Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

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realtreehunter
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by realtreehunter »

I thought the difference in the groups was right at 9 inches, from left to right. :oops:

:P
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by dellet »

sundevil11 wrote:Please explain what your interpretation is of max COL. It can mean a lot of things.


The SAAMI spec for the 300BLK cartridge shows the maximum cartridge overall length as 2.26". This also happens to be the maximum cartridge overall length that will cycle rounds out of a magazine, per SAAMI spec. I'm aware some magazines and receivers have a problem with cycling at 2.26", but my rifle doesn't. It will handle a max COL of 2.26". At least it will now that I'm using a micrometer sizing die and a good caliper to size to within a tolerance of .001".

However, my study was based on rounds sized using the cartridge base to ogive (CBTO) length method.I don't want to take the time to explain that method but I will say a few things about it. CBTO length and COL length do not map one to one with each other. That's the whole point in using the CBTO method - it gives more consistent seating depth because that distance is measured from rifling to ogive. The length of cartridge tips vary from that. Therefore, if you size to a consistent CBTO, the freespace distance will be the same, or closer to the same. This means, of course, that there is no direct way to convert COL into CBTO. The only way that this can be done is empirically. The process used is to gather up a bunch of already loaded rounds for that bullet type, sort them by COL, and then take the average for all the different CBTO lengths for each COL sort interval. That produces a line with a localized variance on it. See Figure 6 in my original post. By generating a straight trendline from the variance line, you now have an effective COL to CBTO conversion formula. Just remember that there is going to be some COL spread for any CBTO length you choose. It’s unavoidable.

Anyway, here are the equations I used for that conversion (See Figure 6):

CBTO = (.97 * COL) - .528
COL = (CBTO + .528) / .97

Just remember, the equations from my data are only good for 220 gr. SMKs. They are based on a single 100 round sample set. The equations are only truly representative for that sample. For that one fixed sample set, maximum COL corresponded to a CBTO of 1.664”.

Using a CBTO equivalent to maximum COL might get you into trouble. The trouble isn’t necessarily in exceeding COL. The shooters who seat their bullets right on the rifling, or just a few .001” intervals away from it, exceed maximum COL all the time. The biggest problem is for people shooting semiautomatics who want to cycle their ammo out of the magazine. That may or may work with a CBTO corresponding to maximum COL. For me, it worked.

I mentioned before that a (16) count interval of evenly spaced .001” test points starting from maximum COL is sufficient for finding your best CBTO length. That interval is way generous. There will be approximately three relative minimums in that test interval. The best, will be the one closest to maximum COL. (See Figures 8, 11 and 12). The relative minimums will get worse the farther away you get from maximum COL. That’s inherent in the mathematics of Pi.

This is going to raise the obvious question of what about those ‘freespace zero’ guys who seat their bullets right on the rifling. I did mathematical modeling to consider that also, but for obvious liability reasons I’m not prepared to submit graphs or charts that might encourage that. The mathematical model I generated suggests that there is no advantage to be had by exceeding maximum COL unless and until you’re within only a few thousandths of an inch from the rifling. The reason for that is that the next and last really good relative minimum on the harmonic curve doesn’t occur until just a few thousandth’s of an inch before the rifling. The relative minimum just short of maximum COL is the next best.

Shooting with bullets seated on the rifling is going to wear a barrel out really quickly. I’m not prepared to state what sort of relative advantage that might produce. I don’t want to encourage that kind of reloading, but I’ll tell you this: The relative advantage isn't much.
I had hoped that by now the OP would have realized some of the shortcomings and safety issues involved with his method of determining maximum length and his general lack of knowledge as to why that number is normally used, and why the way his research as presented, has the potential to seriously hurt or kill someone. Since he has not clarified that I will.

At no point has he established a true maximum Cartridge Base To Ogive length as defined and used by reloaders.

This is the actual distance from the base of the cartridge, to the the point a 220 SMK would touch the lands in his barrel. What he has used is SAAMI max overall length. While he does acknowledge that many can and do load to exceed that lenght, no where does he acknowledge that there are many bullets that can not be loaded to magazine length, because they will engage the rifling long before reaching 2.260". Failure to verify this length, the accepted use of the term "maximum cartridge base to Ogive" can be fatal.

The OP stated that he did not want to explain measuring CTBO and why it is important. While he explained why it is important for load consistency, he has no clue how and why to use it for safety.

Here's the problem with using SAAMI or magazine length as your starting point. Bullet profiles make a difference.

Let's take a look at just one of the most popular bulk bullets used for 300 Blackout. The Hornady 150 FMJ #3037.

