Just picked up a lightly used Ruger SFAR 308 16". What should I expect?

[MarkCO]

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.

[Ricklin]

Seems like they will be forever available. Years ago I had a Spanish Mauser from Century I think. These were originally chambered in 7mm Mauser. Spain had a crap ton of them, and rechambered them to 7.62 NATO.
It was always the caution around these rifles that 7.62 NATO was the only ammunition to be used, no .308 commercial ammo.
That's been 30 years ago or close, I still see these old spanish Mausers for sale. They were always poo pooed as being a weak action, yet I've not ever seen one blown up. I recall some testing done back in the day, they had a very hard time blowing one up. Do not consider this post a recommendation...it is not that.

[davidsog]

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.

[davidsog]

but there is a pressure difference,

CUP used by the military to measure pressure has no conversion to psi. This is the biggest fallacy that has led to so much misinformation. You can find a plethora of "conversion charts" listed by various gun clubs that are ALL based on nonsense.

For many years gun chamber pressure units had been commonly referred to as “pounds per square inch”, which was not technically correct. The older method of pressure measurement involves a piston through the side of the chamber compressing a lead or copper cylinder in which the measurement of the degree of compression is indicative of the maximum relative pressure generated. With the advent of the electronic transducer, it became necessary to indicate by some means the method and equipment used to determine the pressure values given. This is important, since the pressure values determined by one method cannot be mathematically converted to values for another, despite claims to the contrary. Likewise, the limiting pressure values for the different systems are not interchangeable.

https://saami.org/faqs/#lup-cup-psi-preassures

[stagpanther]

The SFAR does look compelling--mostly cause of it's light weight. I looked it up and you are necessarily wed to a proprietary bolt and extension lug schema; so if visions of swapping out different caliber barrels are dancing in your head (and are not produced and available from Ruger) it seems to me you might be disappointed. I have two 308/7.62 x 51/whatever you want to call it AR's, straight up non-adjustable gas blocks and they both will shoot and function with no issues on a mixed diet of cartridges--though the "twang buffer hit" might be a bit more pronounced than that of a tunable machine like the SFAR. I run Burris RT 3 prism optics on them--doing that right there is probably going to save you a pound over conventional scope and rings.

[44 AMP]

Years ago I had a Spanish Mauser from Century I think. These were originally chambered in 7mm Mauser. Spain had a crap ton of them, and rechambered them to 7.62 NATO.
It was always the caution around these rifles that 7.62 NATO was the only ammunition to be used, no .308 commercial ammo.

Century Arms was the US importer. But the Spanish did not convert their old Mausers to 7.62x51mm NATO. They converted them to their own Spanish 7.62x51mm cartridge, which was used in their CETME rifles. It is dimensionally identical to the 7.62 NATO but is loaded to a lower pressure and velocity.

I have not heard of any of the converted Mausers failing due to NATO ammo, but it is considered the upper end of "safe" working limits and since commercial .308 Winchester can be found loaded even higher, it is not recommended for use in the converted Spanish Mausers.

As to the Ruger SFAR, Ruger has a long history of making their guns to only take Ruger parts, other than some models which take the industry standard magazine. Your Ruger may take the standard AR mags but I wouldn't expect any of the other common aftermarket parts to just drop in, fit, and work.

Some might, but I wouldn't count on it.

[Recycled bullet]

Do Modern rifles overcome these obstacles with adjustable gas blocks and replaceable buffer weights and springs?

Is it a matter of the bolt battering the receiver due to excessive bolt velocity from being overgassed, or more a problem of excessive maximum average pressure for a particular chamber or gun mechanism/design?

[davidsog]

I recall some testing done back in the day, they had a very hard time blowing one up. Do not consider this post a recommendation...it is not that.

Yep.

Think about it. If the difference in the volume of powder due to a few thousands of an inch difference in case thickness is the cause of your rifle blowing up.....

Your rifle had a much bigger issue going on and was not serviceable in the first place.

If you are reloading and running out of room in the case to pack the powder charge....you are an accident waiting to happen and using a .308 round in a 7.62mm NATO chamber is not the cause of it.

Is it a matter of the bolt battering the receiver due to excessive bolt velocity from being overgassed, or more a problem of excessive maximum average pressure for a particular chamber or gun mechanism/design?

If it is engineered properly the bolt is not battering the receiver. Mine is not battering it.

[MarkCO]

Originally Posted by Recycled bullet

Do Modern rifles overcome these obstacles with adjustable gas blocks and replaceable buffer weights and springs?

Is it a matter of the bolt battering the receiver due to excessive bolt velocity from being overgassed, or more a problem of excessive maximum average pressure for a particular chamber or gun mechanism/design?

Yes, they are intended to be tuned with gas port size (or adjustable gas), buffer mass and spring rate. It's not a "design" issue as much as the tune for the specific round.

Receivers don't get battered. Triggers, trigger pins and the bolt itself are what take the abuse if an AR pattern rifle is significantly overgassed. It takes thousands of rounds to see the damage manifest.

[stagpanther]

Receivers don't get battered.

Well, not exactly. If there's an issue with the lower's clearance relative to the upper and/or the carrier doesn't properly clear the buffer tube "ears"--it can hammer that baby mercilessly. I've never encountered that with AR 15 parts--but the risk goes up when mix-and-matching AR 10 parts.

[MarkCO]

Originally Posted by stagpanther

Well, not exactly. If there's an issue with the lower's clearance relative to the upper and/or the carrier doesn't properly clear the buffer tube "ears"--it can hammer that baby mercilessly. I've never encountered that with AR 15 parts--but the risk goes up when mix-and-matching AR 10 parts.

Okay you are correct there. In fact, saw a lot of that when the "smaller .308s" were being tried out.

BUT, the title of the post is the Ruger SFAR, and no such issues there.

[veprdude]

Sometimes you get the optic first. Been waiting 8 years.

[Recycled bullet]

Originally Posted by veprdude

Sometimes you get the optic first. Been waiting 8 years.

How does it shoot?

[davidsog]

Sometimes you get the optic first.

Nice Optic.