bearcatrp wrote:Have no issues cycling with H110 and full loads. The upper came with some subs but wouldn't cycle for crap. After I get a good feel with this rifle, think I will try 8208XBR and see what happens. Its a faster burning powder than varget or 4064. I use 8208 with my short barrel 308. Bites pretty good compared to other powders. But I use 42.0 gr with a 168 A-Max. Not sure if the case can get enough to push the bullet very good or not. For now, will learn with whats currently good for the 300 BO.
With a fast burning powder I'm 99% sure you will not cycle your AR. Also the powders you are talking about being faster than one another are way slower burning that the most common 300BLK powders that are considered slow for the 300BLK which is only good for shooting subs
Also, too slow in the 300BLK will not burn the powder up in time and you will still not get cycling so super slow powders for the 300BLK like the ones you mention (8208xbr, varget, etc) are no good even for subs in the 300BLK
Around 2010-2011 when the round was just out (SAAMI approved) many guys tried all kinds of powders and experimentation because there was so little info out there.
What was discovered is that you won't cycle an AR unless you are using a powder on a certain range of the Burn Rate Chart:
Using the image above; Basically if you aren't in the range of #80-92 you won't be cycling a subsonic bullet in a carbine gas system.
If you aren't in the range of #76-79 you won't be cycling a supersonic bullet in a carbine gas system AND getting the near max supersonic velocities.
If you have a pistol gas system the ranges of powder open up for cycling subsonics but you are still basically confined to the same overall range because going outside of #76-92 burn rates will not give you the pressure and dwell time needed to cycle the 300BLK AR.
So, feel free to try any powder you like but just know that if you are not within those ranges then you will likely be getting no cycling, single shot behavior.
If you go past the range (>92) with a powder like IMR8208XBR (#107 on the image) or Varget (#124 on the image) you will have unburnt powder meaning that not only will a bullet be leaving the barrel but so will unburnt powder because the burn rate was too slow and didn't get full burn for pressure.
If you go well before the range (<76) you will likely not generate enough pressure at the gas port before the powder is burnt up or dwell to completely to cycle the rifle.
Other more knowledgable burn rate guys can add on to this for even more accurracy to correct anything I may have misstated but this is what was learned a long while back.
Again, I'm not trying to rain on your parade so feel free to experiment SAFELY and see if you find out something that hasn't been tried before. I just figure this info will help you hone in on where your experimenting may have a better chance in succeeding.
Oh, not all burn rate charts are the same so the numbers on the one above will NOT be identical to the numbers on a different burn rate chart BUT the powders will still be very very very close to one another in grouping where any differences are usually caused by powders included in one chart that are not included in another chart.
Best of luck!