JBM gives less optimistic ballistic performance for the ARC than does Hornady.
Hornady 6mm ARC "New" cartridge
- Thread starter Kimber.204
- Start date
JBM gives less optimistic ballistic performance for the ARC than does Hornady.
4DOF has always been just about spot on for me, out to ELR distances, on all of the cartridges I shoot. I can't speak to JBM, I've not tried it. The data on the bullet in 4DOF is based on doppler radar recorded data for the bullets they have measured, so tends to be very accurate re: drag curve. I would not expect it to be significantly off. They have a web version (it's all free) so you can put in more realistic shooting conditions (environment) and see how you can expect it to perform. I rarely have to fudge with the correction (axial form factor) much to get the real performance to match the projected - I can generally shoot out at 1000yds and get first round hits on steel without tweaking it. Every once in a while I have a rifle that doesn't quite line up, and I'll see a splash on the ground nearby, and can fix it up quickly. I think the thought behind the axial form factor is different barrels/firearms will do different things, and so a little 'touch up' is needed for them.
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I suspect JBM gets their BC number from Hornady website and use that number throughout flight so it's an optimistic prediction so drift will be less. 4DOF is more accurate so I expect it to have more accurate drag numbers and therefore more drift. Not sure how to reconcile them.
Grimstod
Machinist, Designer, and Shooter.
You never heard of the 7.62x51 NATO?
Yes I have and there is no AS ISSUED military rifle that's going to print competitive bench rest groups with military issued ammo. Unless there is a specific bench rest game made for the limitations of the cartridge and rifle. I wouldn't know if there is a specialty game as bench rest shooting does not appeal to me. But to complete against 20th and 21st century developments the 7.62 x 51 is too long in the tooth. To make the 7.62 x 51 a viable bench rest rifle takes alot of work that would be field useless.
Surely today the 7.62 NATO military rifles and ammo are better then my day but the 7.62 x 51 has in my opinion seen it's day 45 years ago. Hence you see the past and present development of other cartridges for the specialty work. My vocalization against the 7.62 x 51 in my day had me working with armorers testing other cartridges. I believed then and now that for 99% of specialty work a smaller caliber was needed not the larger calibers then being tested.
I built myself a 6MM Remington on a 700 action many years ago, clearly not a bench rest rifle but if today I had to cover a team without a spotter I'd rather carry my 6MM Remington then anything I've ever carried chambered in 7.62 x 51 as I can spot my own hits and there's plenty of energy on target.
In my view the 6MM ARC concept is 45 years late. Years ago a 2 man team was a spotter and shooter now with the possibilities presented by the 6MM ARC, if it pans out, a 2 man team can be a 2 man fire team.
That might be because you used a 12 twist and the bullet is tumbling with a stability of 0.637.
Are you trying to argue that the original AR15/M16 was designed for close combat? Are you aware of the original requirements the program had to meet? The round has to penetrate a US-issue helmet at 500y. Is that "close combat" to you?
And if you are referring to the M4, well it missed out on the first desert foray and some of the 2nd. And a 14.5" bbl isn't enough to turn an infantry rifle into a PDW for CQB.
What I'm repeating is the scenario to get more rounds in the Air, hence the concept behind the 5.56 AR platform. Which was a success according to the data crunch'rs of the day after Vietnam. I'm also explaining the weapon that was used to pin down troops during the Sandbox conflicts more often than not was a Cartridge developed in the 1800's. Nobody today is going to use the Tin Hat GI helmet penetration test as a viable concept (500yds). Today's Ammunition has to be able to penetrate the latest Body Armor which is a tall order.
If you would like to debate requirements for the original 5.56 and read through data or testimony feel free. Perhaps you can get someone to challenge you pertaining to that? Then after you've wasted a few pages on the thread you can move on to the Aberdeen field test for the AR15 Platform I bet that could be an interesting and informative read. Then you can debate whether or not there really are any shortcomings from the original Cartridge, which suffered from inadequate powder, excessive fouling, and the wrong twist. Or we can leave the 50's behind us and concentrate on today?
I know I'm jumping in a bit late on this subject, but I have a 24" 6.5 Grendel that I shoot 107 TMK and SMK. I just have not been very impressed with it at 400 yards. So when I seen Brownell was "pre-ordering" 6mm ARC barrels I jumped on one. I would like to shoot steel out to 600 yards and I don't think my 24" Grendel would be much fun...missing too much on the small stuff (softball size plates).
But I seen my new favorite hunting AR mentioned. I loathe the 5.56 for hunting, obviously the military has not been too happy with it for their hunting needs either.
So I built a 7.62X39 AR back when the first barrels came out (at least the first I had seen). I used wolf 123 HP Bi-metal ammo on hogs and deer. I even bought some reloading dies, but the box was never opened. That is until last fall when I decided to give night hog hunting a go.
After the first range trip with reloads in my 7.62x39 I built 3 more out of 5.56 rifles that have been collecting dust for years! I've even taken it out to 400 yards. I have a night hunt coming up this weekend so I took it to the range Sunday to get the zero dead on at 100 yards. I wish I had take a picture of the group. It beat the huge majority of shooters around me.
