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Gunsmithing Did my machinist wreck my barrel?

Mavrykk

Private
Minuteman
May 28, 2020
79
237
Sent my barrel out to get a brake installed and barrel threaded.
It comes back and now shoots 4in groups at 100yard.
Previously was about 1.25in groups with a bone stock factory sako a7 30-06.
But check out the chamfer on the end of the barrel. It looks like he put chamfer there on purpose.
For the life of me I cant recall if it was there before.
Does Any body have a sako a7 barrel to compare this to?
 

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I don't see anything in the picture that would make expect that the gun would shoot that bad. There are many OEM companies that do a chamfer like that at the crown.

My first thought is the scope likely had to be taken off and re-installed in the process of threading. Maybe something didn't back on tight. Check the torque on the rings and mounts.

Also, it looks like you had a brake on it when you shot it. Did you shoot it without the brake on to see if the brake could be the problem?
 
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Once i got it back. It was 7 inches left.
Dialed it in best I could to 0.
Best I could get was about 4in groups.
Took the brake off. And its still shooting like shit.

Also It almost looks like there is a burr edge at the end of the lands.
Although I cant feel anything with my finger nail or little pick i used to check it.
But it sure looks like it in the pic and the little bit of galling on that chamfer looks terrible.
 
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looks like maybe he jacked up the crown, then tried to cut out his mistake, hoping the brake would cover it up and it would shoot ok.
 
Unless you had the barrel shortened, there would be no reason to change the crown area. If done correctly you can thread and time the break without changing that area.
It was not supposed to be shortened.
Plus the face end still looks like it has the factory finish.
 
I'm no gunsmith, but compared to my Vudoo barrel and Krieger/Compass Lake Machine barrel the machining isn't ideal. Crown should be 11* with a very light chamfer at the bore and the section between the barrel and muzzle threads should be slight undercut.

Here's the stock crown on my T3x Varmint in .223. 11* with a slight chamfer.

20190812_190316-L.jpg


Here's the Vudoo.
i-QwmKHcQ-L.jpg


Inspecting with a bore scope may give you some insight. All reassembly methods and optics/ammunition related variables need to be confirmed. If barrel length was changed that could be an issue if the factory barrel blank muzzle length is cut base on a choke point.

I wanted to have my T3x threaded for my .30 cal can but it shoots so good I'm afraid to take the risk. It's a slippery slope.
 
1. That is the typical sako crown . It is unlikely he changed it.
2. This is most likely your scope being loose. Check the base if he took it off, which some lathes may have required.
3. Retorque your action on the stock and see if the barrel is now in touching.
4. Use a Teslong bore scope and check for interior damage.
5. Ask if the barrel was removed from the action - it may not be torqued back on right.
sorry, i guess i am wrong and will defer to you. it just doesn't look like anything factory in my armory. this didn't look right to me.

N14FNKI.jpg
 
That bevel have carbon on it or is it that wonky?

I wonder if barrel had stress in it and the area under the new threads opened up.?
 
Most factory muzzles come with this surface feature. 45 Degree crown or a ball crown is what it’s commonly referred to.

Used to be ground with a crowning ball as it leaves no burr when done right.

The feature you see here that doesn’t look right is probably carbon from the bullet uncorking - it has a non-metallic texture in this picture, but this isn’t a great picture so it could be damage.

Better rifles (custom and semi-custom) typically come with the 11 degree crown shown in the pics above. Many of those also have a small chamfer there to eliminate the burr at the bores edge.
got it.
this is my FN barrel.

pKOvQHd.jpg
 
Possible cause:
Machinist turned the threads between centers. The 60 degree center only contacts the existing 45 degree crown at the smallest point of the taper. That being the lands. The pressure of the center on the small contact point, and threading operation has pushed a small amount of metal into the bore.
Look at the enlarged image theLBC posted. See that line at the junction of the chamfer and the lands? That would be the potential contact point of the center, and the chamfer.
Looking at the photo it looks like there's a tiny lip noticeable on the edge of the land visible on the right hand side of the photo (the enlarged portion). Take a q-tip, put it into the muzzle and pull it back out again, look to see if any spots around the chamfer catch fibers from the q-tip. Take a rigid, but softer than steel tool (brass, copper, plastic) with a sharp edge, and drag it gently from inside the bore out over the chamfer. Feel to see if there is a lip or ridge there.
 
