Of endoscopes, lapping bullets, and accuracy mysteries.

[Jäger]

The barrel "relaxed" everywhere it was reduced in diameter, particularly after the gas block journal and where the grenade launcher mount was machined; in essence the bore dimensionally resembled a snake full of eggs.

Apropos of perhaps nothing, when the Brit MoD contracted with Daemaco (Colt Canada) to build their SAS carbines based on the Canadian C8 with that hammer forged barrel, complete with all the dimensional changes to also fit a grenade launcher, Daemaco claims to have fired about a million rounds through I don't know how many different barrels/barrel profiles, before they decided they had a winner.

And the right barrel length with that barrel profile including the profiling to accommodate mounting a grenade launcher, is 15.7" (or whatever the Commonwealth metric equivalent of 15.7" is in millimeters).

Not 16", not 15.8" or 15.6"... 15.7". Presumably, that's where the harmonics were right with the 62 grain NATO ball round at the time. I don't know if the 77 gr. OTM round developed with Black Hills was around at the time of the contract and purchase.

Maybe the moral of the story isn't how many exterior dimensional changes there are to accommodate grenade launchers or anything else - maybe what really matters is if the length and whatever you have hung on the end produces the best accuracy node - or the worst peak between nodes to get shotgun performance.

For another borescope (or Post Borescope Traumatic Distress Syndrome) story, my benchrest/F Class shooting gunsmith buddy told me about a fellow competitor that he shot with and did the match circuit together with. After Bill finally sprung to get a borescope of his own, his F Class shooting partner brought over his current star performing rifle and asked him to really examine the barrel to see if he saw anything special about it that could maybe be reproduced once the rifle's current barrel started going south.

Bill said he looked in the barrel and instantly burst out laughing. There was a short section where the rifling quit spiriling, ran straight up the barrel parallel to the axis of the barrel - and then started spiriling again for the remainder of the length of the barrel. Showed it to his buddy who owned the rifle. Bill said after he saw the barrel, his competitor friend never shot the rifle with that barrel again - said he just couldn't trust it. Bill said he had the barrel pulled and put a new barrel on it - and it never shot as good as the original barrel with the defect.

So you never know when you see a barrel that looks as wrong as a basketball hoop on a pitcher's mound... But some things just can't be unseen.

Now it's a 3 MOA rifle with factory stuff and about half that with 3,000 fps powder-coated cast bullets.

Really???? With that grouping and velocity, you should be able to at least practice out to at least 200 meters!

Suddenly I have a strange desire to buy my first .224" bullet mould...

 

[fiver]

the 223 has taught me a lot about reloading and casting over the years.
and I mean a lot.
going along without any help like I was I ended up using that round to figure out the simplest of things. like what an ogive is, that primers matter, and probably most importantly of all.
that the quality of the bullet really does matter [had to learn that one twice]

 

[Ian]

Maybe the moral of the story isn't how many exterior dimensional changes there are to accommodate grenade launchers or anything else - maybe what really matters is if the length and whatever you have hung on the end produces the best accuracy node - or the worst peak between nodes to get shotgun performance.

I firelapped it (no other changes) and 10-shot groups with WCC 55-grain solids went from 8" to 3". I draw an entirely different conclusion about harmonics than you have in this instance. Granted, changing throat length without adjusting cartridge overall length affects barrel time slightly, as does reducing the barrel choke between chamber and gas block which had previously caused excessive blowby and copper fouling or the "loose" places further down, but with a 22-ounce suppressor hanging in the end I don't thing harmonics was much of a factor at all.

 

[Ian]

Since the wuhan funny money came already I ordered a stand-alone Teslong rifle borescope with the 26" stiff rod and four different diameter mirror attachments. Tired of my old one not working with my Android phone. Will report on it when it comes in.

 

[Ian]

Report is in, this thing is amazing. No more broken phone apps, no more worrying about messing up the USB-c jack in a $1,000 smartphone while worming the endoscope cable around, no problem. Screen display is smaller than a Galaxy S9+ and has lower resolution but still almost as good, in other words CLEAR images.

Here's what I got. https://www.amazon.com/gp/aw/d/B08D9GDQD5?psc=1&ref=ppx_pop_mob_b_asin_title

It was a package deal for an additional $10 ($149.99 plus tax) came with another little foam lined box containing four additional bore mirrors in .22, .30, .38, and .50 caliber diameters which keep the image in focus by centering the rod in the bore.

Get one, you'll be glad you did.

 

[Ian]

Is this fouling from moly-coated bullets?



The stuff was much thicker toward the chamber and nonexistent by 6" from the muzzle. Solvent wouldn't touch it, so I got after it with a Nylon brush and Iosso bore paste.



Still didn't get it all so I had another go with a lot more paste and about 100 strokes. That got most of the crust off but revealed deep etching underneath:



Does moly do that when left in a bore for years? I never used the stuff and this is a new-to-me rifle so I don't have a clue.

By the way, I haven't learned how to swap the data card and files from my Teslong unit to my smartphone yet so I just took pictures of the borescope monitor, cropped and reduced the resolution to a forum-friendly size, and uploaded.

 

[david s]

My understanding of Moly coated bullets was that it built up in the bore and that Kroil was a decent to good solvent for it. It is also my understanding that Moly is hygroscopic so that it tends to rust underneath. I'm not familiar with bore scopes and cant comment as to what your seeing but could it be rust pitting?

 

[Tomme boy]

Yes you will get corrosion under the moly. That's why it comes and goes as a fad.

 

[fiver]

moly doesn't collect moisture but it can trap moisture underneath the coating.
that's why everyone went to that blue stuff.

 

[Tomme boy]

hbn?

 

[Brad]

I think he means the blue coating Barnes used for a time on the X bullet before they went to the TSX.

I am not a moly user but wonder if TM Solution would work. It is good against copper and carbon. Best thing I have found.

 

[Ian]

I got it clean in short order with the iosso paste and a brush, the bummer is the pitting under the scaly crud. Just was wondering what that crud could have been, it didn't seem like carbon, rust, or PC fouling.

 

[Jäger]

I got it clean in short order with the iosso paste and a brush, the bummer is the pitting under the scaly crud.

I suppose it might matter whether it's simply offensive to the eye - a problem many of us have experienced after looking through a borescope - or offensive to becoming an issue of leading and less than optimal performance.

After my recent experience with a barrel making company, I'd sit and think a bit about marking your probe at some point you can return to look at at will, and then wind a little medium steel wool around a worn out bore brush and then do a little work in the area you're looking at, returning to that point every few strokes to see if you can observe any change in appearance.

One thing I didn't see the barrel shop boys do is use any paste on a barrel. I never thought to ask why, as I presumed they were all about production as they steel wool lapped the newly drilled, reamed, and rifled barrels ten at a time.

 

[L Ross]

I got it clean in short order with the iosso paste and a brush, the bummer is the pitting under the scaly crud. Just was wondering what that crud could have been, it didn't seem like carbon, rust, or PC fouling.

I was on a rimfire forum and guys found pitting in some older .22's now that they have bore scopes that resembles what you found. They had removed an accumulated carbon ring in front of their chambers that had grown with leading added. When removed they found pitting. Aaarrggghhh!