# Back Boring



## bwarren2 (Mar 6, 2008)

I am curious, what is back boring and what are the benefits of doing this? Is this good for  all type of guns?

Thanks


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## bwarren2 (Mar 6, 2008)

*Found teh answer*

I found the answer for anyone else interested.

What is back boring?
 Back boring is the machining process of reaming or boring.
 Back Bored.
 A back bored shotgun barrel simply means that the bore has been altered to a larger inside diameter. Backboring of any imparticular gauge does; beyond any doubt, add to more wider center mass and will help reduce the length of shot strings in shotguns and when done within reason it does not decrease the velocity of the load. The reason that it does not decrease the velocity is todays plastic wads will expand a great deal to seal the bore of the shotgun and not allow gas to escape around the wad. NO gas leak, NO velocity lost!
 Back boring means less choke constriction.
 As you open up the bore of a shotgun it takes less choke constriction to still get the same pattern as one with a standard bore. This is a big bonus to all that love to shoot trap and other sporting clay games because this puts more pellets into the center mass of the shot string and over all shortens the shot string reducing the time frame from first pellet strike to the last.
 Choke constriction can be measured somewhat in thousands of an inch plus or minus from the bore diameter to a designated choke size such as 12 gauge bore.729 full-.035 constriction, modified-.019 or imp.cylinder-.009.
 Open up the bore then you open up the choke for the same choke result.
  To study and understand more about shotgun bores.
  Gun Digest Book of Shotgun Gunsmithing By Ralph T. Walker.
 If you do decide to do this.
 Make sure you send your barrel to someone that is experienced with this procedure and their level of finish work is excellent. This is by no means an easy process to get right. Back boring can have a second advantage also if there are defects in the bore of your shotgun then back boring will most likely remove the defect.
 Shotgun Bore Effects - Back bored barrel:
 Why How?
 (1) Will back boring increase velocity? Yes
 A back bored barrel will increase velocity in a 12 gauge reliably up to .740 diameter. All wads will expand to seal the bore up to .740 diameter. The reason you have increases in velocity is that you are changing the volume of the interior of the bore which changes the expansion ratio for the powder being burned. All of this works with the corelation of barrel length but by decreasing the resistance of the bigger bore you will get an increase in velocity.
 (2) Will back boring shorten shotstrings? Yes
 A shorter shotstring will occur for the simple reason there is more center mass because of the larger bore diameter.


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## Twenty five ought six (Mar 6, 2008)

I wish it were that simple.  First there is no way to increase "center mass" of a shotshell charge.  That's a mathematical fact, and the goal of doing  so is sort of the fool's goal of the shotgun world.

As far as the benefits of backboring, for every person that thinks that it is the cat's meow, there is another that thinks it is total bunkum--

Here is what Bruce Buck, a noted shotgun writer on technical matters said in 1995:



> 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
> ...



Randy Wakeman, "Why Backboring does not Work",  
http://www.chuckhawks.com/backboring_does_not_work.htm



> Backboring (overbore and underbore barrels) have been experimented with for a long time. It was around 75 years ago that the 12 gauge "3 inch magnum" shell was developed. Shotgun barrel bores were intentionally opened up to the British maximum of .750 in. at that time, with the press back in the day bragging of the lower recoil and better patterning that was observed.
> 
> They had it right, but only half right. Anytime a shotgun barrel is increased in inside diameter with the exact same shotshell, both pressure and velocity are reduced due to the increased barrel volume. There is less recoil, but only because muzzle velocity drops. Pattern densities may often improve, but again due primarily to lower velocities that deform less lead shot on initial setback. You can accomplish the same in any shotgun by lowering the muzzle velocity, all other things remaining constant.
> 
> That why touting "backboring" remains one of the pet rocks of shotgunning today. The real reason to backbore is to pull weight out of a heavy set of barrels. Any other significant "benefits" were disproved well over half a century ago.



For a learned discussion of the pro's and con's, :

http://www.shotgunworld.com/bbs/viewtopic.php?t=17386

More highly technical discussion:

http://www.shotgunworld.com/bbs/viewtopic.php?t=130741&postdays=0&postorder=asc&start=15

At the end of the day, you find that the only true money shooters in the shotgun world, live pigeon shooters, do not have their guns backbored or overbored.  These are guys who would gladly sell a testicle for one more (real live) bird.

Most to the top trapshooters do not have their guns backbored.  These are the second tier money shooters.


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