What is your rifle's failure stoppage? Your inconsistency description is a bit vague.
IMR4895 is just about perfect for the rifle, in that rifle I use IMR4895, H4895 or IMR4064 exclusively with 150ish fmj's, 168 noslers, and occasionally 155 noslers.
I use 41 grains of IMR4895 with both the 150s and the 168's.
Somethings to check;
-rifle lubed per the manual with grease on the sliding surfaces, bolt raceway, op rod spring, op rod/barrel contact and a
dry gas cylinder and piston
-good quality magazine, there are plenty of chinese clone mags that will cause stoppages due to improper spring bends, crappy followers
-obviously if you have any cycling of the bolt when fired it's not the gas cylinder cut off.
-do make sure your barrel port isn't partially blocked by the gas cylinder being screwed down too far or too little. (unlikely but possible, IIRC most gas cylider ports are generous and more open than the barrel port, take the plug out and bend a wire or paper clip and make sure you can pass it through from the gas cyclinder to the bore)
if it runs with good surplus then it's unlikely a gun/magazine issue. Do test with known ammo to help diagnose.
loading for the M14, read this http://www.zediker.com/downloads/m14.html
he has a quirky writing style (i like it but many don't) but his experience with the m14 is sound. He may sound the alarm a bit to hard but his explanations bear reading. You really should know the headspace on your rifle and the final headspace on the rounds you make. He'll explain why.
ETA- I will politely disagree with the poster that said shoulders pushed back too far will cause cycling issues. Too small and they will fire and cycle but read on and I'll explain a bit on that. If extremely short you will can get a failure to fire as the case isn't supported for the firing pin hit. More dangerous is that you can get a case rupture and a case head torn off. If you have the equipment you will find that factory ammo is smaller in dimension than what most dies can accomplish. Of course it's only like that once and that's all the factory has to consider. Any reloads the liability is on you.
They do that because they have no idea what gun it will go in so for them it must chamber every time.
ETA2 - also check your fired brass and your chamber, Is your chamber roughly cut, lots of tool marks? SAInc does a fair amount of that. A really rough chamber will imprint those imperfections on the brass and make extraction more difficult sometimes inducing a failure to extract stoppage.
Many new M1 and M1a shooters will have cycling failures due to improperly lubed rifles. Check that first.