02-23-2024, 06:20 PM
Crummy QC could be the problem, yeah. Nothing really you can do there but substitute a different lot of powder and compare. Or a differemt powder, which OP does list
But even some of those values up there confuse me still....
First off however, I will note the QL and Grt both have some trouble effectively replicating these short, fat AR cartridges. Lots of info there on the 65 Grendel forum, which is the original case that the 6Arc comes from. Most times QL/Grt will only claim about 10% or 50 fps accuracy.
One thing I have had to do is change the Sebert factor from stock, dropping it to 0.45. Now that's just me and my own model so can't transpose it for gospel as I am not a software engineer or ballistician.
But on to other points for some clarification..
I have some RE-15 results, 103 Eldx, in my 22" uintah bolt action, of 2728 fps, and an estimated 54 ksi. And 103 Eldx with Lever in this bolt action, 2735 fps; 48 ksi for Lvr.
Your Lvr data for 29.0, estimates 53 ksi, which is above the chamber max but the actual load is below the Hdy data for AR's... Now the 29.5 Hornady max is not a guarantee. But if your barrel is over max, maybe you're too high? Or maybe the OAL is not set right, possibly too close to lands (hard to imagine for the AR's, but chamber dimensions can come into play). Some early 6 Arc barrels were reported to have short throats, there are posts on here about all that.
But back to AR Comp. Taking my RE-15 data (which is in the Hdy data) as a start and substituting Ar Comp for it, I get a massive pressure increase, around 15 Ksi. Implication being the pressure is rising much faster than the bullet can accelerate to give that gas any room. Or alternatively, finding a gas gun charge below 52 ksi, I wind up with 26.something, and only 2640 or so fps. trying your 25.6 shows me only 2550 give or take (admittedly still differs from your actual in the low 2300's). All these numbers are more qualitative than quantitative... But none of this would lead me to use AR Comp in the Arc.
Last observation. And assuming that you are trying to follow the saami limits even out of your QL data... for Ar Comp you exceed 52 ksi at 24.8. It may be true that one can go over the saami limits, but you will pay a price for it later, or maybe even sooner when some load potentially blows up your gun.
So you maybe can see why I would not want to go down the Ar comp trail for your 6Arc, 103. It's safer and you'd have a "more harmonious outcome" (Quigley) using Ar comp elsewhere and buying a pound of something for your 22" 6 Arc, like lever, varget, PPV, 2520, CFE or other one promising better results for you. Unlike a couple years ago, there are powder choices on the shelf now. I can offer no conclusions on whether QC has given you a questionable keg of Comp... Maybe its results from another, known cartridge, can give you info on that. I like mine in 308 with the 110 Ttsx, and a couple other places/calibers.
Stay safe in all of this reloading.
But even some of those values up there confuse me still....
First off however, I will note the QL and Grt both have some trouble effectively replicating these short, fat AR cartridges. Lots of info there on the 65 Grendel forum, which is the original case that the 6Arc comes from. Most times QL/Grt will only claim about 10% or 50 fps accuracy.
One thing I have had to do is change the Sebert factor from stock, dropping it to 0.45. Now that's just me and my own model so can't transpose it for gospel as I am not a software engineer or ballistician.
But on to other points for some clarification..
I have some RE-15 results, 103 Eldx, in my 22" uintah bolt action, of 2728 fps, and an estimated 54 ksi. And 103 Eldx with Lever in this bolt action, 2735 fps; 48 ksi for Lvr.
Your Lvr data for 29.0, estimates 53 ksi, which is above the chamber max but the actual load is below the Hdy data for AR's... Now the 29.5 Hornady max is not a guarantee. But if your barrel is over max, maybe you're too high? Or maybe the OAL is not set right, possibly too close to lands (hard to imagine for the AR's, but chamber dimensions can come into play). Some early 6 Arc barrels were reported to have short throats, there are posts on here about all that.
But back to AR Comp. Taking my RE-15 data (which is in the Hdy data) as a start and substituting Ar Comp for it, I get a massive pressure increase, around 15 Ksi. Implication being the pressure is rising much faster than the bullet can accelerate to give that gas any room. Or alternatively, finding a gas gun charge below 52 ksi, I wind up with 26.something, and only 2640 or so fps. trying your 25.6 shows me only 2550 give or take (admittedly still differs from your actual in the low 2300's). All these numbers are more qualitative than quantitative... But none of this would lead me to use AR Comp in the Arc.
Last observation. And assuming that you are trying to follow the saami limits even out of your QL data... for Ar Comp you exceed 52 ksi at 24.8. It may be true that one can go over the saami limits, but you will pay a price for it later, or maybe even sooner when some load potentially blows up your gun.
So you maybe can see why I would not want to go down the Ar comp trail for your 6Arc, 103. It's safer and you'd have a "more harmonious outcome" (Quigley) using Ar comp elsewhere and buying a pound of something for your 22" 6 Arc, like lever, varget, PPV, 2520, CFE or other one promising better results for you. Unlike a couple years ago, there are powder choices on the shelf now. I can offer no conclusions on whether QC has given you a questionable keg of Comp... Maybe its results from another, known cartridge, can give you info on that. I like mine in 308 with the 110 Ttsx, and a couple other places/calibers.
Stay safe in all of this reloading.