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My first 7.62x39 AR


Lane

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18 hours ago, 98Z5V said:

I LOVE Model 52s!!

Beautiful guns they are; I wish I pulled this out for comparison earlier. I know it's a bit nitpicky, but I might have gone with a 12" handguard to match the profile better. 

I had to go outside and scare off a squirrel, so I figured it was a good time to test the shot timer. It sure was a different experience shooting on command. Not too surprisingly it picked up the shots just fine even with the low input volume. Plenty of programming work left to do, but it is nice to see it functioning in a real world test. 

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No real update today. A ton of strange issues writing to the file system in the shot timer. It usually works ok; but I need to work out an initialization function for first time programming/first boot. I have the settings file reading and writing from the web interface. It's a tiny bit of copy/paste, and variable modification to do the same for the shot timer programming web page. The shot time data already writes to a file, but I haven't worked out the ability to download it; outside of a copy/paste of the webpage.

Many updates in the electronics side of things; but it just made me order more parts, again. Nothing expensive; I think the final unit is still around $20 in component cost. I did a tiny bit of optimization in the shot recording code. I can get 2-3ms audio resolution while still running the display, WiFi, and webserver functions so far. If I turn off the big ones, I should be well below 1ms resolution; and there can be further tuning beyond that. There is very little bounce with the piezo pickup, with an appropriate threshold set, it does not pickup any echo noise at all.

One of the new electronic scales showed up; but it is worse than the first one. Even after warming up and calibration it can't measure small amounts. Interestingly the packaging has cutouts for smaller calibration weights; but none are included or usable in the calibration process. Should have the load cell ADC by Friday if package tracking is accurate. I measured about 15 kernels before the balance of my Lee powder scale moved. I don't think the improvement in weight accuracy is necessary, but I will try to ensure consistency if possible.

This 7.62x39 build needs to be cleaned and broken down yet. Too cold outside to care right now.

 

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Still plugging away at the code but there have been a number of improvements since last night. Turns out some of my file writing woes were due to an undocumented oddity in the file mode commands. You can only seek a file in r+ mode (read+write); but not in w+ (write+read), or a+ (append+read). My programming to do list is shrinking rapidly, but I'm still not sure what day I'll have a fully functional unit. I will soon need to commit to a button layout, solder it, and mount it in the case. The only other thing I really haven't messed with is the battery power supply, and a charger powered by the USB port. I had used a standard USB battery bank for my outdoor testing the other day.

I ported the code to the new larger display microcontroller to work out the first time file initialization functions; turns out the display has a different driver chip, but it is mapped to the same pins. That only took a few minutes to figure out and resolve. Somewhat surprisingly the ADC wiring on the circuit board must be routed much more intelligently; the noise on the new board is about 1/3rd of what I was getting on the module without built in display.

On the electronics side, I had tried one of the silver piezo transducers I picked up from mouser; but couldn't solder to the silver surface no matter what I tried. Then the connection to the crystal element snapped off; so that's a no-go. Looks like they could be mechanically mounted with spring terminals, but that's not a good solution. I ordered some pre-wired 27mm piezo pickups which should have good low frequency response, and also fit perfectly inside the width of the enclosure. The buzzer had always been quiet; so I swapped that with a new unit also from Mouser. That was quite a bit louder but still not loud enough. Even with transistor amplification, it isn't cutting it in terms of volume. The other options are differential drive, or a charge pump; but a quick test of differential drive crashed the microcontroller. I bought a few active and passive buzzer modules which should be louder. If that's not enough, I'm going to have to find and disassemble a LiPo battery alarm that has a deafeningly loud buzzer.

Here is a look at the OSD for the shot timing function. I may have to slow down display updates in the future; but the progress bar currently shows a live view of sound amplitude. I still need to write some code to display timing data for a short period of time; but I don't want to clutter up the screen with nonsense either. 

One thing I was still curious about is; how many shots would reasonably be recorded in a single shot string (or shot timing program)? I currently record up to 127 shots to RAM as the maximum before dumping it to the filesystem. The only problem with a huge number here is RAM consumption. Writing shot data to the file takes time though too; so I want avoid any interruption to the shot timing capture process.

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Minor 7.62x39 update. I stopped by the local gun shop today for some odds and ends. I couldn't find a .30 caliber patch loop, but they did have a brass jag. I asked about online ammo purchases, and they offered to hand it over free of charge since I'm a regular customer. Sweet deal! Either they can order it for me, or I can order online and just stop by and pick it up. I guess I'll be able to stock up on 7.62x39 in brass at $0.40 a round after all.

