Horizontal Stringing

[petroid]

So first, the good news:

My 300BLK upper will feed flat nose bullets.

The bad news:

I can't seem to get them to shoot worth a darn.

Here's the story. I recently bought a Lee C309-170FN mold. It is made a lot better than the older ones and has nice vent lines. It seems to really like being run hot, as I couldn't get good mold fillout until It was hot enough that I had to wait a good 7-8 seconds for the sprue to harden.

Alloy: Indoor range scrap consisting of a lot of 22, jacketed pistol bullets, and commercial cast lead. Unknown composition but it weighs very similar to 50:50 WW/Pb and other bullets cast with it perform well.

Mold: As stated LeeC309-150FN. Dropping at .311-.312 and 178gr.

Copper gator check and Lee Alox tumble lube. Push thru sized at .310

Loaded in converted, mixed headstamp 223 and 5.56 brass over IMR 4227 at 14.1 and 15.3gr test charges.

CCI #41 primer. OAL 2.040"

Platform: Frankenstein AR15 pistol. 12.5" CMMG 1:7 pistol gas barrel. Vortex Strikefire red dot with 2x magnifier. Liberty Mystic suppressor.

Position: Butt on ground, gun on lawn chair.

At about 60 yards I am getting 3" wide by <1" tall groups.
this is the 14.1gr load
the 15.3gr load. I dont know about the flyer. I may have pulled it.

I'm going to try it without the suppressor, although it never has affected group size before, just POI.
I'm going to try it with a better rest. I will have to set up a table, and get my sandbags out.

Started raining, so I wasnt able to complete my testing, but I wanted to get some feedback.

This gun will group 1" @50 yards with weight sorted C312-155s. About 1.5" with unsorted boolits. Dunno why the horizontal stringing with this new load.

[curator]

Try it again with a decent shooting bench and some sand bags. Your lawnchair shooting platform will not give a reliable idea of the gun/ammo's accuracy without a solid rest that dampens vibrations. Depending on the size of your red dot, the sight could be adding to the lack of precision. 1" groups at 50 yards with cast in the .300AAC is pretty good otherwise

[petroid]

Yes the rest leaves something to be desired. I just wanted to try a few rounds and see how they did. The first load didn't appear to be very hot so I was hoping bumping up the charge a bit might tighten up the group. The red dot is four moa so hard to shoot for groups but I can usually make it work. If the weather holds out I'll try again later today

[Dan Cash]

This may not apply to the AR platform but I have experienced groups like yours from M70 Winchester with loose action screws. How does the upper fit the lower?

[petroid]

There is a slight bit of play but it doesn't seem to affect groups with other loads.

[Ballistics in Scotland]

Horizontal is better than vertical, as it practically exonerates the ammunition. This is the rifle, or possibly the way the rest or your fingers are contacting the rifle. The order in which those hits came is also significant. If it is a group starting on the point of aim and then walking (or the reverse, it is probably something that happens as the barrel heats. The cartridge is a pretty tame one compared with some used in similar firearms, but the bullet is in the bore a lot longer.

[petroid]

Didn't get out this weekend. May have some time tomorrow

[maxiblu]

I use the Lyman 311041 - 173 gr with 17.0 of 4227. Tad over an inch @ 100 yrs. Feeds ok with gen 3 mags. Anyone using the Lyman 311332 in their AR? I would be interested in buying some to try before I buy the mold.