G1 as a factor for bullet/round selection

[HeavyAssault]

I’m not into reloading so I’m asking this as a general knowledge question. I realize the G1 is a small percentage of the overall aspect of shooting. There’s PLENTY of other factors to consider.

Would you select a bullet/round based solely on G1 specifications??
Is the G1 factor primary to your bullet/round selection over other factors??
Does the G1 factor cause you to change any sort of recipe data for the same grain weight??
Given two bullets/rounds of the same grain weight but different G1 factors, how do you make your selection??

I ask this as I tend to shoot factory ammunition but I’s suspect it trends when reloading. I find some boxed rounds grouping better while it seems as the G1 factor is lower/higher than other rounds. I would guess a higher G1 “should be” a better bullet/round, from my shooting it seems that’s not always the case. Yea…I’m not a expert in loads/load development nor a range ninja. I just shoot for relaxation and the fun challenging myself to do better. Thanks in advance.

 

[spife7980]

The higher the bc the more easily it moves through the dense air.
Higher bc doesnt always make it a better shooting bullet for you though.



Would you select a bullet/round based solely on G1 specifications?? No
Is the G1 factor primary to your bullet/round selection over other factors?? Depends on what its being used for but its part of it, not sure I would say primary
Does the G1 factor cause you to change any sort of recipe data for the same grain weight?? The BC doesnt change internal ballistics.
Given two bullets/rounds of the same grain weight but different G1 factors, how do you make your selection?? Shoot them both and see which your barrel prefers.

 

[HeavyAssault]

@spife7980 : Thank you!

 

[CK1.0]

A G1 value/number is just a way of measuring/assigning a Ballistic Coefficient (BC) value to a projectile (a G7 is just the newer, better way of coming up with the same type of value/number and is what most use these days). The higher the number the more aerodynamically efficient it is supposed to be.

Generally speaking, a higher BC number is always more desirable... but BC is one of the last things that determines whether a bullet shoots well in a given barrel, marrying the ideal twist (and even chamber when talking .223/5.56 vs .223 Wylde) with your chosen bullet weight matters far more.

In simple terms, if you and I were the same strength and we each threw a rock equally as hard as each other, the guy with the larger higher-BC rock would end up with his flying truer for further.

 

[Dogtown]

And just to add a bit more clarity, the G1 BC is computed using a flat base profile, which was much more common in the olden days, while the G7 is computed using a boat tail profile.

Why not just use G7 for precision shooting if it's more correct ? G1 is often a good enough approximation, and up until more recently it was the most common model used/published publicly. These days a lot people use custom drag models that are neither G1 or G7.

 

[HeavyAssault]

your chosen bullet weight matters far more.

This what I’ve discovered through my shooting for sure. It sort of lead to my question as I have tried a few different rounds of the same weight but the end results didn’t seem right. Which is were I started thinking the G1 could be a bigger factor than I expected. Thank you !

 

[HeavyAssault]

And just to add a bit more clarity, the G1 BC is computed using a flat base profile, which was much more common in the olden days, while the G7 is computed using a boat tail profile.

View attachment 8460858

Why not just use G7 for precision shooting if it's more correct ? G1 is often a good enough approximation, and up until more recently it was the most common model used/published publicly. These days a lot people use custom drag models that are neither G1 or G7.

I’ll look at that G7 number if it’s provided. Not all data is shared or hard to find even on manufacturer sites. Thank you!

 

[Dogtown]

Drag is what slows your bullet down in flight (and gravity to a degree if we're being pedantic), and momentum is the primary value that fights drag, with aerodynamic profile often playing more of a secondary role when it comes to bullets. The momentum of the bullet is basically the mass * velocity, so if two different mass bullets are fired at the same velocity, the more massive bullet will go further because it has more momentum. However, often the more massive bullets can't be shot at the same velocity as less massive bullets, so there's a balancing act going on.

So the best bullet is often the bullet that has the most optimized balance of momentum/aerodynamics.

In the ELR solid bullet realm, this stuff gets interesting. Solid bullets tend to be made with less dense materials than jacketed bullets, so you either get a solid of the same size but lower mass, or more likely the same mass in a longer solid. And that length also plays a role in its aerodynamic profile, where a bit more length can add stability and reduce drag a bit as long as you have a fast enough twist to stabilize. So it's not uncommon to see guys shooting 300gr .338 jacketed bullets and guys shooting 265gr .338 solid. The solid has less mass, but probably a very similar BC and can be pushed at higher velocity.

It's a game of optimizing parameters.

 

[TheOfficeT-Rex]

The OP is an interesting question, because thinking about how I've made bullet selections, it's not entirely logical objective. I hate to admit that the general reputation of a bullet has a higher bearing than BC, for me. Drop is easy to account for, and within a weight and use class, windage differences are negligible for the positional practice that makes up most of my shooting.

I want something that generally produces acceptable precision for multiple users, and is generally consistent (no reported random flyers/jacket meltdowns, etc). Like a good barrel from a good smith, it's more likely to get acceptable results for me.

There is still trial and error, and I do like to experiment, but for the most part... stuff has gotten so good that it's marginal gains and splitting hairs between them. If I played a different game (e.g. ELR) I might view it differently and spend more time optimizing- but my $.02 - the cost of doing that properly (in time, powder, bullets, and barrel life) adds up quickly and most people would not reap an appreciable benefit.

 

[Doom]

The OP might want to consider the Ballistic Coefficient (BC) in the following way. For short range shooting, 100 to about 400-500yds the ballistic coefficient has little effect on drop and windage for different bullets for most centerfire cartridges. The inherent accuracy/precision of the bullet is primarily determined by the design and consistency of construction assuming the spin rate is high enough to make the bullet gyroscopically stable and the velocity remains above the trans sonic region (1350 fps).

As the ballistic coefficient increase for a bullet the drag on the bullet decrease for any given velocity due to a lower coefficient of drag. The bullet begins to lose velocity as soon as it leaves the barrel. The bullet drop due to gravity is a function of the time of flight to a target. The drop from the line of sight of the barrel is proportional to the time of flight squared ( t^2) and its vertical velocity increases in direct relation to the flight time. The longer the flight time the longer wind will affect the bullet flight.

The velocity drop and time to target become significant factors in relation to the external factors of gravity and wind in affecting the on target performance of any round at longer ranges. In essence a higher ballistic coefficient bullet will reach the target with less drop and windage than a lower BC bullet. However, simply because it is less effected by wind and drop it may not be more accurate/precise than another bullet of equal or lesser(or higher) BC.

Generically, a short range bench rest shooter (<300yds) isn't likely to be concerned with the BC of his bullet because the difference in BC will not like be seen on target. For long range (>600Yds) time of flight becomes important especially in windy conditions. So in this case a bench rest or F Class marksman may well consider BC in his selection of a bullet.

Ultimately higher BC bullets extend the effective range and ultimate usable range of any particular cartridge by moving the trans sonic and sonic velocities further downrange.

 

[BrassWhole]

Based off what I've read, it's more likely with your boxed factory ammo that CBTO is one of the main differences causing an influence in what you believe shoots better from your rifle. Measure the CBTO of factory ammo, they are all over the place. I've seen bullet jump in excess of .1" with factory ammo. To really understand CBTO you also need to know the jam CBTO so you can see just how much different bullets jump before contacting the lands.