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Discussion Starter · #1 ·
Hi all - 2 questions here:

1) Lots of sporting models advertise some sort of over-bored barrels and lengthened forcing cones. Does this really make a difference in the beating that your shoulder takes?

2) Specifically, I am wondering about Beretta Optimachoke vs. Mobilchoke. I am looking at the Silver Pigeon II Sporting (optimachoke) and the 686E Sporting (Mobilchoke). Is it worth the extra 300-400 bucks for the optimachoke?

-elber
 

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Back-boring and lengthening of the forcing cones are supposed to primarily give more uniform patterns.

There have also been claims that they "soften" the recoil (insert your own interpretation here), but as long as the mass of the wad, shot, and gas stays the same, and the muzzle velocity stays the same, physics says that the recoil is the same.

An autoloader changes the CHARACTER of the recoil by virtue if its action, spreading it out over a longer time, but the recoil momentum is still the same.
 

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I think WWB explained it very well. This is one of those areas where even the "experts" disagree. Some think that it does reduce recoil, while others are equally convinced it doesn't.

As for whether the Optima choke is worth $300 to $400 dollars more, that too is a matter of opinion. My opinion is NO, since I often shoot a Beretta with the Mobilchoke system. It patterns very well with most loads and I don't think that any of my misses would be hits with the Optima choke. Your mileage may vary. :wink:
 
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Think twice about buying an autoloader with a overbored barrel. With an OU may have some advantage but I don't really believe it.
But a friend had an overbored semi-auto. Loaded for doubles. First shot the extractor pulled the brass off the shell. Second shell pushed the first shells plastic into the barrel. When second shell fired the barrel and reciever exploded. Moderate injuries but fortunately nothing permanent.
Before you buy an overbored semi, cut the brass off a shell and see if it will slided easily into the barrel past the chamber. If so, be forwarned!!!.
King Heiple
 
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I think backboring makes sense on any gun with screw in chokes, because it lets the Manf. size the chokes closer to the bore size to eliminate the jug effect. I know from experience that it can make a difference in getting a gun to shoot a very open pattern.

You might check the Briley site under Shotgun Services and read the articles there about chokes, etc.

I would go ahead and get the backbore and Optima chokes if I were doing it. I do not think Bretta would offer it if it did not make sense. Buying at that level, why scrimp and have to second guess it later.

I do not have and overbore, but I do have a 101 with .735 bores factory bores, Briley chokes, and the cone bored and it shoots smooth and the open chokes work well.
 
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Back boring is not exactly the same as overboring.
With out some type of boring barrels may be of different internal diameters meaning that the chokes fit some barrels better than others (the little ledge behind the choke when you look in from the muzzle).
Backboring lets the manf fit the part of the choke before the constriction closer to the barrel diameter than he can if he has to deal with the barrel variation without boring. Hence the chokes often make more uniform open patterns than guns that are not backbored

I think overboring may reduce recoil a little, either by actually lowering the muzzle velocity a little because of the increased volume of the barrel or by reducing the exit velocity of the gasses behind the shot a little, but that would seem to me to be a secondary benefit to the better patterns.
 

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Think twice about buying an autoloader with a overbored barrel. With an OU may have some advantage but I don't really believe it.
But a friend had an overbored semi-auto. Loaded for doubles. First shot the extractor pulled the brass off the shell. Second shell pushed the first shells plastic into the barrel. When second shell fired the barrel and reciever exploded. Moderate injuries but fortunately nothing permanent.
Before you buy an overbored semi, cut the brass off a shell and see if it will slided easily into the barrel past the chamber. If so, be forwarned!!!.
King Heiple
Backboring should not affect the chamber. I doubt the voracity of this account. At the very least I would hesitate to blame this on backboring.

Mike
 

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I usually consider backboring to be more of pattern control thing than a felt-recoil thing. Backboring increases POC and therefore changes effective choke. I have a fixed-choke IC barrel that is back-bored to essentially give me a modified (or improved modified if you believe in such a thing) choke that also shoots slugs quite nicely.
The theory of the forcing cone as I understand it is to increase the length of the recoil time to reduce felt-recoil. It is also said to improve pattern density (not actually the pattern) but I have nothing to prove this except the results of other folks' testing.
I can tell you that many of the people who have shot my 870's have remarked that they are the softest shooting pump-guns they've ever fired.
I usually have the forcing cone of my barrels lengthened, just because!
Mike
 

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I recently made the decision to have the forcing cones lengthened in a fairly high quality Side Lock 12 ga O&U. The factory length of the cones was 3/4". I did quite a bit of research on the forcing cone issue as well as possibly having the barrels backbored. The original bore dia was a nominal (.729 +/-(.0005). I read articles and book chapters by: M. McIntosh; Davis Trevallion; Bruce Buck - aka "The Technoid"; Les Greevy; STan Baker (thr barrel man); and spoke w/ Rich Cole; Briley Mfg; and other gunsmiths acknowledged to be well informed on this subject. What I learned helped me make an intelligent decision as to what I wanted done to my gun. The following points of information may be of interest to some and enlightening to others. I take no credit for any of this data.

FORCING CONES: Where the chamber & barrels meet. Some guns come w/ fairly long cones - some do not & are maybe 3/4 to 7/8" long. Some recent K-80s come w/ long cones (3to5") & some Beretta come w/ "fairly long cones". Lengths and recommendations can range from 7/8" out to about 6" on aftermarket work. I chose to go w/ 3 3/4" -- this length and on out to 6" lends itself to being polished much more effectively than shorter lengths. It is vital to get the best polishing job possible. ADVANTAGES: The consensus is that "Perceived Recoil" is reduced and up to a 10% increase in pattern tightening and uniformity is achieved due to less shot deformation.

