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SMALLEST GAS PORT SIZE??

6K views 48 replies 8 participants last post by  1biggun 
#1 ·
I am starting on my 17-223 varmit build #2(waiting for reamer) It has occured to me that the gas port hole on a 223 is almost as big as the .17 bore.
What is the smallest gas port hole any one has gotten away with on a 223 build?? I am thinking of trying a custom GB with tighter piston to block clearances and possably having the piston run an inch or so in this block with tighter clearances to try to get the bolth my 223 and the soon to be done 17-223 to cycle with a smaller hole. was also thinking of a lightest possable recoil spring. was also considering a smaller piston as well thinking it would take less volume to move it. was going to try one the same as a FAL

I also need a few AMD 65 pistons to play with If anyone has a few originals laying around CHEAP I could use a few to play with. I gave mine away a year or so ago.
 
#27 ·
WOW - that sounds crazy! I had a hard time centering the reamer on my lathe, but like any operation, lathe work is about 80% set-up and 20% cutting.

The reamer-rentals website instructions assume that a lathe is being used, and to use the lowest speed setting (200-150 RPMs) and some thick cutting fluid or even motor oil. I used motor oil, and besides the smell it worked fine.

The pilot on my .350x39 reamer was only about 3/4" long, and that doesn't seem like enough to compensate for the "freehand" cutting. It was a basic pilot that was simply the front end of the reamer that was honed to the bore size.

I am waiting to see what others say about hand-reaming...
 
#28 ·
Pacific tool and guage advised me to use a sandard type cutting oil and thin it 50% with type f (ford) automatic transmission fluid. some info here

http://www.bryantcustom.com/articles/rebarrel.htm

in the picture it looks to me like the tail stock is supporting the end and used to supply pressure only. I have not completly digested all that is said here but good info. It seems to me that the reamer should cut a concentric hole down the center of the bore the main thing would be to avoid any side pressure like that which would occure if say the reamer was ridigedly clamped into a chuck in the tail stock. if my thinking is correct a floating reamer holder would basicaly supply the forward thrust needed to make it cut the floating part would be very similular to hplding it by hand. In my case there is already a 17 remington chamber gut so I do not have to ream out the whole chamber just go in deaper and rechamber to a 17-223. I am to the point were I think I may need to get professonal training from some one. these guys are talking about talerances to the 100 of a 1000th. I can assure that after cuttin a few remingtona nd savage take of barels down to fit AK trunions that factory stuff can be off several thousands from the bore to the outside of the barrel alone. On the last barrel after setting it up in a 4 jaw and a steady rest to +- .0003 that the bore/chamber was aprox .005 out of true. and the barrel had a slight bow as well this was on a heavy varmit barrel that had never been shot. I only have 3 weeks to get the 17 -223 done and to be honest I may take it to a local smith and have him rechamber it and hopefuly watch the process. I am gong to invest in some gunsmithing vidieos and books as well. I plan on doing a couple of higer end bolt actions in the future and the info would be worth the $$$ to find ut hoe to do it right. there are a few bench rest sights around that may help but dont mention varmit build AK 47 if you want to get taken seriously.
 
#29 ·
Yes, the .001" is too much runout for a precision chambering. It would probably be OK (?) for a "battle" rifle if that's what you were building. I'd leave that to the experts. I recall reading on the homegunsmithing forums way back when that someone did a 9mm chamber with a flat-bottom drill (I think it was a wood drill!) and it worked. But you're talking a 9mm vs. a precision rifle.

The part where they describe the use of a drill is to get the chamber "roughed" to about .10 (1/10th) of an inch, then the finishing reamer does the rest.

I am going to true the jaws of my lathe tonight so I can work on my 9x39 finishing reamer. My jaws are currently about .005" out. .006" is a sheet of typing paper and is noticeable when it spins. That is OK for an AK piston or something where tight tolerances are not a factor, but not really good for chambering.

I have a mini-lathe, the $360 special from HF. After reading the mini-lathe.com links and the Varmint Al mini-lathe links, and all the other "tweaking your lathe" sites, I am confident the mini-lathe can achieve a .0002" runout (out of round) after the jaws are trued and everything is as it should be. I simply have to do the grunt work to tune it up. Not looking forward to that necessary evil :(

My problem is that I can't stick the muzzle end of the barrel into my head stock unless you are talking an AK barrel... the head is simply too small to let a beefy barrel fit into it. I think a bigger lathe would be better for chambering jobs, or any barrel job for that matter!

