16ga.com Forum Index
Author Message
<  16ga. Guns  ~  Citori choke tubes
LiverTick
PostPosted: Thu Aug 18, 2005 9:34 am  Reply with quote



Joined: 18 Jul 2004
Posts: 131
Location: The Great Lakes State

Thanks, 16GG. I am not an engineer, but I play one at work. I have a fairly good feel for how all the factors you listed come in to play, though it comes more from a basic, high-school level understanding of physics and chemistry. Additionally, I am not a reloader, and really don't plan on doing so as long as I can find reasonably-priced, good-quality factory shells that pattern well in my guns. I may have muddied up the waters with even bringing up the issue of variability, so if I may, to better understand, allow me to revisit the original intent of my of my query by asking a couple of questions:

1. Assuming all shotshell variables are removed (identical shells, loaded to 6-Sigma precision), how predictive is constriction in achieving a particular density of pellets (i.e. XX% in a 30 in. circle at 30 yds), from an established baseline? In other words, if we can establish that zero constriction, with this particular shell, produces a result of XX% density, say 38%, then without patterning any greater constriction, can we reasonably predict that 0.0YY constriction will result in XX+ZZ% pattern density?

2. When we begin to introduce the other variables, it seems reasonable that for each variable added, the impact the constriction creates on the result becomes less. As a practical matter, how is constriction "weighted" in relationship to these variables?
Back to top
View user's profile Send private message
longwalker
PostPosted: Thu Aug 18, 2005 7:42 pm  Reply with quote
Member
Member


Joined: 17 Aug 2005
Posts: 75
Location: Saskatchewan Canada

Hello all, this is an interesting thread - I just went to measure my Citori's tubes but have trouble getting a good reading with a standard digtal caliper. I thought I'd just measure the back inside dia. and then the front, then subtract the difference. I have trouble getting good repeatble measurements and the numbers do not seem to match the usual choke designations - I got more questions than answers. Is it my technique or do I need to buy a specialzed tool just to measure a choke tubes? your advice please.

_________________
"At the periphery is where I can come to understand the central issues of living" - Hugh Brody
Back to top
View user's profile Send private message
16gaugeguy
PostPosted: Fri Aug 19, 2005 5:14 am  Reply with quote
Member
Member


Joined: 12 Mar 2005
Posts: 6535
Location: massachusetts

Liverticked, I'd like to answer your question in a meaningful way. However, there is not any realistic way to remove those variables. Each gun and to approximately the same extent, each load is a law unto itself. there just isn't any way to predict. all you can get is a rough idea. you have to test. As an engineer, you already know this.

I work in a quality assurance lab for the MA state highway dept. We see it all, the good, the bad, and the ugly. Designs and specs are only guidelines. All bets are off as soon as you throw in the human factor and real world variables. We test everything because we have to. Then, we cross our fingers and hope the damned bridge doesn't collapse. I know you understand this.

A full choke tube diameter has about 10% less area at the muzzle than the bore diameter. Hypothetically, this is supposed to place 70% of the shot charge inside a 30" circle at 40 yards. The American choke designation system uses terms to specify the percentage of shot placed in that 30" circle. These percentages represent what you can expect with ammo that has a well designed one piece plastic wad including a shot cup that contains 85% or more of the pellets. Ammo with no shot wrapper will usually pattern 5-10% less densely. Cylinder (no choke) 40- 45%, Improved Cylinder 45-55%, Modified 55-65%, Improved modified 65-70% and back to full at 70-80%. However, such terms are very loose guidelines and there is a bunch of overlap.

The only real way to find out is to pattern. If you find a hunting load that works well for you in your gun, buy a case or two of the same batch number, and store it in a cool and dry place. As sure as you are standing on the planet, the next batch may or may not perform as well. If only one of the myriad of variables is changed, like wad thickness, shot hardness, powder burn rate, primer brisance, or any of the others, the shell performance will be altered. Count on change, it is the only constant in the universe.

That is only one of the reasons I reload. I can exert some control over my ammo performance by finding a recipe that works well and then hording up enough componants for that load to ensure I'll be able to produce it myself for years to come. If I run out, I can come up with another, regardless of what the ammo companies are huckstering off on the market. It is part of the life of a 16 gauge fan, and to some extent, the other gauges too.