The barrel could have bell mouthed at the muzzel end when the threads were cut which can happen on hammer forged and button rifled barrels and will hurt accuracy.

Montrose
 
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As stated by the delicious Russian drink @Vodak (close enough to vodka), get a cotton tip (q-tip) and insert into the barrel, and hold ona a side and drag it out. It should not catch on any burr or imperfection. If it does, it will hold a little strand of hair and show you were the imperfection is.
 
What Vodak said.
Likely that your machinist ran the muzzle threads with the muzzle pushed into a live center.
That would have been the fastest way for him to set the barrel up and sorta, kinda cut threads that are sorta, kinda concentric with the bore.

I would not count on the Q-tip trick detecting damage even if it is there. If the live center rolled a bit of a disturbance at the edge of the muzzle, it would likely be smooth and semi-uniform enough to evade the Q-tip thing, yet the problem still exists.


Not all machinists are savy to correct handling of rifle barrels.
Not all gunsmiths are savy to correct machining methodology.
Best results come from the proper blend of both disciplines.


./
 
Judging by the last .100" or so.....the barrel has bell mouthed at the end. If you know anyone with precision ground gage pins.....this is an easy check.

I disagree with the "Re-cutting on a live center is bad"...….but you want to use a little grease on the nose of the live center (and use a quality live center....not chicom junk) and I like to take a skim pass before final assembly with a piloted form to leave perfect edges.

Indicating is a great way to make sure you are spot on......but it comes with measuring error. In my opinion and experience their is a big difference in measuring bore run out over a muzzle thread span (approx .600") vs 2" plus when chambering.

If you don't believe me.....take your .0001" indicator (actually .0002+" with 1.5" tip that most use) and solve for pure measuring error across a span of a 26"+ barrel. In this perfect scenario......it is common to get .020+" of bore runout (actually measuring error) at the muzzle end. This scenario also assumes you indicate the bore over the span of the cartridge EXACTLY......which never really happens......the needle always has a slight heartbeat.

And Grizzly rods......that's a whole 'nother story......I use them to get close but that's it. It's like sorting bullet diameters with calipers........

Just my $.02.......but I don't know shit about fuck.

Ern
 
Not enough info on the setup for anything but wide-ranging speculation at this point. As mentioned, nothing stands out from the pic.

You should call him, query him about the setup he used and explain why you're asking- could be caused by an improper setup. Once you know how the work was done, it's sure as hell easier to narrow down the potential sources of the issue (provided, it's due to the machining and not mount, etc as mentioned).

How is the thread fit? Does the brake come to a hard/solid stop at the shoulder ?
 
Once i got it back. It was 7 inches left.
Dialed it in best I could to 0.
Best I could get was about 4in groups.
Took the brake off. And its still shooting like shit.

Also It almost looks like there is a burr edge at the end of the lands.
Although I cant feel anything with my finger nail or little pick i used to check it.
But it sure looks like it in the pic and the little bit of galling on that chamfer looks terrible.
Try a Q-tip to check for a burr
 
Over torquing the barrel and muzzle device can cause issues... have you tried removing the barrel and re-tourquing to spec? I made this mistake on a MTU contour barrel and caused problems with the bullet getting stuck on the lands. Barrel has to have some room to expand when hot. Usually 35# is plenty.
 
...have you tried shooting another lot of ammo?...

