Jug Choking

[Mortblanc]

A couple of weeks back I got a notice from my favorite gun dealer that they had a good deal on a well known and respected pump shotgun.

One of those deals you just can not refuse.

100 pounds, your money, for a new in the box pump shotgun holding 6 rounds and having a shorty barrel. Over here 18" is legal and this gun is equipped with 18 1/2" cylinder bore tube.

I do not really like a cylinder bore barrel. It is too limiting on the performance capabilities of the firearm and restricts use as an all around shooting tool.

What to do, what to do??

Out to the workshop and time to test a process I have heard about, studied and seen done but have never done myself.

I am going to install a "jug choke" in this shotgun, forming a relief inside the bore to act as a choke device.

All the tooling and materials are in place and I will take photos of the process and progress, as well as shots of patterns on target before and after the work.

My goal is to achieve a modified choke pattern on target at the standard 40 yards from the 18 1/2" barrel. Modified pattern will place almost 1/3 more shot on a 30" circle as the cylinder bore can achieve.

I know this process has worked for other people and if I can achieve the results I want and give instructions it might be just the thing for anyone that wants to cut a barrel down to whatever "legal length" is in your area while still having a controlled shot pattern to work with.

So, out to shoot a couple of control patterns to represent "before".

[CharlesHarris]

Depending upon the thickness of the barrel where it is cut off, this can work quite well.

I once had a T/C New Englander muzzleloading gun which had been jug choked using a brake cylinder hone. The gunsmith enlarged a long 2" section starting about 3/4" behind the muzzle, enlarging the jugged section to about .750" diameter, leaving the rest of the bore untouched at .730". This produced very even 1/4 choke patterns with 3 drams of FFg and 1-1/8 oz. of No. 7-1/2 shot, which I was using for upland birds.

We did not dare take the jugging further as this left only about .030" wall thinkness through the choked section and we were worried about buldging the barrel. I hope this is helpful.

For a modern repeating gun, a useful option, though more expensive, is to have the threaded for choke tubes.
This is only one firm offering such service, and I have not used them, it is only given as an example. Please do your own research as I am not recommending this company, but only offering it as an example.

http://www.colonialarms.com/catalog.html

[Mortblanc]

GH, the shotgun is an H&R Pardner Pump and the cost was only $160 US.

In my area having an existing barrel machined and threaded for choke tubes takes $400 and a 6 month wait for the work.

I can buy Remington 870 barrels that will fit this gun, already threaded for choke tubes, for $125.

My goal was to get the best pattern possible without spending any big bucks on the effort since I already have several shotguns that use the threaded choke tubes. This was bought as a test gun and as an addition to the loaner fleet. I simply could not pass it up at the price.

The barrel walls mike .075" and the bore mikes the standard .730. I have one double gun that has barrels miking at .027" so I have plenty of meat to work with. I can take .045 off each side and still leave more thickness than my double has in unmodified condition.

The smiths I have talked with that do this process also claim that the distance inside the bore the jug is positioned also has an influence on the pattern, with a jug 2-5" inside the bore giving tighter patterns than one closer to the muzzle.

I suppose we will soon find out, since I have decided to test this on an old Mossberg 500 barrel before I do the Pardner Pump barrel. I have a half dozen assorted Mossberg barrels and if I trash this one I can do a repair weld up without suffering much of a guilty conscience. If I screw up the Pardner barrel I will be forced to buy a new barrel for it.

If I get good results on the Mossberg test barrel I will be more confident when doing the H&R, or I simply will not waste my time.

[Steve]

Interesting stuff Mort, a benefit is that you can still use slug loads, although I have no idea how jug choking will affect the accuracy of them. Even if you only achieve 1/4 choke ( IC ) that will be a useful improvement, I really like 1/4 for walking about when you might bolt a rabbit or scare a pigeon out of a tree.

I look forward to seeing your results.

[Mortblanc]

Slug accuracy through the jug choke seems to be variable from one gun to the next.

But thanks for the reminder. I will shoot a couple of test groups with slugs before I do the work just as a comparison.

[Mortblanc]

Went to the range today to fire control groups and patterns to use as comparison for any improvement. O made a significant discovery.

In my memory I have never patterned a cylinder bore shotgun. My patterning has always been to prove choke performance, not to test the performance with NO choke.

After all, cylinder bore/open choke is 40% pattern at 40 yards, right? No need to check the known.

To my amazement I found that my cylinder bore only gave 32% choke.

It was a nice even spread or #7 1/2 shot with a piece of shot about every 3 square inches and would prove a decent rabbit killer at 30-40 yards.

Buckshot was a different matter. I had a slightly better percentage of shot inside the circle but there was a huge donut hole in the center of the pattern almost 12" in diameter.

It appears that any amount of improvement I can provide will be welcome, but I am definitely starting from behind. I feel I will be very lucky to achieve a test proven 1/4 choke when I was speculating that I would want a modified (1/2 choke).

Slug performance??? That was so bad that I am heading back to the range tomorrow with more slugs and an improvised optical system in an attempt at getting all the shots to remain on the paper.

I have seen better performance with slugs from crudely hacksawed shotguns of no great merit and I am very disappointed in this particular barrel which was manufactured specifically for shooting buckshot and slugs.

[Skean Dhude]

This is the stuff I would like to try but in our mickey mouse country I can't. We have to buy our stuff however this is educational and if we ever become free, one way or another, it will be handy to know.

[CharlesHarris]

Mortblanc,

Can you tell us the manufacturer of the barrel. Some after-market barrels I have tested for Remington 870 pump guns, of other than Remington make, performed poorly compared to standard police or miltary, cylinder bore "guard and riot" guns of Remington, Winchester or Ithaca manufacture from the WW2-era into mid-1980s manufacture.

I don't know if interior barrel dimensions have changed in the years since shotgun barrel manufacture has gotten away from the older drill, ream and hone process to cold forging and elongation of the tube, in the same manner as helicopter rotor shafts and the like.

[Mortblanc]

This particular barrel is a Mossberg production barrel.

This one is the standard 18 1/2" riot gun barrel with bead front sight.

It mikes .730 at the muzzle and shows no imperfections the length of the tube.

I have 4 barrels for this shotgun, each a Mossberg production effort. Two of them use screw in choke tubes and produce perfect patterns.

The other is a 24" slug barrel with rifle sights but not rifled internally. I also intend to test that one for pattern just to see if it is as bad as the 18" barrel. I am also anxious to see how that one groups slugs, since it is new and I have not fired groups from it.

I have a couple of shotguns that shoot as well as a rifle out to 75 yards and I will be very disappointed if this barrel does not do as well as some of my hacksawed slug gun projects have turned out.

[CharlesHarris]

If you look into the barrel from the chamber end, you may observe that it has a short forcing cone ahead of the chamber, which tends to increase pellet deformation compared to a longer forcing cone. Firing 2-3/4" shells in a 3 inch chamber accentuates thus effect. My best patterning buckshot gun is a Winchester Model 12 with 26 inch modified barrel, which has a 6" long transition from its 2-3/4" chamber to its .730 bore diameter, and a 3 inch long choke cone 5 inches behind the muzzle, leaving a 2 inch cylindrical section of .705" at the muzzle. It shoots 100% patterns at 40 yards with 9-pellet 00 buck and will keep slugs on an Army E silhouette at 100 yards. It has killed truckloads of deer over the years.