Hand loading .6mm ARC

[Dr. Myk]

Hello All, so I had just prepared some hand loads using data from Lyman’s 51st Edition as follows for .6mm ARC:

Hornady 105 gn. BTHP match, new Hornady brass, 27.5 gns. CFE 223, CCI 400 small rifle primers.  OAL slightly < 2.200”.  Will be shooting out of new CMMG AR.  

Couple of simple questions, because i have a habit of questioning everything.  So why some data states COAL of round at 2.200” and some formulas at 2.260”?  Does anyone know the MINIMAL coal for this reloaded round?  Anything else about this is appreciated.

[Old Bob]

COAL depends on both the bullet length & its seating depth in the case neck along with being able to fit in the magazine without getting into the lands in the barrel. A good place to start for seating depth is seating the bullet the length of the bullet's caliber. For the 6 ARC that would be .243" into the case neck. For boat tail bullets, that would be .243" from the start of the boat tail & up the bullet shank.

2.26" COAL is pretty much a standard for bullets intended for AR type magazines. That length can be assured to fit any AR mag. I've found for longer/heavier 6mm bullets that 2.28" COAL will fit in all the different brands of 6 ARC/6.5 Grendel mags I have without jamming into the lands. I still have some bullet jump in my chambers.

The 55gr Nosler Varmagedden bullets I'm using for fire-forming 6 ARC brass have a COAL of 2.05". Another hand load with Hornady 103gr ELD-X bullets has a COAL of 2.27".

You might have to experiment with bullet depth to find your best accuracy.

[grayfox]

+1 on Bob there. Couple of other things.
Seating depth of a particular bullet is heavily dependent on its ogive shape, the curve part for the end of the parallel shank out to the tip. In the case of the 105 Hdy bthp, it's ogive is rather "stubby", as a "tangent" ogive, so it hits the lands of your rifle quickly, meaning the OAL will be shorter than expected, usually around 2.200.
The only real way to see what any given bullet will do length-wise in your barrel is to use something like hornady's bullet OAL comparator, with the 6 Arc modified case, plus a caliper (preferably digital, they're not too expensive any more).
Bullets such as the 103 eldx, or 108, have a more sleek, "secant" ogive and so can be seated with a longer OAL without hitting any lands.
The final comment is that, for most AR type mags, as stated above, you won't in many cases be able to get close to lands since you are limited to 2.280-2.290 or so and some bullets may need to hit 2.340-2.400 before they touch the lands.
There's a lot more that you can go into on talking distance to lands, what OAL to choose, whether to "jam" or not (I don't jam) and so on... but this ought to get you started.
1000's of theories as to what is the "best" OAL or "best" M.O.... keep a log of what you're doing so you can track any good or bad loads and results, etc... I use a spreadsheet.

[popgun]

In my chamber loading new brass with that bullet, 2.200 would give about a .020" jump. Or you could say at 2.220" it is touching the lands. My resized brass is about .005" longer, so in that case 2.225" it's touching and I load them at 2.215" giving a .010" jump. At 2.260" they would be about .040" into the lands, you don't want to go there.
But like grayfox said, it's best to check with a comparator and gauge.

[Old Bob]

Thanks greyfox for the ogive shape info. Spaced that out in my reply.

There's a tool for checking loaded ammo to see if it will fit in a SAAMI chamber ...

https://sheridanengineering.com/product/...ion-gauge/

If your reloads will drop freely in-and-out of this tool, your ammo should chamber in a SAAMI spec chamber.

I have this tool for my 6 ARC, 6.5 Grendel & .223 Rem. They've been really helpful getting near perfect reloads.

[Rickhem]

In my chamber loading new brass with that bullet, 2.200 would give about a .020" jump. Or you could say at 2.220" it is touching the lands. My resized brass is about .005" longer, so in that case 2.225" it's touching and I load them at 2.215" giving a .010" jump. At 2.260" they would be about .040" into the lands, you don't want to go there.
But like grayfox said, it's best to check with a comparator and gauge.

Does the length of the brass make a difference here?  Since the bullet seats inside the brass, and not on top of it, isn't the length of the brass, from a COAL perspective, a non-issue?

