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All Springer/NP/PCP Air Gun Discussion General > Share Your Simple Home Projects (TRICKS-N-TIPS)

Barrel troubleshooting and accurizing how-to

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nervoustrigger:
The Pro-shot rods are really good.  I have a .22 cal that has served me very well.  In .177, you can currently get a used 22 inch length on Amazon for $22 (free Prime shipping).


I got one myself and it was indistinguishable from new other than the clear tube it ships in had some insignificant damage.

For a long time I used one of the cheapie 3-piece brass cleaning rods.  Originally got it from Walmart for about $10, and I just threadlocked a couple of ball bearings to it and drilled out a dowel to make a handle.  Ends up only slightly lower cost than the Pro-shot rod above but since I already had it, the $3 for some bearings made it a cheap upgrade.

nervoustrigger:
Hey guys, in the original post I gave a brief overview of polishing the bore and then made reference to a couple of posts on the topic, but I thought it might be helpful to put up a step-by-step guide.  This is pretty much my application of the advice of Scott and Sean from those threads with a sprinkling of experience and bits of knowledge taken from related discussions in the intervening years. 

What it does
The goal of polishing the bore is to smooth down the microscopic surface fretting that remains from the manufacturing processes of reaming and rifling.  You can think of it as millions of tiny burrs that cover the landscape of the bore.  As pellets/slugs slide through, soft lead abrades from their surface and sticks and builds up over time which causes accuracy to degrade.

If the bore is especially rough, a polishing regimen may produce a slight velocity increase but the main advantage is to extend cleaning intervals.  It also makes the cleaning go easier when the time comes.

What it doesn't do
This process is not suited for addressing a bore with a tight spot.  Not only will you tire of the effort long before any useful amount of material has been removed, you will have also substantially altered the rifling geometry in the region you opened up.  Working it with a poured lead lap and a more aggressive compound is the best way to deal with that type of issue.  If interested, here is some discussion on my first couple of attempts https://www.gatewaytoairguns.org/GTA/index.php?topic=180011 and I recommend Sean's videos
   


Tools needed
The tools needed are a cleaning rod with a ball bearing swivel [1], brass jag and cotton patches (or Brownell's VFG adapter and pellets), and a fine abrasive like J-B Bore Compound [2].



Step-by-step
1. Always work from the breech end to avoid any chance of damaging the crown.  If you must work from the muzzle end, use a guide bushing or some equivalent means to protect the crown.

2. Lightly oil the patch with a low viscosity oil like Kroil or pneumatic tool oil.  Not saturated and dripping, just a little.  Then smear a uniform coating of the compound onto it.

3. Apply more strokes at the breech end and fewer as you make it toward the muzzle.  A good place to start for most barrels is something like 25 strokes to 1/4 of the length, 50 strokes to 1/2 of the length, 75 strokes to 3/4, and finally 100 strokes the full length.  At first the friction will be quite high but you will soon notice it becoming easier as the compound does its thing.  If not, congratulations...your bore is apparently already in good shape.

4. It pays to spend a little more time at the breech end to smooth the leade...specifically the leading edge of the rifling.  Many barrels have a sharp step where the rifling begins, left behind by the blunt end of the reamer that was used to cut the leade.   If that is left untreated, the pellet will tend to snag as it is being chambered, cutting it and causing it to chamber crooked.  When I see s sharp step, I like to start with something more aggressive like 400 and 600 grit wet/dry on a dowel to break the edge.  Or you can use a Cratex point (rubberized abrasive bit) if you’re careful.  Then the polishing treatment further smooths the transition so pellets can ease into the rifling, staying neatly centered and undamaged.

5. Load a new patch when you feel the pressure against the inside walls of the bore has diminished quite a bit.  If using the Brownell’s VFG adapter and felt pellets, you can incrementally thread the pellet down onto the taper (see photo above) to bump up the pressure again a few times until it eventually shreds.  If using a brass jag and a cotton patch, replacement will need to be more frequent.  It works fine though...don’t feel like you have to get the VFG stuff to do a good job.

6. Do not let the patch exit the muzzle, else a subtle bell mouth will develop.  Clamping a stop block of some kind at the muzzle makes it easy to avoid so you can focus your attention on the fundamental goal.

7. When done, use a cotton swab to clean up any compound trapped in the lead or barrel port, then clean the bore until patches come out clean.

8. If so inclined, do a followup with a finer polish like J-B Bore Bright, Flitz, etc.   I always do because it’s a small additional effort compared to setting up and dragging out my supplies.  I usually apply about half as many strokes as with the previous compound.

9.  Clean again, reassemble and test!

Footnotes:
1.  Cleaning rod:  The purpose of a ball-bearing rod is so the scrubbing action follows the rifling.  Some guys don’t concern themselves with this aspect and seem to get satisfactory results (e.g. Ernest Rowe) but it seems to me it misses the tiny inside corners of the rifling where lead really wants to accumulate.  These comments assume a traditional rifling geometry.  I doubt it matters much with a rifling that has a gentle transition between the hills and valleys (e.g. polygonal).
2.  Abrasives:  If you're wanting to improvise different abrasive compounds, try them on a piece of polished steel like a knife blade and see if it hazes the surface or takes it to a finer polish.  In order to help knock down the surface fretting left over from the drawing and/or rifling processes, most new bores are going to benefit from starting with something coarse enough to haze a polished surface.  Then move on to a finer compound if desired.

customcutter:
IIRC this was made a sticky.  I wanted to bring it up again for some of the new guys like myself that haven't polished a bore before. 

Thanks again for posting this information! ;D

bear air:
Thanks for this great thread Jason.

JPSAXNC:
I make adjustable laps. I pour a slug then chuck it up gently in a lathe collet and drill a hole through it length wise for a piece of small diameter threaded rod. Then turn down two brass nuts slightly smaller than the diameter of the slug. Put the rod through the slug and a brass nut on each end. As the slug wears I hold the nuts with small pliers and give one of the nuts a 1/16 turn and reinsert the slug. I've made the laps for .177 and up.

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