New Reloader with detailed COL numbers looking for double check

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ropedrag
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New Reloader with detailed COL numbers looking for double check

Post by ropedrag » Tue Nov 26, 2019 3:28 pm

VERY New to reloading and being in my mid fifties I’m disappointed I waited this long. The number of rabbit holes to go down is amazing!

So, being a bit older I enjoy trying to apply logic to things but there are plenty of times when I discover I’m not as smart as I think I am. That said I’d like some confirmation on this, or, point out where I’m off track. It might be worth noting that I’m a city boy, meaning I don’t have any mentors I just read what I can get my hands on. I’ve developed a couple loads for my 6.5 Creedmoor bolt gun with great results but this new challenge is for an AR with intentions to bulk load a few thousand rounds for the zombie apocalypse

Gun = Daniels Defense DDM4ISR 300 Blackout, 9” barrel and suppressed.

Working up 3 suppressed loads, 3 bullets and 2 different brass manufactures

Sierra Match King 30 CAL .308, 200gr HPBT
Hornady ELD X, 30 CAL, .308, 200gr
Hornady ELD Match, 30 CAL, .308, 208gr

New Hornady Brass
New Noveske plated Brass

So, here’s the question(s). Using the Hornady OAL gauge with their modified case I came up with the following COL dimensions with the bullet hard on the lands

Sierra Match King 200gr HPBT = 2.2565 (COL on the lands)
Hornady ELD X, 200gr = 2.3216 (COL on the lands)
Hornady ELD Match, 208gr = 2.4000 (COL on the lands)

Using the Hornady headspace comparator to measure base of case to *datum

Hornady “Modified case” used with the OAL gauge = 1.0655

So, If I subtract 1.0655 from the 3 OAL dimensions above I should have the dimension from the *datum to the lands for the 3 bullet profiles in my chamber, which are

Sierra Match King 200gr HPBT = 1.1910 (*Datum to Lands)
Hornady ELD X, 200gr = 1.2561 (*Datum to Lands)
Hornady ELD Match, 208gr = 1.3345 (*Datum to Lands)

If I then take these numbers and add them to the 2 brass types I have it should equal the COL with the bullet hard on the lands. Again, the case *datum was measured with the Hornady headspace comparator

Hornady New Brass = 1.0630 (base to *datum)

Sierra Match King 200gr HPBT = 2.2540
Hornady ELD X, 200gr = 2.3191
Hornady ELD Match, 208gr = 2.3975

Noveske New Brass = 1.0695 (base to *datum)

Sierra Match King 200gr HPBT = 2.2605
Hornady ELD X, 200gr = 2.3256
Hornady ELD Match, 208gr = 2.4040

Note, I do understand that after these cases are fireformed and I FL size pushing the shoulder back these dimension relationships will change. I’ll factor when occurs.

So now I have all this data for various bullets/brass COL’s to the lands. From here I guess I’d subtract .02 for a starting jump distance and go to work dialing in charge weights using the chronograph. HAHA, not so fast. Apart from the SMK 200gr there are no days the other 2 loads would come close to fitting in the magazine (2.30 and 2.38 with a .02 jump). Looks like the 2 Hornady ELD’s are going to be (severely?) limited on dialing in accuracy with jump distance manipulation.

From what I can gather, the max COL for a 556/300 magazine (PMAC, etc.) is 2.26 and honestly, I don’t really see it after looking mine over. Better safe to say the max COL at 2.245… reasonable?

With setting COL at 2.245 to operate in the magazines the following jumps are required

Hornady New Brass = 1.0630 (base to *datum)

Sierra Match King 200gr HPBT = NA I’ll set COL to .04 jump at 2.21
Hornady ELD X, 200gr = .07
Hornady ELD Match, 208gr = .15

Noveske New Brass = 1.0695 (base to *datum)

Sierra Match King 200gr HPBT = NA I’ll set COL to .04 jump at 2.22
Hornady ELD X, 200gr = .08
Hornady ELD Match, 208gr = .16


So, If I’m doing this correctly the 2 ELD bullet/brass combinations will have a range of jumps from .07 to .16. These don’t seem ideal but are ok I guess. I then go and measure COL on my stock of factory subsonics and say BLK?! COL’s in the 2.12 range meaning these factory loads are jumping in the neighborhood of .25”, holy S*it! are these acceptable jumps for an AR?

Thanks!

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rebel
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Re: New Reloader with detailed COL numbers looking for double check

Post by rebel » Tue Nov 26, 2019 5:16 pm

Yes, they are acceptable and a necessary evil with magazine fed rifles.
If you can find some Lancer mags you can load slightly longer than 2.26.
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Re: New Reloader with detailed COL numbers looking for double check

Post by BoomerVF14 » Sat Nov 30, 2019 10:54 am

Welcome to the forum!

