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Gunsmithing Who predrills their chambers?

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chipsfan

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Jun 20, 2009
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Just wondering who predrills their chambers? I'm considering trying it.

Also thinking about maybe running a boring bar after the drill to get everything concentric- maybe an unneeded step?

I currently take small cuts, shut everything down, clean, lubricate and do it again. It works great for a 20 vartarg but takes forever with a 300 win.
 
You would definitely want to clean up with a boring bar after the twist drill to bring it concentric.
 
Pre-drill and pre-bore. Drilling rarely is true to your indicated bore so I feel the boring is essential to start and keep the reamer centered. Once the reamer is well established you should be on your way to a chamber true to your indicated bore. If it isn't your method of holding and driving the reamer would be suspect.
 
As the others have said, you have to bore after you drill. I can't imagine chambering without doing it this way.
 
I used to pre drill, then bore to save wear and tear on my reamers. Was beat into me and I swore by it. Times have changed. If you can do a flush feed system, a finish reamer will do all you need in one fell swoop.
 
As said, drilling and boring should go together. I have a flushing system and decided to try reaming a chamber with the finish reamer from beginning to end: no pre-drilling. I got about .001 runout on the finished chamber versus nil when I pre-bored. I'm now a believer and drill and bore before finishing reaming. Besides, the wear and tear it is saving your reamer also makes it a no-brainer.
 
scotharr said:
As said, drilling and boring should go together. I have a flushing system and decided to try reaming a chamber with the finish reamer from beginning to end: no pre-drilling. I got about .001 runout on the finished chamber versus nil when I pre-bored. I'm now a believer and drill and bore before finishing reaming. Besides, the wear and tear it is saving your reamer also makes it a no-brainer.
Click to expand...

How did you get more runout using the finish reamer from start to finish? Assuming the pilot fits and your reamer holder is doing its job, it seems like you would get less potential runout with the reamer?
 
chipsfan said:
Thanks guys. I'll give it a try. How deep and wide do you typically go?
Click to expand...

The bigger the better. If you have big balls shoulder dia is perfect but as mentioned, if it walks you will have a prob. not to mention stock cutting tools dia's don't always jive. I like to use carbide end mills for an inch or so and then follow it with the largest drill under shoulder dia. I have handy. Unless it's a shorty like a .223 or 6.5 CM 1.25" will still allow the pilot to be supported. I start with the reamer until the shoulder is about .1" in before I drill. Saves tons of time.
 
lw8 said:
How did you get more runout using the finish reamer from start to finish? Assuming the pilot fits and your reamer holder is doing its job, it seems like you would get less potential runout with the reamer?
Click to expand...

You are following a bore that isn't straight, so it induces runout.
 
I really think there is no way you're seeing curvature of a bore in less then 2" of barrel. I've chambered plenty with just a finish reamer and everyone has been under .0002 runout with most .0000. If you're getting more then that you have something not floating, aligning, too small of pilot, or dull reamer causing it.
 
There is plenty of curve in 2". Sometimes a couple thou rather than tenths of a thou. I dial in at the throat and 2" farther. The beginning of the barrel will not be in line ever making the range rod method useless as well. This is why the chamber area should be drilled and prebored out of the way so when the reamer engages it is running true to the new throat location and pointed into the path of the next 2" of bore. I drill and bore .010" - .015" undersized to about .010" - .015" short of the shoulder.
 
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Killswitch Engage said:
I really think there is no way you're seeing curvature of a bore in less then 2" of barrel. I've chambered plenty with just a finish reamer and everyone has been under .0002 runout with most .0000. If you're getting more then that you have something not floating, aligning, too small of pilot, or dull reamer causing it.
Click to expand...

In speaking with several smiths that should know, this is also what I was told. Agree completely.
 
If the barrel was indicated at the beginning and then 2" in then the chamber cut without boring at that point should run true. The reamer simply follows the existing bore. The problem is that perfect zero runout chamber is not lined up from the throat forward. Get your indicator up in the barrel and I bet you see that barrel swirling around like a hula hoop. This misalignment is easy to see with a borescope. It will present as rifling closer to the chamber on one side than the other.
 
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I disagree on the bent barrel notion across 2".

