What makes one bullet more or less accurate than another?

[blockfort]

And I don't mean just the bullet, but the whole cartridge.

I can understand it if the diameters of the bullets are different or vary more / have lower tolerence in one brand than another, but if we say for argument sake that the diameter of the bullet is the same, then why would one make of, say, 9mm be any different in terms of accuracy than another make? Why would the powder make any difference? Why would the bullet type or shape or weight make a difference. Isn't it all in the barrel?

I ask because I was watching a video of a guy who writes a reloading column for a major magazine, and he was doing tests to find the best load for some 9mm. He did two loadings each of three different powders, plus two different factory loads, and the accuracy varied quite a bit on a few of them versus the rest. If he loaded the same bullets into all of his reloads, shouldn't they all come out the same? Why would a little more or less powder throw them off? Is that why bulk reloaded ammo is considered less accurate than some tighter tolerance factory loaded stuff, or precisely measured home loaded ammo? Because a little bit more or less powder changes the accuracy? Wouldn't it just affect velocity, causing the bullets to hit higher or lower?

[HighLander51]

Small changes in velocity can greatly affect accuracy, however it also depends on the brand of powder (different burn rates and resultant pressure for the same velocity), overall length, crimp, brand of case (not so much in pistol), primer, bullet weight, jacketed, or lead, and bullet sectional density (design). That's why spitzer rifle bullets are so much for accurate than, for example, round ball of the same mass. .45acp is more accurate than 40S&W and 9mm right off the get go because it has a more efficient sectional density (bore diameter to length and cross section geometry).

At the end of the day you can only really control powder weight, overall length, and choice of bullet. You can't measure pressure directly, only muzzle velocity thru a chronograph, which is more important to meeting the minimum power floor in competition. Buy a 50 or so, of each 9mm bullet you would like to try, load them all to the same powder charge (from the powder maker's website) and OAL, see what runs best. Keep in mind that your discounts for reloading occur in the 25,000 plus order of bullets, 40 lbs powder, and 50,000 primers.

[grant22]

Each component creating the "whole" affects the outcome. Like Highlander said, powder weight, bullet choice, and oal all factor in.

A better bullet may be more 'true' therefore more consistent shot to shot. It's like if your tires/wheels aren't balanced, there'll be a vibration in your car and disrupt everything.

Powder charge or weight matters for consistency. Variations from cartridge to cartridge would be like all 8 cylinders in a V8 receiving different amounts of fuel creating loss of efficiency and some vibration.......a rough running motor.

The case is like the structure or chassis. If each cartridge has variations in the case (many different variables here) then it would be like two like cars racing, but the two frames or chassis having different geometry, materials, etc. This is why the real precision guys spend so much time on case prep.

Primers play an important role in consistency. They are the 'igniter.' If you have two like campfires and you throw 1 cup of gas on one and 1 cup of ether on the other, the burn or flash will be different.

Bottom line, I believe ammo plays a huge role in accuracy because of consistency. The more consistent the ammo is, the more accurate out of your barrel it'll be.

Sorry for the wordy post.

[XDRoX]

Keep in mind that your discounts for reloading occur in the 25,000 plus order of bullets, 40 lbs powder, and 50,000 primers.

What does this even mean? How many people buy bullets by the 25k? You can't even legally process that many primers at one residence.

[HighLander51]

What does this even mean? How many people buy bullets by the 25k? You can't even legally process that many primers at one residence.

That means that all competition shooters buy in bulk, after all, you can burn 25,000 a year if you shoot every weekend......

I used to buy bullets by the 40 gallon drum direct off the dock from a bullet maker near Lancaster. That equated to about 72,000 bullets, or about 1,300 lbs. We would get 3 - 4 drums between us and load it by pallet on the 3 axle trailer. 70K bullets last about 2-3 year shooting competition. That guy has long since left California, but we have a local source for Bear Creek Moly, and I only buy 20,000 to 25,000, depending on availability. Powder is still readily available in 8lbs, and 4 or more gets you a %10 discount. Still buy primers locally by the sleeve (5,000) and usually 10 sleeves at a time to get the good discount.

Who says you can't have more than 25K primers? Is that a state law? or a San Diego county ordinance? Or a city ordinance? I have never heard of that and have been reloading in California since the late 70's...........

[HighLander51]

blockfort, Chuck Hawks is a well respected old school shooter, and there is lots of info on his site

http://www.chuckhawks.com/bullet.htm

By the way, most bullet makers will send you free 6-10 bullets if you request it from the website.

[Fjold]

One of the major factors that makes a cartridge more or less accurate than another is consistency.

In the bullet itself the consistency of the jacket, in thickness, shape, wall diameter and weight makes a huge difference. The lead core of the bullet has to be consistent in density, amount and fill the cavity in the jacket completely and evenly.