As I read it, the unspoken assumption in your post is that jump to the lands is the single most significant factor to control in ordre to maximize AR-15 precision. I thought so too when I first started down the .300BLK reloading path, but like Rebel said, there's not much you can do about it given magazine dimensions.

I can get my (piston) AR-15 down to about 1.5MOA on average (I've shot sub-MOA groups but not at a rate I would call consistent after re-testing the same load). I track the jump, but have not tried to control for that variable, since the jump for my best load for the Nosler 110gr Varmageddon (1.30MOA average) is 0.195" at a 2.00" OAL - and for the Nosler 125gr BT (1.38MOA average) it's 0.225" at 2.085" OAL. This all presumes the shooter is a perfect machine which in my case it definitely ain't.

So, I would argue that jump (in an AR-15) is less important than working towards low muzzle velocity variance, using a nodal ladder analysis technique (I like the 6.5 Guys' 10-shot method personally), and find the right MV that works for your specific rifle, then play with OAL in very small increments to tune. What makes running the numbers challenging is that 300BLK is such a relatively small cartridge, what might be insignificant factors in big-bore bolt-action rounds have a larger impact on final results for us. If you can get an AR-15 reliably down to 1 MOA that's pretty impressive in my book.

Of course, if you're going to be shooting postcards with subs at 200yds like some of the ninjas around here, I reckon loading beyond mag dimensions and all those extreme case prep / reloading techniques for a single-shot AR are going to become necessary.

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Re: New Reloader with detailed COL numbers looking for double check

Post by dellet » Sat Nov 30, 2019 1:45 pm

I don’t know if you have seen this, the SAAMI spec for cartridge and chamber. If not it will help give your numbers meaning.

Image

Note the headspace lengths compared to your Hornady case.

Jump length is not a number to obsess over. Most bullets will have a couple places where they are very accurate. Part of that equation is also due to powder fill ratio. It’s a balance more so with subs. Bullets like the ELD and Matchking are very jump tolerant. This allows you to seat them deep in the case for a reliable load density and powder ignition.

I have shot many bullets loaded at magazine length of 2.260” with the same accuracy as jammed at 2.420” in a bolt action with a magazine that allow that length. The only difference is velocity.

This cartridge has a lot to offer someone who want to learn about hand loading and the small things that make for really consistent loads. It can also frustrate the crap out of someone who thinks you can just grab data out of a book and shoot better than the worst factory offering.

Your attention to detail will make a huge difference.
300 Blackout, not just for sub-sonics.

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Re: New Reloader with detailed COL numbers looking for double check

Post by ropedrag » Fri Dec 06, 2019 8:28 pm

The responses are very welcomed, thank you.

Having just cut my reloading teeth developing 2 rounds for my 6.5 creedmoor I'll admit to being super anal about lengths, powder weights and pressures. I think I'm doing ok with the 1/2 MOA at 200 and 300 yards the effort produced, might get better when I learn to shoot :lol: .....no, seriously.

I approached the 300 subsonic with the same methodology but like a lot of things, part of learning is understanding where the tolerances need to be tight and where ... not so much. Equally important is understanding why. I appreciate the knowledge shared!

PS, I did find an error in my fist post math process but it amounted to a few thousandths so nothing serious.

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Re: New Reloader with detailed COL numbers looking for double check

Post by Suputin221 » Fri Dec 27, 2019 3:02 pm

ropedrag wrote:
Tue Nov 26, 2019 3:28 pm
VERY New to reloading and being in my mid fifties I’m disappointed I waited this long. The number of rabbit holes to go down is amazing!

So, being a bit older I enjoy trying to apply logic to things but there are plenty of times when I discover I’m not as smart as I think I am.

XXX
XXX
XXX
XXX

So, If I’m doing this correctly the 2 ELD bullet/brass combinations will have a range of jumps from .07 to .16. These don’t seem ideal but are ok I guess. I then go and measure COL on my stock of factory subsonics and say BLK?! COL’s in the 2.12 range meaning these factory loads are jumping in the neighborhood of .25”, holy S*it! are these acceptable jumps for an AR?

Thanks!
Dude, you are WAYYYYYYYYYYYYYYY overthinking this whole thing. :shock:

First, lets clear up a few things.

COL: The measurement from the case head to the tip of the bullet. A mostly useless measurement except for the purposes of fitting the round into a magazine. Otherwise this number has no relevance to the firearm or chamber.

Headspace: Only relevant to ensure the case fits the chamber. Has no relevance to the bullet or the lands/throat.

