varminter .223
Well-known member
Has anyone measured to see what coal the 58 vmax touches the lands on a 6 arc? In my experience the v max bullets touch the lands at shorter coals than most other light 6mm bullets.
6 arc touching the lands
- Thread starter varminter .223
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I did not think there is a set dimension, each barrel maker has there own reamer. Best bet is to just measure you barrel.
I once loaded a bunch of target ammo for the PM Egg Shoot, it was a compressed load in my 6x45 with the bullet just touching the lands. I ran every round through the action from the mag, nary a hiccup. I got to NV and the first round the target blew over so I ejected the round,.the bullet stayed in the barrel and dumped the powder into the action. The rifle was out of action luckily it had a spare along. I ended up having to reseat the whole batch.
I give the lands some clearance now.
I once loaded a bunch of target ammo for the PM Egg Shoot, it was a compressed load in my 6x45 with the bullet just touching the lands. I ran every round through the action from the mag, nary a hiccup. I got to NV and the first round the target blew over so I ejected the round,.the bullet stayed in the barrel and dumped the powder into the action. The rifle was out of action luckily it had a spare along. I ended up having to reseat the whole batch.
I give the lands some clearance now.
Hecouldgoalltheway
Well-known member
I think worrying about the lands are really silly, and not relevant to accuracy unless you have a bullet that is notoriously jump sensitive like a berger vld. The v-max doesn't care about jump. But I can tell you for a certainty that is this exact case, a 6mm arc Sammi spec chamber will hold a 112gr bullet. You would run out of bullet length on that 58gr about a half a mile from your lands. Your max coal for the 58gr is somewhere around 2.08" from memory.
So the word of the day for educational purposes is freebore, commonlyalso called "throat". The entire premise with the 6arc was a long freebore to shoot long and high BC bullets that aren't taking up space in the case, hence they are seated out far.
When you have a longer freebore or throat for the heavies it's impossible for the light bullets to reach the lands because the bullet ain't long enough.
There's zero physical way to have a chamber that's optimum for both heavy and light bullets and why I continuously point out that the 6arc, 224V, 6.5G and similar designs are not optimized for varmint rounds. Cartridges like the 22nosler, 22-250, 243 and 6x6.8spc are and was optimized to run light varmint bullets.
When you have a longer freebore or throat for the heavies it's impossible for the light bullets to reach the lands because the bullet ain't long enough.
There's zero physical way to have a chamber that's optimum for both heavy and light bullets and why I continuously point out that the 6arc, 224V, 6.5G and similar designs are not optimized for varmint rounds. Cartridges like the 22nosler, 22-250, 243 and 6x6.8spc are and was optimized to run light varmint bullets.
varminter .223
Well-known member
Given the cartridge was designed for the AR platform coal would be restricted to 2.295 or a tad longer in steel mags. It appears 80 eld vt factory ammo has a coal of 2.095. I did the measuring and the math comparing the 58 vmax to the 80 eld vt. With the 58 vmax loaded out at 2.235 the ogive would be the same distance from the lands as 80 in the factory cartridge. This only leaves .051" of bullet in the case and given the boattail is about .060 its out. I inquired be cause I do not have a barrel but wondered if anyone had measued this out because I can compare it to many other 6mm bullets that I have all measurements on. I was interested in seeing if there was a coal/bullet combo that would put enough bullet in the case and not eat powder capacity for peak velocity.
varminter .223
Well-known member
Fwiw I should add that the 55 and 70 nosler bt will be .095 farther from the lands than the 58 when loaded at the same coal.
Factory 80s loaded at 2.095 would have .465" of bullet in the case. I keep scratching my head wondering why such a short coal eating case capacity.
Well it appears the 2.095 coal is the gmx bullet. I was certain I read somewhere the 80 eld vt was that as well but can' t find it again.
Factory 80s loaded at 2.095 would have .465" of bullet in the case. I keep scratching my head wondering why such a short coal eating case capacity.
Well it appears the 2.095 coal is the gmx bullet. I was certain I read somewhere the 80 eld vt was that as well but can' t find it again.
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Hecouldgoalltheway
Well-known member
You can't load the 58 gr to 2.095, it's max coal is 2.085, literally almost exactly what I said above. There is no debate here about getting a 58gr bullet into the lands on a 6mm arc, it's not going to happen. You're not getting an 80gr bullet there either. Also, it doesn't matter. There are a few bullet shapes that are actually jump sensitive. I personally hate them and avoid them like the plague. Accuracy is ultimately pressure. There are a dozen+ ways to effect pressure, like powder charge, seating depth, primer, crimping, etc. Almost none of them (with a few notable exceptions), are actually that concerned with jump or being jammed, or whatever you're looking for. I started off reloading believing I had to find the lands and get the seating depth perfect to achieve peak accuracy. Years ago I realized that was folly. You can easily change the pressure with powder charge and accomplish the needed pressure change. I go to the book, find max coal, or max magazine length in the case of a long for caliber bullet, go to a grain or so under recommend max and build 5 rounds. I can count on one hand the number of times that doesn't produce a .5moa cartridge, and I shoot 10k rounds a year in a dozen different chamberings. I have a 400y range 50y from my reloading room. Most ammo loading tradition is unnecessary superstition.
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varminter .223
Well-known member
You guys are missing my point. Im just looking for a dimension to start from so I have a starting point to calculate various bullets from. I do not have a barrel. Im just trying to get an idea of how they are throated. I drop a bullet in the chamber and measure to the rear of it. Then remove it and drop a sized case it and measure to the rear of it and do the math from there. I have no desire to shoot anything that has the bullet clean out of the case before before it hits the lands. Im just trying to get an idea of what might get close.
