Cyclic speed... and why you want it to be correct. ( Or commonly described as being "Overgassed"
I know it sounds a little complicated... but it isn't.
You need everything to be timed correctly to avoid feeding and extraction issues.
The BCG cyclic speed can't run faster then the magazines springs can push the next round up...
If your firearm is "overgassed" the BCG maybe trying to move back, before chamber pressure has dropped enough to "easily" extract the empty case.. and that will rip rims off or cause the extractor to slip off, leaving the empty in the chamber. Also... if the empty case is left in the still under high pressure chamber, lots of times that can cause popped primers ( the primer is no longer being supported by the bolt face, and that pressure will look for a easy place to vent.. pushing the primer out )
The ejector needs a correct amount of time to pull the empty case out...
If your firearm is "overgassed" it is basically from the gas port being to large. I have built numerous different brand large frame AR's, with numerous different brand barrels ( 11 to date ) ... so far all have been overgassed.
The excess gas from a to large gas port ( or even a industry standard gas port ) will cause a very fast cyclic speed. IE... not enough time for the various parts to function properly.
Think of it like a water hose v. a firehose.... same water pressure... but the firehose has more volume of water at the same pressure. The .308 case has considerably more propellant being burned down the barrel.. and much more gas being produced.
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Soooo... to fix the "overgassed" aspect... ( And remember that doesn't mean a firearm is overgassed in all environments ( cold weather with lube that works well in heat, not cold arctic temps ) , gritty nasty conditions, and less then ideal lubing conditions... at those moments, the added gas helps insure function )
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IMHO... an Adjustable GB is the best way to slow down the cyclic speed... you are limiting the volume of gas being used to function the firearm. Limiting the gas means the shove used from the gas to operate the BCG is milder... still the same pressure, just less of a blast of it.
That means the bolt remains closed slightly longer ( milliseconds is all it takes ) and the chamber pressure, drops to a more suitable milder extraction pressure.
The BCG at this resticted gas flow / lower cyclic speed, allows the mag spring to keep up... allows the case milliseconds more time to be ejected ... allows the primer to be fully supported during extraction... and even allows the recoil spring to be more cooperative.
An Adj. GB also allows a softer perceived recoil.... the kick is going to be the same from a .308 / 6.5CM no matter what you do... but if the BCG, buffer and recoil spring aren't flying back and forth super fast ( with a adj. GB ) ... the recoil impulse is spread out over a slightly longer time period.. again milliseconds... but you can tell immediately.
The same thing can typically ( and easily ) be done to a AR15 Carbine gas system ( or any length gas system ) with heavier buffers or recoil springs... all it is doing is slowing down the bolt opening.
You can also add heavier buffers and recoil springs to a Large frame AR, combined with an Adj. GB.
My rifle stocked .308 / 6.5 AR's run smooth as silk with a 9.3oz .308 rifle length buffer, a Tubbs .308 Flatwire recoil spring and a SLR adj. GB.
My carbine stocked Armalite buffer tubed .308 /6.5CM run smooth as silk with 5.4oz buffers, A Tubbs .308 Flatwire recoil spring, and a SLR Adj. GB. ( The Tubbs .. being a flatwire spring takes up lees room ... so it can be used anywhere )
The end result from those add on's is.... fired brass is in great shape( yanked out of the chamber at more moderate pressures )
, easier on all the cycling parts, easier follow up shoots, and very mild perceived recoil.
I wish all .308 / 6.5CM barrels came with smaller gas ports... but so far I have only seen a proper sized gas port ( IMHO ) in my just received Krieger 6.5CM 22" barrel.... or better said.. all the other barrels benefited from all the same add-on's.
IMHO.... plan on installing a Adj. GB on all .308 / 6.5CM barrels.... especially if they are middies or rifle length gas systems.
The added cost of a Adj. GB will transform your large frame AR's perceived recoil like night and day.
On that note... please remember.. I am just some schmuck form the internet... Lol.. and not everyone will agree with me... but everyone that fires my Large frame AR's comments immediately... "there is no recoil"...so I guess I am doing something right.... Lol
Again... Your PSA will run straight out of the box, albeit a little overgassed ( proper parts and assem. required
)... but those add-on's do make it softer shooting.
And when considering the price of decent ammo... they are a small price to pay for a more pleasant to shoot firearm.
