Meat Target

Yes its a USAS-12. The AA-12 pretty much copied the action/gas system other than using a square tube and open bolt. The USAS-12 does cycles much quicker, as it doesn't recoil quite as far into the stock. I have gotten 0.16 splits with mine but I am also running a modded lightweight carrier. Here is a good video of how the action works.

You can make an effective shotgun brake but it needs to be designed for the lower pressures. I call this my Flash Gordon muzzle break its made out of anodized 7068 aluminum. I have been using it for a few years, it's held up better than I expected. It just clamps on and I made an extension for my choke tube wrench to change the chokes.

Is there a way to get practiscore to calculate match results in percentage points when running a time plus match? We are doing 3GN matches at our club and the results need to be in percentage point instead of combined times.

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My intent of posting the results of the computer simulations is to characterize the different compensators in respect to recoil reduction and downforce generated and not rank them as in which one is the best. But there are some that appear to think I am trying to do more than that so I really don’t want to start down that road. A computer simulation could never predict how flat it will hold you barrel, there are too many variables including the fact that everyone holds the gun differently. What I believe that computer simulations do very well is predict how the compensator will react, that by its self isn’t much but when you combine it with building and testing changes to the compensator in the real world its very useful. For example a compensator that works really well on a 18” barrel may have too much down force on a 16” barrel because the muzzle gas pressures are higher. From real world testing and comparing it to the simulation results I have been able to get a fairly good idea on how much down force would probably be too much for any load and barrel length combination.

Thats one of two comps that I don't think I would ever post the results of in this fourm for obvios reasons...

I know everyone is probably tired of seeing posts on compensator lately, but I finally got around to putting together the data on the CFD simulation of the Nordic Corvette comp I did awhile ago. The video is kind of boring compared to the ones with multiple chambers. Here is how it stacks up with the other simulation that I have posted previously. Not much on recoil reduction but because of its three top ports and high pressure chamber it generates a lot of down force. From shooting it my personal opinion is that it has too much down force and makes the barrel jump down. I tried to come up with a better way to display the information on the characteristics of how each of the different comps perform. Here is a graph of the combination of forces 200usec after the bullet has left the barrel. At 200usec the bullet has exited the comp and the gas flows have stabilized. This is basically a vector plot of the forces generated by the compensators showing the direction and magnitude of the force that will be applied to the end of the barrel. Another bit of information you can get from this graph is the longer the line the more "efficient" the comp is in using the available gas energy.

From running a bunch of different CFD analysis on different comp here would be my 2 cents on your design. 1) Your going to have way too much down force, reduce the area of the flats on the bottom of the ports. 2) Ditch the holes in the top, not need. 3) Increase the opening area in the sides of the ports. 4) Make the second port spacing larger (as the pressure drops the gas expands less) 5) As long as you port openings are fairly large there is no need to have more two sets of ports.

I believe he is talking about removing the last baffle on the Rolling Thunder comp shown in this graph. As you can see baffle 3 doesn't contribute very much. There are a few people that have cut off the last port to drop some weight.

I did tweak the design some to add in a little more down force to get it closer the the JP numbers. I have a blank already made up and should have the new version finished in the next few weeks.

Actually I have a Nordic corvette comp on hand that I will eventually get around to modeling and posting the data. But it may be a month or so before I have time to work on it.

Thanks Vanniek71. Knew it had to be easy since so many people are doing it and there wasn't any posts on it, but I didn't think it was going to be that easy.

I have been playing around with this and haven't found any information on it. I am trying to embed a youtube window into a post by selecting the code icon "<>" and then pasting the information from the youtube video: <iframe width="560" height="315" src="//www.youtube.com/embed/ZcINxtHe9II?rel=0" frameborder="0" allowfullscreen></iframe> I have tried selecting the different "PHP/Generic/Auto Detect" options but I just get this text field in the post: <iframe width="560" height="315" src="//www.youtube.com/embed/ZcINxtHe9II?rel=0" frameborder="0" allowfullscreen></iframe> Would somebody please tell me how its done, Thanks.

Finally got around to running a simulation on the JP "Tank" brake to add to the collection of other simulations that I have done. Video Link Actually I was a little surprised that it didn't do better in the simulation when compared to the others just because of its size. The people that use them say they work very well. The JP Brake did generate the highest amount of down force in the simulations, which may be the key to why it seems to work well to the shoots perspective. So its starting to look like down force is more important than overall recoil reduction which would explain why the Rolling Thunder comp is very popular even though its has the lowest recoil reduction numbers. I may need to do some tweaking on my comp to add some more down force and try it out.

