450 Bushmaster, 250 grain bullets

Article by Denny McDaniels, Duck Creek Sporting Goods

A project I have been working on is developing a load for a 450 Bushmaster. The barrel I used to assemble the upper is a Bear Creek Arsenal 16 inch that has a 1 in 24 inch twist. The brass is Starline and the bullets are the Rainier 250 grain .452 dia Flat Point. Cartridge overall length 2.25 inches.

Original testing was with Hodgdon Lil’Gun. Hodgdon’s Manual list a starting load of 25.2 grains, Lyman #50 lists a starting load of 34.0. Both produced a under gassed round. A powder charge of 36.0 grains demonstrated that the action was cycling but not really effectively ejecting the spent case and had several stove piped unless the rifle was fired with one round in the magazine..

Investigation into the gas system revealed a gas port of .070 inch. Several inquiries with Bear Creek revealed they to experienced a lack of gas issue and later barrels being manufactured wit .076 inch gas port. Later trips to the range with the barrel modifications produced better results with the 36.0 grain charge only.

I finally have success with a functioning rifle. Two changes was made, the gas port was enlarged to .082 inches and H-110 powder was used, still shooting the Rainier bullets. Powder charge of 38.5. This round shot consistent and had zero cycling problems with the 50 founds fired at the range that day Average velocity measured 2068 fps, max spread of 81 fps

Later test will be conducted with lighter loads and revisit the use of Lil’Gun powder. I will post my findings here on this article when I learn more.