In the cartridge case it has to be consistent in alloy, weight, wall thickness and uniformity and sized correctly.

Powder has to be evenly mixed with a correct amount of deterrent coating to control burn rate.

Here's a picture of two targets using the same lot of cartridges where the cases were sized the same, timmed to a uniform length, sorted by weight. The bullets were all the same brand from the same lot and it was all assembled on the same equipment. You can see that the difference in powder charge (by as little as 0.2 grains) has a noticeable difference in the accuracy of the cartridge:
The target on the left was using H4895 and shows pretty good consistency until the powder charge got towards max in the bottom left bullseye. The target on the right was using H380 powder and was less much accurate when loaded to similar pressure levels.

[XDRoX]

Who says you can't have more than 25K primers? Is that a state law? or a San Diego county ordinance? Or a city ordinance? I have never heard of that and have been reloading in California since the late 70's...........

Here you go:

Excerpt from the California Fire Code:

3306.4.1 Black powder and smokeless propellants. Propellants for personal use in quantities not exceeding 20 pounds (9 kg) of black powder or 20 pounds (9 kg) of smokeless powder shall be stored in original containers in occupancies limited to Group R-3. Smokeless powder in quantities exceeding 20 pounds (9 kg) but not exceeding 50 pounds (23 kg) kept in a wooden box or cabinet having walls of at least 1 inch (25 mm) nominal thickness shall be allowed to be stored in occupancies limited to Group R-3. Quantities exceeding these amounts shall not be stored in any Group R occupancy.

3306.4.2 Small arms primers. No more than 10,000 small arms primers shall be stored in occupancies limited to Group R-3.

This is a state law. Individual counties could have stricter laws.

Not saying you'll get in trouble for it, but it probably isn't wise to be posting it on the internet.

The question gets brought up once every few months. I did a quick search and this popped up. I've seen different places that site the same rules, but this popped up first.

The main reason to abide by the law is in case your house burns down. If your insurance company found out that you had over 10k primers, they may not pay for your losses.

[oddjob]

What these folks have said is true.....and we haven't even touched the subject of the barrel itself, or the bedding, lockup & etc........

[blockfort]

Thanks everyone so far, you've listed many factors that can cause rounds to differ. I can understand why bullet shape and density have an effect, but I don't understand why the other factors affect accuracy.

Why does the shell wall thickness or length affect accuracy? After the first instant, the bullet leaves the shell and I would assume, is much much more affected by the barrel than the shell, significantly so.

Why does a stronger or weaker charge affect accuracy? (assuming that a whole bunch of rounds have the same charge, and that their accuracy on average will be different from another group that have a different powder charge).

[bluenoise]

Thanks everyone so far, you've listed many factors that can cause rounds to differ. I can understand why bullet shape and density have an effect, but I don't understand why the other factors affect accuracy.

Why does the shell wall thickness or length affect accuracy? After the first instant, the bullet leaves the shell and I would assume, is much much more affected by the barrel than the shell, significantly so.

Why does a stronger or weaker charge affect accuracy? (assuming that a whole bunch of rounds have the same charge, and that their accuracy on average will be different from another group that have a different powder charge).

I'm only guessing here, but it seems reasonable to me that added pressure could introduce more vibration in the barrel. Another thought is the added velocity means increased RPM of the bullet and, therefore, more susceptibility to vibration from inconsistent density in the bullet and jacket.

Likewise, too low of pressure may not give the bullet enough spin to stabilize or it's more prone to the effects of drag within the barrel. Again, I'm just saying what seems plausible to me. I don't really know the answer.

[HighLander51]

Here you go:

Thanks, but I am zoned R1....

[Norsemen308]

most the time... it has less to do about the bullet and more to do about case preparation, the trim, the crimp, the powder, primer...

easiest example is like saying How does one motor make more power then the other... its no single component.


there are however, bullets that are not as aerodynamic, there is a difference in my opinion between boat tails and other bullets, but many will never see the difference without 100 rounds of each being shot and graphed.

[grant22]

Thanks everyone so far, you've listed many factors that can cause rounds to differ. I can understand why bullet shape and density have an effect, but I don't understand why the other factors affect accuracy.

Why does the shell wall thickness or length affect accuracy? After the first instant, the bullet leaves the shell and I would assume, is much much more affected by the barrel than the shell, significantly so.

The wall thickness, length, etc will boil down to case volume. If case 'A' has a thicker wall than case 'B', then 24 gr is intro'd into each, you will have varying pressures upon ignition with each............and therefore you have incosistency.

What I have found when chasing accuracy is that it's all about consistency. Any little variance will affect the consistency and therefore, groupings.

The barrel still matters, though. But whenever I though I had a bad barrel, I found out through experimenting that it was always an ammo issue.

[bumpo628]

Thanks, but I am zoned R1....