80% lower not accepting fire selector switch

[c-wick]

It was milled at a build party using CNC program.
Holes are fine now that I deburred them a little more. Selector goes right in without too much force.

The FSS hole was drilled after the pocket and was done all the way through on 1 side so I know the hole is straight.

Im starting to think the pocket isn't deep enough. pics on the way

[c-wick]

Uploaded with ImageShack.us


Uploaded with ImageShack.us


Uploaded with ImageShack.us

[c-wick]

Uploaded with ImageShack.us


Uploaded with ImageShack.us

[c-wick]

I suppose from the pictures everything looks fairly normal.
What I did find though was that if I drop the trigger in and push it down without inserting the pin through it, I am able to put the FSS in. If I insert the pin to hold the trigger in, there is not enough clearance for the FSS. So now, I am thinking that the hold for the trigger assembly was drilled too high.
That still is a different issue as I also have the issue of the safety not clicking from position to position.

I guess if anything its a good learning experience.

[ott1]

Someone mentioned that if you don't have the pistol grip install with the spring and detent, you'll never get the click.

[ott1]

Measure the depth of the pocket to the top of the receiver. It should be 1.249" +- 0.010".

[c-wick]

Someone mentioned that if you don't have the pistol grip install with the spring and detent, you'll never get the click.

understood. Ive tried this. Almost feels as if the groove in the selector is too long therefore never engaging with the detent.

Ill measure depth tmrw when i get a chance.

[wash]

If your pocket is deep enough but your pin and selector holes are too low, it might be possible to file the selector surfaces to get it working.

If it's done wrong you might create a dangerous situation so make sure you understand the situation and what altering the selector will do.

It also kind of guarantees that you can't swap selectors without altering the new one also.

If you can fix the real problem, do that but if not, modifying the selector might be the way to salvage a scrap lower.

[tanakasan]

Thats a nasty burr in the hole shown in the third pic.

Does the selector go in by it self easily? I would think not, looking at that raggedy burr in those holes. Deburr then and try the selector by it self. Should go in easily and pivot smoothly. Then go forward with the rest of the parts.

Yes, w/o the detent, spring and grip installed, it won't click.

Robert

[MarkInFolsom]

Umm, by the picture of the FCG pocket under the rear of where the trigger hits, it sure doesn't look like a CNC job to me. The pocket should be flat and the same depth across the entire width. I think it needs a little cleanup, mine did when I tried the LPK install.

[wash]

I think it is hard to tell, there can be a lot of reflections if it's a nice cut.

But I agree with deburring things, the last build party I went to I brought along my little Shaviv deburring tool and helped a lot of people clean up the little burrs that remain even after the nicest CNC machining is done.

With a little practice and a few minutes of work, you can get pretty much all of the burrs gone.

It's a funny thing to be proud of but I did a bad-*** deburring job on my last AR.

[c-wick]

I think it is hard to tell, there can be a lot of reflections if it's a nice cut.

But I agree with deburring things, the last build party I went to I brought along my little Shaviv deburring tool and helped a lot of people clean up the little burrs that remain even after the nicest CNC machining is done.

With a little practice and a few minutes of work, you can get pretty much all of the burrs gone.

It's a funny thing to be proud of but I did a bad-*** deburring job on my last AR.

The pocket is completely flush. Its just reflections of the mill finish

yeah pretty nasty looking holes but that was right after i drilled it out a little more. its cleaned up and fits right in there and with no slop. the problem still persists though with the back of the trigger bar sitting too high.

What would be the problem (if any) with filing down the top of the trigger bar that contacts the selector switch? Im thinking that this could solve the issue but not sure of the repercussions.

[c-wick]

This is starting to get a little rediculous. Seeing as how I spent an entire saturday driving to a place to get an 80% then taking it the build party right after and spending the money on this. ok, rant over.

[wash]

This is the problem with CNC 80% lowers.

It's really machinist work and if you run in to a problem because you're not a machinist, then you have some gunsmithing work to do.

Being a ~machinist and fairly mechanically inclined, I can fix issues if they come up but the most important thing is that I know the value of good CNC machining that gets everything right the first time. That's why I'm so pleased with the pocket I milled at Dark Soul's shop.

One other thing to consider is that the selector might be bad. If you can't find another real problem try swapping it out.

[c-wick]

I sure thought what I had was completely legit. The machinist who did it was top notch and the CNC machine was nice. Im going to have a buddy come over with his ar and im gonna try his parts in mine and see if there is any difference.