I called green mountain about the barrel. They said the bore is between 0.300"-0.302", and the groves are 0.310"-0.312". Seems like I'll want to buy .311 projectiles for reloads. Interestingly the load data sheet that came with my dies explicitly warns that the minimum load is the max load for shooting .311s out of a .308 barrel. 

I'll probably get my build ready to fire later tonight. There are two snow storms coming through this weekend; so it's either now, or sometime next week before I'll be able to shoot again. 

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Barrel nut tightened three times and timed up to mount the handguard straight. Headspace checked out and closed snug on the go; not even close to closing on the no-go. The extractor was an absolute nightmare to get back in the bolt. I should have known when it took a hammer to get the pin out; I had to squeeze the spring end with vice grips to get it to align properly. I assume that will wear in some, but it doesn't seem right.

No range report tonight; but I did fire off five rounds of Winchester brass. The first one was a bear to extract; the subsequent rounds were only marginally easier. The brass appears to have gotten chewed up somewhere in the works. Hard to see in the picture but there are some long gouges along the case. Could well be the magazine because I saw marks before I ever chambered a round. 

I'm going to need to wear gloves to be able to cycle the gun more than a few times in a row. It honestly feels like shooting a .22 though; there is no noticeable recoil, and it wasn't even loud enough that I felt like I needed ear protection.

I should be able to take it out tomorrow with the shot timer and test it along side the Ceratac 308. I think my times will be similar despite the 7.62x39 being a straight pull build. I still haven't picked out sights or optics for this build; thought I might find something else to attach for tomorrow.

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On 1/7/2019 at 11:23 PM, Robocop1051 said:

this is what I see...

I brought you some rice to the dinner table. Along side the protection diode. 

On 1/11/2019 at 6:19 PM, Armed Eye Doc said:

You didn't try to reprogram it?

I got two 24 bit ADCs in the mail today. I haven't received the two donor scales yet; but the one I disassembled already is better now than it ever was. After taking it apart and reassembling it with care of course.

I think the load cell cup mount was rubbing on the case initially... Very easy to do given the way it secures with two screws from the bottom. They need to add a third screw to make sure everything centers up; and torque accordingly. Leveling the unit is not even addressed with the plastic case, much less the screw arrangement. 

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I got all my storm prep done this morning and took everything out for a shot timing test. The 7.62x39 build is cycling much better already, and I don't need gloves to extract the rounds anymore (though it is quite cold outside). The shells fall right next to me so policing the brass is a breeze. My battery died just after my first shot test, so I had to charge it up and go back out for more. The second time around I remembered to make an audio recording along side the timer to check my work. Then right after I saved the Ceratac audio file, my phone shut down, presumably because it was too cold (the battery had plenty of charge but it wouldn't turn back on). 

So here is a rundown of the shot timer data collected (ignoring garbage data and the missed shot).Buzzer goes off; I close the bolt on the 7.62x39 and my first shot is 2.844 seconds later. Follow up shots are 1.691, 1.677, 1.677, 1.838 seconds. The two matching numbers are simple division of the delay of to account for the missed shot. The Ceratac build is only marginally better in terms of time between follow up shots. In that case, my first shot was 3.331 seconds after the buzzer, follow ups were 1.348, 1.334, 1.371, 2.716 (yeah, I lost track of the target on that last one).

The missing shot was a known issue, because my audio recording resolution isn't fully optimized; I knew that I could fire a shot in that 2-3ms window between readings. In this case only one shot was missed, and I might have been able to pick it up with a smaller shot volume threshold. That should actually work itself out when I'm done with the code; turning off WiFi alone should bring me below 1ms resolution. I have yet to analyze the audio recordings but I'm quite sure I'm within the 2-3ms range in terms of accuracy at this point. 

That's all I have for the time being. I've worked out the button layout, so I'll start building a final unit soon. The code is perhaps a few more days from being finished as well. I can actually hear this buzzer through hearing protection; but it will be replaced with something much louder. I'll order a lithium battery charging circuit in a few minutes; that should let me finish up sometime next week.

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Getting ready to wrap up the first version of the shot timer hardware. I have to solder on some connectors and header pins yet, and I'm waiting for a lithium charger and voltage regulator module; plenty of room inside for both. The big white thing is a foam spacer to keep things intact until I can design a suitable skeleton or tray to hold all the components in place where they need to be. I also need to 3d print some button hats for the tact switches, and drill for those controls and USB port; the only one currently punched is the jog wheel. 

