300 blackout oddities at the range

[CorvZ061]

Finally got out to shoot my 700 aac-sd for the first time. Got it sighted in with some Winchester Suppressed 200gr rounds. Didn’t run a chrono for these shots, but was getting a 3” group at 50yds. I know the hogue over molded stock is horrible, but damn.

Swapped to some hand loads and this is where it got even more odd. I had some IMR4198 and some 220gr Everglades plated bullets with a starting load at 10.3gr. The first shot was several feet low, garmin read 540fps. Second shot was 4” low and read 730fps, the remaining 3 shots were within 10 of 730fps. Went to my next 5 at 10.5gr. First shot again was 560ish fps the remaining 4 were around 745. From there went to 10.7gr and first shot was 568fps and remaining 4 were 755ish and finally the last set were 10.9gr and all 5 were within 25fps around 770fps. The only difference between the last group and the others were I loaded and shot the last group without letting the rifle cool down. The other low fps shots were all cold bore.

None of the loads grouped well, the best was 3”. But I have a Aero Solus chassis I’m putting it in when my mag gets here to fix the crappy chassis, I’m hoping that will help with grouping.

My issue is the FPS spread. According to the Hodgedon website the 10.9gr load should have been close to 1050 with a 16” test barrel and I was seeing 770 with a 16.5” barrel. Anyone seen this before?

 

[SpeedyR]

My first thought was to check the crimp. I had some weird chrono data a bit ago and started to check some of the remaining rounds. Bullets were loose so guessing they were moving out further and causing slow velocities. Other than that I got nothing.

 

[CorvZ061]

My first thought was to check the crimp. I had some weird chrono data a bit ago and started to check some of the remaining rounds. Bullets were loose so guessing they were moving out further and causing slow velocities. Other than that I got nothing.

I’m using a Lee Factory crimp die. I was talking to another friend about it and I’m wondering, since there is no published load data for these bullets specifically, if they aren’t protruding into the cartridge as much as the jacketed data I’m using to reach the OAL. That very well could cause a pressure drop.

 

[alexs2006]

Here are said chrono results.

It was the damned thing I’ve ever seen in a chrono. The first shots were 2 foot low it seemed like.

 

[myrmidon]

Try a different powder or a different projectile. I,and others, get great results with 190,200 & 208 projectiles. I shoot 220’s but get better results with the other ones.
H110 or CFE BLK?
Anything I’ve loaded under 11.5 grns. don’t perform that well.

 

[CorvZ061]

Try a different powder or a different projectile. I,and others, get great results with 190,200 & 208 projectiles. I shoot 220’s but get better results with the other ones.
H110 or CFE BLK?
Anything I’ve loaded under 11.5 grns. don’t perform that well.

IMR 4198. I’m going to load the next test with 1680 and adjust seating depth a little. These were seated to 2.23. If my measurements are right, the cannelure would have an OAL of 2.089 which I have found for Berry’s plated data too.

 

[cmshoot]

How much unused volume do you have in the cases? If you've got a lot of room for that powder charge to slosh around, you can get a huge difference in velocity depending upon where the powder was in the case when it ignited.

 

[CorvZ061]

How much unused volume do you have in the cases? If you've got a lot of room for that powder charge to slosh around, you can get a huge difference in velocity depending upon where the powder was in the case when it ignited.

The more I’m reading the more I’m thinking this is the case. I’ve been reloading pistol for years, first fore ray into to bottle necked and rifle cartridges. I think I’ve determined that the plated bullets are flat based whereas the jacketed data are boat tailed. From the measuring I'm doing after the fact, the bullets I’m using are shorter than the Sierra matchkings I based the data on which is leaving more empty space than intended.

 

[alexs2006]

You can make it back to the range if you load em!

 

[cmshoot]

The more I’m reading the more I’m thinking this is the case. I’ve been reloading pistol for years, first fore ray into to bottle necked and rifle cartridges. I think I’ve determined that the plated bullets are flat based whereas the jacketed data are boat tailed. From the measuring I'm doing after the fact, the bullets I’m using are shorter than the Sierra matchkings I based the data on which is leaving more empty space than intended.

Long before .300Blk, we were handloading subsonic .308. A metric **** ton of unused case capacity with most of the loads. We would fill the rest of the case after we dropped the powder in. Cream of Wheat, poly pillow filling, etc.

I've seen the same thing happen in early "cowboy" loads for .45 Colt, .44 Magnum/Special, etc.

Happened in my first USPSA Single Stack load, using Titegroup and a Berry's plated hollow-base 185grn bullet. Across the chrono graph, the difference between Major and Minor velocity depended on where the powder was in the case.