Shotgun Screw in Chokes Question.

I was under the impression that a 12 ga. shotgun barrel had a bore size that was the same in all 12ga shotguns no matter what brand of gun. Also didn’t know the relevance , bore size had to the choke tube sizes.
I do finally understand it now.

Thank you all for your input, very much appreciated.
 
Sometimes it helps to think of choke in the same sense that Europeans do. That is to say that choke is in degree's of constriction and one degree is 1 thousand of an inch. The trouble is that not all shotgun barrels are the same ID and a 12 gauge barrels can range from .720 inches to .745 inches ID, give or take some.

Cylinder bore is 0 degree's of constriction. In other words, the choke has the same ID as the shotgun bore ID regardless of what that bore ID might be.

Normally a MOD choke requires 20 degree's of constriction or 20 thou tighter than bore id.

If your Remington bore ID is .730 inches then your MOD choke ID will need to be .710 inches ID. If your Browning barrel is .742 inches then your MOD tube ID will have to be .722 inches. The key here is that your two shotguns have different bore ID's.

A FULL choke will normally be 40 points of constriction.

So if your Remington barrel ID is .730 inches then your full choke tube ID will be .690 inches. If your Browning Barrel ID is .742 inches then the FULL choke ID will be .702 inches.
 
recoil 5 said:
I was under the impression that a 12 ga. shotgun barrel had a bore size that was the same in all 12ga shotguns no matter what brand of gun. Also didn’t know the relevance , bore size had to the choke tube sizes.
I do finally understand it now.

Thank you all for your input, very much appreciated.
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Actually it varies quite a bit, even within the same manufacturer depending on intended purpose.
 
Interesting sidebar: I asked Mossberg to tell me the ID of their fixed cylinder bore barrel as well as the barrel thickness (I don’t have a caliper ); they refused... said it was proprietary. Go figure.
 
military secret, just like the reason for existence of their chain saw model.

Al Bear said:
Interesting sidebar: I asked Mossberg to tell me the ID of their fixed cylinder bore barrel as well as the barrel thickness (I don’t have a caliper ); they refused... said it was proprietary. Go figure.
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Beretta687EELL said:
Basically, a choke tube is matched to the bore of the shotgun and then the difference between the maximum bore diameter and the minimum choke diameter is the constriction. The constriction is the measurement that you see on the choke.

The reason that your tubes are marked the same, but measure differently is because the bore diameter of the two barrels that they go in are different. 12 gauge shotguns can have different bore diameters, which will range from approximately .725 to .800. So a modified (.020) choke for a .725 barrel will measure .705 and a modifed choke for an .800 barrel will measure .780.

Here is a link for you ...

https://www.briley.com/c-456-understanding-chokes.aspx
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Thank you for that, it is very informative. I'm looking at buying a skeet / trap gun in the very near future and this has helped me understand things better.
 
Al Bear said:
Interesting sidebar: I asked Mossberg to tell me the ID of their fixed cylinder bore barrel as well as the barrel thickness (I don’t have a caliper ); they refused... said it was proprietary. Go figure.
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The person you were dealing with most likely had no idea.
 
FLHTCUI said:
Just like opinions everyone has one.
Selling points for the individual manufacturer to suggest their chokes are superior to the competition.
Rob
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FLHTCUI said:
I see your opinion and reject it 100% F/O
Thank You for playing.
Rob
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A useful source of information as per usual.....well aside from your usual standard answer in 99% of shotgun related threads....”buy an 870”. :rolleyes:
 
recoil 5 said:
I was under the impression that a 12 ga. shotgun barrel had a bore size that was the same in all 12ga shotguns no matter what brand of gun. Also didn’t know the relevance , bore size had to the choke tube sizes.
I do finally understand it now.

Thank you all for your input, very much appreciated.
Click to expand...

The chamber diameter in all guns of the same gauge is for all intents and purposes equal. But then the barrel narrows down immediately past the chamber. This is what's called the forcing cone and it is at this point and beyond where the ID of barrels can vary between manufacturers. Then the barrel narrows again near the end of the barrel (the choke), where again the ID can vary.
 
So far as I can see, many charts “show” a 12 bore standard being .730 and it’s cylinder choke the same. Choke diameters change in increments of .005. My Brownings seem to follow this convention. The Beretta charts shows .723 as a bore diameter and cylinder choke. And they don’t change the constrictions in .005 increments either. Moreover, their charts have a disclaimer that there can be variations due to engineering and machining tolerances. In addition to a standard Beretta Full, I bought an after-market Full - through the Beretta store - and, sure enough, there is a difference in ID. Due to these variations, the Beretta disclaimer is followed by a suggestion to simply pattern the shot with whatever choke you use.

Amen, eh.
 
There is no such thing as "standard" bore diameter anymore, at one time 12 gauge bores were said to be .721 give or take but now days they range from .719 to .750 and anywhere in between and... there could be exceptions to this as well. For instance, Beretta Mobil barrels are .720 inches while their optima barrels are .733. Older Browning barrels are .724 but the newer ones are .742. Older Perazzi's were .724 and now .732 is standard but they will make anything you want when ordered. A lot of the Turkish guns I've looked at don't have any bore stamps so they could be any diameter but I suspect they will likely be on the tighter side for the most part. You also have to remember that chokes can vary by a 2 or 3 thou and you won't find many that are exact to a thou of an inch of what they should be in theory.
As has been mentioned several times previously in this thread, choke diameter is dictated by bore diameter and the difference is constriction.
 
Falconflyer said:
There is no such thing as "standard" bore diameter anymore, at one time 12 gauge bores were said to be .721 give or take but now days they range from .719 to .750 and anywhere in between and... there could be exceptions to this as well. For instance, Beretta Mobil barrels are .720 inches while their optima barrels are .733. Older Browning barrels are .724 but the newer ones are .742. Older Perazzi's were .724 and now .732 is standard but they will make anything you want when ordered. A lot of the Turkish guns I've looked at don't have any bore stamps so they could be any diameter but I suspect they will likely be on the tighter side for the most part. You also have to remember that chokes can vary by a 2 or 3 thou and you won't find many that are exact to a thou of an inch of what they should be in theory.
As has been mentioned several times previously in this thread, choke diameter is dictated by bore diameter and the difference is constriction.
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I have four Beretta’s with Mobil chokes that are .721.
 
Al Bear said:
Interesting sidebar: I asked Mossberg to tell me the ID of their fixed cylinder bore barrel as well as the barrel thickness (I don’t have a caliper ); they refused... said it was proprietary. Go figure.
Click to expand...

how is a physical dimension that anyone can measure proprietary secret? Its not like you can patent a thickness.
 
Bore diameters from the major manufacturers have become remarkably consistent with the advent of removable choke tubes, at least where the choke tube meets the bore. I am talking about consistent diameter within proprietary systems, like Browning's Invector Plus.

When that intersection fails, bad things happen to the tube and the threads. A few of those failures have been posted on Gunnutz or other shotgun sites.

From testing by Neil Winston and others, there is no advantage at the pattern board, to the current trend of over-bored barrels.
 
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