.308 same load, different bullet, big POI changes?

[JStem1283]

I know changing bullets can slightly change POI, but changing from Sierra 168gr match king to Hornady 168gr A-max netted me aprox 3.5" right and 2.5" low consistently. I am new to reloading but I have the help of my neighbor who has about 25 years experience. Using the same primers, brass, powder, charge, seating depth aka exactly the same just a different bullet. The Hornady's grouped well in their location it was just significantly off center. Is this something thats normal in finding "optimal load" for my rifle?

[Shodan]

Did you notice the change during the same range trip? Is there a chance that something else is to blame like the scope, rest, shooting position or atmospheric conditions?

[JStem1283]

Not the same trip, scope def didnt move I have all my screws held in with loctite and marked. I shoot off bipod on a table so possibly that but 3-4" is a big miss consistantly in a sub .25 moa rifle. Atmospheric conditions are different but again at 100 yards it shouldnt cause that drastic of a change.

[dk99358]

Not unusual and no big deal. Once you settle on a load, adjust your sights. Until then, as long as they all hit the paper, all you need to care about is group size and maybe velocity.

Dale

[saleen322]

Not the same trip, scope def didnt move I have all my screws held in with loctite and marked. I shoot off bipod on a table so possibly that but 3-4" is a big miss consistantly in a sub .25 moa rifle. Atmospheric conditions are different but again at 100 yards it shouldnt cause that drastic of a change.

If your .308 is a sub .25 moa rifle, what are you shooting to get those groups and why would you want to change? What model of .308 do you have?

[PAallterrain]

Not unusual and no big deal. Once you settle on a load, adjust your sights. Until then, as long as they all hit the paper, all you need to care about is group size and maybe velocity.

Dale

This, but include SD and OS. Where they group on paper is no big deal and that big of a change isn't uncommon.

[JStem1283]

If your .308 is a sub .25 moa rifle, what are you shooting to get those groups and why would you want to change? What model of .308 do you have?

I achieved it's sub .25 moa using a hand loaded 168gr sierra HPBT out of a savage action custom build. Quite frankly I think the .25 grouping was a bit of luck. I do group sub .50 regularly however. I just wanted to try a different bullet since my local reloading supplier had the A-max quite on sale.

[Tomcat088]

I achieved it's sub .25 moa using a hand loaded 168gr sierra HPBT out of a savage action custom build. Quite frankly I think the .25 grouping was a bit of luck. I do group sub .50 regularly however. I just wanted to try a different bullet since my local reloading supplier had the A-max quite on sale.

Others are giving you the correct information. Don't worry too much about the bullets hitting in a different place, as long a they're consistently hitting there, with a group size that you like. I'm kind of surprised that you haven't asked your friend who has 25 years of experience. PLEASE read at least the last paragraph of this post.

Anytime you change ANYTHING about the load, you're going to have differences in how the load performs. Sometimes factors will sort of cancel each other out, and they don't appear that obvious, but many times there are still differences that are present. What you have to understand is just because bullets are the same weight, doesn't mean that they're the same. Different manufacturers will use different shapes of bullets, even if they are the same weight. This can be related to how long their boat tail is, whether or not they have a boat tail (flat base), the angle of the boat tail, how long it is, etc. There are difference in style of ogive, whether secant, tangent, and now from Berger, even hybrid. Even with similar ogives, bullets can also have difference lengths of bearing surfaces. You also have to keep in mind that different bullet makers have different internal designs to their bullets. Some have dividers in the center, some have thicker jackets than others, some have thicker/thinner jackets in different places in the taper, etc. Some will have hollow points, some with polymer tips, obviously different centers of gravity, different types of cannelures, "driving bands", etc. etc. Even the hardness of copper that manufacturers use will vary.

On the surface, being the same bullet weight makes people think that they will shoot in the same place. Unless they're from the same maker and a very similar design, they'll usually shoot in different places. The shapes of the bullets affect how the gas vents around the bullet before it engages the rifling. It will affect how the gases vent around the bullet as it exits the barrel. The shape and bearing surface will also affect how much friction the bullet has as it travels down the barrel, which will obviously affect point of impact. Whether or not a bullet has a cannelure, neck tension, and hardness of the copper will affect how easily the bullet leaves the brass (how much gas vents before the bullet engages the rifling), and the hardness of the copper will affect how easily the bullet seals with the rifling and the amounts of gas as well. I'm guessing that you're probably measuring the "seating depth" of the bullets by measuring the COAL (Cartridge Overall Length). This doesn't mean that the bullets are the same distance from the lands of the barrel, it just means that the tips of the bullets are at the same place relative to the base of the cartridge. Because of the different shapes of the bullets, the ogive (the part that touches the rifling), will be in different places and will have an impact on the gases vented, time it takes for the bullet to engage the rifling, etc. etc. As you're starting to see, this is a bit complicated. Just remember that anytime you change a primer, powder, brass, bullets, or ANYTHING, there will be changes to the load. Lots of times people don't realize this, but even changing lots of powders and brass WILL have an impact on the reload and its performance.

