jid2 Posted February 25, 2014 Share Posted February 25, 2014 Building my own compensator has been on my to-do list for awhile now. I've always found it interesting how many things you hear about how a compensator should be designed. Most of it is just range banter and peoples own ideas, looking to perhaps draw insight from something they feel is similar in function. The same thing happens in the club level of car racing, lots of garage mechanics talking about what thing is going to make their car faster. In car racing there is a strong professional sector that uses the latest engineering tools to optimize every aspect of the car and validate it with all sorts of data. There hasn't been much of this in the shooting sports. I wanted to apply the level of rigor that I put into designing stuff at my day job into some of my hobbies, thus doing a proper computational fluid dynamics study on a compensator. It just so happened that another engineer here on the site was working on the same thing and helped me get up and running with the simulation setup - Thanks Mike! My gun is a 9mm major, and I put two 3/16" holes in the barrel when I first built the gun. So my design was based around this setup. After making somewhere around 30 different design iterations I landed at what you see below. The ports run small to big. The last port is huge. This is what the CFD says to do, so I did it. I wanted to maximize the force down, and so the design focuses on this. This screen shot shows the pressure distribution near the end of the simulation. The simulation is setup with a pressure source based on load data, and then ran as a dynamic external flow. You can't simply tune port size based on steady flow thinking of it like an intake manifold on a car. I think this is why so many comps are designed backwards. The pressure wave behaves different as it progresses through each port and the gas expands. Here's a plot of the total force, and the force in each port. Here is a plot showing the effect of the 3/16" holes I have in my barrel. Holes add down force, without much pull forward. If you want a really flat gun just put a bunch of holes in the barrel, but you will deal with a larger in the hand impulse. I played with changes to the comp design without using the holes in the barrel, but the design ended up the same basically, just with a different force profile. Here I looked at different sized holes in the barrel. 1/8" don't do much. 3/16" work well. 1/4" are pretty serious, make sure you have enough powder and ear protection. Link to comment Share on other sites More sharing options...
jid2 Posted February 25, 2014 Author Share Posted February 25, 2014 (edited) I knew that I wanted to build the Comp out of titanium. I wanted it to be super light weight, because the comp I had on the gun was a heavy pig and it felt unbalanced. I also wanted to machine titanium because I hadn't done it before. So I designed the comp to be as light weight as possible, and removed as much material as I could. Here's a look at the finished part. You can see that the ports have some drafted surfaces, again the simulation showed that it was helpful in certain areas. I believe this is the lightest Comp I've seen. Some photos from the machining. Drilling and threading. Edited February 25, 2014 by jid2 Link to comment Share on other sites More sharing options...
jid2 Posted February 25, 2014 Author Share Posted February 25, 2014 (edited) Cutting the flats on the side and bottom as well as the side bleeders, all on a 4th Axis setup on the CNC. 1st port. 2nd Port. 3rd Port And parting it off. If you had a sweet CNC Lathe with live tooling, or a Mill/Turn center you could do everything in one setup and have a finished part in one operation and setup. Edited February 25, 2014 by jid2 Link to comment Share on other sites More sharing options...
jid2 Posted February 25, 2014 Author Share Posted February 25, 2014 (edited) Here's some kinda crappy video shot through the window in the door of the machine. It shows most of the operations and has video of the gun's maiden voyage with the comp at the end of the video. Here is video from inside the machine focusing on cutting the ports. I tried cutting the ports in the vise instead of hanging out of the 4th axis to see if I could cut faster with a more rigid setup. I promise the comp is in there under all that coolant! Edited February 25, 2014 by jid2 Link to comment Share on other sites More sharing options...
caspian guy Posted February 25, 2014 Share Posted February 25, 2014 (edited) Have you shot it yet? I am curious to see if your perception of shooting it matches your predictions from modeling it? Edited February 25, 2014 by caspian guy Link to comment Share on other sites More sharing options...
