View Full Version : Is the little rubber extractor spring buffer insert really necessary???
Of course I have them in all the extractor springs in all my bolts, but I always wondered if that little rubber buffer really does anything at all? I use the Colt copper colored extractor springs with the black buffer insert, but is there an extractor spring out there that doesn't require them?
I have not used them in some time, but recently began using them about six months ago. I notice no difference.
The colt extractor spring is designed to apply proper tension to the extractor with the rubber buffer installed.
The colt extractor spring is designed to apply proper tension to the extractor with the rubber buffer installed.
So if you find a stronger spring than the Colt spring then I'd imagine you could forgo the little rubber buffer?
Of course I have them in all the extractor springs in all my bolts, but I always wondered if that little rubber buffer really does anything at all? I use the Colt copper colored extractor springs with the black buffer insert, but is there an extractor spring out there that doesn't require them?
The little rubber buffer is exactly what the name implies - a buffer, damper, or shock absorber, whatever name you like to call that part in a spring system. You will note that most other designs have a longer springs in deep holes, and the friction between the spring and the walls on the spring hole provides the damping action. It is primarily there to prevent over-compression of the spring when slammed against the rim.
If you make the spring too much stiffer, you will start to run the risk of not reliably snapping over the rim with dirty or rims with little chamfer, and you still have the issue of possible over-compression.
It is there to prolong the life of the spring, it is not really adding that much "extra tension". So, yes you can remove them and not notice a difference in the short run, but the extractor spring life will be shortened.
So if you find a stronger spring than the Colt spring then I'd imagine you could forgo the little rubber buffer?
However, no one yet has come up with a spring that gives optimal performance without the the buffer. I'm not sure how the buffer makes extraction better. Is it a shock absorber? Does it make a necessary change to the spring rate/curve that cannot be achieved with the coil spring alone? Does it reduce spring fatigue? All or some of the above?
What I do know is, the Colt extractor spring is the best and must be used with the spring buffer. I've seen O rings break down, but never the buffer, even with "other" extractor springs.
NickySantoro
08-27-21, 10:38
The purpose of the insert is to minimize lateral deflection under load, that's it.
The purpose of the insert is to minimize lateral deflection under load, that's it.
That makes sense.
I've seen O rings break down, but never the buffer, even with "other" extractor springs.
I recently changed the extractor springs in several bolts to the Colt copper-color type. One of these was unused, in storage for about 15 years, and the buffer in it was crumbling.
I recently changed the extractor springs in several bolts to the Colt copper-color type. One of these was unused, in storage for about 15 years, and the buffer in it was crumbling.
I'll add that to my notes. Thank you.
The purpose of the insert is to minimize lateral deflection under load, that's it.
Lateral deflection?
What would cause the spring to deflect laterally? It is constrained laterally.
The rubber thing is a damper.
If you apply a sudden load to a mass, such as the angle of the extractor snapping over the rim, the extractor is rotated and the spring is suddenly compressed. As small as it might seem the spring and extractor have inertia and so both will move further than required just to snap over the case rim and compress beyond the spring more than strictly required. With the extractor spring being very short and with few coils, this slight over compression from inertia places very high torsional stresses in the spring wire.
The buffer damps out the extractor over travel.
The early M16s did not have the buffer and broken extractor spring were common.
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Lateral deflection?
What would cause the spring to deflect laterally? It is constrained laterally.
The rubber thing is a damper.
If you apply a sudden load to a mass, such as the angle of the extractor snapping over the rim, the extractor is rotated and the spring is suddenly compressed. As small as it might seem the spring and extractor have inertia and so both will move further than required just to snap over the case rim and compress beyond the spring more than strictly required. With the extractor spring being very short and with few coils, this slight over compression from inertia places very high torsional stresses in the spring wire.
The buffer damps out the extractor over travel.
The early M16s did not have the buffer and broken extractor spring were common.
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Now that first image is interesting (especially with the fairly low round count indicated), but the spring itself has changed since then, so I wonder how the newer copper colored ones would last without the rubber buffer?
I also gotta ask, but is there an issue with installing an extractor spring with the big end of the spring facing the the bolt instead of clicked down into the little pocket in the extractor? I mean, other than the possibility of loosing the spring and insert every time you remove the extractor from the bolt. ;)
Sound like you have project. :blink:
By the way, of the three production variations of extractor spring assembly, there are only two different springs and two different buffers.
The final M16A1/A2 extractor spring assembly (8448755) was made from the 8448753 spring and 8448754 buffer.
The first M4 extractor spring assembly (12972692) was made from the 8448753 spring and 12972693 buffer.
The current M4 extractor spring assembly (13004786) is made from the 12999901 spring ans 12972693 buffer.
The 8448753 spring (silver) has 0.022" dia, music wire, with 4 coils, 0.151" OD, and provides 4.2 lbs when compressed to .112"
The 12999901 spring (gold) has 0.026" dia, music wire, with 4 coils, 0.151" OD, and provides 8.4 lbs when compressed to .112"
The 8448754 buffer (blue) is made from fluorosilicone rubber, with a hardness of 60 Shore.
