Why do we get fanatical over barrel alignment?

[INTJ]

Well... Why wouldn't the throat be straight?

If you're indicating the throat, and an inch foward, the breech end becomes unknown. You pre-bore to solve the potential issue you're talking about. It's to get the body aligned perfect to what you've dialed in for the throat.

If you're letting the pilot take your reamer for a walk, you'll end up with oversized or oval chambers.

If your reamer would have been in a bind due to your concern, it would also be in a bind without the pre-bore.


I started boring with a "TS-C06K-SCLCR06" tiny carbide bar. I use the polished inserts made for aluminum. They take light/finish cuts in stainless and leave a gorgeous finish.


View attachment 1370723

It's not that the throat isn't straight. It's the back end of the chamber that might not be. Yes I understand that when we prebore after drilling--assuming no deflection of the boring bar--the hole we bored is aligned with the spindle.

However, if we don't also dial in the back part of the chamber, then it's very possible that while the throat is straight that the back of the chamber is running out. In fact, the entire back of the chamber up to the throat is running out.

After preboring we have the prebored part running true, a potential area of some runout, and then a true throat. We are hoping that part running out won't influence the reamer. However, if the pilot happens engage the area before the throat that is running out, vs the actual throat, there is misalignment and potential issues.

My method is to dial from near the back of the chamber to a little in front of the throat. That way that 2-3" of bore is running true to the spindle. Then when I cut the chamber the pilot is is staying in the true part of the bore. The hole the reamer is making--using a floating reamer holder--is fully supported and also true to the bore. I think this is a better way of chambering--at least right now. I may change my mind later. If were to prebore I'd still dial in the same way, but based on how I dial in I see no advantage to preboring, but do see possible issues.

Again, don't get too wrapped up in this. We are talking theory here. In actual practice the differences are so minimal that it really doesn't matter. Crud, dialing in the breech and muzzle with range rods and then cutting the chamber has produced a lot of very accurate barrels....

 

[LVLAaron]

Totally respectfully, disagree.

Let's just talk about the chamber and throat. Forget about any dialing in front of the throat for simplicity.

You put the throat area where your jaws are and you get that running dead nuts. Now you pre-bore a section of the chamber. Doesn't matter if there's boring bar deflection. It will deflect the same all the way around. All that matters is that it's centered, and it is.

So how is the back of the chamber running out?

"However, if the pilot happens engage the area before the throat that is running out, vs the actual throat, there is misalignment and potential issues."

If you pre-bore, there's slim chance of that. I pre-drill- and run the indicator in, so my furthest spot towards the breech where the pilot will engage, is centered. Pilot entrance = dead nuts. Pre-bored body = dead nuts. Nothing wanders.

 

[Dusty Stevens]

Right, But dragging a button through it may change it, The cut rifled barrel shouldn't touch the land? I'm not arguing either method, I have both types and they all shoot good.

You ever seen a savage barrel inside? Those buttons dont iron nothin

 

[INTJ]

Totally respectfully, disagree.

Let's just talk about the chamber and throat. Forget about any dialing in front of the throat for simplicity.

You put the throat area where your jaws are and you get that running dead nuts. Now you pre-bore a section of the chamber. Doesn't matter if there's boring bar deflection. It will deflect the same all the way around. All that matters is that it's centered, and it is.

So how is the back of the chamber running out?

"However, if the pilot happens engage the area before the throat that is running out, vs the actual throat, there is misalignment and potential issues."

If you pre-bore, there's slim chance of that. I pre-drill- and run the indicator in, so my furthest spot towards the breech where the pilot will engage, is centered. Pilot entrance = dead nuts. Pre-bored body = dead nuts. Nothing wanders.

No disrespect here either. These are just ideas. What you described is the thinking of those who like to prebore. I am just not yet totally convinced. And since the barrels I chamber keep shooting 1K BR screamer groups, I am not easily dissuaded away from my current method.

 

[X Count]

It's not that the throat isn't straight. It's the back end of the chamber that might not be. Yes I understand that when we prebore after drilling--assuming no deflection of the boring bar--the hole we bored is aligned with the spindle.