LilBunniFuFu Posted February 25, 2014 Share Posted February 25, 2014 Theory doesn't always work in practice so I am curious as well too see how well this works. Link to comment Share on other sites More sharing options...
jid2 Posted February 25, 2014 Author Share Posted February 25, 2014 (edited) Yes, theres video of shooting at the end of that first video. My impressions shooting it tracks exactly with the simulation data. The simulation showed a mild but noticeable improvement over the comp I had on the gun before, which is actually a good comp. The model also showed that it would weight significantly less than the previous comp. Overall I am extremely happy with this setup now. The dot is tracking very predictably up and down well within the glass of an RTS sight. The balance of the gun is dramatically improved, A standard plastic grip built gun doesnt want a heavy comp hanging out there. This change has really made the gun feel perfect now. Edited February 25, 2014 by jid2 Link to comment Share on other sites More sharing options...
LilBunniFuFu Posted February 25, 2014 Share Posted February 25, 2014 Just saw that stage, it doesn't move in your hands. If you don't mind my asking but what comp did you have on the gun before hand? Link to comment Share on other sites More sharing options...
jid2 Posted February 25, 2014 Author Share Posted February 25, 2014 This guy, which I believe is no longer available. Link to comment Share on other sites More sharing options...
LilBunniFuFu Posted February 26, 2014 Share Posted February 26, 2014 Awesome weight reduction. Link to comment Share on other sites More sharing options...
steviesterno Posted February 26, 2014 Share Posted February 26, 2014 Science has no place in shooting! If we proved stuff, how would we continue with caliber wars, striker vs single action, and recoil feel for loads? Seriously though, that's some bad-ass work. you could probably make and sell some here on this forum, and tune comps for each persons individual load data. I would be curious to see if a 223 comp works out to be the same as a 9 major set up Link to comment Share on other sites More sharing options...
LilBunniFuFu Posted February 26, 2014 Share Posted February 26, 2014 Science has no place in shooting! If we proved stuff, how would we continue with caliber wars, striker vs single action, and recoil feel for loads? Seriously though, that's some bad-ass work. you could probably make and sell some here on this forum, and tune comps for each persons individual load data. I would be curious to see if a 223 comp works out to be the same as a 9 major set up Link to comment Share on other sites More sharing options...
jid2 Posted February 26, 2014 Author Share Posted February 26, 2014 Mike has been working on .223 comps and has posted some stuff about it in the thread in open guns section. Rifles don't have much muzzle rise, so the focus is on reducing recoil. So there is a design balance to not put to much porting in the vertical direction, and it needs to be validated with some actual testing. Put the idea of port size running small to large is the same. Link to comment Share on other sites More sharing options...
Shadowrider Posted February 27, 2014 Share Posted February 27, 2014 Very cool jid. Note that I couldn't tell how you were cutting it, but a little tip. When roughing out inside pocket features cut the periphery to your rough dimension first. Use Z axis to ramp into the cut. Doing this allows you to step over (off and away from the wall) and you can go to town since your cutter is only contacting material that's going to disappear anyway. You also get a little more control on your stepover to control your cutter entrance angle and chip thickness if needed to help cutter life and you get better chip evacuation. Of course if you were already doing this just ignore this. But good job all around, I wish I still had access to cool equipment. Link to comment Share on other sites More sharing options...
sperman Posted February 27, 2014 Share Posted February 27, 2014 What software are you using for the CFD? Link to comment Share on other sites More sharing options...
jid2 Posted February 27, 2014 Author Share Posted February 27, 2014 I helixed into the pockets. If I do it again ill likely pre drill an entry hole. Software is the full version of Solidworks Flow Simulation. Link to comment Share on other sites More sharing options...
nick romero Posted February 27, 2014 Share Posted February 27, 2014 awesome work Jid, that comp looks great and loks like it shoot even better. great job on the build and awesome use of flow simulation to determine your ports Link to comment Share on other sites More sharing options...
NMinzghor Posted May 10, 2014 Share Posted May 10, 2014 I PM'd you on Facebook about maybe getting one for my pistol. Link to comment Share on other sites More sharing options...
donnyglock Posted May 11, 2014 Share Posted May 11, 2014 I bought one and its an excellent comp. Link to comment Share on other sites More sharing options...
jid2 Posted December 2, 2014 Author Share Posted December 2, 2014 Just to follow up on this thread, I built a few of these for others and received very positive feedback. I'm a vendor now and have more details here: http://www.brianenos.com/forums/index.php?showtopic=206151&p=2289349 Link to comment Share on other sites More sharing options...
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