07-26-2011, 01:51 PM
I just measured my ST-T2 buffer from Spike's, and it is 3.9 ounces, which is on the heavier side for carbine buffers in 5.56mm. I have been using it in the Grendel, and it works great for me on a mid-length 16" barrel with M16 carrier weight, and a standard AR15/M4 carbine spring from Brownell's. I'm also using a VLTOR low-profile clamp-on gas block. I unitized the carrier key to the bolt after checking gas tube alignment.
The standard carbine buffer weights for 5.56 that are on the market are 2.9 ounces, which is often too light in systems with a lot of gas flow. Understanding the system in context of a balance between buffers, recoil springs, gas port diameters, gas system lengths, bolt carrier weights, brass or case surface smoothness, propellant charge, bullet length/weight, chamber dimensions, chamber smoothness, and rifling twist helps understand how many variables are in play.
I have had problems with MI and bad QC on their gas blocks for my last AR10 build, where we discovered that the gas tube roll pin hole was cut way off of 90 degrees. If you're having inconsistent ejection patterns, something is awry. I would make sure your gas block is secured well, that the port hole is aligned with the gas block hole, and work my way back from there. One issue the bad gas block would have caused is that it torqued the gas tube out of alignment, which could have caused binding if we would have used it. (We didn't, of course.)
Another thing to consider is lubrication. If you're running dry, you will have inconsistent bolt carrier velocity, leading up to failures to chamber. Use some SLIP 2000 on your bolt carrier raceways, cam pin, and bolt band generously.
With buffers, it isn't the total weight of the buffer assembly that equals success, but the independent weights of the buffer body and internal buffer weights. Their combined weight resists the inertia induced on the reciprocating parts to prevent an excessively fast unlocking sequence (dangerous), but when the buffer body reaches the rearward point of the cycle, the internal weights continue rearward until hitting the back of the buffer.
Then the recoil spring drives the buffer and bolt carrier group forward until the parts strip a new round off the mag, feeding into the chamber, and coming to a stop against the barrel extension, then bounces off it often when the cycle is fast. The internal buffer weights continue to move forward until they hit the front of the buffer body to counteract this "bolt bounce" characteristic.
This is why internal buffer weights are more important than external buffer weight in a high power rifle caliber in the AR15. Here are a list of some different buffer weights, keeping in mind that this is the combined weight of the buffer and internal weights:
CMT (Continental Machine & Tool) standard carbine buffer: 2.9 oz.
CMT H Buffer 3.8 oz.
CMT H2 Buffer 4.1 oz.
Spike's ST-T2 4.3 oz. (listed) mine weighs 3.9 oz.
Armalite H3 4.7 oz.
Rifle buffer 5.2 oz.
9mm SMG buffer 5.4-5.5 oz. (but low weight internals-not for high power rifles)
Most buffers are made from Aluminum, with a combination of steel and tungsten internal weights. I think the 2.9 oz. has 3 steel, the H has 1 Tungsten and 2 steel, the H2 has 2 tungsten and 1 steel, and the H3 has 3 Tungsten weights. I'm not sure what's inside the rifle buffer, but it seems to work the best. The Spike's has High Density Tungsten Powder in it, so you don't have the impact of the internal weights rattling around, but you still have the dampening effect of the internal tungsten flying back and forth.
Here are some great high-speed camera videos of different buffer/ammo/gas system length comparisons:
http://www.youtube.com/watch?v=575Q0O41u5s
The standard carbine buffer weights for 5.56 that are on the market are 2.9 ounces, which is often too light in systems with a lot of gas flow. Understanding the system in context of a balance between buffers, recoil springs, gas port diameters, gas system lengths, bolt carrier weights, brass or case surface smoothness, propellant charge, bullet length/weight, chamber dimensions, chamber smoothness, and rifling twist helps understand how many variables are in play.
I have had problems with MI and bad QC on their gas blocks for my last AR10 build, where we discovered that the gas tube roll pin hole was cut way off of 90 degrees. If you're having inconsistent ejection patterns, something is awry. I would make sure your gas block is secured well, that the port hole is aligned with the gas block hole, and work my way back from there. One issue the bad gas block would have caused is that it torqued the gas tube out of alignment, which could have caused binding if we would have used it. (We didn't, of course.)
Another thing to consider is lubrication. If you're running dry, you will have inconsistent bolt carrier velocity, leading up to failures to chamber. Use some SLIP 2000 on your bolt carrier raceways, cam pin, and bolt band generously.
With buffers, it isn't the total weight of the buffer assembly that equals success, but the independent weights of the buffer body and internal buffer weights. Their combined weight resists the inertia induced on the reciprocating parts to prevent an excessively fast unlocking sequence (dangerous), but when the buffer body reaches the rearward point of the cycle, the internal weights continue rearward until hitting the back of the buffer.
Then the recoil spring drives the buffer and bolt carrier group forward until the parts strip a new round off the mag, feeding into the chamber, and coming to a stop against the barrel extension, then bounces off it often when the cycle is fast. The internal buffer weights continue to move forward until they hit the front of the buffer body to counteract this "bolt bounce" characteristic.
This is why internal buffer weights are more important than external buffer weight in a high power rifle caliber in the AR15. Here are a list of some different buffer weights, keeping in mind that this is the combined weight of the buffer and internal weights:
CMT (Continental Machine & Tool) standard carbine buffer: 2.9 oz.
CMT H Buffer 3.8 oz.
CMT H2 Buffer 4.1 oz.
Spike's ST-T2 4.3 oz. (listed) mine weighs 3.9 oz.
Armalite H3 4.7 oz.
Rifle buffer 5.2 oz.
9mm SMG buffer 5.4-5.5 oz. (but low weight internals-not for high power rifles)
Most buffers are made from Aluminum, with a combination of steel and tungsten internal weights. I think the 2.9 oz. has 3 steel, the H has 1 Tungsten and 2 steel, the H2 has 2 tungsten and 1 steel, and the H3 has 3 Tungsten weights. I'm not sure what's inside the rifle buffer, but it seems to work the best. The Spike's has High Density Tungsten Powder in it, so you don't have the impact of the internal weights rattling around, but you still have the dampening effect of the internal tungsten flying back and forth.
Here are some great high-speed camera videos of different buffer/ammo/gas system length comparisons:
http://www.youtube.com/watch?v=575Q0O41u5s