65 grain cast .223 w/ H-335

Hello all,

I have been using published data to load 55 gr cast .223 with 19 grs of H335 with great success, in an AR-15. I do not have a chronograph, but am happy with firearm function, performance and range results.
I have acquired an MP mold, for 65 gr. I have not found published data for 65 gr , using the H335, that I already have, as of yet. How do I determine how much to reduce my H335, to compensate for the 10 additional boolit grains, and be in the same ballpark, data-wise, as the 55 grs?

I do understand that there are calculators, that can take all of the input and project expected results, but to be honest, I am a technological dinosaur, and for the life of me, I don’t understand a great deal of it.

Any help would be greatly appreciated.

10 grain bullet weight difference should not that big a difference. If still concerned knock 10% off which would be 17.1 and go from there with the H335.

Best accuracy for comparison would be helped by a little more data (seating depth, barrel length), but I will make some guesses and run a Quickload comparison.

With an assumed 0.25" seating depth and assumed 22" barrel, your 55 gr load is estimated to be getting 2317 fps with 19700 psi with a 71.8% fill. I would be very surprised if this is cycling your action and I would guess that there is quite a bit of unburned powder.

With a 65 gr bullet and the same 0.25" seating depth, a 19.2 gr charge is estimated to give the same velocity with a pressure of 22024 psi and a 72.7% fill. The increase in pressure should give you a little better burn, but it will still be a dirty load.

To get the same pressure only requires 18.1 grs and you get 2169 fps