Front takedown pin not working with upper/lower

[speeddreamz]

I'm having trouble pushing the front (closest to magwell) pin in on a particular lower/upper combo. It will go in about 1/8 of an inch with a lot of force and then its hard as heck to get out. Back pin works fine. Front pin has problems regardless of which is pushed in first.

The weird thing is that on my 3 other uppers/lowers they all work but not this particular combination. Why this has to work is because the lower is a pistol lower, so it has to work with the pistol upper.

Any ideas? I know its kind of vague, but I figure people would have some areas to start investigating.

[IntoForever]

Try a light coating of oil on the pin. I have to do this and it works fairly well.

[ott1]

More info needed. Who makes the lower? Do you have access to a caliper?

[baih777]

push the front pin in, when you have the upper in a open postion then close and push in the rear pin.

[sdfire]

I had the same problem with my pistol. Sometimes the channel in the rear of the lower receiver is rounded off, and the part that fits in it on the upper is a slightly different shape( square) It keeps the receivers from seating properly. I filed the square edges off off the part of the upper where the rear pin goes through just a little and it went right in. Pm me for pics or more info

[greybeard]

Does the pin go thru the lower without the upper? Does the pin go thru the upper without the lower? If yes to both, you have an alignment problem and discuss it with the manufacturer

[speeddreamz]

push the front pin in, when you have the upper in a open postion then close and push in the rear pin.

Tried this.

[speeddreamz]

More info needed. Who makes the lower? Do you have access to a caliper?

Stag lower, I do have access to calipers!

[sdfire]

alignment fix

here is pics of what I was talking about. It seems counter intuitive, but it worked for me. The upper receiver was squared off and the lower was round. So the corners were pushing the the upper slightly forward. Sometimes its just enough to make the pin not fit. I took a small diamond file and rounded the edges on the front and back parts of where the pins go through the upper and it fits great. Im not sure if that is your problem , but it is worth considering if the lower and upper are different manufacturers

[speeddreamz]

here is pics of what I was talking about. It seems counter intuitive, but it worked for me. The upper receiver was squared off and the lower was round. So the corners were pushing the the upper slightly forward. Sometimes its just enough to make the pin not fit. I took a small diamond file and rounded the edges on the front and back parts of where the pins go through the upper and it fits great. Im not sure if that is your problem , but it is worth considering if the lower and upper are different manufacturers

Even though its the front pin (closest to the magwell) you think the area around the rear pin (closest to stock) is pushing the upper forward and making the front pin not seat?

I can not seat the front pin regardless of whether I put in the rear pin first.

The rear pin ALWAYS goes it, perhaps theres quite a bit of play there?

[adamsreeftank]

It's not uncommon. Especially if the upper and lower are from different makers. There are tolerances that stack up. Sometimes they fit perfectly, sometimes they are loose, and sometimes they are too tight. I have uppers and lowers that only fit in certain combinations.

You might be able to fix it by taking a fine round file and removing a tiny bit of metal from the inside of the hole in the upper's front lug. You need to figure out which way it is out of alignment. Better to remove too little, and then use some oil and a soft hammer to work the pin back and forth a bit.

[kcstott]

Don't use a file. Don't bother with oil. The reason is if you can force the pin in place it means there is very little material interfering with the pin. A file would be over kill.
Get a .250 reamer and ream the hole with the rear pin holding the two together.
You will need to remove the pin, detent and spring.
I had the same problem on my upper with a 80% lower Reamer fixed it no problem.
You will be surprised how little actually needs to be removed to get it to work.

Or if you are in my neck of the woods I can do it for you no charge

[baih777]

try fitting the upper on your other lowers. if it fits fine then its your pistol lower thats off.
if that upper fits your other lowers then you open the hole a little, you now have a dedicated upper for your pistol lower because it might be loose on your other lowers.

you might want to have someone help you and squeeze the two together and see how far off the hole is.

[baih777]

looking at your pics again, is the barrel nut hitting the lower ? if it is just take off the handguard and loosen the nut and install the upper.

[goober]

try fitting the upper on your other lowers. if it fits fine then its your pistol lower thats off.

it's a pistol upper.
even for for testing/fitting purposes, please don't instruct someone to make an SBR.

OP if you're going to do this, you should technically remove the barrel from the upper while you do it, rendering the upper non-pistol/SBR. or, if you have non-rifle lowers around, go for it.