I have no idea why you'd want to know the distance from the shoulder datum to the bullet ogive? With 33 years of reloading experience it has never occurred to me to make such a measurement.

WRT 300 BLK loads, the most important things will be the COL to ensure the rounds fit in the mag and the amount of bullet in the case neck to ensure the bullet stays put inside the case. This can be a problem with some of the lighter, shorter bullets. As such, jump to the lands will become a secondary or even tertiary issue.

Yes, you are correct, factory ammo will tend to have a big jump to the lands. This is so because the ammo makers have to ensure their ammo fits and safely functions in a wide variety of firearms. Jump = safe.

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Re: New Reloader with detailed COL numbers looking for double check

Post by ropedrag » Fri Dec 27, 2019 6:54 pm

Suputin221 wrote:
Fri Dec 27, 2019 3:02 pm
ropedrag wrote:
Tue Nov 26, 2019 3:28 pm
VERY New to reloading and being in my mid fifties I’m disappointed I waited this long. The number of rabbit holes to go down is amazing!

So, being a bit older I enjoy trying to apply logic to things but there are plenty of times when I discover I’m not as smart as I think I am.

XXX
XXX
XXX
XXX

So, If I’m doing this correctly the 2 ELD bullet/brass combinations will have a range of jumps from .07 to .16. These don’t seem ideal but are ok I guess. I then go and measure COL on my stock of factory subsonics and say BLK?! COL’s in the 2.12 range meaning these factory loads are jumping in the neighborhood of .25”, holy S*it! are these acceptable jumps for an AR?

Thanks!
Dude, you are WAYYYYYYYYYYYYYYY overthinking this whole thing. :shock:

First, lets clear up a few things.

COL: The measurement from the case head to the tip of the bullet. A mostly useless measurement except for the purposes of fitting the round into a magazine. Otherwise this number has no relevance to the firearm or chamber.

Headspace: Only relevant to ensure the case fits the chamber. Has no relevance to the bullet or the lands/throat.

I have no idea why you'd want to know the distance from the shoulder datum to the bullet ogive? With 33 years of reloading experience it has never occurred to me to make such a measurement.

WRT 300 BLK loads, the most important things will be the COL to ensure the rounds fit in the mag and the amount of bullet in the case neck to ensure the bullet stays put inside the case. This can be a problem with some of the lighter, shorter bullets. As such, jump to the lands will become a secondary or even tertiary issue.

Yes, you are correct, factory ammo will tend to have a big jump to the lands. This is so because the ammo makers have to ensure their ammo fits and safely functions in a wide variety of firearms. Jump = safe.

Yeah I likely am, but being new I don't know where the tolerances are so I'd rather error on over thinking things I guess :lol:

COL, got it, what's important is that the cartridge fits in the magazine. Recently learned this one while developing loads for my 6.5 creedmoor bolt gun. Thankfully the bullet(s) and loads like to jump!

Base to Datium, Base to Ogive (on lands), Datium to Ogive.

Datium to ogive, help me out with this if I'm not thinking correctly. I thought (think) when the round is chambered the shoulder is basically slammed/pressed up against the chambering (I'm looking at this like a stop) so this is what every other dimension should tie to, it is the constant yes? So the distance from the datium to the lands is also a constant hard steel dimension (subject to change with wear). While the datium to the case base is going to vary with fl or neck sizing bump, new or fire-formed, brand of brass, etc... So if I know the datium to ogive (on the lands) for a particular bullet I can easily control and know where it is in relation to the lands when I seat the bullet by adding this dimension to the jump I want to the datium to base dimension of whatever batch of brass I have to work with.

What you and others have helped me to understand is that for AR work this level of precision doesn't matter, just make sure the cartridge is within SAMMI spec length, fits in the mag and give the thing a bit of a crimping.

Thanks again

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Re: New Reloader with detailed COL numbers looking for double check

Post by dellet » Fri Dec 27, 2019 8:22 pm

ropedrag wrote:
Fri Dec 27, 2019 6:54 pm
Suputin221 wrote:
Fri Dec 27, 2019 3:02 pm
ropedrag wrote:
Tue Nov 26, 2019 3:28 pm
VERY New to reloading and being in my mid fifties I’m disappointed I waited this long. The number of rabbit holes to go down is amazing!

So, being a bit older I enjoy trying to apply logic to things but there are plenty of times when I discover I’m not as smart as I think I am.

XXX
XXX
XXX
XXX

So, If I’m doing this correctly the 2 ELD bullet/brass combinations will have a range of jumps from .07 to .16. These don’t seem ideal but are ok I guess. I then go and measure COL on my stock of factory subsonics and say BLK?! COL’s in the 2.12 range meaning these factory loads are jumping in the neighborhood of .25”, holy S*it! are these acceptable jumps for an AR?

