I always caution my 270 AM customers to not confuse small exit wounds with poor bullet performance concerning the 270 AM and the 169.5 gr ULD RBBT.
What you will see in game will range from what you saw to gaping exit wounds. First big game animal taken with the 270 AM was an exotic sheep my Dad shot at 73 yards in heavy cover with my very first 270 AM test rifle. This was with the 169.5 gr ULD RBBT loaded to 3255 fps, a pretty comfortable load but extremely accurate.
The bullet hit the 120 lb ram just behind the shoulder on a perfect broadside shot as the ram walked out of the thick brush across a pond damn(about the only place we could see them long enough to get a shot). The ram simply folded up, no twitching of any kind, just fell on its nose like it was pole axed. I was figuring we would see a massive exit wound on the ram when we got up to it, quite the opposite in fact, there was a perfectly round exit wound that was about the size of a quarter.
I was amazed, certainly the bullet had to have had its HP plugged by the thick hair of the ram and it acted like a FMJ.
THen I thought, how in the hell would that cause the ram to drop on its nose? I jsut had to know so we took the ram back to the ranch house and opened him up, there was really nothing left intact ahead of the diaphram. In fact he was hit so hard that the liver and paunch was also split by the hydrostatic shock generated by that bullet.
These bullets are made with heavier then normal jackets which is the reason you probably saw what appeared to be a non expanded bullet. I assure you though, the bullet expanded as these jackets are tapered from nose to base. YOu generally just see terminal characteristics more like a premium bullet then a conventional cup jacketed bullet.
This is due to the heavier jacket and high sectional density of the bullet.
On the other end of the spectrum, I have seen deer shot with my 270 AM that when hit in certain areas, like large bone, litterally blow huge exit holes in the game. THe reason is more because of the extreme energy dump causing the bullets to cause secondary damage which is what results in the large exit wounds.
Simply put, I would recommend sticking with the 169.5 gr ULD RBBT. It will make that big case run much more efficently and there is no comparision down range terminally. The 140 gr AB can be made to work well but I generally only recommend this bullet is the 169.5 gr will not shoot in a specific rifle. It is not common but it does happen from time to time, never will you get a barrel that likes ALL bullets and at times you get certain barrels that do not like a specific bullet.
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