Polychoke: A throttle for your scattergun - part 2

Before I continue on with this Polychoke project some correspondence with the company has brought some information to light that I think should be shared here. First of all the Polychoke is best installed at the factory, as of this writing it only costs $65 for them to do it and it is what they do for a living. As I have learned from this project there is a lot more that goes into the installation of these than is thought from the get go. Second, the choke element that is the part that is threaded to the barrel comes in 3 different sizes I feel like few people know this and do not understand that they are also not marked with what size choke element you have. The diameter of your barrel determines the choke size you will need, something to keep in mind when purchasing a USED polychoke. You have to know what the internal diameter of the choke element is in order to see how it matches up with your barrel. There is a number stamped on the choke element, this has nothing to do with the size of the choke or what it goes to. Those numbers were a reference system the company used with the shops that installed the chokes.

More information on the polychoke and its installation may be made available as this project progresses. On with the project!

My goal with this project is to have a short(er) field barrel than the long full choke barrel I have now. This might not be the best balanced barrel when it is all said and done but it will be compact and better for my needs all around on my favorite 870 which I have grown exceedingly fond of in the last few years. The shotgun continues to impress me as to its versatility even though its not very economical in weight of ammo vs game harvested. I looked to polychoke when I realized this barrel was not going to pattern well without the help of some external forces. This post in the project will show the barrel, and the beginnings of the fitting process.

Shortened 870 barrel shown with practice stub from another barrel project threaded and test fitted with the Polychoke.

The Polychoke will add approximately 1.5" in length to the barrel, we will be keeping this in mind as we work making sure we maintain a 18" MINIMUM barrel length when we are all said and done, ideally you want to be 18" and some change over. Installing with high temp solder or welding the choke in place will make it permanent which is required by law to be considered part of the barrel.

Ready for turning and threading

The barrel as it started in the project. 

Long vernier calipers can come in handy when laying out minimums. Making sure to keep in mind its best to be over by 1/4" with shotgun and rifle barrels.

Turning to nominal thread diameter everything looks good here!

I somehow lost pictures of threading the barrel at this point, and then I realized that upon test fitting I had messed up. The live center I used was in poor shape and I think it cause the barrel to be just a fuzz off......sooooooo we need set the barrel back 1/2" and try again. Not a big deal, we still have plenty of barrel to work with.

Hey look threads! WAIT WHAT ARE YOU DOING WITH THAT HACKSAW!!

Parents....talk to your kids about hacksaws before somebody else does.....

Just screwing around: making hard to find replacement screws

I had a guy asking for some replacement stock screws for a Mosin Nagant 91/30 a while ago and having none left in my parts bins I decided it was time to make some.  Not wanting to make them out of the 0-1 I had on hand I secured some 3/8" cold rolled round stock from a good friend who works for one of the big metal suppliers here in town. The general rule with stock screws is that you want the material to be softer than what the receiver is, the idea being the screw is a consumable....the receiver not so much. If the screw was harder than the receiver you might run into some problems.

Anyways on with the screwing around......First determine the rough dimensions by carefully measuring and double checking before cutting, Or if you have a sample already just hold the thing up to the bar stock and mark it with a sharpie....either way works just well for these old war horses.

Classic Sharpie layout

 I used a rounded general turning HSS tool for turning the cold rolled round stock, cold rolled tends to tear easily, its hard to get good cuts on the steel if you're not used to the stuff. I managed to use a rounded general turning tool with slow speeds and feeds with lots of oil and excellent results (I think).

I did not have a square right hand facing tool ground so I was just using a "general turning tool"

 This spring/summer is going to see some changes in the shop, I am finally going to build a proper tool grinding station with a rest. I have been needing one for a long time and its way past due. If you know half of anything about proper lathe tools you'll realize I am making more work out of this than is really needed and not using the carbide tool below correctly. This should be fixed once I get my tool grinding station built.

Backwards way to square up the shoulder of the screw, not proper but it works.

 Using a parting tool we slowly cut the completed screw away from the rest of the round stock. After this we will will take the bolt to a 1/4" (the screw is slightly over 1/4" but it still works) collet and slightly dome the head, radius it and prepare for slotting.

Parting is such sweet sorrow. Here we see the newly threaded screw being parted from the rest of the round stock.

Uhhhhhh, How do they put the slot in?

These little slitting saws are great for soft steel, aluminum and other soft metals/materials. Here we begin the slotting for the flat head screwdriver. 

What we end up with after slotting.  Could be a wider slot though any wider and it becomes easier to mess it up. 

In the white new front and rear stock screws for the Mosin Nagant 91/30

Poly-Choke: A throttle for your scattergun

 Here is a brief introduction into the next project I will attempt to document on here. My problem is I do so much so fast sometimes the camera is often not thought of until the project is done and well, lets admit it a gun blog is boring without pictures.

 The following will show the installation and maybe pattern testing of a Poly-Choke device. "Poly" means many, (like polynomials for educated folks out there....or polygamy for those who like to count past 2 and don't mind factoring a "x" or two).....bad math joke sorry.  The poly-choke is designed to give you options in the pattern your shotgun disperses depending on the situation you find yourself in. Out rabbit hunting in close brush? Turn it down to Cylinder...rabbit jumps and you don't pick it up right away? Crank it up to full and let loose.

Shown below is a "stubbed" poly-choke. "Stubbed" refers to the section of barrel that remains installed in the choke, how its installed I am not sure. It can be sweated on with solder (or jb welded on if somebody got lazy) OR it could be threaded on.  The poly-choke was given to me by a gentleman from Texas who thought I could get more use out of it than he was. He did not know however how in fact the choke was previously installed. The point is this poly-choke was on a gun previously and removed, by cutting it off with a hacksaw with enough of the barrel sticking out so the next guy can remove it and reuse the choke which is what we plan to do.

Remove outside sleeve.

Choke collet  and barrel stub shown

At this point we are needing to firmly secure the choke in a barrel vice to remove the barrel stub. The steel pipe shown opposite the  choke will keep the clamping action from focusing on the center of the vice, it will instead focus it on the thick portion of the choke protecting the collet.

 With top vice sleeve in place the top bracket of the vice is replaced and secured.

A little heat to see if solder or anything else comes out....some good old fashion torque on the stub with some shocking action and presto! The barrel stub turned out to be threaded into the choke....this revelation will require me to gain some more information on the thread pitch (which I am pretty sure is 40 TPI but want to double check) max and min barrel diameters and some other factors that may have to be taken in to consideration for the next phase of this project. The idea is to restore a 870 barrel back to having a choke, the vent ribbed full choke barrel met its demise when a few inches of its previous 26" barrel were removed for home defense use via hacksaw. Making the barrel effectively a cylinder choked gun, useless if you already have a riot barrel and need a field barrel which is what I am lacking currently.

Stubbed portion of barrel shown un-threading from Poly-Choke.