This bullet CAN NOT BE LOADED TO SAAMI MAX LENGTH OF 2.260. The maximum length with brass sized to maximum base to datum line will be approximately (this will vary chamber to chamber) 2.240". It would be possible for this bullet to seat in the lands probably as short as 2.225"

So if we use the OP's method of starting at 2.260", you could have a jam into the lands of more than .030" using a Hornady 150 FMJ. This has the possibility of fatal consequences.

Sundevil, while your idea of timing the bullets entrance, or jump into the chamber for accuracy might have merit. Your lack of knowledge and understanding of what happens in a chamber, combined with your ignorance of and use of terms that you really do not understand, are going to get someone hurt.

Your method of trying to determine MAX. Cartridge Base To Ogive length based on SAAMI length or anything else, other than bolt face/datum line to lands IS BOTH MISGUIDED AND DANGEROUS.

Please, either learn enough to keep others safe that might read your ideas and methods, including terminology and definitions, or just stop sharing.

One more time if I was not clear enough.

NEVER, EVER, USE MAXIMUM SAAMI CARTRIDGE LENGTH AS A STARTING POINT, FOR ANY BULLET WITHOUT DETERMINING IF THAT LENGTH WILL PLACE THE OGIVE OF THE BULLET INTO THE LANDS OR THROAT OF THE CHAMBER.
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by sundevil11 »

dellet wrote:
Let's take a look at just one of the most popular bulk bullets used for 300 Blackout. The Hornady 150 FMJ #3037.

This bullet CAN NOT BE LOADED TO SAAMI MAX LENGTH OF 2.260. The maximum length with brass sized to maximum base to datum line will be approximately (this will vary chamber to chamber) 2.240". It would be possible for this bullet to seat in the lands probably as short as 2.225"

So if we use the OP's method of starting at 2.260", you could have a jam into the lands of more than .030" using a Hornady 150 FMJ. This has the possibility of fatal consequences.

Sundevil, while your idea of timing the bullets entrance, or jump into the chamber for accuracy might have merit. Your lack of knowledge and understanding of what happens in a chamber, combined with your ignorance of and use of terms that you really do not understand, are going to get someone hurt.

Your method of trying to determine MAX. Cartridge Base To Ogive length based on SAAMI length or anything else, other than bolt face/datum line to lands IS BOTH MISGUIDED AND DANGEROUS.

Please, either learn enough to keep others safe that might read your ideas and methods, including terminology and definitions, or just stop sharing.

One more time if I was not clear enough.

NEVER, EVER, USE MAXIMUM SAAMI CARTRIDGE LENGTH AS A STARTING POINT, FOR ANY BULLET WITHOUT DETERMINING IF THAT LENGTH WILL PLACE THE OGIVE OF THE BULLET INTO THE LANDS OR THROAT OF THE CHAMBER.

Really? The data I provided was only for one bullet, specifically the 220gr SMK. I meaured the full base to land distance for this bullet using a Hornady OAL gauge. On my rifle, that distance is at or around 1.993", when measured as CBTO. This means that at maximum COL, there is about .329" of freespace. This means, that for my rifle, you cannot seat a 220gr SMK bullet on the lands using a 300BLK cartridge that has had the neck trimmed properly and the cartridge trim length is in spec. There's simply nothing to hold the bullet.

You keep going on and on about other size bullets. I'm not discussing other size bullets. I only made a report on one load, using one bullet, the 220gr SMK, with measurements for one rifle, my own. You should measure your own rifle and be satisfied that I have measured mine.
Last edited by sundevil11 on Sun Jan 08, 2017 7:47 pm, edited 1 time in total.
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by sundevil11 »

Cold Air Temperature Effects

One question I haven’t had the chance to address until now is the effect temperature has had on the actual velocity of the supersonic threshold shown in my charge weight equivalency curve.

Here is that curve again with approximate temperature information for the beginning of the tests in Dec. 2015 and at the end of the tests in July 2016:

See Figure 15: Updated Charge Weight Equivalency Curve with Temperature Information for End Points.
https://www.facebook.com/photo.php?fbid ... =3&theater


Hodgdon’s originally published load for 4227 was 10.5gr with a muzzle velocity of 1,044 ft/sec. Using a speed of sound calculator, a speed of sound of 1,144 ft/sec can be readily calculated for 85 degF. This would be the temperature and the speed of sound during the day of testing when the charge weight for the optimal CBTO was found.

The speed of sound calculator I used is:

http://www.sengpielaudio.com/calculator-speedsound.htm

Using linear interpolation of the charge weights, an approximate average velocity for this load can be estimated at 1,119 ft/sec. [Value Corrected]. The suppressor doesn't add a lot to an interpolation because the threshold value for supersonic is strictly a function of temperature. But Yes, that includes an added 25 ft/sec to my velocity to account for the increase the suppressor provides over the load's book muzzle velocity value. In any case, my personal rule here is that if the estimates I make don't show a lot of need for worry, I don't worry. If they do, I take real measurements. It's subjective. Where to make the switch is a personal decision. Others can switch over sooner to taking measurements if they want to. It's a free country.

