I shopot both the Sierra and Speer bullets and the only gun that liked one more than the other is my 358. The sierra bullets out perform the Speer bullets by quite a ways in accuracy. In all my other guns there isn't enough difference that I could point to an expanded bullet and tell you who made it. On a target the group sizes are so close that I couldn't tell which bullet was used without looking at the load data on the target.

Report back on Hornady .222 HP Bee subsonic rounds with hollow-point deepened.
Drilled a 3.5mm deep hole in the hollow-point end of the projectile considerably deepening the hollow-point and fired with 3.5 grains Trailboss. These projectiles were fired into non-steel belted old car tyres at a range of 55m. The projectile invariably penetrated one side of the tyre and was caught in the inside of the tyre. The drilled projectiles opened up nicely to at least 2x diameter which is significantly more than the non-drilled projectiles. Accuracy at 55m was just under one inch and drilling does not appear to have significantly impacted accuracy.

Waimabana, this is good news and should make your subsonic rounds more lethal. You'll have to update us on your first hunting/harvest.

Just remembered, I have heard some folks load bullets tail first so they transfer more energy on impact (like a hammer).

Also, I have found that, just removing the ballistic tips, will result in significantly more expansion than when it is left installed. Might save some time and effort.

I have a couple of questions about the use of this modified projectile.
A rubber tire is considerably more dense and resilient than skin and soft tissue. Have you considered testing it in water?
The sidewall of the tire is less than a quarter of an inch thick and there is air beyond that and then the other side of the tire. Did the bullet expand while penetrating the first sidewall or did it flatten out on the opposite sidewall?
Will it expand in a similar fashion in soft tissue and small bones or will it just pencil through?

A water test will answer these questions but so would firing it at small game. I am interested in knowing how it performs on its intended targets.

How much weight did the 3.5 mm hole remove and what was the beginning weight? I deepened the hollow point on some 125 grain 35caliber bullets for my 357 years ago, put in a grain of HP38 and a small pistol primer to seal the powder in. The primer was seated cup out and it ignited the powder on impact with anything harder than card stock. The bullets weighed 115 grains and were fired at 1500 fps from a 38 special case using 14.5 grains of H110. They were tested as an ignition source and for their explosive function. My test showed some possible uses as an ignition source in fuel tanks that had air above the gas and the bullet made a deeper cavity in concrete than a 158 grain 357 magnum factory load. I decided it wasn't worth the work unless there was a need to detonate the fumes in a gas tank or you needed to cause more damage in soft tissue than you could get with a standard hollow point round. They were an answer to a need that is not there.
I hope your experiment turns out better.

Waimahana wrote:

...Drilled a 3.5mm deep hole in the hollow-point end of the projectile considerably deepening the hollow-point and fired with 3.5 grains Trailboss. These projectiles were fired into non-steel belted old car tyres at a range of 55m. The projectile invariably penetrated one side of the tyre and was caught in the inside of the tyre.

Gidday mate. There is no real shortage of them pesky Aussie immigrants...possums...in your neck of the woods. I reckon they would be a very good test medium for your modified boollits. It would be very interesting to see how they perform mate.