GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Share Your Simple Home Projects (TRICKS-N-TIPS) => Topic started by: nervoustrigger on August 03, 2017, 10:24:59 PM
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The following article is intended for the do-it-yourselfer that is interested in either finding and fixing a problem with a barrel, or improving the accuracy of an already good performer. You don't have to be a master machinist to get excellent results. The techniques described here can be done with simple tools like a Dremel and handheld drill. So with that said, here we go...
First off, a short pre-flight inspection:
Before you start removing metal
I like to start by giving the barrel an inspection to get an idea of what I'm working with:
slug the barrel and feel for issues - Push a pellet through the barrel, from breech to muzzle. We're looking for possible issues in 4 areas:
- barrel port - pneumatic rifles only (not springers)
- leade->bore transition
- bore
- crown
Firstly, note whether the pellet felt as though it snagged as it went over the barrel port. Most inexpensive factory barrels have not been deburred. Next up is the transition from the leade to the bore. Often there is a sharp edge where the leade necks down to the bore. Here, the sharp edge at the beginning of the rifling will tend to smear the head and skirt. Usually the skirt is most noticeable. Here's an example of what to look for:
(https://i.imgur.com/PSNYgqa.jpg)
Continuing on, note any loose or tight spots along the barrel's length. What I'm wanting is a pretty consistent, light resistance all the way through...that is, unless the muzzle is choked. Lastly, pay close attention to resistance just as the head and skirt pass over the crown and emerge into the outside world. Hanging up here is an indication of a burr left after crowning that will need to be dealt with. BTW, distinguishing between a choked barrel and a burr at the crown normally is fairly easy. In a choked barrel you'll encounter resistance for the last inch or so. If the crown has a burr, you'll hit a snag just as the pellet comes out the end. (Note: there is one more fairly unusual type of defect that can be potentially mistaken for a choke; that will be covered at the end under "Special case - damaged rifling".
inspect the pellet - Now inspect the pellet(s) with the help of some magnification. Damage in a confined spot around the perimeter of the skirt usually indicates a burr at the barrel port. Smearing of the skirt where it met the rifling usually indicates a sharp edge at the leade->bore transition. Slight rifling marks around the head are a good indication that the pellet is a good fit for the barrel...enough to prevent yawing as it hurtles down the bore but not so much that it damages the head. By contrast, rifling engagement of the skirt should be deeper because the skirt is a larger diameter by a few thousandths.
Now with some expectation of what you have to deal with, on with the barrel treatments...
Down to business
deburr the barrel port - Use a small diamond ball burr to radius the edges of the barrel port. An assortment like this runs less than $10: https://www.amazon.com/Pro-Quality-20-Piece-Diamond-Rotary-Tool/dp/B000MOI9G6 (https://www.amazon.com/Pro-Quality-20-Piece-Diamond-Rotary-Tool/dp/B000MOI9G6). What I do is load a 3/32" (for .177 cal) or 1/8" (for .22 cal or larger) diameter ball into the Dremel running at its lowest speed, and work it from inside the hole and up over the sharp edge all the way around the perimeter of the hole. Don't go crazy with it; the radius need only be five or ten thousandths (0.005" - 0.010"). Just trying to get rid of the wire edge left from the drilling operation. Then take a small dowel or skewer wrapped in 320 then 400 grit to polish the newly-formed radius. Apply some light oil (mineral oil, WD40, etc.) to help shed the swarf. Since this work is done at a shallow angle, round over the end of the dowel so it can dip into the hole as you pass it back and forth. Expect to chew up the paper a couple of times; just keep refreshing the abrasive and work it until it is smooth. It will become apparent when you've done enough because the paper will no longer be as apt to shred.
Refer to the following photo courtesy of Tom/UlteriorModem.
(https://i.imgur.com/gBkxbH2.jpg)
While we're at it, notice the remnants of the rifling and general surface roughness in the photo above. These are indications of an inadequately prepared leade. This region will benefit from being worked smooth.
treat the leade->bore transition - A picture is in order: (thanks to Kirby/K.O.)
(https://i.imgur.com/WC0gXUM.jpg)
Knock down the sharp transition between the leade and the bore. A regimen of 320, 400, and 600 grit is good for this operation. Wrap the paper around a small dowel and sweep it in and out, applying pressure all around the perimeter. The goal here is to help the pellet ease into the rifling without being gouged by a sharp leading edge.
