Will go hunting for moose this fall. My hunting companions all use 30-06 as will I. These guys all use the 180 grain bullet for moose. I would rather use a 150 or 160 grain bullet. We are using factory ammo.
Should I succumb to my partners and use the 180's or can I use the 150 or 160's?
Your question raises a few issues you should consider. First, what advantage do you see in using a lighter bullet? Less recoil? Flatter trajectory? Better accuracy? Or is it that your experience and comfort level leads you to prefer light bullets? I've shot more than a few critters with a .30/06 and I've seen more bullet failures with that cartridge than I have with any other, perhaps because I shoot it more. Those failures have more often than not been from choosing the wrong bullet for the job. A failure I define as a bullet that creates a shallow wound that does not penetrate deeply enough to produce a humane kill. Often these wounds are huge in diameter, but without getting inside the chest cavity, they only produce a horrible wound. But so much for the sermon, lets examine some of the issues related to bullet choice.
We'll begin with recoil. I think you will find that because the 150 gr bullet needs more powder than the 180 gr bullet when both are loaded to the same pressure, the difference in felt recoil is not great enough to make much difference, if you can shoot the 150s, you can shoot the 180s in the same rifle. If recoil is an issue, things like the rifle's length of pull, the lack of or quality of the recoil pad, and your shooting technique are on the checklist of things to address.
With respect to trajectory, the shape of the bullet has a great deal to do with its trajectory, but when a light and a heavy bullet have the same basic shape, the heavier bullet performs better at long range. The heavier bullet gives up velocity more grudgingly, it is effected less by wind, and it puts more power on the target upon arrival than the light bullet does. This matters little though as moose are typically shot at short to moderate ranges in most circumstances.
As for accuracy, the target is a moose, and a rifle has to be pretty miserable before it can't keep its bullets on the vitals of a moose over normal hunting ranges. Having said that, the barrels of most .30/06 rifles have a 1:10 twist which favor heavier bullets. Not that they don't shoot light bullets as well, they do, but a 1:10 twist will stabilize bullets up to 240 grs, by the way I really like the 240 gr Woodleighs in my .30/06. My wife's 1:12 twist .30/06 Husqvarna puts elongated holes in the paper when shooting the long 240s, so her rifle gets 180 gr TSXs. Don't worry about trying to shoot bugholes in a paper target. "Mooses ain't bugs!" Be more concerned with where you bullet prints with respect to your point of aim. Lets say your rifle printed 4" groups at 100 yards. Most folks on here would tell you thats just terrible. The fact is if your rifle shoots a 4" group, much of that group, particularly the first round fired, will be well within 4". If the group is centered on your aiming point, at worse you can be is 2" from it with any one shot. If we consider a moose sized target, 2" isn't worth worrying about. Besides all that, how well do you shoot from field positions? If you can keep each shot within 2" of your point of aim when shooting from field positions, you are a good shot indeed.
But maybe you've got one brand of ammo and one weight of bullet that you are really comfortable with. Well thats great if the load you're comfortable with is a prudent one for the job, but if it isn't, its time to get comfortable with a load that is prudent. That might mean moving up to a 180 gr bullet and if you hunt in the thick stuff where the range is typically on the short side, you can outdo the performance of a 180 with a round nose 220. Whatever advantage the 180 has over the 150, the 220 has over the 180, when the comparison is between conventional lead core bullets. One of the great things about a .30/06 is that due to the variety of bullets available for it, it can do many things very well. But you need the right bullet to make that happen, and the wrong bullet can lead to a nightmare for both you and the animal you wounded.
What brand of ammo and which style of bullet do you intend to use? Not all bullets are created equally, and while its not true of
some premium bullets, a conventional lead core 150 gr expanding bullet is better suited for deer sized game. A .308/165 gr bullet will be much easier to find than a .308/160, but I suspect you meant 165. When I lived down south the Hornady 165 was my go to bullet for the .30/06, and for me, the 165 gr bullet would be the lightest I'd consider for moose. You could expect 10% greater penetration with a 165 compared to a 150 gr bullet of the same style and design. The impact velocity of the 150 at any given range would be higher, resulting in a wider but shallower wound, and on a large animal penetration means more than wound diameter,
"We ain't shootin prairie dogs here!" By contrast, I wouldn't hesitate to shoot a moose with a 150 gr TSX due to that bullet's smaller expanded frontal area and high percentage of retained weight resulting in deeper penetration. I'm a long time handloader so I don't pay much attention to what bullets are available in factory ammo, but I'm sure you would find factory loaded TSXs expensive compared to say Federal blue box stuff, so a box of 180 gr Federal .30/06 is more affordable and equally effective as a box of whatever brand of ammo might have 150 gr TSXs loaded in it.