Barrel indicating Question

S

Steve_Webb

Guest
Greetings

I have seen this 2 times now on custom barrels same manufacturer different calibers. With indicating in a barrel to chamber and crown. My question is when ever indicating in a barrel reading the test gauge. Do you go off of the lands or grooves? 2 barrels I have seen this that there are .0004 to .0006 difference in concentricity between the 2 surfaces.

I'm Confused

Thanks
Steve
 
There are a couple of schools of thought on this. I indicate the grooves at the muzzle and the lands at the throat area. I use a close fitting pilot, so I want to keep my chamber as straight as possible. There are some well known smiths that advocate indicating the grooves at the throat area and using a slightly loose pilot bushing to allow the reamer to follow the pre- bored chamber and stay straight. Either method assumes that you are going to pre bore the chamber so the reamer has a perfectly straight hole to follow and not much metal to remove. I use Krieger or Bartlien barrels for my BR guns and I don't see any significant variance in concentricity with them. With other button rifled blanks, a little difference from the land diameter to the bore is pretty common.

The last time I participated in this discussion, I became convinced that the loose pilot-indicate grooves setup was worth a try, so I plan to use it next time I come across a barrel with some concentricity error.
 
IMO, on the chambering operation indicate the lands. I start there then drill and pre-bore. The reamer pilot tracks the lands. This makes the leade ramps even and lessens the chance of the bullet starting with in-bore yaw. This is particularly important with high ogive bullets like VLD's.

On the muzzle,especially if you are going to put any bevel, indicate the grooves since that is the last thing the bullet sees.
 
SGS said:
There are a couple of schools of thought on this. I indicate the grooves at the muzzle and the lands at the throat area. I use a close fitting pilot, so I want to keep my chamber as straight as possible. There are some well known smiths that advocate indicating the grooves at the throat area and using a slightly loose pilot bushing to allow the reamer to follow the pre- bored chamber and stay straight. Either method assumes that you are going to pre bore the chamber so the reamer has a perfectly straight hole to follow and not much metal to remove. I use Krieger or Bartlien barrels for my BR guns and I don't see any significant variance in concentricity with them. With other button rifled blanks, a little difference from the land diameter to the bore is pretty common.

The last time I participated in this discussion, I became convinced that the loose pilot-indicate grooves setup was worth a try, so I plan to use it next time I come across a barrel with some concentricity error.
Click to expand...

If you start to get a squeal, may I suggest you go to a tighter bushing before it turns into chatter..... saves heartache :)
 
Where the confusion came into play was. That the bullet I figured would follow more of the land bore diameter and the pilot of the reamer would follow the groove diameter.
Both of the rifles shot really well.

But me over thinking makes my head hurt sometimes.
On one barrel indicating across the land diameter it was a like .0003 to .0004 from edge of groove to edge of groove all of them were relatively symmetrical. But it was still making my head hurt more. Knowing I have egg shaped bullets flying thru the air.

Thanks

Steve
 
Steve_Webb said:
Where the confusion came into play was. That the bullet I figured would follow more of the land bore diameter and the pilot of the reamer would follow the groove diameter.
Both of the rifles shot really well.

Steve
Click to expand...

Steve, the bullet has to follow the grooves and the reamer pilot has to follow the lands.
 
Last May we had this discussion about the subject:


http://http://benchrest.com/showthread.php?86591-chamber-runout-issues&highlight=indicating+barrel

It goes to show that there is some support for the indicate grooves-loose pilot strategy. I haven't tried it yet, and Al's caution is one thing that has concerned me. I haven't experienced but one case of reamer chatter, and it is definitely a pain. Still, the guys advocating in favor of indicating the lands build some winning rifles. I don't have much personal experience to influence my opinion because I have not chambered any BR barrels that had much runout from lands to grooves.
 
If I have a BR barrel in which the lands and grooves are not co-axial, the mail truck travels both ways. When I buy a select match barrel, I like to think it will be one. Regards, Bill.
 
Bill Leeper said:
If I have a BR barrel in which the lands and grooves are not co-axial, the mail truck travels both ways. When I buy a select match barrel, I like to think it will be one. Regards, Bill.
Click to expand...

Bill, I agree 100% but it makes me feel good to do something for a reason, even though that reason may be very shallow.
 
Steve_Webb said:
Where the confusion came into play was. That the bullet I figured would follow more of the land bore diameter and the pilot of the reamer would follow the groove diameter.
Both of the rifles shot really well.

