velocity issues

[elmr007]

Shooting 240gr mk. OAL 2.260 H110 powder 10gr.
First shot is 1147, second 1109, third 1083, fourth 1060 and then it stays there for the rest of the string. Hence vertical patterns. Doesn't matter what primers I use. Have tried benchrest,magnum ,standard ,Winchester ,cci, federal. All the above. Also tried 220mk and 200mk ammo, same thing.

[Titleiiredneck]

Originally Posted by elmr007

Shooting 240gr mk. OAL 2.260 H110 powder 10gr.
First shot is 1147, second 1109, third 1083, fourth 1060 and then it stays there for the rest of the string. Hence vertical patterns. Doesn't matter what primers I use. Have tried benchrest,magnum ,standard ,Winchester ,cci, federal. All the above. Also tried 220mk and 200mk ammo, same thing.

H110 can be finicky, try viathouri or others listed here for possible better results. This is from the sierra manual for 220 smk's

Powder /Velocity
1000 1100 1200 1250 1300
AA-No.9 9.4 10.3 11.2 11.7 12.2
2400 10.0 10.7 11.5 11.9 12.3
Viht N110 9.4 10.2 11.1 11.6
H110 9.9 10.9 11.9 12.4
296 9.8 10.7 11.7 12.2 12.7
Viht N120 11.5 12.5 13.4
AA-1680 11.7 12.7 13.8 14.3 14.9
Energy/ft.lbs. 489 591 704 763 826
Powder Grains Velocity Ft. lbs.
Accuracy Load Viht N110 11.6 1250

[snipecatcher]

Originally Posted by elmr007

Shooting 240gr mk. OAL 2.260 H110 powder 10gr.
First shot is 1147, second 1109, third 1083, fourth 1060 and then it stays there for the rest of the string. Hence vertical patterns. Doesn't matter what primers I use. Have tried benchrest,magnum ,standard ,Winchester ,cci, federal. All the above. Also tried 220mk and 200mk ammo, same thing.

Are you cleaning your barrel in between shot strings? All of my barrels do that to some extent when they have been cleaned.

[amafrank]

I'll add a +1 to the H110 being crap statement. We've had some problems with consistancy and a lot of trouble with temperature changes making huge differences in velocity. N110 from Vihta Vouri works much better....so does 2400 or H4227.
You may also find that your dropping velocity is due to the oil wearing out of the barrel. I find that my first shot from a cleaned barrel is supersonic and they drop from there for a few rounds and then become consistant. If you run an oil patch or a patch with cleaning solvent through the bore and start shooting again you can get very repeatable change which mirrors your result.

Frank

[Retooferab]

Switch to N110 or AA9 you will get better results.

[elmr007]

Thanks for the info..I am not cleaning the bbl, so that's not the issue. This was also happening with reddot powder. I will try the vihta vouri and see how it works. Will probably be Tuesday before anyone opens up that has it. :( that's what happens when you live in a remote part of the country.

[N310toN170]

To start, 10gn of H110 with a 240 SMK @ 2.260" is about 75% case capacity.

H110 is designed first and foremost as a magnum pistol powder and works best with a heavy roll crimp. This allows for a fairly high pressure build before bullet release.

When used in a .300/WTF there isn't much for neck tension and it can be erratic based on the cases and how they were formed (.221 expanded or varying 5.56mm trimmed) this in turn makes them very prone to being temp and position sensitive. If at all possible adjust the bullet seating to balance with powder charge to be between 90-100% case capacity.

9.4gn of H110 with a 240 SMK @ 2.095" is about 95% case capacity. You can fine tune the exact powder/ COL length once you're in the ballpark.

If you want to go the extra mile you can measure neck thickness and once the cases are fire formed, trimmed and neck turned...anneal them.

The other options are of course to move to IMR 4227 or AA1680.

[HUNTER2]

Good post -all. Had simular results until I started turning necks, anneal and use h110 or 296. Have good consistent results, but I use single shots and bolt guns only. Hope you get it straightened out.