View Full Version : Why use taper pins (instead of roll pins) on gas blocks?
What's the advantage of a taper pin over other types of pins- roll pins, or even tapping the hole for a screw or piece of all-thread?
Suwannee Tim
11-26-11, 19:21
Taper pins self lock. As they are seated a friction force develops along the whole length and diameter of the pin which locks the pin in place. I think locking a gas block is a challenging application with thermal cycling and a lot of high amplitude vibration. Taper pins seem to be a pretty effective solution. Small, single wrap roll pins have much less locking force and multi-wrap or coiled roll pins are too large to use in this application. Screws work but are prone to working loose unless locked by some method. A screw and a tapped hole to screw it in costs a lot more money than a taper pin and reamed hole.
Taper pins are about as strong a connection as you can make short of actulaly welding.
The taper itself offers more surface contact area than a straight pin of simular diameter, and also acts like a wedge. The harder you shove it in, the tighter it grabs.
Threaded fixtures can come loose through heat expansion and vibration, both of which are abundant in a barrel assembly.
When put straight in like a set screw, they don't have as much surface contact area as a cross pin of any type since its only the very tip that provides all the locking area, so don't hold things as solidly even if reefed with huge torque values.
When put in crosswise they are actually weaker than a pin of equal diameter and require a few more steps in the machining process to install.
Removing a stripped one that was installed in either direction would not be a pleasant experience by any stretch of the imagination.
Spring pins and roll pins are subject to fatigue from heat expansion and vibration. In time they can literally loosen up and fall out on thier own if used in an improper way. Holding a gas block onto a rifle barrel would be one of those improper ways.
Occasionally they've been known to split apart, so not only does it no longer hold what it was driven through, it won't come out without some distruction of the retained parts involved.
Being a form of tube, they would also collect dirt and debris which could lead to eventual failure if not regularly and deliberately cleaned.
Look at the retaining pin on the froward assist on a handful of rifles and you'll likely find more than one that's clogged with crap.
And again, as a tube and of stright profile, it has less surface area to create friction with and isn't as strong in shear as a standard taper pin.
Taper pins are far superior to roll pins, not to mention the standard for FSBs. Roll pins are rather flimsy and not ideal for such a critical component.
Threaded fixtures can come loose through heat expansion and vibration, both of which are abundant in a barrel assembly.
When put straight in like a set screw, they don't have as much surface contact area as a cross pin of any type since its only the very tip that provides all the locking area, so don't hold things as solidly even if reefed with huge torque values.
When put in crosswise they are actually weaker than a pin of equal diameter and require a few more steps in the machining process to install.
Removing a stripped one that was installed in either direction would not be a pleasant experience by any stretch of the imagination.
As for tapping it for a long set screw across it instead of a taper pin, I've seen it done. Although now, I dont think it was such a cool idea afterall.
Spring pins and roll pins are subject to fatigue from heat expansion and vibration. In time they can literally loosen up and fall out on thier own if used in an improper way. Holding a gas block onto a rifle barrel would be one of those improper ways.
HK uses a single spring pin to hold the gas block on the G36 - a piston gun with actual impact force on the gas block. A DI rifle has vastly less stress on the gas block.
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Just wondering, when a FSB is pinned in place with tapered pins, is the hole drilled with some type of tapered bit or is a regular straight hole drilled and then reamed with a tapered reamer?
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HK uses a single spring pin to hold the gas block on the G36 - a piston gun with actual impact force on the gas block. A DI rifle has vastly less stress on the gas block.
Yes, a very large single pin
according to the HKPro (http://www.hkpro.com/forum/hk-long-gun-talk/144225-sl8-g36-gas-block-roll-pin-size.html) forum,
20.30mm Length and 6.06mm Diameter
roughly 3/4" lg by 1/4" dia
http://www.rksplus.com/WebRoot/comalis/Shops/lno1J350m/4DFB/B553/C41C/219A/78ED/7F00/0001/59FA/G36_Gas_Block.jpg
I have always thought this was a very good method that seems to lend itself to mass production well.
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Just wondering, when a FSB is pinned in place with tapered pins, is the hole drilled with some type of tapered bit or is a regular straight hole drilled and then reamed with a tapered reamer?
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It's drilled and then reamed for a taper pin. A 2/0 taper pin reamer is the standard, IINM.
20.30mm Length and 6.06mm Diameter
roughly 3/4" lg by 1/4" dia
My calipers say about 0.196 diameter and 5mm.
Suwannee Tim
11-27-11, 11:45
Yes, a very large single pin
according to the HKPro (http://www.hkpro.com/forum/hk-long-gun-talk/144225-sl8-g36-gas-block-roll-pin-size.html) forum,
20.30mm Length and 6.06mm Diameter
roughly 3/4" lg by 1/4" dia
http://www.rksplus.com/WebRoot/comalis/Shops/lno1J350m/4DFB/B553/C41C/219A/78ED/7F00/0001/59FA/G36_Gas_Block.jpg
I have always thought this was a very good method that seems to lend itself to mass production well.
Is the black circle on the bottom of the part the pin? It looks solid to me.
That is the pin hole.
This is the barrel:
http://img850.imageshack.us/img850/6392/g36s.jpg
If I'm looking at it right, the G36 gas block doesn't have the front sight sling swivel or bayonet lug as part of its construction.
