Gunsmithing Thoughts on roughing out with a twist drill

[wadcutter]

I have commissioned a gunsmith to machine up some forming dies for a wildcat cartridge of my own design.
I provided him with some blank dies and a new resizer reamer of quite a large size as the wildcat is based on a 505 Gibbs cartridge.

He said he would rough out the hole from its .308 cal pilot hole with a 1/2" twist drill to save on time reaming out the dies.

I'm not sure this is the best thing to do? Your thoughts.

 

[Wintermute]

Depends on how concentric it is. It's just removing metal to enlarge the hole to fit the larger reamer, however, if it's bored out non-concentric to the bore, then it's a problem since it would set the reamer up for a non concentric bore. If I were doing it, I'd use a boring bar to remove the material after using a range rod in the lathe to ensure the bore concentricity. With that setup, I feel I'd have a much greater level of control over the concentricity of the initial boring operation. Twist drills tend to pull to one side in my experience (even high quality jobber drill bits). A gundrill is better at holding concentricity, however, a 1/2" gun drill would be a pretty expensive one time purchase, and you'd have to have the proper machine to run it.

--Wintermute

 

[wtopace]

Its standard practice when cutting chambers to drill, bore, then ream to cut down on time and wear on the chamber reamer. I don't think cutting a die would be any different.

Reamers aren't really meant to be heavy cutting tools, they are very precise cutters that are designed to bring a cut to the final dimension.

Good luck with your wildcat!

 

[Geno C.]

Its standard practice when cutting chambers to drill, bore, then ream to cut down on time and wear on the chamber reamer. I don't think cutting a die would be any different.

Reamers aren't really meant to be heavy cutting tools, they are very precise cutters that are designed to bring a cut to the final dimension.

Good luck with your wildcat!

This is exactly it. You're probably going to get a better cut at the neck and shoulder if the reamer doesn't have to cut its way all the way down.

If the reamer and die are held rigid and true in a lathe I would say it shoud end up very true.

 

[skeetlee]

I use end mills in place of drill bits. Then I bore and ream. Lee

 

[eddieharren]

Lee, ever get any chatter when doing that? How long of an end mill do you use on a 300 RUM?

 

[jonesturf]

As long as he is going to true up the drilling with a boring bar prior to reaming you should be fine. Like said before a reamer will only follow what's in front of it. If the drilled holed is nonconcentric you're gonna have problems. I would assume boring would be included in the "predrill" but it wouldn't hurt to ask.

 

[Delta4-3]

I do it all the time.

 

[wadcutter]

Thanks for the answers. I feel better about it now..

Out of interest, how far do you rough out a chamber before using the reamer?

 

[bward]

It will vary from person to person, but about .100'' from your final headspace and .010'' under your diameter at the shoulder.

Thanks for the answers. I feel better about it now..

Out of interest, how far do you rough out a chamber before using the reamer?

 

[Clark]

I agree with the above posts that the 1) drill, 2) boring bar, 3) reamer is a good system for staying concentric, saving time, and keeping the reamer sharp.

I make a sketch to hang over the lathe to remind me what I am doing.
I try to keep a minimum of reamer pilot engaged in the bore.

I got the notion from the Jim Bryant web site a long time ago:
Precision Riflesmithing by Bryant Custom: Barreling

 

[wadcutter]

Clark,
That drawing helps to explain it very well.
Thank you.

 

[skeetlee]

Doc
I haven't ever chambered anything longer than a .308 so no sir,I haven't had any chatter issues. I do use that carbide rougher bought from you though. I love that reamer. I chamber 22 and 6ppc chambers 80 percent of the time.
I dial everything in the best I can, then I use two different size end mills boring out to approx .365. Then use my boring bar to open and true to about .400 .800 deep. I go .800 deep with all my mills. I then use the carbide rougher to about .050 short of final headspace. Then come the finished dreamer. Pretty simple and fast. Lee

 

[eddieharren]

Amazing, simply amazing!

 

[jonaddis84]

I drill 1.3" no further, due to direct indicating the bore AFTER drilling. So indicate close, drill undersized, indicate perfect, bore, chamber.

1.3" is the length of the body on the indicator.

Galaxy S3 on tapatalk

 

[DAVETOOLEY]

Standard procedure around here if I don't have a caliber specific roughing drill.