If 2.220" is touching the lands with a specific bullet seated in a piece of brass, then any other piece of brass into which that same bullet is seated would still touch at 2.220", even if those pieces of brass vary in length.  The bullet would be deeper in some cases, and less deep in others, but if the COAL is the same, the length of the brass doesn't impact distance to lands..........right????

[grayfox]

Actual brass length doesn't matter from measuring strictly a COAL dimension, it could affect whether the bullet is seated with enough shank in contact with the neck (which gives seating stability).

But there is a distinct difference between reality vs ideal, and in reloading, reality is king. In reality every brass piece is a different length (which most times is not an issue, since that length may vary +/- 0.001 or 0.002).
Every bullet has a variances both dimensionally within a lot (length/oal, shank length, ogive start, grs weight, etc), as well as differing from lot to lot. So you can't really say that every bullet would hit lands at 2.220 for example... there will always be some variance.

But the biggest variable for seating is the chamber dimensions from barrel to barrel, which can be enough to ruin your day if you are trying to seat some of the more "stubby" of bullets. Example, of my ARCs (both now and prior), some hornady bthp 105's for example, would hit lands at 2.277 down to 2.232 among 4 barrels. The nosler 95 BT would vary to lands from 2.228 down to 2.181, among 4 barrels. This is why you really need to do seating depths for Your Barrel(s), and write them down.

Personally I don't try to chase or seat close to the lands because of all the variables involved, which would also include seating tolerances for your equipment as well as the ones above. (The competitors who do, and "need" to, are typically using an expensive, special order barrel, single powder, and single match grade bullet, and custom expensive reloading equipment... so they reduce all of these variables down to virtually 1 or 2 maybe; so these things they follow are not everyday guidelines for everyday shooters like me)
So bottom line, here are the takeaways I recommend:
1. Size and trim your brass to a consistent length within Saami limits. ARs, full length sizing.
2. Test your bullets in your barrel(s) for oal and choose a length - I say shorter, by 0.020" or up to 0.060-ish depending on the bullet, while still ensuring that bullet has enough shank (min of 1-caliber) inserted/riding against the neck for proper seating - boattail portions don't count for this. Write down these measurements. Each bullet, each barrel. You need an oal comparator like the hornady gage, the hornady modified case+digital calipers, or whatever mfr trips your fancy. You need to be able to distinguish down to the 0.001's for chamber seating-lands, etc., hence the digital calipers.
3. Keep powder loads within mfr recommended limits but always work up from low, for each barrel, each load setup. The eyes/rifle/life you save may be your own. You might not make it up to a mfr listing of max, so be prepared to stop before that... you don't have to shoot it just because you loaded it!!! Too hot is too hot.
4. After you get lots of run time with this caliber, then maybe you can consider using some off-book powder, carefully and working up as above. These grendel-based cartridges don't show hot overloads as commonly-observable or as easily as 308/223-based cartridges. This is a fact of life and you are well to keep it in mind.

Safety is first and foremost in all of this.

[popgun]

Does brass length matter? It depends on how precise you want to reload, but more importantly in relaying information. I stated that these are the measurements in my chamber and you should use a comparator and gauge.
Why brass length matters is, when using a OAL gauge your datums are actually the shoulder and the ogive but are measured from the base to ogive ( preferably ) or to the tip ( COAL ). If you take that measurement with two different lengths of brass when measured from base to shoulder you will get two different measurements.
I know it's common to share load data in COAL but I'm not a fan of it, it's imprecise information. That's why I gave MY info in MY chamber as precisely measured as I could given in a COAL measurement and of course there are always .002+- differences.
I hope my answer wasn't to confusing.

[grayfox]

I see what you mean now. I usually don't worry about shoulder datums b/c I have my dies set, and setbacks are already set along with. I have potentially 5-6 Arc's I load for/could load for (not all are in rotation right now), and I'm not ocd enough to have a resizing die setup for each one, I found one that moves the should back 005 or so for all of them... so base to tip (what I'm using now) doesn't vary much. I should probably confess that for lead tips and even some poly's, an OAL can vary by +/- 0.003, sometimes the sierras (lead) go +/-0.004. The only mfr I've found that can show me loads +/- 0.001 are the nosler ones... so for me if I have cartridges of +/- typically 0.003 I use load lengths accordingly, so there isn't any problem of winding up in the lands or anything (not my cup of tea, others may want to do that and that's ok...).
Edit to add: since this is all real world, a person will pretty much always find some variances in virtually all measurements... so if I were to check my shoulder setbacks after a resize I would find a 0.001-0.002 delta from one case to another... with my tools that is within a combined error tolerance. So for me I'm comfortable operating there.

