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Fire lapping a barrel?

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bigHUN

bigHUN

Member
Jan 16, 2020
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Canada/L4G7X4
I have one .22x500 poly barrel giving me really a hard time.
Tried with 5-6 different pellets in range between 16 and 25 gr 5.50 and 5.52.
I re-crown it several times - until figure how to eliminate the thin wire edge.
I polished the lead-in.
I am regularely cleaning and polishing it.
So far nothing really worked well as I was expecting, I just cannot get tighter then 1" groups @50.
Latest idea to try to fire lap it.
Reading through several online blogs and how-to's, but all of them are firearms, I have not seen any story doing it with airgun barrels.
What lapping or polishing compounds you guys using? And normally how many shots? I understand what lapping means in tooling manufacturing, that is still more as a material removal and not just a simple polishing.
 
Can't answer your main question, but...
As you probably know from your tooling experience...ANY...polishing or lapping IS...removing material, despite what the experts will tell you ! It may be in micro-inches, but it's STILL material removal.
Just a fact of physics !

On another side - has anyone "electro-polished" the I.D. of a barrel ?

Good luck with your problem.

Mike
 
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Is this on your Leshiy?

There's a few possibilities for your irregularities.

1) Irregular pressures in the barrel -- perhaps due either to sealing issues at the magazine, regulator issues or something in the semi-automatic mechanism.

2) End of your barrel isn't perpendicular to the pellet trajectory, perhaps causing some instability in the pellet.

It sounds like this is trying to address (2), but what about (1)?
 
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You could try putting some JB bore paste on some pellets and firing them, then cleaning the bbl. You would have to fire a few dozen fouling shots then shoot groups to check for improvement. I have read of others polishing a bore using a patched jag with JB paste on a cleaning rod. Are you sure it’s the bbl? Check for issues like loose scope mount screws, loose stock screws, bad o rings, bad scope etc.
 
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If the bore has subtle tight and loose spots along its length that you can feel when pushing a pellet through, or that you noticed when you were previously polishing it, fire lapping is worth a try. Another scenario where it can be helpful is for a choke that is a bit too aggressive and prone to leading.

Like a poured lead lap, it preferentially removes material from the high spots. When I say "removes material", that's somewhat misleading because it would take a long time to remove a meaningful amount. We're talking on a microscopic scale. Something in the ballpark of 300 grit (e.g. Loctite Clover grade A or 1A) is a good compound for this purpose. J-B is too fine unless you want to be fire lapping for hours on end.

Standard wasp-waisted diabolo pellets have too little bearing surface so use slugs or something with many driving bands (heavy Eun Jin / Seneca pellets) or something like the H&N Rabbit Magnum II pellets. Every barrel is different so you might want to start with 10 shots and then stop and clean and push through a couple of pellets to see how it's responding, and then use that feedback to decide how to proceed.
 
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I got into this rabbit hole when I decided going with longer - custom (Russian made) 500mm barrel, poly rifling, no choke, and I sold in meantime the short original 350mm AP with a good offset. My expectation was the longer barrel shall be more efficient and user friendly, 500 vs 350.
Just because I had initially the L2 in .22 I spent $CAD for tonns of pellets, and that escalated to next - $CAD buying .22 pellets in extra various weights.
I can just scrap the .22 idea completely but a big pile of pellets...and I have no other .22 gun only the L2. And I am way too stubborn to give up.

The other thing I am tinkering for years, and looks like I will get into this very soon - to get myself a mini lathe. I got really tired chasing friends and machine shops to "help me out this and that". But a problem is everything sold in America is mainly in inches, but as we know on airguns all the threads are mm, so I am researching some lill machines that can cut or fix a M14x1.25 for example.

What I noticed also that my custom barrel doesn't have that 4 degree taper, also last night I just did some measurements, and looks like the breach end lead-in is not centred, but offset for 0.09/2 mm. So I may have a combination of "errors" that I could fix with a small lathe, on my own in weird time at midnight if comes to that level :) .

Barrel Lead-in offset.JPG


barrel breach end machining.JPG
 
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for one thing if your recrowning and getting a wire ring, it isnt being crowned right .. its being aced by a home method without proper tooling most likely and swishing a barrel out looking for the magic fix probably wont do the trick unless you get lucky .. more likely it will be damaged beyond what a now needed proper crown is gonna fix ..
 
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MikeVV said:
On another side - has anyone "electro-polished" the I.D. of a barrel ?
Click to expand...
I spent the past four years working with electro-polishing (EP). EP occurs and is the result of something called “anodic leveling”. The leveling is the removal of metal to create a smoother surface. So just like lapping, metal is being removed.
I have four FX barrels sitting waiting for me to fire them someday. Hopefully they will behave.
 
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No taper needed for pellets...just use a reamer at 0.1mm over the nominal caliber. I remember Scott (motorhead) describing having successfully used a normal drill bit with the corners blunted ever so slightly with a stone (ensures the bit will follow the bore rather than cut slightly off-axis). So the 5.61mm drill you described will work fine for .22 cal. I've only used reamers myself but I have every confidence in Scott's advice.

Go to a depth that allows the pellet head to seat into the rifling when the bolt is closed. In most cases it's as simple as going just past the barrel port.

Then wet sand or use a Cratex abrasive bit to smooth any rough marks and break any potential burrs or sharpness at the ends of the lands so the pellet can ease into the rifling without being gouged.
 
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nervoustrig
I believe my .22 barrel lead-in pocket is off (as I measured 0.09/2 off center) this may come from off center rifling or off center barrel bore in the action clamp. I will measure this on the CNC before doing anything further. If anything smaller then the offset mentioned above, I will just do a slight 4-5 deg angle into lead-in edge, but if the offset is still bigger (I did not index the barrel to measure that scenario) I may need to enlarge the lead in for 5.61+ 0.09/2 centered to rifling.
Edit: I have a decent specialty tools in my toolbox, including a nice selection of rubberized abrasive bits, also a brass adjustable lapping tool
 
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I had a RTI .25 cal barrel that had zero chamfer at the breech end, just flat cut. I could see evidence of where the previous owner was struggling, trying to chamber a pellet from the magazine. My fix was the same as the brass screw crown touch up, just more aggressively at first. This worked very well for my situation. I also got some 8-32 brass ball nuts, and they work great for this …uninterrupted sphere no bumps or divots. It’s a nice polished chamfer now.
 
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So, yesterday I did the fire-lapping with eunjin heavy hitting (3 groove 28.5 gr)
- 6 shots with red diamond lapping paste,
- 6 shots with green lapping paste,
then I changed to 25gr MRD's
- 10-12 shots with green lapping paste,
- a mag of 8 shots with yellow lapping paste.
Cleaned a rifling at least 50 or so times with J-B bore cleaner (blue), the clots were still coming out black. This telling me also that the J-B is abrasive.
Polished with J-B bore bright (red) a next maybe 15 patches.
Testing today afternoon at my range, shooting rings at 50 meters.
And the POI was higher about 4-5" and to the right 2" with the same H&N Baracuda 16gr from last weekend.
I wanted to test the next the MRD's, but about 7pm the mosquitoes got really aggressive and chase me away.
 
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