How to Avoid Getting a Crooked Barrel??

[daved]

During the course of a recent build, my smith told me that the barrel I had sent him (from a major manufacturer with an excellent rep) was "crooked" - basically not concentric with the bore - at the point he was fitting a brake and thread protector. He explained that this was due to the barrel flexing during turning and was a common problem that didn't affect accuracy. My barrel, however, was more "crooked" than most and this caused difficulty when trying to fit a muzzle device - he could ensure that the device was concentric with the bore but it would not blend in smoothly to the barrel without sanding and shaping the device and end of the barrel. Even then, he cold not knurl the thread protector because of the problem.

I was curious as to whether others with more experience had run into this problem, and more importantly, how I might avoid it in future barrel purchases. Specifically, is it worth ordering a custom barrel to the correct finished length from the manufacturer rather than buying one finished to a longer length from a retailer?

Thanks for any input--

Dave

 

[HodgdonExtreme]

Hopefully a barrelmaker like Frank Green or Shawn Burkholder will jump in here and correct me if I'm wrong, but I'll take a stab at this:

To make a barrel, barstock is put into a lathe and turned, so the OD of the bar is now running true to the spindle of the lathe. Then they rough drill the bore. If the bar wasn't turned true prior to drilling, the drill would REALLY wander, but nonetheless, I think it's nearly impossible to consistently drill a truly straight hole ~.25" in diameter, 30" deep.

So, most EVERY barrel is going to exhibit some degree of non-concentricity between the bore and the OD of the barrel. That is not to say there is anything "wrong" with the barrel, and it doesn't mean it won't shoot great.

What it does mean, however, is the gunsmith will have to use some trickery to get muzzle devices (which have been correctly indicated true to the BORE) to neatly mate up with the OD of the barrel at the muzzle.

It also makes it best practice to time the barrel to the receiver so the crookedness of the barrel itself (think bananna) is pointed directly up. That will make the barrel fit the barrel channel in the stock more neatly and evenly, and probably also gives us long range shooters a little extra "free elevation travel", if you know what I mean.

 

[Edds]

You should order the barrel as close to the finished length as possible. Cutting the barrel off can make it less concentric. He should still be able to blend them but it will require him to indicate the barrel twice. He would indicate the bore to thread it and then indicate the barrel od to blend it.

 

[T2CH]

Hopefully a barrelmaker like Frank Green or Shawn Burkholder will jump in here and correct me if I'm wrong, but I'll take a stab at this:

To make a barrel, barstock is put into a lathe and turned, so the OD of the bar is now running true to the spindle of the lathe. Then they rough drill the bore. If the bar wasn't turned true prior to drilling, the drill would REALLY wander, but nonetheless, I think it's nearly impossible to consistently drill a truly straight hole ~.25" in diameter, 30" deep.

.

This is how I understand it as well but when the final contour is cut that is when the bore should become centered (or as close as possible) to the OD of the barrel.

To OP: Seems to me your smith should have seen this when he chambered the barrel. Or was the chamber cut prior to your smith receiving the barrel?

 

[trigger29]

Hopefully a barrelmaker like Frank Green or Shawn Burkholder will jump in here and correct me if I'm wrong, but I'll take a stab at this:

To make a barrel, barstock is put into a lathe and turned, so the OD of the bar is now running true to the spindle of the lathe. Then they rough drill the bore. If the bar wasn't turned true prior to drilling, the drill would REALLY wander, but nonetheless, I think it's nearly impossible to consistently drill a truly straight hole ~.25" in diameter, 30" deep.

So, most EVERY barrel is going to exhibit some degree of non-concentricity between the bore and the OD of the barrel. .

Well, I'm not a barrel maker, but I do machine parts. I'll take a stab at it too. If it were me, I'd gun drill it first, because the drill will wander. When it was time to contour the barrel, I'd contour it between centers to center the bore in the contour. Now this may not center the hole perfectly all the way through, but it should be very close at the ends. I think this is why if you order a blank as close to the finished length as possible, the bore is very close to concentric with the outside profile. If you cut off a bunch, you get further from the center, that it was turned on, and the drill wandering effect is more noticeable. I just threaded a Bartlein 5R MTU contour finished at 28" that started as a 29" blank, and it was concentric to less than .001"Was able to get a brake, and a thread protector to blend to where you can't see the seam on either one very easily.

 

[AK-Bandit]

So what did the smith say he was going to do? Does one just shitcan the barrel at that point? I've been a little worried about this because I'm having a rifle put together with a 30" heavy palma contour barrel that's cut down to 26".

Kind of unrelated, but I found a cool video a couple months back showing Krieger's cut rifling process.

https://www.youtube.com/watch?v=aLUTL5S6yFE

 

[Bill Larson]

most barrels bores are nor perfectly straight........ o.d. of bore also not being concentric with o.d. of barrel......COMMON....to get a M.brake,silencer or thread protector to look good... it requires 2 set-ups.... 1-to machine o.d...and another to bore the clearance hole the bullets exits....with bore...
H.S.machine shop.stuff

 

[alphadogg56]

Thanks for that video I have a krieger 338 barrel that came 29 in being cut to 28 also at Accurate Ordnance being threaded for a 5 port pain killer hope all goes well.learned a lot from that video,I'd hate to have that problem.

