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Post by kiwicollectorar15 on May 30, 2015 22:41:46 GMT -5
Tim, Good to see you still moving on with these
Been tweaking and playing with my 9mm DI a lot lately and can say that I get zero crap in the bolt carrier now, it just runs all day long
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Post by HMC710 on May 31, 2015 17:29:13 GMT -5
Good deal kiwi, glad to hear that. It takes some time but can be done! Good Job
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Post by HMC710 on May 31, 2015 18:04:21 GMT -5
Worked on both Gen4 and Gen5 set ups today. Barrel I had made up for G4 looked like it was a better fit for G5 so I decided to make another barrel for G4. Now to put this in perspective, I've been tuning up my stuff for a week now. Last night (yes, last night, saturday night, when most people are out having adult beverages and what not...) I had enough. A thou here and thou there and pretty soon we are talking some major run out! So I pulled the plug, had a beer, and came to the conclusion my lathe head stock was out. Went home and ate, got up at 3:45 for some unknown reason (actually been working on a blow back project) and decided to go after the lathe. Jumped in the truck and headed to town and figured I would treat myself to breakfast. Went to the town joint, 5:30 am, closed. So I drive around the block and head for the shop. Well bless my soul, there was someone else up that early, blue lights in the mirror. Pull over, dome light on, hands on wheel, hmmm, I wonder if hes going to notice those 500 rounds of brass in that box.... After the yankee version of "whachu doin in my town boy." Just looking for bacon and eggs sir. I stopped at the other joint in town that was open. Oh, Im sorry, we dont cook until 6... WTF are the bacon gods against me here? Anyway, worked on the lathe and checked and worked and checked and worked. That Gen4 barrel, #111, been sitting on the bench for 2 years, when I pulled the tail stock after profile, didn't move a bit. Zero, Zilch, Nada. So I put the dial indicator on the end, 10" out from the chuck, no tail stock. 4/10ths runout. Hmm, thats not bad. So I took a rag and wiped the barrel off and put the indicator back on, 2/10ths run out. Must be the bacon gods owed me one! So tune up your stuff and don't expect breakfast before 6! SO both barrels are done and getting the piston set ups together. If I can stay on track should be testing Wednesday. 2/10ths, dammit boy!
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Post by kiwicollectorar15 on May 31, 2015 23:32:49 GMT -5
Did he actual pull you over for anything special or was he bored and looking to fill in time having a chat.
Strange concept you guys have of buying breakfast, over here its cereal's or toast at home
Good to hear your getting close with the testing on the GEN 5 version
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Post by HMC710 on Jun 2, 2015 17:40:49 GMT -5
There were only two cars in town and I happened to be one! I figured working on Sunday, treat myself to breakfast..... right.
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Post by HMC710 on Jun 2, 2015 18:56:02 GMT -5
Got Gen 4 piston together today. I'm happy with the format, I think it is something I can work with. I put it on the 10" pistol barrel I did the other day. Before I get into the results, lets just compare some things. The reason I'm going after the piston system is that the DI, when tuned, runs fine, in a range of factory ammo. It seems the reason the DI version came out is the smoother operation compared with the blow back. The blow back, requires sheer weight to slow the recoil of the fired round so the barrel doesn't open under pressure. That extra weight has mass and that mass has velocity, etc. The DI runs smoother. My DI version port was about 1.25" if I remember from the back of the extension and the round just seemed to fight itself out of the chamber. My Toks run at 2" and if the wind is slow, those surplus rounds will gas you to death. So using Quick Load charts I looked at what it said was happening in the barrel. My last reload session for 9mm was 124 gr FMJ and 5gr of Universal. Good for 1350 fps from a 10" barrel. Max pressure happens at .25" of bullet travel, 34,000 psi. At 4" of travel we're down to 4000 psi. There is not the volume of power in the 9mm compared with the 5.56 obviously. So when is my bolt opening and when is the bullet coming out? The gas port to bolt was about 4" from port to carrier piston. Figure the gas travels about 4x the the speed of the bullet, it goes 4" for every inch of bullet travel after the port is open. At the port the bullet is accelerating and moving at 900 fps on its way to 1400. So lets just use 1400 fps. To travel the remaining 8" it will take the bullet about .006 seconds. But our gas is doing 4x that and only has to go 4" to unlock the bolt. My thought on the whole process was "is the DI a DI like the 5.56 or is it a delayed blow back like the 30 Carbine"? The numbers say 30 carbine. My other issue was the range of ammo you can run, so I started playing with the pistons. G1-3 were based off the old Rhino System. It was kind of a hybrid and had some success, but it was before the piston carriers came out and shearing gas key bolts was common. My goal was to get a longer gas system, make sure we were pure "DI" and keep weight and stress to a minimum. We all want smooth