Why do we get fanatical over barrel alignment?

[X Count]

Couple of things I ponder late at night. I'm planning on changing from using gritters rods to direct indicating .

Why do you dial in the groove when the reamer is aligned by the bush riding on the lands. In a cut rifle barrel at least the top of the land was drilled and honed and measured round before the grooves went in.

We worry so much about dialling in the throat and in front of the throat, pre boring to ensure everything is straight and aligned to virtually zero yet most would say the runout of loaded ammo has little effect on final accuracy. Both chamber to bore runout and loaded round to bore runout effectively cause a bullet be misaligned with the start of the bore

I'm not trying to be a smart a$$ or looking for an argument but these things seem to contradict the intent to get everything in perfect alignment.

 

[Rockchuck]

In short its because we want everything to be straight and true with the center of the bore right where everything starts. Kind of simple when you think about it. Why you would want that. Just not so simple to get there.

 

[clowdis]

Don't get me started!!

 

[LVLAaron]

We worry so much about dialling in the throat and in front of the throat, pre boring to ensure everything is straight and aligned to virtually zero yet most would say the runout of loaded ammo has little effect on final accuracy. Both chamber to bore runout and loaded round to bore runout effectively cause a bullet be misaligned with the start of the bore

If you do all of that, and do it well, your pilot isn't guiding much of anything. I had to do a chamber with no pilot because it was one of bartleins .299 underbore barrels. Chamber was as concentric as one could measure, gun shoots bugholes... I believe if the setup is good, the pilot shouldn't do anything.


The pilot has clearance on the ID and OD. So to your first point, on a quality barrel I doubt the lands/grooves are more misaligned than those pilot clearances... hope that makes sense.

 

[6bra1k]

you be looking at it all wrong,
we are not fanatical about bbl alignment.
we are fanatical about throat alignment with the bore.
the bullet needs to start straight, not off set.
using a bushing MAY cause the reamer to move wallow just as the bore actually does.
dial in the throat, drill, taper to match the reamer, check it all and let the reamer follow your taper which is pointed at the throat.

 

[X Count]

If you do all of that, and do it well, your pilot isn't guiding much of anything. I had to do a chamber with no pilot because it was one of bartleins .299 underbore barrels. Chamber was as concentric as one could measure, gun shoots bugholes... I believe if the setup is good, the pilot shouldn't do anything.


The pilot has clearance on the ID and OD. So to your first point, on a quality barrel I doubt the lands/grooves are more misaligned than those pilot clearances... hope that makes sense.

Pilot clearance is why I'm looking to move away from using rods so I understand your point.

 

[jkohler]

I don’t even use pilots anymore. Just drill and bore to my dialed in throat get the reamer started about .250 or so in to the chamber pushing with a dead center then switch to my pusher. Chambers have came out nice and on size. I still use a Gordy rod to get the throat roughed in then go to direct reading

 

[FireMedic]

If you do all of that, and do it well, your pilot isn't guiding much of anything. I had to do a chamber with no pilot because it was one of bartleins .299 underbore barrels. Chamber was as concentric as one could measure, gun shoots bugholes... I believe if the setup is good, the pilot shouldn't do anything.


The pilot has clearance on the ID and OD. So to your first point, on a quality barrel I doubt the lands/grooves are more misaligned than those pilot clearances... hope that makes sense.

Unless it’s a 5R….lol

Sorry I couldn’t resist!

 

[X Count]

you be looking at it all wrong,
we are not fanatical about bbl alignment.
we are fanatical about throat alignment with the bore.
the bullet needs to start straight, not off set.
using a bushing MAY cause the reamer to move wallow just as the bore actually does.
dial in the throat, drill, taper to match the reamer, check it all and let the reamer follow your taper which is pointed at the throat.

So why does throat and bore alignment matter significantly more than loaded round to throat alignment? Both things seem to be directly related to getting the bullet heading down the barrel and spinning about its axis correctly

 

[X Count]

I don’t even use pilots anymore. Just drill and bore to my dialed in throat get the reamer started about .250 or so in to the chamber pushing with a dead center then switch to my pusher. Chambers have came out nice and on size. I still use a Gordy rod to get the throat roughed in then go to direct reading

If your using a dead centre to get the first .250 started are you boring parallel and if so how much under shoulder diameter are you going?

