Will A 15 Grain Ammo Change Effect A .308 At 250+ Yards?

[BowVista]

I shot over a does back yesterday afternoon at just over 260 yards with my Encore .308. I made that shot twice last year with the same gun, and the scope is not off at 100 yards. I was dead steady, and very comfortable with the shot, but can't quite figure what happened. The only thing I can think of is that I ran out of the 165gr ammo I was using, and just grabbed some 150gr at the last minute.

Will that make a big difference at that distance?

[Dr. D]

Yes.

[kyle1974]

yes.

you could have even picked up a different load with a 165 grain bullet that might have a different ballistic coeffecient, and it could potentially throw you off by a considerable amount. not all 150 grain loads shoot the same, or 165 grain loads, for whatever reasons, they all shoot different.

whenever I buy ammo, I usually buy several boxes at a time, and see if they're out of the same batch. just a couple weeks ago, I bought the exact same type of ammo for my 7mm that my gun was sighted in for after I ran out from my stash that was a couple years old, and I had to adjust the windage a couple clicks.

[Jackalope]

yes

[BowVista]

Will it effect it at short distances as well?
Under 100 yards?

[scotty]

Different bullet weights, and even the same weight from different manufacturers can shoot to very different points of impact. Trajectory will be close with similar bullet weights, if sighted in the same. Whenever you make any change in ammunition, make sure that the gun still shoots to the same zero.

[texag93]

Any time you change loads, rifle needs to be rezeroed. There is no telling where that shot went at over 200yds.

[Texas Grown]

Will, under 100 yards won't be as critical as the longer shots. But anytime any of the following variables are changed, point of impact can change. Variables include: powder charge, case brand or “lot run”, primers (brand or “lot run”), projectiles (brand or “lot run”), crimp on projectile, lead of projectile (how far out the projectile is crimped or seated in case).
Even though you may use the same brand of factory ammo and projectiles, if you bought it from a different store, or different point in time, or years later, point of impact can change due to different "Lot Runs". Most of those changes are very minimal though, and point of impact is usually very minimal and usually not noticed by the average shooter. But, with factory ammo, it is always best to check your zero when opening a new box if the boxes were not bought from the same case. Simplest way to check is to look on the box flaps. Most mfgs print their “lot run” numbers on the flaps for standard commercial ammo.

And to answer your thread topic question: Yes, 15 grains can make that much difference at 260 yards in .308

[BowVista]

Will, under 100 yards won't be as critical as the longer shots. But anytime any of the following variables are changed, point of impact can change. Variables include: powder charge, case brand or “lot run”, primers (brand or “lot run”), projectiles (brand or “lot run”), crimp on projectile, lead of projectile (how far out the projectile is crimped or seated in case).
Even though you may use the same brand of factory ammo and projectiles, if you bought it from a different store, or different point in time, or years later, point of impact can change due to different "Lot Runs". Most of those changes are very minimal though, and point of impact is usually very minimal and usually not noticed by the average shooter. But, with factory ammo, it is always best to check your zero when opening a new box if the boxes were not bought from the same case. Simplest way to check is to look on the box flaps. Most mfgs print their “lot run” numbers on the flaps for standard commercial ammo.

Thanks Mike (and everyone else as well ). I was mainly worried about the under 100 part for now. I'm hunting with this gun tomorrow, but all my shots will be under 100, so I'll take solid body shots.

The ammo I originally shot was the Federal Fusion in 165, but I couldn't find it last time I went to buy, so I just grabbed the blue box Federal 150. I'll be more aware next time, and make sure I shoot a few with anything that's different.

[Mike Javi Cooper]

Will it effect it at short distances as well?
Under 100 yards?

Yes but the effect will be less

[tvc184]

I usually shoot some 62 grain Federal rounds out of my bolt action .223. I got my hands on some 63 grain rounds and at 100 yards, there is a three inch difference in impact. That is a huge difference for a round that is one grain in weight different. Obviously there are other factors than just the weight but it just goes to show, anytime you are shooting a different round, being of similar weight doesn't equate to same point of impact at any given range.

[DaveC]

You've already got your answer, but here's something odd I found with my .308 this year.

With my .308 sighted in at ~3/4 " high at 100 with 150 corelokts, the gun shot ~6" high & to the right with 168 gr. black hills match ammo.

You'd figure the bullet would drop with the heavier weight, but I'm guessing the charge was a lot hotter.

[Texas Grown]

DaveC, if you were to fire both rounds at the same time, a heavier projectile takes longer to leave the barrel. In the mean time, inertia of the gun moving reward, and barrel jump, is approximately the same for both rounds. By the time the heavier projectile leaves the barrel, the barrel is at a slightly higher position, causing a higher point of impact with the heavier projectile.

Looking at it from a lighter projectile's point that is traveling faster down the barrel, it exits faster than the heavier one before inertia has as much effect on where the barel is pointing, resulting in a lower point of impact at 100 yards or meters.

This is true in most cases at 100 yards, but not all, for most given rifle cartridges.

Hope this helps some

[DaveC]

Wow, way more complicated than I thought.
Thanks for the insight, I learned something today .

[BowVista]

Wow, way more complicated than I thought.
Thanks for the insight, I learned something today .

Those were my thoughts exactly. I've never been much of a "how stuff works" kind of guy, and this is one of those situations where I didn't think it would have made as big of a difference as it made.

Now I know - and knowing is half the battle (at least that's what I learned from watching G.I. Joe as a kid).