Hi. Was wondering if someone can explain why I keep reading different amounts to ream for different gauges to achieve certain choke restrictions. Should all gauges not be the same in what amount to ream? If it is different could someone please tell me the actual numbers for 16 and 12 gauge choke reaming so that I can understand and make a good decision. Thnx very much in advance.
Choke reaming different gauges
- Thread starter Lawney
- Start date
I have a choke booklet (50 years old) that gives all the amounts of constriction for various chokes through the gauges. Too much info to type out. You need to accurately measure the bore diameter too.
Perhaps describe what you are trying to achieve?
Perhaps describe what you are trying to achieve?
It's not an exact science because pattern percentage has as much to do with loads as it does barrel dimensions.
But as a general rule:
Skeet -.005"
Imp cyl (1/4) -.010
Modified (1/2) -.020
Imp Mod (3/4) -.030
Full -.040"
Aim for a couple thou short of finished dimension to allow for finish honing.
But as a general rule:
Skeet -.005"
Imp cyl (1/4) -.010
Modified (1/2) -.020
Imp Mod (3/4) -.030
Full -.040"
Aim for a couple thou short of finished dimension to allow for finish honing.
Last edited:
The constrictions you quote only apply to 12 gauge.
Less construction in smaller gauges will obtain the same choke effect.
About 28 thousandthsof an inch in 20 gauge corresponds to full choke. Actual bore diameter must be known to adjust choke, and performance is still dependent on the cartridges used.
There is an element of "art" in choke adjustment, which can only be demonstrated by using a pattern board with statistically significant number of patterns.
Less construction in smaller gauges will obtain the same choke effect.
About 28 thousandthsof an inch in 20 gauge corresponds to full choke. Actual bore diameter must be known to adjust choke, and performance is still dependent on the cartridges used.
There is an element of "art" in choke adjustment, which can only be demonstrated by using a pattern board with statistically significant number of patterns.
What I am trying to do is open up all the full chokes on two 16 gauge sxs shotguns. Looks like adjustable reamers is the way to go from Brownells with the T handle, but bushings for the bores of each sxs seems to be a chore to find?? The product is Gilchrist precision choke reamer with the "D" adjustable reamer from .656" to .718". Luckily both sxs bores are pretty much identical at .675". The D adjustable reamer is also going to serve me for a 12 gauge .722 bore size as well. Any help would be appreciated. Thanks
Last edited:
I post this info with some reservations - 0.675 sounds somewhat overbore for 16 gauge, in light of the fact that many 16 gauge doubles, particularly European guns, are actually tighter than nominal bore diameter.
http://www.hallowellco.com/choke_chart.htm You will note a significant range of choke diameters for supposedly the same choke rating.
Choke adjustment is not a simple ream a certain amount out. Cartridge choice and shot size makes a difference to choke performance. A little knowledge can be a dangerous thing with shotgun gunsmithing.
http://www.hallowellco.com/choke_chart.htm You will note a significant range of choke diameters for supposedly the same choke rating.
Choke adjustment is not a simple ream a certain amount out. Cartridge choice and shot size makes a difference to choke performance. A little knowledge can be a dangerous thing with shotgun gunsmithing.
I did my 16 gauge SxS 45 years ago. It had both extra full choke 6 inches long... I cut 3 inches off the barrels and then opened the chokes to improved cylinder and modified. I also had a custom reamer made to do the forcing cones. I still have it. I use expanding reamers to alter the chokes and I can measure the bore diameter as far as 12 inches in from the muzzle.
https://www.canadiangunnutz.com/forum/showthread.php/1811329-Opening-up-fixed-chokes
Last edited:
I guess what everybody is trying to say here is : after you determine the true choke in a barrel by sutracting the measured choke diameter from the measured bore diameter, the result will be your amount of choke, in decimal inches ( eg .030"). For a 16 gauge, approximately each .009" you open that choke will change your effective choke by a nominal amount ( eg, full to modified). These amounts are not absolute and are variable and subjective to a certain extent, as has been noted. The true amount of choke is determined by pellet count ( average of ten shots) and there will usually be a spread in this string of 10-20 pellets between the maximum and the minimum count. Try a different load and your results will be different, so unless you are only ever going to use one load you will need to do this with a number of different loads and average them! Most people don't have the time or patience to shoot all these targets, count thousands of pellet hits and tabulate the results, which won't apply the same in a different gun.
Choke results are based on averages, they are not exact and trying to split hairs will only result in confusion and frustration.
If you insist on opening these chokes yourself be sure to carefully check your patterns after the job to make sure that your point of impact is correct and that your barrel convergence is correct and that your double isn't now shooting the different barrels to different places. I have seen far too many guns ruined by improper opening of the chokes and is now cross eyed, wall eyed or even one barrel high and one low or any combination thereof. Personally I now avoid guns with altered chokes unless I know and respect who did the work or unless I can do a quick live fire test.
Choke results are based on averages, they are not exact and trying to split hairs will only result in confusion and frustration.
If you insist on opening these chokes yourself be sure to carefully check your patterns after the job to make sure that your point of impact is correct and that your barrel convergence is correct and that your double isn't now shooting the different barrels to different places. I have seen far too many guns ruined by improper opening of the chokes and is now cross eyed, wall eyed or even one barrel high and one low or any combination thereof. Personally I now avoid guns with altered chokes unless I know and respect who did the work or unless I can do a quick live fire test.
Thanks guys for the info. I will say that I am waiting for a way better tool to measure the bore diameter in my 16s cause now getting .666 to .668 in the bore with chokes at .640 in one barrel and .640 in the next. Before I do any reaming at all I will wait for the better bore gauge.
