The last few thou.........

I've been chambering barrels now for a few years. Got about 30 chambers under my belt. But I still have a hard time judging the last few thousands before the bolt closes. I've tried a bunch of different methods including mounting the floating reamer holder in the cross slide and using my DRO to guage how close I am. Didn't work as good as I expected. So at this point, it's hit and miss. Ream a little bit, remount the receiver, check with go guage, ream a bit more, etc. I saw in another post a rig that uses a dial indicator to measure this. I've also seen a device that was turned to fit over the barrel stub that uses a dial indicator to measure how much the go guage is extending out of the chamber. This is nice, but I still find it hard to judge the amount to advance the tailstock. BTW, I have a dial indicator mounted on my tailstock so I can see how much it is progressing.
How about some hints and pictures?
THANKS!

I have mounted a 6" mill quil DRO on my tailstock and get very close to dead on using a floating reamer holder in the tailstock.

Roy,

Assuming all is good and rigid in your machine your difficulty could lie more in determining how much to feed the reamer. I've noticed that you can get a wide (.000" - .004") variation in how much the headspace gage protrudes from the mouth of the chamber when taking measurements with a depth micrometer.

This stems from the fact that most headspace gages are sigificantly smaller in diameter than the chambers they are to be used in. This is so that when using an undersized reamer, like a rougher or resize reamer, the gage will go all the way into the chamber and touch the shoulder. (Talking bottle-necked cartridges here.)

Since it can tilt from one side to the other, where the gage is oriented makes a real difference in the measurement that you get from the depth micrometer.

In order to keep the gage and partially cut chamber as coaxial as possible, I wrap a piece of paper around the gage just forward of the extractor groove. The paper goes almost completely around and does not overlap itself. You have to try different kinds of paper for thickness.

By doing this I get very consistent readings off the micrometer. If it says I've got .011" more to go and I feed the tailstock quill .011" from where it was stopped on the last pass, my chamber will be .011" deeper every time.

This depends on not moving the tailstock between passes, using the paper around the gage for each measurement, and if using a floating reamer holder making sure there is some kind of positive stop for the reamer shank in the holder.

There is some technique here too. That is to say that you have to pay close attention to where you stop cranking the tailstock feed and allow a short dwell at the end of the pass to allow the reamer to finish cutting at that depth. Do not overdue pause at the end of the pass or the finish will suffer. You will feel the reamer stop cutting. Back out at that instant. On the very last pass, I stop the machine as soon as the reamer quits cutting and back out the reamer when the barrel has stopped turning. This avoids getting any helix shaped swirls in the chamber finish. They do not hurt the dimensions, they just don't look professional.

FWIW

rigging a second indicator against the front of TAILOSTOCK BASE ( as well as one on t/stock barrel ),allows me to return t/stock to battery accurately for final ream .....made life a lot more pleasant ....tnx to walt mueller & his single shot action

best wishes
docn8as

RoyB, I saw your post on BR too and I know you've received some great advise. I use a method very similar to doc here.

I chamber through the headstock, I turn and thread the tennon, then cut the cone to length by threading the action on until it bottoms with the bolt in. Measure space at shoulder with feeler gauges, then add .007 or .008.

I drill and bore out the chamber short, then start with the finish reamer, and barrel flush system. To determine the last bit of depth, agian using the action/bolt/go-gauge, I measure the gap at the action/shoulder.

I have a block that clamps to the quill, use an indicator on the tailstock, and push the tailstock against the saddle which is locked down. I can advance the reamer, pull the tailstock back and clear, and measure progress. Pushing the tailstock back against the saddle has proven to repeat very well. Doc is using an indicator to locate the tailstock each time, which is great and probably more accurate than what I do. But I've never over-advanced a reamer and had to adjust shoulder/cone etc. Hope this helps some. I'm sure you can combine all these methods and come out with something that will work for you.

Thanks Guys! Some real good ideas here. The idea of locating the saddle never occured to me...Duh! But I'm going to rig up a device to hold an indicator so I can return it to the exact same spot and then the indicator on my quill will be a better reference for depth. I'll let you know how I make out.......