panabax
-
Posts
32 -
Joined
-
Last visited
Posts posted by panabax
-
-
Lest some of you think I am all talk and no game, attached below are pictures of the latest prototypes of a US manufactured M4 gas piston. This is a lot of 20 CNC turned pistons. I will need to make the radial cuts in the rings manually and do the heat traeting. Hopefully this will be done in the next two weeks so I can test them out, which I will do thoroughly (that's really the fun part, right?).
I was very pleased with how these turned out. I will keep you posted.
Panabax
-
I don't have any experience with the B&T, but I am confident that it is a very high quality piece. I suspect it probably has the edge on the KZ, but the price is a lot to swallow, especially since it does not help with the potential 922r issue. That said, the KZ is very well made and sturdy. I was pleasently surprised by its construction quality.
However, all of these rail forearms suffer from excessive girth. Someone described the Surefire as similar to holding a pringles can. To be sure, the KZ was the same. Ultimately, I milled about 70% of the material off my KZ forearm to create a sleek aluminum forearm, US manufactured, with short trial rails. It is every bit as comfortable as the stock handguards. I would be concerned that, after spending the money on the B&T, you are not going to be satisfied with it, compared to the factory hand guards.
My $0.02. Do with it as you like. Good luck.
PanaBax
-
The lowest hardness I have seen for S7 is HRC 45. At that hardness it has a Charpy C-notch (not V, could not find V for it) of over 200J
I am curious how hard the OEM piston and OEM BCG are. Would be worth testing.
Yes, the S7 is very tough and very hard.
Max hardness for 15-5 is attained at a 900 degree temp with a Rockwell C of 44 and a yield strength of 175,000 psi. At 1150 degrees is goes to Rockwell C 28 and a yield strength of 125,000 psi.
I agree that a hardness test on the factory piston would provide very useful information. Unfortunately, with all my skill and good looks, I don't have the necessary equipment. Anyone out there have a hardness tester in their garage?
Panabax
-
The outside diameter of the factory piston appears to be ground and polished. Are you planning on undertaking that step as well. I too was contemplating the issues in duplicating the part. As you pointed out the radial grooves is the biggest headache. I was concerned about the seal to the cylinder. If the piston is too rough (or the material too hard, or you leave a burr) I would be concerned about damaging the cylinders. Near as I can tell that means buying a whole new barrel assembly.
I am not planning on grinding the diameters on the rings. They will be polished. I agree that the wear part must be the piston not the cylinder.
Panabax
-
Have you thought about using S7? I think that it has considerable merit for this application as compared to 15-5. You will note that the Charpy tests for this material at an HRC in the mid 40's are...impressive. Many times that of 15-5 PH at a comparable hardness."
I had not considered it. I understands that the original is stainless and I wanted to duplicate the original as closely as possible. If you go through the stainless alloys generally available, 15-5 and 17-4 look like very good candidates for the original material.
S7 is tool steel. S7 is used in machin tool applications for its combination of toughness and hardness. However, I think it is would end up harder than I want it to be. In addition to potential stress and fracture issues, there are also wear issues. Toughness generally goes up as hardness and yield strength go down. Between the gas cylinders on the barrel, the bolt carrier face and the piston, I want the piston to be the softess of the three such that any wear occurs only on the piston. It should have only enough yield strength to handle max loads. Any unneccessary increase in yield strength and hardness will reduce toughness.
I plan to heat treat to the low end of the hardness scale and then test for deformation and wear. The 15-5 also has the advantage of very good corrosian resistance in hot caustic environments which I think is a plus for the 15-5 over the S7 given the hot gas working environment.
Panabax
-
Properties of 15-5 PH Stainless Steel
15Cr-5Ni is a martensitic precipitation hardening stainless steel offering high strength and hardness along with excellent corrosion resistance. Generally similar to Custom 630 (17Cr-4Ni) in composition and properties, 15Cr-5Ni is chemically balanced to eliminate all but trace amounts of delta ferrite, thus providing superior transverse toughness and ductility plus a higher degree of forgeability.
15Cr-5Ni has fabrication characteristics similar to those of other precipitation hardening stainlesses, and can be age-hardened by a single-step, low temperature treatment.
