What is your optic? What accessories have been added?
Optic is a Primary Arms 3x Microprism. I was gifted one. I used it on this rifle for it's weight of only 8 oz. It has been a good optic. It is extremely rugged, shockproof, waterproof, and prism's are known for their toughness. The reticle is etched and illuminated. It does not require a battery to use which adds addition resilience.
The 3X works at close quarters with both eyes open very well and offers magnification at some distance allowing me to keep the weapon light while still being able to use the longer range advantages of 7.62mm NATO. The optic is mounted on a LaRue Tactical Mini-ACOG QD mount.
The handguards are Midwest Industries G4 10.5" handguards. There is plenty of room for the gas block however the Riflespeed gas block does prevent use of the sling QD attachment at the very front of the handguard. It has not been an issue as the center QD mount works find. The sling is a Magpul MS1 two point sling and in the center QD mount is adjusted perfectly for both operating the weapon while wearing the sling, transitions, and keeping the weapon out of the way should you need both your hands.
The Gas Block is a Riflespeed .750 RS7521 with Riflespeed straight gas tube. It is pinned. It offers a robust and tool free adjustment and will be familiar to anyone owning an FN-FAL. Unsuppressed, it locks back on setting 8 reliably and ejects at 3 o'clock with a clean rifle. At full open on 12 with a clean rifle, it will rip the rims off the case every ~5th round. That is normal behavior in a fouled setting with a clean weapon. I broke the drive spring on the first M249 we got because it was "cool" to fire it on the fouled setting when clean as it's cyclic rate was ~1500 rpm. About the third burst, the weapon broke. My Squad Leader, SSG Luewellen, put his boot up my behind for it and I did not look so cool low crawling around the range.
That leaves me 4 adjustments unsuppressed to compensate for a fouled rifle or underpowered ammunition and 7 adjustments for suppressor's. It is exactly where RifleSpeed recommends.
The stock is a B5 Systems Bravo stock. It offers a solid cheek weld on the rifle without being bulky or adding unnecessary weight.
I mounted a Streamlight HL-X multifuel light on it. It is powerful enough to turn night into day. I do not use a remote pad as I like to keep my rifles clean and simple. With a Magpul Offset Aluminum light mount places the light exactly where my thumb rest's to operate the lights push button end cap. The light has a flip up cover to prevent light AD's and protect it when not in use. We would use NOD's to get to the target and get in place. When bullets were being launched, it was all taclights. Good taclight use makes nightwork much safer and much easier.
The rail covers are Magpul Type 2 with a Magpul Hand Stop kit. It gives me a good barrier stop, solid upright stance just like a vertical grip, and proper hand placement for taclight operation.
The BUIS are Meprolight FRBS self illuminated sights. They are zeroed for a 300 meter point blank zero meaning anything 300 meters or less requires no hold off to hit center mass.
The rifle was built as General Purpose Rifle not as a Designated Marksman rifle. Ruggedness, Reliability, and ease of use was the focus over precision fires. It is a a 1.2MOA rifle with Igman M80 ball which is more than sufficient for its purpose.
I selected the SFAR not only for its weight but the fact is the only lightweight .308 AR variant that uses a heavy profile CHF barrel as well as having many parts that are interchangeable with an AR15 so most parts are commonly available. The bolt is proprietary however and is an alloy of Ruger's design. So far it has held up to all the abuse I have put on the rifle but it is a "watch item". One of the things I really like about this rifle is the fact it offers very fast follow on shots compared to any other 7.62mm rifle I have shot. The bolt cycles extremely fast for a .308. Some guys with stock gas blocks have added heavier buffers as the stock buffer is a carbine length buffer at ~2.9 oz.
I never said they were dimensionally different, but there is a pressure difference, which you conveniently failed to cite. The differences, operationally, can be in the range of 4 to 14 Kpsi. So yes, some mil-surp ammo is going to be lower pressure and will fail to cycle some .308Win ARs. The chambers are the same and there really is no "danger" issues, just poor cycling with some ammo loaded to the lower pressures.