Taper is what your seeing. Ever wonder why your supposed to lop off an inch prior to crowning? It's cause hand lapped barrels typically have some Bellmouth at the ends from lapping. Human hands are involved so Bob at Bartlein may/may not have more than Fred at Krieger.

point is it matters little when you cut it off or machine past it. Where it does matter is during setup. The fancy little rods and pins are a bitch when you start looking at repeatability. A fact well documented here and on other sites.

solve that issue first, then move onto drilling, boring, and chambering.

C.
 
if you have that much curve in a barrel in 2" of the breech end straight shooter i would either send it back or use it for a recurve bow. when they drill and rifle a barrel i have a hard time believing it will have induced curve or walk in the first two inches of barrel let alone the first half. that just doesnt compute. taper as chad says...i will buy that.
 
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Killswitch Engage said:
if you have that much curve in a barrel in 2" of the breech end straight shooter i would either send it back or use it for a recurve bow. when they drill and rifle a barrel i have a hard time believing it will have induced curve or walk in the first two inches of barrel let alone the first half. that just doesnt compute. taper as chad says...i will buy that.
Click to expand...

I 100% agree with Straight Shooter. If you have the throat at zero TIR and 1"-1.5" in forward of the throat at zero TIR, there will almost always be measurable runout at the breech before you prebore. It may be due to the angle of the bore or it may be taper, but it is there. THAT is the reason I prebore. After prebore and before I cut the chamber, I have a zero TIR at the breech, where the chamber will be, where the throat will be and at least and at least the first inch or so of the actual bore are all running at zero TIR. With all those spots zero TIR, if I allow my reamer to follow that hole, it will net a very round and concentric chamber.

Edit: think I need to add another video to my runout series...
 
I've chambered just about all the different ways you can, and it didn't make a damn bit of difference on paper, they all shoot little knots. Gordy's method is great when you have a barrel that you want to time at 12'oclock with more run-out than what you want at the muzzle. A good barrel with minimal run-out doesn't benefit with being timed and centers in the barrel channel.

I can say if I have a barrel with .002" or a little more run-out within 2" it sure as hell wouldn't be going on a customers gun. Think about it....you dial in the throat where the bullet engages the rifling and the muzzle crown, predrill and then pre-bore back from the throat. You now have three points in line, length of chamber, throat and muzzle. Okay, you look through the bore in the lathe and see the jump-rope effect that the bullet rides through in the middle, no avoiding it. The cartridge and bullet is lined up and concentric with the throat, fired travels through the bore and leaves the bore lined up with where it first started.

Gordys method, you dial in the throat and a couple of inches forward, then pre-drill and pre-bore. Now you have three points in line, length of chamber, throat and a couple of inches ahead, assuming within that couple of inches ahead of the throat there is no run-out that was mentioned before. The bullet leaves lined up with the chamber, throat and first couple of inches, then goes through the same jump-rope effect and leaves the barrel however you timed it, but it doesn't leave lined up with where it started.

Now go back to the comment of a barrel having .002" run-out within 2"......plug that into the above method in that instance. Bullet leaves lined up with throat and rear of chamber, travels short distance, does the jump-rope (our .002" runout within 2") hits the next dialed in spot and then into another jump-rope until it exits the bore.

Now go beat your ahead against the wall and think this over some more...... Get your damn chamber and throat dialed in as good as you can, so the bullet is concentric when it engages the riflling. After that pray to the barrel god's that you got a good one. Finally, pull a single hair out of your head and look at it, .002"-.003" thick...think some more. If you are dialing in as good as you can (a few tenths or better) and your practicing good machining, I think you'll be just fine.

With all that said, consistent bore and groove dimensions and overall bore condition after final lapping is paramount in a good shooting barrel, IMHO
 
FCrifles said:
I've chambered just about all the different ways you can, and it didn't make a damn bit of difference on paper, they all shoot little knots. Gordy's method is great when you have a barrel that you want to time at 12'oclock with more run-out than what you want at the muzzle. A good barrel with minimal run-out doesn't benefit with being timed and centers in the barrel channel.

I can say if I have a barrel with .002" or a little more run-out within 2" it sure as hell wouldn't be going on a customers gun. Think about it....you dial in the throat where the bullet engages the rifling and the muzzle crown, predrill and then pre-bore back from the throat. You now have three points in line, length of chamber, throat and muzzle. Okay, you look through the bore in the lathe and see the jump-rope effect that the bullet rides through in the middle, no avoiding it. The cartridge and bullet is lined up and concentric with the throat, fired travels through the bore and leaves the bore lined up with where it first started.

