Oversize Chamber

[Curious]

I understand and accept that the idea is not to have our reamers cutting oversize but please humour me guys, how much oversize, if any would be acceptable?

I ask this because yesterday I tried cutting a chamber on a scrap blank end using a collet chuck in my tailstock to hold the reamer instead of pushing with the dead centre, runout was well under 0.0005" in all parts of the chamber but the chamber mouth was 0.0007" bigger than the reamer. My plan is to use a good quality floating reamer holder in the tailstock which I have on order but until yesterday Ive never had a problem with oversize and it got me thinking, it was ever so slightly discernible to the wiggle test so I measured it.

How good or bad is 0.0007" oversize measured at the chamber mouth and what effect, if any would it have on brass or accuracy?

 

[JerrySharrett]

I understand and accept that the idea is not to have our reamers cutting oversize but please humour me guys, how much oversize, if any would be acceptable?

I ask this because yesterday I tried cutting a chamber on a scrap blank end using a collet chuck in my tailstock to hold the reamer instead of pushing with the dead centre, runout was well under 0.0005" in all parts of the chamber but the chamber mouth was 0.0007" bigger than the reamer. My plan is to use a good quality floating reamer holder in the tailstock which I have on order but until yesterday Ive never had a problem with oversize and it got me thinking, it was ever so slightly discernible to the wiggle test so I measured it.

How good or bad is 0.0007" oversize measured at the chamber mouth and what effect, if any would it have on brass or accuracy?

If you can cut them all 0.0007" Over, and have a sizing dies for that size, ok. Bench rest accuracy is all about consistency, consistency AND, consistency.

There are several "standard" reamers, JGS1045, Boyer 3, Borden, etc. they are different by a few thousands. They all work. Take your pick and tool for it and set up to where you can duplicate within about 0.0002" each time.

Consistency, consistency, consistency....

.

 

[Curious]

If you can cut them all 0.0007" Over, and have a sizing dies for that size, ok. Bench rest accuracy is all about consistency, consistency AND, consistency.

There are several "standard" reamers, JGS1045, Boyer 3, Borden, etc. they are different by a few thousands. They all work. Take your pick and tool for it and set up to where you can duplicate within about 0.0002" each time.

Consistency, consistency, consistency....

.

OK, thanks for that Jerry.

I dont build bench rest rifles, Im more into long range varminters or accurate hunting rifles where brass will be specific to one chamber and never need to be interchanged. I figured that it shouldn't make any difference to anything as the brass will form to its chamber and if a F/L die is used it would bring it back undersize anyway.

Using the pusher method I can't say I had ever noticed any wiggle on the reamer when it was in the chamber at full depth, because I used this collet chuck I was expecting some degree of oversize and so looked closely for it. Once I measured it I wasn't sure it it was relevant in the context of a rifle chamber. If I had been reaming a hole the diameter of a .243 at the chamber mouth then 0.0007" would be a lot of oversize.

I guess Im trying to put what I ended up with into context for a precision rifle build.

 

[Mike Bryant]

It's pretty hard to discern any reamer shake when the reamer is in the bottom of the chamber by eye. You might take and rest a dial indicator stylus against the rear of an unsupported reamer when it's bottomed out and see if you can discern any wiggle in the reamer with the dial indicator. We are so used to checking alignment to a few ten thousandths that we forget how actually small a thousandth is. IMO more oversized chambers have been caused by floating reamer holders than probably just about anything. I've tried several floating reamer holders and haven't found one that I like yet. I haven't found a one that works better than Dave Tooley's pusher.

 

[SGS]

If you can cut them all 0.0007" Over, and have a sizing dies for that size, ok. Bench rest accuracy is all about consistency, consistency AND, consistency.

There are several "standard" reamers, JGS1045, Boyer 3, Borden, etc. they are different by a few thousands. They all work. Take your pick and tool for it and set up to where you can duplicate within about 0.0002" each time.

Consistency, consistency, consistency....

.

I completely agree. To further address the OP's question, .0007 oversize at the chamber mouth is not enough to be significant in most cases.

