Heavy for Caliber: Definition

03psd

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I have a basic understanding of the meaning from seeing repeated use in context but are their set weights for each caliber that are considered Heavy? Also does length have anything to do with it? For example the 155 Scenar being a lighter 30 cal by weight but long for its weight.

Also what are the pros and cons of Heavy for Caliber projectiles?

Thanks
 

Sig685

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Re: Heavy for Caliber: Definition

Good questions, actually.

Let's take 2 calibers that are well represented here; .223 Remington (5.56 NATO) and .308 Winchester (7.62 NATO).

The original .223 used a .75 inch 55 grain bullet with originaly a 1:14 twist then a 1:12 twist. Some years later, the bullet weight grew to 62 grains but since it had a steel penetrator, the bullet was longer because of the lower density of the steel. These bullets are fine for the original intent which was short range, 300 yards and under.

The 7.62X51 (T-65) .308 Winchester was originally loaded with a 147gr bullet (I forget the length) and it did well for its intended use, up to mid-range (600 yards and under).

When people started wanting to shoot longer distances, the low ballistic coefficient of these original bullets was working against them. In order to reah longer distances. you can try to push a bullet as fast as you can, but if the bullet has a low BC, it simply sheds this extra velocity faster. So, you try to increase the ballistic coefficient of the bullet such that it will retain more of its initial velocity longer.

The ballistic coeeficient is a function of sectional density and shape of the bullet. Sectional density is a function of the weight of the bullet in a specific caliber. In order to increase the sectional density of a bullet, you can make it heavier (and if it's in the same caliber, it will be longer) or you can use materials than have a higher specific gravity (density) than jacketed lead. Depleted uranium works well for that, as does gold, platinum, carbide, tungsten, etc. Consult you nearest periodic table and alloy manufacturer. The point is that we are currently stuck with jacketed lead, unless you have access to materials that mere mortals do not. So we make the bullets longer.

Back to our .223. If you use an 80 grain bullet, the SD for that bullet will jump from .157 for the 55gr bullet to .228 for that 80gr bullet. The BC value will go from .243 to as high as .510 for the 80gr bullets I use. This is such a big increase that even though my 80gr start out almost 400FPS slower than the 55gr bullets, by the time they get to 500 yards, my 80gr bullet has overtaken the 55gr bullet, which is now falling on the ground as it goes subsonic, my bullet will stay supersonic past 1000 yards.

On the .308 front, the 155gr bullet is making use of its very aerodynamic shape to increase its BC value. Remember what I said earlier, the BC is a function of the SD and the shape. The 147 had an SD if .221, which is pretty good but its shape was not very aerodynamic. The 155SMK has an SD of .233 and a listed BC between .430 to as high as .504 above 2700FPS. This bullet is very streamlined. The 175SMK has a BC about the same at the top end as the 155 Palma, but as the velocity reduces, it has a higher BC value, because its sectional density is higher that the 155gr Palma. This tells you that streamlining or increased SD can take you further by increasing the BC, but a combination of streamlining and especially an increased SD will do a better job over the longer distance. In other words, substance is somewhat more important than style, but you still need style.

And for the long distance, you still need a certain muzzle velocity to have the BC work for you. Finally, launching a 200gr bullet with a high BC, will require a minimum MV so that the recoil might be more than you want to deal with.

Trade-offs, everywhere.
 

srv656s

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Re: Heavy for Caliber: Definition

Great answer Sig, thanks for taking the time to write it up, very informative.
 

03psd

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Re: Heavy for Caliber: Definition

great detail, thank you.

the more i consider your response the more complicated the subject actually becomes. while everyone loves the high BC and SD, in most cases unless you have a specific twist barrel capable of stabilizing these HfC bullets, you are leaving performance on the table, of course then COAL and mag fitment becomes an issue.....ouch...this is all enough to make your head hurt trying to ponder my new build
 

Sig685

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Re: Heavy for Caliber: Definition

srv656s and koolnhard, thank you for the kind words.

03psd, yes it is an interesting subject and it is easy to let it get complicated but let me boil it down for you.

It comes down to one simple question: What do you want to do with your rifle?

When you have decided what the answer is to that question, you build the rifle so that it will be at its best for most of its use.

In my case, I recently built a .308 rifle for one single purpose; F-TR at Long Range (800/900/1000yards.) The rifle is NOT suited for anything else (well, it will do fine at shorter ranges, but it is almost overkill.) It has a very long heavy barrel and its twist was selected to properly stabilize a narrow range of bullets, I am not talking this rifle hunting. It will of course, stabilize any bullet shorter than my selected ones, but a slower twist would have sufficed for that and I am a big proponent of using the slowest twist needed to statically stabilize the bullet you want to shoot. In other words, there is no need to spin a bullet faster than it needs unless you have no choice.

So, if you tell us what you intend to do with your build, we can lay out the pros and cons of each choice and help you select the proper pros and minimize the cons.
 

03psd

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Re: Heavy for Caliber: Definition

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sig685</div><div class="ubbcode-body">

So, if you tell us what you intend to do with your build, we can lay out the pros and cons of each choice and help you select the proper pros and minimize the cons. </div></div>

I am wanting a rifle that will be well suited for 400-750 yards. I am leaning towards a long action build but may consider SA with..... you guessed it, heavy for caliber projectiles. I have gotten into reloading and love the ability it gives to allow for consideration of calibers either not factory loaded for or bullet/powder combinations not factory loaded.

