08-22-2011, 06:25 PM
Yup. Your buffer is way too light for the Grendel and especially 120gr pills. I would try an H2, ST-T2, and even an H3. You have a carbine spring, and most likely an AR15 bolt carrier at 9.0 oz. I just weighed an M16 bolt carrier and it was 9.4 oz., and I also weighed a Bushmaster (shaved) AR15 bolt carrier at 8.7 oz. Tactical machining has a great deal on H2 buffers right now for about half the market price.
https://www.tacticalmachining.com/
What happens with a lighter weight operating system is that the bolt carrier moves too quickly to the rear, and not enough gas pressure builds in that chamber formed by the back of the bolt gas ring flange, gas rings, and carrier recess for the bolt. As it moves rearward too quickly, it bleeds gas out the vent holes in the carrier that you can clearly see from the ejection port, and you get a short stroke sometimes. This is where the balanced operating system needs either more weight to resist the gas impulse, or less gas. I would suggest more weight to the bolt carrier and buffer.
A fast unlock time will also run your brass harder, so you definitely need to adjust your system to provide the correct balance for the gas you're running through it. The adjustable gas block would be a potential solution to that particular load, giving you milder handling, but I would still recommend starting with your carrier and buffer weights first. Those 2.9-3.0oz carbine buffers are good for .223 carbines pushing 45gr bullets, and maybe 55gr through a 14.5" pipe with carbine gas system, or shaved AR15 carriers pushing the lighter loads. They are not anywhere near ideal for the Grendel or even 5.56 NATO loads in carbines.
https://www.tacticalmachining.com/
What happens with a lighter weight operating system is that the bolt carrier moves too quickly to the rear, and not enough gas pressure builds in that chamber formed by the back of the bolt gas ring flange, gas rings, and carrier recess for the bolt. As it moves rearward too quickly, it bleeds gas out the vent holes in the carrier that you can clearly see from the ejection port, and you get a short stroke sometimes. This is where the balanced operating system needs either more weight to resist the gas impulse, or less gas. I would suggest more weight to the bolt carrier and buffer.
A fast unlock time will also run your brass harder, so you definitely need to adjust your system to provide the correct balance for the gas you're running through it. The adjustable gas block would be a potential solution to that particular load, giving you milder handling, but I would still recommend starting with your carrier and buffer weights first. Those 2.9-3.0oz carbine buffers are good for .223 carbines pushing 45gr bullets, and maybe 55gr through a 14.5" pipe with carbine gas system, or shaved AR15 carriers pushing the lighter loads. They are not anywhere near ideal for the Grendel or even 5.56 NATO loads in carbines.