Given all things equal save fpr different pwder loads, if you get two exact group sizes only one is 4" higher than the other one does that "nessesarily" mean the higher group is at a slower velocity? caliber in question is a 338 Win Mag with 210gr Partitions. The higher group was H-414 and the lower was RL-19. jorge

Nope. It just means the bullet exited at a differnt point in the barrels vibration, although in pistols recoil is more pronounced in its effects on raising the POI as it increases.

I agree w/ oljoe. I've seen this a number of time w/ diff. calibers I load for. Same bullet & diff. powder charge giving almost identical vel. & POI can shift as much as 2" @ 100.

One of my 7mmstw's shows over 2" difference in point of impact at 100 yards if you substitute the 140gr partition for the 140gr ballistic tip.Velocity is virtually identical.

Ol' Joe for Prez!

Jorge, I've several guns that do that, most pronounced in longer barrel. Velocity is not the issue at all.

From a logical POV, barrel harmonics is probably the right answer, but I'd sure like to put the other theory to the test. Started to today, but my friend's chrono gave up the ghost on us. jorge

when much lower velocities are concerned there is a definite raise in impact.

Among my favorite "tiny ten" rifles is the old M-92 winchester in .25-20.....yes this is one of my african rifle battery just for duiker and steenbok etc.

Years ago winchester came out with an 86 grain bullet at about 1500'/sec and later winchester cameout with a 60 grain hollow point at 2,200'/sec. This drastic increase in velocity caused the need for a higher front sight in the M-92 winchester, As a result most folks didn't want to install the new sight and the 60 grain loading from Winchester died on the vine. My gun has the new higher front sight and therefore I reload the Hornady 60 grain soft point to the 2,200'/sec as the only ammo facrory produced for it shoots almost six inches low at 75 yards.

Jorge, you're on the right track but when we're talking velocities of 3,000'/sec the laws of physics don't uphold the drop of that much. Barrel harmonics will win out this time.

quote:

Originally posted by vapodog:
when much lower velocities are concerned there is a definite raise in impact..

VD I've seen it booth ways. In my .358x404 IMP. a 250 gr. psp with 94 gr. of 4350 hits 9" + higher at 50 yds than does the same bullet with a case load of 5020. The heavey lead bullets also hit a lot lower than the jacketed bullets in this rifle.????? roger

Yeah vapo, I'm w bartche here. I have a fireforming load for my .338x74K that is 300fps lower than my working load & POI is -4". Every rifle is diff.

Joe is dead on. Jorge, I don't know how you could set up a test to confirm what you're trying to learn. Harmonics will always be present, and how can you eliminate them from a test to get some clarity on the velocity issue?
Don

Gentlemen....do the math...at 3,000'/sec the bullet travels the 100 yards in .1 seconds.

drop =1/2AT^2=1.92 inches....(where A=32)
at 3,300 '/sec the drop is based on .09 seconds

drop=1.57 inches.....a difference of about 1/2"

Something else is causing this to happen and velocity difference is a minor contributor here.

I'm not denying that it's happening but the physics says it's not the result of bullet drop due to velocity change in that distance.

Thanks for the stimulating discussion gents. I think the best answer so far is "it depends" and there is no clear cut rule. I think I'll stick with the one that prints lower though, for the simple reason that it's the same POI as my 250gr Noslers. How's that for an excuse? jorge

a lot of my comments follow the 80/20 rule.. or that it works about 80% of the time, admitting and knowing that there are 20% other chances of it being not right..

this assumes generally the same bullet (not 110gr .308 vs 220gr 308)

so, in general on a scoped/sighted gun if you have the same gun and the group moves UP that load is slower, while down the load is faster..

why? (partly based on dwell time under recoil in the barrel) flatter arch of trajectory in the faster.

So, in part, back into the math of what MOA is a .24" (barrel muzzle) vs 100 yards (3600")...then say, hey, if the bullet is in the barrel longer, it will hit higher....

jeffe

I have several, about half of my guns, that all else being equal an increase in the powder charge results in the point of impact shifting higher usually off center to 11:00 or 1:00 o'clock, a few are the opposite and some move more horizontally than vertically. Then theres some that maintain their point of impact over a wide range of powder variation.

quote:

Originally posted by jorge:
Given all things equal save fpr different pwder loads, if you get two exact group sizes only one is 4" higher than the other one does that "nessesarily" mean the higher group is at a slower velocity? caliber in question is a 338 Win Mag with 210gr Partitions. The higher group was H-414 and the lower was RL-19. jorge

It could mean that, but not necessarily! As a matter of fact, the MV's could both be the same - just as different powder types can produce identical MV's with the same bullet, but shoot groups of entirely different sizes......

Good topic, I've wondered the same thing. So, for you guys who know about this stuff, would you say that a free-floated barrel will tend to have more variation between POI of different type bullets (of the same weight and same powder charge) as barrels that have forened pressure?
Also, take this example - if I have two bullets (let's say a .308 180 Hornady Interlock and a Nosler Partion of same weight), and both impact 2" high at 100 yards, but one impacts higher at 200 yds. Is it safe to say that one has a higher average velocity?

quote:

Originally posted by McInnis:
Good topic,Is it safe to say that one has a higher average velocity?

Maybe, but they could be on different spiral paths. roger