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Lane

My first 7.62x39 AR

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14 hours ago, Matt.Cross said:

computational anomaly

None that I'm aware of. I'm just happy to be over the hump on this project after who knows how many hours writing the core code. Obviously I've enjoyed some other threads around here along the way; like the gun pusher chronicles. But I really have no idea about this blueberry thing. I was simply poking fun at it, and making light of the fact that I was using rejected nail polish to mark the otherwise mostly hidden button locations. 

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31 minutes ago, Lane said:

None that I'm aware of. I'm just happy to be over the hump on this project after who knows how many hours writing the core code. Obviously I've enjoyed some other threads around here along the way; like the gun pusher chronicles. But I really have no idea about this blueberry thing. I was simply poking fun at it, and making light of the fact that I was using rejected nail polish to mark the otherwise mostly hidden button locations. 

No worries, it's a massively inside joke. Come to the Fall Shoot and we'll give you all the gory details.

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1 hour ago, Matt.Cross said:

No worries, it's a massively inside joke. Come to the Fall Shoot and we'll give you all the gory details.

I've been considering this quite seriously. I took an Amtrak all the way around the US a few years back and it was an absolute blast. Looks like they'll carry up to 50 pounds of guns; and legally I should be good to go as long as I stay out of New Jersey (totally fine with me). 

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Decided to take a short break on the timer software. I will probably revisit it later tonight; but in the mean time I want to get started on another lower. The jig that comes with a polymer80 is much taller than what I normally use (but the lower's profile doesn't fit in my regular side plates). The mill bit it comes with it also useless in my setup because of it's length. I'm impressed at how easy this material is to mill (it's my first polymer lower), but it does smell a bit strange. I think I'm better than half done and have only been at it for about 10 minutes. 

I upgraded the button location markers with some temperature sensitive "blueberry" paint; it turns bright blue when warm.

Also ordered three doppler radar modules to test; not because I'm sure it will work to measure bullet speed, but it's something to try. One of them in particular looks like it might be made to function with an antenna modification.

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I haven't done any P80 AR lowers, but I've done 3 pistol lowers - incredibly easy to do, and I like them.  Alot!...  

If you get out here for the Fall Shoot, you'll have a riot, meet great, great people, and you might be enticed into relocating to AZ...    :lmao:  When you see the freedom that you don't really have, it will make you think twice.  :thumbup:

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14 minutes ago, 98Z5V said:

I haven't done any P80 AR lowers, but I've done 3 pistol lowers - incredibly easy to do, and I like them.  Alot!...  

If you get out here for the Fall Shoot, you'll have a riot, meet great, great people, and you might be enticed into relocating to AZ...    :lmao:  When you see the freedom that you don't really have, it will make you think twice.  :thumbup:

I've been eyeballing those pistols lowers too. From a legal perspective I would need to get a pistol permit, which takes forever here and isn't exactly guaranteed. I did read somewhere that you can't be denied for a premises only permit though; which is totally fine if I'm making my own. I would really like to do a 1911 from scratch too. 

I have a friend in NM, and really enjoy being the southwest. I'm started to get more comfortable with the twisted gun laws here; though I would prefer they were repealed for upstate residents at least. Besides having no chance to play with a full-auto, I don't see that I'm missing all that much. There are a couple of oddballs though; like I can't build an Uzi with a 16" barrel, because of where the magazine lives. 

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5 minutes ago, Lane said:

Besides having no chance to play with a full-auto, I don't see that I'm missing all that much.

You hang onto that thought, until after the shoot.  Let me know about it, after the shoot...   We'll revisit this quote, man, in the future...   :thumbup:

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18 minutes ago, 98Z5V said:

You hang onto that thought, until after the shoot.  We'll revisit this quote, man, in the future...   :thumbup:

Alright; I will do that. I'm well aware there are things I don't know, and haven't tried. 

While I don't like the giant lips on the jig; I'm really am impressed with this polymer lower. It mills so fast, smooth, and quietly; I'm well over 75% done. I think I could finish one in half an hour if I tried to do it in one sitting. Honestly going to need at least two more of these; though I'm still not sure how I feel about using one on a 308. I don't recall seeing anyone else around here with a polymer80 Warrhogg build. 

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I'm really pumped up by this one day lower build. I've had this sitting around for months; I don't know why I waited so long. It's quiet hours right now, but I'm planning to go out shooting with my morning coffee. It's going to be very windy; but still worth testing the shot timer with quiet .22lr, and whatever else I feel like dragging out there. Certainly going to put a few more 7.62x39 rounds through as well.

Looks like the Pelican 1750 long is the way to go for rail travel; it has an interior size of 50.5" × 13.5" × 5.3". That should fit about 50 pounds of rifles without too much trouble. I don't see why I can't finish a .260 before fall. I don't know what I should bring really; having never been to a fall shoot before...

Got back in to the shot timer code and just about to add decimal points to the recorded times, and increase the resolution recorded to include the tenth of a ms. My to do list is getting quite short. I need to add a few routines to help me profile my code, and look at memory in real time. I was just reading about a cycle count variable I wasn't aware of; and that can help with timing accuracy by counting instructions instead of microseconds. 

