Pre bore the chamber results?

[DSMWerks]

I've always used a finish reamer from start to finish and been very happy. To me reamers are cheap enough and I get plenty of life out of them still. But I want to try drill and bore on the next chamber. I've seen people say they drill and bore to a diameter and depth that the pilot is still the thing to make contact which can't be much of a drill and bore. Basically just under the shoulder diameter maybe .030" and just short of the end of the pilot to the shoulder dimension? On the attached 7mm WSM that might be like .480" diameter and .400" deep? is that worth it?
Also see people say drill and bore just under size and short of the dimension to the shoulder. This removes most of the material and the finish reamer will be cutting full body and diameter the last .100" or so. But then the pilot does nothing until it finds the bore after the reamer has cut a long ways already.
Which way do you use and why?
As an example on this 7mm WSM would you drill and bore .480" diameter say 1.500" deep from the bolt face and turn a 45 degree chamfer on the the entrance to guide the reamer?

thanks

 

[LVLAaron]

For the print, I'd just drill a half inch hole about 250 thou short of the neck/shoulder junction. Then use a small ccmt boring bar to clean up the drilled hole.

If your bore is dialed straight and your setup is good the pilot isn't doing anything anyway.

 

[swd]

I use a drill .020”-.030” smaller than the shoulder diameter and stop .020 or so short of the base of the shoulder. The I true it up to with a boring bar about .005-.008” under the shoulder diameter. If the case has a lot of taper sometimes I use the boring bar and cut a step towards the back of the chamber. For fat chambers it’s faster than just using the reamer and the lack of run out is awesome.

 

[SKWERLZ]

Following this closely as I’m wanting to try preboring on my next barrel next week.

 

[WSnyder]

I pre-dril just short of shoulder then step bore so that there are two or more steps to support the reamer. Easy starts as the reamer eases into the cutting and is always supported by two or more points of contact. I bore the smallest deepest first and work out to the largest shortest. Sharpie marks on the bar for your target depths. It takes more time to pencil out your targets than it takes to actually do it.

 

[Tucker65]

When I set up to prebore I'll drill about .020 to .030 under the body diameter at the body shoulder intersection. I'll then take my reamer and chuck it up in the tailstock with a flute horizontal to the ways of the lathe. I turn my compound and indicate the reamer flute so it's at the same angle a the body taper. Once indicated in I'll bore a tapered hole using the compound so I can insert a case about half way before it starts to get snug. After that I go in with the reamer to finish the chamber. I still use a pilot but I did do one barrel without a pilot installed and the results came out the same when looking at the neck throat area with my bore scope.

 

[butchlambert]

I drill and taper bore. I don't want a bushing influencing my chamber.

 

[Alan Warner]

I always drill 30 40 under the dia @ the top of the body. bore .005 or 6 under the the shoulder junction, set a zero, and step bore every .4 or .2 less with using the taper of the case before use the reamer. Saves reamer degradation and allows the pilot to pick up first. Final ream take about 5 minutes, max.

 

[SKWERLZ]

When I set up to prebore I'll drill about .020 to .030 under the body diameter at the body shoulder intersection. I'll then take my reamer and chuck it up in the tailstock with a flute horizontal to the ways of the lathe. I turn my compound and indicate the reamer flute so it's at the same angle a the body taper. Once indicated in I'll bore a tapered hole using the compound so I can insert a case about half way before it starts to get snug. After that I go in with the reamer to finish the chamber. I still use a pilot but I did do one barrel without a pilot installed and the results came out the same when looking at the neck throat area with my bore scope.

This what I was considering, setting the compound to match body taper using a reamer or sine bar to set it.

 

[LVLAaron]

Seems like a lot of extra work considering you already have a tool to do the hard part.

 

[SKWERLZ]

Seems like a lot of extra work considering you already have a tool to do the hard part.

lol!
As I chamber barrels for fun a bit extra work or extra steps really doesn’t bother me.

 

[LVLAaron]

I'm all about finding new ways to do things. I do a lot of 308's and got a core drill / rougher for it... I use it after the drill-bore process... It's spiral fluted and cuts like butter. It's an extra step but it certainly saves a lot of time.

A bunch of extra steps that don't save time are steps that can go wrong, imo.

 

[SKWERLZ]

I'm all about finding new ways to do things. I do a lot of 308's and got a core drill / rougher for it... I use it after the drill-bore process... It's spiral fluted and cuts like butter. It's an extra step but it certainly saves a lot of time.

A bunch of extra steps that don't save time are steps that can go wrong, imo.

I can’t argue with that, I just like experimenting.
Considering how long it takes with just a reamer I’m looking forward to the speed of drilling and boring first.

 

[LVLAaron]

or just put the bullet in the CENTER of the lands with a straight CHAMBER.
BORES worm down the bore, bushings try to follow the worm, forcing the body to also wiggle and in not size to spec/concentric.
prebore, taper bore AFTER ENSURING throat is zero'd
ream with n bushing, the taper guiding the reamer.
do a search on jackie schimdt method

I'm good.

 

[Dusty Stevens]

Ill keep on reaming. Never cost me any time over setup and potential failure of boring.

 

[LVLAaron]

Illegal.

 

[Jud96]

I’m personally pretty fresh to chambering, but pre-boring seems to be more work and more risk. I don’t find using the finish reamer the whole way to be that troubling. I’d rather send a reamer off to get resharpened after 15-20 barrels than deal with pre-boring even if it means doubling or tripling reamer life.

 

[Dusty Stevens]

it has nothing o do with reamer life.
it is all about putting the bullet at the lands inline with the bore AT THAT POINT.

You sure have came a long ways fast, and like to yell alot. Im guessing this isnt your first username on here.

 

[Spotshooter]

I may not pre-bore as far as some do because I don’t do tons of Volume… where I have to worry about tool where.

BUT…. Precision Wise I use the Gritters Method so I’m dialed into the bore coaxially at the throat area, then I drill and bore out the drill hole so the reamer gets into the hole past the reamer shoulder.

I don’t like the shoulder of the reamer engaging the front edge on the hole… I want the shoulder inside when it starts to cut. - and at the same time I want the bushing of the reamer to be in the uncut bore so everything is good as it can get as it starts cutting.

 

[urbanrifleman]

Pre drilling ensures a small chip which results in a very consistent body finish.