right? G1 was too small for the 9 but will run the Tok, SSig, 9x23 etc. You can use a CMMG piston system to run a Tok if you shorten it up. But I wanted a universal piston system. G2 & 3 got a bit bigger and started to run the 9. Working on design and materials to try and make it fit a hand guard for one and get some life out of it has taken much longer than I had ever imagined. Of course 4 yrs on the road..... Gen 3 is my smallest, most compact system, and kind looks like an AR. But I still wanted to get to a pistol port location. Now remember, max pressure at .25" of bullet travel and burned up at 2.25", that puts you about a 3" port from extension. Pistol is about 3.9". So I decided to try the Gen 4 at pistol port and see what happens. My first test was with stock carrier, buffer and spring. The rounds would eject but not reload. I put in my light buffer and spring and , pop, pop, pop. The carrier would not lock back but it would pick up another round. Then I tried my mid weight carrier figuring the less weight would get better acceleration. We'll it didn't. This is the exact duplication of my Gen 3 test by the way. The lighter carrier moves less than the heavy one. The super light, barely ejects the case. Physics says F=ma and if you have fixed F and you reduce "m", you should get more "a". But more "a" with less "m" won't do the work. Its kinda like the 45 vs 9mm debate. To make matters worse today I decided to add more GO by opening the port a bit and that also made things worse. I believe the pressures are dropping so fast the smaller port to the piston holds the pressures in longer is the only explanation I can have. So I'm going to do some port work and gas system tweaking tomorrow and see if I can duplicate my 2nd test. If I can't, then we'll end up with a Gen 3 system with a Gen 4 package and see how it goes. Time frame? Don't know, was hoping to get more time, but opportunity has knocked and wheels up in a few weeks. We'll see what happens. Nope, no pictures yet... Sorry.
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Post by kiwicollectorar15 on Jun 2, 2015 19:22:49 GMT -5
Good explanation on the workings Tim
So the lighter carrier and buffer /spring combo is unlocking to soon and your not building up the pressure momentum to cycle ??
I found with some loads if you balance everything bolt weight/ buffer/ spring the cases come out clean and everything works 100% because it stays shut long enough for the gas pressure to load up and cycle things properly,
Sometimes it was unlocking and cycling to soon and causing problems if I tried to speed up the process
Are you running the pin mod for extraction issues ??
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Post by 22boomer on Jun 3, 2015 6:58:58 GMT -5
Tim, You're building a piston system for the 9mm cartridge? After reading a bunch of the pages I kinda got lost on what the caliber was you were working on. 9mm would be super since it's easy to find and is popular. Of course if you can figure the 9mm out the rest of the calibers should be easy. Sorry if I'm wrong with the type of cartridge.
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Post by HMC710 on Jun 3, 2015 7:46:47 GMT -5
You are exactly right kiwi, balance is the key to the DI system. We unlock our G4 piston system past the G3 systems so pressures are lower and bullet velocity is higher. The impulse is much different. What I am finding that I didn't do enough homework on the energy of the system, or more accurately, the resistances in the system. I'm starting to chart this in a spread sheet to see where numbers are starting to make sense. For the carrier weight issue I should theoretically get more acceleration from the lighter carrier (it worked when I reduced buffer and spring preload right), but the reality is the work is not getting done. So the energy of the carrier is a function of the of the velocity so cutting its mass in half requires about 40% more velocity to get the same work. Which brings up your point on the pin mod. No, I have not done the pin mod yet, but that is going to change today. I guess I just didn't want to cut a lug off my bolt. But, I have to tell you, with the super light carrier, the case made it to the barrel extension lugs and stopped. period. I knock the back corners off the lugs to keep the gouges down on the brass, but I still get claw marks. And it takes more force to pull the BCG back at that point than any hand cycling, by a factor of 3 or 4 so it plays a huge role with the short cases. Another issue with piston systems is you are increasing available volume which drops pressures faster. In the AR, the piston area is about .138 sq in and the stroke is .375" give or take. Not a lot of volume especially dealing with 5x the powder available to burn. Remember the 9mm peak pressure of 35ksi happens in 1/4" and drops like a rock. When we add our big piston, it drops faster. Gen3 piston travel might be .3". I was surprised that I could get it that short, but in the nature of the short stroke world, that's what it takes to get the job done. Like when you had to fight that big guy, as hard and as fast as you can. With Gen4 I tried to slow things down practically to a long stroke system and we're not getting there. That means there isn't enough mass or velocity to get the work done, or there is a bunch more work to get done than meets the eye! I've got 3 things I want to try today to see how it impacts operation.