Its a low block shrouded by bodywork that is only stressed by gas pressure pulses and the occasional bump of the piston if it comes back into battery a bit out of alignment.
The M16 gas block is exposed to gas pulses also, along with the regular stress of a sling pulling on it and if not locked down well the potential for the whole thing to rotate if the side of the sight tower is baffed. Little things that happen dozens of times a day on a work rifle.
There's even obscure incidences of people putting a bayonet on one and putting it to use on hard training targets or actual soft targets.
In any event, its not really an apples to apples comparison as the M16 gas block has so much more going on at once while the G36 block is neatly tucked out of harms way under protective coverings and does nothing but channel gas.
The G36 block has much more stress on it than an M4 because each shot jack-jammers the gas block.
Even if the Piston system imparts more stress on the G36s gas block than the DI on the AR, isnt the stress only being implied in one direction? It just seems like the FSB on an AR is being asked to cope with other sorts of multi directional stresses that the G36s block isnt exposed to at all. These may be nonfiring related stresses, but they are stresses none the less. The stress applied by bayonet use may not be taken very seriously today, but 50 years ago it was a very real consideration.
The 416 uses roll pins as well. They have a sling mount, bayonet lug and front sight.
Swiss SIG 55x series uses two large spring pins.
The stress applied by bayonet use may not be taken very seriously today, but 50 years ago it was a very real consideration.
Sure - and the taper pins worked well. They are a little more tricky to drill as the depth maters. With a spring pin you just do a hole all the way through. I would consider the spring pins to be the more modern way to do it.
All excellent points guys, especially the bit on the 416, a pretty parallel application. Im interested in knowing if the roll/spring pins are in fact more durable or if HK used them because thats what they prefer to use. I can see them being lower cost from manufacturers standpoint, taper pins seem to be more labor intensive.
Spirol(R) pins come in light, standard, or heavy duty versions. So one can always find a pin to meet the requirement - either by using a larger diameter or going to a heavier duty version. It should not take much to secure a low-profile gas block that is protected by a rail.
With a spring pin you just do a hole all the way through. I would consider the spring pins to be the more modern way to do it.
I would bet that the large groove in the barrel is machined when the gas port is drilled.
Notice in many of these euro designs, there is no shoulder behind the gas block journal.
The pin groove is the sole locating feature for the gas port.
The gas block is pre-machined with the pin hole.
Assembly should not require any special alignment jigs.
Just fit them together and knock the pin in.
The heavy duty 3/16" (.187") Spirol has a double shear strength of 4500 lbs, which is probably about 150% of a single 2/0 taper pin (can't find exact info), that seems like plenty.
Wow, excellent info in this thread.
With all the lo-pro gas blocks tucked under rails on ARs these days i wonder if these spirol pins make more sense for us too?
Do the HKs use Spirol pins or spring roll pins? Big difference.
Do the HKs use Spirol pins or spring roll pins? Big difference.
Spirol pins are coiled spring roll pins.
Slotted spring roll pins are the kind to avoid.
HK uses the Spirol style.
Using taper pins I have had the sight tower get canted from receiving a hit to the gas block. I doubt using a less firm mounting solution is a good idea.....
HK uses the Spirol style.
Thank you.
K.L. Davis
11-28-11, 15:12
Taper pins are strong, but are also easy to assemble... they do not gall and bend, time is money. The correct size for a FSB pin is a 2/0 pin. A 2/0 pin has a head diameter of 0.141, the taper is 1/4 inch for every foot and the small end size is determined by the length of the pin.
To really impress the chics, the size of the small end is the diameter of the large end, minus (the length of the pin X 0.02083) :lazy2:
To really impress the chics, the size of the small end is the diameter of the large end, minus (the length of the pin X 0.02083) :lazy2:
Those must be some real party girls... :lol:
Suwannee Tim
11-29-11, 17:34
....To really impress the chics, the size of the small end is the diameter of the large end, minus (the length of the pin X 0.02083) :lazy2:
It is actually 0.02083487643024583302.....:D
apexcncshop
11-29-11, 20:30
I have been experimenting with using coil spring pins for a couple of years, allows notching the barrel in the same op as fluting and drilling the gas port. I might lean toward solid pins if I was mounting a bayo, but for a concealed low pro there are advantages, including no risk of bore deformation by driving a wedge perpendicular to it.
so, it sounds like we need a straight, solid pin with a keeper on it.
so, it sounds like we need a straight, solid pin with a keeper on it.
Thats a joke, right?
I kinda like the idea. The keeper would have to be pretty damn well engineered. Not sure if something like the internal spring clips geiselle uses on their trigger pins would hold up but that seems like a reasonable place to start.
Thats a joke, right?
;):thank_you2:
Ned Christiansen
11-30-11, 11:42
A single split pin is adequate for low-pro gas blocks-- 3/16 or even 1/8. Since they don't have the height, a bonk on one imparts much less stress on the pin-- and of course they are often protected anyway by the fore end.
For original-design FSB, taper pins only as far as I'm concerned. Several outfits are using straight pins but they are too dependent upon a perfectly-sized, reamed hole. I've seen a good many of them missing or hanging out 1/2" getting ready to take a trip. I LocTite them. tap them back in, and stake them. Might create a hassle for whoever tries to take it off some day but.... I only care about keeping the gun running now.
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