Some folks prefer to instead use a Cratex point for this operation. These grinding/polishing bits are a rubber material impregnated with abrasive. What you would do is shape it to a diameter that fits the leade and taper the point. In this way, it smooths the leade and applies a bevel to the leading edge of the rifling...all in one go. Very quick and effective, just be careful not to remove more material than is necessary. It's easy to do with power tools.
My advice to beginners is the dowel approach because you can feel when you've done enough.
polish the bore - The pros swear by this. I've only done it a handful of times and I haven't formed a strong opinion about it yet. It does seem to improve precision a bit and will extend cleaning intervals (lead will not abrade and stick to the walls as readily). Some claim it also makes a barrel less pellet fussy; I don't doubt it but I haven't noticed it in my limited experience. Things you will need:
- cleaning rod - Critical that it be a good double ball bearing cleaning rod to ensure the cleaning pellet/wad/patch follows the riflings
- rod adapter - Brownell's VFG stuff (http://www.brownells.com/gun-cleaning-chemicals/patches-mops/cleaning-pellets/weapons-care-system-pellets-prod13839.aspx) is recommended for .22 cal and above. Specifically, the 084-000-002WB adapter (http://www.brownells.com/gun-cleaning-chemicals/patches-mops/cleaning-pellets/22-cal-vfg-adapter-sku084000002-25903-4136.aspx). For .177, use a good jag and cotton patches.
- cleaning pellets - firm felt pellets for Brownell's VFG system (http://www.brownells.com/gun-cleaning-chemicals/patches-mops/cleaning-pellets/weapons-care-system-pellets-prod13839.aspx) such as part number 610 for .22 cal.
- abrasive - A fine friable abrasive like J-B Bore Paste seems to be the most recommended but folks have successfully used stuff like Flitz metal polish or rottenstone.
- lubricant - Kano Kroil seems to be preferred but another light oil can be substituted. Its role is to help float away the swarf.
See these two excellent threads for more information, in particular the guidance offered by Motorhead and SeanMP:
J-B bore paste (http://www.gatewaytoairguns.org/GTA/index.php?topic=64525)
Deburring riflings - JB Bore Paste (http://www.gatewaytoairguns.org/GTA/index.php?topic=47627)
touch up the crown - Firstly, there are many different geometries that can be applied to a crown but most air rifle barrels will have a simple chamfer so that's what I will focus on. Give the crown a closeup visual inspection. If the chamfer is a uniform width all the way around the perimeter, a little touchup with a brass screw will do. What you will need is a round head (not pan head) brass machine screw. #6-32 is good for .177 cal and a #8-32 is good for .22 and .25 cal. Whereas most everything that has been discussed thus far should be done with the barrel removed, you can do this procedure with the barrel installed. Secure the barrel in an upright position so you can have both hands free. Stuff a small piece of cotton into the muzzle to keep debris from falling down into the barrel. Chuck up the screw into a handheld drill. Coat the head of the screw in polishing compound and hold it against the muzzle and operate the drill at low speed, moving it in an irregular circular or figure 8 pattern. I use the term "pattern" loosely; you expressly want to randomize the movements. If you try to hold the drill in one position, invariably more pressure will be applied to one side which will abrade an irregular bevel into the crown.
Do not apply downward pressure to speed things along. If you do, a wire edge will get pushed into the bore. I don't even use the full weight of my drill; I support it to limit the pressure to something between 0.5 and 1 pound. The idea is to let the abrasive slowly do the work. Refresh it often and keep at it until you see a clean, polished ring appear. A good crown will also have a distinct cog-like appearance when viewed under magnification, owing this to sharp, burr-free lands and grooves. Here's a before and after for reference...hopefully your before won't be this bad:
(https://i.imgur.com/4TjPZL1.jpg) (https://i.imgur.com/FeH8uE0.jpg)
When you think you've done enough, check that there is no burr remaining. The usual way is to very gently drag a cotton swab over the crown (from inside the bore and onto the bevel) and see if it snags. If it does, you still have a burr that needs to be worked down. When dealing with an unchoked barrel, I like to check by pushing a pellet through from breech to muzzle. I find it easier to detect a slight burr this way. I know it's right when the head of the pellet slips out the end with no more resistance than it takes to push it down the barrel.
