Ballistics: Non-physics involvement

[BigBear]

Ok,
We know x bullet fired out of x length with x power will travel x amount and variable forces outside of the barrel will affect it's path and impact, etc.

I'm interested in figuring out how to figure out what the best grain weight is and why.

I.E.: 24 inch heavy barrel, .308, 1:12 twist. There are grains from 120-190+. why so many and how do I find out what works best? (without spending hundreds on different types of ammo I can't afford or will never use again).

Along the same lines, how do you know what is "good" ammo? See below.

I've shot thousands of rounds of 9mm with varying bullets/grains and they all hit teh target.... how do I differentiate the good from the bad.

Is it really just about the groupings?

[Irving]

When it comes to rifles, the twist of the barrel will only stabilize so heavy of a bullet, so you should be able to narrow the field as far as weight right off the bat depending on your twist rate.

[BigBear]

I'm looking at that with my Google-fu but I'm getting really confused as to the grain of bullet, and the grain of powder being used interchangeably it seems.... I see everything from 55 grains to 210 grains but half of them are about bullets and half about powders.... lol

[newracer]

Unfortunately when finding out what will shoot best out of your rifle it really comes down to trial and error. You should be able to narrow it down by other peoples findings though.

[BigBear]

Rgr newracer.... here's what I understand:

I have a 24 inch, 1:12 twist, .308 heavy barrel.

It will take 168-170 GRAINS best and is reccomended with a 55-70 GRAIN bullet. That still leaves a lot of play.

I also understand that BTHP's are the new "thing" in bullets and they stabilize better. I do not want to use too light a bullet as even the 55's are known to "skip" in the barrel... I might have the bullets/grains numbers backwards....

So confused.

Am I assuming what shoots best is what comes up with the best groupings on the target?

[newracer]

I think you are confusing the bullet wieght and powder weight.
168 to 170 grain bullet
55-70 grains of powder

Are you going to purchase cartridges or reload?

Yes, you will eventually need to shoot several different combinations and see what groups the best.

[BigBear]

I think you are confusing the bullet wieght and powder weight.
168 to 170 grain bullet
55-70 grains of powder

Are you going to purchase cartridges or reload?

Yes, you will eventually need to shoot several different combinations and see what groups the best.


I don't have teh money, knowledge, equipment, or space to reload... for now. So, for now I'm stuck with off the shelf things. Someone did mention HSM bullets... anyone know anything about them? Supposed to be for long range precision.

Thanks for the catch on bullet weight and powder... thought the numbers sounded odd.

[SA Friday]

Rule of thumb: the bullet weight will be more than the powder charge if the round is a centerfire cartridge.

Factory .308 Win ammo for long distance accuracy: Fed Match 168gr Sierra Match King ammo is very good. Others to look at are Hornady and Lapua factory ammo. Avoid Win factory ammo. For a cheap ammo that is good to sight in the scope and seems to shoot amazingly well for the price Rem PSP (the cheap stuff in the the old green and yellow box).

Stay in the 165 to 170gr bullet range initially. It should give you the best accuracy from factory rounds. Sierra Match King bullet and Lapua bullets are very good.

[Troublco]

Generally speaking, the heavier the bullet you want to shoot the faster the twist rate needs to be. Most rifle calibers have a bullet weight range that isn't too different from light to heavy, and are generally only available in one twist rate. That takes the guesswork out of that part of the equation. Two that don't fit that profile are the .223/5.56 and the .308/7.62. There are such a wide range of bullet weights available for these that you really have to have an idea of what you're going to do with the rifle, and therefore what bullet weights you want to use, when selecting your barrel/twist rate. Folks are generally more familiar with the .223 bullet weight/barrel twist rates since the AR platform is widely available with different twist rates, and they're informed as to which bullet weights work with those twist rates. My rule of thumb is 1-12 up to about 55 grains, 1-8 up to around 77, and 1-7 for heavier. 1-9 is sort of a compromise that works OK with most weights but not great for any, although I've had good luck with 55-69 grain bullets.
The following is just from my experience, and is my opinion, but I've found that 1-12 barrels in .308 work best from 150 up to about 175 grain bullets, as the original twist rate for the M14 is 1-12 for shooting 147gr FMJ's. They work well with 175's, but everything I've ever seen and heard is that 180 is basically the ceiling for 1-12 barrels. M14's are limited to 180's due to their design and construction and you have to be careful when loading for these to keep the pressure curve close to original ammo to prevent damage, and .308 converted Garands are basically the same. You can probably shoot heavier bullets in a bolt gun with a 1-12, although I've never done it. I shoot Sierra 175 Match Kings in my M14 (1-11), my .308 Rem 700, and my built myself pseudoscout which are both 1-12, and they work fine. I've shot them out of a heavy barrel custom Rem 700 and gotten slightly better accuracy, but that could be the twist rate or it could be the difference in the way the guns are built. Now .300 Win Mags are normally set up with a 1-10 to be able to use bullets up to 240 grain. In fact, for a .300 WM a 180 is a fairly light bullet, if you look at the ballistics for some of the more efficient bullets for smaller calibers the "optimum" bullet for a .30 cal is supposedly around 240-some odd grains if you follow the chart.
Also remember that some guns like certain loads, and an almost identical rifle can do crappy with the same load another one does well with. But if a gun doesn't do well with a certain load, all you can do is try others and see which one(s) it likes. Handloaders can spend hours trying to find a load a gun likes with a certain bullet, powder type and weight, and so on.

Bottom line? I'd say try 150's up to 175's and see what your gun seems to work better with, then try other companies loads in those ranges to see what works for your gun.

Oh, yeah - SA Friday is right about the powder charge/bullet weight difference. My pet .308 hunting load is a 165 gr Sierra Game King HP over about 41 grains of 2460 and I don't have a lot of leftover room in the case. I don't think it's physically possible to cram 55-70 grains of powder in the case; I think you'd be spilling out the top before you got to 50 depending on the powder.

[theGinsue]

I'm interested in figuring out how to figure out what the best grain weight is and why.

BigBear - I think I know what you are getting at, but there are so many variables to consider and in the end, the biggest consideration is personal preference.

Of course, you'll need to consider things such as barrell twist rate, etc. but your gun will shoot the same ammo differently that your best friends gun of the same make/model.

You also have to consider the intended purpose of the ammo. Different ammo features are designed for different purposes.

[smchop]

You should also look at Black Hills ammo for .308, I use that in my 20" 168gr and it shoots better than I do. Its 1:12 also but only 20".

[BigBear]

Hmmm... guess this'll need to wait until I win the lottery then, lol. Thanks guys, some great explanations in there.