However, if we don't also dial in the back part of the chamber, then it's very possible that while the throat is straight that the back of the chamber is running out. In fact, the entire back of the chamber up to the throat is running out.

After preboring we have the prebored part running true, a potential area of some runout, and then a true throat. We are hoping that part running out won't influence the reamer. However, if the pilot happens engage the area before the throat that is running out, vs the actual throat, there is misalignment and potential issues.

My method is to dial from near the back of the chamber to a little in front of the throat. That way that 2-3" of bore is running true to the spindle. Then when I cut the chamber the pilot is is staying in the true part of the bore. The hole the reamer is making--using a floating reamer holder--is fully supported and also true to the bore. I think this is a better way of chambering--at least right now. I may change my mind later. If were to prebore I'd still dial in the same way, but based on how I dial in I see no advantage to preboring, but do see possible issues.

Again, don't get too wrapped up in this. We are talking theory here. In actual practice the differences are so minimal that it really doesn't matter. Crud, dialing in the breech and muzzle with range rods and then cutting the chamber has produced a lot of very accurate barrels....

I understand what your saying about dialling in the back of the chamber and the throat so the reamer runs straight for that section but what Aaron is suggesting it to dial in the throat and in front of the throat and bore out any misalignment what would be at the back end of the chamber. Once your chamber is done you'll only have one point that's correct and that will be the throat. What Aaron is suggesting will give you 3 points correctly aligned being back of chamber, throat and barrel in front of throat.

I agree though that there is a lot of additional steps and a lot more things to go wrong for something that may not give a noticeable improvement on most good barrels.

 

[FireMedic]

I understand what your saying about dialling in the back of the chamber and the throat so the reamer runs straight for that section but what Aaron is suggesting it to dial in the throat and in front of the throat and bore out any misalignment what would be at the back end of the chamber. Once your chamber is done you'll only have one point that's correct and that will be the throat. What Aaron is suggesting will give you 3 points correctly aligned being back of chamber, throat and barrel in front of throat.

I agree though that there is a lot of additional steps and a lot more things to go wrong for something that may not give a noticeable improvement on most good barrels.

We can all agree that you can only dial in at two points.

Let’s say we dial in at the throat, and the muzzle like a lot of people suggest. Then we bore a perfectly concentric hole just short of the shoulder of the chamber.

So now we have the prebore and throat perfectly concentric, what is happening with the 1/2” between these two points? It’s not running true. Will that not cause any deflection with the reamer?

I agree with INTJ on his approach.

Has anyone ever had a chamber that measured perfect….throat, neck, shoulder, base, and the lead still looked less then perfect? There is a lot to be learned with a borescope.

 

[LVLAaron]

I like to indicate in approximately these two places.

I never understood indicating the muzzle end. On a barrel that's 40-50 thou out, you're garunteed a crooked bullet entry.

 

[Lucky Shooter]

FireMedic, I don't think you have a problem with your 1/2" of uncertainty.

You've dialed in your throat and muzzle to be on the spindle centerline.

At this point, with a quality barrel, you have to accept two things:
1) The barrel between these two points is assumed not to be straight but
this will not deter accuracy.
2) By predrilling and preboring the chamber area you've removed some metal
and reduced the wear on the reamer-----also----your bored hole will be concentric
with the spindle centerline.

With each pass of the boring bar, the increased diameter of the bored hole allows
the reamer to sink further into the bored hole----and eventually the reamer will go
far enough into the hole to allow the pilot bushing to enter the throat.

It is now time be begin reaming the chamber----the muzzle and throat are on the spindle
centerline, everything that's been bored behind the throat is concentric with the muzzle
and throat-----the pilot bushing supports the front end of the reamer and the rear end of the
bored hole supports the reamer.

Within unspecified tolerances----the muzzle, throat, and bored hole are lined up.

Advancing the reamer with a floating pusher gives the reamer increasing lateral support.

When the reamer is advanced to it's desired depth, there shouldn't be any wiggle room
for the reamer----some refer to this as reaming the chamber exactly to reamer dimensions.

If a guy wants to brag a bit, he can indicate way back on the end of the reamer.

Butch Lambert asked a question a while back to the effect-----If you taper bore,
why use a pilot bushing ? I don't have an answer to that.