If the chamfer is irregular, the end of the barrel will need to be reworked. If you can have someone with a lathe do it for you, that is probably best for most weekend warriors but if you are confident in your abilities, you can chop and recrown on your own. Here is a link to my DIY crowning guide (http://www.gatewaytoairguns.org/GTA/index.php?topic=55681) using a drill press to achieve a perfectly square crown without a lathe. There are many different ways to go about it and some good videos can be found by searching youtube.
Here's an example of an irregular chamfer, before and after:
(https://i.imgur.com/orOAK5x.jpg) (https://i.imgur.com/DMivF9Q.jpg)
Checking your work
After all the work has been completed, I like to use compressed air to blow away any loose and/or heavy debris, then run a few cleaning patches through the barrel. Then I slug the barrel again, looking for any remaining trouble spots. If all looks good, back on the gun it goes and then off to shoot groups with various pellets to see what it likes.
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Special case - damaged rifling
Earlier in the writeup I made reference to a defect that may be confused with a choked barrel, and that is damaged rifling caused by an unfloating piloted crowning tool. What happens is the spinning mandrel scuffs up the rifling near the muzzle. When pushing a pellet through, it will drag on the damaged rifling and it feels similar to a constriction (choke). Thankfully it is fairly easy to identify visually with good lighting. Here's an example:
(https://i.imgur.com/NFSyRSM.jpg)
If your barrel has this type of damage, it will be necessary to cut off that section and recrown the barrel. Here is a before and after:
(https://i.imgur.com/bLWxmkm.jpg)
For more info and others' experiences with this issue, refer to this thread http://www.gatewaytoairguns.org/GTA/index.php?topic=110179 (http://www.gatewaytoairguns.org/GTA/index.php?topic=110179)
Here's another example that has smeared rifling near the muzzle, then after chopping and recrowning:
(https://i.imgur.com/GyYMImb.jpg) (https://i.imgur.com/vyfevrC.jpg)
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Good info and photos.
When buying brass hardware be sure it's solid brass and not just plated.
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Thanks Mr. Jason for the tips. Nicely done
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Wow, that's some great info, and extremely timely! I'm fighting a barrel issue right now on my .22 Maximus. Shoots great without the LDC, but once added I can't even hit the target! The same LDC on my 2400KT or modified 2240 have no impact on poi at all. I'm thinking it has to have something to do with the barrel on the Maximus... Maybe this will help me find and fix the problem. Thank you for sharing this, I'm definitely bookmarking it for future reference!
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Great guide! Please make this a sticky!
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very nice writeup Jason.
Thanks for taking the time to share your knowledge for everyone's benefit.
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Great write-up Jason. Valuable info.
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Thanks guys, I hope it can help a few people solve a problem or wring out a little better accuracy from their rifle. If it does, please let me know. Keep in mind that's my payment :) And perhaps just as importantly, let me know if it doesn't help or if something doesn't make sense.
By the way, I see the thread got moved to what is probably a more appropriate location but I'm disappointed that it got carted off so quickly because it won't get seen by nearly as many people here.
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Jason, many thanks for the excellent guide!!!
I have made it a sticky. As for it not getting viewed, it has as much opportunity as ANY thread to be viewed. Especially if folks would simply use the "Show unread posts..." option when they come to the forum. Every thread in every gate has an equal chance to be viewed....
Thanks again and I'll be trying out your guide as soon as my shop is back up and going.
:)
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Wow Dez, thank you! I'm honored that you felt it worthy of being stickied, and honestly even more so that there could potentially be something in there for you.
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Wow, that's some great info, and extremely timely! I'm fighting a barrel issue right now on my .22 Maximus. Shoots great without the LDC, but once added I can't even hit the target!
Hi Paul
Could be the pellets are clipping the LDC. Trying insert a knitting needle down the barrel from the muzzle through the LDC. It should sit central to the hole. If not try a shim of paper under the LDC until the knitting needle is central to the hole.
One of mine needs a small piece at "20 minutes before", as you look at it.
Neil
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Wow, that's some great info, and extremely timely! I'm fighting a barrel issue right now on my .22 Maximus. Shoots great without the LDC, but once added I can't even hit the target!
Hi Paul
Could be the pellets are clipping the LDC. Trying insert a knitting needle down the barrel from the muzzle through the LDC. It should sit central to the hole. If not try a shim of paper under the LDC until the knitting needle is central to the hole.
One of mine needs a small piece at "20 minutes before", as you look at it.
Neil
Neil,
Mine turned out to be harmonics from adding the LDC. I added a second barrel band and it's now more accurate than it shot before without the LDC! Thanks...
