What is backboring and what's it do?
- Thread starter MISFIRE
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Harry Bonar
New member
Back-boring
Dear Sir:
Backboring is the legthening of the taper in front of the chamber to allow a more gradual effect on the shot pattern.
On a shotgun that is not designed this way at the factory, that is, with a more gradual taper at the reinforce on the O.D. of the bbl. it, in my opinion, is a very, very, dangerous practice!
Not knowing the steel used in a shotgun bb. is akin to our recent discussions on re-heat-treating Mauser actions. If the factory designs a bbl. taper, taking into consideration the leade or "freebore" of the chamber and if after the fact we go in and decrease the thickness by "back-boring" we decrease the safety of that bbl.
Max pressure is achieved within inches of the breech-face and the further the charge moves down the bbl. on a hi-power rifle the pressure drops at muzzle (starting out at 55000 cup to start with and droping to roughly 7000 cup at the muzzle) to about 7000 cup. - of course a shotgun is much lower pressure.
Now, if after consulting the manufacturer, then if they give clearance for you to "back-bore" then do it if you must.
Sorry, but that's my opinion. Harry B.
Dear Sir:
Backboring is the legthening of the taper in front of the chamber to allow a more gradual effect on the shot pattern.
On a shotgun that is not designed this way at the factory, that is, with a more gradual taper at the reinforce on the O.D. of the bbl. it, in my opinion, is a very, very, dangerous practice!
Not knowing the steel used in a shotgun bb. is akin to our recent discussions on re-heat-treating Mauser actions. If the factory designs a bbl. taper, taking into consideration the leade or "freebore" of the chamber and if after the fact we go in and decrease the thickness by "back-boring" we decrease the safety of that bbl.
Max pressure is achieved within inches of the breech-face and the further the charge moves down the bbl. on a hi-power rifle the pressure drops at muzzle (starting out at 55000 cup to start with and droping to roughly 7000 cup at the muzzle) to about 7000 cup. - of course a shotgun is much lower pressure.
Now, if after consulting the manufacturer, then if they give clearance for you to "back-bore" then do it if you must.
Sorry, but that's my opinion. Harry B.
I am not sure what Harry is talking about but it seems we understand the term differently.
As I know it, and did it, backboring, or what we used to call "jug choking", is a process of reaming out a shotgun barrel at the front, but behind the regular choke. It can also be used to put a choke in a barrel that has none. The widened out area is about 2 1/2" long and does not go anywhere near the chamber.
The idea is that the shot charge expands into the widened area, then is constricted down to the smaller diameter part of the barrel ahead of it, thus providing (or increasing) a choke. There is another use.
It was once commonly used in shotgun card shoots, where the idea is to get a shot pellet as close as possible to an X mark on the target card. Naturally, close patterning guns have the best chance of doing so, and a jug choke gives a tighter pattern than even full choke. More important, those games usually prohibit use of a choke device, so a jug choke enables the gunner to cheat. (I am shocked, I tell you, shocked!)
I will agree with Harry that some shotguns might not be suitable for jug choking; we would never do it on double guns or on any kind of Damascus barrel, a thin wall barrel, or a Winchester 59 with a fiberglas barrel. For most repeaters and newer single shots, it works fine.
Jim
As I know it, and did it, backboring, or what we used to call "jug choking", is a process of reaming out a shotgun barrel at the front, but behind the regular choke. It can also be used to put a choke in a barrel that has none. The widened out area is about 2 1/2" long and does not go anywhere near the chamber.
The idea is that the shot charge expands into the widened area, then is constricted down to the smaller diameter part of the barrel ahead of it, thus providing (or increasing) a choke. There is another use.
It was once commonly used in shotgun card shoots, where the idea is to get a shot pellet as close as possible to an X mark on the target card. Naturally, close patterning guns have the best chance of doing so, and a jug choke gives a tighter pattern than even full choke. More important, those games usually prohibit use of a choke device, so a jug choke enables the gunner to cheat. (I am shocked, I tell you, shocked!)
I will agree with Harry that some shotguns might not be suitable for jug choking; we would never do it on double guns or on any kind of Damascus barrel, a thin wall barrel, or a Winchester 59 with a fiberglas barrel. For most repeaters and newer single shots, it works fine.
Jim
cntryboy1289
New member
I think Harry may have been talking about lengthening the forcing cone. What he is talking about in that regard though is correct as well as what Jim said about doing the backboring. Mossberg does a fairly decent job of backboring and their guns from the factory, and I'll leave it up to you to decide if you want to undertake it. It can only be done to barrels that mic well within the specs of the minimum. I would make sure you have the ID and OD measurements and make sure you have enough to ream out long before you ever think about reaming the barrel.