Before we go down the route of finding a potential machining problem.... lets first rule out the most likely culprit
 
Over torquing the barrel and muzzle device can cause issues... have you tried removing the barrel and re-tourquing to spec? I made this mistake on a MTU contour barrel and caused problems with the bullet getting stuck on the lands. Barrel has to have some room to expand when hot. Usually 35# is plenty.

Dang, sure is weird that literally every OEM manufacturer torques to over 100 FT-LB and they generally seem to work. Almost like you have no idea what you are talking about and should refrain from giving advice in the gunsmithing sub forum?
 
Crown looks good to me. Probably cut with a center drill. I cut all my own crowns flat and break the edge with a sharp high speed steel center drill. I do 11 degree crowns, recessed crowns of all sorts. I haven’t seen an accuracy difference and I like the way I do it.
I’ve seen guys hack saw off a muzzle with no crown even attempted still shoot.

I torque to 80 lb-ft.
 
Dang, sure is weird that literally every OEM manufacturer torques to over 100 FT-LB and they generally seem to work. Almost like you have no idea what you are talking about and should refrain from giving advice in the gunsmithing sub forum?
Just think about how good a gunsmith I would be if I knew everything like you do. BTW, I don’t worry about OEM manufacturers... just custom builders. You should look at what Short Action Customs, Surgeon and the like do... usually 35lbs and no more than 65lbs, especially with a heavy contour barrel.
 
Dang, sure is weird that literally every OEM manufacturer torques to over 100 FT-LB and they generally seem to work. Almost like you have no idea what you are talking about and should refrain from giving advice in the gunsmithing sub forum?
Which OEM torques 5/8-24 muzzle threads over 100 ftlbs? It’s not a lug nut. Will 100 ftlbs do it, I’m not sure, but you absolutely can constrict a bore by over torquing a muzzle device.

is that the problem here? I doubt it. I also doubt the threads or machining setup is causing the issue. 4 MOA is pretty bad. I think something is loose, but I’ve been wrong before.

To the OP, I’d double check the obvious first to rule our mechanical issues.
 
I would try another lot/brand of ammo?
Is this the same ammo you shot before the threading?
I have one barrel that will do .80 MOA with one brand/load and do 5 MOA with another.
My Gen 1 Sig 716 looks like that for the crown.
 
Sent my barrel out to get a brake installed and barrel threaded.
It comes back and now shoots 4in groups at 100yard.
Previously was about 1.25in groups with a bone stock factory sako a7 30-06.
But check out the chamfer on the end of the barrel. It looks like he put chamfer there on purpose.
For the life of me I cant recall if it was there before.
Does Any body have a sako a7 barrel to compare this to?
That's not a common precision crown. Typically precision crown is around 11 degrees. Reference Sieg's picture posts above. Doesn't look very uniform. ....buggers at 10 and 1 o'clock. Light reflections indicate roughness, lack of precision.
 
986755D9-B45B-413F-9407-CF9B9DDF0072.jpeg
Here is the crown on my a7 roughtech range .308. 290 rounds down the tube.
 
Which OEM torques 5/8-24 muzzle threads over 100 ftlbs? It’s not a lug nut. Will 100 ftlbs do it, I’m not sure, but you absolutely can constrict a bore by over torquing a muzzle device.

is that the problem here? I doubt it. I also doubt the threads or machining setup is causing the issue. 4 MOA is pretty bad. I think something is loose, but I’ve been wrong before.

To the OP, I’d double check the obvious first to rule our mechanical issues.
Dude, you have to read the the post I was quoting. We were talking about receiver to barrel torque.
 
Crown geometry really doesn't matter IME. I've run 0, 11, 13, 25, 45 degree crowns and not seen anything that leads me to believe that one is any better than any other. I've even shot a few 'by the inch' cut-downs and left the barrel face saw cut (cleaned up with a deburr tool) with honestly surprisingly good accuracy.