Paul
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I ran across this again and I was again wowed by the great write up shared knowledge. I have started lapping all my barrels and find it makes a world of difference. My experience as been only with Crosman barrels and find that while the QC has improved, there is almost always a sharp edge transition from leade to rifling.
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Excellent post in the link, thank you Jason!
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Great thread! Jason:)
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Neil, Dave, Mike, and Erik,
Thanks guys, I really appreciate your kind words! (https://www.gatewaytoairguns.org/GTA/Themes/CustomGTA2012/images/post/thumbup.gif)
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I have a barrel with an extremely choked last inch. Pressing a pellet through takes great effort at the last inch, like pounding in a nail.
How much increase in pressure for common choked barrels?
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It varies but for small calibers (.177 - .25), usually in the range of 5 - 15lbs. My right arm is long overdue for calibration so that's just a rough idea.
For a sanity check, I grabbed a .22 Lothar Walther from the closet and it felt like about 10lbs with a Crosman 14.3gr but only about 5lbs with a JSB 15.9gr, presumably due to the harder alloy of the Crosman.
If you can manage a good closeup photo of a pellet you've pushed through, that would be telling.
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This a great topic. Honestly, I was super confused reading some of the stuff here on the forum, like crown, lead-in, chamfers, and lapping.
This topic made me understand now what some of our other members are doing. Thanks, Jason, for the work you put into this. I'm going to read this topic again...maybe another several times so that I can really get an understanding of what to do and how to do it.
Then I'm going to take the plunge and see if I can utilize what I've learned to improve accuracy on an already accurate rifle. If it helps to shrink groupings by 1/8", then I can say it was a success. If it doesn't do anything, then it's still a win; I will be more knowledgeable not only in concept, but in actual application as well.
Thanks a bunch!!
Oh, and by the way: just by looking at the pellet examples, I think I can say that my leade needs to be worked on. Just a tad...not a lot. I do have those pronounced rifling marks on my pellets.
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NT, Thanks for a detailed and thorough explanation of these techniques. I need to pick up couple of items at the local outdoor shop and I'll have some basic machining to do.
Best, Fran
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Jason, can one use the brass screw and abrasive method in a lathe? I have already faced off the barrel. The idea would be to put some rags over the ways, and chuck a brass round head screw in the tailstock. Add bore paste to screw as needed. Extremely slowly advance the tailstock spindle as the abrasive cuts the crown. I've heard one should reverse the lathe direction to get even cutting of the lands. Or is it better to do this 'manually' with a brass tool while the barrel is spinning?
I have a mini-lathe and can't do an 11 degree crown, because my compound slide fouls with the DRO on the cross slide. This annoys the heck out of me for some reason. From pictures I've seen, even the 11 degree crowns get crowned right at the rifling lands to ensure there are no burrs.
Disclaimer, I'm a novice with a lathe. My first project is converting a P17 to 0.22 cal. using a 1322 barrel. Everything fits, but it's not quite as designed. Managed to fire some rounds through it to chrony it. The barrel needs a decent crown.
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Hi Bruce, my preference is to do the facing operation in a lathe but I remove the barrel to do the crown with a handheld drill. The concern with doing it in the lathe is that it's likely to produce an irregular bevel. Well, that would be my expectation if the screw were installed in the tailstock. If instead you were to support the screw by hand and randomize the angle at which it's being introduced to the barrel, that would produce a good result.
If this sounds counterintuitive--that a hand operation can do better than a machine--well, here's the thing. To cut a uniform bevel, the tailstock would have to be perfectly aligned to the headstock, the workpiece indexed perfectly to the bore (not the OD), and the whole arrangement free of any vibration or resonance while it's running. The alignment thing is probably self-explanatory but the resonance thing perhaps not so much. It's not about chatter per se but the risk of producing a Reuleaux triangle. That could probably be managed by dialing the speed up and down as you go but I just find it more convenient to do with a handheld drill. I also like to reverse occasionally as you described.
BTW, here are a couple I did this weekend for reference. Facing operation in the lathe, then removed and clamped vertically and crowned with a brass screw in a handheld drill.
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=7064)
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=7065)
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Great work there Jason! They look fantastic.
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Thank you Jason!
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Jason, thanks for the well written and thought out exposition. I was aware of some of the errors in lathes, but haven't heard such a clear explanation of why this manual method would be better for crowning. Have to admit, had to Google Reuleaux triangles. What an interesting sidetrack for me. Thanks for the lesson.
