I have done a search and cannot find what I want. What exactly does lengthening the force cone do? Do I need to do this for my stock 11-87P or 870P barrels? Would it help my 28 inch 870 bird barrel? Is this procedure much different from the Vang Comp without porting? Is this something I can entrust to the average gunsmith or is it something best left to a specialist?
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Question for Msrs Lupin or McCracken re: force cones
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Fred Fuller
Moderator Emeritus
I will defer to the Internet's greatest shotgun expert, that living legend in his own mind, The Technoid:
==============================================
http://www.shotgunreport.com/TechTech/TechnicalTracts/ConesBores.html
THE TECHNOID BARRELS ALONG (continued from last month- it
just never ends)...
In the first part of this article, the Technoid held forth on the
subject of modifications you can make to the barrel of your shotgun to
(theoretically) improve performance. He touched upon 1) screw choking
(he likes it) and 2) barrel porting (he likes it not). This month the
Technoid earns even more general admiration, adoration and awe by
delving into the mysteries of forcing cones and backboring. Here goes.
Pull on those barnyard boots and jump on in with the Technoid. He may
not be right, but he is always positive.
3) Forcing Cones: We refer here to lengthening the taper where
the chamber and the barrels meet, not where the barrels and the choke
meet. Technically, they are both forcing cones. Some modern shotgun
come with long cones, some do not. The softest shooting (but most log-
like) O/U ever made, the Krieghof K80, has long cones. However, it is
interesting to note that most of their high end Ulm pigeon guns have
short cones. Most current production Berettas come with fairly long
cones. Japanese Brownings do not, although they come backbored and
ported. Obviously, there is no universality of opinion here either. Well,
you don't have to worry about what the manufacturers say, listen to the
Technoid. Grind 'em out!
Lengthened forcing cones are the one barrel modification which
the Technoid has found to unfailingly reduce perceived recoil and
slightly improve pattern. John McDougall, in the Australian magazine
Guns & Game, wrote that his tests have shown a consistent 10% pattern
tightening when cones are lengthened. This is attributed to less shot
deformation.
Long cones appear to take a touch of the peak off of the recoil.
The area under the recoil curve remains the same (Newton still has to be
accommodated and apples still fall to the ground), but the slope of the
curve seems to change and the recoil is drawn out a bit. This is the
"shove vs punch" comparison which makes semi-automatics seem so soft
shooting.
It is vital that the lengthened cones be properly polished as any
roughness in this area will pick up a lot of plastic from the wads. Tom
Roster claims that the maximum beneficial cone length is 1 3/4" and that
longer cones do not improve things. This may be so, but the Technoid
has observed that extra long 4" to 6" cones as done by The Shotgun
Shop and Seminole seem to be able to take an absolutely mirror polish.
The shorter cones with their sharper angle may be more difficult to
polish correctly and never seem to buff up as well.
Rumor has it that fiber wads do not perform well in guns with
long cones due to gas blowby. This is baloney. The Technoid's
checkered past included shooting tens of thousands of 3 1/2 dram Federal
T123 fiber wad International Skeet loads through Belgian B-25s with
lengthened cones and there was never a problem. Modern plastic wads
present no difficulty whatsoever and appear to be able to properly
obturate in a sewer pipe. Long forcing cones should cost you $50 to
$150 and are worth it.
4) Backboring: The nominal interior diameter of a 12 gauge
shotgun barrel is .729", but your barrel could measure anything from
.720" to .800" and still handle a 12 gauge shell. Anything bigger than
.729" is technically overbore or backbored. Stan Baker, Seattle
gunsmith, claims to have coined the term "backbore" in order to avoid
the less attractive connotation of "overbore". They mean the same thing.
The Technoid, in one of his denser moments, had some guns
backbored in an attempt to reduce recoil. It did not work and should not
have come as a surprise. If you look at the formula for free recoil, bore
size is not one of the components. From a purely subjective (not
mathematical) point of view, it also failed to lower the recoil sensation
the way that elongating the cones did. Don't know why.
In theory, backboring decreases friction and provides a larger
wad base for the powder gases to push upon. Both of these should
increase velocity and they may to a slight extent. Stan Baker claimed
that his extreme and maximum .800" Big Bore barrels added 50 fps.
Even so, normal shell to shell factory variation is 30 fps, so the most
extreme backboring does not really affect velocity for all practical
purposes.
Very often when people have guns backbored, they also run the
cones out and may also have the gun ported. When everything is done
at once it is impossible to tell if one particular change had a measurable
effect. Subjective recoil reduction caused by elongated cones is often
attributed to backboring or porting.
Instead of decreasing recoil, aftermarket backboring actually
increases it because the weight of the gun is reduced by the amount of
metal removed and ejecta velocity may be increased slightly. Gun
weight and ejecta velocity are important components of the recoil
formula.