It has been used for applications requiring high transverse strength and toughness, such as valve parts, fittings, and fasteners, shafts, gears, engine parts, chemical process equipment, paper mill equipment, aircraft components and nuclear reactor components.
-
Nice job Panabax! Thanks for attempting to tackle this.
No problem. I have a degree in Mechanical Engineering and a machine shop in my garage so it is more hobby than altruism. I am going to machine another prototype by hand and use the prototypes to test various hardness/toughness combinations. The material is 15-5 stainless which is a precipitation hardening material. That means you heat to a time and temp for a specific hardness. No quenching, no tempering. It is much easier to hit targets with than with more conventional alloys. The strength and toughness characteristics of this material are very good. It is used extensively in the aerospace industry for mission critical parts. I am sure it is very much up to the fairly simple task of transmitting energy from the barrel to the bolt face.
I think I will apply different heat treatments to the two pistons, one softer one harder, and see if one bends or breaks.
Really, you should see some of the materials I have seen used for semi-auto rifle pistons. I have an original Rhino M-16 piston conversion and the piston is quite simply 1/8" drill rod. It actually worked quite well, although it has long since been retired to the old gun parts pile.
Clearly, the only reason for these pistons would be 922r compliance and, for that reason, it is a dumb project. Still, I try to do what I can to abide by all of the laws that govern our society, even the stupid ones.
I will post pictures when I get the other made and then, to the range. Now that will be the best part, trying to break them.
Panabax
-
Fair enough on the eye-ball. If you get take your mics to it you will find other deviations that are harder to see. However, the diameters of the rings is right on and it fits perfectly. I will cut the radial grooves, heat treat it and see if I can break it. If the prototype works, I am already modeling a cad version for a small production run to get a more precise product.
The 3d model is below. I will kepp you posted.
Panabax
-
Why did you deviate from the original dimensions of the piston?
You're kidding, right? You should see me with my micrometers in hand trying to measure the distances on that damn thing and then trying to recreate it on my miniture lathe. The groove between the two rings at the end is only .055" There is not much room in there for a tool. In other words, any variation in the dimensions is purely non-intentional. However, I suspect the most critical dimensions will be diameter of gas rings and length of piston. Just a guess.
I was just glad that it is clearly recognizable as an M4 piston. I will keep you posted as the project progresses.
Panabax
-
Just thought you might want to see the gas piston coming into being. This picture is the work in progress prototype next to the factory original. I still need to make the radial cuts in the gas rings and then heat treat. Then, I need to make one more just like this one. The shame is that these would be super easy to turn on a CNC lathe and pretty cheap too, but the radial cuts add a lot of complexity to the CNC manufacturing.
Perhaps if these work well, I will order a lot of pistons without the radial cuts (cheap to manufacture) and then do the radial cuts by hand. Might not be too bad. The lathe work on a manual lathe is a real time hog. I have many hours in this one piston.
Panabax
-
We're working with stainless also, I forget the exact type. It's not really my field. P17 H or something. It is in the annealed state to machine. Then the heat treatment will be outsourced.
Probably you are using 17-4 PH. The PH stand for precipitation hardening. It refers to the way the metal is heat treated. It is not heated, quenched and heated again to temper. It is simply heated to a particular target temperature and then allowed to air cool. The 17-4 is very similar to the 15-5 I decided to use. I will also do my best to break them. It should be fun.
Panabax
-
The cuts in the pistons are carbon scrapers. There is 4 sets. The outside rings are aligned. The two between them are indexed 120 degrees offset and 240 degrees offset. The purpose is to scrap carbon build up and to moderate gas discharge.
The pistons are a grade of stainless. Unknown exactly which one from the factory.
The cuts around the pistons are complex. They will likely require custom bits to cut the steep angles in such small areas. The hole at the end of the piston is likely present as a live guide.
Establishing a heat treatment will be the hardest part along with some in the field testing.
Awesome job with the KZ rail. It looks very clean. Have you tried shooting high base rounds with it in place? The ARGO rarely vents from the front with low base shells.
I shot both target loads and 3" 00 buckshot without problems.