You can probably do it by hand, but darned if it is going to take some time to finish! :D
 
#30 ·
My problem is that I can't stick the muzzle end of the barrel into my head stock unless you are talking an AK barrel... the head is simply too small to let a beefy barrel fit into it. I think a bigger lathe would be better for chambering jobs, or any barrel job for that matter!
I have the same problem on my 9" southbend. I take it you do not have a steady rest. My local smith uses a a steady rest on the chamber end after he trues it to the bore by workng off of a live center. I have a 12" clausinng lath that I need to get mounted on a I beam and install a motor I hacve had for 10 years just to many projects. I also assume that you do not have a 4 jaw since you are truing your 3 jaw. I never seem to have enough tooling myself.
I doubt that the 17-223 will get done by the end of the month and to be honest it may be a good thing I am starting to get stressed on trying to get a build done buy a certain date. the worst part is on that build I have no reason to shot it except on the anuall P dog trip. so I will be wating a year to use it if it is not done.
I do not know if my tail stock is true to the spindel or not I may check it and if it is I may just chuck the reamer in it a do it that way. I plan on doing a few other chambers in the future so a floating reamer holder may pay off. I want to have a big bore done by dear season this year (possably the 450 bushmaster) and I I have a couple mausers to play with as well.
 
#31 ·
This is what I did on on touching up the chamber because of the different shoulder angles. Index off the bore with a rod and 4 jaw chuck. Place a piece of flat stock in the tool holder facing the chuck. Place the reamer in the chamber and a ball from a bearing between the reamer and flat stock. Then use a wrench to hold the flats and feed with the compound feed. Very little at a time and clean chips. If there is slight movement the ball on the flat surface will move around.

Might not work real well for a barrel blank.
 
#32 ·
Yes I have a steady rest, but my biggest problem is that I can't get the tailstock and drill aligned, no matter what. I managed to true my jaws with a dremel and after some testing, I can definitely say they are more true than before. It seems that no matter what, I can't get the darned tailstock to center. That's what causes the reamer to cut off-center chambers. I had one cut at about .003" out. That is probably true enough for a "battle" rifle like an AK, but definitely not good enough for a target-match-grade rifle build IMO.

The problem with the tailstock is that I have to take it off to align it, so it is a real PITA to use. In theory, you are supposed to get the tailstock aligned before hand, but I have observed that the alignment changes depending on how much torque I put down on the 17mm set screw. It seems the way the tail stock is attached to the lathe bed gives it some room to creep when it gets tighter. I would imagine the tail stock on a HUGE lathe has more meat, and therefore less room to "creep" when it is tightened down on the lathe bed.

Now that I think about it, I am going to true the tail stock before I use the lathe next, and I am going to torque it down to a certain point, mark the nut, and afterwards torque it down to that same point every single time. That's next on the list - the tool steel rod arrived for my 9x39 finishing reamer, so I have some cutting to do! :D



If you haven't already bought some, you should get some chamber casting alloy from MidwayUSA. This stuff is like solder that you melt and pour into a plugged barrel so as to get a good casting of the chamber. That lets you know if the chamber if out of round or not, and then you can choose to either use it or cut it off and redo the reaming. The alloy block is only about $8 and you can reuse it, so it will probably last a lifetime.
 
#33 ·
the tool steel rod arrived for my 9x39 finishing reamer, so I have some cutting to do!
Are you planing to make your own reamer??
I have been kicking that around for a over a year now. the main thing I see being hard is getting the temper correct after you cut it with out warping it. the 450 bush master or my 458x1.5" rebated special seems to be pretty easy to cut as they are straight taper with no neck. I was also considering boring the chamber with my tool post set at the correct angle and then reaming the neck and throat seperatly. it would be tough to do on a .22 cal bore but on a .458 0r.50 it would give enough room to get a small boring bar in there. on could make the dies as well from blanks in the same manner. once the angle was determined it would be just a matter of boring the the dies a few though smaller. I have been planing to try this on a soft piece of scrap tuping to see how it works.
 