There is a big difference between "aftermarket" backboring and
"factory" backbored new guns. The factory backbored barrels are
actually a little heavier because wall thickness is maintained while barrel
diameter is increased. There is more metal. If you want an example of
road hugging weight brought on by factory "backboring", try to swing a
new Browning 425 Ultra with 32" barrels.
Large bores may help slightly when using extremely heavy
hunting loads, but there is no proven meaningful change in velocity or
recoil with standard target loads. The aforementioned Australian tests
found that backboring neither meaningfully increased velocity nor
consistently improved patterns. Sorry folks, factory "backboring" is just
another marketing ploy to go along with barrel porting.
Does aftermarket (not factory) backboring have any benefit at all?
You can bet your Junior Technoid magic slide rule ring that it does.
While aftermarket backboring may not reduce recoil or improve patterns,
it sure reduces weight. If the barrels on your gun feel too heavy and
unresponsive, you may be able to put them on a diet. Most standard
barrels have a wall thickness of around .040". This is a lot of meat and
might be substantially reduced. On a standard 30" set of barrels,
backboring .010" will reduce barrel weight by 2.77 ounces. A .020
backbore will take off a monumental 5.58 ounces. A change of 3 ounces
is a lot, so go easy. Check first with your gunsmith. He will know
what is safe. Be aware, however, that aftermarket backboring will void
any factory warrantee. Briley charges about $150 per tube for
backboring.
Good news/bad news. Backboring works well to reduce the
weight of solid choke barrels. Unfortunately, solid choked barrels are
usually pretty well balanced and seldom need it. It is the factory screw
choke barrels that are usually too loady up front, especially the 32" jobs.
A backbore of 3 to 4 ounces could transform these guns from pigs to
peacocks. That is the good news. The bad news is that Briley does not
want to hear about backboring a gun with factory screw chokes. Now
you know how Tantalus felt when the Greek gods kept the water and
grapes just out of reach. The problem is that enlargement of the bore
may cause the skirt of the unaltered choke tube to intrude into the bore
itself. This would cause the choke to be added to the ejecta on the first
shot! Bad move.
Though Briley will not touch your screw choked Beretta or 425,
Ken Eyster and several other custom gunsmiths may still be willing to
backbore a screw choked gun. Whatever you do, make sure your
backboring is done by a pro
.
There you go Junior Technoids. You now have four separate and
efficient ways to ruin a perfectly good set of barrels. Remember the
Technoid's motto: "The factory never does it right. It is up to us."
===============================================
Personally I like forcing cones a bit longer, it really does seem to help patterns a bit- or more, depending on the gun and load. I note no recoil changes due to lengthened cones but then I am an insensitive lout so YMMV on that point.
I prefer to let Colonial Arms in Selma, AL do my barrel work, number one they are home town folks so it gives me an excuse to go visit when I am home and chew the fat. Number two, they are stone professionals and have the equipment plus years of expertise in messing about with shotgun barrels to do what needs doing and leave the rest alone, plus they are honest enough to tell you what will best produce the results you want. Or in some cases, that there isn't much you can do, as they did with the no-patterning apparent factory overbored 18" RS 870P barrel I was plagued with for so long (they measured the bore and the barrel walls and said it looked to them like a factory barrel with a .739 bore and .729 choke and unless I wanted to put in Invector choke tubes I was pretty well stuck with it as it was). If you have someone you trust it isn't really rocket science to 'do' forcing cones.
Backboring I can't see any benefit in for its own sake, YMMV. The Vang deal basically backbores up to within a couple of inches of the muzzle in order to leave a constriction at the muzzle for choke, that works well for its intended purpose- but I would leave off the porting if I were going to have that done. It costs about the same as having a forcing cone job done and having choke tubes put in, and the results should be pretty close to the same. With the Vang treatment you get a fixed choke barrel, a theoretical plus for strength, with choke tubes you get versatility- again, some advantage either way, a personal choice as to which serves better.
lpl/nc
==============================================
http://www.shotgunreport.com/TechTech/TechnicalTracts/ConesBores.html
THE TECHNOID BARRELS ALONG (continued from last month- it
just never ends)...
In the first part of this article, the Technoid held forth on the
subject of modifications you can make to the barrel of your shotgun to
(theoretically) improve performance. He touched upon 1) screw choking
(he likes it) and 2) barrel porting (he likes it not). This month the
Technoid earns even more general admiration, adoration and awe by
delving into the mysteries of forcing cones and backboring. Here goes.
Pull on those barnyard boots and jump on in with the Technoid. He may
not be right, but he is always positive.