Im sure hornady picked that coal for the 58 because that leaves .202" of bullet in the case. Gotta keep something in it.
In other words Im not one to take a willy nilly approach. I prefer to do the math. With the single dimension of a 58 whether its in the case or out I can calculate distance to lands with any bullet I have.
Im sure hornady picked that coal for the 58 because that leaves .202" of bullet in the case. Gotta keep something in it.
In other words Im not one to take a willy nilly approach. I prefer to do the math. With the single dimension of a 58 whether its in the case or out I can calculate distance to lands with any bullet I have.
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Hecouldgoalltheway
Well-known member
I'm shooting a 55gr ballistic tip over 33gr x-terminator. Shoots just under 3,300fps in my 18" ar. Shoots under .5moa, 2.07" coal. I didn't measure anything. The 6mm arc Shoots everything precisely, from the 55gr to the 109gr+. It doesn't require a bunch of measuring and tuning, it's like loading for a 6.5 creedmoor, it's hard to get it to shoot poorly, (assuming you don't buy a junk barrel)..
varminter .223
Well-known member
The fact thay my 16" 6x45 will push 55s 3300 out of a 16" poly 3 10 twist is what has kept me from experimenting with the arc. Looking at the Ruger American 2 is what me think about one today.
varminter .223
Well-known member
We spec'd our hagar reamer freebore out to put 60 sierras on the lands at 2.260 and 58 and 65 vmax on the lands at 2.280 ish if I recall. Those barrels received a top notch chamber job but they are hands down the most accurate barrels Ive had and with several different bullets. Not really picky about charge weight either. It sold me on specing things out.
Hecouldgoalltheway
Well-known member
The arc really isn't the right choice for varmint bullets, as stated above. It's serviceable, but not te best option.
varminter .223
Well-known member
I always figure if something needs killed way da hell over yonder probably something with case capacity more like the creed is more pratical. These mag length restricted shortened case cartridges all seem to add up to be designed for slow paper punches or steel bangers.
Bowhunt
Active member
I'm sorry but this is just plain wrong. "Accuracy is ultimately pressure"? Pressure effects velocity and ultimately harmonics, which both have effects on accuracy and consistency. Your saying that seating depth (jump to lands) has zero effect on accuracy? Not only does it have an effect, but it is a fairly significant one in many (not all) cases. Make that statement on a bench rest forum and see what response you get. Lol
Hecouldgoalltheway
Well-known member
Everything you do inside a closed chamber changes the pressure. What I'm saying has been clearly proven for years. It's really pretty straightforward when you think about it. I never said seating depth has no effect on accuracy, clearly there is a range that it will be accurate in. Chasing seating depth is unnecessary, except when shooting those ridiculous sensitive bullets.
Nothing wrong with a starting point. Just know there are other variables that come into play. Ahead of the freebore is the leade. The leade will have a specific angle. They aren't all the same. The bullet will have either a secant, tangent or even hybrid ogive. Each of those will touch the lands in the leade at different points. So, unless your OAL measuring tool has the same leade as a particular barrel, measuring off the ogive at the exact same point as it actually touches isn't happening. And that leade angle starts changing as soon as you start putting rounds through it.
- DAA
Or shooting ridiculous small groups. I've never seen any really accurate barrel that doesn't respond to changes in seating depth with any bullet. Pressure isn't accuracy. Pressure is velocity. Since pressure is the work being done under the curve and that is precisely what creates velocity.
- DAA
Hecouldgoalltheway
Well-known member
When you change seating depth, you're also changing pressure. You've been told forever that the accuracy change you've seen is because you changed the jump or jam. As an experiment, the next time you are tuning a load and you seat a bullet out further or closer and you see an accuracy improvement, mark it, then go back to the original coal and adjust your charge in the corresponding direction and see if the results are not the same. When you realize that this is a fact, you stop worrying about seating depth so much. Load it as long as your magazine allows, (minus a hundred thousand or so for proper operation), and then play with your charge weights. If you happen to get maxed out on powder and haven't found what you want, then sure, start shortening your coal, but the idea that the distance to the lands (again, with some exceptions) is that critical to accuracy is fudd lore. I can prove it with a simple example already discussed here. You can have a 55gr bt in a 6arc chamber that shoots .5moa or better, (a half mile from the lands), or you can take a 55gr bt and stuff it in a short chambered 22-250, extended out long enough to have to be single fed, and you can make it shoot .5moa. They are polar opposites in jump, and it doesn't matter. Most loading processes are fuddlore and superstition..
Hecouldgoalltheway
Well-known member
I'm not a bench rest competitor, and I imagine very few here are. I'm a hunter. .5moa is the end of my accuracy pursuit. When I achieve that, I'm done playing with it. When you're in the field shooting at an animal, whether it be off a tripod, bipod, or shooting sticks, you will never be better than a .5moa shooter, and most folks would be lucky to shoot 2moa. I shot prs for years, and never once saw a target smaller than .5moa. 99.99% of shooters will ever shoot a group smaller than .5moa in their lives, they lack the ability. Chasing anything better than that is for F-class and benchrest guys, not hunters or even dedicated shooters. Anyone claiming they can shoot a group under .5moa with any real consistency is probably either lying or they are shooting for one of the disciplines listed above, and they have been for a long time. I was a sniper in the army for years, shot around some of the best in the world. Shot prs matches around the south, some of the best in the world, and very, very few of them could lay down on command and shoot a sub .5moa group, and that's the truth. I'm glad there are people out there who are obsessed with chasing one hole groups, but it won't put one more animal on the skinning board, and that's all most folks are after..