#35 ·
hcpookie said:
Yes I have a steady rest, but my biggest problem is that I can't get the tailstock and drill aligned, no matter what. I managed to true my jaws with a dremel and after some testing, I can definitely say they are more true than before. It seems that no matter what, I can't get the darned tailstock to center. That's what causes the reamer to cut off-center chambers. I had one cut at about .003" out. That is probably true enough for a "battle" rifle like an AK, but definitely not good enough for a target-match-grade rifle build IMO.

The problem with the tailstock is that I have to take it off to align it, so it is a real PITA to use. In theory, you are supposed to get the tailstock aligned before hand, but I have observed that the alignment changes depending on how much torque I put down on the 17mm set screw. It seems the way the tail stock is attached to the lathe bed gives it some room to creep when it gets tighter. I would imagine the tail stock on a HUGE lathe has more meat, and therefore less room to "creep" when it is tightened down on the lathe bed.

Now that I think about it, I am going to true the tail stock before I use the lathe next, and I am going to torque it down to a certain point, mark the nut, and afterwards torque it down to that same point every single time. That's next on the list - the tool steel rod arrived for my 9x39 finishing reamer, so I have some cutting to do! :D



If you haven't already bought some, you should get some chamber casting alloy from MidwayUSA. This stuff is like solder that you melt and pour into a plugged barrel so as to get a good casting of the chamber. That lets you know if the chamber if out of round or not, and then you can choose to either use it or cut it off and redo the reaming. The alloy block is only about $8 and you can reuse it, so it will probably last a lifetime.
hcpookie,
I'm not sure that you are moving in the right direction with this problem. the tail stock should clamp down to the lathe bed and not move side to side but will move head to tail if pushed realy hard. on most of the lathe's that Ive used seting of the drill chuck to the lathe jaws is adjusted by backing out two set screws and one clamping screw. a trued round bar is then chucked up and the tailstock is then set. you might need to look at the lathe chuck not just the jaws. the last time I had a problem with a lathe at work the chuck was .004 out of true compaired to the chuck mount. just my $.02 muttman
 
#36 ·
Hc I have seen that site in fact I think we bolth exchanged it or spoke of it a year or so ago. I am thinking some stainless heat treat foil might be a good idea. still not sure how it does not get warped. I do know that if you pull of the reamer build and sucessfull champer ream in a true original one of a kind wildcat, that you have deffinatly raised the bar and taken home AK building to the next level. I was thinking that keeping the over all length as short as possable and using a a larger shank might also prevent some possable warping or at least reduce it. It might pay to practice on some unturned drill rod just to see what happens.
 
#37 ·
I remember the heat treat part... the guy chucked it up in the drill press to polish the end. He kept it there, and used a MAPP or Propane torch to heat it cherry-red while it was spinning in the press. Then, he instantly quenched it in a container full of used motor oil that he had ready. Then pull the platorm around to sit the container on, and let it sit until cool. I rememeber he talked about the stinky oil smoke it made. *SO* - since the reamer will be spinning, the heat will be even all around it, and so no warpage should occur.

The part I don't exactly recall was the sharpening part. I know enough how to machine the flutes for the cutters, but I don't recall the exact method to sharpen it. I think it used a file or perhaps a knife whetstone to sharpen it. I need to look at the one chamber reamer I have to see how it is sharpened...

My reamer will be putting the shoulder "back" onto the 350x39 chamber. The one I have puts the "roughing" chamber into it, and there is about .1" to go for the shoulder. I basically have a straight-walled 9mm chamber until I get the finishing reamer completed. I may just start over... I don't want to because I've already got the barrel down into an AK config, but I want to get it right. I'm afraid that my "finishing" reamer won't be able to get a good enough connection on the pilot end and it won't cut true.
 
#38 ·
Hardend drill rod is going to be as hard a the file. you'll need stones to do the cutting edges. make sure your back relif is done before you heat treat or your in for a long tedious task with the stones. A lot of the hand reaming you hear about is done on short chambered barrels. These barrels are already reamed but not to full depth. It allows for proper head spacing. since the short chamber profile matches the profile of the chamber reamer for finishing the depth it is self centering to the already partially reamed chamber. Doing this by hand will help keep the hole from being cut over size, but can increase the chance of run out.
but thats a pretty slim chance. Where if a reamer mounted ridgidly in a lathe is .001 off center it will cut .002 over size but still centered.
 