3) Forcing Cones: We refer here to lengthening the taper where
the chamber and the barrels meet, not where the barrels and the choke
meet. Technically, they are both forcing cones. Some modern shotgun
come with long cones, some do not. The softest shooting (but most log-
like) O/U ever made, the Krieghof K80, has long cones. However, it is
interesting to note that most of their high end Ulm pigeon guns have
short cones. Most current production Berettas come with fairly long
cones. Japanese Brownings do not, although they come backbored and
ported. Obviously, there is no universality of opinion here either. Well,
you don't have to worry about what the manufacturers say, listen to the
Technoid. Grind 'em out!
Lengthened forcing cones are the one barrel modification which
the Technoid has found to unfailingly reduce perceived recoil and
slightly improve pattern. John McDougall, in the Australian magazine
Guns & Game, wrote that his tests have shown a consistent 10% pattern
tightening when cones are lengthened. This is attributed to less shot
deformation.
Long cones appear to take a touch of the peak off of the recoil.
The area under the recoil curve remains the same (Newton still has to be
accommodated and apples still fall to the ground), but the slope of the
curve seems to change and the recoil is drawn out a bit. This is the
"shove vs punch" comparison which makes semi-automatics seem so soft
shooting.
It is vital that the lengthened cones be properly polished as any
roughness in this area will pick up a lot of plastic from the wads. Tom
Roster claims that the maximum beneficial cone length is 1 3/4" and that
longer cones do not improve things. This may be so, but the Technoid
has observed that extra long 4" to 6" cones as done by The Shotgun
Shop and Seminole seem to be able to take an absolutely mirror polish.
The shorter cones with their sharper angle may be more difficult to
polish correctly and never seem to buff up as well.
Rumor has it that fiber wads do not perform well in guns with
long cones due to gas blowby. This is baloney. The Technoid's
checkered past included shooting tens of thousands of 3 1/2 dram Federal
T123 fiber wad International Skeet loads through Belgian B-25s with
lengthened cones and there was never a problem. Modern plastic wads
present no difficulty whatsoever and appear to be able to properly
obturate in a sewer pipe. Long forcing cones should cost you $50 to
$150 and are worth it.
4) Backboring: The nominal interior diameter of a 12 gauge
shotgun barrel is .729", but your barrel could measure anything from
.720" to .800" and still handle a 12 gauge shell. Anything bigger than
.729" is technically overbore or backbored. Stan Baker, Seattle
gunsmith, claims to have coined the term "backbore" in order to avoid
the less attractive connotation of "overbore". They mean the same thing.
The Technoid, in one of his denser moments, had some guns
backbored in an attempt to reduce recoil. It did not work and should not
have come as a surprise. If you look at the formula for free recoil, bore
size is not one of the components. From a purely subjective (not
mathematical) point of view, it also failed to lower the recoil sensation
the way that elongating the cones did. Don't know why.
In theory, backboring decreases friction and provides a larger
wad base for the powder gases to push upon. Both of these should
increase velocity and they may to a slight extent. Stan Baker claimed
that his extreme and maximum .800" Big Bore barrels added 50 fps.
Even so, normal shell to shell factory variation is 30 fps, so the most
extreme backboring does not really affect velocity for all practical
purposes.
Very often when people have guns backbored, they also run the
cones out and may also have the gun ported. When everything is done
at once it is impossible to tell if one particular change had a measurable
effect. Subjective recoil reduction caused by elongated cones is often
attributed to backboring or porting.
Instead of decreasing recoil, aftermarket backboring actually
increases it because the weight of the gun is reduced by the amount of
metal removed and ejecta velocity may be increased slightly. Gun
weight and ejecta velocity are important components of the recoil
formula.
There is a big difference between "aftermarket" backboring and
"factory" backbored new guns. The factory backbored barrels are
actually a little heavier because wall thickness is maintained while barrel
diameter is increased. There is more metal. If you want an example of
road hugging weight brought on by factory "backboring", try to swing a
new Browning 425 Ultra with 32" barrels.
Large bores may help slightly when using extremely heavy
hunting loads, but there is no proven meaningful change in velocity or
recoil with standard target loads. The aforementioned Australian tests
found that backboring neither meaningfully increased velocity nor
consistently improved patterns. Sorry folks, factory "backboring" is just
another marketing ploy to go along with barrel porting.
Does aftermarket (not factory) backboring have any benefit at all?
You can bet your Junior Technoid magic slide rule ring that it does.
While aftermarket backboring may not reduce recoil or improve patterns,
it sure reduces weight. If the barrels on your gun feel too heavy and
unresponsive, you may be able to put them on a diet. Most standard
barrels have a wall thickness of around .040". This is a lot of meat and
might be substantially reduced. On a standard 30" set of barrels,
backboring .010" will reduce barrel weight by 2.77 ounces. A .020
backbore will take off a monumental 5.58 ounces. A change of 3 ounces
is a lot, so go easy. Check first with your gunsmith. He will know
what is safe. Be aware, however, that aftermarket backboring will void
any factory warrantee. Briley charges about $150 per tube for
backboring.
