Something you have noticed too -yes\no?

kenjs1 · September 28, 2009, 09:09 AM

Noticed something and wonder how common it is - or isn't. My question is- in your experience do you find that loads of similar hotness for a given caliber shoot to the same p.o.i. for different bullet weights? My middle of the road loads for the 270 shoot to the same p.o.i. for both 130 and 140 grain. Same powder, not identical amount - but both lets say on the same point of the scale between min and max. Increasing to near max changed the poi for the 140's. Wondering if the 130 would continue to mimic it? Your guesses welcome. Just curious as to how some of y'alls rifles responded and if things trend that way for you.

**Unclenick** · September 28, 2009, 09:51 AM

Not necessarily. In handguns, heavier bullets impact almost uniformly higher because the heavier, slower bullets give the muzzle more time to rise before they exit. At ranges too close for the bullet to lose much velocity, that will remain true even at different power/velocity levels because even though a hotter load has a shorter barrel time, it also recoils harder and the two tend to cancel each other out.

Rifles are more complicated because the barrel flexes far more significantly during firing than a pistol barrel does. If the flex is on the high side at the moment your light bullets exit and on the lower side at the moment your heavier bullets exit, the tendency of the muzzle to rise can be neutralized by that.

Scroll down to the third animation of this page to look at the finite element model of a firing done by Varmint Al. His flexing is on the low frequency side because he does it with a barrel tuning weight at the muzzle, but it shows how the barrel starts to move in its second vibration mode on firing. This can be reduced by a tensioning barrel tube that reaches forward so the portion of the muzzle that is free to whip is short and rigid. The Steyr scout-type rifle is an example of that, and it tends to shoot a lot of ammo accurately as a result.

kenjs1 · September 30, 2009, 08:10 AM

Unclenick -I appreciate the time you spent. I was already aware of the flexing etc.. That is why the idea of a trend interested me. Still wondering if loads of given similar 'strengths' develop a pattern for p.o.i. Just thinking back - what about your loads- you notice anything like this?

**Unclenick** · September 30, 2009, 10:15 AM

Sure. It varies with barrel time of the rounds, rifle to rifle. Some will do that and some won't. Chances are that if you cut a few inches off your barrel, this would change in one way or another, or adding a tuner weight would change it. In the FEA animation you can see the muzzle start to flex up as recoil progresses, but that will happen faster without a tuner weight at the tip and it will begin to flex down again before a lower velocity load gets its bullet to the muzzle. At that point the whole gun is slightly elevated by recoil, so the net effect on the target is often a flat spot in elevation change with charge. This is the principle the Audette ladder method of tuning loads is intended to take advantage of. My third graph (the polynomial fit) reveals the flat spot in post #13 of this thread on another fourm. It is for one bullet stepped through different loads, but the same can apply comparing any sets of loads that have different barrel times.

I don't use the Audette ladder these days because I like Dan Newberry's round robin method better.

September 28, 2009, 09:51 AM	#2
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Not necessarily. In handguns, heavier bullets impact almost uniformly higher because the heavier, slower bullets give the muzzle more time to rise before they exit. At ranges too close for the bullet to lose much velocity, that will remain true even at different power/velocity levels because even though a hotter load has a shorter barrel time, it also recoils harder and the two tend to cancel each other out. Rifles are more complicated because the barrel flexes far more significantly during firing than a pistol barrel does. If the flex is on the high side at the moment your light bullets exit and on the lower side at the moment your heavier bullets exit, the tendency of the muzzle to rise can be neutralized by that. Scroll down to the third animation of this page to look at the finite element model of a firing done by Varmint Al. His flexing is on the low frequency side because he does it with a barrel tuning weight at the muzzle, but it shows how the barrel starts to move in its second vibration mode on firing. This can be reduced by a tensioning barrel tube that reaches forward so the portion of the muzzle that is free to whip is short and rigid. The Steyr scout-type rifle is an example of that, and it tends to shoot a lot of ammo accurately as a result. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; September 30, 2009 at 10:16 AM.

September 30, 2009, 10:15 AM	#4
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Sure. It varies with barrel time of the rounds, rifle to rifle. Some will do that and some won't. Chances are that if you cut a few inches off your barrel, this would change in one way or another, or adding a tuner weight would change it. In the FEA animation you can see the muzzle start to flex up as recoil progresses, but that will happen faster without a tuner weight at the tip and it will begin to flex down again before a lower velocity load gets its bullet to the muzzle. At that point the whole gun is slightly elevated by recoil, so the net effect on the target is often a flat spot in elevation change with charge. This is the principle the Audette ladder method of tuning loads is intended to take advantage of. My third graph (the polynomial fit) reveals the flat spot in post #13 of this thread on another fourm. It is for one bullet stepped through different loads, but the same can apply comparing any sets of loads that have different barrel times. I don't use the Audette ladder these days because I like Dan Newberry's round robin method better. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

September 28, 2009, 09:09 AM	#1
kenjs1 Senior Member Join Date: July 10, 2006 Location: Texas Posts: 129	Something you have noticed too -yes\no? Noticed something and wonder how common it is - or isn't. My question is- in your experience do you find that loads of similar hotness for a given caliber shoot to the same p.o.i. for different bullet weights? My middle of the road loads for the 270 shoot to the same p.o.i. for both 130 and 140 grain. Same powder, not identical amount - but both lets say on the same point of the scale between min and max. Increasing to near max changed the poi for the 140's. Wondering if the 130 would continue to mimic it? Your guesses welcome. Just curious as to how some of y'alls rifles responded and if things trend that way for you.

September 30, 2009, 08:10 AM	#3
kenjs1 Senior Member Join Date: July 10, 2006 Location: Texas Posts: 129	Unclenick -I appreciate the time you spent. I was already aware of the flexing etc.. That is why the idea of a trend interested me. Still wondering if loads of given similar 'strengths' develop a pattern for p.o.i. Just thinking back - what about your loads- you notice anything like this?