This is my understanding of this process and I accept the possibiity that I could
wrong.

A. Weldy

 

[LVLAaron]

1) The barrel between these two points is assumed not to be straight but
this will not deter accuracy.

The bore can be more than not straight... it can be shaped like an S. It can have more taper out of alignment at the muzzle end... especially on a long barrel. The further you drill a long skinny hole the more the drill wanders.

Do you want your bullet to be at an angle when it enters the barrel? Probably not. I'm sure it's fine on a lot of barrels... but again, it's about eliminating variables and controlling the ones we can control.

 

[FireMedic]

FireMedic, I don't think you have a problem with your 1/2" of uncertainty.

You've dialed in your throat and muzzle to be on the spindle centerline.

At this point, with a quality barrel, you have to accept two things:
1) The barrel between these two points is assumed not to be straight but
this will not deter accuracy.
2) By predrilling and preboring the chamber area you've removed some metal
and reduced the wear on the reamer-----also----your bored hole will be concentric
with the spindle centerline.

With each pass of the boring bar, the increased diameter of the bored hole allows
the reamer to sink further into the bored hole----and eventually the reamer will go
far enough into the hole to allow the pilot bushing to enter the throat.

It is now time be begin reaming the chamber----the muzzle and throat are on the spindle
centerline, everything that's been bored behind the throat is concentric with the muzzle
and throat-----the pilot bushing supports the front end of the reamer and the rear end of the
bored hole supports the reamer.

Within unspecified tolerances----the muzzle, throat, and bored hole are lined up.

Advancing the reamer with a floating pusher gives the reamer increasing lateral support.

When the reamer is advanced to it's desired depth, there shouldn't be any wiggle room
for the reamer----some refer to this as reaming the chamber exactly to reamer dimensions.

If a guy wants to brag a bit, he can indicate way back on the end of the reamer.

Butch Lambert asked a question a while back to the effect-----If you taper bore,
why use a pilot bushing ? I don't have an answer to that.

This is my understanding of this process and I accept the possibiity that I could
wrong.

A. Weldy

I’m satisfied with my current way of chambering. It gives me the REPEATABLE results I require.

I do study this stuff constantly and I’m always curious about others processes and theory behind them.

I will say this from my experience… if you do not dial your barrel in perfectly, and/or something moves in your setup while preboring, your results will be worse then if you used a tight fitting bushing and a the reamer then entire way.

The reamer wants to follow the hole it’s put into.

If the pre-bored hole isn’t done perfectly you make things worse.

 

[gunsandgunsmithing]

I’m satisfied with my current way of chambering. It gives me the REPEATABLE results I require.

I do study this stuff constantly and I’m always curious about others processes and theory behind them.

I will say this from my experience… if you do not dial your barrel in perfectly, and/or something moves in your setup while preboring, your results will be worse then if you used a tight fitting bushing and a the reamer then entire way.

The reamer wants to follow the hole it’s put into.

If the pre-bored hole isn’t done perfectly you make things worse.

^^^^THIS is very true^^^^

 

[urbanrifleman]

Correlation is not causation

Simply because two events are correlated does not mean that one caused the other.

medium.datadriveninvestor.com

 

[LVLAaron]

^^^^THIS is very true^^^^

Sure. That's why you check everything again before starting the reamer. Leave a little meat on the pre-bored section... If something moved, take a light pass and move on.

 

[rickhirsch]

what this boils down to is that some people just want to be right . I'm a machinist 45years in trade.
and I have been chambering 20 years. there's a lot of ways to skin a cat .
when i first stated I chambered mike brain way he was one of the first to give information
away. so i did it his way for years and it works . his guns have set records. these days i use indiacating rod
and prebore . this thread stated with a guy wanting to learn a better way . I thinks its never to late to learn .that's why we as a shooting community we to need talk. and learn . most shooters obsess over
rifles and loads and don't practice in the wind.??? Rick

 

[INTJ]

What's important is to chamber in a way that gives you confidence you have things as perfect as possible. And it's good to discuss and debate the merits of various methods. There are pros and cons to each approach.

