The Firing Line Forums - View Single Post - Savage 30-06 take off barrel

HiBC · March 7, 2018, 02:20 PM

Steve,
For a time I earned my wages running a broach machine.I know something about broaches.
A broach is a CUTTING tool .You start it in an existing geometry in the workpiece,usually a hole.The broach has a series of teeth,each taking a small cut.Over the length of the broach,which is often one,or two,or three feet long,the original hole in the part is transformed to the desired geometry.
It might be a keyway in a pulley,a square,a hex,splines,etc.
They area great tool!
But they have a limitation . Each tooth makes a chip.That chip cannot escape via coolant flushing .Its trapped.
Each tooth on the broach has to have enough gullet to contain the chip for the entire length of the cut.
The broach is pulled through the work piece,so just like with a tap,you have to have a core of steel to turn the tap,you have to have a core of steel to pull a broach.
On a .308 caliber "broach",how large of a gullet can you grind in the broach for chip clearance?Not enough to pull through over 20 inches of barrel.

What happens when you pack up the flutes of a tap or reamer or drill or mill cutter? It breaks.

A broach is a wonderful tool,but chip clearance limits the length of cut possible with one.

Rifle barrels are not broach cut. I don't doubt a handgun barrel,such as a1911 barrel,can be broach cut.

The common method for most production rifled barrels and some excellent custom barrels is Button rifling. A very hard button with the desired rifling form and helix is forced through a finish reamed round bore. The button forms the steel,it does not cut. It makes no chips.

Cut rifling is an excellent method for making custom barrels.It cuts chips for the full length of the barrel.The difference from a broach is that chips can be controlled with the single cutter on the end of the mandrel.

Most of us are capable of learning a variety of skills,Steve,and I expect you could learn how to lead lap a barrel .
I do not think an internet thread is the place to learn.
I do not suggest you use a hard to afford barrel you want to shoot as a practice piece.
Actually,not just every fine rookie off the street can lap barrels for Lilja or Shilen or Krieger without some training and practice.

"A little knowledge....." and "Fools rush in..."

Note,for example,barrel makers sell barrels at a supplied length,but the recommend cutting 1 1'2" or so off and recrowning. Why is that?

Because the lapping will funnel the entry. Chambering takes care of it at the breech.

While I am not a great advocate of fire lapping,David Tubbs is not a moron.
If you need to do a little improvement on a production bore,fire lapping IS a viable DYI option.

Not all grit is created equal.Particularly in regard to grit size control.
There are grits the embed,grits that break down,etc.

Coarser grits cut more clearance,larger holes,than fine grits. And,they leave their own tracks.

I'm not a fan of grit progression,as in 220 to 600,or whatever. I'd use the finish grit.
If you decide to buy the barrel,shoot it. See how it does.

If you have to tinker, I have fire lapped a rough 30-06 barrel using cast lead 30-30 bullets and diamond mold polishing compound .Only one,very fine grit.

It became a very accurate barrel.

March 7, 2018, 02:20 PM	#43
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,289	Steve, For a time I earned my wages running a broach machine.I know something about broaches. A broach is a CUTTING tool .You start it in an existing geometry in the workpiece,usually a hole.The broach has a series of teeth,each taking a small cut.Over the length of the broach,which is often one,or two,or three feet long,the original hole in the part is transformed to the desired geometry. It might be a keyway in a pulley,a square,a hex,splines,etc. They area great tool! But they have a limitation . Each tooth makes a chip.That chip cannot escape via coolant flushing .Its trapped. Each tooth on the broach has to have enough gullet to contain the chip for the entire length of the cut. The broach is pulled through the work piece,so just like with a tap,you have to have a core of steel to turn the tap,you have to have a core of steel to pull a broach. On a .308 caliber "broach",how large of a gullet can you grind in the broach for chip clearance?Not enough to pull through over 20 inches of barrel. What happens when you pack up the flutes of a tap or reamer or drill or mill cutter? It breaks. A broach is a wonderful tool,but chip clearance limits the length of cut possible with one. Rifle barrels are not broach cut. I don't doubt a handgun barrel,such as a1911 barrel,can be broach cut. The common method for most production rifled barrels and some excellent custom barrels is Button rifling. A very hard button with the desired rifling form and helix is forced through a finish reamed round bore. The button forms the steel,it does not cut. It makes no chips. Cut rifling is an excellent method for making custom barrels.It cuts chips for the full length of the barrel.The difference from a broach is that chips can be controlled with the single cutter on the end of the mandrel. Most of us are capable of learning a variety of skills,Steve,and I expect you could learn how to lead lap a barrel . I do not think an internet thread is the place to learn. I do not suggest you use a hard to afford barrel you want to shoot as a practice piece. Actually,not just every fine rookie off the street can lap barrels for Lilja or Shilen or Krieger without some training and practice. "A little knowledge....." and "Fools rush in..." Note,for example,barrel makers sell barrels at a supplied length,but the recommend cutting 1 1'2" or so off and recrowning. Why is that? Because the lapping will funnel the entry. Chambering takes care of it at the breech. While I am not a great advocate of fire lapping,David Tubbs is not a moron. If you need to do a little improvement on a production bore,fire lapping IS a viable DYI option. Not all grit is created equal.Particularly in regard to grit size control. There are grits the embed,grits that break down,etc. Coarser grits cut more clearance,larger holes,than fine grits. And,they leave their own tracks. I'm not a fan of grit progression,as in 220 to 600,or whatever. I'd use the finish grit. If you decide to buy the barrel,shoot it. See how it does. If you have to tinker, I have fire lapped a rough 30-06 barrel using cast lead 30-30 bullets and diamond mold polishing compound .Only one,very fine grit. It became a very accurate barrel.