Guess I'll try this sometime today. Is JB Bore Paste ok for crowning? Or do you recommend some other lapping compound?
Beautiful pictures, (and work) by the way, how do you take such nice close ups?
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thank you for the write up .. i will refer to this when i get back into tearing down my rifles. it will come in handy
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I will say that IF you get the ball bearing steady rest you can get very good results in the lathe once set up properly.
In fact? I'd suggest a couple of them as I've yet to find a perfect barrel!
By having a couple adjusted properly you can force the barrel to perfect alignment for any operation you may need to do.
Yes. It takes a few more bucks to buy them but once you go that way? Saves so much time.
Not to mention Jason is a Master at doing it by hand!
I tried a few times and I am no where near his level at doing this by hand!
Now with the lathe and steady rests?
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I use the lathe equally in both directions and hand hold the brass screw working it in circles. To speed things up I start with 400 alum oxide paper then move to 600 grit paste and finish with polish. The paper takes the profile of the brass head immediately and makes short work of it. I did 16 P-17 barrels a couple weeks ago, got it down to a 3 minute process. Anything past the lands provides protection, but adds significant time.
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Hey guys, thanks for jumping into the discussion. It makes me happy to see activity on this topic. It sure has benefitted me greatly and I hope it will do the same for others.
Bruce, I think you’ll want to start with something a bit more aggressive. J-B is a very mild abrasive…I’ve used it by itself and it will get the job done but it was probably a 20-30 minute job. I still like to go somewhat slow compared to most folks but not quite that slow. My preferred approach is to use 3 progressively finer abrasives:
1. I have a stick of “medium” polishing compound that I use with my bench polishing wheel. What I do is use a box cutter to shave off some and mix it into a slurry with J-B. It cuts considerably faster than the J-B alone but nowhere near as fast as, say, valve grinding compound. I typically spend between 5-10 minutes of intermittent work with this material…including stops to rotate the barrel in the vise by ¼ turn increments, switching direction with the drill, and refreshing the compound. Actual time spent grinding is only 50% or so.
2. J-B Bore Compound by itself. Just a couple of minutes with this one to smooth down the finish left from the previous step.
3. J-B Bore Bright by itself. Another couple of minutes with this one leaves a near polished finish.
I don’t know what the top speed of my handheld drill is off the top of my head but I seldom go as high as 50%. Most of it is done at 20-30%. Also I’m probably belaboring the point but I use very little pressure throughout the whole process. As mentioned in the original post, less than the weight of my drill so it’s probably better to say I’m limiting pressure as opposed to applying pressure. It’s tempting to press down to speed things along but that will leave a burr so go slow and let the abrasive do the work. This isn’t gospel by any means, it’s just what I’ve settled on.
Oh, and the photos? Lighting is everything. Sunlight! The camera is just a 12 year old Fuji 7MP in “super macro” (closeup) mode. No manual override settings, no photo wizardry, no nothing.
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Hi Thane, thanks for sharing your process. Just one comment about the depth of the crown. I think it’s important to carry it all the way to the grooves. True, the head will only touch the lands but the skirt generally obturates to fill the grooves. Thus if a burr remains there, it will scar the skirt on the way out.
Granted damage to the skirt is not as detrimental as damage to the head but we’d like to eliminate both.
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I agree and finish to the face of grooves stopping just as a full bright circle appears.
I don't know the nomenclature for the sides of the lands, or is it the walls of the grooves?...
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Okay we’re on the same page...for some reason I too still have to stop and think about land vs groove. It’s easiest for me to think of the groove as the deepest part the pellet can touch.
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Wow, this is some fantastic information. Thanks for taking the time to put all this together. I'll be saving this thread.
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Sorry if I jump into an old discussion, but i guide like this should never die!
Recently purchesed a chinese co2 pistol carbine, the well known Artemis (snowpeak) CP2 AKA Diana Chaser and, after having experimented some trouble wit pellet feed due to the poor finish of the barrel breach (patially solved by some needle file work a wet and dry), I took a look at the crow and it seems a little smeared to me. With that corona virus lock down my scope has yet to arrive so i didn't bother installig the long barrel for a test (my basement in only 8 meters long and i tested pistol barrel that seem non that bad). Well reading your posts about recrowning i've come to the conclusion that the brass screw method is the ohe i could try without screwing up all (pun intended). The problem is : i cannot find such machine screws here in europe, can somebody sugest me how to find some screw that would do the job here in Italy or in the UK also? Us metric guys are complicated. Forgive my english, I'm italian and i don't have many chanches to write your language.
