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 Post subject: Shotgun Bore Dimensions
PostPosted: Sun Mar 21, 2021 1:11 pm 
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Joined: Mon Sep 28, 2020 1:44 pm
Posts: 22
I have a 12 gauge barrel that has screw in chokes. According to my bore gauge the barrel measures between .732/.733. Just prior to entering the choke tube the barrel dimension reduces down to about .727/.726 and then opens up at the entrance of the choke tube skirt and then reduces down to the marked choke constriction.

So for a .005 choke constriction the barrel goes from .732/.733 bore size to .727/.726 just prior to entering choke tube and then opens up at choke tube skirt entrance and then reduces back down to .727 for the .005 constriction.

For a .015 choke constriction the barrel goes from .732/.733 bore size to .727/.726 just prior to entering choke tube and then opens up at choke tube skirt entrance and then reduces back down to .717 for the .015 constriction.

The barrel performs well and breaks the targets well when I do my part. The patterns appear to be tight and even spread when I shoot the pattern board from various distances.

Would there be any benefit to having the barrel back bored just at the area prior to entering the choke tube so the barrel has the bore size of .732/.733 all the way through?




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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Sun Mar 21, 2021 1:16 pm 
Tournament Grade

Joined: Wed Feb 17, 2021 2:57 pm
Posts: 182
I’d say ‘HECK NO!’

If your barrels perform well, never, ever mess with them is my rule.


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Sun Mar 21, 2021 1:25 pm 
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RAT 3323 wrote:
Would there be any benefit to having the barrel back bored just at the area prior to entering the choke tube so the barrel has the bore size of .732/.733 all the way through?


None. That's nothing but problems with no potential benefit.


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Mon Mar 22, 2021 12:19 pm 
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Joined: Fri Mar 19, 2004 9:07 pm
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Flyingtargets! wrote:
I’d say ‘HECK NO!’

If your barrels perform well, never, ever mess with them is my rule.


^^^^^^^^^^^^


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Mon Mar 22, 2021 1:15 pm 
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RAT 3323 wrote:
I have a 12 gauge barrel that has screw in chokes. According to my bore gauge the barrel measures between .732/.733. Just prior to entering the choke tube the barrel dimension reduces down to about .727/.726 and then opens up at the entrance of the choke tube skirt and then reduces down to the marked choke constriction.

So for a .005 choke constriction the barrel goes from .732/.733 bore size to .727/.726 just prior to entering choke tube and then opens up at choke tube skirt entrance and then reduces back down to .727 for the .005 constriction.

For a .015 choke constriction the barrel goes from .732/.733 bore size to .727/.726 just prior to entering choke tube and then opens up at choke tube skirt entrance and then reduces back down to .717 for the .015 constriction.

The barrel performs well and breaks the targets well when I do my part. The patterns appear to be tight and even spread when I shoot the pattern board from various distances.

Would there be any benefit to having the barrel back bored just at the area prior to entering the choke tube so the barrel has the bore size of .732/.733 all the way through?


What make of gun are you referring to? I don't think it's common practice for the bore to taper down in diameter just before the choke tube ledge. I can understand why they might do that, but also realize that it imparts about 0.005" constriction even with no choke tube present. Some people may not want that.

To answer your question, No, I wouldn't mess with it. Increasing the bore diameter there will likely expose the skirt of the choke tube to being snagged by the wad. This would likely cause the launching of the choke tube downrange and perhaps rupture the end of the barrel. Better to tolerate this idiosyncrasy than to risk ruining the barrel(s).

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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Mon Mar 22, 2021 2:03 pm 
Tournament Grade

Joined: Wed Feb 17, 2021 2:57 pm
Posts: 182
If you translated the ID measurements of any shotgun bore to a graph, and that graph looked like an EKG or roller coaster, but I was getting good target breaks and good looking patterns, I’d take it all day long over more serious issues such as convergence issues or whacky POI.

Shoot it, be happy. It’s a shotgun barrel not a BR rifle.


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Mon Mar 22, 2021 5:25 pm 
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Randy, twenty yards is in my opinion the right yardage to check your chokes and it should never be done with a rest. You want to know how it performs when mounting the gun and pulling the trigger. Using a rest, you may put your head in a different place on the comb because you may worm your head into the stock.

The pattern that you posted looks to be a full choke, especially at 35 yards. Your gun looks to be shooting left because the pellets on the right are not centered and most are closer to the center of the of the target. This can be caused by a lot of things. It could be cause by the way the barrel was threaded but more likely it is a gun fit or even a eye dominance problem. I am more concerned where the gun's point of impact is. I am like the other guys that said if it is breaking targets you might want to leave it alone. If you are having problems with targets that or right to or left to right check you POI. If there is no problem, forget it If there are problems, This will tell you to look at these things.

