doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Backboring a 20ga

A while back, someone stated that enlarging a 20g bore over the standard by a certain amount, had a very beneficial effect on the pattern.

I'm contemplating backboring for a few reasons. I'd like to lighten the gun a little in the front to shift the balance back a bit, and lighten it. I'd also be interested in optimizing the pattern.

Can any of you that have experience in overboring 20ga's weigh in?

BTW, who would be best qualified to do the work?

Chuck H!
Are you thinking about backboring that Browning BSS?

Chuck;
You can quite easily calculate how much wt reduction you will get for a given amount of metal removed, I know you are aware of this. As to pattern enhancment I would be skeptical. When one considers all available types & sizes of shot, all usable powder types & charges, all hulls & primers availabe you would likely end up with some 37 million possible combinations to be evaluated. When someone says the backbored a bbl & got immediate dramatic "Improvement" well did they change the degree of choke? did in the process they change the angle of choke etc, etc. There is so much to be considered I would simply not look for any magic to happen because of a few thousandths difference in bore size of a nominal gauge.
I have shot different guns of several gauges with bores standard, oversize & undersize. I have not done enough extensive pattern testing to really speak athoritivly, but from a practical use aspect I really could never tell if a bbl was +.010 or -.010 in either shootability or recoil, in spite of the many claims made to the contrare.
I think it highly likely that many making the claims have likewise not made extensive enough teating to speak athoratitivly either.
Perhaps a given bore size would enhance the "Fit" of a given shot size in the bore, but could just as easily give a less good fit of a size just one number off. Possibilities are endless.

Anecdotally, I will add this. I own a Bruchet built Darne, circa 1997, in 20 that was built with larger than standard 20 bores, per customer order, and choked in IC and IM. I am having a devil of a time trying to find a 7/8ths production load that prints a decent pattern. Now, 1 oz loads are a different story, they all pattern as nice or better than my usual 1 oz 16 gauge load, in my usual 16 gauge gun. I am pretty close to giving up, and just calling the thing my light 16, and shooting 1 oz loads in it the rest of my life, which a poster has suggested I do.
I have no firm answers, just questions.
Best,
Ted

Chuck;

I have a 20ga O/U with .640 bores....nominally closer to a 16ga than a 20ga. It doesn't pattren any better or worse than any other I've shot.

As to backboring to reduce weight, excellent method! I had one of the first of a handful of 32" Beretta 680 barrels to come into the country nearly 15 years ago. At that time I was chasing all the fads in sporting clays and I came upon a set of custom extended and ported choke tubes that Larry Nailon had made for a backbored Beretta trap gun. Those tubes, and the pig-on-a-shovel handling of my new 32" barrels were all the reason I needed to have them backbored from .725 to .738. I had ProPort do it, the same outfit that was "pigeon porting" all my clays guns. The result was about 5 ounces of weight removed over the entire length of the barrels. I rebalanced by hollowing the butt and had a super sleek 32" O/U comp gun, way ahead of the crowd! Not only that, but it hammered targets with miraculous authority; must be magic in those big bores?

One day I was plinking at skeet with some serious skeeters, including a former world champion, and the smoke clouds I got when I connected led them to ask what chokes I had in. I told them they were cylinders and they didn't believe me. So I removed a tube and showed them the .738/Cyl etched on the tube. Everybody was suddenly a believer in backboring.

Some time later, I actually miked the bores and found that ProPort had left about 1/2" of the original .725 bore at the end, just behind the choke seat. That was their insurance against someone installing a factory choke and blowing it out. Trouble is, it added about .013 fixed choke so when I screwed in the Cyl tube I was shooting LMod!

I contacted them about having it removed and they said they didn't backbore anymore, but they recommended Tom Wilkinson in NC....

Tom Wilkinson
Oxford, NC
(919) 603-0167
twrayw@earthlink.net

I thought it would be a fairly trivial (inexpensive?) thing for him to backbore 1/2" of metal, but he actually backbored the entire lenghth, taking the .738 bores to .741 and it cost me about $400 as I recall.

I still think it was feasible and worthwhile at the time...a $750 set of barrels could become a lightweight set for $1150. Years later I paid $1200 for a virtually identical set of Beretta "Optima" barrels. I'd also considering backboring or jugging to restore choke to an open SxS, but I wouldn't backbore soley for any mythical ballistic efficiency.

Awolf,
Yeah, the 20g BSS. Just tossing it around. Nothing set in concrete. I cancelled my $4k fully loaded RBL earlier and elected to pick up this additional 20g BSS in strght stk 26"bbls (I have a PG 28"/20g already). It's right at 6lbs 8oz and handles nice, but is a bit forward balanced. BSS guns have fairly thick barrels or at least all mine have. So, it was thought to lighten them and I also recall a thread a while back where someone had done some overbore comparisions on the 20g and found good results. I have found the BSS guns to be of excellent machining and well above average for hardness and wear of the components. So, I'm giving some thought to a customized 20g quail gun to supplant the RBL.

Miller,
You're probably right about any conclusive evidence on pattern improvement across the board, but even if it was an improvement with only a handfull of my commonly used loads, I may consider it.

Oh Mike, oh Mike, sit down on my knee. Let me hold you. Those barrel borers lied to you about what they did to your barrels. Let me dry your eyes. Oh, you paid hundreds of dollars to fix the barrels that they fouled up. Oh, did you spend a few thousand dollars in entry fees for shoots where you missed a bunch of birds with those tight bored barrels? Oh, I'm so sorry. The long and the short of it is that backbored barrels may or may not improve patterns but they will 100% sure allow a separated case to lodge in the barrel and allow a new shell to be inserted behind the obstruction and blow up your gun. A backbored repeating shotgun or Darne is a smooth path to a blown up gun for an inattentive shooter. End of story.

Geez Bill, you know how to hurt a guy.

I just ran the nos. for taking .010 out of the bore for 23" of length (I'm not planning to overbore the chambers)and it comes out to just over 2 oz. Not exactly a cheap way to remove weight.

Well, gee, Eightbore....thanks for the sympathy, I guess.

I sure didn't mean to sound like I was wallowing in self-pity; I was just sharing a chuckle at my (considerable) expense. I guess I won't share an accounting of all the other mods I wasted $$$$ on.

FWIW, I don't think overbored barrels are any more prone to blow-ups than any other barrels...."inattentive shooters" are the culprits in every case I know where a cause can be identified. A nice set of unaltered Perazzi barrels opened up at my club just last week.

Just this week a good friend had a blooper, knew he had a stuck wad, but couldn't open the bolt. He had to disassemble the gun to get the fired case out. After dicking around for 5 minutes, he removed the empty and reassembled it and was about to load it when he remembered what started the whole mess....there was stil a wad in the barrel.

Hi Chuck,
First of all, what does/did "had a very beneficial effect on the pattern" mean? Was it tighter? That would be expected, since the bore is now larger in relation to the choke. Was it more evenly dispersed?
As usual, I'm with 2-piper on the idea. IMO, the only thing it will do for sure, is make the barrels lighter, separate you from some money(you've got plenty of that, though) and increase the choke, assuming you don't also work on the choke I.D.
I think this is where I came in. Isn't this how we met?
I'm sure Mikey O. could do the work at a reasonable fee and quick turnaround. Let us know how it turns out. That gun will also need a second trigger, too. And a manual safety.
JL