We go to all sorts of trouble for pneumags. I decided to put some effort into making a ULT work in a classic. This bit is putting a magnet into the ULT pin base to get it to stick to the sear, which it does well. I got a couple of extra ULT pins from Tuna for these experiments, which was good since one escaped into the wilds of the garage pretty quickly.
For this setup, I went with a classic frame so that I could play with stops, springs and magnets to trim up the trigger pull. I made it to the field this weekend for a couple of hours, forgetting every tool. I had set it up in the back yard, and it threw out 450 rounds without a trigger problem. I had one fat ball that the level 10 took about a dozen tries to choke down during a game (didn't have my squeegee either).
On ULT breathe-ability, I drilled the top to 0.120". This maintains support of the centerline of the top o-ring plus 0.010" additional crush surface, while opening the area between the sides and the pin by a factor of four. I used a needle file to horizontally widen and taper the side ports. Shooting easy strings of 4 bps or 5 bps shots, I wasn't seeing any shootdown. I'm thinking with an electronic frame, it should be able to pull 8 bps at least.
For now, I have a plain looking hopper-right power-feed classic automag, with a level 10 and a ULT.
The first attempt was a little difficult to assemble and keep aligned. This is a 1/8" diameter by 1/8" long magnet.
The second attempt slid itself together. The ULT stainless is mildly magnetic. This is a 1/10" diameter by 1/10" long magnet.
Added a trigger over-travel stop;
Added a magnet in the trigger to give it a little breaking feel. It is almost too small, it is 1/16" diameter by 1/8" long (iirc). That is epoxy showing.
and a set screw target in the frame for the magnet. Top,
and bottom view. The target ended up getting adjusted as close as possible to the magnet. It has a "break", but it is very light.
added a return spring for the sear. This spring got trimmed by at least half. It is in a hole I dremeled into the very convenient pocket in the back of the frame, to keep it steady.
I'll have to see how the magnet wears. I polished the sear face under the pin and put a layer of grease on it. It doesn't have a huge grip compared to the nickel plating of the magnet, so I have hope on wear.
I have another setup with a 1/4" long spring with a 1/8" of unsprung space inside the ULT (no magnets). This works fine as far as the ULT goes. However, getting the valve out requires lifting the body off as the ULT pin ends up poking into every recess along the way. I will probably find a way to get it over the ULE rail pockets, but the first time was a PITA. The magnetic pin doesn't bother with the stainless and aluminum parts, so it comes out fairly normal except you have to push the trigger rod back.
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Originally Posted by rawbutter
I try to stay at #6 (32) or larger. I batted both around at the time, but I found that nice stainless set screw among my spares and settled it that way. It's not a high load, and it's easy to tap, so #4 or #6 will work. Set it where the trigger trips reliably before you put any additional pressure on the trigger (without taking up hinge slack), and you won't notice it is there (except when you go to take the valve out). If you just take one pass with the tap, the CF stays pretty grippy on the screw, and the screw stays in place well.