AA9 velocity variation issues

[rumlover]

All,

Took 50 rounds of 220 SMKs loaded with 8.3 grains of AA9 to the range and put them over the chrony. The powder weights were thrown by an RCBS chargemaster/scale combo. I had velocity variations from 968 to 1160fps. Wiskey Tango Foxtrot?

Is there another powder that is more consistent? I imagine the difference in veolcity with AA9 is in the fraction variations (ie 8.357 grains v/s 8.321 grains) but our scales can measure past the 1/10th of a grain.

Is 1680 more tolerant?

Is there another powder that is better suited?

Because I know someone will ask:
8.5" Pacnor barrel
1/8 twist
7.62SD

The good news, however....I was getting good groups when the velocity was under a 20fps standard deviation. Consistently 3/4" groups at 100y.

[buffetdestroyer]

I ran a 40 fps spread with Vihtavuori N110 for 10 rounds (not individually weighed - dropped from a Lee Perfect Powder Measure). This is the most accurate of 3 powders tried in my gun (2400, 1680 & N110). I would try this powder as the first step to see how if it is just that your gun doesn't like AA9.

But here are so many factors when shooting subs that can affect consistency. The length of the 220 SMK creates a lot of surface area drag on the barrel and the case mouth. Additionally the gas required to unlock the bolt and cycle the action may vary depending on conditions and the cleanliness of your weapon.

My scale is accurate to within 1/10th of a grain and if I measure it 3 times (by lifting the pan and setting it back down), I will usually have 1 that is 1/10th off from the other 2.

.1 grain will make a big difference in consistency when your load is under 10 grains (proportionately .1 grain is a 1%+ variance where on a 45 grain load it is equivalent to a .5 grain difference to achieve the same overall percentage of variance).

The other solutions I would recommend trying are:

Trim and Prep your brass with a chamfer to make sure they are trimmed to a consistent length and the bullet feeds in smoothly - checking neck thickness and to see if they are concentric after being resized may help too.

Try a different type of primer (try a match or benchrest brand to see if it makes a difference - inconsistent primers can add to a significant variance that you wouldn't see as much in higher capacity loads as discussed before).

Double Check your powder weight for each load. It takes a long time, but it is the only way to be sure.

Clean chamber and barrel between each shot to see if it is because the case is sticking or your barrel fouls too easily (you may need to fire lap it to smooth out machining burrs and imperfections to get the consistency you want). Moly lube might also be an option for bullets if this is the problem.

If that doesn't help, then it may be that your powder lot is inconsistent (it is too settled or has been exposed to excessive heat, humidity etc.).

Oh the fun of troubleshooting!

[Retooferab]

I am having the same issue. Post your lot numbers and I will post mine and maybe we can figure this out. You are using the same charge that I am. I was getting good groups also. I have AA9, 1680, and N110. I have been loading 8.7 gns N110 with good results. My gun is a 10.5" ar

[snipecatcher]

I throw my charges with a Chargemaster also. While this is not typical, I looked through my load book and found this 5 shot string:

240 SMK @ 2.21", 9.4 grains VVN110:
1121
1122
1123
1123
1120

That just shows that it IS possible to have VERY low StDev, if only occasionally. :grin: That is out of an AR. Between VVN110, 2400, and 1680, the VVN110 is the winner when it comes to consistency. Most of my velocities for a given load vary no more than 50 fps from lowest to highest velocity. Try some VVN110. It's a good thing it lasts so long with this cartridge, because it's been my experience that it isn't an easy powder to find.
-Dan

[ezed]

I have seen the same variation the different powders, specifically the AA9. I weigh each and every charge, individually, to get to try and eliminate this problem, but there is still a wide variance with AA9. The best powders I have the least variation with, are the 4227 and 322 with as little as 35-45 ft/s variation in 10 round shots.

[rumlover]

I'll pick up some N110 this weekend and I've got 2lbs of 1680 sitting on the front porch waiting for me now. I trimmed and primed 100 cases last night and will load them up tonight.

I'll try to report back NLT Monday PM.

[rumlover]

Well, it doesn't look like I'm going to be able to get to a range where I can set up the chrony today. Hopefully next weekend...sucks living in N VA territory.
Stand by...

[rumlover]

Finally got to the range on Sat. I tried 1680 and LilGun. The 1680 was consistently cycling and fairly velocity consistent. I didn't shoot for groups...there was a suppressor issue sending the occasional shot far to the right by several feet. Strangely though, while a few brass shavings came out of the can, there were no smudges on the rim of the exit end and I couldn't see any damage or rub marks inside the can.

I'll take the raw data to work tomorrow, load it into excel to crunch the data, and report back. Ballpark...10.5 gr 1680 should be right on 1040 in a 8.5" with a 762SD attached.

[rumlover]

AA 1680
Barrel: 8.5" Pacnor TEMP: 38 Pressure 29.6"
Can: AAC 762SD Altitude 800' Overcast
Powder measured with a RCBS Chargemaster combo.
Win SR primers
LC 2004 Brass

220 SMK 10.0GR
SHOT VELOCITY Average: 842.8
1 890 SD: 34.08
2 873
3 843
4 854
5 849
6 849
7 819
8 767
9 862
10 822

220 SMK 10.4GR
SHOT VELOCITYAverage: 913.68
1 921 SD: 44.92
2 962
3 933
4 828
5 889
6 961
7 911
8 968
9 892.8
10 871

220 SMK 9.8GR Average 811
1 829 SD: 47.14
2 717
3 821
4 765
5 895
6 834
7 839
8 807
9 796
10 807

Here's the results from Sunday. I tried to post a chart, but it wouldn't paste to the post. I'll bump it up to 10.6 grains and try for accuracy this weekend. That's a little better than AA9...but there are still a few oddballs that would have equated to a miss.