Exterior Ballistics - POI vs Velocity Question

[MrBamboo]

Today I sighted in my 30-06 using 180gr Gamekings at 100yds (54gr IMR 4350, Win Cases & primers). After sighting in and getting 3/4" groups I switched to begin pressure testing for some RL-19 powder. These loads are 180gr Horandy Interlock (NOT SST) with 53gr in Fed cases and Win primers. When referring to Sierra's reloading book 54gr gives about 2700fps, and Horandy shows 53gr gives 2400fps. (Bear in mind the Gamekings have a higher BC than the Interlocks. I don't have a chrono to check velocities to check is.)

My Question is after zeroing with the Gamekings and switching to the Interlock's my POI went up 3" with a 3/4" group and there was signs of pressure . Did my velocity increase with the Interlocks over that of the Gamekings?

 

[Deleted member 46119]

No but the bullet exit point in the barrel vibration/whip/harmonics did.

Holy grail of optimal barrel timing.

 

[royinidaho]

What jfseaman said....

 

[den]

I am pretty sure that Federal 30-06 cases hold less powder than winchester by approx. 2 grains so unless those load books are using federal brand cases you may be about 2 grains over book max at those charges with the Rl 19 & federal brass vs the Winchester & the Imr 4350

 

[Deleted member 46119]

The velocity alone won't move poi 2" over 100 yards but whip will. Optimal charge weight uses POI shift to see where the velocity move in/out of node sycn.

The Nosler wildcat testing shows both very well. When passing into a node range the impacts will be close together. Passing back out and the POI moves dramatically.

The Nosler wildcats are good for showing this because the charges are so big the window of charges in node are big. The explanation may not be as clear as I want because I'm doing this on my phone.

 

[MrBamboo]

Thanks everyone, I was thinking it could have been barrel whip from the harmonics, along with federals soft brass which showed signs of pressure. I just ordered a chrono and am going to re-do the test using R-P or Winchester brass.

Yes, it didn't make sense to me that a slower bullet would impact higher.

 

[elkaholic]

You probably did have higher pressure, but that was not the reason for the change in poi; or at least to that extent. It was harmonics, as has already been mentioned........Rich

 

[MrBamboo]

OK, now knowing its harmonics, what rifles have less harmonic shift than others. If someone has a list of "Preferred" rifles with little or no shift please let me know.

Paul

 

[justgoto]

OK, now knowing its harmonics, what rifles have less harmonic shift than others. If someone has a list of "Preferred" rifles with little or no shift please let me know.

Paul

Bull barrels have lesser harmonic vibrations. A shorter barrel does too, because it is stiffer; but for long range hunting, a longer barrel gives you the much needed velocity.