Quite frankly I'm less than sold on this particular case material and design. It was convenient because that's what the microcontroller shipped in; but either wood or metal would be better in the long run. The case is currently less than 2" wide, so if I used a hardwood 2x4 I could get ~35 cases out of a 6' board. That comes out to about $0.60 a piece for a wood enclosure. Finding a pre-made aluminum enclosure in these specific dimensions isn't quite as simple. It would probably have to be either a custom build or a redesign of the internals to fit what is available.

I updated my CAD drawing to match this current prototype, and another with top side controls which also appears to be an option in terms of fitment and ease of use.

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The plastic box is the fastest build.

I was thinking earlier today that I should try to get it done before the opening of the show. There is a bit of electrical tape involved in making this current build work on the inside; I guess I can add a piece of duct tape too. You got it.

I have a whole string of new updates on this build; but it's better if I just keep working and get it done. All I can say is; this B works! 

Also, it's definitely going to become a part of my daily shooting routine. I had no idea how bad my reaction times were. 

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On 1/7/2019 at 11:23 PM, Robocop1051 said:

I’m messing with ya brother.

I wasn't talking trash with the grain of rice post. This is all chinese hardware with an American fabricator. I always buy two or three of everything when I work with electronics because you never know if you'll get a dud. It also helps with testing and swapping things around to make it work right in the end.

Every single one of the piezo shot sensors I got are wired backwards; which means, applied backwards on the brass plate substrate. Sold as seconds for cheap; you just have to figure it out; the red wire is ground, or else you'll get a negative voltage. That could fry the micro on a bad day. 

This shot timer build has been running 72 hours nonstop on the demo loop; and no crashes or false shots read. Memory management is pretty solid. I'm going to get back to work. Can you shoot in Vegas? Last time I was there it was 110F and I was sweating.

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On 1/7/2019 at 11:23 PM, Robocop1051 said:

I’m messing with ya brother.

I wasn't talking trash with the grain of rice post. This is all chinese hardware with an American fabricator. I always buy two or three of everything when I work with electronics because you never know if you'll get a dud. It also helps with testing and swapping things around to make it work right in the end.

Every single one of the piezo shot sensors I got are wired backwards; which means, applied backwards on the brass plate substrate. Sold as seconds for cheap; you just have to figure it out; the red wire is ground, or else you'll get a negative voltage. That could fry the micro on a bad day. 

This shot timer build has been running 72 hours nonstop on the demo loop; and no crashes or false shots read. Memory management is pretty solid. I'm going to get back to work. Can you shoot in Vegas? Last time I was there it was 110F and I was sweating.

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46 minutes ago, Lane said:

Also, it's definitely going to become a part of my daily shooting routine. I had no idea how bad my reaction times were. 

That's the scariest thing that you discover, once you start using a shot timer, no joke.  As SOON as you start making improvements that you can see (right there, on the timer display), you just get better and better - and realize that you sucked before...  :laffs:   I've been using one since 2011 or 2012. It'san invaluable training tool, if you are intent on "training to improve."  You simply cannot do it, without one. 

I use this video often, as a demonstration of timer use - keep in mind, this is "slow motion" draw strokes...   :lmao:

 

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No "draw" for me. Shouldering a rifle for the time being. But yes; I can see how every motion counts. 

Tell me about how many calibers you shoot with your shot timer. If you set it to record all day; do you have to adjust it at all? It is perfect with a quiet .22 through whatever monster cannon you guys have going off now and then?

Shooting a shot timer is more fun than I wanted it to be. I only wanted to illustrate how much slower my 7.62x39 straight pull was. Thanks for the gas tube roll pin Sir.

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6 minutes ago, Robocop1051 said:

I’m jealous of your skills here

No you're not. You make guns. I only fabricate my own stock. 

I only want a set of reloading dies for that 500 Blackout before I can commit. And I also need a kit so I can build it myself. No barrel threads thanks to NYS law.

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45 minutes ago, Lane said:

No "draw" for me. Shouldering a rifle for the time being. But yes; I can see how every motion counts. 

Tell me about how many calibers you shoot with your shot timer. If you set it to record all day; do you have to adjust it at all? It is perfect with a quiet .22 through whatever monster cannon you guys have going off now and then?

Shooting a shot timer is more fun than I wanted it to be. I only wanted to illustrate how much slower my 7.62x39 straight pull was. Thanks for the gas tube roll pin Sir.