Last edited by 16gaugeguy on Fri Aug 19, 2005 7:28 am; edited 1 time in total
Back to top
View user's profile Send private message
Orry
PostPosted: Fri Aug 19, 2005 6:58 am  Reply with quote



Joined: 22 Mar 2005
Posts: 14
Location: Northeast Ohio

longwalker wrote:
Hello all, this is an interesting thread - I just went to measure my Citori's tubes but have trouble getting a good reading with a standard digtal caliper. I thought I'd just measure the back inside dia. and then the front, then subtract the difference. I have trouble getting good repeatble measurements and the numbers do not seem to match the usual choke designations - I got more questions than answers. Is it my technique or do I need to buy a specialzed tool just to measure a choke tubes? your advice please.


I am not sure measuring a choke tube by itself means anything. A barrel constriction (ie choke) is the difference between the bore size and the diameter at the end of the choke. I think you will find that the choke tube has a greater inside diameter than the bore where it meets the bore to allow unrestricted flow down the barrel.

If you pull bore gauge down the barrel the size is consistent. When it gets to the choke tube, there is an abrupt increase of the diameter and then the taper to the final choke size.
Back to top
View user's profile Send private message Send e-mail
L Kenney
PostPosted: Mon Aug 22, 2005 12:08 pm  Reply with quote



Joined: 12 Aug 2005
Posts: 54
Location: San Francisco

I said I'd post info on the choke tubes in my new Lightning Feather 16 as soon as I picked it up. I've not yet had the opportunity to use a friend's equipment to mike the bores, but my dial calipers show muzzle-end internal diameters of .622" for the Full tube, .653" for the Mod tube and .662" for the IC tube. Internal diameter at the rear end of the tubes is .673" to .675" which I assume iss somewhat larger than the bore itself. But whatever the actualbore diameter, it's pretty clear that the factory Full tube is significantly tighter than the others. I'll follow up again after I measure the bores and after I do some patterning with both the factory tubes and some Briley-made ones that I've ordered.
Back to top
View user's profile Send private message
pumpgun
PostPosted: Thu Aug 25, 2005 6:17 am  Reply with quote
Member
Member


Joined: 02 Oct 2004
Posts: 425
Location: Maine

I just picked up a new citori lightning. So do the bores on these new guns run ~.670? I don't have access to a bore gauge, but I'd like to order some aftermarket chokes for it.
Back to top
View user's profile Send private message
16gaugeguy
PostPosted: Thu Aug 25, 2005 7:27 am  Reply with quote
Member
Member


Joined: 12 Mar 2005
Posts: 6535
Location: massachusetts

the Browning 16 ga.Citori generally runs .668 to .670 which works out to 17 MM. However, its always best to measure if you can. If you don't have a bore gauge, try casting a plug out of plaster of Paris just ahead of your forcing cone. Lightly coat the inside of your barrels ahead of the forcing cones with vaseline and plug the bore with a wad of newsprint wrapped in masking tape. then pour enough plaster into the bore to make a plug an inch or so long. Keep it close to the forcing cones so it will be easy to remove. When it hardens, knock it out with your cleaning rod or a stick. It will be easy to measure with a set of verniers or sanded off square and measured across with a scale. then it should be easy to figure what size tubes you need.

A true full choke should have an exit bore of 10% less area. A .670 bore has an area of about .352" ( .670 x .670 X 3.14 divided by 4). Multiply by .9 to get the area of the full choke tube which is .317". The diameter of that will be .635-.636" (.317 divided by 3.14 X 4 then find the square root of the result).

This works out to .033 to .034" points of choke for full choke in a .670 diameter barrel. You can then extrapolate all the other tubes through percentage of choke. -2% = skeet, -3 or 4% = improved Cyl, -6 to 7%= modified, -8.5 to9% = improved modified, and -10% is full

You will notice that bigger bores require more points of choke to get an equal effect on the shot pattern. At 12 ga, .729' bore needs about .040" points for a full. Where a 28 ga. or .550 bore only needs only .028" for full choke. This is due to choke being determined by constriction based on percentage of muzzle area. Also keep in mind that 12 ga. through 20 ga. guns are patterned at 40 yards, 28 ga. at 30 yards, and .410 at 25 yards. This will have an effect on the predicted percentages of shot inside a 30" diameter circle.