I had my timer in the truck with me the other day while running errands and noticed it rolled over the microsecond counter. Apparently that happens after 71 minutes, and will write negative time values to the file if it does. I'm not sure the best way to get around that besides a timed sleep function. My only concern is; what if it's running a course at that time? I could do filtering to look for that; but I would also have to count how many times the counter rolled over for very long sessions (like running all day). Seems like a pointless exercise; but there are a few cases where I can see this happening at something like a fall shoot. 

I did a search earlier and found a few threads with polymer80 .308s. Nobody complained; but I didn't see any long term reporting either. I don't plan to use polymer lowers for anything violent; and I would worry about my current .308 on a polymer lower. On the AR-15 side; the .22lr CMMG doesn't even use the buffer tube, so that seems like a good choice. My 7.62x39 is also a very tame gun; so why not? I haven't weighed it yet; but it feels great even with an aluminum lower. The balance is spot on right now, so I'm curious to see how it feels with something lighter. I've dug out the LPK, buffer tube, and buttstock to finish this lower. Only a few more hours and I can assemble it at sunrise. 

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7 hours ago, 98Z5V said:

but I've done 3 pistol lowers

Do you have any more in the works? I've been reading some of those threads. I wish I could do one tomorrow; but I live by the rule of law. 

Sunrise here. I'm going to birth a new one.

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11 hours ago, Lane said:

Do you have any more in the works?

I only have one of them completed and fired.  The other two, the lowers are completely built, but I haven't put together and slides and barrels for them yet. 

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My excitement about this polymer80 has waned considerably. The milling all went off without a hitch, but drilling the selector holes was problematic. In hindsight I should have drilled a number of pilot holes first; but there was nothing in the instructions about that. The drill bit punched through the right side making a bow tie shaped hole that I had to mill out before I could finish drilling. The red plastic also tended to clog up the bit on those larger holes. 

The fire control group all went in smoothly and functions perfectly. The bolt catch is stiff in the slot; but the real issue was the buffer retainer got stuck and I can't get it back out. I put some oil down the hole, and took it out to the workshop to chill down. The mag well is very tight with my ACS 7.62x39 magazine. I was surprised to find out that the rear takedown pin can't be operated without a tool. Furthermore; the lower itself almost seems warped, and I can see light between the upper and lower. The rear takedown also seems to be just a little bit off front to back; and it came from the factory that way.

I have a pistol grip on this build for the time being; but I find it more comfortable to operate with a slanted grip. That feels more like a rifle stock; and having to charge for each shot, I naturally want to grab for a swept back grip. I skipped testing today because it was unpleasant outside. No idea what the wind chills were earlier, but even a few minutes was too much; checking this evening it said -14 degrees F.

I do still need to pick out optics for this build. My next lower is aluminum for a 300 blackout build; I simply need a barrel and gas tube to get that done. I assume someone sells longer rear takedown pins that work in polymer lowers...

Here are a couple shots pre and post stock adjustment along side my .22lr. I guess I could have a collapsable stock on this build; but I don't know that it matters much. I always shoot fully extended for comfort; and these both have fixed installs. 

Update: I got the buffer retainer pin to pull back up with needle nose pliers finally. I don't think it sees enough abuse during regular operation to fix itself though. I suspect I will need to remove it later and bore out the hole a bit more. As I recall it is drilled at something like a 4 degree angle, so I'll need to be careful how I do that. 

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51 minutes ago, Lane said:

Update: I got the buffer retainer pin to pull back up with needle nose pliers finally. I don't think it sees enough abuse during regular operation to fix itself though. I suspect I will need to remove it later and bore out the hole a bit more. As I recall it is drilled at something like a 4 degree angle, so I'll need to be careful how I do that. 

 

6o angle, if I recall correctly. The prints are out there, and searching them out will give the details.  I'll try to find them, but we talked about this recently, with @308kiwi

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41 minutes ago, 98Z5V said:

6o angle, if I recall correctly.

Yes; you are correct; numbers are hard. Looks like a drill bit could ride up against the top of the area where the buffer tube threads in. Probably be able to twist it by hand until I get the buffer retainer to fit in like it should.

Seems like some others have had issues with the rear takedown pin location too. Most people egg out those holes which I'm not ready to do yet. I would be happier to find a long replacement pin and sand down the diameter slightly. I looked around and only found "long pins" that had a protrusions on the right side to grab. Nothing I found has a longer shaft to make it stick out through the wider polymer lower. I guess if I really had to I could make one on the lathe out of 6061.

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Shouldn't be too difficult to make a drill guide that could simply be threaded into the receiver using the existing buffer tube threads.

I've got several ideas for a basic drill guide that could get you there.

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10 minutes ago, Matt.Cross said:

Shouldn't be too difficult to make a drill guide

That's not a bad call; if I'm going to do it, might as well do it right.

I have a tilting vise on my drill press already (simply can't load the lower in that way). I can drill 1.125" wooden dowel at 6º though. Then put it in the buffer tube threads; line it up, and go.