 

[jkohler]

I go for .015 under shoulder diameter then step bore in enough to get the reamer started. I use the dead center for supporting the reamer tell its cutting good and have never had a problem with chatter doing it that way so far. I do check my tail stock for alignment often also.

 

[LVLAaron]

Unless it’s a 5R….lol

Sorry I couldn’t resist!

Don't tell anyone, but that particular barrel was a 5R. I pre-bore the lands out as far as I can... and it was a carbide reamer, so... no biggie.

 

[LVLAaron]

Pilot clearance is why I'm looking to move away from using rods so I understand your point.

I use grizzly/gordy rods on long cartridges. You can take up the slack in the pilot fit by hanging something on the rod (I use a 1 dollar spring clamp from home depot) - Hang the weight near the barrel, put your indicator between the weight and barrel.

I'm nobody but I do that, then compare by directly indicating on the bore and... at least with the couple barrels I've done that on see MAYBE a tenth difference. Maybe.

 

[B Nettesheim]

The groove is what the bullet is going to follow, another thing to watch for when dialing it in is an eccentric bore

 

[tobnpr]

Pilot clearance is why I'm looking to move away from using rods so I understand your point.

For me, the Grizzly rod is by far faster for getting dialed in initially. I intentionally use a somewhat undersized pilot, and suspend a small weight from the rod to ensure the pilot rides only on the bottom grooves as they rotate around it. When I've got it as close as I can to zero, I'll check with the Interapid. Most of the time, I don't need to go any further.

 

[Alex Wheeler]

So why does throat and bore alignment matter significantly more than loaded round to throat alignment? Both things seem to be directly related to getting the bullet heading down the barrel and spinning about its axis correctly

Because a loaded round, once in the chamber can only be off the center of the lands or grooves by the amount the freebore diameter will allow. Usually less than .0005. But only if the throat is aligned with the lands or grooves, depending on which you choose to dial in. In a competition rifle everything matters. You can get lucky with sloppy work from time to time. But there are other guys out there your competing with that are doing everything in their control to produce the best work possible. At the end of the day it comes down to what the customers needs are and what your charging. For a 200 dollar chamber job I wouldnt expect the best work, for 400 I would. There is room, and a need for different levels of chambering.

 

[INTJ]

I use grizzly/gordy rods on long cartridges. You can take up the slack in the pilot fit by hanging something on the rod (I use a 1 dollar spring clamp from home depot) - Hang the weight near the barrel, put your indicator between the weight and barrel.

I'm nobody but I do that, then compare by directly indicating on the bore and... at least with the couple barrels I've done that on see MAYBE a tenth difference. Maybe.

You can use one of these for long chambers.

Extra Long Interapid Indicator Contact Point

5.5

www.longislandindicator.com

 

[LVLAaron]

You can use one of these for long chambers.

Extra Long Interapid Indicator Contact Point

5.5

www.longislandindicator.com

Ordered one. I was actually looking for one this morning. The mity isn't cutting it on longer chambers.

 

[jackieschmidt]

The OP kinda answered his own inquiry in his last sentence.

Just as in any precision work, we strive to eliminate the variables over which we have control.

 

[Carl S]

If you're fitting a new barrel for a customer or yourself why wouldn't you want to set it up correctly and cut the most concentric-true chamber as can be.if you do you're bit correctly and the barrel don't shoot that's not you're fault.i did a 30-06 last week customer supplied barrel blank and solid piloted reamer.the reamer pilot was like a dick in a shirt sleeve in the bore.i set barrel up in the lathe dialed in the muzzle and throat.cut and threaded tennon,prebored and cut chamber head spaced all done.from throat to rear of chamber may be two tenths run out.customer watched process from start to finish..he always does.that barrel now has every chance of being a good shooter.