Barrel bore very off center.(Updated new barrel issues)

[redlined_b16a]

.25 cal BullBoss.
Groups arent as tight as Id like them to be.
I re cut my barrel crown on my AT44 .22 to an 11 degree target crown.
I machined a bore alignment tool.
Shimmed my 3 jaw chuck until I got a about a 1/2 thousands run out.
The at44 bore was about .005" from being center of the barrel.

The bullboss measures .024" off center.
My 3 jaw or my ablities do not allow me to compensate that much accurately.
Next step is to buy a 4 jaw or get an outside machinists involved.

My question is:
How much off center is too much?
My scope has to be shimmed already or I can not zero.Shimmed to the left.

Gun is about 4 months old.
I already modified the crown so I think sending it back to hatsan is not gonna fly

[redlined_b16a]

Google searches show its a common old rifle issue.
Some say it effects some say it does not.

With a LDC it would effect with clipping and two of my plastic hair curler baffles are chipped

[tkerrigan]

Instead of doing 11deg. just cut it off square and use a brass round head machine screw in a drill with abrasive lightly both directions on the bore.  Works the same but hole doesn't have to be in the center.  Regards, Tom 

[redlined_b16a]

I'll give it a try.
I like to over think stuff.Figured I have a lathe I can machine it!
The phrase that always gets me in over my head.

[KnifeMaker]

That, and since you have a lathe, I would move the breach forward, cut the rear off, and re-locate port to be at 6 o'clock and the bbl bore centerline  indexed the 12 o'clock.

Has been done for decades on older out of center bbls and modern AG barrels quite a bit. 

Knife

[rkr]

Instead of doing 11deg. just cut it off square and use a brass round head machine screw in a drill with abrasive lightly both directions on the bore.  Works the same but hole doesn't have to be in the center.  Regards, Tom 

If the bore is off center, then even if you cut the barrel square the crown will still be at slight angle won't it? Will the round head screw method correct that by removing some more material from one side then?

[KnifeMaker]

No Sir. The end, (Crown will be at 90* to barrel. Regardless whether it is centered in the actual barrel steel. Look at many Smith & Wesson Revolvers. With the rib, and underlug being from the same piece of stock, it is not in the center of the piece of steel. Same/Same.

The screw will index off the edges of the actual bore, not the outer walls of the barrel. Therefore, it will still find dead center. 

Knife

[Wayne52]

I remember about a year ago a guy on this forum was putting a LW barrel on his gun, he even showed a video of the barrel in his lathe chuck spinning to show how badly it was off center, I don't recall if he ended up sending the barrel back or not nor even if he used the barrel.  This is really bad news especially of you have a long LDC, it's likely you'll get clipping, I'd let them know about the situation myself, chances are they're going to say sorry, no can do.  Five thousand's is way too much for sure.

[redlined_b16a]

My bullboss bore is .025" off center.

[nervoustrigger]

Actually although I am a proponent of the brass screw method, i want to point out it only has a self-indexing, auto-squaring feature if the bore is drilled off center AND completely parallel to the outside of the barrel.  Well, at least for the last inch or so near the muzzle.  My understanding from having cut and recrowned a number of barrels is that it’s more common that the bore wanders along the length of the barrel, following an arc for example.  That being the case, the axis of the bore is more likely at a slight angle relative to the OD, so if you square off the end based on the OD, the bore intersects the muzzle at a slight angle.
 
If that doesn’t make sense, let’s look at an extreme example.  If you imagine a solid block of steel with a grossly mis-drilled hole that goes through at a 30 degree angle, the hole you see on the outside of this block is an obvious oval.  This oval hole is our muzzle in this hypothetical example.  No amount of spinning a round head screw against that oval hole is going to produce a “muzzle” that is precisely perpendicular to the axis of the hole.  As such, a pellet sent out of it would not experience an even release of expanding gas around its skirt and therefore would leave somewhat destabilized.
 
How would one go about solving that?  Well, it seems you would need to index off of a snug gauge pin inserted into the muzzle and then make your facing cut.
 
With that being said, my experience tells me it’s all pretty academic.  I’ve recrowned a few barrels whose bores were probably 0.020” or more out of concentricity at the muzzle and, after making a beveled crown with the brass screw method, on average they grouped as well as barrels that didn’t have this issue.  I know at least some of these had a wandering bore because the concentricity offset moved when I lopped off a short section from the end.  To be fair, there are far too many variables at play to proclaim it makes no difference whatsoever but from a practical standpoint, I think that’s a close enough approximation to be useful.
 
Tl;dr  Don’t immediately blame poor groups on a bore that is off center.  More than likely the problem lies somewhere else.