Gordys method, you dial in the throat and a couple of inches forward, then pre-drill and pre-bore. Now you have three points in line, length of chamber, throat and a couple of inches ahead, assuming within that couple of inches ahead of the throat there is no run-out that was mentioned before. The bullet leaves lined up with the chamber, throat and first couple of inches, then goes through the same jump-rope effect and leaves the barrel however you timed it, but it doesn't leave lined up with where it started.

Now go back to the comment of a barrel having .002" run-out within 2"......plug that into the above method in that instance. Bullet leaves lined up with throat and rear of chamber, travels short distance, does the jump-rope (our .002" runout within 2") hits the next dialed in spot and then into another jump-rope until it exits the bore.

Now go beat your ahead against the wall and think this over some more...... Get your damn chamber and throat dialed in as good as you can, so the bullet is concentric when it engages the riflling. After that pray to the barrel god's that you got a good one. Finally, pull a single hair out of your head and look at it, .002"-.003" thick...think some more. If you are dialing in as good as you can (a few tenths or better) and your practicing good machining, I think you'll be just fine.

With all that said, consistent bore and groove dimensions and overall bore condition after final lapping is paramount in a good shooting barrel, IMHO
Click to expand...

now this^^^^^^is exactly how I feel.
 
300sniper said:
I 100% agree with Straight Shooter. If you have the throat at zero TIR and 1"-1.5" in forward of the throat at zero TIR, there will almost always be measurable runout at the breech before you prebore. It may be due to the angle of the bore or it may be taper, but it is there. THAT is the reason I prebore. After prebore and before I cut the chamber, I have a zero TIR at the breech, where the chamber will be, where the throat will be and at least and at least the first inch or so of the actual bore are all running at zero TIR. With all those spots zero TIR, if I allow my reamer to follow that hole, it will net a very round and concentric chamber.

Edit: think I need to add another video to my runout series...
Click to expand...

Links to your videos please.

Sent from my Note 3 using Tapatalk
 
FCrifles said:
....you dial in the throat where the bullet engages the rifling and the muzzle crown, predrill and then pre-bore back from the throat. You now have three points in line, length of chamber, throat and muzzle. Okay, you look through the bore in the lathe and see the jump-rope effect that the bullet rides through in the middle, no avoiding it. The cartridge and bullet is lined up and concentric with the throat, fired travels through the bore and leaves the bore lined up with where it first started.
Click to expand...

What is the shortest barrel you can chamber, using this method?
 
300sniper said:
Runout compared to what?
Click to expand...

I was referring to straight shooters comment on seeing .002" of curve within 2" of barrel. Of course this wouldn't matter in the chamber area that is going to get bored away. 2" in front of the throat wouldn't fly for me, and yes I have checked a few over the past several years.
 
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FCrifles said:
I was referring to straight shooters comment on seeing .002" of curve within 2" of barrel. Of course this wouldn't matter in the chamber area that is going to get bored away. 2" in front of the throat wouldn't fly for me, and yes I have checked a few over the past several years.
Click to expand...


One can induce as much runout as they want over 2" depending on how they are holding it. I am pretty sure he was saying that if he has zero TIR at the throat and 2" forward of the throat, there will be runout at the breech. I must have missed the .002" in 2" part. Where Straight Shooter has zero TIR, there will almost always, if not always be measurable runout at the breech.
 
I agree, this why we pre-drill and pre-bore the chamber first, assuming proper holding of the barrel as you said. I was referring to....
Straight Shooter said:
There is plenty of curve in 2". Sometimes a couple thou rather than tenths of a thou.
Click to expand...
You should never see .002" of curvature in a 2" stretch of good barrel IMHO (excluding the bellmouth end where the lap reverses).

In the end, at least we have more than one way to get the results we want:)
 
The topic of accuracy with the various methods has been beat to death. I thought we were talking about pre-drilling before chambering. I drill and prebore not to save reamers but to cut away the curve in the bore where I want my chamber. I use the method I use because it seems most correct to me. If someone can demonstrate a more precise method of getting the bullet into the lands straighter and through the crown more square to the bore I will adopt it on the spot. Sure there is lot's of easier ways, but it's just not my way.

If I sent back every curved barrel, no one would sell me barrels. Not that I haven't. How many times have you cut a barrel for a muzzle brake only to find the bore is off center when you went to taper the joint? Would you tell the customer his fine proven barrel is a POS and make him wait 6 more months for a new one? Banana bores area fact of life so we make it work. Barrels are contoured based off centers in the ends of the barrel. Now an inch has been cut off and it's off center? On the aftermarket barrels, not by much but on factory barrels it happens a lot. How did this happen? The only answer I can come up with is the bore has a curve inside the barrel. I'm not guessing. I can measure it.

