Loose spot in barrel of S&W

[BSA1]

This is more of a general interest question rather than a gunsmithing question as I do not consider the gun "broke" at this time.

I picked up a used S&W Model 10-5 with a skinny barrel in very good condition. Upon cleaning it after my first range session with it I discovered that there is loose spot in the interior of the barrel where the barrel is screwed into the frame. I have ran several patches through it and measured the spot carefully and it is in the barrel where it screws into the frame.

My first thought is a bulge from a stuck bullet once upon a time. While there is no sign of cracking or any other damage on the forcing cone or the barrel or on the frame there is a slight hump or maybe more correctly a "taper" in the contour on the barrel where it meets the frame. It is barely noticeable and seems to go all the way around the barrel except the bottom where the barrel is milled flat for the ejector rod. Also the loose spot is farther back in the barrel under the frame where the barrel is screwed in. It would seem the pressure from a stuck bullet would have caused more obvious damage. So I attribute the slight "hump" or "taper" or "contour" as being the the way the barrel is made by the factory correct?


The cylinder and chambers appear to be fine.

My first range session was a bit of disappointment to me with the gun shooting to 2 1/2" to 3" to the left from 7 - 10 yards. However I attributed much of it due to using the magna service grips which are way to small for my hand, pain in my shoulder from recent surgery and white paint on the front sight causing me to lose the sight picture in the bright sunlight. At three yards firing double action it put 4 rounds plum center inside the X-ring of the target measuring less than 1" outside hole to outside hole

Bear in mind that this is a 30 year old cop gun so who knows what has been shot in it. I was using 158 gr. SWC I reloaded myself so there were not any ammo problems at all. I am unwilling to state the gun has accuracy issues until I can get back out onto the range with grips that fit my hand without the dang white paint and shoot it side by side with another Model 10.

As this is the first revolver I have ever had with loose spot in the barrel I am looking for feedback about what, if any, problems it might cause.

 

[MutinousDoug]

I have a model 66 with the opposite problem: the bore is tight where the barrel goes through the frame. I assume this is from the "crush fit" of the barrel indexing without having a barrel pin like earlier models. I assume this affects accuracy as the gun shoots 2.5-3.0" groups at 25 yds.
Police 38 Spl loads should not cause damage to a model 10 even after thousands of rounds. If your gun shows no sign of damage and it shoots to your satisfaction, I'd guess there is nothing wrong with it.

 

[dfariswheel]

Probably no problems at all, depending on how big the spot is.

The chances the barrel was made this way is very slim.
My best guess is, being a cop gun, something was fired in the gun that shouldn't have been, or something was in the barrel.

A common cause of bulges, rings, or "loose spots" in barrels is "Shooting the lead out".
This is where after shooting lead bullets someone fires a couple of jacketed bullets to shoot or blow the lead out.
You can get away with this for years, then one day you shoot a few more rounds then usual or shoot different ammo that leads up more.

The jacketed bullet has to push the leading in front of it like the bow wave on a boat.
If there's a little too much lead, the jacketed bullet can't push it out in front of it fast enough and something has to give.
What often gives is the extreme pressures cause a bulge, ring, or expanded spot somewhere in the bore.

 

[788Ham]

Thanks for explaining that dfaris, I've always wondered about guys saying to do that at the range. That makes total sense, won't be "blowing the lead out" any time soon. Thank you for your expertise.

 

[Coyote3855]

A common cause of bulges, rings, or "loose spots" in barrels is "Shooting the lead out".
This is where after shooting lead bullets someone fires a couple of jacketed bullets to shoot or blow the lead out.
The jacketed bullet has to push the leading in front of it like the bow wave on a boat.
If there's a little too much lead, the jacketed bullet can't push it out in front of it fast enough and something has to give.
What often gives is the extreme pressures cause a bulge, ring, or expanded spot somewhere in the bore.

Source? Explain please how the rounded contour of a jacketed bullet can possibly "push" or "blow" accumulated lead out of the barrel.

