View Full Version : Getting FSB pins in
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.
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.
Can't say. They were mixed up on extraction. I would have preferred putting them back in the same holes, but ...
I was not sure if it mattered because, to my knowledge, the pins had not been fully installed (new barrel and the pins were not fully seated).
Should I pull the pins and swap?
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. :)
This post was timely for me as I am about to venture by shaving down my first FSB and I was looking for issues to keep an eye on
An Undocumented Worker
12-04-11, 23:13
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.
Don't worry about it, your barrel/FSB are fine.
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.
Look at Colt FSB pins. they don't seat flush either.
Yeah... They stick out a little on both sides. ;)
Is there a certain punch that would make the job easier? I believe I read somewhere that a concave tip is the way to go...
Is there a certain punch that would make the job easier? I believe I read somewhere that a concave tip is the way to go...
The hardware store has a fat nail set punch that's perfect. I foret which size or number it was.... but the tip is perfect for drifting taper pins.
Yeah... They stick out a little on both sides. ;)
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 probably stating the obvious, but are you sure you're punching the pins in from the right side?
I'm probably stating the obvious, but are you sure you're punching the pins in from the right side?
Tapered pins; inserting from right to left. I doubt I could get them to within 1/10th of an inch of full insertion otherwise. :D
But, it is a proper question.
I haven't done this a lot, but I have never had this much trouble with installing a FSB before.
An Undocumented Worker
12-05-11, 22:01
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.
http://www.midwayusa.com/product/545766/ar-stoner-front-sight-taper-pin-reamer-ar-15
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).
http://www.victornet.com/subdepartments/Taper-Pin-Reamers/2548.html
(bottom of the page).
Of course, sending it back is also an option, but that takes the fun and learning out of it! :D
Wrench, Undocumented, p., everyone:
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.
A few responses below.
IIRC DD taper pins are 3/4" long, 1/8" shorter then the standard AR taper pin.
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).
IIRC DD taper pins are 3/4" long, 1/8" shorter then the standard AR taper pin.
By my measurements, it looks like they are intended for a close to exact fit.
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).
It sounds intimidating, but it's actually very easy. If you use some oil, and go slow, clearing chips, and checking fit, it's easy to do. Feel free to PM me.
buckshot1220
12-06-11, 09:20
This is the third or fourth thread I've seen mentioning short taper pins on DD uppers (even after fully seating since they come loose from factory).
My DD upper is the same way, even after pounding them in they are not flush on the smaller side. That being said, I can't see them going anywhere anytime soon and I've decided to leave well enough alone.
I'm installing a rail later this month and at that point, since it will be apart anyway, I may go ahead and put new pins in during reassembly.
Right now my plan is to shoot it this weekend with my son, see what happens. It should function fine. I am also mildly curious to see if it has any "special" qualities.
(Don't get me wrong. I come from a science and law background, and they are pretty logical and unforgiving disciplines. But, every so often, you run into situations where you are in the presence of something unexplainable and mysterious. I've seen this with weapons, autos, musical instruments, occasionally with old watches -- things that can create a fairly intense meaning to the user. I have hopes for this rifle, but I won't bet the farm on it.)
You mean "Special qualities" like turning lead into diamonds? :D
I'd like a gun with qualities like that. I'd just shoot it into a barrel of water all day long... ;)
In all seriousness, if the pins are indeed inserted correctly (which I believe they are), your rifle should be fine, aside from a slight cosmetic issue that will only be apparent upon close inspection, and should have no effect on the function of the weapon itself.
Just a quick update. The upper has been in DD's hands for about two weeks, and I expect that they will take care of any "issues." I am glad they were so friendly about it, but I never expected anything else.
Part of the reason I sent it back to DD was that I thought they might benefit from taking a look at the barrel. The pins were not the only aspect of the barrel that I did not like (but, I won't go into that).
I felt that I had reached the limit of my competence, and I should learn to take stock of the situation before attempting my own work. I will get a reamer (or two) before I try this again, and now I know another thing to look out for. Since this was my seventh build, I thought I knew what I was doing. Ha!