Thanks!
Dude, you are WAYYYYYYYYYYYYYYY overthinking this whole thing. :shock:

First, lets clear up a few things.

COL: The measurement from the case head to the tip of the bullet. A mostly useless measurement except for the purposes of fitting the round into a magazine. Otherwise this number has no relevance to the firearm or chamber.

Headspace: Only relevant to ensure the case fits the chamber. Has no relevance to the bullet or the lands/throat.

I have no idea why you'd want to know the distance from the shoulder datum to the bullet ogive? With 33 years of reloading experience it has never occurred to me to make such a measurement.

WRT 300 BLK loads, the most important things will be the COL to ensure the rounds fit in the mag and the amount of bullet in the case neck to ensure the bullet stays put inside the case. This can be a problem with some of the lighter, shorter bullets. As such, jump to the lands will become a secondary or even tertiary issue.

Yes, you are correct, factory ammo will tend to have a big jump to the lands. This is so because the ammo makers have to ensure their ammo fits and safely functions in a wide variety of firearms. Jump = safe.

Yeah I likely am, but being new I don't know where the tolerances are so I'd rather error on over thinking things I guess :lol:

COL, got it, what's important is that the cartridge fits in the magazine. Recently learned this one while developing loads for my 6.5 creedmoor bolt gun. Thankfully the bullet(s) and loads like to jump!

Base to Datium, Base to Ogive (on lands), Datium to Ogive.

Datium to ogive, help me out with this if I'm not thinking correctly. I thought (think) when the round is chambered the shoulder is basically slammed/pressed up against the chambering (I'm looking at this like a stop) so this is what every other dimension should tie to, it is the constant yes? So the distance from the datium to the lands is also a constant hard steel dimension (subject to change with wear). While the datium to the case base is going to vary with fl or neck sizing bump, new or fire-formed, brand of brass, etc... So if I know the datium to ogive (on the lands) for a particular bullet I can easily control and know where it is in relation to the lands when I seat the bullet by adding this dimension to the jump I want to the datium to base dimension of whatever batch of brass I have to work with.

What you and others have helped me to understand is that for AR work this level of precision doesn't matter, just make sure the cartridge is within SAMMI spec length, fits in the mag and give the thing a bit of a crimping.

Thanks again
Datum to ogive can be useless or it can save your ass. Whether you know or not will depend on if you ever check it.

There are plenty of 308 bullets that will jam at less than magazine length. My favorite to pick on are the 147-150 FMJ cheap plinking bullets. Hornady for sure and I think Privi will jam, Hornady will even jam at the factory published length in the 9 edition data book.

There are a couple other bullets that will jam at 2.250" or 2.260" depending on where the shoulder is set.

Most people that load that long either think everything should be loaded to SAAMI max, are chasing velocity or want a short jump.

A cartridge loaded with a bullet set to touch the lands, in theory is headspacing of the bullet and shoulder at the same time. Move the shoulder forward, it headspaces off the shoulder. Move the shoulder back, it headspaces off the bullet. That is a safety reason for knowing the the datum to ogive measurement. Jam when you think you are jumpingcan add as much as 10,000 psi. Do that chasing velocity with a max load and it could get interesting.

The other reason to know that measurement and to use the same case and bullet each time you measure is to check throat erosion.
300 Blackout, not just for sub-sonics.

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Re: New Reloader with detailed COL numbers looking for double check

Post by ropedrag » Sat Dec 28, 2019 12:51 pm

Thanks for the input dellet!

I have no intention of not doing the full workup math on any round development and I'll always know where things are in relationship to the lands, if I came across as sounding like that it wasn't my intent. I will always invest the 15 minutes with each new bullet and the hornady OAL/Stony Point gauge to learn this dimension.

What I should have said is that I appreciate the help understanding tolerances with the AR platform so I don't drive myself crazy over a thousandth, which I will. The whole concept of a 1/4" jump being in the realm of Ok kind of spun me up a bit.

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Re: New Reloader with detailed COL numbers looking for double check

Post by Suputin221 » Sat Dec 28, 2019 5:21 pm

While the benchers guys made a thing out of jamming bullets into the lands, that is not a good idea for most of us. Once had an issue where I ejected an unfired round and left the bullet in the throat. That wasn't the worst part though. The case spilled ball powder into the bolt locking lugs and action. Basically the result was an inoperable rifle. Ball powder is just nasty to try to clean out of locking lugs and it very effectively prevents the bolt going into battery properly.

Thus we should always shoot for at least some jump to the lands.

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