The 12972693 buffer (black) is made from Buna-N elastomer, with a hardness of 80 Shore, and 6.5% larger in diameter.
If you have a regular old 20" barrel AR-15 any of these will work just fine. With a 16" mid-length, any should work but the latter two (12972692 or 13004786) would be better.
Carbine length gas systems, unless full auto, also should work with the latter two (12972692 or 13004786), with the gold being preferred.
In short, unless you are currently experiencing extraction problems, there is no need to be changing springs or buffers.
Sound like you have project. :blink:
By the way, of the three production variations of extractor spring assembly, there are only two different springs and two different buffers.
The final M16A1/A2 extractor spring assembly (8448755) was made from the 8448753 spring and 8448754 buffer.
The first M4 extractor spring assembly (12972692) was made from the 8448753 spring and 12972693 buffer.
The current M4 extractor spring assembly (13004786) is made from the 12999901 spring ans 12972693 buffer.
The 8448753 spring (silver) has 0.022" dia, music wire, with 4 coils, 0.151" OD, and provides 4.2 lbs when compressed to .112"
The 12999901 spring (gold) has 0.026" dia, music wire, with 4 coils, 0.151" OD, and provides 8.4 lbs when compressed to .112"
The 8448754 buffer (blue) is made from fluorosilicone rubber, with a hardness of 60 Shore.
The 12972693 buffer (black) is made from Buna-N elastomer, with a hardness of 80 Shore, and 6.5% larger in diameter.
If you have a regular old 20" barrel AR-15 any of these will work just fine. With a 16" mid-length, any should work but the latter two (12972692 or 13004786) would be better.
Carbine length gas systems, unless full auto, also should work with the latter two (12972692 or 13004786), with the gold being preferred.
In short, unless you are currently experiencing extraction problems, there is no need to be changing springs or buffers.
Ha! No real project here, but I've just always been curious about that dang little insert that I always assumed was mostly pointless... Now I know it's not so pointless after all and I appreciate you clearing that up for me. :smile:
The other question I had regarding if it matters which part (bolt or extractor) you install the big end of the spring towards is because I do have a few stripped bolts that I'm finally getting around to assembling and I'm not finding an easy way to get the spring popped down into that little recess in the extractor... Sure you can press it straight down into the extractor and get it to seat kinda crookedly, but the manual says you need to push down while twisting it (of course I know the correct way to twist is determined by which way the spring is wound). I just haven found a small enough pair of pliers to fit inside of and grab hold of the spring to give it that twist while pushing it down... I'd really love to see how Colt would go about assembling the springs into the extractors, but I'd love to see how Colt would go about any aspect of AR15 assembly.
I have nothing but the newer Colt copper colored extractor springs with black buffer inserts in my inventory, so I'm set there. But I'm always looking for improvements that can simplify things and eliminate parts.
Looks like I'll just end up having to push the springs straight down in and seat them with a punch I guess... I'm kinda out of ideas to find a more "proper" way to do it, but I'm also thinking I might end up over compressing and possibly damaging the spring in going about it using that method?
The big end of the spring is around 0.165". The hole in the extractor is around 0.156". there is only 0.009" interference.
The hole in the extractor is not straight in, but angled backward 3 degrees, so the spring will always look a little "crooked" even when installed properly.
If the twist-and-push method doesn't seat the spring completely, you can use a jeweler's screwdriver and press directly on the last coil to seat it best you can. No need to worry about perfect seating, as long as you have it in there well enough it doesn't move, you can install the extractor. Once you've put a few rounds through the bolt, the extractor spring will be fully seated.
And, there is no reason to remove the spring, once installed, unless it becomes broken.
The big end of the spring is around 0.165". The hole in the extractor is around 0.156". there is only 0.009" interference.
The hole in the extractor is not straight in, but angled backward 3 degrees, so the spring will always look a little "crooked" even when installed properly.
If the twist-and-push method doesn't seat the spring completely, you can use a jeweler's screwdriver and press directly on the last coil to seat it best you can. No need to worry about perfect seating, as long as you have it in there well enough it doesn't move, you can install the extractor. Once you've put a few rounds through the bolt, the extractor spring will be fully seated.
And, there is no reason to remove the spring, once installed, unless it becomes broken.
Thanks for the advice! And I had no idea that the hole in the extractor was actually angled. I'm surprised that I'm still learning little things like this even after being at this for 20 years.
The big end of the spring is around 0.165". The hole in the extractor is around 0.156". there is only 0.009" interference.
The hole in the extractor is not straight in, but angled backward 3 degrees, so the spring will always look a little "crooked" even when installed properly.
If the twist-and-push method doesn't seat the spring completely, you can use a jeweler's screwdriver and press directly on the last coil to seat it best you can. No need to worry about perfect seating, as long as you have it in there well enough it doesn't move, you can install the extractor. Once you've put a few rounds through the bolt, the extractor spring will be fully seated.
And, there is no reason to remove the spring, once installed, unless it becomes broken.
lysander to the rescue! Thanks dude.
Lysander, thank you for your contributions to this thread. I learned something that will be added to my notes.
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