i guess i have a few questions..

1. is grain a measure of the amount of powder, or weight of the bullet?

2. if it is a measure of the powder, does the weight of the bullet always correspond to the grain?

3. besides cost, what are the disadvantage to using a higher grain bullet (assuming ratio between powder and bullet mass is so that it will have the same velocity as a lower grain bullet)?

4. advantages?

5. will all different grains of .223/5.56 be compatible with the same guns that typically use 55gr?

Grains are a measure of weight (bullet, powder or tiny rocks).  There are 7000 grains in a pound.

Heavier bullets typicall have a lower velocity for any one type of round due to pressure limits (i.e. can not keep adding powder, run into limits of case size, brass flow and/or action).  If you want heavier bullets to go faster then have to either increase the case size and/or increase the caliber for the same bullet weight (of course a short large bullet tends to loose velocity faster ... such as pistol bullets).

For .223 with a 1 in 12 barrel twist (1 turn in 12 inches) the 55 gr bullet is typical.  The faster barrel twist (1 in 8 or 1 in 7) can use heavier bullets (at a slower velocity ... no free lunch) including 75+ grains, however, that is another discussion in and of it's self.

My short recommendation is to get some good .223 ball ammo (Win Q3131A or Federal XM193) and then pick up some of the Federal Gold Metal Match (68 grain) if your barrel twist will handle the heavier loading (if not Hornday makes some TAP ammo in almost every weight).

Regards
John

1. Both

2. 1 grain (gr) = 64.8 mg = 0.35 oz

3. Heavier bullets will start off slower and will drop more at short range.  Lighter bullets are faster and do better against small creatures in ballistic tip form.  Light weight rounds shed velocity quickly so they dont over penetrate in urban environments as much.

4. They hold velocity better so they end up dropping less at long range.  They buck the wind better.  They have better terminal ballistics (in 5.56)

5. No.  the ideal twist for 55 grain is 1/12 twist.  It will not stabilize 62, 68, 69, 75 or 77 grain ammo.  However if you get a 1/8 or 1/7 twist barrel it will shoot 55 grain ammo almost as accuratly as a 1/12 and will stabilize all weights of commonly used ammo.

Ok, so the heavier grains slow down less quickly so that's [i]better[/i] for longer distances...but they shoot slower, which is [i]worse[/i] for longer distances.  

So, is there a chart or something that will show what grains work best for what distances, based on their velocity and weight?

DevL, by "will they be compatible", I meant, will they all physically fit into the chamber of the gun?  Becuase it seems some of these bullets would be different shapes, lengths, etc.

They all fit in the chamber the only odd ball thing is the 80 grain ammo which is so long it wont fit in the magazine and has to be loaded one at a time through the ejection port. They also make a follower that will only hold the one bullet just for this for the guys who shoot 1000 yards.

I will try to find you a chart for different ammo.

OK this is an extreme example of the difference in ballistic coefficient vs speed but I will compare a 50 grain American Eagle jacketed hollow point and a 69 grain boat tail hollow point.

Velocity at 0 yards:
50 grain: 3400 fps
69 grain: 3000 fps

Velocity at 100 yards:
50 grain: 2910 fps
69 grain: 2720 fps

Velocity at 200 yards:
50 grain: 2460 fps
69 grain: 2460 fps

Velocity at 300 yards:
50 grain: 2060 fps
69 grain: 2210 fps

Now in this particular example the 69 grain ammo wont pass the 50 grain till after 300 yards.  It only began to catch up due to superior ballistic coefficient at 200 yards.

In general boat tailed bullets will have a better ballistic coefficient and most match bullets are hindered by the hole in the tip.  The real differennce is that at very long ranges the heavy bullets reign supreme.  They hold that velocity longer and buck the wind better.  It really does not matter than they are moving slower at first.  If you know the amount of drop at every range its the consistency that is key.  My advise is to be able to select a twist that allows accurate fire with both light and heavy bullets.  I ended up selling a 1/9 twist barrel because it would not stabilise 75 grain ammo.  I noticed no loss in accuacy going to a 1/7 with 55 grain ammo.  Of course I dont shoot the light weight ammo at long range.  I use heavy ammo for that.

Commercial rifle and pistol loads have a listed weight in grains that refers to the bullet.  Only reloaders need to worry about the measure of powder, which is also measured by weight (grains).  Powder also has various densities and burn rates.  This means that you cannot determine the appropriate charge of powder without knowing what kind of powder you are using.  Likewise, a cartridge has certain pressure limits.  More powder and heavier bullets will raise pressure.  At a certain point, a gun will be damaged.  This is why heavier bullets are fired more slowly then lighter bullets of the same diameter.  Ballistic performance depends on the shape of the bullet.  Pointed, Boat-tailed bullets tend to retain their velocity longer upon firing than flat based, round nose bullets.  



As stated before, heavier bullets in the same gun will shoot slower, but may retain their veloicity longer.  Heavier bullets also penetrate deeper than their lighter counterparts.  They are good for larger game, and long range target shooting.