Anyway, a first cut linear interpolation suggests that for air temperatures just above 54 degF, this load probably goes supersonic. If that were true, it would make this a summertime only load for use only for temperatures above 54 degF. Or does it? With colder temperatures, air becomes denser. According to Hornaday's ballistics calculator, I can expect to lose another 12 ft/sec of velocity with a temperature drop from 85 degF to 55 degF, and another 4 ft/sec from 55 degF to 45 degF. That brings my estimated velocity down another 16 ft/sec to 1,095 ft/sec. At an estimated velocity of 1,095 ft/sec, I'm not likely to cross the supersonic threshold until the temperature drops to about 39 degF. I can't really test that because it never really gets that cold up here during the day near the Puget Sound. To give you a little bit of anecdotal information about where I live, I have neighbors who are pig farmers, or at least they have Vietnamese pot bellied pigs. They keep them as pets. Anyway, their pig slop never freezes in the winter.

It seldom gets below freezing up here within a few miles of the Puget Sound, and that's where my range is. Too bad the South is so much colder. In the winter here, the daytime temperature doesn’t usually get below 40 degF. That’s not much of a test opportunity - when I'm not likely to encounter the phenomena I'm looking for within the temperature ranges experienced here.

Because of the Puget Sound’s influence on the local weather, we have a false spring with warm balmy weather that occurs sometime around late January. By the end of that false spring, the average daily temperatures will have gone back up into the 50s. It won’t go back down into the 40s again until next December. If you want to know how this load handles cold temperatures below 40 degF and whether or not it goes supersonic, I guess you'll just have to test it yourself. I simply don't have a horse entered in that race.
Last edited by sundevil11 on Mon Jan 09, 2017 2:49 am, edited 3 times in total.
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by dellet »

sundevil11 wrote:
dellet wrote:
Let's take a look at just one of the most popular bulk bullets used for 300 Blackout. The Hornady 150 FMJ #3037.

This bullet CAN NOT BE LOADED TO SAAMI MAX LENGTH OF 2.260. The maximum length with brass sized to maximum base to datum line will be approximately (this will vary chamber to chamber) 2.240". It would be possible for this bullet to seat in the lands probably as short as 2.225"

So if we use the OP's method of starting at 2.260", you could have a jam into the lands of more than .030" using a Hornady 150 FMJ. This has the possibility of fatal consequences.

Sundevil, while your idea of timing the bullets entrance, or jump into the chamber for accuracy might have merit. Your lack of knowledge and understanding of what happens in a chamber, combined with your ignorance of and use of terms that you really do not understand, are going to get someone hurt.

Your method of trying to determine MAX. Cartridge Base To Ogive length based on SAAMI length or anything else, other than bolt face/datum line to lands IS BOTH MISGUIDED AND DANGEROUS.

Please, either learn enough to keep others safe that might read your ideas and methods, including terminology and definitions, or just stop sharing.

One more time if I was not clear enough.

NEVER, EVER, USE MAXIMUM SAAMI CARTRIDGE LENGTH AS A STARTING POINT, FOR ANY BULLET WITHOUT DETERMINING IF THAT LENGTH WILL PLACE THE OGIVE OF THE BULLET INTO THE LANDS OR THROAT OF THE CHAMBER.

Really? The data I provided was only for one bullet, specifically the 220gr SMK. I meaured the full base to land distance for this bullet using a Hornady OAL gauge. On my rifle, that distance is at or around 1.993", when measured as CBTO. This means that at maximum COL, there is about .329" of freespace. This means, that for my rifle, you cannot seat a 220gr SMK bullet on the lands using a 300BLK cartridge that has had the neck trimmed properly and the cartridge trim length is in spec. There's simply nothing to hold the bullet.

You keep going on and on about other size bullets. I'm not discussing other size bullets. I only made a report on one load, using one bullet, the 220gr SMK, with measurements for one rifle, my own. You should measure your own rifle and be satisfied that I have measured mine.
.

And this is exactly why I have continued to pop up in this thread.

You either do not know how to measure base to ogive and compare it to the seated depth where the bullet hits the lands. You have the wrong tools. Your chamber is so completely out of spec that your barrel is useless. Or what is likely the problem you have no clue and should not be loading.

The chamber was designed so that a 220 SMK would have a .010" jump at 2.260".

If you can load a 220 Match King so long it falls out of the neck you should throw your barrel in the garbage. That would also explain you you have had so much trouble with accuracy.