 

[Hal]

And after you did your best job of clambering. As Jackie Schmidt says check your work while it's still in the lathe. You can see if anything moved.
Than comes the only test that really matters,
take it to the range.

Hal

 

[gunsandgunsmithing]

And after you did your best job of clambering. As Jackie Schmidt says check your work while it's still in the lathe. You can see if anything moved.
Than comes the only test that really matters,
take it to the range.

Hal

This...Otherwise, you really have no way of knowing if anything moved or not. There's several reasons to check your work but the single most likely issue with some setups is that something moved. There's no other way to know and it's too late when it happens after the reamer goes in. I wasn't born last night. I seldom get into these discussions though, because someone always knows a better way. Just do what works. There are several methods that are PROVEN methods. It doesn't mean anything until you win some Nationals and set some records. And if a gun doesn't set the world on fire, it's often the gunsmiths fault, right? Again, just do what works and gives good results for you. There is more than one way and there's more than one way that have set records. I do all I can to give every single bbl the best chance of doing just that, that I know how to do. That's exactly what I get paid to do...just like bbl makers and action makers, etc. These threads come up from time to time but most of the posters read more threads than cut them, frankly. I appreciate anyone wanting to learn but there are multiple ways that are proven to work and the last thing an experienced smith wants is to have his methods questioned publicly by someone still learning the basics.
Check your work from the exact setup it was chambered in. Otherwise, you're checking your setup and lathe more so than the actual work. A good test fixture and setup should be at least twice as accurate as the lathe the chamber is cut in or else, it's pretty useless. So it's best done in the same setup. Many new lathes come brand new with more runout than you read about on the internet, checked by people that do it all day, with the right equipment. So, to have two different setups, in two different fixtures that are barely worth the claimed runout on their own is farting in the wind. Check your work from a single setup. There is no better way at all.

I enjoy reading these threads because there are often some good ideas presented. I think that's what should be the focus of these threads rather than one proven method being superior to another proven method. A hands on class by a winning smith is what's needed but you won't see many winning br smiths posting on these kinda threads, with a few exceptions. Is that because they don't want to share or because of the nature of these threads? That's obvious to me but it's still a good discussion. Carry on.

 

[LVLAaron]

Probably the nature of the threads... Things seem pretty sane in this forum. Other places, not so much. The kind of stuff we're trying to talk about is hard to describe with just words, as well. A lot of it you need to see and feel.

Sinclair and my dad were pretty good friends before I was born... Sinclair and the other smiths were all pretty secretive from what I've been told.

I want to know everything and help anyone... I want everyone to have a top notch rifle. It makes the matches a lot more fun. It makes it more like Stadium Super Trucks where everyone has the same rig, and less like drag racing, where it's an arms race to the top.

 

[gunsandgunsmithing]

Probably the nature of the threads... Things seem pretty sane in this forum. Other places, not so much. The kind of stuff we're trying to talk about is hard to describe with just words, as well. A lot of it you need to see and feel.

Sinclair and my dad were pretty good friends before I was born... Sinclair and the other smiths were all pretty secretive from what I've been told.

I want to know everything and help anyone... I want everyone to have a top notch rifle. It makes the matches a lot more fun. It makes it more like Stadium Super Trucks where everyone has the same rig, and less like drag racing, where it's an arms race to the top.

I agree but one thing I've seen in BR is that it is NOT an arms race. Yes, someone can cut corners and cost themselves dearly but that almost every rifle, amongst several smiths and processes, is a winning rifle, IN THE RIGHT HANDS. BR is much like golf. It's much more about the bad shots than it is the good ones. We know exactly what the good ones will do. The bad ones decide the winners, though. The bad shots are very often the wind or something about the setup that is not directly related to the gun or the work on it. Lots of variables.

 

[gunsandgunsmithing]

I'll add to that a bit, to be more clear.
We can debate chambering methods until we all go crazy but until our methods can overcome a missed wind switch, we are all pissing in the wind, when screw ups are more important than getting everything just perfect. Shooting 0's in perfect conditions but getting your ass handed to you at a match, is not the smith's fault. Worry more about shooting in the wind and less about things that are very good but done by a different method than the guy next to you...and you'll be beating the guy next to you soon. Then he'll be wanting to know who chambered your bbl.