It's amazing we get barrels as good as we do. I visited a barrel manufacturer and while he was showing me his deep hole drills in action, a cutter went out the side of the barrel. They will not admit this happens on the phone or in their advertising but it happens fairly frequently. Right near the drill was a reject bin and it was half full just from the barrels from that day. As long as the final exit is close to the middle and fairly straight they can hide the curve by contouring between centers. PTG has put some thought into this topic of bent bores. I wonder how bent would a bore has to be to fail this test? https://shop.pacifictoolandgauge.com/index.php?main_page=index&cPath=5_124

How to tolerate and live with a banana bore in varying degrees.

Assuming perfect alignment with each method ponder this:

Ignore the curve and dial both ends. A laser bore sighter is centered in the throat and exits the muzzle dead center is pointed at a target 100 yards away.
verses
Adapt to the curve by dialing in one end at a time. A laser bore sighter stuck in the last 2" of bore pointed at a target 100 yards away.

Which one will impact the bullet closer to the intended target?


 
Okay, I will type real slow so we don't loose anyone. Dialed in at the throat and 2" farther, not backwards into the chamber area. We get that section running as perfect as possible with zero runout in those two spots. Advance 2 more inches and I have seen up to .002" more runout. This is over 4" length of barrel. Now follow that curve .002" per 2" of barrel and when you get out to 24" more inches observe .024" runout. I have actually seen much worse and now avoid those brands of barrels. My favorite two average .005" or less in 30".
 
Straight Shooter said:
Assuming perfect alignment with each method ponder this:

Ignore the curve and dial both ends. A laser bore sighter is centered in the throat and exits the muzzle dead center is pointed at a target 100 yards away.
verses
Adapt to the curve by dialing in one end at a time. A laser bore sighter stuck in the last 2" of bore pointed at a target 100 yards away.

Which one will impact the bullet closer to the intended target?


[/SIZE][/FONT]
Click to expand...

The first method will.
 
HEAVY Sigh!!!!!!!!!! Screw the sip and down the double shot of whiskey, chase it with some beer and huff the cig. Ok I'm ready ;-)

If you want to be impressed, check out STR's sticky vid on indicating on the 'smithing page. Pretty impressive to say the least! My life is too short to go to that extreme.

I find it humorous that you guys think that there is .002" curvature in 2". Killswitch nailed it. I don't think you could do that with a drill bit.

Indicating on a point of an arc, (throat) would definitely result in a chamber that wasn't in line with the arc. (bore)

Threading between centers and chambering in a steady rest cuts out all of the crap and saves time. The pilot follows the bore, the reamer follows the pilot. Floating reamer holders aren't friendly to bbls that have hard spots so it's time wasted to over indicate unless you single point cut the chamber (cnc) or ream with a ridgid reamer holder.
 
RJBGuns00 said:
HEAVY Sigh!!!!!!!!!! Screw the sip and down the double shot of whiskey, chase it with some beer and huff the cig. Ok I'm ready ;-)

If you want to be impressed, check out STR's sticky vid on indicating on the 'smithing page. Pretty impressive to say the least! My life is too short to go to that extreme.

I find it humorous that you guys think that there is .002" curvature in 2". Killswitch nailed it. I don't think you could do that with a drill bit.

Indicating on a point of an arc, (throat) would definitely result in a chamber that wasn't in line with the arc. (bore)

Threading between centers and chambering in a steady rest cuts out all of the crap and saves time. The pilot follows the bore, the reamer follows the pilot. Floating reamer holders aren't friendly to bbls that have hard spots so it's time wasted to over indicate unless you single point cut the chamber (cnc) or ream with a ridgid reamer holder.
Click to expand...


Once you've figured out how to not get grooves in your chambers, maybe you can video your finished chamber TIR in a few different places.
 
300sniper said:
Once you've figured out how to not get grooves in your chambers, maybe you can video your finished chamber TIR in a few different places.
Click to expand...