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Sorry if I jump into an old discussion, but i guide like this should never die!
Recently purchesed a chinese co2 pistol carbine, the well known Artemis (snowpeak) CP2 AKA Diana Chaser and, after having experimented some trouble wit pellet feed due to the poor finish of the barrel breach (patially solved by some needle file work a wet and dry), I took a look at the crow and it seems a little smeared to me. With that corona virus lock down my scope has yet to arrive so i didn't bother installig the long barrel for a test (my basement in only 8 meters long and i tested pistol barrel that seem non that bad). Well reading your posts about recrowning i've come to the conclusion that the brass screw method is the ohe i could try without screwing up all (pun intended). The problem is : i cannot find such machine screws here in europe, can somebody sugest me how to find some screw that would do the job here in Italy or in the UK also? Us metric guys are complicated. Forgive my english, I'm italian and i don't have many chanches to write your language.
Here, brass screws are most often used for furniture or in boating. That may help you know where to look.
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Firstly, your English is great!
Am I correct to assume the difficulty is not in finding a round head screw but in finding one that is brass? If so, be advised you can use a common steel screw if you will start by removing any burrs it has on the head. Run a small triangular file through the slot to break the sharp edges and then spin it against fine sandpaper held in your hand until it’s smooth. When that is done, use it just as you would a brass screw. Just avoid adding pressure and let the abrasive slowly do the work and you’ll be fine.
By the way, I don’t know if you ran across the thread but my son’s CP2 / Diana Chaser purchased in December not only had the usual poor crown but also had smeared rifling at the muzzle. I had to cut off the bad portion and re-crown it:
https://www.gatewaytoairguns.org/GTA/index.php?topic=166821 (https://www.gatewaytoairguns.org/GTA/index.php?topic=166821)
If you find that to be the case with yours, there is a method linked in the original post for using a drill press to square the muzzle. You can even do it with a hand-held drill by clamping it to a bench and then supporting the muzzle with a bushing block (just a wooden block with a hole drilled in it). In other words, cut off the bad portion with a hacksaw, then square the cut with a drill press, and then do the crowning step.
Oh and I should mention the crown you see on the Chaser was done with a steel screw.
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Adding an ATI Liberty .22 factory crown for the list of terrible things done to barrels.
Pellets grouped nice and tight, but slugs would scatter over 10" groups at 10 yards!
Brass screw method crown and now slug group 3/8" at 25 yds, pellets 1/4" at 25 yds.
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Thaks you all, guys. Well the problem with screws is finding one with round head, is made for flat scrwdrivers and isn't a wood screw. Here machine screws are common in allen or torx head, boating screws al almost AISI304 or other marine grade stainless steel, brass is mainly used in atique boat and for wood screws. The diameter of the head is also crucial, but it's on me to do metric conversions. The joke here is "Americans did a revolution to free themselves from an empire but they still use imperials", but we are simple folk: to count by ten is easier. On the weekend i will make the effort to put a macro lense on my reflex and try to shoot some picture of my breach and muzzle, i don't have a boroscope.
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This is a timely bump of this post for me too! I've been trying to problem solve accuracy issues on a B19 variant Crosman. There is a restriction in the middle of the barrel that I can feel when I push a pellet through. I have cleaned several times with ballistol and patches until all patches came out clean, I've used patches with JB paste, and I've even used a brass bore brush with JB paste. but the rough spot is still there? What should I do? It isn't mentioned in this thread, but do you even recommend the brass brush with JB paste method? Should I do it again?
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David, if you can tell, please distinguish the defect as being a constriction versus a rough spot. Both the approach and how aggressively you’d need to deal with it are likely to be quite different.
For example if it’s a rough spot, I think the optimal approach would be to use a solid lap to help bring the surfaces into continuity with the rest of the bore, without necessarily having to remove so much material that the surfaces are rendered completely level. In other words, there could remain some low spots that would have no impact whatsoever. The pellet will have already been swaged to shape by the time it gets there so it would just ride on by the low spots.