This distance factor might be why Browning 16 ga. full chokes are so tight at .042-.044" points. I think this is too much choke for a balanced pattern and not good for big shot like #4 either. I have found that .034" of choke is all I need for nicely even and effective full 16 gauge patterns out to 40 yards on pheasant, especially with the #4 or #5 shot I use for 1-1/4 oz, late season loads. Inside of 35 yards, 1 ounce of #6 at 1250-1300 FPS out of an improved cyl. or modified tube is all I ever need. Even 7/8 oz. #7 @ 1300 fps out of a skeet tube drops them at 30 yards like a hammer in the early season.

Past 40 yards, I don't shoot. That means if the bird gets up outside 30 yards, I let it fly and mark it down for another attempt at a point. I want that shot pattern on target by 40 yards and no further, period. Any shot past that distance is a "Hail Mary" attempt. Thats Ok in ball games. It is not when we are trying to kill a living animal cleanly and mecifully.

Briley figures their chokes out in .005" jumps. However, in the smaller bores than 12 ga. that does not always work out the best. I prefer to order chokes exactly or have them reamed to my own specs in exact measurements for each gun. hope the info helps you.
Back to top
View user's profile Send private message
Rodney Roe
PostPosted: Sat Sep 03, 2005 7:34 am  Reply with quote



Joined: 03 Sep 2005
Posts: 1

Several years ago I bought a Citori Gran Lightning and purchased a set of Briley extended tubes in addition. I have no means to measure the actual bores of the various tubes, but did pattern the gun with both Browning tubes and Briley tubes. What I found was that the Briley tubes patterned about a degree of choke tighter than the Browning tubes through Mod. I didn't purchase a Full Briley choke so couldn't compare. Part of this difference may have been due to the fact that Briley makes their tubes in .005" steps - Sk is .005, IC is .010 etc. My experience with Citori tubes in all gauges is that they are very open through Modified and Full is Full. I attribute this to their anticipated use of steel shot in the guns.

What I also found - maybe someone has an explanation - was that Remington 1 ounce game loads patterned about a degree of choke more open than Winchester 1 ounce game loads with both sets of chokes. I no longer have the data for either set of comparisons so I can't give you actual percentages. My bad.
Back to top
View user's profile Send private message
L Kenney
PostPosted: Sat Sep 03, 2005 11:21 am  Reply with quote



Joined: 12 Aug 2005
Posts: 54
Location: San Francisco

I finally got a chance to mike the bores of my new Lightning Feather on a gunsmith friends gauge. .668 in each barrel +/- .001.

I wanted addtional tubes to go with the three that came with the gun and called Briley who told me they were out of stock on flush tubes until, maybe, next year. They did have extended tubes in stock I didn't want any more weight out in front on an already barrel heavy gun so I ended up ordering from Midwest Gunworks. Midwest was out of Skeet tubes, but sold me additional IC and Mod tubes. It's interesting how these bright finished tubes compare to the black factory tubes. Measurements are for the back and front ends, respectively and should be within .001":

Black IC .674 to .662
Bright IC .672 to .652

Black M .674 to .655
Bright M .672 to .642

Black F .674 to .622

Constriction of the tubes seems to be simply a straight taper from more open to less open, with no parallel.

Actual patterns shot with given loads are of course what counts, but it's interesting to consider whether choke constriction is measured against the barrel i.d. (.668) , or against the back end of the tube (.674)? In either case, except for the factory black full choke tube, there are some useful differences between the four other tubes. And I'll have no trouble remembering that the bright tubes are somwhat tighter than the similarly labelled black tubes. I'm tempted to see if I can open up the Full tube myself; though on my lathe with my skill that would likely amount to cutting a flat section of smaller i.d. at the front end and who knows how that would shoot.
Back to top
View user's profile Send private message
pumpgun
PostPosted: Tue Sep 13, 2005 8:48 am  Reply with quote
Member
Member


Joined: 02 Oct 2004
Posts: 425
Location: Maine

I wanted addtional tubes to go with the three that came with the gun and called Briley who told me they were out of stock on flush tubes until, maybe, next year. ]

Funny. I just ordered a flush skeet tube a week ago. Just came this morning.
Back to top
View user's profile Send private message
16gaugeguy
PostPosted: Tue Sep 13, 2005 9:26 am  Reply with quote
Member
Member


Joined: 12 Mar 2005
Posts: 6535
Location: massachusetts

L Kenney wrote:
I finally got a chance to mike the bores of my new Lightning Feather on a gunsmith friends gauge. .668 in each barrel +/- .001.