 

[BSA1]

I would like to know your source of information for that statement also.

 

[dfariswheel]

The NRA Dope Bag Tech staff did a study many years ago.

Whether a jacketed bullet has a round nose or not, it can't physically "ride over" enough heavy leading to prevent having to push most of it in front of the bullet.
Boats also have bows that are shaped to break through water as efficiently as possible, but put a big enough engine in it and try to go too fast, you'll get the bow stove in, as any boatman can tell you.

In the case of a boat, the motor is usually unable generate enough power to damage the boat, the boat just can't go any faster.
In the case of a bullet you have a tremendous amount of pressure behind the bullet with only one way out, and that's down the bore.
If the bullet can't move fast enough to relieve the pressure spike, something WILL give.
The barrel may burst, the breech may fail, or in the case of heavy leading and a jacketed bullet, the barrel will bulge or ring.

This ain't rocket science. You have an un-yielding jacketed bullet, a heavy layer of leading that's partially obstructing the bore, and a lot of pressure behind the bullet pushing it faster then the lead can be pushed out of the way.

 

[BSA1]

Shame that article isn't available. Since shooting jacketed bullets in revolvers after shooting lead bullets have been done for decades without reports such as this there must be a lot of lead in the barrel.

 

[murf]

and shooting .357" and .358" diameter bullets down .355" groove diameter colt barrels would have blown the barrel with the first shot.

i'm thinking that copper and lead are much softer than barrel steel and will yield (deform) way before the barrel (even at 800 fps). there would have to be a lot of lead or copper in that barrel (like a stuck bullet) to bulge it. imop

murf

 

[Jim K]

I am not sure I see a lead "bow wave", either. Normally, a jacketed bullet fired into lead fouling simply irons the lead onto the barrel, creating a very thin lead covering. I have seen those layers literally peel out under vigorous cleaning with a steel brush.

But I will say that barrel bulging is not normally due to a bullet encountering fouling unless the fouling is so thick as to actually stop the bullet. When a moving bullet is suddenly stopped, as by an obstuction like a stuck bullet, the moving bullet's energy is dumped in the form of heat. This heat lasts only an instant, but is so intense as to actually soften the steel of the barrel, allowing the pressure on or behind the moving bullet to bulge or burst it. I know no reason why that could not happen if the obstruction were in that part of the barrel inside the frame, although the frame should provide some extra metal to absorb the heat and resist bulging.

Jim

 

[murf]

might want to give that barrel a real good scrubbing and then slug the barrel. also, let someone else shoot it. their hand may fit those grips better.

murf

 

[Driftwood Johnson]

Howdy

One of my old Smiths has a very minor bulge partway down the barrel. Just about impossible to see on the outside, the only way I noticed it was looking down the bore I noticed a 'halo'.

I always assumed it was caused because sometime in the last 100 years somebody got a bullet stuck in the bore and fired another one after it. Never heard this business about waves and lead and jacketed bullets. Sometimes a barrel blockage like a stuck bullet will cause something to fail when another bullet slams into it. Sometimes it just causes a bulge.

 

[buck460XVR]

This is one of those subjects that over the years on these types of forums always ends up bein' "I heard this" or "I've been doin' it for years and ain't blown my gun up yet!" kinda thing. I too have read that a bulged barrel can happen from shooting jacketed after lead in extreme cases. I have heard bullet manufacturers claim that it does indeed raise pressures to dangerous levels. I have read gun rag articles advising against doing it. But I still see folks doin' it at the range without any problems....that they know of. I really would like to read/hear from somebody with legitimate knowledge tell us all, what is right and what is wrong. Only bulged barrel I ever saw in person was done while I watched a friend of mine shoot. After shooting for a while with ear protection, when a new hole didn't appear on the target, he figured he missed paper....till two holes appeared on the next shot. Barrel was ever so slightly bulged and only reason we really looked for it was because we knew what had happened. Otherwise, I don't know if he woulda ever noticed it. The 686 still shot fine and continued to be fairly accurate. He still has it and shoots it. If this can happen with a stuck bullet and not be noticed, I can see how shooting lead fouling out could produce it and folks wouldn't realize it. But the question remains, is it really a danger and does it really happen?