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Post by HMC710 on Jun 3, 2015 9:20:03 GMT -5
OK, we are back in business! Made a few adjustments and actually cut gas port down and things are working. Will do the light / heavy tests before I do the pin mod. Brass is still getting dented by the lugs... Update: Same results with the lighter carriers = less travel. Have the gas port approx 30% open because I wanted to start small. Will open it a bit and see if we go backwards again. Adjusted open a bit and didn't hurt, but turning the gas down sure stops it. Definitely different than the Gen3 system where I had some room to play. Is the pistol port location just not enough?
Update: Put the pin in to help stop the case canting into the lugs and had to completely remove the "lug" on the extractor to get it over the case while chambering. I didn't notice that much difference on the stock carrier, but the mid wgt carrier will now cycle about 50%. Another observation seems to be cycle rate might be down a bit, but we'll dig more into that. Making another change and see what happens..
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Post by kiwicollectorar15 on Jun 3, 2015 14:07:35 GMT -5
The pin mod was the biggest improvement that I made to my DI, before I had an ejection pattern that was not consistent and throwing case's in different arc's, now they all eject in one arc and and land in the same spot every time.
The energy wasted in muscling out the case hitting the lugs is alot.
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Post by HMC710 on Jun 3, 2015 16:58:43 GMT -5
Here's a pic of the pin installation I step drilled it and sunk it in, whacked it once to many times and bent it a bit... dammit As I said, it did make a difference on the mid weight carrier as it now cycles better than it did, which was almost zero. With G4 Piston, I wanted more travel to reduce the short stroke and sudden stop of the piston at end of travel to reduce stress on the operating rod. Full stroke on an AR is 3.75". With a pistol port and the AR configuration, G4 with piston 1 strokes 2.25", Not enough to get it to lock back unless it puts enough energy into the carrier to let it go farther. I made two pistons and P2 is shorter so I installed it and got 2.56" of stroke. Still way short, which by the way, G5 will cure, if its got the balls to push the carrier out that far. Test 1 with the P2 piston was a step back. I figured maybe there was more gas leakage because of the shorter body. I was going to swap it out with P1 but I decided to try something with it. I made the change and it was night and day. The bolt didn't lock back, but just from the shell ejection angle and speed I could tell bolt velocity was up. I think I'll make a couple more pistons to try some different configurations and see what happens. P1 already had more of the "change" I did for P2. Sure would be nice to have some transducers set up to read all this stuff... I was pretty down yesterday after moving what I thought was backwards. Looking at the graphs I knew it would be an up hill battle. Today we made some of that ground up. I am curious how much load was reduced because of the extension pin kiwi suggested? I do know the mid wgt set up did cycle after it was installed. One thing we did do, was add more length to the system by getting to the pistol port location, which proved we have enough power (maybe) with our standard set up. I've tried smaller pistons before, G1, and it would almost cycle the 9mm. G2-3 cycled fine. The Tok and 9x23 class can use G1 size, but they can also use the cmmmg in the right spot, which I had just short of the G2-3 port location. The main reason I'm trying this is I want to be able to dial in loads from factory, subs, reloads, everything - in a package that looks like that's what its made to do. G4 has the beginnings of that. AR people are different (as we all know If its not AR it ain't right to many. So when something is a bit different, it has to work.
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Post by kiwicollectorar15 on Jun 3, 2015 17:15:04 GMT -5
Tim the pin length is too short, need to extend it so its flush with the outside edge.
Made a big different to ejection on mine when I tried the short and long version and keep the end square
Also with a case held under the extractor make sure the extractor is not dragging on the pin, put some dye marker on it and hand cycle a few times
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Post by 22boomer on Jun 4, 2015 6:20:05 GMT -5
For those that don't know -- what does the pin do? Does it hold the extractor against the case longer or stronger? Does the short lug on the extractor have to be removed or modified so it doesn't get involved with the pin?
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Post by HMC710 on Jun 4, 2015 7:23:01 GMT -5
Great point 22! Set a 9mm case next to a .223 to compare lengths and then put them both into the BCG and see how far to the right they are pushed by the ejector while held in the bolt. If you had both rounds chambered, how far back would the bolt travel before the cases cleared the barrel extension? When the rounds are being extracted, the 9mm, being so short, is forced into the back of the barrel extension lugs. Go look at some fired cases and you will see 2 claw marks on the sides of the cases. Bolt speed determines if they are dents or claw marks. I've had them hit so hard the case deformed between the lugs. The pin reduces the sideways travel of the case which guides it past the lugs and reduces (hopefully) that friction. Yes, you have to grind off the reinforcing "lug" on the back of the extractor. It leaves it thin, but at this point we're testin! Any case shorter than 1" really shows up, 9mm is the worse.... til we do a .380 or a .25... and another reason we're working on the BB versions... less parts....
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