I have a F-style FSB and stripped barrel. I need to pin the FSB to the bbl and was wondering if a straight grooved pin would be as good (if not better) than a tapered pin? I have all the tooling for a straight pin installation but would need to purchase a tapered reamer, which are $20 (Brownells) to $30 (McMaster).
Also, is .750" gtg with the length? Colt uses .850" length 2/0 tapered pin, which explains the little “nubs” on either side of the FSB.
– ale
0.750 is too short. Measure the width of the gas block where the pins go through and you’ll understand why.
Straight pins should be fine as long as they are not too loose or too tight. Tight and you can warp the barrel and loose the pins will fall out.
Taper pins were designed to draw the gas manifold/FSB down against the barrel port, creating a tight seal. A straight pin will not apply the downward pressure.
In an “over gassed” it should not be a problem. Also, if you have a tight fit between the barrel and gas manifold it should not be an issue.
Try your straight pins. You can always go to a taper pin later on.
Sorry, but the pins can not “pull” the FSB down in any way.
The measurement between the flats on the FSB is .755" so my choice is either .750" or 1.00" and machine off the excess. I would order the correct pins from Brownells but 1) they are out of stock, 2) the reviews are horrible to non-existant, and 3) they are way overpriced.
Here is the description of a grooved dowel pin: Each pin is grooved so it contracts as it’s forced into a hole, creating tension to lock it in place. Pin ends are beveled or rounded. For the best fit, your hole should be equal to or slightly larger than the diameter shown. Full Groove — Also known as Type A grooved pins. Use them in place of standard dowel, spring, and taper pins.
A tapered pin will act as a wedge between the barrel and fsb.
These pins are in stock if you can find something else to meet the minimum order amount: http://www.bravocompanyusa.com/BCM-Taper-Pins-for-Front-Sight-Base-AR15-M16-M4-p/taper%20pins%20fsb%202.htm
Correct, it is known as a self-holding taper, with 1/4" taper per foot. designed to wedge its’ self with friction to stay in place. But, it will not wedge the FSB down to the barrel like said above. That is all dependent upon the tightness of the fit between the two parts. It you want to use the straight pins, and already have the equipment to do it, I say go ahead and do it. Just make sure you have the jigs to properlly align the front sight so it is not canted before you do anything.
I know this is batshit crazy but maybe you should just use the parts that gun was designed for. Sure, you might have to buy the correct tools but why not do it right?
Yes taper pins can and do if properly reamed. Randall at AR15barrels would disagree with you.
Not much else I need for this build except a BCG, which never seem to be in stock. Now with the price increase (NRA donation), it’s cRaZy to try and combine these two items. That is, by the time I add a set of pins to my shopping cart, the BCG’s will be sold out!
Unfortunately, the grooved pins only come in zinc-plated steel and stainless whereas the taper pins come in plain steel. I want to park these so maybe taper it is…
SAW seems to have some in stock…
http://www.specializedarmament.com/products/Taper_Pin_Front_Sight-227-289.html
30 day lead time and minimum order of $50.00 before shipping.
I just ordered and the notice came after I put in order.:eek:
I ordered the taper pins from Midway along with an AR-Stoner 2/0 taper reamer (seemed like a good price, too). I had a couple other small parts to order so it’s all good…
Do you have a jig to secure both the barrel and the FSB for pinning? If not, how are you going to go about it?
Also, sorry for the thread drift but What ever happened to your low pro gas block that you “roll pinned”? Curious as to how that turned out.
I don’t have a jig but I’ll be sure to line up everything so that the FSB and upper receiver are square before drilling.
Funny you should ask about the lo-pro gas block. I went ahead and drilled the hole for the spring pin but messed up on my measurement in the y-axis and missed contacting the barrel completely :o I call it a “lightening cut”. lol. I should have known better than to start makin’ chips while still recovering from the flu. I’m feeling better now so no eph’ups on this build 
Replacement parts are scarce…
I got an email from Mark at SAW this morning.
He’s taking care of the order.
Good customer service!
It depends on where the pin is installed.
I consider the “correct” location for the center of the pin hole to be right at the bottom edge of the barrel.
So if I drill a 1/8" pilot hole before I run the taper pin reamer down I want 1/16" Ito the barrel and 1/16" into the front sight base.
As you install the pin, the fsb will indeed draw down against the barrel.
Amazingly, when you pull off a colt barrel, you find it done the same way:
There are some other companies who take no regard for pin placement.
The most common offender in this respect has a snake on the side of the lower receiver.
That kind of a taper pinning job will NOT draw the FSB down against the barrel:
And as much as I love LMT, I have to throw them under the bus for this same behavior.
They actually drill the hole completely through the barrel, leaving pin sticking out both sides:
Thanks for responding to my thread. I drilled and taper reamed a bbl/FSB for a buddy just last week. Interestingly, in order to index the pins in the center of the FSB “flats”, the holes ended up being drilled about 3/4ths (75%) through the bbl. This is using a F-style FSB. Of course, the only factory sample I have to work with has a snake as its logo so it is what it is. I may be wrong but I don’t think it will make any difference. Setup is 90% of doing.
Speaking of setup…never trust your DROS. After my failed pin install on the lo-pro gas block mentioned above, I realized that my Y-axis was set to DIA…something I never do on purpose but was obviously a mistake when drilling that hole. I’m cool with taking blame for my mistakes At least it was on my upper and not my buddy’s. Lol
I am pretty sure that they did not change the location of the “flats” on the forging when they went from 0.625" barrels to 0.750" barrels.
They just used the same fsb forgings and punched bigger holes in them.
This is why the pins end up centered on the flats on 0.625" diameter barrels and you need to drill at the lower edge of the flats on 0.750" barrels to have the pin end up centered at the edge of the barrel.
I do so much fsb work the I made a proper fixture.
I have my y axis zeros written on the fixture for each barrel diameter.
My dro is always spot on and puts the drill bit right where I want it…