I wanted addtional tubes to go with the three that came with the gun and called Briley who told me they were out of stock on flush tubes until, maybe, next year. They did have extended tubes in stock I didn't want any more weight out in front on an already barrel heavy gun so I ended up ordering from Midwest Gunworks. Midwest was out of Skeet tubes, but sold me additional IC and Mod tubes. It's interesting how these bright finished tubes compare to the black factory tubes. Measurements are for the back and front ends, respectively and should be within .001":

Black IC .674 to .662
Bright IC .672 to .652

Black M .674 to .655
Bright M .672 to .642

Black F .674 to .622

Constriction of the tubes seems to be simply a straight taper from more open to less open, with no parallel.

Actual patterns shot with given loads are of course what counts, but it's interesting to consider whether choke constriction is measured against the barrel i.d. (.668) , or against the back end of the tube (.674)? In either case, except for the factory black full choke tube, there are some useful differences between the four other tubes. And I'll have no trouble remembering that the bright tubes are somwhat tighter than the similarly labelled black tubes. I'm tempted to see if I can open up the Full tube myself; though on my lathe with my skill that would likely amount to cutting a flat section of smaller i.d. at the front end and who knows how that would shoot.
\

Could that full choke be .632? .622 is nearly .048 points of choke. That is much too tight for a standard invector length choke tube. Try about .034 points. I've found it is about perfect. You should take a parallel .017 final cut from the inside wall at the muzzle end. That little bit of parallel or straight bore at the muzzle end seems to help very nicely in stabilizing the pattern and will keep your POI unchanged. Shortening the choke taper will not hurt a thing, because you are not changing the original taper. However, monkeying with the taper could change the overall effect and deregulate your gun's point of impact. do it the simple way. It usually is best 99% of the time.
Back to top
View user's profile Send private message
kgb
PostPosted: Tue Sep 13, 2005 5:02 pm  Reply with quote
Member
Member


Joined: 31 Aug 2005
Posts: 1256
Location: Nebraska

16gg, likely it really is .040" or more of constriction in a Browning Full choke. I posted some results from my Citori elsewhere, here's a cut/paste:

To kind of wrap up all I think I'll do with this gun for now, I just got in 3 more choke tubes for the 16. Cyl, Skeet and Mod in Browning packages. Unlike the Browning tubes that came with the gun, these look to be stainless. The packages state "made exclusively for Browning by Briley". The chokes seem to follow the designations listed on the Briley site.

Measuring them the same as all the others, I got:

Cyl .002"
Skeet .007"
Mod .021"
and according to the site they should have been .000", .005" and .020"

The blued chokes that came with the gun measure:

IC .003"
Mod .010"
Full .046"


I have a pull-through gauge that measures 12's and 16's, barrel bore diameters on my Citori are .667" for the under, .668" for the upper. All kinds of boring details in my posting about this citori are at:

http://bbs.shootingsportsman.com/viewtopic.php?t=21854&highlight=

Wholesale Hunter is where I got my Briley/Browning choke tubes, at $15.00 each I think they're a bargain especially if you buy several so shipping is most cost effective. Like I posted, they're made by Briley and they measure to what Briley lists on their website. You want known choke constrictions, these should be way better than the factory tubes--call and confirm that the chokes you order mention Briley on the packaging.

kgb

_________________
Bore, n. Shotgun enthusiast's synonym for "gauge" ; everybody else's synonym for "shotgun enthusiast." - Ed Zern
Back to top
View user's profile Send private message
L Kenney
PostPosted: Thu Sep 15, 2005 3:11 pm  Reply with quote



Joined: 12 Aug 2005
Posts: 54
Location: San Francisco

16GuageGuy: I just now noticed your post. No question that the Full tube mikes at .622 at the muzzle end. I'll take your advice and see about cutting a parallel section of larger diameter at the muzzle and report back when I have a chance to pattern it. As it stands I don't see shooting it.
Back to top
View user's profile Send private message
Display posts from previous:   
All times are GMT - 7 Hours

View next topic
View previous topic
Page 2 of 2
Goto page Previous  1, 2
16ga.com Forum Index  ~  16ga. Guns

Post new topic   Reply to topic


 
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum




Powered by phpBB and NoseBleed v1.09