[Rickhem]

Does brass length matter? It depends on how precise you want to reload, but more importantly in relaying information. I stated that these are the measurements in my chamber and you should use a comparator and gauge.
Why brass length matters is, when using a OAL gauge your datums are actually the shoulder and the ogive but are measured from the base to ogive ( preferably ) or to the tip ( COAL ). If you take that measurement with two different lengths of brass when measured from base to shoulder you will get two different measurements.
I know it's common to share load data in COAL but I'm not a fan of it, it's imprecise information. That's why I gave MY info in MY chamber as precisely measured as I could given in a COAL measurement and of course there are always .002+- differences.
I hope my answer wasn't to confusing.

Maybe I'm mixing up some terminology, but when measuring COAL, or OAL, you are measuring the length of the cartridge, both brass and seated bullet.  Even using a comparator, you are measuring the cartridge base to ogive distance, which I agree, is a much more meaningful piece of data.  In any of those, the length of the brass is not impacting the final reading, since the bullet is inside of the brass.  The bullet, in effect, telescopes inside the brass, and the depth of that seating determins the COAL, not the length of the brass.

Now if we are talking about headspace, which is the measurement of the cartridge base to that datum line on the shoulder of that specific case, then that most surely matters, but that does not include a bullet in that measurement.  That measurement is also used in conjunction with the measurement of the chamber, which we get from a piece of brass fired in that chamber.  (actually an average of several pieces, but I digress)  What is interesting is that if you look up the SAAMI specifications for some cartridges, and look at the drawings for both the cartridge dimensions, and the chamber dimensions, there is occasionally an overlap.  The tolerance for a cartridge at it's longest "in spec" measurement, is longer than a chamber at it's shortest "in spec" measurement by a thousandth or two.  You'd think that couldn't happen, but it occasionally does.  

I think we're probably saying similar things differently, and I also think that giving a COAL without saying what chamber one has, or some other details, is not of much value.  A .223 service rifle frequently has a Wylde chamber, so sharing that COAL helps, but if one barrel has 3500 rounds on it, and another is new, that COAL has less value.  We definitely agree on that.  Every chamber is different.

Anyway, all this in the best intentions and in the spirit of good discussion.  I learn a lot from these kinds of threads between posters that forgot more than I know, so maybe we're helping someone just reading about the 6ARC, or loading for one.  

[Rickhem]

Here's the drawings for the 6mmARC. Check out the measurement range for headspace and you'll see what I mean by the "overlap".

https://saami.org/wp-content/uploads/202...-07-29.pdf

[popgun]

I think what you are missing is the distance from the shoulder to the ogive.
In my example it only makes a .005" difference and the difference would basically be the jump or where the bullet is in relation to the lands, because the bullet had to be seated further in the longer brass to get the same OAL as the shorter brass used to measure with the gauge. The distance between the shoulder and ogive is smaller.
It is not that important if starting a load for yourself if your jumping the bullet. most people will start .010 to .020" shorter and increase the jump from there, but in reality your starting your Jump at .015 to .025".
But when looking for load data it's my experience that particular bullets generally like a specific window of jump or is at least a good place to start. So knowing your jump and relaying info that way is beneficial.
When seating bullets into the lands that .005" now becomes even more important to take into account.

[popgun]

The 6 ARC saami drawing doesn't overlap but a Max case and a Min chamber would only have .0001" headspace.

[Rickhem]

I have to say that in several decades of reloading, and being a voracious reader of the same, I have never heard of measuring the shoulder to ogive distance, or benefit of having that value.
I'll have to think on that one for a while.
Thanks for responding though, and I like that little trickler/vibrator thing you whipped up in the Berger box. Very clever!