 

[Curious]

I completely agree. To further address the OP's question, .0007 oversize at the chamber mouth is not enough to be significant in most cases.

Could I ask in which cases it would be enough to be significant as you used the term 'most cases' rather than 'all cases'

 

[Curious]

It's pretty hard to discern any reamer shake when the reamer is in the bottom of the chamber by eye. You might take and rest a dial indicator stylus against the rear of an unsupported reamer when it's bottomed out and see if you can discern any wiggle in the reamer with the dial indicator. We are so used to checking alignment to a few ten thousandths that we forget how actually small a thousandth is. IMO more oversized chambers have been caused by floating reamer holders than probably just about anything. I've tried several floating reamer holders and haven't found one that I like yet. I haven't found a one that works better than Dave Tooley's pusher.

I clocked the reamer Mike as you suggest, unsupported but pushed to the bottom of the chamber and with the stylus maybe an inch from the chamber mouth which I guess will also give a bigger reading that the chamber mouth.

Interestingly I cut another but this time I didn't apply any preload on the quill lock to see if the play might help it float but that time it cut just over a thou big so it was better with the tailstock quill under some lock pressure.

 

[alinwa]

I clocked the reamer Mike as you suggest, unsupported but pushed to the bottom of the chamber and with the stylus maybe an inch from the chamber mouth which I guess will also give a bigger reading that the chamber mouth.

Interestingly I cut another but this time I didn't apply any preload on the quill lock to see if the play might help it float but that time it cut just over a thou big so it was better with the tailstock quill under some lock pressure.

And here's where I completely lose ya......

it was better with the tailstock quill under some lock pressure.

I simply cannot think this way.....



IMO if I can affect something ("I drive better when I'm sober" or "I shoot pool better when I'm drunk") All I've really proven is that I'm not doing it BEST....I've not achieved repeatable consistency.

but that's just just me

 

[JerrySharrett]

I clocked the reamer Mike


Interestingly I cut another but this time I didn't apply any preload on the quill lock to see if the play might help it float but that time it cut just over a thou big so it was better with the tailstock quill under some lock pressure.

If you are depending on preload on the quill lock to bring your tailstock on axis with your headstock. ROTS OV RUCK.

What ever your brand of lathe and whatever your lathes foundation construction, there is a good chance the two don't perfectly align. And remember, the tailstock being out of line with the headstock a mere 0.002" can make a chamber oversize by 0.004" if the tailstock controls the reamer. That is why a floating pusher like the Tooley/Bryant type is important.

.

 

[SGS]

Could I ask in which cases it would be enough to be significant as you used the term 'most cases' rather than 'all cases'

If the relationship between your nominal chamber size and your sizing die is resulting in overworking the brass which causes rapid work hardening and shorter case life, then any amount larger would tend to worsen the situation. Still, .0007 is very slight. If it causes any issue, the situation was already not good.

Accuracy minded smiths shoot for a method that results in chambers nearly exactly at reamer dimensions mostly so they know what they have. They like to order a reamer to very specific dimensions and then be able to reproduce those specs. This may not be the most important factor in producing accurate barrels but it is in line with chasing perfection.

 

[Curious]

If the relationship between your nominal chamber size and your sizing die is resulting in overworking the brass which causes rapid work hardening and shorter case life, then any amount larger would tend to worsen the situation. Still, .0007 is very slight. If it causes any issue, the situation was already not good.

Accuracy minded smiths shoot for a method that results in chambers nearly exactly at reamer dimensions mostly so they know what they have. They like to order a reamer to very specific dimensions and then be able to reproduce those specs. This may not be the most important factor in producing accurate barrels but it is in line with chasing perfection.

I dont disagree with this at all.

That said my question was about what you describe as a slight amount of oversize, I wonder how many rifle builders actually check for this? I see lots of videos showing low runout figures but nothing about oversize. Ive chambered a couple of barrels since I started this thread, one had no discernible oversize, the other had so little (0.0002") it could could be normal and wasn't something I used to check for in the past, I will do it every time now.