Backbored bbls as advertised today, like Browning for example, are bbls with a larger bore diameter than standard. I believe standard runs around .729.
I think backbored bbls can be .740, etc.
People that do that modification and factory guns that offer it, make the claim of reduced recoil and better patterns. That's debatable IMO and I have both.
What it does do, without a doubt, is lighten the bbls and change the balance if you backbore a standard bbl, since you are removing metal and making the bbls thinner.
Factory backbored bbls like Browning are heavier because they maintain the wall thickness, so more metal.
I think backbored bbls can be .740, etc.
People that do that modification and factory guns that offer it, make the claim of reduced recoil and better patterns. That's debatable IMO and I have both.
What it does do, without a doubt, is lighten the bbls and change the balance if you backbore a standard bbl, since you are removing metal and making the bbls thinner.
Factory backbored bbls like Browning are heavier because they maintain the wall thickness, so more metal.
Harry Bonar
New member
back-boring
Yes to backboring:
Several of you have said it correctly.
I agree that making the taper in front of the chamber on shotguns is a boon to shot patterns, and as you mention, sreveral makers are offering back-bored guns now! These companies have ascertained that it is acceptable and have contoured their bbls. to accept that.
My problen was doing it to bbls. that were already in the minimum configuration. Back-boring these bbls. was removing bbl. thickness at the point of max pressure.
As an aside, A-Square advocates a paralel throat in their rifle cartridges for a ways and then the standard leade. this way you can seat your bullets as far out as magazine allows and tune your rifle for accuracy by changing bullet seating depth! This is different from "free-boring."
Shooters can use bullet seating depths to do the same thing the BOSS system does to increase accuracy as bullet seating depth has a marked effect on bbl. vibration!
Harry B.
Yes to backboring:
Several of you have said it correctly.
I agree that making the taper in front of the chamber on shotguns is a boon to shot patterns, and as you mention, sreveral makers are offering back-bored guns now! These companies have ascertained that it is acceptable and have contoured their bbls. to accept that.
My problen was doing it to bbls. that were already in the minimum configuration. Back-boring these bbls. was removing bbl. thickness at the point of max pressure.
As an aside, A-Square advocates a paralel throat in their rifle cartridges for a ways and then the standard leade. this way you can seat your bullets as far out as magazine allows and tune your rifle for accuracy by changing bullet seating depth! This is different from "free-boring."
Shooters can use bullet seating depths to do the same thing the BOSS system does to increase accuracy as bullet seating depth has a marked effect on bbl. vibration!
Harry B.
Harry Bonar
New member
backboring
Hey! Guys!
One of, no, the best manual I've ever used has been the A-Square Shooters Manual - ANY SHOT YOU WANT.
You can still order it on internet for about $39.00.
These guys, headed by Col. Art Alphin, and Boddington, F.A. and others cover rifle, big game hunting, head-spacing, bullets, all of the large calibers (from 223 up to the 500 Tyranosaurus)! They give more info on all subjects!
I have learned volumes from those men - even built a 416 Taylor, and a 9.3X62, from their recommendations!
Some of these men have died and someday It will be out of print and gone! They taught me things I'd always wondered about and had thought about before.
These guys are REAL HUNTERS, from prarie dogs to Cape Buffalo!
It would be the best money you could spend - it's FILLED with technical data and charts etc!
They used the Enfield action to build their rifles on and today these rifles are in the $2,000.00 range!
They have gotten SAAMI to standardize many calibers!
Harry B.
Hey! Guys!
One of, no, the best manual I've ever used has been the A-Square Shooters Manual - ANY SHOT YOU WANT.
You can still order it on internet for about $39.00.
These guys, headed by Col. Art Alphin, and Boddington, F.A. and others cover rifle, big game hunting, head-spacing, bullets, all of the large calibers (from 223 up to the 500 Tyranosaurus)! They give more info on all subjects!
I have learned volumes from those men - even built a 416 Taylor, and a 9.3X62, from their recommendations!
Some of these men have died and someday It will be out of print and gone! They taught me things I'd always wondered about and had thought about before.
These guys are REAL HUNTERS, from prarie dogs to Cape Buffalo!
It would be the best money you could spend - it's FILLED with technical data and charts etc!
They used the Enfield action to build their rifles on and today these rifles are in the $2,000.00 range!
They have gotten SAAMI to standardize many calibers!
Harry B.
cntryboy1289
New member
Thanks Harry
Appreciate the info on the book Harry. I'll have to get a copy of it myself.
Appreciate the info on the book Harry. I'll have to get a copy of it myself.
