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Thread: Making choke tubes...
11-18-2005, 11:58 AM #1
Now Im not trying to do this as a money maker, just that no one makes the tubes, contrictions, styles that I want for my 28 and 410. So Im lloking at building some and starting the learning process. Right now I have the means to do and learn and study the actual cutting and internals of the chokes, and the material of choice... the one thing I lack, is any knowledge or anyone to ask about the hardness and hardening.
From what Ive seen, 17-4 Stainless is the animal of choice for tubes, and its a "precipitation hardening" material... which I dont really understand. I dont have a furnace, but I know someone that does, but they dont know much about hardening. Can anyone shed some light on how hard chokes need to be, and maybe a little on the process involved with dealing with 17-4 ss?
Thanks a ton.
11-18-2005, 08:05 PM #2
Precipitation hardening, this is probably a little outside the capabilities of the home shop.
Its been a while sense my material classes in school, so I could miss a few things.
The basic mechanics – get it hot, cool it off - are not much different than typical heat treatment of carbon steels, but it’s a lot more sensitive to time and temperature. Also the hardening mechanism at a micro structural level is completely different.
The idea is that at certain, often very narrow, temperature bands that you can precipitate some of the alloying elements out of the solid solution. The ”precipitates” basically reinforce the iron around them much like fiberglass in epoxy. Not to the degree we could call it a metal matrix composite or anything like that, but the same idea. Stiff crud keeping the softer iron around it from moving.
The temperature bands needed to make this happen can be touchy, and how long you hold at a particular temperature, how quick you drop from it and how quick you got to temp to begin with can all have an effect.
Unless you have a furnace with ramp controls on the temperature and a “recipe” to start with, its not something to try your self.
Conventional martensitic hardening of carbon steel is a whole other ball game, and not hard to do, but does not work in many stainless alloys.
11-18-2005, 10:15 PM #3
Before Jess Briley got to be big time, he made tube sets as you may know. These consisted of a 17-4 PH chamber liner (with extractor) and hard anodized 2024 aluminum tubes. The 17-4 was probably H1150 which can be bought all day long already heat treated. Hard anodizing on the aluminum was extremely thin, but worked well enough to sell these sets and so launch the Briley we know today. In those days, Jess worked out of his garage.
11-19-2005, 10:06 PM #4
Thanks for the info... If I do this, Ill have someone with the proper equipment to do the hardening, assuming I can be very sure as to what it needs to be hardened to...
Ive been doing some homework... and this seemed to have some good info...
But I still dont know what the "standard" is for chokes... I was kinda guessing in the H1150 area... because I figured harder (read as more brittle) would not be as good as hard, and less brittle...
Makes me wish I had a tester, and then at least I would know the RC...
Im planning on doing my homework before I ever even start a CAD file or even mess with converting to g-code... Cause Im not all that interested in messing up a gun or myself cause of my over active curiousity...
THanks for the info, if you have any more thoughts, ideas or tips... My ears are wide open!
12-17-2005, 10:19 PM #5
I read your post of last month with some interest. I posted a message on the Chaski board several weeks ago asking if anyone had ever made a choke. Not much response, but then I wasn't really surprised given that chokes are really pretty cheap so going to the trouble to make one might not make sense for most users.
Your question seems to be as much about the material to use to make the choke as the actual machining. I have read that many of the commercial choke makers seem to use 17-4 stainless and I don't know exactly why. I did a little research on shotgun barrels and found that at least several manufacturers (Beretta for one) use 8640 steel. I would think that 8640 could be used for chokes or perhaps even 4140 which has commonly be used for rifle barrels. I guess there must be some reason for using stainless, but then I have not found any explanation for this among the choke manufacturing sites I have seen.
In any case the real challenge to me would be the actual machining. I am thinking that if I can make one from 12L14 then I could start thinking about what other steel (17-4, 8640, etc) would be better. The 12L14 would obviously be much easier to machine, although probably not so great for wear. I started with a Browning Invector choke because they are used in the Stoeger Condor shotgun I own. They are also not very long and have regular threads (opposed to the square threads on the Beretta choke for another shotgun). One problem I ran into was making the threads so that the choke would screw into the barrel. To do this right I would really need something like a barrel to test the threads while the WP is in the lathe. Since I haven't gotten beyond that point yet, boring and tapering of the choke may not be that difficult. In any case this seems to be a lot of trouble for a choke that I can buy for less than $15. Your situation doesn't appear the same.
You also raise the issue of heat treating of 17-4 something that I know nothing about. I may be mistaken about this but I thought barrel manufacturers didn't heat treat their barrels? If not, then 8640 would seem to be fine and you wouldn't have to heat treat at all. Even if the barrels are heat treated and you are shooting lead shot, an unheat treated choke would probably last a pretty long time.
