Barrel Flex-moa does not match velocity

[Humdawg]

I'm shooting a 308,26" w 1/12 twist,185 berger long range, .020 off lands, 43.5 varget, at 1000 yards it was spot on 10 and x ring, was up 34.5 min from 100 yard base line, temp around 80f,elavation around 1000 ft,humidity around 50%.
The moa suggested that the bullets where flying around 2575 fps and at 1000 yard @ 1329 fps.
I should have had a lower moa,I noticed in my testing that as I came up on the powder charge the bullets where dropping on the target.
Is the shock wave traveling down the barrel at this point catching the barrel on it's downward flex?
The barrel is all free floating in an accuracy intl. stock.
If my thought process is wrong on this, please help me understand, thank you.

 

[wrhunter]

Re: Barrel Flex-moa does not match velocity

If you re-zeroed for this load then the poi change should not affect the amount of come-up (MOA) you need. Are you thinking that it is going faster than 2575? What are you using to calculate this?

 

[wrhunter]

Re: Barrel Flex-moa does not match velocity

Just ran those numbers through SHOOTER and it called for 34.75moa.

DA 984ft. 63 degrees.

 

[Rick 324]

Re: Barrel Flex-moa does not match velocity

First, always test your own velocity using a Chrono and do not go by the book. Right now with the load that I am testing with 43.0 gr of H4350 pushing a 142 gr. SMK in .260 Remmy(22" bbl.), The book says I should be at 2600 fps, but my chrono is showing well over 2800 (2835-2860 fps to be exact). The book may be showing a faster speed than what you are getting or slower.

Secondly when I ran the Ladder Test on my .308 Savage with a 24" bbl, the Node on my rifle (High Spot where the barrel flexes at the top) was at 42.5 gr. of Varget pushing a 175 SMK. I ran the ladder test up to 46.0 gr of Varget and my rounds got lower on the target. That is the exact reason why people say to run a ladder test, because the Node is where you want the bullet to leave the barrel, not necessarily the highest velocity.

So I load my .308 at 42.5 gr Varget and I will not run my .260 higher that 43 gr of H4350 to make sure that I do not prematurely burn out my barrell by pushing the bullet faster than it needs to go. Whether the barrel is free floated or not does not really matter because the barrel will flex no matter what.

Always enter your exact information into the software program to ensure that you know exactly what your rifle is doing. And I suggest running the Ladder Test to find the Node before going further. The information in the book is just that, for informational purposes ONLY!!!

Get back to the Node of your rifle and put the rounds thru the Chrono. Then enter all of your info in and see what it gets you!

Good Luck!!

 

[Humdawg]

Re: Barrel Flex-moa does not match velocity

I did find that at 42.5 grains the point of impact was at it's highest point on the target, and that above that charge the poi started to drop, But I also found that at 43.5 grains the accuracy was at it's tightest.
To me it does not matter if the barrel is flexing up or down as long as the accuracy is at its best, or am I missing the point and should I always have the node at its highest point?
Is this Node concept written in stone?

 

[Humdawg]

Re: Barrel Flex-moa does not match velocity

One last thing is that I know my bullets are traveling faster than 2575 fps, it's just the that the barrel flex got me screwed up when I was trying to figure out the moa on paper.
Having others' inputs really helps in working out these little bumps in the road, and I am always open to suggestions.
Thank you all for your interest.

 

[wrhunter]

Re: Barrel Flex-moa does not match velocity

How do you know your bullets are going faster?

 

[Rick 324]

Re: Barrel Flex-moa does not match velocity

xmark asked a great question... Just because there is more powder does not make it shoot faster.. if the powder is not burning in the barrel you are just blowing powder out the end and may not be getting more velocity... Hence the reason to always check with a Chrono...

I was told to use the node because it is automatically shooting higher (Exiting the barrel at the highest point) so it could counter the loss of velocity you would get by increasng the powder charge. Higher impact = less MOA to target for given velocity...

I got lucky and found the node and the .5 MOA powder charge at the same time... Remember the first ladder test is to find the node.. from there you fine tune the groups...

Good Luck!!!

 

[Deadshot2]

Re: Barrel Flex-moa does not match velocity

When I'm developing a load I don't look for the "highest point" I merely look for a load that causes bullets to leave the barrel when it's at the SAME point. This may or may not be the "highest".

The tried and true Audette "Ladder" isn't looking for the highest impact point, just points where the bullets 'group' with loads that are close in weight. This is how the "sweet spots" or "nodes" are ID'd. Now if you want the load that will deliver the most energy on a distant target, then select the "node" that was achieved with the highest speed load. Without a chronograph your just guessing.

 

[Humdawg]

Re: Barrel Flex-moa does not match velocity

@ 41.5 grains 2521,2527,2545
@ 41.7 grains 2563,2559,2563
@ 42 grains 2582,2597,2594
Had no pressure signs at 43.5 grains, but did not have a crono at 43.5 load. it just shot very good at 1000 yards, the other lighter loads did not group tightly.
Yes I need to crono all loads,will have to by one instead of using a friends.
I thought mayby I could do the math to help find my way, but as I have found out ( I am in the learning curve) the proof is more in actuallity, and not as much in theroy, so my next step is to start from new and see if I can get it done with better results.

 

[Rick 324]

Re: Barrel Flex-moa does not match velocity

If you did not have any pressure signs with the 43.5 gr and the rounds shot good then try that again and run with it.

I only chrono during load development and then to make sure that the information that I am putting into my ballistic software is accurate. Remember too that the ballistic software will get you close to your dope, but you always need to shoot it and check the ballistic software... It is not always right either...

Good Luck!!