Wrench: I haven't forgotten that I was going to PM you. I do have a few questions, but I haven't quite figured out what they are.
Seems like this post is timely for several here...me included. I'm putting my FSB back on tomorrow after shaving it down today. Fun project to do actually. I was considering replacing the pins as it seems like those are a one-time-use-only type of thing. Is this something that would benefit from a bit of loc-tite prior to driving the pins in or does it really not matter? While I've never seen on pop out during use mind you, I just have a habit of adding it to items like that.
Quiet-Matt
12-28-11, 20:04
https://lh6.googleusercontent.com/-ZIfgcE6wK4Y/Tpm_qsrC93I/AAAAAAAAJKE/ETW-xmilbHU/s800/DSC02616.JPG?gl=US
Taper pins are cheap enough that it's a good idea to replace. With the beating that they take going in and out, they're bound to suffer some deformation. The result may be that they wont fully seat because the trailing end has flared out, or they may cause the gas block to have a slight wobble. The wobble was a result of the pin on the right in the picture. The old pin was a DD taper pin, and didn't hold up to repeat installation. I get hardened steel taper pins from a local source for about .60ea and trim them after installation, leaving about 1/8" exposed. A little chemical blackening and we're good to go.
https://lh6.googleusercontent.com/-ZIfgcE6wK4Y/Tpm_qsrC93I/AAAAAAAAJKE/ETW-xmilbHU/s800/DSC02616.JPG?gl=US
I get hardened steel taper pins from a local source for about .60ea and trim them after installation, leaving about 1/8" exposed. A little chemical blackening and we're good to go.
What kind of source for hardened taper pins? Are they made specifically for ARs, or have you repurposed?
Thomas M-4
12-28-11, 23:05
I will just throw this out here after replacing to many damn press fit bearing that I cant count any more.
Put the Damn pins in the freezer for a couple of hrs or better yet over nite before you try to drive them in.;)
Quiet-Matt
12-29-11, 06:50
What kind of source for hardened taper pins? Are they made specifically for ARs, or have you repurposed?
A friend at a local hardware store got them for me and I bought enough to cover my needs for a while. I got 1" long 2/0 pins which are too long and were not AR specific. If you can not source them locally, Bravo Co. sells them HERE (http://www.bravocompanyusa.com/BCM-Taper-Pins-for-Front-Sight-Base-AR15-M16-M4-p/taper%20pins%20fsb%202.htm) and you wont have to cut or re-finish them.
I have some 3/4" SS 2/0 pins I use for doing low pro gas blocks. On the 0.625" Vltor block The pin only needs to be 5/8 or so long. I have a 2" block of steel with a #31 through hole, on one side I have taper reamed it to give me a pin length of 5/8". Insert pin, grind flush with 90 degree die grinder. Pop out the pin, chamfer and clean up by hand.
Final Update:
If you've followed my comments here, I had some minor problems with a DD barrel that cropped up during assembly of the upper. I considered pulling the whole thing apart, returning the barrel to the vendor, and starting over, but I thought that DD would like to see the situation as I did. I sent them the whole package (DD barrel, DD lite rail, VLTOR upper). DD paid for shipping.
Received the thing back last week, but did not have time to examine everything until yesterday.
DD did everything right for a customer that I could ask for. I now have a complete upper from those parts, assembled by them. The barrel appears to be new (i.e., different from the one I sent in). Pins are correctly inserted and no finish problem. Perfect. Now I just have to find time to shoot it. :D
Of course, this is no surprise for a company of their caliber. :rolleyes: (Had to pun.) Just thought you might want to know.
azoutdoorsman
01-18-12, 00:01
I usually start the pins in with a jig/hammer/punch, and the finish up in a vise lined with leather, and use a pipe to tighten the vise for leverage. However, I don't get calipers out and measure a small protrusion. If it is close to flush, I am satisfied.
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