I was doing an upper build with my son today. I removed the FSB from a new barrel for rail installation. Because it was a new barrel (DD), the FSB pins were loose on arrival. When I replaced the FSB and set to putting the FSB pins in, the tapered pins would not fully seat in the FSB. As of now, one pin protrudes by about 0.07", the other by 0.09". The recesses in the pin holes (the left side) are just about the same, so the pins are the correct size.
When pounding on the pins, I started with a 'smith hammer and brass punch, then aluminum, then steel, going to a heavier (carpenter) hammer along the way. I gave it more than a few good blows (not like a removal, but pretty good). The FSB was well supported and solidly backed.
While I have had less than perfect FSB installations before, I have never had pins protrude this much. They seem solidly in, but I have begun to mushroom the heads. Should I start over, get new pins and start over, not worry about it? Advice?
Did you put the pins in the same holes? The whole FSB removal and installation process can be very tricky and they don’t always like to go back together.
As long as they’re tight, and they protrude through both sides, at least a little, I wouldn’t worry about it. A press is really the best way to put them in, but a 3 lb mini sledge will do the trick in a pinch.
I’ve got a DD custom URG with FSB and the small end of the pins do not protrude out from the other side of the FSB. They aslo aren’t coming out unless I REALLY want them out. It also has somewhere around 750 rounds through it with no trouble, and almost no windage adjustment necessary on the rear sight.
Look at Colt FSB pins. they don’t seat flush either. Finish the build, shoot a few hundred rounds than check the pins. If they are still tight than your good. If after shooting you decide you need to replace them than your no worse off than now.
I wouldn’t mind that. The problem is they only stick out on one side and have a corresponding recess on the other. I found my three lb. sledge and had at it, no movement. This is somehow wrong. I contacted DD this morning and they said they would take care of it. (No surprise there.) I’m waiting for a call back.
But, it seems perfectly functional. It just shouldn’t have occurred this way. Pending its return, I may shoot it to see if any other problems crop up.
A concave tip for a drift/nail punch might help reduce mushrooming, but I do not believe, based on previous builds, that this should be happening or that such a punch would solve the problem.
I’m repeating myself, but on my DD upper the FSB pins are positioned just like you described, and are not in any danger of coming out on their own. From what I can tell this is just a product of the reaming process and how far out it gets reamed. The depth the pins seat at is a function of the diameter of the reamed hole. It is fully possible to have full and tight engagement of the taper pin with the barrel and FSB and the small end to not be flush or protrude from the other side. As such it is also possible for the same to be true for a pin that has the big end pushed past flush of the FSB.
The beauty of taper pins is that a solid fit is not dependant on a perfectly dimensioned hole or pin, the taper makes up for any variances between the parts. This is not to say that DD’s FSB holes are not dimensioned perfectly.
I would consider the way they ream their holes a good thing if you ever have to replace your pins and the ones from the new supplier could possibly be undersized. With the way DD reams the holes you wouldn’t have to worry about over inserting an underspecced pin.
In that case, it’s probably only cosmetic at this point. If it bothers you, you can pull them out and replace the pins, reaming slightly, if necessary.
If the looks don’t bother you, I wouldn’t worry about it.
If you want, I can throw a couple of fresh pins in an envelope for you (I’ve got hundreds). If you want to get a reamer, it’s just a 2/0 taper pin reamer, that you can get from just about anywhere.
I picked up a NOS Colt 1/12 twist 20" chrome chamber unlined bore pencil barrel with fsb for an A1 build and had difficulty seating both pins fully and evenly. It may be the case that the fsb that actually went with the barrel got swapped over the years. But even off the barrel, I couldn’t tap the pins into the fsb anywhere near where they should be. It seemed the bores may have intentionally been left undersized a bit.
I used this reamer and a tap T-handle to ream the bores and fit the fsb to the barrel until things fit up properly.
Before reaming the bores, I lightly tapped the pins in and assembled the rifle and test fired it to determine windage at the rear sight, and see if seating one or the other fsb taper pin got me closer to zeroing the rear sight in its range of adjustment.
Then back in the workshop I fitted the pins by tapping in the fsb pin that put the fsb closer to zeroing the rear sight and reaming the other bore. When I could seat the pin in the bore I was working on just about flush on the exit side, I did so to secure the fsb to the barrel, then tapped out the first pin and reamed that bore, then just went back and forth with one pin seated reaming the other bore and sneaking up on where I wanted the pins to seat.
Used plenty of Tap Magic while reaming, took my time and went in small increments, cleaned the bores out before test fitting the pins, tapped the pins in with moly lube on them each time I test fit. With everything together, the rifle zeroed with 2 clicks left windage, which I thought was pretty good for a guy working at home and not having a jig to hold the fsb in alignment with the upper during fitting.
Now, that said, if DD wants to take the barrel back and do the work for you… that’s a no brainer.
I get my reamers from Victornet. Their HSS reamers are about 7 bucks, but you can get the standard tool steel ones (which are MORE than adequate for doing even 10-15+ sight blocks), are only $2 each.
Get a couple, in case you drop one (reamers can be brittle).
Thanks for the replies and suggestions. A couple of notes:
(1) Diagnosing problems like this by BBS is close to futile, I understand. I have great respect for DD and do not want to say anything like “it’s their fault.” It could be a case of “tolerance stacking” or simply something out of spec, or, something I did. It happens.
(2) This is a little different than other builds for me. I am definitely a function over form guy. But, in this case, I invited my son to help me build a new upper. He helped make all the choices as to components and the accessories – VLTOR upper, DD bbl, DD Lite rail, sling adapter, sling, BUIS. He did some of the work of assembling the parts and held the thing down while I worked on the pins. What he doesn’t know is it is intended as a Christmas gift for him. So, in this case, cosmetics do count a bit.
Undocumented: Your comments on taper pins and their function are well-taken and I will file that away. After reading that, I am almost glad they didn’t fit. Almost.
wrench: Reamers? I suspect that I have reached my level of incompetence and this is not the upper I want to learn on. I will PM you later on a few things. I hope you don’t mind.
p.: Thanks for the additional comments on the reaming process. That too I will file away. Under the circumstances, DD may be the way to go, but I have to get this done quickly (for the reason stated previously).
