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POLISH AN LW POLYGONAL BARREL?

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Aldhy said:
Hi Mike, Thank you for sharing this information. This is something that gunsmiths in my country will never share to anyone ;)
I have 2 LW Poly SS and 1 LW Poly steel for my 25m benchrest units. All of it has choke. And I can confirm that all of it has tight line few inchs at the loading.
Currently I'm experiencing flyer every 5-7 shoots on one of my HR unit that love hard heavy pellet. So my plan is try to lap it to see if there is improvement after the lap.

BTW, Should I do the same check on the choke to find the offending spot?
And will JB paste do the job on Poly SS ?

Thank you very much.

Aldhy
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JB paste is very fine. To do any real metal removal you will need 120-180 grit.

It seems that nobody with a micrometer has ever checked to see how long it takes to remove .0001" of steel with 1500-5000 grit.

Lapping barrels with chokes is a more difficult process than without.
 
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So I finally got around to polishing the .30 cal CZ barrel on my Uragan 2. Scoped it after I was done, and I'm horrified at the bullpoop quality of this barrel. This kind of pitting is through the entire barrel. No idea how it even shot as good as it did. Have not yet shot it after, likely will tomorrow night, I can only hope it's better.

I really have to consider reaching out to AGT to get a replacement.

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thomasair said:
JB paste is very fine. To do any real metal removal you will need 120-180 grit.

It seems that nobody with a micrometer has ever checked to see how long it takes to remove .0001" of steel with 1500-5000 grit.

Lapping barrels with chokes is a more difficult process than without.
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I'm sorry mike , lapping is a new world for me 😅
Anyway I never have JB paste before. What is the grit grade of JB paste? is it around 800-1000 grit?
And based on your observation, what is the grit grade of LW SS factory default?

Thank you.
Aldhy
 
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Jaxjax said:
Yeah, that isn't good. You shooting pellets or slugs.? 1st pic shows edge of crown.? I take it that last pic is after polishing? & lastly how does the barrel feel for restriction by running slugs thru it end to end.?
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I shoot AVS slugs (.3033). All those pics are after the polish, and yes that first one is near the crown. I haven't pushed a slug through in quite some time, but IIRC it was pretty even pressure the whole way (unchoked). I suppose, if there are no burs, it might be ok like that. But it's poor quality for what you pay for those rifles.
 
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Aldhy said:
What is the grit grade of JB paste? is it around 800-1000 grit?
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The manufacturer doesn’t specify but the approximate value often cited is around 1000. In practice, it seems to behave as something even finer because the abrasive is highly friable (breaks down into smaller particles). So as Mike indicated, it is not a useful abrasive for lapping.
 
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zer0dev said:
I shoot AVS slugs (.3033). All those pics are after the polish, and yes that first one is near the crown. I haven't pushed a slug through in quite some time, but IIRC it was pretty even pressure the whole way (unchoked). I suppose, if there are no burs, it might be ok like that. But it's poor quality for what you pay for those rifles.
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Totally agree on they shouldn't be sending those barrels out like that. It does intrigue me that the unchoked CZ''s , at least that one seems consistent for bore from factory. Also make me wonder if hammer forging is much more forgiving for random tight spots being in bore. Every LW I have machined up has random tight spots which drives me nuts.....I run all unchoked PCP barrels. At least that's what there listed as when I purchase them but the LW's in SS I mess with all have one which I lap out along with the other restricted areas. with slug & pin gauge .. I would send those pics to AGT & get a backup barrel from em.
 
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The last image, taken at more of an angle looks the most like pitting with some depth to it. Yes, there appears to be chemical deposits around that, that may be raised above the surrounding metal.

Raised, or pitted are both unacceptable in a new barrel. Pitted seems worse because raised material may be removable. While a pitted barrel can shoot well, that is making excuses; like saying the Pretoria blade runner had an advantage, because of his carbon fiber shin bones.

I would not assume that CZ released a pitted barrel from the factory, unless you bought it from them. As soon as someone else has stored or machined a piece of kit, the opportunity for corrosion increases, outside of the barrel maker's control.

This includes machining with coolant emulsions that are 99 percent water, that gets left in a partially machined barrel, over a holiday shut-down, for example.
 
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zer0dev said:
So I finally got around to polishing the .30 cal CZ barrel on my Uragan 2. Scoped it after I was done, and I'm horrified at the bullpoop quality of this barrel. This kind of pitting is through the entire barrel. No idea how it even shot as good as it did. Have not yet shot it after, likely will tomorrow night, I can only hope it's better.

I really have to consider reaching out to AGT to get a replacement.

View attachment 529762View attachment 529763View attachment 529764
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Are you using a cleaning patch, or a lead lap?
 
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Ricochet said:
Also is the pitting consistently where you reversed direction with your "polishing" procedure? perhaps?
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I use a mop and firelap it. There is no way I pitted the barrel with JB bore paste and Autosol and some slugs. Not a chance. The pitting is in the full length of the barrel.

I wish I had more pictures from before the polish. I either missed it, or it was covered / filled with lead.
 
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I gave the muzzle end a thorough cleaning (because it was easiest) first with Gunzilla and then with BoreTech Eliminator (a firearms solvent), both applied liberally with cotton swabs and scrubbed with a nylon brush. Here are pictures from after (compare to first pic above). I see no difference and didn't see any material on the dry cotton swabs used to clean the solvents. I'm open to other theories but I would have expected any lead to be removed.

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