Odd 'step' in the bore?

Hi all,

A bit of a quandary....

One of my L1A1's UK spec Straight pull, has a slightly odd issue in the bore.
I popped my cheap bore viewer down it yesterday and as the camera proceeded down the bore, about 6 inches from the chamber, a bright 'ring' came into view.

I have had this rifle for over 10 years and put hundred of rounds down range with it, probably about a 1000, without any issues.

There is absolutely no evidence of it with the MK1 eyeball....

These is no bulge in that area, no obvious issue in the exterior of the barrel, just this tiny raised, perfectly circular ring. You can just feel the slightest of resistance as the camera rides over it.

The low resolution of the bore viewer prevents a really good look at it.

This rifle happened to be the very first UK assembled Section 1 compliant L1A1, completed and proofed in 2009. As no new L1A1 Barrels were available then, the barrel was (allegedly) a machined .30 Cal M1919 N.O.S barrel.

I don't know if this is correct, but it is four grove left hand twist and the M1919 barrel certainly has more than enough meat and length to profile an L1A1 barrel from.

So it's certainly plausible.

Is this slight ring a simple wartime expediency measure?

Hypothetically speaking, were long lengths of M1919 barrel Bored, rifled, cut and profiled, with this ring simply part of where the cutter was replaced on the production line?

Was the 'ring' some obscure part of the function or design of the M1919, slight increase in back pressure to aid its operation, etc, etc??

Or am I about to get a hook for a left hand??

I obviously won't be shooting her again until I am sure she's safe to shoot

All opinions welcome guys....

I'll take a stab.
Warning: Cheaper bore cams can be misleading. I have a teslong, which can film birds-eye like yours as well as sideways. If you want to talk someone down in price...show them the Birdseye of the rifle they are selling. It always looks like crap. The reason is due to the reflective properties of the metal surface. After firing, no matter how much you clean, all of the metals microscopic 'imperfections' are going in the same direction. Makes even a new barrel look dull grey, perhaps even frosty (note I said microscopic. happens even on a brand new barrel after hand-lapping), whereas the side-view will show perfect, bright, and shiny.

I'm not saying you are wrong, just advising to double check. To double check without buying an expensive camera -- I would simply slug the bore. Before tapping my slug in, I would mark my driving rod for where to expect the flaw, and carefully note any difference in the force required to tap it through the area. Next, I would perform a straightness test. This involves dropping an index pin of a certain diameter and length down the bore. If it's in spec, it will fall all the way through with no resistance. Someone with a bigger library than me can pull up the spec for your rifle.

EDIT: here you go...https://pacifictoolandgauge.com/bore...lerances_-_001
and https://feeds.brownells.com/userdocs/learn/Inst-478.pdf

Some other general but related things about bore pictures I have noticed in the past:
It could be an illusion. I've heard first hand from someone that would put a patch in the chamber after slathering the bore with hoppe's benchers...and forgot about it. Well, he got a ring where the patch was, that remained after cleaning. It was a stain.

Sometimes tool marks remain on the lands, especially on milsurp barrels. I've installed several NOS still in the wrap barrels...tool marks all the way down. can't be seen with the eye, very hard to see with a Birdseye camera, but if a set of marks line up in just the right way, looks like a ring.

On shotgun barrels, there is always a "ring" visible after cleaning. It's the end of the forcing cone though. the light is reflected differently and changes reflection abruptly at that spot. Not generally visible when dirty as reflection that area is uniformly poor.

I've seen shotgun barrels that bubba clamped too hard in his barrel vise. These can be swaged out with tapered index pins driven down the barrel. I very very much doubt such a thing could happen in a rifle barrel.

Broken bit, or other reason to change tools in the middle of production back when the barrel was made?

If it shoots good, don't worry about it. I've slugged even a brand new taken out of the wrap by me No.4 before shooting for the first time...and guess what. there was at least 2 places along the bore where resistance felt noticeably different.

Quote:

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Originally Posted by ssgross

I'll take a stab.
Warning: Cheaper bore cams can be misleading. I have a teslong, which can film birds-eye like yours as well as sideways. If you want to talk someone down in price...show them the Birdseye of the rifle they are selling. It always looks like crap. The reason is due to the reflective properties of the metal surface. After firing, no matter how much you clean, all of the metals microscopic 'imperfections' are going in the same direction. Makes even a new barrel look dull grey, perhaps even frosty (note I said microscopic. happens even on a brand new barrel after hand-lapping), whereas the side-view will show perfect, bright, and shiny.

I'm not saying you are wrong, just advising to double check. To double check without buying an expensive camera -- I would simply slug the bore. Before tapping my slug in, I would mark my driving rod for where to expect the flaw, and carefully note any difference in the force required to tap it through the area. Next, I would perform a straightness test. This involves dropping an index pin of a certain diameter and length down the bore. If it's in spec, it will fall all the way through with no resistance. Someone with a bigger library than me can pull up the spec for your rifle.

EDIT: here you go...https://pacifictoolandgauge.com/bore...lerances_-_001
and https://feeds.brownells.com/userdocs/learn/Inst-478.pdf

Some other general but related things about bore pictures I have noticed in the past:
It could be an illusion. I've heard first hand from someone that would put a patch in the chamber after slathering the bore with hoppe's benchers...and forgot about it. Well, he got a ring where the patch was, that remained after cleaning. It was a stain.

Sometimes tool marks remain on the lands, especially on milsurp barrels. I've installed several NOS still in the wrap barrels...tool marks all the way down. can't be seen with the eye, very hard to see with a Birdseye camera, but if a set of marks line up in just the right way, looks like a ring.