 

[Frank Green]

Hopefully a barrelmaker like Frank Green or Shawn Burkholder will jump in here and correct me if I'm wrong, but I'll take a stab at this:

To make a barrel, barstock is put into a lathe and turned, so the OD of the bar is now running true to the spindle of the lathe. Then they rough drill the bore. If the bar wasn't turned true prior to drilling, the drill would REALLY wander, but nonetheless, I think it's nearly impossible to consistently drill a truly straight hole ~.25" in diameter, 30" deep.

So, most EVERY barrel is going to exhibit some degree of non-concentricity between the bore and the OD of the barrel. That is not to say there is anything "wrong" with the barrel, and it doesn't mean it won't shoot great.

What it does mean, however, is the gunsmith will have to use some trickery to get muzzle devices (which have been correctly indicated true to the BORE) to neatly mate up with the OD of the barrel at the muzzle.

It also makes it best practice to time the barrel to the receiver so the crookedness of the barrel itself (think bananna) is pointed directly up. That will make the barrel fit the barrel channel in the stock more neatly and evenly, and probably also gives us long range shooters a little extra "free elevation travel", if you know what I mean.

You are correct....it's nearly impossible to drill a perfectly straight hole for a lack of general discussion but there are also manufacturing methods during the making of a gun barrel that helps with drill run out, the bore run out to the o.d. of the finished barrel etc...and not all barrel makers take the extra steps to make a barrel that has the least amount of run out. Some barrel makers take short cuts because they feel this or that operation or set up takes an extra 3-5 min. and it's costing them money! In the end they're short cuts actually will cost them money.

If memory serves me correctly gun drilling a piece of material weather it's for a gun barrel or anything else a normal industry standard is .001" drill run out per inch length of the piece you are drilling. Not everyone weather it be a custom barrel maker or big gun manufacturer will hold to that. To a lot of places time is money.

I just checked our .30cal. set up for gun drilling. We are averaging .015" or less drill run out on the exit end of the barrel blank and this for 32" blanks that we are drilling right now. Do the math.....that is less than .0005" drill run out per inch. We know that if that .30cal. drill set up starts giving us more than .015" run out the drill needs resharpening or the drill guide bushing needs to be changed out for a new one etc....

The bar of steel is not perfectly straight or perfectly round to begin with. Depending on the barrel contour we will rough turn the barrel/take a clean up cut on the blank etc...before gun drilling it. After it's gun drilled we will cut a center on the ends of the blank and pilot off of the drilled hole. We have to buy special pilots/bushings for the tools to fit our drill sizes. They are not standard so we pay extra money for all of those bushings. After we cut a center then the barrel goes into the lathe and it will get finish turned. A lot of places skip this step or you will find they're set up for cutting the center is not a good set up. If they're set up is not good or they skip it all together than when the barrel is put in the lathe and weather it's not turned between centers or it is (everyone does it differently) they're set up can induce even more run out into the barrel blank.

The better we can make it the better the overall product. The easier it is for the gunsmith to do the install and finish work like muzzle brakes etc....the old saying holds true, "You get what you pay for!"

Later, Frank
Bartlein Barrels

 

[Frank Green]

Also the gunsmith that is doing the work on your installation of your barrel. His lathe has to be properly set up as well. Any error in alignment with the tail stock/centers etc....can effect the run out and the work performed on the barrel. We're only one part of it.

Later, Frank
Bartlein Barrels

 

[daved]

Thanks for all the comments.

-The barrel was contoured to med Palma specs and finished at 30" by the manufacturer.
-The smith chambered the barrel first, cut it for a 24" final length, then threaded the barrel and fitted the brake and thread protector. That's when the lack of concentricity became apparent.
-Cutting the barrel short of its finished length seems to be a factor - as you get farther away from the ends, concentricity increases. So ordering a barrel finished by the manufacturer to the final length should minimize the lack of concentricity, at least at the muzzle.
-The smith did an exceptional job fitting the brake - it obviously required more work but the result is good.
-I haven't checked the thread protector that he also fitted - but its function is only to protect the threads so no biggy.
-Since the lack of concentricity apparently doesn't affect accuracy, and he could fix the disparity with a little extra work = no need to trash/exchange the barrel. Not certain that contacting the manufacturer might not have been a good idea. The smith didn't mention it and I trust his expertise. I'll probably give them a call just for curiosity.
-As far as "you get what you pay for", both the manufacturer and smith are top line. If I didn't get what I paid for, it wasn't because either was less than top quality.

Thanks again,

Dave

 

[Frank Green]

Daved, kinda take a little grain of salt with what I said with you get what you pay for. What I was referring to there was some guys say I can get a barrel for $150......etc....that's what I was referring to. The cheaper the barrel usually the poorer the bore finish, overall quality etc....

Yes if you take a 30" barrel and cut 6" off it and don't know of a single barrel maker that will guarantee/can guarantee you won't find that it might have more run out at that cut section etc....the drill can wonder and come back etc...it's hard to control. Also how the barrel makers does the contouring like you mentioned in your original post, that during the contouring depending on how it's done can cause that as well.

Later, Frank