[redlined_b16a]

I contacted Hatsan just to see.
Rolling my barrel across a flat surface ir wobbles too.
Ill recrown and hope for the best.Right now I can get 3/4" groups at 35 yards which is fine for my hunting needs but at 50 yards groups are just above 1".

[SilentMatt]

The bore being not concentric to the OD of the barrel is common on all guns. Every PB that I've threaded has had this issue(Remington, Savage, Ruger). Not too much of an issue with air rifles, as the barrel doesn't heat up with use. I use gauge pins to indicate the bore in with the four jaw to thread or re-crown.

[Gerard]

My used QB78D came to me with the .22" barrel chopped to 14". Not only was the last 1/2" of the bore scratched up from some lame effort someone made at guiding a crowning device of some kind, but the bore was over 1mm off centre. As I wanted to use a long-ish air stripper this was a problem. I cut it down to 13.4" where the bore was still intact, then centred on the bore in my 4 jaw and trimmed the 15mm OD down to 1/2" and threaded it, then crowned the new muzzle on the lathe. Worked out nicely. But lacking the lathe I wouldn't have bothered.

You seem also to have a warped barrel, if I'm understanding the wobble on the table thing. I'd put that against a straight edge and get to work correcting the bend, using whatever improvised means come to mind. Sighting down the bore combined with a good straight edge and rolling on a known-flat surface would eventually help in adjusting it to truly straight, using whatever leverage I could put together.

[nervoustrigger]

Indeed, straightening a barrel can be done reasonably easy by hand with the barrel clamped between wood blocks in a bench vise, provided the curvature is over a fairly broad distance.  But it’s also unlikely to affect your group sizes in a meaningful way, just where they land relative to where your scope is pointed. 

[redlined_b16a]

A little update

Played a few hours with the boss.Got the barrel strighter.
Did not measure it but against a stright edge it was about a .050c bend.A slow steady long curve.
The o.d. runout was within .005 thousandths measuring breech midle and muzzle read outs.

I noticed if you look down the barrel o.d. you can see a bunch of hills.The barrel o.d. has about 10 spots ranging from .010"-.022" diffrences in heights.I guess that's part of the fordging process.

Used the drill and brass with lapping compound method.
Barely tightened groups up if any.
35 yards and I tried many diffrent holds.
Best I can do is a 13/16" ctc.
The intresting thing was I tried with no baffles or end cap to eliminate clipping(even though baffles are already clipped)and the group opened to a 1.125" ctc group.
Install baffles in the q.e. and tightened back up.

I think I need to chop off 5/16" off of my barrel to get that damaged land out to rule that out.

Perhaps it is the shooter but my at44 can pull 1/2" ctc at 50 yards

[nervoustrigger]

Sorry if I missed it but try pushing a couple different pellets through from breech to muzzle and see if you catch any rough spots or loose spots.  And at the crown, if you feel any increase in resistance as the head of the pellet emerges, there's a burr.  I think your barrel is choked, so it won't be quite as obvious an an unchoked barrel because you will already be encountering a restriction near the muzzle but if you watch carefully, you can distinguish the difference.  It's pretty easy to raise a burr if you put a little too much pressure when spinning the screw against it...it's the most common problem I see when helping people with the process for the first time.  There's a more comprehensive DIY accurizing article in my signature if you are interested.

[edit]Just re-read and noticed your comment about a damaged land.  Yeah if you can see damage, I agree address that first.[/edit]

[Ribbonstone]

Just to be sure we're taling the same thing here.  Which of the two are we talking about here?

Are barrels that aren't stright along the outside, which willnever run ture (at least unless you straighten them).


Are barrels with a bore that is off-center, that will run a true as can be on the outside, but the bore is well off of dead center.

[redlined_b16a]

I have both a curved barrel that I strightened today

And my bore is not concentric with the barrel o.d.
But that is no longer my concern.The damaged land is now.
I will post up a picture.

[redlined_b16a]

[Ribbonstone]

Not that I wouldn't LIKE the bore to be on-center, but I don't sweat it if it isn't so long as the barrel shoots well.


This one is off center.  Does make an LDC a bit more of a problem, but other than that, the barrel shoots so well I've no plans to replace it.




And if you want to get all "ticky" about it, this RWS 34's bore at the breech  is likely slightly off center too...but it hasn't kept me from shooting it for the last 24 years.




If it makes a rat'srump of difference, I can't proove it.  These aren't firearms, so uneven heating/expansion isn't going to play a part like it would in a powder burner,

I won't condem a crooked outside barrel, or a straight outside/crooked inside barrel until I've shot it.  If it shoots well. I'll leave it alone (as there are many more viusually perfect barrels that won't shoot real well).