On shotgun barrels, there is always a "ring" visible after cleaning. It's the end of the forcing cone though. the light is reflected differently and changes reflection abruptly at that spot. Not generally visible when dirty as reflection that area is uniformly poor.

I've seen shotgun barrels that bubba clamped too hard in his barrel vise. These can be swaged out with tapered index pins driven down the barrel. I very very much doubt such a thing could happen in a rifle barrel.

Broken bit, or other reason to change tools in the middle of production back when the barrel was made?

If it shoots good, don't worry about it. I've slugged even a brand new taken out of the wrap by me No.4 before shooting for the first time...and guess what. there was at least 2 places along the bore where resistance felt noticeably different.

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Many thanks for your thoughts, all taken on board, you can actually feel the bump on the 'ring' as the right angle of the camera probe glides over it, so it's not a mirage....

I'm minded to think this has always been there, it's as if the boring/ rifling bit was withdrawn and they just started again, a definitive circular step, although a very tiny one.

You can't see it by eye, no matter how hard you look.....

In terms of safety shooting...slug the bore, before after and at your ring.
have you noticed a lot of copper deposits in that area after you shot? I'd imagine if it's pronounced it would be ripping off jacket material.

I would say that what you have is most certainly a bulge, without any shadow oof a doubt. They don't necessarily show on the outside of the barrel. Just a good view by an experienced inspector identifies them. They were most common at the muzzle end as a rule.

If it were my rifle, and providing that it was accurate, I'd keep using it but just keep an eye on it.

One day, ask me about the lorograph machines we had............

Thought it might have been this:

By using two light beams (usually by splitting one beam into two), an interference pattern can be formed when these two beams superpose. Because the wavelength of the visible light is very short, small changes in the differences in the optical paths (distance travelled) between the two beams can be detected (as these differences will produce noticeable changes in the interference pattern). Hence, the optical interferometry has been a valuable measurement technique for more than a hundred years. Its accuracy has later been improved with the invention of lasers.

It could just be a reflection of the light from barrel straitening or “setting in” from the manufacturing process.

I wouldn't worry about it.

Many thanks for everyone's feedback. So, I popped the camera in today from the muzzle to the same point, bright ring and slight bump felt.
It's either a manufacturing oddity, or a bulge from it's previous life, as the reflected light is clearly bouncing off the dip.

This barrel is very heavy in profile, far heavier than a standard L1A1' barrel and there is is zero evidence of a bulge on the exterior profile. With that in mind, I m quite satisfied it's historic in nature.

However, belt and braces time, safety comes first, I won't be shooting her again until she's professionally looked at in the new year.

It's probably fine, but nice quality Faz made forend wood is impossible to come by these days and I've become quite attached to my left hand and would rather keep it attached to my arm!

I've plenty of toys in the toy box, including another L1A1, so it's not a particular problem....

---------- Post added at 03:14 AM ---------- Previous post was at 03:08 AM ----------

Quote:

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Originally Posted by Peter Laidler

I would say that what you have is most certainly a bulge, without any shadow oof a doubt. They don't necessarily show on the outside of the barrel. Just a good view by an experienced inspector identifies them. They were most common at the muzzle end as a rule.

If it were my rifle, and providing that it was accurate, I'd keep using it but just keep an eye on it.

One day, ask me about the lorograph machines we had............

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I'm asking, please do tell me about the lorograph machines Peter ..

Ring from the muzzle direction and it's appropriate bore location, you can see it's a somewhat muscular barrel profile compared to factory specs...

looks like a lot of copper in there from the second pic.

MrClark, I believe your modified BMG M1919 barrel would have been manufactured with a stellite barrel liner which would only extend part way
into the barrel. The stellite barrel liners are very hard and still used in modern US machine guns. The ring in your barrel is from the stellite liner
as it only extends for a short distance.

Quote:

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Originally Posted by RCS

MrClark, I believe your modified BMG M1919 barrel would have been manufactured with a stellite barrel liner which would only extend part way
into the barrel. The stellite barrel liners are very hard and still used in modern US machine guns. The ring in your barrel is from the stellite liner
as it only extends for a short distance.

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Many thanks Robert, I think you really are onto something there. A quick Google shows the liners pressed in at approx 6/ 7 inches, so allowing for cutting, threading and reprofiling, it would put this ring in the correct appropriate location of the butting from the liner to the barrel.

Very plausible, I will get some high resolution side images of the effected area in the new year. That should hopefully confirm one way or another.
If the liner is significantly harder than the rest of the barrel, then it would certainly explain why a slight rring has appeared, as the softer material gives way as opposed to the harder material, ultimately creating a very slight hollow...

Many thanks again Robert, it's certainly a possibility, every day's a school day!

The attached is a cutaway M60 barrel stellite liner, you can certainly see that this is a distinct possibility for the ring in my barrel

The Stellite liner is the most likely reason. As a gunsmith I have never found any need to own a bore scope. If something in a barrel is not visible to the trained eye then it is not likely to ever be a problem. I have had many customers over the years (that have purchased expensive bore scopes) come in to have non-existent problems "rectified". The only common problem that is not easy to see by eye is a bulge right at the muzzle, but it is easily detected with a bore plug gauge.

I can remember years ago when these BMG M1919A4 barrels in new condition were very cheap to buy. Gunsmiths would use these heavy barrels to
build inexpensive target rifles. Having to deal with the stellite liner was always a problem when these barrels were used on Model 1903 and US Enfields
Model 1917.

Mr Clark, the boys in the machine gun groups would really like your FAL on full auto down in Arizona as your barrel would last along time !