Concerning back boring, lengthening the forcing cone and porting, Chuck Web formally the General Manager Of Briley, once told me when I asked him about all of these things, His comment was unless you do all three things you would not be able to see any difference. I then asked him what his opinion was about doing these things. This was after he left Briley. He told me that for the majority of shooters, just to shoot lighter shells. Remember that Chuck was one of the top gunsmiths in the country and really knew he stuff.

I had a couple of trap guns that I had all of these things done to. I couldn't tell any difference. When you look at the constriction that is marked on your chokes, many times, they are wrong. Most manufactures use a standard bore size on all gauges and brands of guns and mass produce their chokes. If you want to have perfect constriction, You need to hire a smith that does custom work and matches the actual bore size and then make the chokes to this constructions.

Mike McAlpine {hs#

The are just my opinions from 31 years as a professional clay target coach. Some people may have other ideas and that is fine.


Last edited by Mike McAlpine on Mon Mar 22, 2021 10:43 pm, edited 1 time in total.

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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Mon Mar 22, 2021 5:27 pm 
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Posts: 2528
Randy, twenty yards is in my opinion the right yardage to check your chokes and it should never be done with a rest. You want to know how it performs when mounting the gun and pulling the trigger. Using a rest, you may put your head in a different place on the comb because you may worm your head into the stock.

The pattern that you posted looks to be a full choke, especially at 35 yards. Your gun looks to be shooting left because the pellets on the right are not centered and most are closer to the center of the of the target. This can be caused by a lot of things. It could be cause by the way the barrel was threaded but more likely it is a gun fit or even a eye dominance problem. I am more concerned where the gun's point of impact is. I am like the other guys that said if it is breaking targets you might want to leave it alone. If you are having problems with targets that or right to or left, check you POI. If there is no problem, forget it If there are problems, This will tell you to look at these other things.

Concerning back boring, lengthening the forcing cone and porting, Chuck Web formally the General Manager Of Briley, once told me when I asked him about all of these things, His comment was unless you do all three things you would not be able to see any difference. I then asked him what his opinion was about doing these things. This was after he left Briley. He told me that for the majority of shooters, just to shoot lighter shells. Remember that Chuck was one of the top gunsmiths in the country and really knew he stuff.

I had a couple of trap guns that I had all of these things done to. I couldn't tell any difference. When you look at the constriction that is marked on your chokes, many times, they are wrong. Most manufactures use a standard bore size on all gauges and different brands of guns and mass produce their chokes. If you want to have perfect constriction, You need to hire a smith that does custom work and matches the actual bore size and then make the chokes to this constructions.

Mike McAlpine {hs#

The are just my opinions from 31 years as a professional clay target coach. Some people
may have other ideas and that is fine.

Also I have found that most shooters, me included worry too much about minor things when buying a new gun. Many think that because they have spent a lot of money on the gun and work they had done that their scores will improve dramatically. For most people this is simply not true. The best thing you can do is get with a coach and find out if is actually and not the gun. Perfect practice make perfect. You can hurt your shooting by practicing bad mistakes. I went through this when I first started shooting. I had many well meaning friends they thought were giving me good advice, when they really didn't know what they were talking about.


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Tue Mar 23, 2021 10:49 am 
Field Grade

Joined: Mon Sep 28, 2020 1:44 pm
Posts: 22
The make of gun is Beretta. The barrel opens up at the choke tube entrance to about .742, so if I had the barrel opened to .732/.733 all the way through from forcing cone to choke tube entrance I don't see an issue with exposing choke tube skirt.

I am not looking to have the entire barrel back bored, just open up the area just prior to the choke tube entrance so I have a barrel that is .732/.733 all the way through.

It seems from the responses I have received that everyone would leave the barrel alone.

Has anyone run into this before on any of your barrels?

Thank you


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Tue Mar 23, 2021 1:06 pm 
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RAT 3323 wrote:
The make of gun is Beretta. The barrel opens up at the choke tube entrance to about .742, so if I had the barrel opened to .732/.733 all the way through from forcing cone to choke tube entrance I don't see an issue with exposing choke tube skirt.

I am not looking to have the entire barrel back bored, just open up the area just prior to the choke tube entrance so I have a barrel that is .732/.733 all the way through.

It seems from the responses I have received that everyone would leave the barrel alone.

Has anyone run into this before on any of your barrels?

Thank you


There's something off with your measuring. I just measured the wall thickness of the skirt of a Beretta choke tube and came up with about 0.025". Since the choke tube has two sides, we can double that number to see how much the bore diameter is reduced by the thickness of the metal in the choke tube. That would be 2 x 0.025 = 0.050".

Now we can subtract that 0.050" from the exterior dimension of the choke tube bore diameter at the ledge. That would give us (according to your numbers) 0.742 - 0.050 = 0.692" as the ID of the skirt entrance of the choke tube (assuming a PERFECT fit). That spells BIG TROUBLE when you have the choke tube opening that is smaller than the bore diameter. And this doesn't even take into account that sometimes a choke tube skirt is not perfectly round due to manufacturing tolerances or perhaps due to being dropped or mishandled in some way.

