300 BLK - load data with Unique

[ER308]

Sharing some load data. None of the loads below showed any signs of high pressure.

300 AAC Blackout/Whisper
AAC Model 7 - 16"
(velocities are average of 5 shots through two chronographs)

bullet powder wt grns velocity fps comments
Missouri 245 cast Unique 5.6 997
Missouri 245 cast Unique 5.8 1014
Missouri 245 cast Unique 6.0 1042
Missouri 245 cast Unique 6.4 1072
Missouri 245 cast Unique 6.8 1116
Missouri 245 cast Unique 7.2 1153 very large groups
Missouri 245 cast Unique 7.6 1187
Xtreme 150 plated Unique 5.4 1140
Xtreme 150 plated Unique 5.6 1144
Xtreme 150 plated Unique 5.8 1168

[ironhorse1]

Be very afraid!

I have no experience with the .300 but the posted loads leave me concerned for your safety.

Using a 245 grain cast bullet with 7.6 grains of Unique has got to produce more pressure than a .357 using 7.7 grains of Unique with a 158 grain jacketed bullet.

Just because you see no pressure signs does not mean you are not over pressure in your loads.

My only holy crap moment with Unique was when I tried 7.5 grains in and .30 carbine pistol with 110 grain bullet.

Recoil and blast was loud and the primers were flat and the cases needed to be forced out of the cylinder.

Unique at top end loads will generate a lot of pressure quickly and that is why its best use is medium loads.

I'm looking forward to additional input on this thread.

irh

I noticed that the last three 245 grain loads gained very little velocity despite the increase in the powder charge.

This is what happens when a powder is maxed out and all you get is increased pressure without an increase in velocity.

[ER308]

Thanks for the concern. I have seen others go as high as 8.2 with no problems. Really... the primers showed no difference from the low to the high loading. Perhaps this is of the much higher operating pressure of the rifle round. The intent was to establish a stable subsonic load. The 5.6 gr load was quite accurate and is my recommendation. I believe the reason for the gross inaccuracy of the 7.2 gr load is that it right at the transition from sub to super sonic and is probably experiencing a lot of turbulence a expected. I expected that in theory, but cool to see it play out in this test.

[ER308]

Also, if you plot velocity vs powder weight, you will find a very linear relationship, so it is not 'topping out', as you suggested. Thanks for your concern.

[ironhorse1]

Also, if you plot velocity vs powder weight, you will find a very linear relationship, so it is not 'topping out', as you suggested. Thanks for your concern.

On a chart it would appear to be true. If you divide velocity by weight charge

you have topped out in the 6.8 - 7.2 loads and are getting less velocity per grain at the 7.6 grain load.

Knowing the properties of Unique, even small increases in charge weight, will increase pressure without much added velocity.

You usually won't know you are over pressure until something bad happens.

You might want to try another powder such as 4227, IMR 4198 or Reloader 10X.

As far as turbulence affecting group size I doubt it. Perhaps the top load listed is causing issues with the bullet base, if not gas checked, with Unique powder.

Do the math and you will see the slow reduction of velocity per grain as your load increases.

If it can be done safely I would like to see more data with different powders with the cast bullet.

I hope others have some additional experiences to share.

irh

[ER308]

The math you are proposing in that fps/charge weight decreases as you go up is true for just about every safe load sequence. Just apply what you have suggested to any loading manual and you will see that. That's not an indicator of an unsafe load. I know your intent here is good, and I don't propose anyone load anything that they are uncomfortable with, but the numbers and observations I generated on this are not suggesting anything unsafe. With regards to the inaccuracy, the turbulence I think is real, as the groups tightened back up with the next higher loading at 7.6 grains. The intent of this test was to specifically test a pistol powder, to achieve a reasonable subsonic velocity while minimizing gas generation (and noise). Compared to a load achieving similar velocity with a slower powder (H-110), the Unique loads were quieter.

[Spaceghost]

Does the the action cycle with these loads?

[ar15barrels]

Using a 245 grain cast bullet with 7.6 grains of Unique has got to produce more pressure than a .357 using 7.7 grains of Unique with a 158 grain jacketed bullet.

Normal operating pressure for 300 blackout cases/primers is around 60,000 PSI.
Normal operating pressure for 357 magnum cases/primers is around 35,000 PSI.

There really should be no problem with exceeding 35,000 PSI in a cartridge designed around a 60,000 PSI use.

[ER308]

Does the the action cycle with these loads?

Tests were done with 16" bolt action. Model 7 action. I would think these would NOT cycle a gas gun. With fast pistol powder, pressure should be way too low by the time the bullet reaches the gas port.

[ironhorse1]

First let me say I found your data to be of great interest as far as loading heavy lead bullets in the .300 blk.

Lots of good information for everyone to review. The math is just a way of seeing when one is getting the best use out of a particular powder. It does apply to all powder data.

Honestly I never stated that I thought your loads were over pressure.
It was just a heads up that there is a point when the next slower burn rate powder might be best.

When working up loads there are many factors to consider. One is case capacity. At 24 grains of water for the .300blk as opposed to 31 grains for the .223 there is less capacity. The .357 holds 27 grains and the .30 carbine 21.

Now there is a very heavy bullet to consider as well. All these things must be taken into account as loads are worked up to the desired levels of velocity and accuracy.

Without pressure testing the only way we can determine if we have exceeded specs is to measure the case web with a micrometer. A fired factory case will give the maximum case web expansion. Fired reloads which exceed the factory measurements will have increased pressure. That's old school as used by Ken Waters.

I'm happy that you got the results that you wanted. The chronograph data shows the sweet spot for subsonic up to 6.8 grains.

I also use Unique as do many others for 30-30 cast bullet loads. The case does have a greater capacity @ 45 grains of water and ten grains with a 180 cast GC bullet is a nice load.

So I never doubted your loads or data and it's been the best that I have seen for awhile.

irh

[ER308]

additional data - 208 gr Hornady AMAX

Hornady 208 gr AMAX
COL: 2.27 no crimp
Ballistic coefficient: G7=0.325
Powder: Unique
CCI SRP
Rifle: AAC Micro 7 1:7" twist

gr pwdr/ velocity fps
6.2 / 1040
6.4 / 1075
6.6 / 1108

There were no signs of high pressure with any of these loads.

The 6.6 gr loading grouped best at 5 shots in 1.25" @ 100 yds.

JBM calculator gives the following:

distance yds / drop in. / velocity fps
50 / +2.4 / 1078
100 / ZERO / 1055
150 /-10.2 / 1037
200 / -28.4 / 1020
250 / -55.0 / 1006
300 / -90.2 / 992
350 / -134.2 / 979
400 / -187.3 / 966
450 / -249.7 / 954
500 / -321.6 / 942