If instead it is a constriction, you’re gonna have to remove comparatively more material. Even a few ten-thousandths of an inch (say, 0.0003”) will take an inordinate amount of time with a very mild abrasive like J-B Bore Compound. I don’t know that I’d go as far as to use valve grinding compound. I’d probably have a go at it with a slurry of J-B and a medium polishing compound like I had described a few posts earlier for crowning with a brass screw (step 1 of a 3-step process). A polishing felt like a Brownell VFG pellet can be used for this procedure. After a hundred strokes concentrated at the constriction, I’d check my progress by cleaning and then pushing through a pellet or two. Then another hundred strokes and re-check. Then maybe a third time. If at that point it’s obvious that progress is being made, continue. If not, move to something more aggressive.
Backing up a bit here, how to tell if it’s a rough spot or a constriction…I would look through the bore toward a light source and see how the light reflects off the surface. If it changes sheen in the suspect area, it’s roughness of some kind. If it maintains the same sheen throughout but the light bends ever so slightly at the suspect area, it’s a constriction. I suppose there is a possibility it could be both…for example if there was insufficient lubrication when the rifling button was passed through and it got hung up, maybe it lifted material in its wake and left a rough surface that stands proud. I don’t know, I’m just speculating here and trying to give you some food for thought.
I hope this helps!
BTW, did you ever get your 22xx barrel machined?
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Take a look with a borescope digital camera. Nothing like seeing for yourself and how the polish job is doing.
I picked up one that fits .177 for $20. USB to laptop and your off inspecting bores, transfer ports, air tubes...
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Here is what the inside of my barrel looks like. I have problems you can see on both ends and a problem you can't see somewhere in the middle. I'm not sure it's worth fixing, maybe time to call Crosman for a new barrel. What do you think?
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Thaks you all, guys. Well the problem with screws is finding one with round head, is made for flat scrwdrivers and isn't a wood screw. Here machine screws are common in allen or torx head, boating screws al almost AISI304 or other marine grade stainless steel, brass is mainly used in atique boat and for wood screws. The diameter of the head is also crucial, but it's on me to do metric conversions. The joke here is "Americans did a revolution to free themselves from an empire but they still use imperials", but we are simple folk: to count by ten is easier. On the weekend i will make the effort to put a macro lense on my reflex and try to shoot some picture of my breach and muzzle, i don't have a boroscope.
I think I have a brass screw I could send you if it's for .177. Just PM me.
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Thaks you all, guys. Well the problem with screws is finding one with round head, is made for flat scrwdrivers and isn't a wood screw. Here machine screws are common in allen or torx head, boating screws al almost AISI304 or other marine grade stainless steel, brass is mainly used in atique boat and for wood screws. The diameter of the head is also crucial, but it's on me to do metric conversions. The joke here is "Americans did a revolution to free themselves from an empire but they still use imperials", but we are simple folk: to count by ten is easier. On the weekend i will make the effort to put a macro lense on my reflex and try to shoot some picture of my breach and muzzle, i don't have a boroscope.
I think I have a brass screw I could send you if it's for .177. Just PM me.
Understood!
Brass, round head screw for dressing the crown.
sf the slot for flat blade screwdriver essential, or will Phillips & Torx heads work?
Ed
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So long as it is a true round head, I would not hesitate to use one with a different drive type. Can’t say I’ve ever seen a round head with a Torx drive though. Maybe a Philips. From what I’ve seen online, in stores, and hardware I’ve accumulated over the years, other drive types are almost always going to be a pan head, truss head, or some other semi-round head.
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So long as it is a true round head, I would not hesitate to use one with a different drive type. Can’t say I’ve ever seen a round head with a Torx drive though. Maybe a Philips. From what I’ve seen online, in stores, and hardware I’ve accumulated over the years, other drive types are almost always going to be a pan head, truss head, or some other semi-round head.
Thanks, nervoustrigger
I was curious if the slot cut in the round head had anything to do with the process of dressing the crown
Obviously, from your reply, it does not
Ed
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Ed
The slot will hold any abrasive you are using, when the screw head is spinning around etc. ;)
Don
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Ed
The slot will hold any abrasive you are using, when the screw head is spinning around etc. ;)
Don
Understood!
Thanks, Don
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Awesome thread. How often is this barrel work helpful on a higher end barrel, like Lothar Walther? I recently got a 2nd 1720T (.177 Lothar Walther) that seems a little more pellet picky than the first one. I haven't inspected the barrel yet, but plan to take a look and push through some pellets, per the instructions.