Do what you want, but if you blow the end off your barrels, don't say that you weren't warned.

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Semi-Auto Classifieds is ONLY for Complete Semi-Auto shotguns.
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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Tue Mar 23, 2021 1:53 pm 
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Joined: Mon Sep 28, 2020 1:44 pm
Posts: 22
Ulysses,

The entrance to the choke tube flares out to about .745 where it seats into the barrels.

On the .005 choke constriction the actual choke from where it seats to the barrel is about .745 and then reduces down to the .727 to give me the constriction based off the .732 bore diameter.

I measured choke tubes for the other various guns I own and all the choke tubes have this in common. The choke tube entrance where it seats into the barrel is between .008 to .012 larger than the actual bore diameter. This gives the safety measure you were noting about not blowing the choke tube out the end of the barrel


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Tue Mar 23, 2021 2:14 pm 
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Mike McAlpine wrote:
Randy, twenty yards is in my opinion the right yardage to check your chokes and it should never be done with a rest.


Sorry, Miked, you can take it from six-time Olympic medal winner, including three gold medals, and six-time national champion in double trap Kim Rhode: "BAG IT UP!"

The "right" range to check patterns for the individual is, of course, the ranges the individual plans on shooting at, although the industry standard is 40 yards.

No, the pattern posted is hardly just a "full choke"-- it is a 100% pattern @ 40 yards.

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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Tue Mar 23, 2021 2:28 pm 
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Rat--you can't make your gun shoot better by "fixing" this thing with your chokes.

But you should do it anyway , since it has driven you crazy. :wink:

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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Tue Mar 23, 2021 3:09 pm 
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Randy, as I said, this is my opinion and the opinion of many coaches. I know Kim too and if this is what she does, then it must be right for her. I'm teaching shooters (Amature) how to find problems. The pattern looks to me very tight that is why I made the statement. Also why did you pattern your gun a 35 yards if Kim recommends 40?

Randy,

You are talking about a bunker or olympic shooter, not an everyday shooter. Why would you check at pattern this far if you will be shooting targets (International Skeet) at a much closer range? I am not trying to make you mad or belittle you..
Please don't be offended. {hs#


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Tue Mar 23, 2021 4:03 pm 
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Randy,

I was sitting here and something popped in my mind. I owe you a partial apology. You are closer to right than I was. When patterning a gun, ammo or chokes to find the best overall disbursement of the shot (pattern) It seems that my mind remembers 30 / 35 yards. When checking point of impact, 20 yards is the right distance. These are two different things and using a rest when patterning is okay. it is not when checking point of impact. I have always owned up to my mistakes. I didn't look up any answers to these questions but my memory sometimes let's me down. Getting old is hard for a lot of people and that includes me.

My bad!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Mike McAlpine

Your gun is still shooting to the right. POI :oops: {hs#

Randy,

I started thinking about Kim. She was a Bunker shooter and her preferred game was Double Rise. (similar to ATA Doubles) This was an Olympic discipline and was where Kim won most of her medals.

Several years ago, the Olympic committee dropped this discipline for women. Kim then became an International Skeet shooter. She is the only human that has won medals in all of the Olympics that she has shot in. In the last Olympics, she won the gold in international skeet. This was an astounding achievement because she had to switch sports. She has won silver medals and I am not sure about the brozens medals but she is a great ambassador for America.

I met her at the Old Triple B gun club many many years ago. She and her dad had built some kind of a car I believe from a kit and one of the guy's in my class that knew her very well talked her into taking me for a ride in the car. She scare the holy $hit out of me of on the turnpike. I have always like Kim a lot because she is such a nice person and great shooter. I think her dad got her in to clay target shooting and was her coach too.

Now I could be wrong here because we know I have been before, :lol:


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Thu Mar 25, 2021 8:34 am 
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"The patterns appear to be tight and even spread when I shoot the pattern board from various distances."


Go with this.

Most of the choking process of a screw in choke happens within the choke. The shot expands a little into the skirt of the choke and then is constricted. A few thousands before the choke probably has little effect one way or the other.


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 Post subject: Re: Shotgun Bore Dimensions
PostPosted: Sat Apr 03, 2021 8:15 pm 
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Joined: Mon Sep 28, 2020 1:44 pm
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I have reached out to one of the noted barrel "Gurus" that does work on shotguns to improve performance for various clay target disciplines and I was told this is rather common. Further stated that as long as the constriction of the choke is more than the taper behind the choke in the barrel, it will work according to the constriction of the choke tube.

Since I mainly shoot .015 or .025 constriction I am good.

Thanks to everyone that offered advice.




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