Just got my Benelli M4 and taking a 1 day shotgun class to break it in tomorrow.. What cheap/bulk birdshot loads are people running? I'm reading probably want to keep at least 3 and 1/4  Dram for reliable cycling in a new gun.

Break in with Turkey loads?

Just kidding but have been told high brass and not light loads for break in.  True or not not sure but all my semi duck guns have worked when I did that.

Number 4 high brass birdshot functions well. Avoid the value pack stuff from Walmart. The Federal 7.5 and 8 will work most of the time, but it is prone to short stroking. The Winchester stuff is even worse. Their recoil profile would not be good to train with at a school. You want something with some thump.

My usual 'cheap' go to ammo is the Remington buckshot they sell at Walmart. Never a single failure with it. My first M4 has around 15k rounds through it now. It patterns fairly well. It's no flight controlled loads, but for the price it performs well. I prefer running buckshot since there is much less chance of having it blow back on you like birdshot does. Getting smacked in the forehead with birdshot sucks.

The Walmart value pack stuff (1 1/8oz, 1200fps) runs fine in my M4.  It will run with 1oz 1180fps loads too.

High brass for 2-300 rounds for break in, and run it wet. They like a lot of lube on the bolt carrier.

After break in you should be able to run almost any ammo without any issues, except maybe some of the cheapest walmart crap.

I've had horrible reliability with my M4 and Winchester #7.5 and #8 birdshot. I have run Federal without issue.

Thanks for the replies. I'm gonna clean and lube it up tonight. Got a variety of loads but Got 2 large cases of #7.5 brass federal brass so hopefully that will work. I think it's 1 1/4 ounce.

I've had great luck with Winchester Super X Heavy Game Load 12 Gauge 7&1/2 shot. The velocity is 1255 FPS.

Keep your FPS 1200 or better and you should be GTG

Jus got home. Ran about 350 flawless rounds! Lubed it up good last night and ran perfect all day with mix of buckshot, slugs and cheap bulk pack Winchester and federal birdshot. Very happy overall with the gun.

Mine cycles the cheap Federal 3.25 dram 1 oz birdshot shells.  The only shell I've ever had an intermittent  cycling issue with is cheap Winchester #4 birdshot 1 1/8oz when the gun was new.  Now as long as I buy 3 dram or higher it runs it all.

Run a couple hundred rounds of high brass stuff to break in. Should run almost anything after that. Mine runs cheap walmart 7.5 reliably.

I have a famous video of my M4 chewing up bird shot rounds because it's short stroking etc. there's no need to "break in" an M4.  You just need to take it apart and smear TW25 machine gun grease on the rail section of the bolt and it'll cycle anything all day long. I use it in competitions all the time with bird shot and it runs great with the grease. If you want to be sure, Remington Nitro birdshot rounds are guaranteed to have enough force. 

https://www.youtube.com/watch?v=bzuC3SXXPl0

I bought mine used so I didn't have to worry about break in.  Mine runs the federal value pack like a champ.  I also don't have any issues with reduced recoil rounds.