To start this off, I should tell you that I have been reloading for a LONG time. A VERY LONG time. More than 35 years, in fact. That being said, I don't claim to know everything, and I still find myself wondering why things just don't seem to add up.
Case in point :
I have finally started to load the .300 AAC Blackout. I have no less than 6 respectable sources of data for this cartridge. Hornady, Speer, Nosler, Sierra, Hodgdon/IMR/Winchester powders, Western powders ( Accurate/Ramshot ), and a few more as well. After studying all the data sources I have, I have come up with 5 different bullet/powder combinations I think will produce the results I'm looking for. 3 of these combinations involved what I will classify as "light" bullets, and used Hodgdon Li'l Gun powder. The other 2 "heavy" bullets used Accurate 1680 powder.
Today I went to the range equipped with the LabRadar chronograph, and 10 of each of these carefully constructed test loads. Today's mission was more about making sure there were no pressure problems and establishing a baseline of velocities to compare. First, I shot 10 rounds of FACTORY ammunition to establish an average velocity. Then, 10 rounds of my comparable handloads. I did this with each bullet weight. ( you with me so far ? )
The light bullets ( 110, 125, & 135 gr ) with Li'l Gun showed no issues at this point, however having used Li'l Gun previously, I'm aware that it has a tendency to go from "no problems" to signs of high pressure ( flattened and cratered primers, possibly worse ) very quickly, sometimes in as little as 1/2 gr. Therefore, I will proceed with load development with these.
Here's where I run into problems. The heavy bullets ( 150 & 190 gr ) with A1680 load data is all over the place. That in and of itself, I could deal with. The problem I'm having is that ALL of it is impossibly wrong ! Here's what I mean A1680 under 150 gr bullet: ( Sierra HPBT Matchking ) [ disclaimer: this is not the EXACT bullet I'm loading, but is very close ]
Source : Western powder - start load 19.4 gr @ 1895 fps. Max load 21.6 gr @ 2086 fps.
Source : Hornady 10th edition - start load 15.4 gr @ 1500 fps. Max load 22.0 gr @ 2050 fps.
Not a whole lot of issues yet...until you realize that a sized and properly trimmed to length case cannot possibly hold that amount of powder and still seat a bullet. A case will hold 20.0 gr of A1680 and be able to compress it enough to seat a flat base bullet to the bottom of the neck. A1680 is a VERY fine spherical powder which fills the case tightly, and leaves very little room to compress it. In testing, with a 150 gr bullet, I found that I could fit no more than 20.0 gr and that was heavily compressed.
Wait, it gets worse. With a 190 gr bullet and A1680 the problem is even more pronounced. Data for a 190 is not shown from Western powders, but one can make a reasonable assumption that it would fall between the next lower and next higher data. Thus, for comparison, start load for a 175 gr bullet is 17.7gr @ 1637 fps. Max load is 19.7gr @ 1801fps. And for a 210 gr bullet, it is 12.9gr @ 1308 fps. and max load is 14.4gr @ 1458 fps.
Hornady data for a 190 is as follows: start 12.9gr @ 1200 fps, and max is 17.8 gr @ 1650 fps.
Once again, in testing, I find that I can fit no more than 15.5 gr under a 190 gr bullet and still be able to seat it. I know that 2.3 gr doesn't seem like very much, but how the hell does Hornady come up with these numbers ? Talk about putting 10 pounds of shit in a 5 pound bag....!!
Ok, if you've read this far and actually understand what I'm trying to say, tell me where I F'ed up.
For the record, All test loads shot today were well below any Max load data. Li'l gun powders produced velocities higher than expected given the short (12") barrel, but showed a wide standard deviation in velocities. Accurate 1680 produced velocities perhaps slightly higher than expected, but the standard deviation was exceptional. The 10 shot group of 150 gr bullets producer a SD of only 29 fps. The 9 shot group ( chrono didn't capture 1 round ) of 190 's produced a SD of 16 fps.
Thoughts ?
Case in point :
I have finally started to load the .300 AAC Blackout. I have no less than 6 respectable sources of data for this cartridge. Hornady, Speer, Nosler, Sierra, Hodgdon/IMR/Winchester powders, Western powders ( Accurate/Ramshot ), and a few more as well. After studying all the data sources I have, I have come up with 5 different bullet/powder combinations I think will produce the results I'm looking for. 3 of these combinations involved what I will classify as "light" bullets, and used Hodgdon Li'l Gun powder. The other 2 "heavy" bullets used Accurate 1680 powder.
Today I went to the range equipped with the LabRadar chronograph, and 10 of each of these carefully constructed test loads. Today's mission was more about making sure there were no pressure problems and establishing a baseline of velocities to compare. First, I shot 10 rounds of FACTORY ammunition to establish an average velocity. Then, 10 rounds of my comparable handloads. I did this with each bullet weight. ( you with me so far ? )
The light bullets ( 110, 125, & 135 gr ) with Li'l Gun showed no issues at this point, however having used Li'l Gun previously, I'm aware that it has a tendency to go from "no problems" to signs of high pressure ( flattened and cratered primers, possibly worse ) very quickly, sometimes in as little as 1/2 gr. Therefore, I will proceed with load development with these.
Here's where I run into problems. The heavy bullets ( 150 & 190 gr ) with A1680 load data is all over the place. That in and of itself, I could deal with. The problem I'm having is that ALL of it is impossibly wrong ! Here's what I mean A1680 under 150 gr bullet: ( Sierra HPBT Matchking ) [ disclaimer: this is not the EXACT bullet I'm loading, but is very close ]
Source : Western powder - start load 19.4 gr @ 1895 fps. Max load 21.6 gr @ 2086 fps.
Source : Hornady 10th edition - start load 15.4 gr @ 1500 fps. Max load 22.0 gr @ 2050 fps.
Not a whole lot of issues yet...until you realize that a sized and properly trimmed to length case cannot possibly hold that amount of powder and still seat a bullet. A case will hold 20.0 gr of A1680 and be able to compress it enough to seat a flat base bullet to the bottom of the neck. A1680 is a VERY fine spherical powder which fills the case tightly, and leaves very little room to compress it. In testing, with a 150 gr bullet, I found that I could fit no more than 20.0 gr and that was heavily compressed.
Wait, it gets worse. With a 190 gr bullet and A1680 the problem is even more pronounced. Data for a 190 is not shown from Western powders, but one can make a reasonable assumption that it would fall between the next lower and next higher data. Thus, for comparison, start load for a 175 gr bullet is 17.7gr @ 1637 fps. Max load is 19.7gr @ 1801fps. And for a 210 gr bullet, it is 12.9gr @ 1308 fps. and max load is 14.4gr @ 1458 fps.
Hornady data for a 190 is as follows: start 12.9gr @ 1200 fps, and max is 17.8 gr @ 1650 fps.
Once again, in testing, I find that I can fit no more than 15.5 gr under a 190 gr bullet and still be able to seat it. I know that 2.3 gr doesn't seem like very much, but how the hell does Hornady come up with these numbers ? Talk about putting 10 pounds of shit in a 5 pound bag....!!
Ok, if you've read this far and actually understand what I'm trying to say, tell me where I F'ed up.
For the record, All test loads shot today were well below any Max load data. Li'l gun powders produced velocities higher than expected given the short (12") barrel, but showed a wide standard deviation in velocities. Accurate 1680 produced velocities perhaps slightly higher than expected, but the standard deviation was exceptional. The 10 shot group of 150 gr bullets producer a SD of only 29 fps. The 9 shot group ( chrono didn't capture 1 round ) of 190 's produced a SD of 16 fps.
Thoughts ?