#39 ·
HC what are you planning to use for dies? if you are making a custom reamer then wont you have to also make a set of dies as well. if so this will require a sligtly different reamer to do that. You may be able to case form in the chamber but on a auto loader I doubt it will feed as it will likley be to tight.

Ford galaxy. I havent got to it yet but I am hping that i will be able to hand ream from a 17 remington to the new 17-223 chamber. I havent had a chance to even put it in the barrel yet as i am feveriosuly tring to get the gas to my 223 varmit buil (last years build and) and help a friend get his ak pistol done buy the end of the month.
If I get the 223 to cycle this week end I may try to pull of a 1 1/2 week custom 17-223 build. the basic gun i can do in a few nights its the custom gas block scope rails ,sight block mdifed stock and the 500 rounds of ammo that have to be loaded and = it needs to be sighted in and have the barrel broke in as well. Not sure I can get r done.
 
#40 ·
1biggun said:
HC what are you planning to use for dies? if you are making a custom reamer then wont you have to also make a set of dies as well. if so this will require a sligtly different reamer to do that. You may be able to case form in the chamber but on a auto loader I doubt it will feed as it will likley be to tight.
Yep, I'm starting with a 7.62x39 die and working from there. For now. I may get one of those "blank" dies from MidwayUSA and ream it out. Either way, I'll have a complete reloading set, start to finish. The advantage with mine is that it is based on the 7.62x39 cartridge. I have also considered doing it on a .308 cartridge and opening up the 7.62x39 bolt face the .015" or whatever it is to fit a .308 rim. I already have an AK bolt in 308 and I agree with you on fire forming the brass... the brass may be easier to neck down vs. form out.
 
#41 ·
Well I've been watching your 223 build for a long time now, must be close to a year.

for 10 or 11 months now I've had a real nice like new Browning A bolt 223 take off with the boss system comp on it. Waiting to see how yours comes out. well that and finish putting my lathe back together.

havent decided if I want to build it on a romy or a yugo have an unfired romy kit and a couple wood stock yugos, but one of them already has a tabuk barrel in the box with it.
and I think a 24" barrel would look corny on an underfolder.

got a romy and yugo done they still need some tweeking, the rails on the romy are to tight at the back and the carrier on the yugo is hanging on the hammer, dam tapco yugo flat,

The .17 rem case is longer than a 223. are you shortening the camber end of the barrel and then rechambering?
 
#42 ·
What, my build? If you mean mine, FYI I'm working on it this weekend as a matter of fact - I sleeved the Galil barrel for an AK-74 trunion and sleeved the muzzle for AK threads. I'm currently polishing the combo gas block and bayonet lug ring, and the tube for the gas tube arrived, so I need to make me a long piston and a handguard retainer, then press it all together. That will give me a working gun that is missing only handguards, that I am going to work on shortly hereafter:

http://pookieweb.dyndns.org:61129/stg-940/build/stg-940.htm
 
#43 ·
My 223 has been done except for the gas block for over a year. it shoot,s 1/2-3/4 groups cycled by hand with factory winchester ammo I killed about 300 praire dogs with it last year. I have been putting off the gas block because I wanted to start reloding for it and do some testing to see how much differance there is with out the gas port and with. That browning barrel should work great those boss systems are susposed to work pretty good. what twist rate is that barrel? mine has a 1-9 so it can handel the heavier bullets. going to load up some 69 grain boat tail for it and see how it will really shoot in the near future. the main thing with getting these guns to shoot is trigger work and a good scope mount. I got the pistol pretty much done today so I may start working on a gas block tommorow . I have been wondering if an aluminum one would work. AR,s have them but there is no piston in them I would like to keep the weight off the barrel
 
#44 ·
h
avent decided if I want to build it on a romy or a yugo have an unfired romy kit and a couple wood stock yugos, but one of them already has a tabuk barrel in the box with it.
and I think a 24" barrel would look corny on an underfolder.
I used a rusty rommy kit for mine as will be the 17-223. about the only thing from it used was the trunions carrier and trigger guard. for pure function the advanced technoligys stock works great for a varmit/target set up. the yugo would give it a little more of a saftey margin remember that 223 is over 50,000 psi. and hand loads are even hotter. I try not to use mint kits on my conversions if I can help it I would rather save those for a original build. I have around 1000 rounds through mine now and have not had any problems, it uses a bulgarian bolt.
 
