Learning about ARs.  i got most of my lower receiver complete.   I lost my bolt-open lever pin when it went flying.  I have a second parts kit for another build that i took one out of, but I need another one.  Maybe I will find it.  I guess I lubed it up too well and it slipped when I was trying to get it started with a pair of needle nose pliers.  i was expecting the other spring and detent to go flying, but that installed easily  I hope I don't have to buy a whole lower parts kit to get it that pin.  What really has me frustrated was i bought a buffer tube last week.  i was told that it was milspec and would work for my carbine build.  However, there is no groove and I am questioning whether or not it is Milspec.  i have a Milspec stock that is coming in and i am afraid that it is NOT going to to work with this buffer tube.  't'he little tab on the receiver endplate will not slide on.  Can i grind it down a little and screw it on the grooveless buffer tube?  Why doesn't the buffer tube have a groove?

1 hour ago, Underdog said:

Learning about ARs.  i got most of my lower receiver complete.   I lost my bolt-open lever pin when it went flying.  I have a second parts kit for another build that i took one out of, but I need another one.  Maybe I will find it.  I guess I lubed it up too well and it slipped when I was trying to get it started with a pair of needle nose pliers.  i was expecting the other spring and detent to go flying, but that installed easily  I hope I don't have to buy a whole lower parts kit to get it that pin.  What really has me frustrated was i bought a buffer tube last week.  i was told that it was milspec and would work for my carbine build.  However, there is no groove and I am questioning whether or not it is Milspec.  i have a Milspec stock that is coming in and i am afraid that it is NOT going to to work with this buffer tube.  't'he little tab on the receiver endplate will not slide on.  Can i grind it down a little and screw it on the grooveless buffer tube?  Why doesn't the buffer tube have a groove?

No grooves as in the grove through the threads? if so i have never seen a buffer tube without one. I was once told an easy way to tell is by looking at the rear of the tube. A Milspec will be flat were a commercial will have a slight angle to it.

Post some pictures of the tube maybe someone here will be able to help further

oh and to where you can get replacement springs check out the link

https://palmettostatearmory.com/ar-15/lower-parts/individual-parts.html

 Don’t know where your located, but Howell Gun Works stocks all pins detent springs etc needed for a build, I would assume any gun smith that does AR builds or compliance work should have it. 

Quote

SARCO in Easton is awesome.  You can pretty much get any part you want there.   I was able to get everything I need including a buffer set. Once I pin the stock it should be finished.  

 

Do you have a pic of that receiver extension?

Reason I ask, I wonder if you have a rifle tube instead of a carbine tube. 

Edited to add, if it looks like one of the pictured tubes, you have a rifle receiver extension.