Good news/bad news. Backboring works well to reduce the
weight of solid choke barrels. Unfortunately, solid choked barrels are
usually pretty well balanced and seldom need it. It is the factory screw
choke barrels that are usually too loady up front, especially the 32" jobs.
A backbore of 3 to 4 ounces could transform these guns from pigs to
peacocks. That is the good news. The bad news is that Briley does not
want to hear about backboring a gun with factory screw chokes. Now
you know how Tantalus felt when the Greek gods kept the water and
grapes just out of reach. The problem is that enlargement of the bore
may cause the skirt of the unaltered choke tube to intrude into the bore
itself. This would cause the choke to be added to the ejecta on the first
shot! Bad move.
Though Briley will not touch your screw choked Beretta or 425,
Ken Eyster and several other custom gunsmiths may still be willing to
backbore a screw choked gun. Whatever you do, make sure your
backboring is done by a pro
.
There you go Junior Technoids. You now have four separate and
efficient ways to ruin a perfectly good set of barrels. Remember the
Technoid's motto: "The factory never does it right. It is up to us."
===============================================
Personally I like forcing cones a bit longer, it really does seem to help patterns a bit- or more, depending on the gun and load. I note no recoil changes due to lengthened cones but then I am an insensitive lout so YMMV on that point.
I prefer to let Colonial Arms in Selma, AL do my barrel work, number one they are home town folks so it gives me an excuse to go visit when I am home and chew the fat. Number two, they are stone professionals and have the equipment plus years of expertise in messing about with shotgun barrels to do what needs doing and leave the rest alone, plus they are honest enough to tell you what will best produce the results you want. Or in some cases, that there isn't much you can do, as they did with the no-patterning apparent factory overbored 18" RS 870P barrel I was plagued with for so long (they measured the bore and the barrel walls and said it looked to them like a factory barrel with a .739 bore and .729 choke and unless I wanted to put in Invector choke tubes I was pretty well stuck with it as it was). If you have someone you trust it isn't really rocket science to 'do' forcing cones.
Backboring I can't see any benefit in for its own sake, YMMV. The Vang deal basically backbores up to within a couple of inches of the muzzle in order to leave a constriction at the muzzle for choke, that works well for its intended purpose- but I would leave off the porting if I were going to have that done. It costs about the same as having a forcing cone job done and having choke tubes put in, and the results should be pretty close to the same. With the Vang treatment you get a fixed choke barrel, a theoretical plus for strength, with choke tubes you get versatility- again, some advantage either way, a personal choice as to which serves better.
lpl/nc
JohnBT
Member
"Remember the Technoid's motto: "The factory never does it right. It is up to us." "
Meeting this guy is one of my goals in life.
John
Meeting this guy is one of my goals in life.
John
Dave McCracken
Moderator In Memoriam
Lee nailed it as he is habitually doing. Let me add a little something...
The slightly overbored(.733") barrel on the TB seems a soft shooter compared to my other 30" barrels. Trouble is, it's a couple oz heavier, so it's hard to gauge what is what.
It has, like several other barrels here, a lengthened cone, maybe 1 3/4 ".
Dunno if the long cone helps patterns with bird shot. IIRC, doing one of my other barrels tightened buck patterns a couple inches at 25 yards.
Roster states that long cones do not help with small shot. He says it takes 4s or larger to see the effects.
Fine. While I shoot mostly small shot these days, I like optimum large pellet patterns JIC.
Counting the longer than usual cones on the two LC barrels here, about half my barrels have longer cones than those of old. The rest may not be altered.
Longer cones is something to do when 99/100 is simply unacceptable or when we just HAVE to do something to scratch the tinkering itch.
The slightly overbored(.733") barrel on the TB seems a soft shooter compared to my other 30" barrels. Trouble is, it's a couple oz heavier, so it's hard to gauge what is what.
It has, like several other barrels here, a lengthened cone, maybe 1 3/4 ".
Dunno if the long cone helps patterns with bird shot. IIRC, doing one of my other barrels tightened buck patterns a couple inches at 25 yards.
Roster states that long cones do not help with small shot. He says it takes 4s or larger to see the effects.
Fine. While I shoot mostly small shot these days, I like optimum large pellet patterns JIC.
Counting the longer than usual cones on the two LC barrels here, about half my barrels have longer cones than those of old. The rest may not be altered.
Longer cones is something to do when 99/100 is simply unacceptable or when we just HAVE to do something to scratch the tinkering itch.
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