For my first build I went to great lengths to find an ideal buffer and spring configuration for my gun. I wanted my build to be a sweet shooter, so I started out with a 14.5" middy for its purported benefits over a carbine length gas system in combination with an M16 BCG. To tune the buffer and spring to the rest of the gun I turned to the forums but I was discouraged by the trial-and-error approach that is commonly advised. I didn't want to buy a bunch of extra parts and I wanted an answer that would satisfy my perfectionist side.
Due to the lack of hard numbers out there I had to find a way to mathematically represent different combinations of buffer weight and spring tension in order to find an optimal compromise between reliability and reduced recoil. Now, I am by no means an engineer or an expert so take all this with a grain of salt.
To start with, I dug up a chart of technical info on the forums that states that a Colt GI carbine spring imparts 6.040 lbs of force when compressed to 6.902". A standard H buffer weighs 3.8 oz. Since both of these components work in combination with each other I decided to use the product of the measurements as a unit of comparison. In order to do so I multiplied the spring weight by 16 so that the measurement would be in oz. So 6.040 x 16 = 96.64 and when multiplied by the buffer weight of 3.8 oz, we get a product of 367 units. Units of what you ask? **** if I know; like I said, I'm not an engineer. Think of this number as a unit of comparison.
So now that we have a number for the intended setup for a 14.5 middy we need to find a number for the point at which a setup will induce short cycling with the weakest ammo that you intend to use. According to various anecdotal reports, a Sprinco blue spring with an H2 buffer is where we will commonly start to see short stroking.
To get the info needed for this, I emailed Sprinco to find out how much heavier their blue spring is than stock. I got a prompt response of 17% (thanks Alan). This info coincided with the numbers on the chart that I dug up earlier so at this point I was starting to feel pretty good. So using our previous formula, a Sprinco blue with H2 buffer gets us 548 units.
By now, I assume that we are both on the same page, so in the interest of brevity I am going to present to you the information just as it appears on my notepad.
GI spring H buffer 367* intended weight
Sprinco blue H2 short cycles wolf 548
GI spring H2 does not 444
Failure point is somewhere in the middle at 496 (presumed)
15% below failure rate is ideal
(421)
367* 26% below failure rate of 496
405 18% below failure rate
429 14% below failure rate
452 9% below failure rate
GI spring H 367* intended weight
GI spring ST-T2 406
GI spring H2 444
Blue spring C 357
Blue spring H 452
Blue spring ST-T2 500
JP spring H 393
JP spring ST-T2 434
The setup I arrived at is the JP tuned and polished extra power buffer spring (7% stronger than USGI) and the Spikes ST-T2 buffer. This setup is a comfortable margin below the failure rate while still being 15% heavier than the stock setup. As a basis for comparison, M193 ammo is very roughly 10% "hotter" than bottom of the barrel (think wolf) .223 ammo. As an added benefit, both of these components offer a reduction in cycling noise, and the ST-T2 does not rattle when shaken like a standard buffer would. I should also mention that my rifle functions perfectly with whatever I feed it.
So there you have it. I realize the unscientificness of this study, so feel free to pick it apart.
Bookmarks