If you look at the cuts in the gas rings you will see that the cuts are made with an ordinary end mill while the piston is turning. It is the rotation of the piston that creates the apparent complexity in the cuts. If you look down the angle of the cut you will notice that all the cuts are aligned on that angle. I don't believe the angle of the cuts is critical to function, while the offset from ring to ring may be. I will recreate the offset but probably not the angle of the cut. If I was programing it on CNC equipment, the angled cut would be the most efficient way to manufacture as you can make one cut on each ring with a single pass.
Panabax
-
hey PANABAX, if you do make a set of gas pistons that seem to fit/work well in the nelli m4, id be interested in a pair of them whatever the cost. seriously, if you get it all figured out and they work let me know. i know your time is valuable and i dont expect you to spend all that time on parts for me for just peanuts. TS
I will let you know how the project progresses. I have ordered a small amount of Stainless 15-5 to turn the pistons out of. I will need to figure out what hardness to shoot for. I went with the 15-5 because it has good tensile strength and toughness and is quite abit easier to heat treat that other steel allows. The PH stainless alloys only require heating to a particular temperature for a particular time and then are air cooled. There is no quench and no subsequent tempering involved. The material is used extensivley in areospace applications so I suspect it is up to the job of opening the M4 bolt.
I am pretty sure I read that the factory pistons are stainless, but I have no idea how to figure out what alloy it is or what heat treatment was involved.
Just curoius, from your name I assume you are in Texas, where? I live in Dallas.
Panabax
-
very nice., I was thinking it would be real nice to remove the first 3 or4 inches off the side and bottom rails. panabox I'll be your first customer, how much to shave the rails?
I appreciate the confidence in my machining skills, but I am just a hobbyist with a mill and a lathe. Not looking for customers. The mod is very simple if you have access to a milling machine. I am happy to continue to offer my prototyping services.
That said, I was considering having a batch of US made gas pistons made. They can be turned on a CNC lathe pretty cheaply, but in order to justify the cost, you would need to manufacture twenty or thirty sets to bring the cost per set down to a reasonable amount. I would consider pursuing this if there was enough interest.
In the mean time, I am planning on turning a pair of gas pistons on my lathe and testing them in the next couple of weeks. It seems like the gas pistons are the next most obvious 922r part to manufacture domestically. If it were not for the three grooves cut into each piston ring, it would be a pure lathe job which would be very cost effective on CNC equipment. I wonder what would happen if the grooves were omitted. I am not sure what their intended function is. I assume to slow down the piston stroke.
Panabax
Panabax
-
Has anyone been having problems with Botach lately? They used to have such a bad rep, but it sounds like they've improved to judge by the lack of recent complaints.
I've only order the KZ rail from them and they shipped the same day and the order arrived without problem.
Panabax
-
Here is what I did with a KZ rail. I have a Sidearmor on order to complete the package.
http://www.benelliusa.com/forum/showthread.php?t=19590&page=7
Panabax
-
Just got back from the range. The modified KZ hand guard is very comfortable to shoot. The proof is in the fact that I forgot I had it on there. No heat, no venting gas, nada. I was so fixated on the pellet patterns at different distances that I simply forgot the stock was not OEM.
If anyone has a KZ rail and access to a bridgeport or other suitable milling machine, the end result is a very good, very practical product. No more Pringles can for me.
Panabax
-
-
-
-
Here it is with a little more metal removed and with some brownell's bake on epoxy. It feels really good.
-
I don't know about that, but there is no reason you could not drill and tap the hanguard to receive a rail. I am thinking about milling the side rails off as well and combining the modified KZ with a Sidearmor rail. It will give side rails in line with the barrel and reduce, even further, the width of the hanguard to something very closely approximating the original.
Seems like a lot of work. There must not be enough of a market for aftermarket stuff. Seems like plastic replacement handguards would not be that difficult.
Oh well.
Panabax
-
Right now, the only plan is for a sling swivel. I know, pathetic. The stock is really just for 922r compliance. What a pain in the ass. However, I may throw a laser max on the right side for hip shooting. I put a verticle foregrip on the bottom, but I prefer the horizontal so I took it off. I am happy with the way it turned out but will probably continue to tweak it some more. The best part is that it feels right, like it belongs on there, which a lot of rails do not.
Panabax
-
USA Made M4 Gas Piston Prototype
in Benelli
Posted
Here is a picture of a pair of completed pistons with the gas cuts made in the appropriate locations. Time to heat treat and then the fun part, testing.
Panabax