One of the first designs I started on had conical surfaces for a full 360deg with stand-off posts keeping the spacing between the baffles. Its about the most efficient design you can do but I scrapped it because of the need to shoot prone. The amount of dirt it would kick up would suck big time so I went to the more conventional design. Using curved surfaces would make it a little more efficient but probably not to the extent that you would notice the difference. I did look at ways to machine it using a rotary table but its just way easier to make with flat baffles. If I ever get a CNC mill it would be much easier to try out the more complex designs.

OD is 0.99" I wanted it to be tactical class legal.

I had a A5 years ago, a common problem with the A5 is that the wood forearm would split because when the barrel returns to the forward position it slams into the forearm which is held in place by only the nut "Magazine cap" there is nothing else that stops the barrel moving forward. Any tube extensions that you put on a A5 will need to hold up to the beating from the barrel cycling and impacting against the forearm and extension. So unless the extension tube coupler was designed to be as strong as the original steel magazine cap of the A5 there is a good chance it will eventually have its threads sheared off.

Picked this USAS-12 up in 1992. I have done a bunch of work on it over the years to lighten it up some. Parts are a little hard to find for it now.

I was taking some measurement for fitting a .355 KKM barrel to a STI slide and it turns out that the hood clearance on the ejection port side will 0.013" before doing any fitting. This is my first time using a KKM and was wondering if this is normal. I know some would say 0.013" is no problem, but that's a bit looser than I would like to go with. Here is the Jack Weigand worksheet and my measurement setup.

I have been using a BF20L knockoff from Lathemaster its about the same as the G0704 and not bad for a mini mill (don't have room for a full size mill), but you kind of need to treat the machines from China like a kit in that you will need to do a bunch of tweaking and modifications to get them working well. The biggest problem I have is running out of height adjustment. It will get most jobs done but you need to take you time as the vertical column isn't very stiff. Once I move into my new home and get a knee mill I was planning on converting this one to CNC as there are a lot of kits out for it. But I am thinking it would be better to spend the money and move up to a bigger mill such as the RF45 to convert like Jared did. Basically because I don't think the BF20 type is rigid enough for fast CNC cutting.

Thanks for the complements, but it sure didn't come out of the mill like that I ended up doing a lot more surface prep than I was intending. I originally wiped on some cold bluing for rust protection and it came out very blotchy, so I stripped it by lightly sandblasting with 100grit and hit the flat areas with a few pass on the surface plate and 1000 emery. There is also a 0.5mil of cobalt plating on everything which helps it look a little cleaner. I am from Livonia, Michigan.

Toolguy, You are right it was a little crooked. I was throwing parts together for the pictures and the bar was set just a hair too far forward and wouldn't let the barrel sit flat. I readjusted the bar and checked it out on a surface plate and indicator, now its showing flat within a thou or so.

Here are a few more pictues. The fixture base is 1" thick to allow for using a micrometer to measure the hood widths without removing the barrel from the fixture. You can also measure the hood length. Here is a side shot of the fixture, there is about 0.01" clearance under the round section of the barrel.

Just finished up my fixture this week. It works like the Weigand fixture but I used a little 6" rotary table for cutting the radius. The fixture is made from precision ground 1" stock because the surface holds the barrel's lower lug parallel to the table. Doing this aligns the hood and lower lug surface without needing to adjust set screws to level the barrel like with the Weigand. This design will also work with any 1911 barrel. The barrel is held a lot tighter than it looks, you need to pull the barrel perfectly strait up to remove it from the fixture. The fixture once dialed in allows you to do the following operations: Cut all three surfaces of the hood. Cut the lower lug flat surface and radius. Trim feed ramp to match angle of mag well. The picture below show the setup for fitting the hood length, cutting the front face of the hood and lower lug surfaces. The fixture is located on the table by a pin mounted into a cut down MT center, this pin is concentric with the pin on the fixture that locates the barrel using the link pin hole. To dial in the fixture: Set the table to 0 degrees and place the barrel on the fixture. Adjust the block to be snug against the barrel and tighten down bolts Remove barrel and indicate the fixture using the front face of the block, tighten fixture down to table. Replace barrel, clamp down and indicate the link pin hole to zero the x-y axis. Fitting the barrel is the same as the Weigand fixture: Fit hood with fixture set at 0 degrees Set fixture CW 1 degree, cut lower lug flat. Return back to zero, rotate fixture CCW 61.5 degrees and cut front surface. Repeat 2-3 as needed. Setup to cut the back side of the hood you just flip the barrel over. Setup to trim the feed ramp, just dial in the mag will angle.

Been through a couple of slide mounted Fast Fires versions II and III, had problems shearing off the small screws on the sides and cracked the lens on another. I did like the FF3's multi-mode button (on/off, auto and three fixed levels of brightness) and top access battery too bad it wasn't a little more robust. I was glad to hear the DP2 was going to this type of configuration, I know a few people that have been shooting a slide mounted DeltaPoint for a few years with out any problems. I am looking forward to giving the DP2 a try.