I sent an email to ARP asking what size of port they drill on their 16" 5.56 Lightweight barrel, 4150 CMV, Wylde chamber.
In their FAQ section the question was asked if steel cased ammo can be used in an ARP chamber, Answer is
Can I use steel case ammo in ARP rifles?
Yes, the mid gas system allows more time for the cases to shrink back down aiding extraction. The Nitro treatment makes the chambers 70 Rockwell and very slick also aiding extraction, Our Nitro carburized barrels were made to handle steel cased ammo.
The question was asked what buffer did they recommend with their barrel. Answer to both questions are as follows:
.082”
The standard carbine buffer should work fine.
If the ammo you choose to shoot ejects forward of 3 O’clock you can change to an H2 buffer.
Apparently someone complained about accuracy from sustained firing with this barrel. Answer from them:
These are lightweight combat type barrels not target barrels. Common accuracy with decent ammo is 3/4-1.5" at 100yds, 55gr FMJ can be worse.
Not a point but an FYI. Seems lots of discussion has come up on what the port size does your barrel have and what buffer weight should I use.
I asked the manufacture what size they drill their ports and what they have seen work buffer wise.
Just a matter of reference.
Thank You Grant. From what I had found here, The .082" gas port seemed to be a little larger, needing a heavier buffer, spring or both to keep from battering it’self to death.
Midlength gas setup so .082" is not as huge as it would be on a carbine setup.
I’ve been using one of their 16" midlength uppers (slightly heavier SOCOM barrel weight, but still a 5.56 16" midlength) for a little over a year now. It’s been used with several lowers, being setup with (1) H buffer and GI spring, (2) H buffer and Springco blue spring, and (3) VLTOR A5 system with standard A5 buffer. The BCG was lubed with Froglube paste prior to any use. In the first 10 rounds from new, using H buffer and GI spring, I had 3 failures to extract. Since that time I have had no failures of any kind, in temperatures from 80’s to 20’s, much of it competition use (fairly rapid fire for 1-3 minutes at a time). ITS/ARP mentions that their bolts fit very tight when new, and that plus ordinary break-in is what I attribute the 3 initial FTEs to. Felt recoil and speed of operation seem normal for a 16" midlength, neither harsh nor sluggish.
I think a standard H buffer will work fine. The carbine weight or H2 probably also fine.
I was going to say something about this earlier and I wish I had.
There has been an ongoing discussion on 68forums about port sizes and Clint’s data matches that. I’m running an older ARP 18" 6.8 middy barrel and the port on that is .086. Harrison normally runs a .082 port on those barrels but mine was made around the time that he was trying to make them run reliably with Remington UMC SAAMI ammo so he wanted more gas for the weaker rounds.
The only flaw I can think of with that theory is that (and I’m not sure about this) with the increased dwell time of an 18" barrrel over a 16" barrel, you would think that the port would be slightly larger for a 16" barrel. I could be over-thinking the whole thing though…
If you port barrels to run with true m193 and everyone uses cheap ammo how many call backs do you get and how many shipping charges do you eat?
The OP asked about shooting steel case Tula, it takes a .082 just like it does to run American Eagle and Remington UMC.
As a manufacturer I think it’s better to port the barrels to run what works with a wider range of ammo and what most shoot not just the upper end and everything else short strokes.
How many times have you been to the range and hear someone say “this POS wont cycle”…and most are using the cheapest ammo they can find at Wally World. That same crowd wouldn’t notice the m193 cases landing forward of 3 O’clock.
The high speed low drag crowd runs H2 buffers and heavy springs anyway. m193 drops right around 3-3:30 setup that way.
OP, what I told you is how we port the barrels. If you use cheap steel case they will run fine, if you use m193then you may need a H2 buffer to slow things down. As far as the accuracy thing, I’m just truthful. Some guys will buy a $200 lightweight barrel and then say “this thing wont shoot 3/4” with the cheapest ammo made, what’s wrong with this thing".
Shoot 69 or 77gr SMKs with 24gr Re15 off a bench with a good trigger and scope and shooting skills and they’ll shoot under an inch.
I have no idea how they will shoot with Tula off the tailgate of a truck using a $28 red dot from Walmart.
I owned an ARPerformance upper in 6.8SPC (a mid-length SOCOM barrel), and with factory ammo (Barret 6.8), the thing was a tack driver: sub-MOA as long as I did my part, and sometimes even when I didn’t do my part.
When I buy from Harrison, I buy with confidence and without hesitation.
He answered my question and confirmed it before the masses.
Most of my ammo is brass cased M193 and Amer Eagle A223, but I do have a good bit of Tula and Silver Bear left over when this upper wore a Spike’s Tactical 5.56 chamber CL barrel. I purchased this barrel after reading and others personal experience with ARP products. Not being a precision shooter with my AR, I would not expect TULA to shoot like match ammo.
Come on Fall so I can enjoy shooting more.
RDS is a Aimpoint H-1 2MOA on a Seekins fixed mount.
Just sighted in my rifle with 16" scout barrel and five shot groups were right at 1" with factory SSA 110gr accubonds. Haven’t had the change to roll some of my own loads but when I do I’m positive the group will shrink up. For the price, Harrison’s barrels can not be beat.