I'm not sure if someone has told you this or not, but I want to make sure that they have. You CANNOT just change out some component of a "safe" or "good" load, and load it up like no big deal, business as usual. This is DANGEROUS and should NOT be done. Differences in the bullet shapes, bearing surfaces, lengths, etc. can change the pressures that are occurring while the load is fired. Because more or less bullet will be seated in the brass with different bullets, it WILL affect the pressures. Because of the differences in bearing surfaces and the force it takes to push the bullet down the barrel, it WILL affect the pressure curve. It's possible to have a load that you worked up that is "safe" and good, but that can completely blow up or be way too "hot" if you change one thing. So do NOT think that just because you feel like changing bullets, and it's the same weight, that it'll be safe and you don't have to work up a load. If you have worked up lots of loads in your rifle, and know what it likes, you can get away with stepping down the load a bit, and then working up. It may seem like a pain to have to start over and work up a safe load, and it may seem like a waste of powder and other stuff, but it's for YOUR safety. The last thing you want to do is blow up a rifle and cause injury, blindness, or death because you wanted to save a few dollars on components, or wanted to be lazy. If you change any component or components, you have to back off and work up a safe load. Sorry if I sound like I'm preaching, but we have to encourage safe reloading practices, and I'd hate for you or someone else to be injured or killed by a reload. Best of luck, and please let us know if you have any other questions, we're happy to help.

[JStem1283]

Others are giving you the correct information. Don't worry too much about the bullets hitting in a different place, as long a they're consistently hitting there, with a group size that you like. I'm kind of surprised that you haven't asked your friend who has 25 years of experience. PLEASE read at least the last paragraph of this post.

Anytime you change ANYTHING about the load, you're going to have differences in how the load performs. Sometimes factors will sort of cancel each other out, and they don't appear that obvious, but many times there are still differences that are present. What you have to understand is just because bullets are the same weight, doesn't mean that they're the same. Different manufacturers will use different shapes of bullets, even if they are the same weight. This can be related to how long their boat tail is, whether or not they have a boat tail (flat base), the angle of the boat tail, how long it is, etc. There are difference in style of ogive, whether secant, tangent, and now from Berger, even hybrid. Even with similar ogives, bullets can also have difference lengths of bearing surfaces. You also have to keep in mind that different bullet makers have different internal designs to their bullets. Some have dividers in the center, some have thicker jackets than others, some have thicker/thinner jackets in different places in the taper, etc. Some will have hollow points, some with polymer tips, obviously different centers of gravity, different types of cannelures, "driving bands", etc. etc. Even the hardness of copper that manufacturers use will vary.

On the surface, being the same bullet weight makes people think that they will shoot in the same place. Unless they're from the same maker and a very similar design, they'll usually shoot in different places. The shapes of the bullets affect how the gas vents around the bullet before it engages the rifling. It will affect how the gases vent around the bullet as it exits the barrel. The shape and bearing surface will also affect how much friction the bullet has as it travels down the barrel, which will obviously affect point of impact. Whether or not a bullet has a cannelure, neck tension, and hardness of the copper will affect how easily the bullet leaves the brass (how much gas vents before the bullet engages the rifling), and the hardness of the copper will affect how easily the bullet seals with the rifling and the amounts of gas as well. I'm guessing that you're probably measuring the "seating depth" of the bullets by measuring the COAL (Cartridge Overall Length). This doesn't mean that the bullets are the same distance from the lands of the barrel, it just means that the tips of the bullets are at the same place relative to the base of the cartridge. Because of the different shapes of the bullets, the ogive (the part that touches the rifling), will be in different places and will have an impact on the gases vented, time it takes for the bullet to engage the rifling, etc. etc. As you're starting to see, this is a bit complicated. Just remember that anytime you change a primer, powder, brass, bullets, or ANYTHING, there will be changes to the load. Lots of times people don't realize this, but even changing lots of powders and brass WILL have an impact on the reload and its performance.

I'm not sure if someone has told you this or not, but I want to make sure that they have. You CANNOT just change out some component of a "safe" or "good" load, and load it up like no big deal, business as usual. This is DANGEROUS and should NOT be done. Differences in the bullet shapes, bearing surfaces, lengths, etc. can change the pressures that are occurring while the load is fired. Because more or less bullet will be seated in the brass with different bullets, it WILL affect the pressures. Because of the differences in bearing surfaces and the force it takes to push the bullet down the barrel, it WILL affect the pressure curve. It's possible to have a load that you worked up that is "safe" and good, but that can completely blow up or be way too "hot" if you change one thing. So do NOT think that just because you feel like changing bullets, and it's the same weight, that it'll be safe and you don't have to work up a load. If you have worked up lots of loads in your rifle, and know what it likes, you can get away with stepping down the load a bit, and then working up. It may seem like a pain to have to start over and work up a safe load, and it may seem like a waste of powder and other stuff, but it's for YOUR safety. The last thing you want to do is blow up a rifle and cause injury, blindness, or death because you wanted to save a few dollars on components, or wanted to be lazy. If you change any component or components, you have to back off and work up a safe load. Sorry if I sound like I'm preaching, but we have to encourage safe reloading practices, and I'd hate for you or someone else to be injured or killed by a reload. Best of luck, and please let us know if you have any other questions, we're happy to help.

Well sir, thank you so much for all that great info. I should make it known that due to not having any longer distance ranges, I do in fact load at the minimum of the spectrum for charges according to the Hornady reloading manual. I know that changing anything can change hits, I just wasnt expecting it to be that far off. Your explanation of actual bullet shape and design makes a ton of sense. I just wanted to make sure that what happened to me wasnt out of normal possibility.

[markshere2]

I am not a long term reloader and goodness knows I am not a great shot...

but it strikes me that when loading at the bottom end of the scale, changing a component out may have a more significant impact than if you were loading at the middle of the recommended scale.

I would also expect a large change in POI if you were loading at the hot end of the scale. However the experience of the gurus tells us it's a mistake to change a component at the hot end of the scale, so hopefully we'll never know.