new mag body will not shoot

[LK-13]

working with my prototype mag unibody
while un-gassed the sear has the normal loose feel
when gassed up the sear is rock solid and will not move at all even with
200+lbs pushing on it.

any ideas what may be causing this lock up?
the sear is in the correct position on the on/off and while un-gassed you can feel the on/off move.

I have tried 4 valves, all do the exact same thing.
But, all of the valves shoot just fine in 3 other factory body/rail combinations;
all 4 valves also function fine in my prototype unibody but not in this one copy
and all measurements are identical.
I can't figure out just what I've done here that would yield this result.

Ratzo has suggested that the on/off pin maybe the wrong size and I may need to grind it down slightly.
but I want more options before I go grinding on valves that work fine in other bodies.

if possible can someone out there check my measurements:

[Ando]

Can't trip it by moving the sear with your finger?

[LK-13]

Can't trip it by moving the sear with your finger?

that is what I was attempting, can't move the sear at all once gassed up.
not even putting 200+lbs on the sear (full body weight) could we get the gun to shoot.

[reckid1986]

is it by any chance binding in the body maybe the sear pin isnt straight and the pressure is making it bind. i remember one of my mags doing this once but i cant remember why it did it.

[Spider-TW]

put some blue on the sear back under the on/off pin and see if it is landing on the middle of the pin hump?

[XM15]

When making a mag body the three bores for the valve are very critical along with the sear location in relation to the thumb screw. I don't know how you machined the body or what your tolerance were but the 1.125" diameter of the valve I hold to +.002"-+.005. The bore for the front section of the valve I do at 1.01 +.005. and the breech bore is .690. The back portion of the valve sits in contact with the rail and the rest should have clearance around the diameter. If your bores are not concentric with one another and straight it's going to bind. If the sear and thumb screw relationship is off the sear is not going to work. If all the above is happening it's not going to work at all. Another possible problem is with your design. Since the back half of the valve is like the foundation of the valve your only locating on a 1/2" of the valve. The majority of the valve along with the valves weight is unsupported. The valve can cock many different ways. When I do the bores I do them in the lathe all at the same time rough drilling them and then boring them with boring bars to finished dimensions so I now they are all straight and concentric.

[LK-13]

When making a mag body the three bores for the valve are very critical along with the sear location in relation to the thumb screw. I don't know how you machined the body or what your tolerance were but the 1.125" diameter of the valve I hold to +.002"-+.005. The bore for the front section of the valve I do at 1.01 +.005. and the breech bore is .690. The back portion of the valve sits in contact with the rail and the rest should have clearance around the diameter. If your bores are not concentric with one another and straight it's going to bind. If the sear and thumb screw relationship is off the sear is not going to work. If all the above is happening it's not going to work at all. Another possible problem is with your design. Since the back half of the valve is like the foundation of the valve your only locating on a 1/2" of the valve. The majority of the valve along with the valves weight is unsupported. The valve can cock many different ways. When I do the bores I do them in the lathe all at the same time rough drilling them and then boring them with boring bars to finished dimensions so I now they are all straight and concentric.

good points all of them,
but I have checked and rechecked the measurements against the rails I have in hand, and against the prototype unibody and everything matches up.
as for the fact the valve is not 100% in contact with the rail;
the prototype functions perfectly; so it's a non-issue.
I'm actually thinking that it may be the sear itself that is the problem.
the sears that seem to work are the big triangle shaped ones that take a 3/16" pic/axle;
but in the unibody I'm using the same sear used in the Micromag with the brass bushing accepting a 1/8" axle/pin.
is the axle to thumb screw center distance different for the different sears?

[XM15]

One thing I forgot in my post is the sear depth in the rail. It has to be correct too. As far as the micromag sear it should be the same. The valve other than being laser engraved differently is no different than any other mag valve and mag on/off. I use the standard 3/16 sear in all my bodies except for my emag which is a similar sear and pin set up to yours. It's the same as the other guns as far as sear location. Have you checked to make sure the sear pin is straight and not at a angle? Is there any chance the sear you are using is bent or out of spec in some way? I don't know what trigger frame your using but is there any chance it's some thing with the frame and not the body at all?

[LK-13]

One thing I forgot in my post is the sear depth in the rail. It has to be correct too. As far as the micromag sear it should be the same. The valve other than being laser engraved differently is no different than any other mag valve and mag on/off. I use the standard 3/16 sear in all my bodies except for my emag which is a similar sear and pin set up to yours. It's the same as the other guns as far as sear location. Have you checked to make sure the sear pin is straight and not at a angle? Is there any chance the sear you are using is bent or out of spec in some way? I don't know what trigger frame your using but is there any chance it's some thing with the frame and not the body at all?

there is no trigger frame being used at this time.
these are all going into rifles stocks and being fed from below by magazines.
kinda like this:


trigger group looks more or less like this only more refined:

[athomas]

Without the valve installed, check where the on-off portion of the sear assembly enters the valve cavity of the body. Is it centered properly? If you put pressure on the back of the sear from inside the body, does it affect the trigger movement and feel? ie; does it bind?

[Spider-TW]

From that picture, it looks a little like your linkage could cam-lock with some pressure from the sear. Does the pivot point on the trigger stay below the linkage pivot on the trigger? It looks close.

[BigEvil]

Have you tried it with a grip frame bolted up?

[Xmagterror]

The 1" bore is just for clearance. The 1.125 bore is what the valve really sits on and aligns it. Looks to me like your 1.125 bore is not long enough to make the valve sit right. I bet your valve is sitting at an angle and binding the valve.

[LK-13]

Without the valve installed, check where the on-off portion of the sear assembly enters the valve cavity of the body. Is it centered properly? If you put pressure on the back of the sear from inside the body, does it affect the trigger movement and feel? ie; does it bind?

there is no trigger installed, using the sear only.

[LK-13]

From that picture, it looks a little like your linkage could cam-lock with some pressure from the sear. Does the pivot point on the trigger stay below the linkage pivot on the trigger? It looks close.

that is a completely different build that functions perfectly.