I would be interested to hear about your experiences in making a choke. It sounds like you must have some more automated equipment than I do ( a 12 x 36 lathe) so maybe cranking out the choke is much easier.
12-20-2005, 10:22 AM #6
12-21-2005, 01:07 AM #7
I've made a few dozen choke tubes over the years for various shotguns. When I started, there was no such thing as a "Turkey Choke" and I experimented much with various constrictions and even made some with muzzle breaks on them.
I've made choke tubes that were extremely tight for turkey hunting, more open chokes for steel shot and have produced several for friends that participate in "Turkey Shoots" in which the most shot in a playing card at 30 yards would win the contest.
For most, I use StressProof a material that has a tensile strength of 125,000 PSI. I have also used ETD 150, a material that is 150,000 PSI. Both of these require no further heat treating and work quite well for the purpose.
I've been using various chokes for years without any show of wear at all. I've killed around 3 dozen turkeys with my turkey choke and hundreds of ducks and geese with the more open chokes.
Most of these were for a Remington 870,1100 and Mossberg 835 Ultimag. Ive also made one for a .410 barrel on a T/C Contender pistol that work better than the original choke.
Making a tube isnt that difficult. The important thing is getting a good fit on the threads. Ive used various tapered reamers for the bore as well as boring bars to get the needed taper.When I started getting into it, I made a die nut for the threads so as to insure the proper fit for a barrel and tested it with a factory choke.
12-22-2005, 04:19 PM #8
Thanks for your response. Yours is the first I have read of someone who has actually made a choke. I understand about getting the threads right on the choke. My first attempt showed me that this was a critical step. The choice of steel seems to be a matter of preference. Obviously there is a great range of choices. As I suspect, you don't need 17-4 stainless to make a choke that can last. I am not so sure that I really need to make a range of chokes, but to satisfy my curiosity I may at least try one.
12-27-2005, 06:01 AM #9
You can buy 17-4 all ready heattreated to about 32/36 c scale rockwell. 4140 is likely to gaul in a chrome moly barrel ,and can rust in place , stainless usually will not. Bootsnhats
01-06-2006, 01:02 PM #10
Yeah the main reason for the Stainless is corrosion/rust resistance...
AS for the machine, I have a CNC lathe... an Okuma machining center, so really its going to be generically easy to do... just a more time in design and writing the gcode. Also with help from the folks here, I have some ideas on how to do the double lead thread.
My main concerns about the hardness is, there are going to be chokes for a 28ga and they arent going to have lead shot through them... they are going to be for HeviShot loads. A friend of mine worked up a hevishot load, and we are having it tested... and everything whould come in just fine... or at least be able to make it within safe pressures easily. Anyway, thats why the hardness of the material is important to me. SInce hevishot is harder than steel shot... and they dont make any stell/hevi wads for the 28ga, my friend came up with an idea that works very well... but I just dont want to take any chances with getting a tube stuck or anything. I figure scratches I can live with if it happens.... and just make another one.
Ive heard you can buy prehardened 17-4... but I dont know how hard the choke manufacturers are using for their chokes... and understandably so... they arent talking. Im assuming they use seamless tube to start with, rather than bore a solid rod and waste that much material....
Im doing this cause almost no one makes chokes for the Truchoke 28ga... and all the ones that are made say "lead shot only" and I dont know if its a difference in material used or just a "head off people". Plus the only constrictions I can find are SK, IC, M, & F and Id like some tweeners.
Thanks a ton for all the info so far!
01-08-2006, 11:13 AM #11
I dont think that "hardness" of a choke is really a factor due to the plastic shot cup that surrounds the lead. If you'll notice the choke after ts been shot quite a bit, its not lead streaks that'll you see but plastic streaks.
Tru Ckokes are very thin. They are made for old shotguns with thin barrels and they are very short. They have the shortest taper of all chokes made. As a result I have never heard of one that could hold a very tight pattern and have known of several "blowing out" meaning that the fine threads jusy gave up and the choke shot out some where never to be found again. The longest possible taper that you can put in a choke is going to pattern the best...that is why the tight patterening commercial chokes are all extended chokes. Since they say "Lead Shot" only, they pprobably cant take the force of the steel shot constricting in such a small taper. Since you are wanting to use Hevi Shot, you ought to look at building a longer choke than standard. FWIW, Heavy shot acts more like steel shot in the fact that a more oopen choke than the traditional tight choked tubes usually gives better results.