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Thank you sir! A large portion of this guide is about addressing workmanship issues or things that aren’t really bad per se but just less than ideal. So for example you can reasonably expect a LW barrel to have a good bore but the crown, leade, and
barrel port are all at the mercy of the person who machined it for whatever gun it’s going into. Hopefully they’ve put in a level of care commensurate with the barrel’s pedigree but maybe not.
If you are concerned about potentially doing more harm than good, my suggestion would be to at least push through a few different pellets, just as you’ve said, and inspect them under magnification.
Personally, I almost always retouch the crown and I hit the leade if I can detect even the slightest smearing at the skirts. And if the imprinting of the lands onto the pellet head shows any striations under a 5x loupe, I go ahead and do the J-B bore polishing.
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Thank you sir! A large portion of this guide is about addressing workmanship issues or things that aren’t really bad per se but just less than ideal. So for example you can reasonably expect a LW barrel to have a good bore but the crown, leade, and
barrel port are all at the mercy of the person who machined it for whatever gun it’s going into. Hopefully they’ve put in a level of care commensurate with the barrel’s pedigree but maybe not.
If you are concerned about potentially doing more harm than good, my suggestion would be to at least push through a few different pellets, just as you’ve said, and inspect them under magnification.
Personally, I almost always retouch the crown and I hit the leade if I can detect even the slightest smearing at the skirts. And if the imprinting of the lands onto the pellet head shows any striations under a 5x loupe, I go ahead and do the J-B bore polishing.
Thanks! If I decided to polish the bore, would this work? I have some .177 cleaning pellets. Could a put on a dab of kroil and some J-B on the cleaning pellet and push from the breech to the muzzle the cleaning pellet with a 1/8” wood dowel and before the cleaning pellet exits the muzzle, flip the barrel over and push back towards the breech, then rinse and repeat? Maybe 100 strokes or so, periodically refreshing the cleaning pellets?
Prior to messing with the barrel if I do, I’ll probably confirm that I can buy a replacement from Crosman should I jack things up. :)
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Those barrels are actually harder than you think. Even when lapping with a lead slug and JB it takes some effort to get out the tight or rough spots. Of course if using a steel rod make sure there is no metal to metal contact.
Using the higher grits will work faster and care must be taken to go slow. Always check as you work by pushing pellets down the barrel to get a feel of what is taking place. I personally push about 5 pellets through and mark on the barrel with blue tape and a marker where the tight and loose spots are. I keep checking as as I work to monitor was is actually happening inside the barrel.
I personally think pouring lead into the barrel with the jag method allows for a better feel of what is taking place inside the barrel. While more work it really concentrates the polishing where it most needed.
I went off on a tangent and what you are wanting to do will help a little and smooth out some of the rough spots. IMHO you will not hurt the barrel doing what you are suggesting. I'm not sure your wood dowel is going to be able to handle it however. Just my 3 cents.
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Well I don’t like doing anything from the muzzle end that deals with bore polishing. Pretty well assured to round over the rifling at the crown. Probably okay if you’re going to turn right around and dress the crown with the brass screw technique. Otherwise I would avoid it.
If you don’t have a suitable ball-bearing cleaning rod to do the job, consider fire lapping. It’s a pretty conservative approach that can do no harm. It’s kind of at the opposite end of the spectrum of a poured lead lap.
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Those are wise words Jason and goes for any barrel. Thanks for catching that.
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I had to look up fire lapping. Can’t say how disappointed I was that it didn’t involve lighting anything on fire :). Also had to look up poured lead lap. Wow, I’m learning a lot.
I researched some double ball bearing cleaning rods in .177 and saw some that were 36” long. Seemed a like might be a little unwieldy for my 12” barrel? Were there any recommendations?
I might be getting a little ahead of myself, but I’m enjoying the knowledge. I’ll plan to touch up my crown with the brass screw technique and assess the leade, barrel port, and bore. Thanks for all the good info!
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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).
https://www.amazon.com/gp/product/B008PL7DRE (https://www.amazon.com/gp/product/B008PL7DRE)
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.
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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 (https://www.gatewaytoairguns.org/GTA/index.php?topic=180011) and I recommend Sean's videos
https://www.youtube.com/watch?v=WM8xaaUaTTY (https://www.youtube.com/watch?v=WM8xaaUaTTY)
https://www.youtube.com/watch?v=IXzmlDT-yxE (https://www.youtube.com/watch?v=IXzmlDT-yxE)
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].
(https://i.imgur.com/OKU4zkd.jpg)
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.
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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
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Thanks for this great thread Jason.
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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.