choke alteration question

[stevehaun]

I purchased an old stevens 311 20 gauge to use as a grouse gun. It has a 28 inch barrel. I patterned the gun and at 27 yards I got a 22-24 inch pattern with the right barrel and an 18-20 inch pattern with the left barrel. I took it to a gunsmith to have the chokes reamed out. I asked for cylinder in the right barrel and improved cylinder in the left barrel. After the ream job I went back to the patterning board and was dismayed to find that the patterns had changed very little. The shot patterned more homogenously which makes me happy. However I now have a 24-26 inch pattern in the right barrel and a 20-22 inch pattern in the left barrel at 27 yards. I was hoping for a 30 inch pattern at 20 yards from my right barrel...
Is this the best I can do or should I take it back to the gunsmith?
steve haun

 

[JohnBT]

I'll be interested to see what the responses are. My two thoughts are that it might be hard to open the Full/Mod chokes in that 28" barrel up that much and that plastic shells and wads just shoot tight patterns. Third thought, I've been told that the original chokes in those guns tended to be even tighter than advertised.

Still, it couldn't hurt to talk it over with the gunsmith.

John

Edited to add: Oh, and have you tried some different brands of shells?

 

[Dave McCracken]

Lots of us older types know to use cheap shells if a pattern needs more spread or trap loads for tighter ones.

Try some value pack 8s in that left barrel. Betcha that does the trick.

 

[stevehaun]

Dave,
I only shoot cheap ammo. I patterned the gun with Federal target load (8 shot) from Fleet Farm. I also shot 7.5 & 6 shot Federal upland loads. The patterns were very similar. I did get a little more spread (1-2 inches) with 6 shot upland load.
steve h

 

[kirbythegunsmith]

What to know, what to see

If you pay someone to open a choke, try to discover what type of tools are used for the work. I advise to run away from any shop that uses an adjustable sizing reamer that is inserted into the muzzle. That arrangement has created more crooked choke openings than straight since starting in thin air has no alignment basis.
The shop should be able to measure the choke amount accurately in front of you to show the amount existing, and then show the amount remaining after opening the choke.
There should have been some discussion about the pattern that you had and desired to have after the work. Asking for test patterns in any future dealing may cost more than just opening a choke, but will provide an immediate verification (or lack) at once.
The pictures show some of the special tools for measuring chokes and barrels.
There are 2 bore comparison dial gauges, not the most accurate for determining exact size, but useful for comparison, but lacking in reach, the one being 2.2", the other 3.3".
The bore micrometers shown reach 2.5" and over 8" and are very accurate for size determination.
The dial bore gauge with the multiple interchangeable heads also has setting rings to allow for precision size readings via calibration of each head to the corresponding ring. The bore mikes are the most accurate of the bunch.
The extra long gauges are for severe duty use, such as barrel manufacture, where they originated. The skinny one can reach over 30" in a .410 with the extension rods. The long one at an angle can fit an 8 gauge and larger bore. These gauges can fall off a bench and probably still go back to work.
That pile of tools in both pictures is over $5000, but I can get inexpensive versions of the dial comparitors for under a hundred bucks. They are just right to put in a shirt pocket when going to a gun show, etc. Better safe than surprised.

[email protected]
trained gunsmith, custom choke installer

 

[stevehaun]

Kirby,
I patterned the gun before taking it to the gunsmith. I told him the pattern that I got from each barrel and my distance from the patterning board. I told him I wanted open chokes for grouse hunting. I told him cylinder on the right barrel and improved cylinder on the left barrel. I did not inquire what type of tool he was going to use as I have no knowledge of how one opens a choke. Maybe I am wrong but I think a cylinder choke should give you more than a 24-26" pattern at 27 yards.
steve

 

[kirbythegunsmith]

Ask for confirmation

I did see that you had patterned and requested open chokes for your barrels. I sometimes include obvious details for other people reading these posts. I did also want to know if you had been given any measurement data.
I showed the types of measuring instruments that could be shown to you and used to prove whether or not there were open choke constrictions in your barrels now.
For other readers, this is your object lesson to ask for direct measurements in front of you, and be given details of the amount of choke to be removed.
Steve, I know this is after the horse has left the barn, but you can still go to that shop and have them measure the amount of choke still remaining in the barrels (if they have measuring tools to compare the constriction). If it is within the expected specs, with a small margin, then you may need more open amount of constriction than normal for IC, for instance.
If they don't have tools similar to the ones that I showed, they may be counting on the bore of the barrels being of a normal size, and open the choke to a DIAMETER rather than a CONSTRICTION. That is not a proper way to get the correct choke amount.
What sort of finish smoothness is present in the altered area? Rough reamer marks will add to the tightness, sometimes, and a small amount of honing may provide more open and even more consistent patterns, since fouling is usually lessened compared to roughened surfaces. If there is obvious roughness present, as opposed to a few minor tool marks in with a polished surface, the tools might have had a problem cutting the steel, or have been dull, or other unknown conditions. Rough marks are not normal or expected from proper work.

