Lee 312-155-2r powder coated for 300 blackout. Poor accuracy?

I need some help with the poor accuracy of this bullet as others have reported that it groups well for them.
Bullet:
Lee 312-155-2r mold using wheel weights, powder coated with smokes powder. Sized to .309, LC brass and ginex primers. No gas check. OAL 2.010
Load: 5 shot group @ 50yrds
Shooters world blackout 17gr 4-3/4”
Shooters world socom 15.5 gr 5-1/2”
Socom 16gr 4-1/4”
Note: just to compare I show FMJBT with each load and hit 1-1/4” to 2” groups
I am using an AR 1/8 twist 10.5” barrel slugs at .308 using brown and sharp micrometer
Hammer test on the powder coat passed with great results.

Thanks for any help or ideas.

Are you giving consideration making the bullet a little larger? How much distance from the first driving band to the beginning of the lands in the barrel ahead of the chamber. If you can recover a fired bullet, that can tell you if the bullet diameter is sufficient to seal the bore or needs to be larger. Gas cutting will remove the PC and ruin accuracy. No mention of leading though. Also heavy crimping could result in reducing the bullet diameter.

Without data on those powders, kind of hard to see if velocity/pressure is high or low for the alloy. Assumed is that the bullets have been allowed to reach mature hardness (2-3 Weeks?)

Try with gas checks?

Using that bullet, lubed, and gas checked. I have never had any problem with leading or poor accuracy. However, I size it at .311, not because it is better than .309 but because it is what I have. I think a larger diameter may help you also, it's worth a try.

Ken

"No gas check"

Yup, that be the problem with those loads.......

Quote:

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Originally Posted by skeet1

Using that bullet, lubed, and gas checked. I have never had any problem with leading or poor accuracy. However, I size it at .311, not because it is better than .309 but because it is what I have. I think a larger diameter may help you also, it's worth a try.

Ken

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I agree why so small??

I have always had best results with fat bullets. Fat cast are NOT the pressure issue its a fitment issue. Fit is ALWAYS KING BUT too
Small is far worse then too fat and none are dangerous.

TRY .310 then .311. I have shot .314!!!

CW

Doable but not with a soft alloy. Yes, normally a GC load. My barrel is the same, KAK, 309 works OK. Might try WD after cooking ( hardens alloy) and add a GC.

Sorry I forgot to add FPS.
Blackout 17gr 1610fps
Socom 15.5gr 1645fps
Socom 16gr 1696fps

What little I have learned was to go .001 or .002 over. Sounds like that is not enough. Thanks for all the reply’s and information.
Kevin

I agree with both Skeet1 and Larry G.

General rule over 1400 fps use the gas check.

Update. I took that advice and now I have install gas check and sized lee 312-155-2r powder coated bullets to.310. I still use shooters world Socom. (Just a little faster then 1680) at 16 grains 1663fps OAL 2.010 100yrd it grouped 5”. Same load with 150fmjbt will shoot 2” groups.
Not sure what to try now? The max on this bullet for my gun is 2.020 so .010 less should be about right? I would like to capture a bullet but I have not found a good way to do it. I really want to get the lead bullets to work but I am at a loss. Help.
Thank for all the information.
Lee 312-155 powder coated with gas check
Attachment 306092
150 FMJBT
Attachment 306093

Still no luck. I captured these in a 5 gal bucket filled with rubber mulch. There sized at .310 smokes powder coat (shake and bake) 1580fps 158gr. Couple weeks aged harden. I do not have anything to test hardness with.
Attachment 306451
So does this look like gas cutting? Does not look like it has much powder coat left on it.
Here is the bullets testing the powder coat.
Attachment 306452

Anyone have anymore ideas??? I am running out of things to try.
Or if I can provide more of better information let me know.
Thanks