I would be surprised if resizing the base of a case by 0.0007" more would really have a significant impact on case work hardening but then again I dont know for sure.

As with all that we strive for I would want errors to be as small as possible in my work but within sensible and practical tolerances that dont effect accuracy

If you are depending on preload on the quill lock to bring your tailstock on axis with your headstock. ROTS OV RUCK.

What ever your brand of lathe and whatever your lathes foundation construction, there is a good chance the two don't perfectly align. And remember, the tailstock being out of line with the headstock a mere 0.002" can make a chamber oversize by 0.004" if the tailstock controls the reamer. That is why a floating pusher like the Tooley/Bryant type is important.

.

Ive not found many things in life that didn't have a little play in them, tailstock quills dont appear to be excluded from this just as tailstocks themselves will register different readings when tightened down to the bed with different amounts of torque. As we will agree 0.0001" is a relatively small amount and I would be surprised if anyone here had a tailstock quill that didn't have some play if tested and measured properly.

The difference between results with some preload on the quill was 0.0003" from 0.0007" to 0.001" - I usually push the reamer with a dead centre all the way and get runout well below 0.0005" every time as my tailstock is very well aligned and regularly checked, again all alignment and use will be with a very similar amount of preload on the quill lock, I dont resort to a torque wrench but I would say consistent feel will be very close evrey time. I also like the fact that with a little lock applied it stops me feeding too fast and personally I think the feel is better for me.

 

[Curious]

And here's where I completely lose ya......





I simply cannot think this way.....



IMO if I can affect something ("I drive better when I'm sober" or "I shoot pool better when I'm drunk") All I've really proven is that I'm not doing it BEST....I've not achieved repeatable consistency.

but that's just just me

With respect Al I can't discuss anything with you, you ramble or talk in riddles far too much for me

 

[JerrySharrett]

I dont disagree with this at all.

That said my question was about what you describe as a slight amount of oversize, I wonder how many rifle builders actually check for this? I see lots of videos showing low runout figures but nothing about oversize. Ive chambered a couple of barrels since I started this thread, one had no discernible oversize, the other had so little (0.0002") it could could be normal and wasn't something I used to check for in the past, I will do it every time now.

I would be surprised if resizing the base of a case by 0.0007" more would really have a significant impact on case work hardening but then again I dont know for sure.

As with all that we strive for I would want errors to be as small as possible in my work but within sensible and practical tolerances that dont effect

Ive not found many things in life that didn't have a little play in them, tailstock quills dont appear to be excluded from this just as tailstocks themselves will register different readings when tightened down to the bed with different amounts of torque. As we will agree 0.0001" is a relatively small amount and I would be surprised if anyone here had a tailstock quill that didn't have some play if tested and measured properly.

The difference between results with some preload on the quill was 0.0003" from 0.0007" to 0.001" - I usually push the reamer with a dead centre all the way and get runout well below 0.0005" every time as my tailstock is very well aligned and regularly checked, again all alignment and use will be with a very similar amount of preload on the quill lock, I dont resort to a torque wrench but I would say consistent feel will be very close evrey time. I also like the fact that with a little lock applied it stops me feeding too fast and personally I think the feel is better for me.

PUSHING a reamer with the point of a tailstock center pushing in the reamers center hole will not give you chamber runout but IT CAN shift the back of the reamer enough to cause an oversized chamber. FACT!!

If you have chamber runout, you have big problems, many times caused by defective spindle bearings. This is why lathes that run on bushings give better surface finish.

Wheelheads on precision cylindrical grinders don't run on bearings, they run in bushings.

.

.

 

[Curious]

PUSHING a reamer with the point of a tailstock center pushing in the reamers center hole will not give you chamber runout but IT CAN shift the back of the reamer enough to cause an oversized chamber. FACT!!

Yes, I would agree Jerry but if your tailstock centre is very close then it shouldn't be an issue.

I check my tailstock about once a month by turning between enters over 18" - taper is kept to less than 0.0005" over that distance which would mean much less at the distances between centers that we chamber. I cut a chamber yesterday using my usual dead centre method, runout was nothing and the chamber mouth showed no oversize to my wiggle test and the 0.0002" it was picking up on the indicator was questionable.

