Pre-boring 5R lands on small bores (22 / 6mm)

[LVLAaron]

I've never chambered a 5R barrel. In theory I understand the challenges of chambering them (in short, chatter)

Gordy Gritters recommends pre-boring the lands in the neck area.


In a .300 bore barrel the tools needed to do this seem pretty easy. Just use my 6mm indexable carbide boring bar.

What about small bores like 22 and 6mm? I have an Accupro carbide boring bar that's tiny, and can fit in a .200 bore - but can only reach 1.3" - Not enough to reach the neck of a 223 or 6GT.

Do I forgo the pre-boring of the lands and manage chatter with wax paper / patches? Is there a longer boring bar that I can't find?

 

[GeneT]

I've never chambered a 5R barrel. In theory I understand the challenges of chambering them (in short, chatter)

Gordy Gritters recommends pre-boring the lands in the neck area.


In a .300 bore barrel the tools needed to do this seem pretty easy. Just use my 6mm indexable carbide boring bar.

What about small bores like 22 and 6mm? I have an Accupro carbide boring bar that's tiny, and can fit in a .200 bore - but can only reach 1.3" - Not enough to reach the neck of a 223 or 6GT.

Do I forgo the pre-boring of the lands and manage chatter with wax paper / patches? Is there a longer boring bar that I can't find?

Use a twist drill to open it up for your boring bar. Failing that, use a twist drill to remove the rifling for *almost* the length of the chamber, then use your tiny bar to get a chamber-taper started (which will guide your reamer) and you should be able to chamber without 5R-related chatter.

GsT

 

[LVLAaron]

Use a twist drill to open it up for your boring bar. Failing that, use a twist drill to remove the rifling for *almost* the length of the chamber, then use your tiny bar to get a chamber-taper started (which will guide your reamer) and you should be able to chamber without 5R-related chatter.

GsT

Would it be nuts to use a chucking reamer to pull the lands out?

 

[GeneT]

Would it be nuts to use a chucking reamer to pull the lands out?

Not nuts, but to do any better than your chamber reamer, you'd have to take a deep enough cut to get "under" the lands. Otherwise you may suffer the same chatter you're trying to avoid. You could drill out the lands, then go in with a chucking reamer, but at that point you could probably go directly to a boring bar or your chamber reamer in any case.

In part, your approach depends on how you dial in your barrel and how you center your reamer. Are you using a floating reamer holder and relying on a pilot to follow the bore? Do you use a rigid reamer holder and 'force' the chamber into position? If you need the reamer to find an accurate hole (either the pilot, or the walls of the reamer) then your approach needs to take that into account, either by preserving the bore (note you can rough out the chamber, but the pilot should engage the bore OR the edges of the reamer should engage a mating, centered, surface before anything else touches. If you're holding the reamer rigidly and driving with no pilot, I'd rough things out (at least enough to get rid of the rifling) and then chamber.

There are probably a half-dozen methods of dialing a barrel in, another half-dozen methods of pre-chambering prep, and a half-dozen methods of cutting a chamber. That makes a metric crap-ton (actually 6*720!) (that's "!" mathematical factorial, not exclamation mark) of possibilities. At the end of the day, each of us does the best they can and we all produce some winners and some losers. (Well, I only produce winners, just don't look behind the curtain...).

GsT

 

[LVLAaron]

Not nuts, but to do any better than your chamber reamer, you'd have to take a deep enough cut to get "under" the lands. Otherwise you may suffer the same chatter you're trying to avoid. You could drill out the lands, then go in with a chucking reamer, but at that point you could probably go directly to a boring bar or your chamber reamer in any case.

In part, your approach depends on how you dial in your barrel and how you center your reamer. Are you using a floating reamer holder and relying on a pilot to follow the bore? Do you use a rigid reamer holder and 'force' the chamber into position? If you need the reamer to find an accurate hole (either the pilot, or the walls of the reamer) then your approach needs to take that into account, either by preserving the bore (note you can rough out the chamber, but the pilot should engage the bore OR the edges of the reamer should engage a mating, centered, surface before anything else touches. If you're holding the reamer rigidly and driving with no pilot, I'd rough things out (at least enough to get rid of the rifling) and then chamber.

There are probably a half-dozen methods of dialing a barrel in, another half-dozen methods of pre-chambering prep, and a half-dozen methods of cutting a chamber. That makes a metric crap-ton (actually 6*720!) (that's "!" mathematical factorial, not exclamation mark) of possibilities. At the end of the day, each of us does the best they can and we all produce some winners and some losers. (Well, I only produce winners, just don't look behind the curtain...).

GsT

Some really good and concise points in there.

I am using a floating reamer holder.
I am chambering in the headstock and dialing the bore with a long indicator.

What you said about the reamer needing support makes sense... I wouldn't need to cut away the lands where the pilot would be... so the pilot would always be supported. I'd have to work back and forth between the reamer and boring bar a couple of times until I got as far as I could without cutting into the lead. I'll sleep on it.