OK, here is "the word" from SAAMI from their official glossary:
"CHOKE, JUG
A type of shotgun barrel choke, wherein a slight recess is formed in the bore approximately one inch behind the muzzle. The recess causes the shot to gather before leaving the muzzle resulting in a denser pattern.
BACK BORE
A shotgun, chambered for a specified gauge, whose barrel bore diameter is greater than the nominal specified for that gauge, but does not exceed SAAMI maximum."
My apology for confusing the terms.
Jim
"CHOKE, JUG
A type of shotgun barrel choke, wherein a slight recess is formed in the bore approximately one inch behind the muzzle. The recess causes the shot to gather before leaving the muzzle resulting in a denser pattern.
BACK BORE
A shotgun, chambered for a specified gauge, whose barrel bore diameter is greater than the nominal specified for that gauge, but does not exceed SAAMI maximum."
My apology for confusing the terms.
Jim
cntryboy1289
New member
no problem here
Mossberg actually makes there barrels slightly bigger and then reduces them down at the choke if I am not mistaken. I can not remember right this sec, but there are some drawbacks with this system. Nothing major, but some chokes cannot be used with it if I am correect on it.
Mossberg actually makes there barrels slightly bigger and then reduces them down at the choke if I am not mistaken. I can not remember right this sec, but there are some drawbacks with this system. Nothing major, but some chokes cannot be used with it if I am correect on it.
Will Fennell
New member
different modifications.....
Gentlemen,
Backboring is a shotgun barrel modification the involves opening the inside diameter of the barrel's bore to a larger diameter. This can be done for several reasons.....slight decrease in recoil, slightly better patterns, and decrease barrel weight. The wieght reduction is not as noticeable with a single barreled gun, but it can certainly change the balance of a O/U when you do both barrels. Of course barrel wall thickness must be taken into consideration, and I have seen backboring jobs that have been done incorrectly lead to problems. Conversly, I have fired many hundreds of thousands of 12 ga rounds through barrels that have been safely backbored, with no ill effect.
Harry, the operation the you are refering to, lenghtening the taper[ called the Forcing Cone] ahead of the chamber, can also be done safely, or by the inexperienced, unsafely. Lenghtening the forcing cones, correctly of course, can noticeably reduce recoil, and improve pattern. Again, of course the gunsmith need to take into consideration the wall thickness ahead of the chamber before taking on any such jobs.
This leads to the question, if these mod's are so good, why don't the factories do this to start with....the answer is that shotshells have advanced. In the days of felt and cardboard wads, you needed a short, steep forcing cone and tight bore to seal the gas behing the relatively stiff wad. Now the virtually every shell uses plastic wads, which are softer and easily expand to seal the gases behind the wad in the bore, you can open up the bore, and leghten the forcing cones to "smooth out" the transition of the shot column from the shell[chambe area] through the forcing cone, and down the bore. This means a reduction in chamber pressure[peak pressure] and less shot deformation, resulting in better patterns and slightly reduced recoil.
And every little bit helps
Gentlemen,
Backboring is a shotgun barrel modification the involves opening the inside diameter of the barrel's bore to a larger diameter. This can be done for several reasons.....slight decrease in recoil, slightly better patterns, and decrease barrel weight. The wieght reduction is not as noticeable with a single barreled gun, but it can certainly change the balance of a O/U when you do both barrels. Of course barrel wall thickness must be taken into consideration, and I have seen backboring jobs that have been done incorrectly lead to problems. Conversly, I have fired many hundreds of thousands of 12 ga rounds through barrels that have been safely backbored, with no ill effect.
Harry, the operation the you are refering to, lenghtening the taper[ called the Forcing Cone] ahead of the chamber, can also be done safely, or by the inexperienced, unsafely. Lenghtening the forcing cones, correctly of course, can noticeably reduce recoil, and improve pattern. Again, of course the gunsmith need to take into consideration the wall thickness ahead of the chamber before taking on any such jobs.
This leads to the question, if these mod's are so good, why don't the factories do this to start with....the answer is that shotshells have advanced. In the days of felt and cardboard wads, you needed a short, steep forcing cone and tight bore to seal the gas behing the relatively stiff wad. Now the virtually every shell uses plastic wads, which are softer and easily expand to seal the gases behind the wad in the bore, you can open up the bore, and leghten the forcing cones to "smooth out" the transition of the shot column from the shell[chambe area] through the forcing cone, and down the bore. This means a reduction in chamber pressure[peak pressure] and less shot deformation, resulting in better patterns and slightly reduced recoil.
And every little bit helps
Harry Bonar
New member
backboring
Dear Shooters:
Sounds good!
Harry B.
Dear Shooters:
Sounds good!
Harry B.