 

[stevehaun]

Kirby,
Thank you for your assistance.
If I understand you properly, my chokes should have been reamed out to a relative constriction rather than a fixed diameter.
There are some rough reamer marks (see attached photo).
steve h

 

[Dave McCracken]

EEEWwww!....

Whoever butchered those barrels deserves 10 strokes of the bastinado and a millenium in Purgatory.

Hope they can be cleaned up OK....

 

[kirbythegunsmith]

Comments of appearance, etc.

Those marks in the one barrel are certainly a bit rough, but the other is not obviously in the same condition for the little bit that can be seen. How do they look when you see through the barrels from the muzzle?
I have attached a picture that shows a barrel reamed in a rough manner for comparison.
The next 2 pictures are of a .410 choke that had already been butchered by someone wanting to open the chokes to skeet or cylinder, with atrocious results. The pictures show before and then after I improved the finish and altered the poor angling of the choke area. This barrel was not the worse of the 2 on the over/under sent to me. If you look closely at picture #2, you can see the shadow of what looks to be a low spot in the contour.
I wrote an article about a year ago on the plethora of problems that appeared the deeper I got into the mechanism.
The next 2 pictures show the off-center nature of the point of impact, and the improved centering of the pattern after some judicious choke alteration. I was not actually sure how close to center that I could influence the pattern, but knew that I could improve what it was previously.

I am the guy that tries to fix problems caused by somebody else. Challenge jobs aren't what you'd call easy money.

[email protected]

 

[stevehaun]

Kirby,
The photo shows the worst spot but both are fairly rough. I will try to take a pic of the muzzle with some light in the bore.
I think I am going to take it back to the gunsmith and have him measure the constriction. Am I correct in thinking that the bore diameter and the diameter at the muzzle should be the same in a cylinder bore? How about for improved cylinder?
I have to think that there is some constriction on my right barrel (cylinder) in that it gives me a 24-26" pattern at 27 yards.
steve haun

 

[Dave McCracken]

In a 12 gauge,Steve, IC has traditionally been the same as English "Quarter Choke" or about .010" or 10 Points Of Constriction.

In a 20 I'd say about 8 POC is Quarter Choke.

Cylinder bore is in theory a straight cylinder all the way down.

While we all talk about 30" patterns, oft all we get is a bit less. For most targets I perfer to choke up and work with the core of the pattern, which may be as tight as 20-24".

Get the chokes cleaned up and shoot it at a pattern board. Use all the loads you plan to hunt and target shoot with. An hour or so of checking patterns will yeild dividends.....

 

[kirbythegunsmith]

details

Dave, you are very close to what I would have said, in that my typical IC for 20's is .006 to a max of maybe .008
12 ga. I try for .008, but realize that plus or minus .001 or .002 is minimal on the significance


Always remember that constriction (being the difference between the bore and exit diameter) is only a number, and almost any other aspect can have more bearing on the pattern.

Taper length
interior alignment
parallel or lack thereof at the end of the choke taper
angling of the parallel vs. the taper (especially with improperly opened chokes)
bore finish, choke taper finish, parallel finish, reamer mark remnants
occasional bead shank intruding into the bore area in the choke
Cut in place (bore ream production is most common)
Swaged by sticking the barrel end into a tapered die, sometimes angled, too (many H & R, NEF etc)
Some rolled into size, with spirally-looking marks through the taper- worst offender in recent memory, S&W 916, Eastfield variant, mediocre patterning

[email protected]

 

[Dave McCracken]

Glad we agree, Kirby. Many factors affect patterns and choke besides constriction. You name most of them.

Are you familiar with Miroku trapguns? CR Sam, Moderator Emeritus here, has one with no forcing cone per se. The bore tapers slowly over the whole length of the barrel to a parallel section at the muzzle that gives a total constriction of about .015",IIRC. According to Sam, it shoots very nicely and efficiently.

The barrel gurus do not agree on how long a cone should be, but most think 1.5" is a good start for ammo with one piece plastic wads. Seems to me that the tapers in a choke should be at least the same.

And polished to a mirror sheen.

 

[berettashotgun]

The reamer used on your shotgun must have been used to scrape some ice from roadways and bridges, and it appears some polishing is gonna be needed. Med clover lapping compound, a bore mop and a cordless drill will get a little more pattern out of that horrible looking barrel(s). Might smooth it up a little, but a brake hone might need to be next.:banghead:

 

[stevehaun]

Is polishing the chokes something I can do at home or is that best left to the gunsmith. I do get a nice homogenous shot pattern (just too tight) and I would hate to screw that up. Shouldn't the gunsmith have polished the reamed out area when he did the job in the first place? Am I expecting too much for $65/barrel?
Thanks for everyone's help!

 

[kirbythegunsmith]

Observation

If a shop had opened the choke and not made the finish satisfactory, take it back ane see if they will make the chokes opened enough (at least in the constriction amount) for your situation, and with a finish somewhat consistent with the finish already in the bore.
If their tools are dull, or if they have poor knowledge of how to make them cut properly, then don't waste any more time with them.
You probably will not be satisfied if you do a little smoothing yourself, since the chokes are still too tight for you.
You will then need someone to properly open and test the patterns for you, or just live with what you have.

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