I would hate to suggest that you have wasted all of this time, so I will just say it is so.

You sir are a toxic mix if ignorance and arrogance that will get anybody who listens to your careful findings hurt.
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by bangbangping »

sundevil11 wrote:You keep going on and on about other size bullets. I'm not discussing other size bullets.
Bullshit.
bangbangping wrote:Please explain what your interpretation is of max COL. It can mean a lot of things.
sundevil11 wrote:The SAAMI spec for the 300BLK cartridge shows the maximum cartridge overall length as 2.26".
sundevil11 wrote:It comes down to this, the pattern with the minimum most repeatable dispersion will always be found one relative minimum of the highest frequency component below maximum COL, and is best measured as CBTO. This minimum is always going to be less than (16) .001" intervals from max COL. The mathematics proves it.... Start at max COL and work down...
dellet is absolutely correct. You say:
sundevil11 wrote:If I can make things easier for the next guy coming up the trail, I will.
I say, you're going to hurt the next guy who doesn't know any better and follows your advice. dellet is also correct about your 1.993" CBTO. That's at least 1/4" off.
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by rebel »

I don't know about the Puget sound, here in the mountains of the South, we call it going to horses's ass to get a bucket of pig crap.
Your information is flawed and dangerous as pointed out. Dealing in absolutes is never wise.
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by bangbangping »

sundevil11 wrote:Using linear interpolation of the charge weights, an approximate average velocity for this load can be estimated at 1,111 ft/sec.
It cannot, unless you say 1111 +/- 100. First off, Hodgdon data is without a suppressor, which adds ~30 fps. Different chamber, different barrel, different brass, different primer, different lot of powder, different conditions. Without a chrono you're just guessing. You can spend hours doing math, typing crap, and making charts, but you're guessing. It means nothing.

For only one simple real world example, the 208 AMAX:
Hodgdon 16" barrel => 9.8g. IMR 4227 @ 1041 fps
My 14.5" barrel (suppressed) => 9.5g 4227 @ 1116 fps
0.3 grains less powder, 1 1/2" shorter barrel, 75 fps more velocity.
Last edited by bangbangping on Mon Jan 09, 2017 4:29 pm, edited 1 time in total.
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by dellet »

There will be plenty of people that will take one look at the OP's numbers that he claimed to have measured, in his barrel, and come to the conclusion he is either completely full of shit, or has a barrel that is so very far out of spec that no one can trust his results. He is too arrogant to admit he made a mistake in his level of knowledge needed to take on the project that he has.

After repeated attempts to point him in the right direction, sometimes polite, sometimes not, it's time to show him why his numbers are complete and utter garbage.

After measuring his chamber he came up with this
sundevil11 wrote:Really? The data I provided was only for one bullet, specifically the 220gr SMK. I meaured the full base to land distance for this bullet using a Hornady OAL gauge. On my rifle, that distance is at or around 1.993", when measured as CBTO. This means that at maximum COL, there is about .329" of freespace. This means, that for my rifle, you cannot seat a 220gr SMK bullet on the lands using a 300BLK cartridge that has had the neck trimmed properly and the cartridge trim length is in spec. There's simply nothing to hold the bullet.


Let's take a look at what that would look like, CTBO 1.993".
Image

It would have an overall length of roughly 2.375"
Image

Here's what it looks like in a Sheriden Gauge, cut with a reamer to simulate a chamber.
Image

Here's what it looks like if it had been loaded correctly to max SAAMI spec of 2.260"
Image

I did not pull the the idea of in a proper chamber a 220 SMK, would have a jump of .010" when loaded to 2.260". That is a direct quote from Robert Silvers who designed the chamber and submitted the specs to SAAMI.
300Blk wrote:The throat was designed so that if you loaded a Sierra 220 or 240 to 2.260 there would be a 0.010 jump to the lands.
Here is one of the times he shared that nugget with us.
viewtopic.php?f=141&t=85385

To make this type of error and publishing data here or anywhere else, with these kinds of mistakes either in use of tools or understanding of the subject matter, is not only a garbage finding but as I said before possibly dangerous.

All of the math, all of the equations all of the findings are based on either a false scenario or incorrect measurements of travel.

Garbage in, garbage out.

You either have a barrel that is garbage, or you did not measure it properly. The third possibility is that you do not have the tools you claim to have used and counted on reading the SAAMI drawings which you interpreted incorrectly.

Bottom line, do not trust this mans numbers or conclusions
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Re: Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

Post by plant.one »

what are the chances of getting this thread locked, and for safety reasons the OP edited to note that the information contained herein is unsafe and should never be used.


i can see the merit of leaving the thread otherwise in tact as an example of what NOT to do, but it should probably be noted as such.
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