IC and back boring.

9mmMike · August 12, 2001, 06:18 PM

So, as I now understand (I think) that an IC barrel would be un-IC'd if it were back-bored.
Is that right?
Perhaps I need a back-bore 101 lesson.
Mike

Dave McC · August 13, 2001, 05:57 AM

Let's say your bore now runs right at .729", and the IC marked choke has 10 points of constriction, so it's .719".

You backbore/overbore it to .740 but leave the choke alone. Now you've got 21 points of constriction, more like Modified than IC.

9mmMike · August 13, 2001, 12:30 PM

Ah. So backboring is done from the breech end?

Dave McC · August 13, 2001, 12:37 PM

Yup.These days it's almost always done in conjunction with a long cone, custom chokes, and even (P'tui) porting.

DML · August 14, 2001, 01:00 AM

There are none so blind as those who will not see.

(Jab Jab)

Want to guess how Remington produces their chokes? They back bore.

One interesting thing I have seen on their fixed choke barrel.....
they don't pay much attention to SAAMI specs. I have 870P barrels marked IC with bores as large as .745". They have the required .008" to .010" constriction, but that's all you can say about them. Quality control? What's that?

K80Geoff · August 14, 2001, 06:06 PM

Remington produces chokes by Back Boring???? Uh I fail to see how. Do you mean they bore out the barrel to whatever oversize dimension to get the choke area to the proper constriction?

I have watched them make barrels. They are stretched out by pounding a short tube and stretching it over a mandrel. I understood the mandrel allowed for the choke constriction at the muzzle.

Maybe I'm wrong

Most legitimate gunsmiths who backbore will discuss the choke with you and whether you want the choke altered. Tight chokes can be reamed out to more open dimensions.

The folks who do backboring on competition guns usually supply new choke tubes with the backboring job. The old tubes will not work properly with the backbored barrel.

Geoff Ross

DML · August 14, 2001, 08:21 PM

Perhaps I shouldn't have used such a wide brush. Most of the barrels I see are 20" long or shorter. On many, it is obvious that the bore was reamed. if they are not reaming them, then they have the poorest excuse for mandrels I can imagine.

One thing I don't understand is how they maintain .727" bores on their sporting barrels with screw-in chokes and can't seem to stay within .020" on their Police Magnum and Express HD barrels. Poor quality control? I have 18" barrels in the shop right now that measure from .725" to .745" at the muzzle.

August 12, 2001, 06:18 PM	#1
9mmMike Senior Member Join Date: January 6, 2000 Location: SE PA Posts: 1,049	IC and back boring. So, as I now understand (I think) that an IC barrel would be un-IC'd if it were back-bored. Is that right? Perhaps I need a back-bore 101 lesson. Mike __________________ "Freedom is not free" Visit TheRallyPoint.org TheRallyPoint at LRGC- Saturday August 26th IF YOU LIVE IN PA AND DID NOT VOTE, YOU DESERVE TO LOSE YOUR GUNS!

August 13, 2001, 12:30 PM	#3
9mmMike Senior Member Join Date: January 6, 2000 Location: SE PA Posts: 1,049	Ah. So backboring is done from the breech end? __________________ "Freedom is not free" Visit TheRallyPoint.org TheRallyPoint at LRGC- Saturday August 26th IF YOU LIVE IN PA AND DID NOT VOTE, YOU DESERVE TO LOSE YOUR GUNS!

August 14, 2001, 01:00 AM	#5
DML Senior Member Join Date: November 24, 2000 Location: Aridzona Posts: 257	There are none so blind as those who will not see. (Jab Jab) Want to guess how Remington produces their chokes? They back bore. One interesting thing I have seen on their fixed choke barrel..... they don't pay much attention to SAAMI specs. I have 870P barrels marked IC with bores as large as .745". They have the required .008" to .010" constriction, but that's all you can say about them. Quality control? What's that? __________________ Experience is what you get when you were expecting something else.

August 14, 2001, 06:06 PM	#6
K80Geoff Senior Member Join Date: December 20, 1998 Location: NE Pennsylvania Posts: 3,639	Remington produces chokes by Back Boring???? Uh I fail to see how. Do you mean they bore out the barrel to whatever oversize dimension to get the choke area to the proper constriction? I have watched them make barrels. They are stretched out by pounding a short tube and stretching it over a mandrel. I understood the mandrel allowed for the choke constriction at the muzzle. Maybe I'm wrong Most legitimate gunsmiths who backbore will discuss the choke with you and whether you want the choke altered. Tight chokes can be reamed out to more open dimensions. The folks who do backboring on competition guns usually supply new choke tubes with the backboring job. The old tubes will not work properly with the backbored barrel. Geoff Ross __________________ I am no longer a member of this forum. Bye!

August 14, 2001, 08:21 PM	#7
DML Senior Member Join Date: November 24, 2000 Location: Aridzona Posts: 257	Perhaps I shouldn't have used such a wide brush. Most of the barrels I see are 20" long or shorter. On many, it is obvious that the bore was reamed. if they are not reaming them, then they have the poorest excuse for mandrels I can imagine. One thing I don't understand is how they maintain .727" bores on their sporting barrels with screw-in chokes and can't seem to stay within .020" on their Police Magnum and Express HD barrels. Poor quality control? I have 18" barrels in the shop right now that measure from .725" to .745" at the muzzle. __________________ Experience is what you get when you were expecting something else.

August 13, 2001, 05:57 AM	#2
Dave McC Staff In Memoriam Join Date: October 13, 1999 Location: Columbia, Md, USA Posts: 8,811	Let's say your bore now runs right at .729", and the IC marked choke has 10 points of constriction, so it's .719". You backbore/overbore it to .740 but leave the choke alone. Now you've got 21 points of constriction, more like Modified than IC.

August 13, 2001, 12:37 PM	#4
Dave McC Staff In Memoriam Join Date: October 13, 1999 Location: Columbia, Md, USA Posts: 8,811	Yup.These days it's almost always done in conjunction with a long cone, custom chokes, and even (P'tui) porting.