What I have seen that causes accuracy loss after threading is a poorly stress relieved barrel that trumpets when you remove material. I would find someone with gauge pins and see if one that's .001" over land diameter (i.e. if it's a .308, a .301" gauge pin. If it's a 6.5mm a .257 or .258" pin) will fit about 1/4-1/2" into the muzzle then stop.

If that's the case, it's the barrel maker, not your machinist/GS.
 
Just think about how good a gunsmith I would be if I knew everything like you do. BTW, I don’t worry about OEM manufacturers... just custom builders. You should look at what Short Action Customs, Surgeon and the like do... usually 35lbs and no more than 65lbs, especially with a heavy contour barrel.

This is a tangent but what you're talking about doesn't matter in a practical sense. LRI torques everything to 100 ft-lb. Some guys go 25, some 35, some 50, some 75. They all shoot. If it was an industrial use for a 1.063x 16 or 20 tpi bolt, it would certainly be torqued into the hundreds of ft-lb (apples and oranges to this application, but the point I'm getting at is you're not distorting anything at 100ft-lb).

If you cut headspace exactly to the GO gauge with it hand tight on the lathe, you will lose .001-.002" when you torque it up. It's on the GS to make it correct when everything is assembled. If you're that close to the lands that a little extra torque causes you to jam, you're too close to the lands IMO. Heat in the barrel makes it expand (I.D. and O.D.) so you should have more room not less.
 
Not that it pertains to the OP......just wanted to clarify the above posting with a "crush" range. I simply like to state that "crush" is a direct reflection of surface finish. If you finish the shoulders like a vinyl record......then you will get X number of "crush"......the more smooth the surfaces are....the less "crush".

Ern
 
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Crown geometry really doesn't matter IME. I've run 0, 11, 13, 25, 45 degree crowns and not seen anything that leads me to believe that one is any better than any other. I've even shot a few 'by the inch' cut-downs and left the barrel face saw cut (cleaned up with a deburr tool) with honestly surprisingly good accuracy.
Rifleshooter.com did exactly that and they were getting on average 1 MOA with several sub-MOA groups with even the jankiest of crowns


Crowns are a lot lesson important than the gun community tend to thinks they are
 
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Crown geometry really doesn't matter IME. I've run 0, 11, 13, 25, 45 degree crowns and not seen anything that leads me to believe that one is any better than any other. I've even shot a few 'by the inch' cut-downs and left the barrel face saw cut (cleaned up with a deburr tool) with honestly surprisingly good accuracy.

What I have seen that causes accuracy loss after threading is a poorly stress relieved barrel that trumpets when you remove material. I would find someone with gauge pins and see if one that's .001" over land diameter (i.e. if it's a .308, a .301" gauge pin. If it's a 6.5mm a .257 or .258" pin) will fit about 1/4-1/2" into the muzzle then stop.

If that's the case, it's the barrel maker, not your machinist/GS.
That’s my suspicion.
 
The size of that chamfer is IMO excessive and looks galled unless that's some carbon buildup. Look at the first 1/2" of lands to see if there are concentric tool marks as if he used one of those solid pilot chamfer tools vs. a turning tool. Concept of stress relieving and getting bell mouthed is interesting.
 
You can tell pretty clearly the crown is off center...
 
You can tell pretty clearly the crown is off center...
I think you are seeing the threads that make it appear off center. Then again I dont have the rifle in hand so cant see it.
I ASSuME it's either slight bell mouth or has had the lands deformed from a live center.
 
So what was the outcome on this?

I don't recall seeing what the thread size is nor what caliber it is. Not that it would make any significant difference other than this...

Is indicated above, when you thread a barrel and remove material the mouth can Bell out. This isn't a function of the barrel maker nor the gunsmith. That material that was removed previously was basically holding that Barrel bore parallel. Does it affect accuracy? Absolutely not. Will it make a difference between what load you can develop today versus the load that you had previously developed ... probably.

The good thing is that it's really easy to fix. If you have your appropriate gauges you can simply torque your muzzle brake to push it back in parallel.

