Hello, Just talked to a friend today about his 30-06, he mentioned that when he shot his factory Rem 150 PSPCL, they were 6" higher @100yds. than with his handloaded 150NBT loaded with 55grs. 760. Can anyone explain this big POI change? I know you would need alot more velocity difference than what these two loads are putting out to get 6" Thanks for your input, Jay

Barrel harmonics deteremine where a bullet lands more than the velocity difference. E

The faster a bullet leaves the barrel the lower it prints. That is why heavier (slow) bullets tend to print higher at close range. The barrel has recoiled up a fraction more as the bullet leaves the barrel.

I would expect the handloads are a bit faster than than the factory loads.

It is more noticeable in handguns, but it occurs in rifles as well.

Kurt C, These are both 150gr bullets, and 55grs. of 760 works out to be around 2800fps, the factory 150Rem is around 2900fps, with what your saying, the Nosler should be printing higher, and with my own 7mm08 with 120Hornady HP against 150MK, the 120s are 400fps faster and print 1.5" higher than the 150MKs @100yds. Jay

Barrel harmonics cause a bullet to strike higher or lower.Just because a bullet is travelling at a higher velocity does not mean that it will print higher or lower than another bullet.You can add a grain of powder to a load and it may strike higher.If you add one more grain it could strike lower.

stubblejumper is right on the money. You might want to try chronographing the loads, but the reality is that different bullets shoot differently. This is why it's so important to work out the zero at all ranges for the bullet you'll be using in the field.

I agree with Kurt C. However, stubblejumper's description of the influience of barrel harmonics is also applicable. In some cases, BOTH influences are involved.

As a matter of interest, your buddy might like to chronograph the two loads involved, to see what the velocity difference may be. Often, factory ammo falls FAR short of their ballistics table's level. For instance, I have seen factory '06 180-grain ammo that produced velocities in the low 2400's, vs the claimed 2700... and most shooters didn't even know the difference!!

[ 08-21-2003, 00:57: Message edited by: eldeguello ]

definetly bbl. harmonics. I hunt w/ Nosler Part. & always have a diff. time finding a "practice bullet that has the same POI. I find Speer hot cores have been pretty close to NPs.

Talked to Gerry again today, he said he just tried these same loads in a buddies Ruger with the same results, 6" higher for the 150gr Rem. bullet, I told him he should try them at 200 or 300yds. to see if the Nosler catches up to the Remington bullet at longer range, he doesn't have access to a chronograph, which might explain alot. I've got another example that kinda puts a kabosh to Kurt's theory, (No Offence) got some 190gr Hornadys loaded with 50grs. IMR4350 which shoot a few inches lower than my 150grNBT with 50.5grs. of Varget, and I remember trying the 190s at 200yds. against some 180gr Core-Lokts, and again the the 190s were like 8" lower, even though they have a better BC, but at 200fps slower, according to my manual. Jay

barrel harmonics are part of it. Also, the various bullet companies have differing ideas as to what is the best size to make a .308 bullet. Add to that, the relative bearing surface of the different bullets and so forth. This is why, when you're reloading, you back off and work up again when you switch components. Also, if you're shooting ready rolled, buy enough boxes of ammo with the same lot number at the start of the season to last you and then sight in with that ammo. Just because it sez remington 150grs doesn't mean it will shoot to the same point as that box you sighted in with.

lets assume two things. the bullets have different velocity, and the powders have different burn rates.

Both of these can mean the bullets leave the barrel under different conditions of barrel whip due to harmonics and also barrel jump due to recoil.

Add to this that different powder/bullet combinations may make different magnitudes of oscillation, and different frequencies, and it is a wonder that two bullets from the same box ever land close to one another on the target at all!

My money is on the concept that muzzle flip (raise) accounts for most of the verticality variance.

Further to the last post: As an aside, this is one of the reasons why you usually see a huge point-of-impact shift when you stick a business card or shim under a free-floated barrel to create a pressure point. The barrel now has a different "whip" and the bullet gets released at a different point on that "whip".

Theoretically, this could mean that setting your BOSS on your Browning rifle to a different position could change the point of impact, too. This is just conjecture on my part, however, because I've never fired a BOSS-equipped rifle.

fredj338

Very interesting...I have found the same relationship with Speers and Nosler P's.

WN

POI changes lower with increased powder charges.