BACKBORING: First -- the terms "backbored" & "overbored" mean the same thing. Technically speaking, anything over(.729) is a backbored barrel. You can find barrels that go from (.730) to (.799) and still effectively handle a 12 ga shell.
FACTORY Backbored barrels: These guns are heavier because wall thickness standards have been maintained while barrel O.D. has increased. This greater weight CAN result in less percieved recoil! Example: Brng 425 Ultra - w/ 30 or 32" barrels, it is a "mite heavy".

AFTERMARKET backbored barrels: Most standard barrels have a wall thickness of about (.040). Let's say you have your 32" (.729) barrels backbored out to (.749). You now have an O&U or SxS that is almost 6 oz lighter. You also have a gun whose balance has changed significantly!! Also, aftermarket backboring VOIDS your factory warranty!! Oh, and by the way, the consesus is split 50/50 as to whether there is any benefit to patterns and/or recoil reduction! Most important........never consider having an aftermarket backbore job done on a gun w/ Factory Screw-in Chokes. There is a very high risk that the enlargement of the bore dia could cause the skirt of the unaltered choke tube to intrude into the bore space---- you can imagine what would happen when a shell is fired!!!

Briley won't even discuss backboreing a screw-in choke gun!
I pass this info along for whatever it's worth -- these are not my statements, but my summary of what I learned. "Grizzly"
 
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When I talked to Briley they told me that on older guns with tigher bores the backboring has some benefits in patterning results. I'd guess most newer guns the bore's have opened up a little to start with so the benefits are probably not worth it. Only way to tell there is to mic the barrel bore.

Another side benefit of backboring is if you have a slight pitting or a poorly finished barrel backboring can clean it up quite a bit. I wouldn't say it offers any recoil reduction, maybe some tiny % since it allows better gas expansion and less shot constriction than a tight bore. You'll get more recoil reduction out of a softer pad, and a lighter load or porting.

Actually at the Grand American I discussed having a MX3 sporting perazzi with factory tubes backbored with briley. They not only discussed it but had a option for doing it. They certainly did mention it's harder to do and more costly but they didn't recommend against it.

What they do is backbore the barrels, then depending on the gun recut the choke tube area and make custom tubes for the new setup. I'm sure both options are very expensive but it can be done.

Having talked with Briley quite a bit, I don't think there is much they won't discuss doing. In fact they called me yesterday on a gun I'm having them backbore, port, and put tubes in saying on the O/U barrel it turned out a little too tight of spacing for the extended chokes I wanted. They offered to turn down the extended tubes to make them fit by using a lathe to remove the knurling and then black oxide them. You won't find many places willing to do that. I went with just the flush chokes but the fact they offered to do it alone is impressive.
 
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Great discussion. I have learned a lot.

But the originial question was whether to get a factory backbore on a Bretta or go with the mobile chokes and the tighter barrel. I still think that I would get the Optima system, because I think that the backboring allows Bretta to produce a better performing choke system, and I think that is why they went to it.
 

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Anyone here ever heard the term "planned obsolescence"? I think it is appropriate in this situation involving Beretta automatics.

By introducing new models of their automatics every 3 to 5 years, Beretta has given hundreds of thousands of Beretta owners a reason (excuse?) to trade in their 2 or 3 year old gun for a "new improved" gun. Remember how the 303 was replaced by the 390? Great improvement, right? Remember how the 390 was replaced by the 391? Great improvement, right? Now the 391 is being replaced by the 391 Optima. Great improvement, right?

Actually, many of these "great improvements" don't seem to be an improvement at all to people who spend a lot of time actually shooting guns. If you talk to someone who has actually shot a Beretta automatic for 8 to 10 years, you may find that he/she is still shooting the 303. Why, because it works fine and continues to work year after year. There's an even larger number of serious shooters shooting the 390 because they aren't convinced the 391 is an improvement at all.

Bottom line? Don't be so quick to believe the marketing hype about how great the latest model is. After all, Beretta DOES have a financial interest in continuing to sell more new guns. Even if that means you have to trade in your old Beretta to get one.
 

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Discussion Starter · #13 ·
Thanks all for the great information!

Here is where I think I'm at: When I go to look at two guns, I will not make the decision based upon the forcing cone/back bored barrel issue. I will pick the gun that fits better and feels better.

-elber
 

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Re: my 3/3/03/post and Guest (TODDMP23) post: Perhaps I should have made the obvious somewhat more clear by stating:
"Briley won't even discuss backboreing a screw-in choke gun"---- [without being able to remove the existing screw-in choke set up and modify the barrels to accept their "thin-wall" or custom fabricated choke tube(s)].

The bottom line is: Unless you extensively & expensively modify the existing screw-in choke system on a given gun - if, in fact, there is sufficient barrel wall thickness to do this - you cannot backbore (go from .729 to .750) the barrel(s) because it will leave the skirt of a standard factory choke tube intruding into the bore.

In other words: You can't backbore (example: go from .729 to .750) a typical gun (example: B. Rizzini Artemis) that is equipped w/ an un-altered standard factory screw-in choke system! Well........... you can........ but not w/ my gun!!
I rest my case! "Grizzly"
 

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Sorry..... regarding the above post.... error in 1st line: Regarding my 8/3/03.post,,,,, not 3/3/03. See ya!
 
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