That said, I seriously doubt that's the issue. But it seems on so many of these shooting forums there's an excuse for everything...so, maybe.

Personally I think if the barrel was separated from the action that it wasn't properly indexed / torqued properly when reinstalled.

Or, maybe it needs to be renowned.

Could be a harmonic issue. Since you remove material and threaded the barrel, the natural harmonic is different. Very well could have changed that accuracy mode you previously found.

There is one other thing to consider... Squirrel Factor. I was in the process of typing this, realized I needed to fill the water bottle, cat jumped up on the couch, listening to how the state's got their name... Now I have no fucken clue as to what else I was going to say.
 
If it's harmonic, you can experiment with retuning it to shoot the required load.

Wind several turns of copper electrical wire (jnsulated/uninsulated, it doesn't matter; it's the weight we're concerned with here) around the muzzle end. Begin trimming the wire and shooting, while keeping track of dispersion.

When you get to where it begins to open up again; stop, take the last piece you had cut off and halve it. Then mark the front and rear lines where the copper wire rides with masking tape, and weigh one of the halved pieces along with the remaining coils. A reloading scale would be good for this.

Go to the auto parts store and buy some stick-on wheel weights. Trim one down to where its weight is identical to the wire weight. Stick it to the bottom of the barrel, centered between the two masking tape lines. If it still shoots true, remove it and epoxy it in place.

This should return your barrel to tune.

Me, I'd wait until I had permanently mounted the brake first.

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Once, I built a wooden balance beam scale for measuring rubber powered indoor free flight model aircraft and parts. Many of these entire planes weighed as little as 2 grams. The beam was made of balsa and was two feet long, The balance weights were made by balancing 1 cc of water against a length of fine copper wire, deriving a 1 gram weight. Cut maybe ten more, same length. Take a couple and cut the wire in half, 1/2 gram, in quarters, .25gm, and so on down to about .0125 gm.

These planes were flown for duration indoors, some managing over 30 minutes. My daughter set a National Youth Penny Plane (must weigh more than one penny) duration record at age 17. Not easy, but the real competition was among the bearded old guys who had been doing this same thing for decades. We flew in The Columbia University Lowe Memorial Rotunda on Morningside Heights, in Manhattan, for one Sunday a month. The Rotunda was 80 ft across, hexagonal, and 105 ft tall. I sponsored the Bill Tyler Memorial Trophy for Manhattan Cabin designs (basically an ROG - 'Rise Off Ground' Penny Plane with a Cabin Fuselage).

The strategy was to build successive versions of the same plane design, while incrementally building each major component a bit lighter in weight each time. Eventually parts failed. You'd then build the next one using A) the previous part that didn't fail, and B) the other parts built a bit lighter. Eventually you had your competition plane, because anything lighter would fall apart. They flew at a slow walking speed.

You can't stand up and watch the longer lights, your neck cramps up on you. We'd all bring a pillow and lie back flat on the floor to watch. The sport has been going on for a large several score years, and is still going strong; although venues are disappearing. We lost Columbia in the '80's or early '90's due to Nanny liability caution.

Something for the real addicts...; they are just prototype testing, and are only winding the rubber part way That fuselage motor stick is a tube rolled up around a mandrel from balsa wood sanded down to about 1/64", or less. If you can't read newsprint through it, the balsa sheet is too heavy.

There's a bit more to my world than just the guns...

Greg
 
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A live center in the muzzle can cause that. Lots of gunsmiths thread that way with no regard. Some fix it afterwards with a cleanup pass on the crown, some dont. But that requires proper indexing of the barrel. And if they threaded it with a live center, they probably arent going to dial it in for the crown either and will just use a 3-jaw :cry: .

As already said, do the q-tip trick. Also look and see if the rifling is flattened at the very end from the pressure of the live center.

(Also try shooting it with no muzzle device and check the group. Sometimes it the brake)