Still have to find a piece of aluminum rod to turn a new rear takedown pin. I think I can make a full diameter pin, and then take a crescent shaped side off with sandpaper. I want at least 1/4" in additional length, and I might as well add a right side grip if I'm going to make my own.

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I warmed myself up today and went out for timer testing. Glad I waited because it was actually relatively nice out for winter. Picked up all but one of the .22lr rounds; sadly not a single one of the CCI quiet rounds triggered my current threshold. That would need to be adjusted a bit to pickup anything less than a .22lr supersonic round, but it's a simple setting to change. I nailed about 200ms between rounds very consistently since it barely moves off target when firing. 

I roughed out a CAD drawing for a new rear takedown pin only to realize that the front takedown pin looks almost exactly like what I want. I plan to swap one of those into my polymer lower and hopefully address the buffer retainer hole at the same time. 

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Fixed.

I modified the detent channel on a front takedown pin and added a new detent. I didn't see a good way to fill the existing detent; though epoxy might work. At the moment it has a dummy detent that won't release the upper. I took a bit of meat off the one face to account for the apparent shortness of the lower between takedown pins. I had to grind out the slot a bit further than what is shown to clear the upper when pulled all the way out. Now the pin sticks out the left side enough to operate with human fingers (as intended). 

The buffer retainer is now functioning as it should. It took quite a bit of bit spinning to open it up enough. The bit went straight in the hole though; as others had noticed before me, it needed a good de-burring for some reason. 

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Got back into the shot timer code after thinking more about today's testing. I was aware that cheap .22lr rounds don't always sound the same, but there was a pretty wide spread in variation between the loud and quiet shot peaks recorded.

I'm not sure if the code is efficient enough yet; but I did revisit the shot peak detection. It currently runs for about 25ms after hearing the first peak over the volume threshold, and collects audio input as fast as possible. If any of those samples is louder than the initial, it is sent back along with a new time. The main function writes an update in that case; and proceeds with the rest of a short delay to make up for echo. My goal here is to pick up the initial shot peak for a tighter timing accuracy; while still allowing for multiple calibers without any threshold adjustment.

The extra decimal points are displayed in the shot timing file, along with a dummy text identifier. It looks like the last serious thing to do is link the programming data into the shot timer itself. I've been putting it off because it's a huge number of variables to store; which will most certainly have an effect on my overall memory footprint. I doubt I can get away with a file read between each station; I expect I'll need fill a two dimensional array with the entire course programming up front.

Of course, after posting this photo I see an error in the file display routine (one missing digit when scrolled to a certain position). I'll have to record some longer shot strings to debug that since I just nuked my file again. I think the last column (peak volume) will be dropped from the file outside of debug mode. There is a better way to show that to the user; and it's mostly useless data inside the shot file. I've been using it to keep an eye where my threshold needs to be set up until now.

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Here are a few new observations. If I'm going to do this right; I'll need another field in the programming data. Select a range of preset thresholds; or a specific value. I know some people shoot multiple gun courses; and that's the only way this is going to work for everything. Shotgun seems to be in the etc category so far; but I haven't tested everything explicitly.

Those are my .22lr times from earlier. There were actually two missed shots the first magazine; and one fail to fire the second. I didn't even bother to record the 10th shot on the latter. I did clean the FTF off; manually load, and fire it afterward. Pretty much what I expect from this last bit of cheap ammo. Those CCI quiets just jam the gun and it wasn't worth the effort to record quite yet. I'll get into that after I can select a per station threshold. 

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I finally got through the bulk of this last bit of code. I can write, read, and parse the course programming files through the web interface. The last bit is to rewrite the shot timing display screen, and link all those variables to relevant code functions. That will honestly be easy in comparison to debugging the dynamically generated HTML I had been working on. I might be able to save some RAM and increase station count if I remove every last useless space character from the html, and make it a giant block of text. Seems to work in the limited situations I've tested so far.

The new threshold code is now modeled in to the course programming. The default will be "0" for system shot threshold. One would only need to modify the variable if they wanted to shoot quiet firearms. Any other single digit value will divide the global threshold setting; so setting a 1 would be 10% of the system threshold, up through 9 for 90%. Beyond that the number will set the threshold explicitly for that station up through 1024 which is the maximum. 

I'm about to sketch out the new shot timing display screen based on these variables. There isn't much to add as most of the programming variables are either delays in the code, or endpoints for existing shot timing code. I ended up devising a very elegant means of parsing the data file which didn't require any kind of array so far (near zero memory footprint). I think the shot timer will use a single 1D array; but it won't impact memory in any significant way.

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On 2/10/2019 at 7:36 PM, Lane said:

I took a bit of meat off the one face to account for the apparent shortness of the lower between takedown pins

That's the other way around actually. I'm taking off the BACK side of the pin, so the lower is actually too long. I thought it might be a shrinkage issue originally; but it seems like it's the other way around. It's cold here, so there is no reason to believe this problem gets better in the summer time (or in the desert). Is there some reverse shrinkage with polymer; or is this overcompensation during manufacturing? When casting metal there is a shrinkage calculation; I presume someone did that wrong in this case. 

I am curious to try other polymer lowers though; and perhaps casting my own one day. 

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