Thanks Edds. Maybe I will check that out someday ;-)

300, Grooves is a bit harsh. I'm sure you never polish a chamber after you cut it. Only a fool would spend time checking runout on a chamber unless he was trying to prove something. Once it's cut. it's range time. You can't change history ;-)
 
RJBGuns00 said:
Thanks Edds. Maybe I will check that out someday ;-)

300, Grooves is a bit harsh. I'm sure you never polish a chamber after you cut it. Only a fool would spend time checking runout on a chamber unless he was trying to prove something. Once it's cut. it's range time. You can't change history ;-)
Click to expand...


I guess I'm that fool trying to prove I did my best work.

And sure, I polish my chambers. Well, actually, I run some 400 grit wet/dry wrapped around a Bic pen tube and some WD40 to give the chamber some "bite" after reaming.
 
Don't you know 320 grit with WD-40 will make it shoot better than 400 grit.....(big grin)

If you really want them to shoot I'll let you use my throat knurler on your next chamber.LOL
 
300sniper said:
I guess I'm that fool trying to prove I did my best work.

And sure, I polish my chambers. Well, actually, I run some 400 grit wet/dry wrapped around a Bic pen tube and some WD40 to give the chamber some "bite" after reaming.
Click to expand...

Well bless your pointed little head ;-) I guess you have to test fire 'em after you're done to to prove you did your best work as well. Not to mention covering your ass in case you f'ed up.

Bic pen is a nice touch. I'm sure it works but I would recommend a wooden dowel with a bevel similar to the shoulder angle to address my issue with the shoulder.

I get a kick out of you guys carrying on about chamber "bite". That is the stupidest thing anyone has come up with.

Maybe it helps keep them form blowing up ;-)
 
RJBGuns00 said:
Well bless your pointed little head ;-) I guess you have to test fire 'em after you're done to to prove you did your best work as well. Not to mention covering your ass in case you f'ed up.

Bic pen is a nice touch. I'm sure it works but I would recommend a wooden dowel with a bevel similar to the shoulder angle to address my issue with the shoulder.

I get a kick out of you guys carrying on about chamber "bite". That is the stupidest thing anyone has come up with.

Maybe it helps keep them form blowing up ;-)
Click to expand...

Sounds like you've got it all figured out.
 
Straight Shooter said:
I visited a barrel manufacturer and while he was showing me his deep hole drills in action, a cutter went out the side of the barrel. They will not admit this happens on the phone or in their advertising but it happens fairly frequently.
Click to expand...

That's funny because it's not me ;-) I suspect this happens but not as frequent as you make it sound. Otherwise, blanks would be $1k
 
300sniper said:
I've posted my results in video. No one is stopping you from posting your results.
Click to expand...

Ok, I'll humor you and watch your vids if you will tell me where they are. A link maybe?? As said, only a fool would waste time with this. Yes, I tend to be foolish at times.

Please be advised that I suspect 400 grit sandpaper will cut more than .0001" even with a "one pass in and out" so I will be skeptical regardless. Dwell time seems to be omitted.
 
They buy barrel stock by the semi truck load and I bet they are pretty cheap as unmachined blanks. There finished barrels start out at over $300. I don't know if the deep drill goes out the side every day but they get off center fairly often. Barrels go in the garbage at almost every station and over the course of 3 hours we spent in the shop I personally saw about 20 barrels go in the garbage. The most went in the garbage after contouring. That was where one of the last inspections was done. Part was just putting his hand on the barrel at 4500 rpm at the end of the contouring cycle. I was surprised to see that the final inspection is done by eyeballing through the barrel. At the end of the tour they gave me a stack of rejects to use in displays or experiment on.
 
Straight Shooter said:
They buy barrel stock by the semi truck load and I bet they are pretty cheap as unmachined blanks. There finished barrels start out at over $300. I don't know if the deep drill goes out the side every day but they get off center fairly often. Barrels go in the garbage at almost every station and over the course of 3 hours we spent in the shop I personally saw about 20 barrels go in the garbage. The most went in the garbage after contouring. That was where one of the last inspections was done. Part was just putting his hand on the barrel at 4500 rpm at the end of the contouring cycle. I was surprised to see that the final inspection is done by eyeballing through the barrel. At the end of the tour they gave me a stack of rejects to use in displays or experiment on.
Click to expand...

You are so full of shit! I bet your brown eyes were blue before you grew up and started lying.

Show us the stack!
 
A big shop like that has huge overhead and must produce in volume or they can't survive. The faster the production goes the more compromises must be made. The guys running those lathes were most likely on a broom not that long ago.


Check out this curved barrel video by jonaddis84.


 
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