anyway.

Then again I read many airgunners seem to really want and have a burning desire to intentionally ruin their guns accuracy since they just are too bored with their perfect shooting guns so not surprised here. Most times once shooting phenomenal and perfect it can only get worst with tinkering.

Chopping the barrel would definitely remove the choke. Hope it's still shoots phenomenal after that and would really like to hear what kind of accuracy you get after that.

Be advised after a lot of remorse after the fact, a replacement LW barrel may not necessarily give you the same phenomenal accuracy as you are currently experiencing due to barrel to barrel variances and preferences so if you can't replicate you phenomenal long range accuracy just don't shoot as far if that happens. Cut your shooting distance range drastically shorter then you should be fine.
 
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I would never ever mess with a phenomenal shooting long range shooting barrel and tinker with the gun in any way shape or form period. I leave well enough alone. Perfect is enough for me anyway.

Then again I read many airgunners seem to really want and have a burning desire to intentionally ruin their guns accuracy since they just are too bored with their perfect shooting guns so not surprised here. Most times once shooting phenomenal and perfect it can only get worst with tinkering.

Chopping the barrel would definitely remove the choke. Hope it's still shoots phenomenal after that and would really like to hear what kind of accuracy you get after that.

Be advised after a lot of remorse after the fact, a replacement LW barrel may not necessarily give you the same phenomenal accuracy as you are currently experiencing due to barrel to barrel variances and preferences so if you can't replicate you phenomenal long range accuracy just don't shoot as far if that happens. Cut your shooting distance range drastically shorter then you should be fine.
Click to expand...

Thanks for the insight Yo. 

Go back and read my initial post and you'll see that I'm after higher fpe with accuracy. It won't shoot higher weight projectiles accurately, and that was the intent when I bought the gun. 

So much of your response is irrelevant, like usual. I asked if it could be done WITHOUT chopping, you say chop. I already said it shoots poorly with heavy projectiles but you respond that it is shooting perfectly. Reading comprehension YO!!!!

Lots of us actually spend time shooting airguns instead of excessively posting usually unhelpful information. 
 
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The trick with opening up a constriction (choke) is to do it without significantly altering the geometry of the rifling. Therefore you do not want to use a compressible material like you might use to polish a barrel. This is a job better suited for a poured lead lap. It's a somewhat advanced procedure. Sean Pero made an excellent how-to here
Click to expand...

Thank you sir. I'll give em a watch. Much appreciated.
 
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No witch hunt, just come here to learn and share. Certain individuals have a pretty good track record for being annoying, rude, and ill-informed. Those guys are usually asked to change their behavior or leave. Some do, some just change their name. 

Didn't need to "bash" thumper because his response lacked the impolite language and attitude that yours was full of. 
 
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@Franklink I didn't intend to grind your gears, I was just trying to say that I've done the lead lap and paste routine before, as well as other polishing, and the only way that I got the noticeable results that I wanted was to "start fresh". That's by removing the choke altogether and adding my own, that was much less restrictive. 

Not saying the lead lap thing won't work. I just meant that it will only do a little, but that may be all you need. But it didn't make much difference for me and my stuff. 
 
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Completely understand. You initial comments didn't get me riled up either. HOW we say things makes all the difference. You were civil in both comments. 

I've been told the same by an experienced machinist who has spent lots of time playing with airgun barrels. I was just wondering if anyone out there had gotten the guts to be brave and just go real aggressive on the tight choke with non-conventional methods. 

Your input and sharing of experience is appreciated. 
 
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If you go for the lapping technique, I bought a set of scope lapping compound from Wheeler for reasonable money. Has three grits and I found them to work well. 

Some of the barrel lapping compounds aren't fine enough IMO for a cast lap method. 

Or maybe I'm just lazy and looking for quick results, it's quite the possibility lol 😁

Have fun with it and good luck. 


 
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If I were in your position I would be tempted to try another barrel that is known to shoot your chosen projectile well. A good machinist should be able to set it up without spending too much. Once it is sorted you can probably ask a premium for the barrel you currently have since it has proven results. Trying anything else has no guarantee to work with the projectiles you desire and worse yet may ruin the great barrel you have now.

Just 2 cents. 


 
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If I were in your position I would be tempted to try another barrel that is known to shoot your chosen projectile well. A good machinist should be able to set it up without spending too much. Once it is sorted you can probably ask a premium for the barrel you currently have since it has proven results. Trying anything else has no guarantee to work with the projectiles you desire and worse yet may ruin the great barrel you have now.

Just 2 cents. 

Click to expand...

Your 2 cents is likely how this is going to play out. 

Even though I'm not brave enough to go for it, I'm curious to see what would happen. The math shows that there would still be some rifling left.

theory.1601250400.jpg


Nothing to scale there, just using the bore and groove diameters listed by LW and the sized pellet as an approximation to the size of the choke. By bringing that 0.211 choke down to maybe 0.214 (removal of 0.003) there should still be about 0.003 inches of land in that choke section. That's still deeper than polygonal rifling. And removal could be stopped to still have a very slight choke if done slowly and carefully by pushing pellets through it lots of times during the process, would also need to polish up the roughness before each how much have I removed measurement, otherwise the roughness could be mistaken for tightness (ie leave the "choke" at 0.214 and the rest of the bore at 0.215). 

As has been pointed out, with as good as this barrel is with the 18.1s, I think I've talked myself out of possibly ruining a good barrel. Still curious what effect a gentle transition from 0.006 deep rifling into 0.003deep rifling, with an overall slight choke (from 0.215 to 0.213?) would have on accuracy. 
 
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