If you have chamber runout, you have big problems, many times caused by defective spindle bearings.

Thats interesting, typically I get TIR at the case mouth of around 0.0002"-0.0003" and quite often less, maybe one in five show no runout. Are you getting zero TIR to four decimals every time?

Yesterday I pre-bored to 0.015" over shoulder diameter and within 0.030" of full depth and cut my best chamber ever using the dead centre, I could not detect any runout anywhere from throat to case mouth.

 

[JerrySharrett]

Yes, I would agree Jerry but if your tailstock centre is very close then it shouldn't be an issue.

Close? Close as in hand grenades or close as in horse shoes?

If your tailstock is off center 0.004" your chamber will be oversize of the reamers diameter by 0.008".


.

 

[Zebra13]

Curious,

Turning something between centers and having it come out straight, and having your tailstock aligned dead-nuts to your lathe's spindle axis are two different things. Having one doesn't mean you have the other.

Next time you turn something between centers, and are happy with the result, mount a test indicator in or on your lathe chuck and sweep the center in your tailstock. I'll eat my hat if you read zero movement 360 degrees around that center. Or, sweep the center in as close as you can get (very unlikely you'll be able to get zero run out) and turn something between centers. Probably not gonna be real straight. As they come from the factory, most tailstocks sit high to account for wear over time. So if you have a piece of metal between centers, with the tailstock being a bit high, and your cutting tool setting dead-nuts level with the spindle axis, picture the tool traveling down the length of the work...it's going to cut less material at the tailstock end than it will at the headstock. On every lathe I've played with, you had to off-set the tailstock to one side or the other...to cut straight.

So why don't we just sweep the center in to dead nuts and push with a center? As I said, chances are you won't be able to get it to read zero the full 360 degrees. But if you could, is the tailstock spindle moving dead nuts straight on both the vertical and horizontal planes when you extend and retract it? Probably not. And if it's not, and you're pushing a reamer with a center, you're pushing the reamer one way or the other...neither of them being straight.

Next time you're at the lathe, put a test indicator on the tailstock ram and zero it. Now put different clamping pressures on the bed lock and watch the indicator move around. Same thing with the ram lock. There are a lot of moving parts on a tailstock to contend with...a lot of variables.

All of this is why most serious accuracy gunsmiths use a reamer holder/pusher of some sort as it allows a bit of movement, or float, to off-set the inaccuracies inherent to most, if not all tailstocks.

That's as I see it. Hope it helps.
Justin

 

[Curious]

Thanks for your thoughts guys.

 

[alinwa]

Curious,

Turning something between centers and having it come out straight, and having your tailstock aligned dead-nuts to your lathe's spindle axis are two different things. Having one doesn't mean you have the other...............

Justin

WHuhh BAMM!

There is no such thing as "straight" and "stiff"......and even if there was, the REAMER humps up like pushin a rope thru a knothole...in fact, IMO if one is achieving "runout" this is the root of it. It sure ain't about the tailstock alignment.

And "alignment" is as ephemeral as mayfly wings...


In the end the only true "measurement" is the gaging of brass cases chamber-to-chamber, and caselife. If one cannot interchange cases from gun to gun and fire the cases 50+ times each then one IS NOT making identical chambers. No matter what the "measurements" say.

 

[alinwa]

And may I say that if one CAN interchange cases and dies, and is getting infinite caselife then IT DOES NOT MATTER how one gets there! Because if they do, anything beyond that is moot IMO.

I think chambers can vary as much as .002 diameter at the rear and still make this spec.......

 

[Dave Tooley]

And may I say that if one CAN interchange cases and dies, and is getting infinite caselife then IT DOES NOT MATTER how one gets there! Because if they do, anything beyond that is moot IMO.

I think chambers can vary as much as .002 diameter at the rear and still make this spec.......

Al

If they vary .002" on the rear what effect does that have on the front or should I say the important end of the chamber?