I'm dyin' over here, over that one!!!   :laffs:

I don't have to set it to record - just hit the GO button, and it's recording time from the beep, either immediate beep, or preset for a delay - it starts counting time right then, once the beep goes off. It never gets any adjustment, and it doesn't have any adjustment capability in it, besides how you set it to run for you, with presets. 

I've honestly never tried the shot timer with a suppressed rifle - but I will in March, at the Spring Shoot.  Feedback will hit this thread, with videos.  I'll shoot anything, any caliber with the shot timer, if I want to work on that particular gun.  I've shot the 45-70 lever gun with the shot timer, so I could see how fast (SLOW) I was with running the lever, and getting the next round on target.  Pistols, rifles, run-n-gun courses of fire, pistol multi target courses of fire, whatever.  I've run the shot timer on the 450 yard target and the Mk12 Mod 1, to see how long it takes me to get a 20-rd mag into the target, and check my time between shots.  I can tell when my Natural Point of Aim is off, by the times - I'll rock the hell out of that target once my NPOA is set, 20 round on steel at 450, no misses, much less than 20 seconds. If I'm off with my NPOA, I have to muscle it a few times, and I go over 20 seconds.   Next time I set the 450 up, I'll run a solid time on it - and snatch a video.

For an accurate caliber count, I'd have to say it's measured .22LR, 9mm, .40, .45ACP, .45 Long Colt, 5.56, .308 Win, .338 Fed, and 45-70.  We might have run the timer against the .458 SOCOM a few years ago, when guys were using it to make a giant fireball at night - but I'm not sure. 

Shot timers have a million uses, from pistol work to precision, distance work.  You just gave me an idea that we'll try out at the Spring Shoot - timer goes off, THEN you get down behind your distance gun and see how long it takes to make your first hit on the 845 yard target...  :thumbup::banana:

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41 minutes ago, Lane said:

No you're not. You make guns. I only fabricate my own stock. 

I only want a set of reloading dies for that 500 Blackout before I can commit. And I also need a kit so I can build it myself. No barrel threads thanks to NYS law.

All reloading dies are through Pacific Tool & Gauge. Dave Kiff (owner of PT&G) helped me finalize the design. He’s already making them and thy will be available. 

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12 hours ago, 98Z5V said:

I don't have to set it to record - just hit the GO button, and it's recording time from the beep, either immediate beep, or preset for a delay

That's how this timer works as well. I thought I remember you saying earlier you can press GO and let it run all day long though. 

I had to add a few extra settings to make this run consistently with both loud and quiet shots. The 7.62x39 build is significantly quieter than my .308 AR which clued me in to that. It really happened because I'm not processing any kind of delay after the initial shot peak shows up; I'm aware there should be a dead space to let the shot ring out and echo back. The quiet stuff needs a much smaller shot threshold (volume) which, if set improperly, can lead to multiple readings per shot on large calibers. I actually built auto-threshold into the code early on; but it never really worked the way I wanted it to. Something I want to revisit after this next bit... 

That all lead me to add a second piezo shot pickup to the build. After thinking about it; there is no reason not to add a third and call it 3D sound. Those extra pickups are very cheap and fit into the case perfectly. That also allows me to look at each shot in more detail to determine it if was really a gunshot, or something less explosive; like getting slapped by an angry primate, or dropping the shot timer on a rock.

12 hours ago, Robocop1051 said:

He’s already making them and they will be available.

I was pretty sure you needed to have that worked out already... "Copper" grounding rod is really steel core; but C101 is about $24 a foot in 5/8"; if each one is 3" long that's about $6 per projectile. I'll turn some test projectiles on the Unimat when I get all this other stuff all finished up, (just for fun of course). ... 911 grains to grams is about 60; thats about two troy ounces, a forged gold projectile would be about $2,570 a round; but silver on the other hand is closer to $31 a pop. You know; just in case...

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13 hours ago, 98Z5V said:

You just gave me an idea that we'll try out at the Spring Shoot - timer goes off, THEN you get down behind your distance gun

Oh yeah; that's close to how I ran my game in the cold weather. Shooting from a rest is a waste of time to setup in the winter since my body temp and motor skills get worse by the second out there.

I put the shot timer directly in front of my barrel, between me and the target. When it goes off I echo-locate to the target the best I can, shoulder the rifle, drop the bolt on a magazine; and fire when I can see the target clearly. Similar game when already prone would involve inspecting the ground around you, hearing the buzzer, grab the rifle, etc...

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