The only advantage to using a stainless choke is if you leave it in there for a long time it wont rust up to the threads which makes it very difficult to extract. A gunsmith friend of mine makes a good living removing stuck chokes that owners have left in there for a season or two and they eventually grew together. That happens even with the 17-4 chokes as they all get crude in the threads after being shot awhile.
01-08-2006, 01:50 PM #12
I Think youre thinking of the "Thin Walled" Truchokes... those are infact thin and for older guns. I have a couple guns, that if I want chokes in, I have no choice but to go with the thinwalled TruChoke... which arent even meant to handle magnum lead loads... so I I just left the barrels alone.
But the larger TruChoke sysem is thicker and better than the thin wall.. Actually... of the 4 types of 12 ga chokes I have here... (benelli, browning invector, Truchoke, and Rem) The all thickness of the truchoke is second thickest... at .048" and the thinest is the browning invector. So Im pretty competent the Truchoke threads and external design will be adequate... assuing I dont screw up the ID and material hardness.
What ever I build will be extended. And likely longer than the Colonial Extended 28ga chokes I have currently. My plan is to have the leading parallel secion continue (bare bore at choke tube +.002 .003") until it is outside the barrel, then start the forcing cone and then the exiting parallel section. Fortuneatly, with the CNC it will be a lot faster and easier to tinker with that stuff.
From what I have seen... Hevi has an odd "fluid" characteristic about it... something that makes it very interesting to deal with. Chokes that are too tight to handle steel, can handle lead and hevi. ie turkey chokes. WHich really surprised me. So Im guessing, with the proper hardness, hard enough to not expand too much upon firing, but still soft enough to not be brittle, something very usable could be made. Thats my plan anyway
Yeah... Ive helped get some tubes out myself... SS and non-SS... as long as one side of the threads can rust... you can get yourself in trouble... no better reason to keep the tubes lubed. I use a heavier grease... to help add to the stability of the choke and add some structural support and buffer via a hydraulic means for any expansion that might come about from larger shot sizes.
Thanks again for all the info! I really appreciate it.
01-08-2006, 01:56 PM #13
I would be very careful with HeviShot loads in a thin or constricted choke. I shot trap 500 or so round with an extra full choke on my double, after a year or so the choke wouldn't unscrew. I had to make a tool to unscrew the stubborn tube. I never went back to an extra full again.
If your 28 ga isn't a show or collector grade I would think about making an extended choke silver soldered to the barrel. Not a good idea, just an idea. I did shoot a 28 ga at trap one time, just a few rounds, it was sweet.
01-08-2006, 02:36 PM #14
Its not a show gun... by any means... and I have two... just incase... Baikal IZH27s with 26" barrel, IC/Mod fixed tubes in one, and Truchoke threads in the other one. I have let some of the wildcat load through the tubed gun, with no ill effects yet... but I would feel better about a tube that doesnt do any constricting until the charge is out side the barrel. Thats the plan anyway.. Similar to what I hear the Terror chokes are like... heavy thick walled and the constriction happens outside the barrel.
Im not too worried... just anal... Il likely never shoot larger than Hevi 5s or maybe 4s out of the gun... close deke goose work and duck work... but I guess anything is possible if i get feeling brave and compitent.
Im still pretty sure, with the right steel, and hardness..... that I can make a tube that is the cats meow since hardly anyone makes tubes for the lil gun. Plus the addition of Hevishot to the line up for the 28, it becomes a much more viable gun. Not to mention that darn little mouse cannon just kills way better than it should. Ive used Bizmuth for the last year or so... and have had no problems killing ducks and pummeled a goose this year with biz 4s at about 20 yards.... and my dad took a goose with his two years ago with biz 6s. But Id like something that i know has a bit more punch pellet wise... out of respect for the birds, as we know how tough they can be sometimes.
Thanks again for the input. More knowledge is always good.
So far Ive heard 32-36RC (here) and 45-48 RC (from a buddy of mine who is a machinist for Ball AeroSpace) as guesses. I just wish I could get some confirmation from someone who knows the average range. Then I can start struggling to find hardened seamless tubing or solid rod.
01-08-2006, 04:57 PM #15
Wade, around here a lot of choke tubes are made from 4130 seamless aircraft tubing. Machines nice and holds up to a lot of "turkey shoot" matches. Also, you can get the tubing in sizes that cut down on the amount of machining i.d. and o.d. No heat treating is done.
02-17-2006, 02:33 PM #16
Making some headway...
17-4 annealed condition choke cut from round stock...
Hardened to 44RC (H900?)
So far no 17-4 seamless tubing is available... at least not that I can find.
You can harden 17-4 easily.. no special gasses or anything. Heat according to specs and cool.