Pic request for USC internals install into 4-pos lower.

[SweedishMurdrMachine]

Hey all,

I sent my UMP lower that I converted to semi using the USC internals and there seems to be some confusion if I did it right.

Does anybody here have a 4-pos 2rd burst lower they installed the USC internals in that they can take a picture of from top down??

I think it's important it be a 4-position 2 round burst lower, because the Navy and Semi only ones might use different internal parts...

Thanks guys!

[seven.sixtwo]

Shouldn't a pic of USC internals installed in anything look the same? (IOW if you take out the 4 position internals there is nothing different to see) They will only work if installed the same as in a USC.

Edit I just checked my photobucket and I must have deleted my USC internals pics, sorry!

[SweedishMurdrMachine]

Well, AviatorDave is helping me with my lower so there's some question as to if the 4-pos burst lowers are different than the Navy lowers. Was hoping to get him a picture of a conversion that was done right since I may have messed something up.

[AviatorDave]

Here's what's going on - on the navy and FBI ump packs, the notches in the housing that control the alignment of the selectors when they are installed are the same as the USC pack, which means all the usc parts will fit right in. And also, the bumps and notches on the selectors are oriented the same, so the selectors are almost interchangeable. There are a few notches that I add so the ump selector works with the USC slider and notched disk.

But on a burst pack (this one at least, it's a new one) the notches in the housing are rotated almost 180 degrees around the selector hole on both sides. The ribs on the UMP selector are in a completely different orientation, so it won't work with the USC slider and USC notched disk. (The notch in the USC disk is also in a different orientation since the corresponding notch in the housing is also rotated 180 degrees).

So the USC selector and notched disk can't be used with the ump burst housing since you can't get all the notches to line up properly to insert the selector, and the UMP selector can't be used with the USC slider.

I'm starting to think the easiest way will be to add the correctly oriented notches to the UMP burst housing so the USC selector will fit correctly.

It's not that he messed anything up, just that the parts don't really fit together properly and I was wondering how others have solved the problem with converting a burst pack.

Edit: Hang on a sec, pictures forthcoming.

[SweedishMurdrMachine]

Dave,

That's really weird because when I put it back together and played around with it it seemed to function fine. Or, is it not until you get it installed on a USC upper til problems arise?

[AviatorDave]

Here's the selectors themselves. The notches in the right and left sides of the housing must be at the same angle for the selector to be inserted correctly. On the UMP Navy and FBI packs, this angle is the same. On a burst selector, you can see they are very different.

Here is the left side of the housings:



And here is the right side:



And here are the two notched disks. You can see how the range of the bumps is clocked very differently when the two notches are aligned:



So the dilemma is that the USC slider is a requirement, as is the USC notched disk, but they won't work with the UMP burst selector. And the USC selector won't work because it's bumps don't align with the cuts in the housing, nor is the slot in the notched disk aligned with the slot in the right side of the housing.

I really was hoping to use the UMP selector and make it fit with the USC slider, but I can't since their shape is so different.

I think the solution may be to use a UMP selector from a navy or FBI pack, and then just cut the right notches in the housing so it can be inserted.

Anybody have a spare UMP navy or FBI selector set lying around?

[SweedishMurdrMachine]

Dave,

Let me check with Adam Webber and see if he has any laying around. Either that or if anyone who did their conversion and had the USC selector remarked should have an extra one.

[AviatorDave]

Dave,

Let me check with Adam Webber and see if he has any laying around. Either that or if anyone who did their conversion and had the USC selector remarked should have an extra one.

A UMP selector would be better because it wouldn't need to be remarked, only the housing would have to be broached.

But I have some extra USC selectors.

I'm working on something else though. I've got another idea I need to investigate.

[SweedishMurdrMachine]

If you have to just use a USC selector, I included them in the baggie of all the "left over" parts.

Just don't forget my Hooters shirt! :D

[AviatorDave]

Dave,

That's really weird because when I put it back together and played around with it it seemed to function fine. Or, is it not until you get it installed on a USC upper til problems arise?

Yeah, it seemed to function, but it didn't. The parts were binding up on the selector and the sear wouldn't always catch the hammer notch. If you held pressure on the selector, it could possibly go into runaway full-auto. But I think my other idea will work better anyways.