2 lbs of flaked oats, and 3 lbs of oat malts.
First of all, these adjuncts add a huge amount of beta glucan to the mash. Beta glucan was often call "gum" in the past. The mash with excess beta glucan is gummy, thick and difficult to manage. The beta glucan can also trap many of the starch molecules from coming in contact with the amylase enzyme. As a result, mash efficiencies are lowered, sparge and lautering come to a trickle. Brewers will sometimes falsely believe it's the starch in the mash that's causing it. Beta glucan in barley is broken down during the malting process and maltsters try to keep it to a minimum. Well modified malt will contain less beta glucan then a malt that has less modification, that's one of the reasons to rest between 125F-130F with lower modified malt, it give what's left of the beta glucanase enzyme a chance at breaking down more completely the beta glucan.
Beta glucanase is naturally occurring in barley malt, but is quickly denatured above 125F. That's why it may be beneficial to use exogenous enzyme beta glucanase in the mash. In addition to the amylase enzyme added to the mash, beta glucanase can be added to deal with the gummy mash. This will allow the both beta and alpha amylase to covert the mash more completely.
Beta glucanase enzyme derived from a bacteria source has a higher temperature threshold than the what naturally occurs in barley malt. These bacteria derived exogenous beta glucan enzymes can work up to 168F. The effects are noticeable with 30-60 seconds of adding it to the mash. The additional amylase enzyme that was added, needs to work in conjunction with the beta amylase found in the barley malt. So to get a better conversion, it's important to rest when a beta and alpha are both active or rest at lower temperatures longer. Even though the alpha enzyme is more active above 152F the beta enzyme works off the alpha enzyme. The beta can't break down the more complex starch molecules until the alpha has broken down to a size that beta can work on it. It's a misunderstood idea that alpha is not active until it's above 150 and beta stops above 152. Alpha is active at 144, but it's at a slower rate than at 154F. Beta continues to work above 150F but begins to denature and is soon gone. That's why a mash at 150-152 is a good temperature for most beers.
Long story short. It's very helpful to add beta glucanase enzyme in addition to the alpha amylase enzyme to the mash to increase starch conversion. Lower temperatures are okay, but a step up in temperature will increase overall mash conversion. Rice hulls in the mash may also help.
This is where you can get beta glacanase:
https://www.morebeer.com/products/cellarscience-glucabuster-placeholder.html
Be careful about dosages, a 1/4 tsp will treat 10-15 pounds of grain, add to much and the cellulose will begin to break down and create the same problem you were trying to solve. This stuff makes RIMS and HERMS systems work better too. i use it with every brew.
Edit: Mash pH also plays a big role in conversion efficiencies, but that's long explanation.