But me over thinking makes my head hurt sometimes.
On one barrel indicating across the land diameter it was a like .0003 to .0004 from edge of groove to edge of groove all of them were relatively symmetrical. But it was still making my head hurt more. Knowing I have egg shaped bullets flying thru the air.

Thanks

Steve
Click to expand...

Steve are you saying you have a different height, indicator reading, on top of each land? I have seen that over and over again with button rifled barrels. I pick one edge, leading or trailing to indicate off of. I've seen them with a .001" spike on one edge before. All shot just fine.

Dave
 
I'll go one step further.....while I normally set up dedicated long range barrels by the Gordy method it definitely is extra work so most of the time on hunting and short range stuff my procedure is to turn the muzzle to fit pre machined bushings that slide up in the spindle and indicate just the throat area and pre bore the chamber. This leaves one problem, even after that, especially on long cases there is still enough original bore between the end of the pre drill and the throat to have a short area that is not concentric. I have had great luck reaming with no pilot until the very end and when the pilot area is in the indicated area I will put the pilot on the reamer and finish. I use a dead center Gre Tan holder and if I push a reamer with a snug fitting pilot through that short non indicated area I'll get runout from the neck back in the chamber. I know everyone will say use a floating holder or pusher but my method works and I like having both hands free. Never have a problem with chatter reaming without a pilot.
 
ndh78 said:
I'll go one step further.....while I normally set up dedicated long range barrels by the Gordy method it definitely is extra work so most of the time on hunting and short range stuff my procedure is to turn the muzzle to fit pre machined bushings that slide up in the spindle and indicate just the throat area and pre bore the chamber. This leaves one problem, even after that, especially on long cases there is still enough original bore between the end of the pre drill and the throat to have a short area that is not concentric. I have had great luck reaming with no pilot until the very end and when the pilot area is in the indicated area I will put the pilot on the reamer and finish. I use a dead center Gre Tan holder and if I push a reamer with a snug fitting pilot through that short non indicated area I'll get runout from the neck back in the chamber. I know everyone will say use a floating holder or pusher but my method works and I like having both hands free. Never have a problem with chatter reaming without a pilot.
Click to expand...


You are getting barrels with that much curve in the breech??
 
Dave Tooley said:
Steve are you saying you have a different height, indicator reading, on top of each land? I have seen that over and over again with button rifled barrels. I pick one edge, leading or trailing to indicate off of. I've seen them with a .001" spike on one edge before. All shot just fine.

Dave
Click to expand...

Dave,

This one barrel a 6.5 caliber 8 twist After getting the breech and muzzle indicated in as close to true as possible. Indicating from the edge of the groove rotated slowly to the next edge of groove. I seen like .0003 to .0004 variation in the diameter. Being largest in the center of the groove. In other words the bore was Egg shaped. The only thing I figured it was from Either the Button being worn slightly or the lapping process to get the desired finish in it. or a combination of both. Looking at it with a bore scope I couldn't see anything obvious. Not that I would have known what to look for in the beginning. LOL and at that time taking readings on the lands it was not concentric with the groove diameter. On both ends. Hopefully that makes sense.

I have polished a lot of bores and journal diameters in my life and it is always the hardest getting the diameter next to a shoulder to polish in to size. I just figured that was what it was.

This is the 2nd custom barrel I have machined on. I just would have assumed it would have been closer to being round and concentric. I know with the equipment I have at my disposal It would take me a couple months to build a barrel from scratch and then I still don't think I would feel safe shooting it. I also know it wouldn't be straight So I guess It was near perfect for what I could make on my own.


I am no professional gunsmith by no means. I just tinker with them for my own consumption. But i have worked in the metal machining industry for over 30 years. Mostly oilfield type stuff. surface, sub surface and stuff that went in the ocean. Also I have done tool and die, valve industry, areo space, semiconductor cleaning equipment, automotive, machine tool repair. 2 3 4 & 5 axis programming and machining, rock quarry, mining, hydraulics to name some of the stuff i have done in this industry. I ran the 2nd largest surface grinder in the world or according to the guy I was working for at the time Mike Daniluk back in the mid 90's a 21' x 7' table. The column height was about 7 ft and 9 ft in between. This was a hair pulling experience indicating in a 3 surfaced bedway 6 feet wide and 20 feet long. The top had to be indicated in within .0002 all 3 surfaces entire length. and running down the side within .0005 it took us a day and a half to get it indicated in running 3 shifts. We had 6 sections that bolted together making a 120 ft long bed that we had to match grind to each other.


Back on topic it shoots fine it does what it was intended to do thank you all for your replys
 
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