Large POI difference between 223 loads

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CDB18

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I've got a large difference in POI between two loads (10" left at 200y - load #2) and was hoping someone could explain it to me. Both group consistently under 2" at 200 yards and elevation difference is less than an inch.

1. 55gr Hornady FMJ bulk - 25gr 4064
2. 55gr Hornady VMAX - 25.5gr varget

Same cases and primers. Rifle is a Savage 10 FCP-K 223.
 
Different bullets have different flight characteristics. Not surprising they have different POI's as they are constructed differently with different materials. FMJ VS polymer tipped.

Then different powders = different burn rates and such. Not surprising they have different POI.
 
Listen to stubblejumper on this. He is correct. bsand, you aren't wrong but you aren't explaining why this occurs.

Whenever anything changes at all, primer lots, powder lots and even bullet lots, as well as designs of the projectiles even if they are the same weight the harmonics of the barrel will change and this will give you a different POI. Theoretically all that should happen is either a drop or rise in elevation. In reality the vibrations cause different stresses to occur at different points in the barrel and you can get just about anything.

By the way, if you cleaned the bore between the different loads the first shot will likely be way off POA but it should settle into a group after some fouling occurs.
 
Back when I had a 223 I loaded 36-60gr bullets with 27gr of varget all seated as long as I could all shot to the same poi at 200 yards. I also loaded 53gr vmax with 25.7gr of varget seated to something like 2.244"(same as the factory superformance I had) that also shot to the same poi at 200.
 
Firstly, without a chronograph its only speculation of deemed velocity.

Secondly, you guys can debate all you want on the physics of why this effect goes on? but at the end of the day, one goes with the bullet they like the best that has the best group.


Left is interesting. I'd say vertically would be velocity more.

Shawn, that bullet is spinning 360 degrees, you're only thinking in two dimensions instead of three. The slightest change in velocity can make that bullet move any direction.
 
CDB18 said:
I've got a large difference in POI between two loads (10" left at 200y - load #2) and was hoping someone could explain it to me. Both group consistently under 2" at 200 yards and elevation difference is less than an inch.

1. 55gr Hornady FMJ bulk - 25gr 4064
2. 55gr Hornady VMAX - 25.5gr varget

Same cases and primers. Rifle is a Savage 10 FCP-K 223.
Click to expand...

One bullet is a boat tail and one is a flat base bullet, I had a similar problem and the crown was the cause. "BUT" my boat tail bullet was hitting over a foot to the right at 100 yards.

The illustration below was used in Enfield forums to explain why flat base bullets shoot better in worn mil-surp barrels. And the British used rebated boat tail bullets to improve accuracy, the rebated boat tail was less effected by uneven muzzle blast.

boattail-a1_zps57c50062.jpg
 
fiddler said:
Firstly, without a chronograph its only speculation of deemed velocity.

Secondly, you guys can debate all you want on the physics of why this effect goes on? but at the end of the day, one goes with the bullet they like the best that has the best group.


Left is interesting. I'd say vertically would be velocity more.

Shawn, that bullet is spinning 360 degrees, you're only thinking in two dimensions instead of three. The slightest change in velocity can make that bullet move any direction.
Click to expand...

While that's true, Gravity effects everything the same. Slower round is flying longer.. And therefore would drop more. Regardless of it went left also.
 
fiddler said:
Shawn, that bullet is spinning 360 degrees, you're only thinking in two dimensions instead of three. The slightest change in velocity can make that bullet move any direction.
Click to expand...

Yes and that results in any forces on the bullet being equally distributed around the bullet, this having no effect.

A large POI change at short range is most likely a result of barrel harmonics. Powder burn rate and bullet bearing surface along with the acceleration rate will have the largest effects on barrel harmonics and whip.
 
hometownhero said:
This doesn't explaine why 36gr fb, 40gr bt, 52gr fb, 53gr bt and 60gr fb would all shoot the same poi at 100, 200 yards for me. By "the same" I am meanng eather dead on of +/- 3/4". Not really enougt to matter on creatures
Click to expand...

I said in my post above the problem was the crown, meaning the boat tail base was being deflected by the uneven crown and gas flow over the base of the bullet, read the red section in red.

Inspection Method for Your Barrel Crown
http://bulletin.accurateshooter.com/2008/03/inspection-method-for-your-barrel-crown/
 
fiddler said:
Do some more test loads and go with the tightest group. Adjust your scope to suite the load you like best.
Click to expand...

X2.
it can be debated forever, and we may still not know what is causing it. internal or external ballistic issues, but knowing how it groups is more important. I dont switch from one bullet to another and expect the same POI; in fact when switching bullets, I have to go sit at the bench and dial everything in again. I try and pick one bullet and stick with it. Sure I have switched bullets lots, but it was to see how other bullets would perform and suit my needs.
From the sounds of it, you say that the 55FMJ is interchangeable with your other bullets, its just the Vmax giving you trouble. Ditch the Vmax and carry on.
 
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