I’m currently researching parts for a general purpose carbine I’m building for my father. This isn’t a dilemma or issue per se, more like a point of curiosity brought on by the research I’ve done.
From reading other threads, including the knowledge base stickies, the consensus seems to be:
“You want the heaviest buffer your gun will run reliably when dirty and less than optimally lubed… but not a buffer that only runs well in perfect conditions. (MarkM)” The purpose as I understand it being to eliminate bolt bounce and reduce felt recoil impulse. Most other threads I see here recommend an H2 buffer weight on a carbine-length system.
However, if used in conjunction with an adjustable gas block, you effectively reduce the force with which the BCG impacts the buffer assembly. So my question is: what is the optimum balance between buffer weight and an adjustable gas system? Should I lean on the adjustable gas block to tune the force down to run a standard carbine buffer? Or go with a heavier buffer and rely less on the gas adjustment? The barrel that will be used is a 16" mid-length, no plans to run a suppressor.
Also, if I’m dramatically over thinking this, let me know.
Welcome! I think we all dramatically over think things on occasion. You can accomplish what you’re after with a Springco blue spring and an H or H2 buffer. My thoughts on building for someone else would be their propensity to adjust the GB if it was available and whether or not they would have a monogamous and good quality ammo supply.
IMO, where the AGB shines is in a SBR that may be suppressed or used both ways. It’s also a good choice for tuning a competition rifle. Here you want enough spring and buffer to run reliably. Make sure you get a high quality BCG and bbl like BCM, etc. that way you are sure to be in spec.
I have a BCM 16" and 14.5" middies and both run very well with blue Springco springs and H buffers. They both have std FSBs. I’m building a 10.3" MK18 to suppress and that will have a Syrac AGB on it.
It’s basically choice but, as a gun builder, I take the customer’s tendency to tinker into account when building a gun.
IMHO it depends on the purpose the carbine will serve. You said “general purpose” so that implies home defense might be included. Some folks with much more experience than me would recommend staying away from devices that can shit the bed at the worst possible time due to unneeded complexity. Not much to go wrong with a fixed gas block, other than it moving if set screw loosened up on a lopro. Thus staking, loctite and/or pinning are reommended. In addition to block coming loose, adjustable gas blocks have an adjustment screw that can potentially move. Not an issue if it unscrews, but can turn firearm into single shot if it turns clockwise, reducing gas to gas key. Is this likely? Probably not. More likely is adjustment screw freezing in place due to firing residue and heat.
In the 3gun world adjustable gas is a staple, as it allows a significant reduction in recoil and sight picture movement, as you mentioned, but mostly in conjunction with a low mass bolt carrier and buffer. Lots of info on this in the Rifle subforum on brianenos.com. The one one that seems most liked is the Sentry model by SLR.
Without going to a lighter carrier and especially buffer, an adjustable gas block would help little, unless the barrel’s gas port is significantly oversized, unlikely with a quality manufacturer. Curious as to which barrel you plan to use.
Personally, even though I use my 16" carbine for 3gun competition, for now am going the route of heavier buffer, but reserve the option of using an adjustable gas block in the future, as the gun is pretty stable with the A5 system. Of course, I could easily change my mind if I fired a similar rifle with adjustable gas and light bcg/buffer and saw a really big difference…
Suspect a middle of the road answer to your dilemma is to run a midlength gas sysem rather than carbine, and the A5 system. If your dad finds the recoil/muzzle rise harsh,then go with adjustable gas and/or a muzzle brake.
Sparky - I think it very unlikely that he would tinker with the gas block, however your point on homogeneous ammo is something I hadn’t considered, thanks.
mpom - You are correct on likely uses, as this will probably be his only AR. I definitely agree on keeping things simple if the weapon will ever be used for personal defense. The barrel I will be using is a 16" BCM lightweight profile with midlength gas system, with a standard weight BCG.
I think for this specific build I will go with a fixed gas block and play with the buffer weights, but if anyone has any further information or experiences on balancing buffer weight and gas regulation I would be interested to hear it.
I would stay away from adjustable gas blocks for serious use guns. There are multiple reasons, but it’s mainly because it’s introducing another potential point of failure.
In my opinion a gun should run with a Rifle buffer, A5 H2, or Carbine H2 to be gassed right. Too light can be nice for recoil, but give up that forward mass for reliable feeding and chambering… leave that to the match homos.
I’ve been running a Syrac adjustable on a suppressed 11.5 that would otherwise have been scraped (the barrel) because is was retardedly over gassed.
I’d trust that sucker for serious use. I treat that thing poorly… just blast away a mag or two every week, never clean it… It runs like a mofo. I did do a spot check to see if the adjustment was froze up with carbon, and it was just fine.