 

[Zaydok Allen]

Yeah that sounds possible, but a squib fire with a second shot afterwarsd seems more likely to me. Probably happened during rapid fire practice at a range if it was a cop gun. I'm no expert though.

 

[BSA1]

Without supporting documentation or references this one goes into the Internet Myth trash can.

 

[CraigC]

I have heard bullet manufacturers claim that it does indeed raise pressures to dangerous levels.

Sorry but nothing that happens in the barrel is going to affect chamber pressure. Chamber pressure peaks and falls before the bullet even leaves the cartridge case.

Without supporting documentation or references this one goes into the Internet Myth trash can.

I've never heard of this before either but dfariswheel has been around the block enough times that if he says it, it should at least be considered.

A lot of wisdom has been lost to the masses over the years. Much of what experienced sixgunners accept as fact was written by people like Phil Sharpe, John Lachuk and Elmer Keith 80yrs ago but is often scoffed at by internet experts.

 

[buck460XVR]

Sorry but nothing that happens in the barrel is going to affect chamber pressure. Chamber pressure peaks and falls before the bullet even leaves the cartridge case.

I was not necessarily talking only of chamber pressure, but also pressure in the barrel behind the projectile. There is still pressure behind the bullet while in the barrel, correct? While not common in revolvers, extreme leading in pistols and rifles, if it is relatively close to the chambered cartridge, resulting in a partial barrel obstruction will, like any other partial obstruction close to the chambered cartridge, indeed result in increased chamber pressure. Good article about it from Owen Guns.

An obstruction close in front of the cartridge in the chamber has the effect of increasing the chamber pressure. An obstruction in the middle or forward part of the barrel produces a local injury.
The action of an obstruction does not depend on trapping air. Experiments with coils of wire and other open obstructions resulted in damage about the same as solid obstructions of the same weight.

The action of an obstruction at or very near the chamber appears to be simply that of increasing the projectile weight, of course raising the powder pressure accordingly. Damaged to the firearm and shooter depends on the extent of this pressure increase, and on construction of the action and barrel breech and strength of the cartridge case. Often these withstand a moderate pressure increase without harm

The action of an obstruction at middle or forward part of the barrel appears to result from impact of the bullet or shot charge against the obstruction. The resultant injury is located at that place. It is always a characteristic ring bulge or burst. Its severity depends on weight of the obstruction, sometimes apparently assisted by a wedging action from pointed bullets; on the speed with which the projectile strikes the obstruction; and on strength of the barrel wall at that point. A light obstruction makes only a small ring bulge, and such an item as a bullet jacket may be ironed into the rifle bore by successive bullets and not be noticeable. A heavy obstruction results in a heavy ring, which if sufficiently severe shatters or severs the barrel at that point, without effect in the barrel elsewhere.

Whole article here......barrel-blockages

Here is another good article from "The Bullshooter" about bulged barrels. He too states in the 4th "what constitutes a blockage" that while he has no proof shooting jacketed bullets after lead has bulged a barrel, he believes it has. The 1st "what constitutes a blockage" is one that surprised me and may be one reason you see many old military rifles with bulged barrels.

Article here......bulged-barrels

After searching the web under several topics, I have yet to find anything but anecdotal evidence about cleaning a leaded bore with jacketed bullets, pro and con.

 

[CraigC]

An obstruction close in front of the cartridge in the chamber has the effect of increasing the chamber pressure.

When we're talking about firearms and internal ballistics, "pressure" usually means chamber pressure.

Any increase in whatever pressure exists in a revolver barrel will be alleviated by the barrel/cylinder gap.