#45 ·
I have'nt checked the twist rate on tha A bolt barrel, it's more than likely 1-14 but thats fine by me, my .222 rem contender has lower velocity and stabilizes .55 grain bullets great, it likes the 52 grain hornady match better though. I'm not very concerned about the extra pressure, Its a comercial barrel with much thicker chamber walls. almost all of the pressure to the rear is held by the case expanding into the chamber walls. The 50k pressure is acting on a lot less surface area at the base of the round. As long as the head space is good, and the cases are monitored for stretch it should be fine.

yea I think I feel an off the top romy comming up in the not to distant future.

If you left the sleave that goes around the barrel thicker, an aluminum gas block should work, it will erode faster than steel, but I dont see much of an advantage in using aluminum, I think the force of the gas tube pressing the block forward will have more of an effect on accuracy than the weight of the block.

I follow all of the threads where people are doing more than just assembling aks on already finished parts, loved pookies 308 bullpup build, the soumi drum guns,and this varment gun build since mtdew did a 223 romy on the cheap.
saw one where a guy tigged a ring made from a scrap barrel into a bolt, for a 223 conversion
 
#46 ·
the force of the gas tube pressing the block forward will have more of an effect on accuracy

the gas tube will not be touching the block it is held onto the custom rsb by a screw so it will suport itself. I will have it a few thou awy from the block I plan on having the piston ride in the custom block for a few inches before it gets to the tube the gap I leave will be less area than the vents on a standard build


I shot my 223 today with a few different hand loads. I had groups from 3" to 3/8". I had the best luck with 50 gr hornady vmax loaded with h322 powder i had a 3 shot group do just under 3/8" at 100 yards and a 5 shot group come in at 3/4" it would have been 1/2 but got one slight flyer. I had some loads loaded with 748 powdser do pretty good also but 29 grains was to hot and I was piercing primers so I had to quit. sierra boat tail hollow points were the worst they averaged around 3" no matter what the load. this is my first try at reloading but with a 1/2 " average ffrom one load I think I am doing pretty good I will now start playing with seating depth and amount of powder. I was shooting of the back of a flat bed truck with sand bags and had a slight wind. with the scope on 32X I could actually see my heart beat affecting my aim I think it will do better with a good rest and and adjusting the trigger down as low as I dare. Time to build a gas block and drill a hole.
 
#47 ·
I finaly put a gas block made fromk 2"x3" steel ( abought 8 hours on the mill by hand) the piston rides in a fairly tight fitting bore for 1.5" bfore entering the AMSD 65 gas tube. I tried gas port holes from .035 in . incriments up to the final size of .071 this was the smallest hole that would reliably cycle every load a had on hand. .040 would barely move the bolt back .060 would cycle a single round with no mag installed. I got a chance to shoot it before my trip and it still shot as good if not better than before I had a 4 shot group that is basicaly one hole and a 5th shot that was 1/4 inch from that this was done with a 50 GR nosler ballistic tips with 22.5 grains of h322 powder. I ran aproximently 400 rounds through it praire dog hunting and it was deadly at 250 yards. I had kills out to 450 yards but they were not one shot kills I was able to make several one shot kills at 300 yards. this appears to be about all any of the 8 other guys with bolt actions were able to do as well. I started to get doubles toward the end due to the poor disconector ingagement this is my falt as I have the trigger set right at the edge of not catching and it gives very little room to allow the disconector to catch to to almost complete lack of trigger movement. when it was working correctly I was able to clear of a mound of dogs 5 in a row with out taking my off the target. at the very least I have proven that with enough work a very accurarte AK can be buillt weather it was worth all the work and money I cant say,but shooting a soda can sized target at over a quater of a mile with some thing built in my shop is very self satisfiing. I would really like to see how some guy got a smaller port to work ( I do not doubt they did it) but .071 was what this one needed.
 
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