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I do like 5/8-24 threads on 5.56 barrels too. 1/2-28 was designed around the super skinny A1 profile. Outside of pencil barrels it’s just too small…

I love most everything about your 6.8 barrels and prefer 4150 nitride over stainless (keep the bare steel barrel extensions though- that’s the best way to go and are conducive to feed ramp polishing).
The only thing I would like to see change is to use smaller gas ports for less gassing with hand loads and suppressor use. At least for the shorter 12.5” barrels and such. On an SBR with a can I’m not gonna run anemic (and expensive) factory loads…
 

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Discussion Starter · #22 ·
I do like 5/8-24 threads on 5.56 barrels too. 1/2-28 was designed around the super skinny A1 profile. Outside of pencil barrels it’s just too small…

I love most everything about your 6.8 barrels and prefer 4150 nitride over stainless (keep the bare steel barrel extensions though- that’s the best way to go and are conducive to feed ramp polishing).
The only thing I would like to see change is to use smaller gas ports for less gassing with hand loads and suppressor use. At least for the shorter 12.5” barrels and such. On an SBR with a can I’m not gonna run anemic (and expensive) factory loads…
Once I am running more efficiently I'll offer customer requested port size
 

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Have you guys shot a 5R side by side with a 3R to compare them? Curious as to why you say the 5R is better
Same, I'm curious as to what the perceived difference is. I had an ARP 16" Scout 3R, currently running a DD 16" 5R. I've not noticed any difference with lead bullets, but the 3R is faster with monolithic, then again it's also ARP vs. SPC II chamber, so that will have an effect as well. I only currently shoot factory loads or custom shop loads like Druid Hill.
 

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Here's what I do know, that 5R has some perceived advantages over 6 Groove or even 4 Groove because of the angles at the edge of the rifling that limit or reduce deposits. The same would apply to 3R. They tend to run cleaner and be easier to clean. Aside from the maintenance issue, generally there isn't much difference except maybe with really hard projectiles.

I am building a new upper for a relative over the next few weeks as parts arrive (just an upper) and suggested ARP's scout barrel to him, so I may have a chance coming up to test directly, side by side, my DD 16" 5R against the ARP 16" 3R Scout on the same lower, same lots of ammo, same day, same chrono, same weather conditions. Both barrels are 16" mid-length gas ports and both are hand built by me using the same process, same LWRC bolts, carriers etc. They are clones aside from the barrels. All ammo is factory loaded (Hornady, DHA and S&B).

I'll try to test either 110gr OTM or 110gr VMax, 110gr FMJ, 120gr SST loaded by DHA and maybe some 120gr MKZ loaded by DHA BEFORE they changed the powder charge. I'll be sure to watch for signs of pressure in the ARP as I know some of the more recent ARP's had issues with the older loadings of MKZ by DHA. I've not had any such issues with my SPC II chamber and that load.

5R vs. 3R
Chrome Lined vs. Nitrided
SPC II vs. ARP chambers

Three key differences, but do they add up to significant advantages in velocity? That I don't know and I think it's going to highly depend on the specific load and bullet. I'd expect MKZ to benefit the most from the ARP vs. my DD.

I do know for a FACT that 110gr OTM factory (Hornady) was NO faster with my own 16" Scout barrel than it is with my 16" DD. I also got 50 FPS lower with 110gr TSX from my 16" ARP than what was listed on the box by Wilson Combat (I got 2505 vs. the spec 2550 FPS), but that load may have been tuned for Wilson's 4 grove stainless barrels, but it was solid copper.

I'm curious to see the results side by side, because chrono's can indeed vary as does MV based on a variety of ambient conditions, but at least I can do a direct comparative study as I set up this new upper.
 
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