I was originally wanting a .257 Weatherby Mag but I think I can do better with handloads and a more conventional case. If I go LA .300WM would be a top contender. If I go SA .260 Remington would be tough to beat. It will be used for both punching paper and some hunting. Befor anyone gets their panties in a wad, I would not take a 750yard shot on game but would take a 400-500 yard shot under the right conditions.
 

9sigman45

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Re: Heavy for Caliber: Definition

Sorry for the hijack.

Sig,
George and the gange are building me a rifle for that exact same purpose (long range F-TR Class competition). I've asked for a 28" Bartlein with 1:11.25 twist. George provided me with these chamber specs "342 jk. 90fb 1deg 30". I will be using Lapua brass and 175gr SMK (possibly some 190s as well). Does these specs sound good to you? If it were yours, what would you do differently?
 

Sig685

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Re: Heavy for Caliber: Definition

Ok, I will take a crack at it. However, let me preface this by saying that I am not much of a hunter, I am a long range competition shooter; all I ask of my bullets at the end of their trip it that they punch the paper.

I would think that you need a couple of things here; 1- over 1000 ft/lbs of energy at the target and 2) the best BC bullet for the distance.

Energy is a function of bullet mass and velocity, in fact the equation is Energy= 1/2(mass times the square of the velocity). Since we have a square for the velocity, keeping that one up is a VERY good thing. On the other hand we also need something to multiply it with, so the mass is important also. If we can keep the mass going as quickly as we can, we get a twofer.

We already discussed the sectional density issue, so we can see here that a long bullet. heavy for caliber is actually working in the same direction as we are aiming for. So, the best bet here is a high BC heavy bullet for the long range.

However, we do have to contend with the fact that in a hunting situation, distances are not well known, unless you use a LRF and you have a range card that is granular enough to give you drops very close to the range provided by the LRF. So we want to eliminate some of the drop and also the wind deflection and for that higher velocity is the best remedy; spend less time in the wind and you get deflected less.

I also believe that your bullet will expand more if the terminal velocity is higher. There I am a little shaky on the various thresholds, but I think that at 2000FPS and up, most bullets will do the job. A ballistic tip will help them expland even more and will provide a better profile for the bullet, increasing its BC. What's not to like?

The choice of action size is entirely up to you, either one will work, but I am partial to the SA, simply because I think they are more rigid and I love the .308 cartridge family. The short magnums were designed to be fired from SAs and yet achieve the performance of the belted magnums. So that may be something to consider. I also believe the short magnums to be more efficient in the use of propellants compared to the long action magnums. To me, using 10gr less of powder and to get the same performance is a bonus. Less recoil, less muzzle blast, etc.

For the long distance, I let the barrel do its job in generating additional velocity with the same charge, but for hunting, a long barrel may be contra-indicated. Then again, you are talking about 500 yard shot at game. For that, I would want the longest barrel I can carry, with the best bullets I can find.

The other thing with a hunting rifle, is that you do not take 20 shots or more in a row like in a competition, you are looking at one perhaps two shots for one outing. This means you do not need to have a heavy barrel; you just need a quality barrel.

I would look at something in the 6.5, 7mm or 30 caliber range. Swift bullets has a 165gr Scirroco II bullet that may be just the thing you are looking for. They also have one in 6.5. Hornady has some neat bulletrs like the GMS and V-max and others. Barnes has interesting bullets also.

 

Sig685

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Re: Heavy for Caliber: Definition

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 9sigman45</div><div class="ubbcode-body">Sorry for the hijack.

Sig,
George and the gange are building me a rifle for that exact same purpose (long range F-TR Class competition). I've asked for a 28" Bartlein with 1:11.25 twist. George provided me with these chamber specs "342 jk. 90fb 1deg 30". I will be using Lapua brass and 175gr SMK (possibly some 190s as well). Does these specs sound good to you? If it were yours, what would you do differently? </div></div>

I do not believe that I am in any position to really recommend anything specific or critique someone else's build. Let me just say that I wanted to use heavier bullets (with better BC values,) and in order to shoot them at decent velocities, I needed a longer barrel. The (very) preliminary results show the logic to be sound, so far. I like your twist. I like it so much I did the same.
 

Coyote3

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Re: Heavy for Caliber: Definition

Personally, I would not go with a 257 Weatherby Mag. I have a buddy that shoots one and has taken elk at 400 yds., but will not trust that little 120 grain bullet past that distance. A 270 Winchester will do about the same with not near the abuse from the recoil. A 300 WM with a 22-24 inch barrel, say a .75-.80 muzzle, set on a 700 action, top with a nice Leupold Vari XIII 6.5-20 scope would suit a hunting and target rifle pretty nicely without breaking the bank. Not just thinking, actually built one but has a 1 inch muzzle and 28 inch barrel. Tickled pink with it. Cannot go wrong with the 300 WM..... BTW with the .270 I have dropped a cow elk at 578 yds and my dad has dropped one at 540 yds. They didn't go 50 yds and tipped over. Just my opinion......