Lighter bullets are faster and shoot flatter than heavier ones.  They also tend to break up more easily due to their speed and construction.  They are good for immediate kills on smaller game or varmints, and short range accuracy.



Not really.  As mentioned before, the twist rate of the barrel is very important.  In 5.56/.223 Rem, the 1-12" twist rate is suitable only for bullets 55 gr. and lighter, and is found mostly in old military rifles, and varmint rifles.  1-9" twist barrels are probably the most common on the civilian market.  They work well on all bullet weights up to and including SOME 75 grain bullets.  1-7" is considered a fast twist rate, and is used in current military rifles and is getting more common on the civilian market, due to it's flexibility in bullet compatibility.  1-7" will shoot all available bullet weights well, except for SOME lighter varmint bullets.  Unfortunately the twist rate is TOO HIGH for some bullets to take, and they break up in flight.

Hope this helps!

Thanks DevL,

now that I see that different higher grains can be fired out of the same gun I will definitely go with the 1/8 twist we were discussing earlier.  I think I read that 1/8 can do up to 80gr.

all i need now is some data that i can use to figure out what grains are good for what ranges.  i could do this with the following information about each common grain size:

62gr:
distance where surpasses 55 gr velocity = ?

69 gr:
distance where surpasses 62 gr velocity = ?

77gr:
distance where surpasses 69 gr velocity = ?

80gr:
distance where surpasses 77gr velocity = ?

using this information, the optimum range for each grain would be the distance between where it's velocity surpasses the velocity of the preceeding grain and the distance where the superceding grain's velocity surpasses it's velocity.

obviously the subsonic range (range where bullet drops below 1085 fps) would be a cutoff for a bullet's range as well

does anyone have any idea about these numbers or where i can get them?  seems impossible to logically pick a bullet grain w/o them..

Thanks Troy, I fixed those last velocities.

As to bullet weight and when the velocity allows the heavier bullet to pass the lighter bullet:

Its not that easy.  Most of this has to do with bullet construction more so than weight.  A blunt nose (think soft point or hollow point) is less efficient than a thin tapered FMJ nose.  A boat tail taper is more aerodynamic than a flat base.  These things have more effect on external ballistics than the weight in many cases.  You have to look at the ballistic coefficient of the bullets more so than the weight.  Heavy bullets do tend to have better ballistic coefficients though, but not always.  Every bullet is different.

Also what YOUR rifle barrel will shoot accurately is dependant on what that rilfe likes.  Like my previos example, a 1/9 twist is optimal for 62 grains but your rifle may like a particular load that is lighter than this, becasue of how deep the bullet is seated, rate of powder burn etc.  This is why many people shoot several types of ammo in several different weights to see what their particular rifle likes.  So an overstabilised light weight bullet could in fact be far more accurate than a weight that is perfectly stabilised for the twist rate of your rifle.  For you this will be total trial and error to see what rounds your rifle shoots best.  

I would not even begin to consider stabilization and bullet weight unless you are doing hand loads and can get the more important factors custom tuned to your barrel first such as as bullet seating depth (closer to the lands is better) etc. (with the exception that you dont want an understabilised bullet)

You are going way off and too indepth on a tangent that is not really going to mean much in so far as what your real world results will be.  Like we have all said go buy the 1/8 custom twist and buy several lots, weights and types of ammo.  Go shoot these rounds at 100, 200 and 300 yards and see what your rifle likes best.  Then work up dopes (ballistic drop charts) for your rifles favorite loads at long ranges then go practice, practice, practice.  THEN when you are so awesome with a custom gun at hundreds of yards, with ammo your rifle likes, that the only way to improve the groups is to handload, consider bullet weight and stabilisation.  Untill then your rifle could like 55 grain ballistic tips over the more appropriate 69 grain ammo out to several hundred yards.  You just have to figure out what works instead of what SHOULD work.  You may be supprised by what strange weights your rifle shoots well.

If your rifle shoots 5" groups at 600 yards with 55 grain ammo with more drop than 69 grain ammo., but the 69 grain ammo puts up 6.5" groups it is better to just use the 55 grain ammo and know how many clicks to adjust the scope for the 600 yard range.  The amount of drop is not that important so long as you adjust.  The actual group size is much more important.

ok, i hear what you are saying.  but i still feel its good to understand things even if my understanding won't be making much of a difference in my groupings.  when you look at a bullet, is there any kind of intended range or something?  obviously an 80gr bullet will be designed for longer range shooting than a 55gr...is there anything that lets you know what range its designed for, or are you just supposed to buy everything and test it?

Buy one box of everything and test it in YOUR rifle.  Make choices from that.  REAL WORLD results is what counts here not theory.

Oh yeah two rounds made with the same bullet cany vary a great deal in their accuracy in your rifle.  The 69 grain Sierra match bullet loaded in Federal Gold Medal and Black Hills can have totally different results in your rifle.  They use different powders, primers, etc.  One Oly match 1/8 barrel barrel may like Black Hills better, another the Federal.  Your just gonna have to figure that out for yourself.

Alright, I hear what you are saying.  

Ironically, I found a chart showing what I was looking for just after I stopped looking:

http://www.botach.com/Hornady_TAP.htm