Back in the day I wouldn't think about head shooting pigs with my 7.62x39 AR at 100 yards and beyond but now I don't hesitate for a second!
Pretty sweet rig!
I used it all deer season and recorded all my wife and I shots...way cool!
Any way...really looking forward to having something to shoot steel with at 600 yards! Going to do a barrel swap with 24" Grendel.
I have both on order...dies should be here Thursday...sadly don't have a delivery date on the barrel....
Good catch! But JBM trajectory calculaltions does take into account tumbling since it requires a more sophisticated model such as 6DOF.
For those who've indicated they don't trust the velocity numbers or performance, here's a video someone recently made, with a 16" barrel:
(Set to start when talking about 6mm ARC/throws up the velocity chart/drop table). Later, he proceeds to shoot using those calculated drop numbers, demonstrating they are actually correct.
(Set to start when talking about 6mm ARC/throws up the velocity chart/drop table). Later, he proceeds to shoot using those calculated drop numbers, demonstrating they are actually correct.
"Bad to the bone"
jghoghunter
Gold $$ Contributor
Hey guys
Thats Kotaboy 32 and that range is our 1000 yard range pa.
mifflincosportsmens.com
I got a chance to shoot my 20" 1:7 twist gas gun 6mm ARC today with hand loads and for the first time with factory Hornady 105 Black ammo. The factory 105s did not shoot well for me and looks like it is on a scatter node for my barrel (Ballistic Advantage) as it was all vertical at 1.97 MOA at 100 yards. It shot at 2662 FPS with an SD of 11 FPS. I did use a direct-thread Ultra 9 suppressor on my rig today. For support, I used my Joy-Pod bipod and Bigfoot rear bag along with an older NF 5.5-22 scope from prone.
My hand loads, 108 ELD-Ms over VARGET, did much better than factory, maintaining group sizes in the .5 to .52 MOA range at 100 yards. My speed was much lower than factory at 2554 FPS with an SD of 6 FPS. Quickload indicates that this speed is much closer to an OBT node for my barrel length. I took a few shots at the 900 yard gong using my ammo and observed the same .5 MOA or better accuracy at that distance. There was no (zero) wind today which certainly helped with the accuracy.
I didn't shoot at 1000 because AB indicated that 900 was the limit for supersonic flight and I only had handful of rounds left after testing at 100 and 700. Going to load 50 for the next outing and see how far it will go. I will note that while you can see and hear impacts at 700 and 900 it does not move the gong much--not surprising given the low MV.
I am not much of an AR guy these days but thought it would be fun to have a relatively light weight, low recoiling, semi-auto capable of 1000 yard target shooting. Will report in with additional results.
Henryrifle
My hand loads, 108 ELD-Ms over VARGET, did much better than factory, maintaining group sizes in the .5 to .52 MOA range at 100 yards. My speed was much lower than factory at 2554 FPS with an SD of 6 FPS. Quickload indicates that this speed is much closer to an OBT node for my barrel length. I took a few shots at the 900 yard gong using my ammo and observed the same .5 MOA or better accuracy at that distance. There was no (zero) wind today which certainly helped with the accuracy.
I didn't shoot at 1000 because AB indicated that 900 was the limit for supersonic flight and I only had handful of rounds left after testing at 100 and 700. Going to load 50 for the next outing and see how far it will go. I will note that while you can see and hear impacts at 700 and 900 it does not move the gong much--not surprising given the low MV.
I am not much of an AR guy these days but thought it would be fun to have a relatively light weight, low recoiling, semi-auto capable of 1000 yard target shooting. Will report in with additional results.
Henryrifle
Thanks for the information, much appreciated.
Awesome thanks.
If you're talking hunting/tactical in my opinion it runs all over the Grendel, low pressures like the Grendel, but lighter projectile, less recoil makes rapid up close work easier.
It depends on who you ask. A MK262 shooter is generally going to rave about the performance of the 5.56. A M855 shooter will tell you one horror story after another about lack of capability (unpredictable yaw-- tendency to ice pick). A MK318 SOST shooter is likely to report being pleased with the round too.
The shortcomings of the 5.56 as a cartridge are just the nature of a small projectile at only 1200 lb-ft of energy. It's not reasonable to expect consistent lethal performance to 600-700-800 yards.
There are loads in 5.56 that are plenty effective on things smaller than a deer-- even hogs. These tend to be expensive bullets from Barnes or Lehigh. Small calibers place a premium on projectile choice.
The 7.62x39 and 6.5G have comparable muzzle energies and the 6.5 has higher sectional density. So if there is an instance where 7.62 is outperforming, it's due to poor choice of 6.5G ammo. Indeed, hunting to 400y with a very light-for-caliber MATCH bullet seems like a poor choice and suggests you are blaming the cartridge for your poor choice of load.
CarpeSus on youtube hunts pigs with a 90TNT very successfully with his 6.5G. And I'd suggest that ANY AR-designed caliber is near or beyond its limits at 400y for reliable hunting of hogs.
If you need 400y performance, choose a better tool for the job.
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