Little things...

[M14AMU]

sometimes mean a lot!

My target rifle has a .3365" neck diameter. I use Lapua brass and my normal neck turn thickness is .012". I turned ten rounds to .013" and shooting the same load...alternating shots at 800 yards betwixt different turned necks, the .012" neck thickness shot 8" lower using same zero for both sets of rounds fired. Both shot knots; just that there was that much difference in POI.

Untitled by Rick Mulhern, on Flickr

 

[MGYSGT]

8" is a lot. Wouldn't have thought that much. Wow!

 

[dkhunt14]

Was it the same day and conditions? I would have thought it would be the other way around. Matt

 

[M14AMU]

Same day/time and conditions as I was alternating shots and watching two different groups build! Would have taken photo but phone battery kaput!

 

[ShootDots]

What was the wind deflection difference IF there was enough wind to gain that info??

 

[M14AMU]

What was the wind deflection difference IF there was enough wind to gain that info??

Dead calm! Fired 1645 hrs. just prior to no light for shooting!

Untitled by Rick Mulhern, on Flickr

Was shooting on 28"x30" AR500 plate at lower left in photo. This is a sunrise photo; just opposite from what I had when I was testing.

 

[ShootDots]

Thank You! I wish there was a bit of a breeze so that you could have seen if there was more / less or the same drift! Well there is always the next time! Thanks again..

 

[BoydAllen]

Very interesting! It would have been nice to have had the chrono data as well, although I suppose that that could be done after the fact. If there was not a difference in velocity that was sufficient to correlate to the difference in POI then the question would be where did it come from, but since we have no data, guessing would be premature. Thanks for the information and pictures. Perhaps it will inspire others to do similar tests.

 

[johara1]

Neck tension was more on one than the other……. jim

 

[johara1]

What was your loaded round with both? …jim

 

[M14AMU]

Neck tension was more on one than the other……. jim

Nope! Ammo loaded one hour before being fired, Lapua cases annealed, prior to charging the cases all run up into a .3075" arbor and all Berger 185 VLDs seated using this:

Wilson Inline Seater by Rick Mulhern, on Flickr

All bullets seated with basically the same feel for pressure and THAT was the reason for the limited test to begin with.

 

[M14AMU]

What was your loaded round with both? …jim

.3320" and .3340" diameter of loaded round neck OD!

 

[johara1]

A neck thickness change of .001 will change the neck tension. Feel don't get it, you need numbers, a seating force will tell you and i would bet it's a great deal more than you think. I bet the ES was big. ….jim

 

[noload]

Thats hard to believe, but I do believe you, goes to show you the smallest change can make things go to hell in a hand bag.

 

[johara1]

What was your loaded round with both? …jim

.3320" and .3340" diameter of loaded round neck OD!

Your bullet was dead on .3080? I never saw one perfect .3080+.013+.013 = .334 ……… jim

 

[JRS]

Too many cooks spoil the broth!

 

[M14AMU]

What was your loaded round with both? …jim

.3320" and .3340" diameter of loaded round neck OD!

Your bullet was dead on .3080? I never saw one perfect .3080+.013+.013 = .334 ……… jim

I've found LOTS of them perfect....using a 1" Starrett Mic as close as it could be read!!

 

[chkunz]

Interesting How many rounds fired? This is significant enough that it would be worth repeating the test to see if you get similar results. Also it would be interesting to see someone else with a similar set up repeat this test.

 

[M14AMU]

Interesting How many rounds fired? This is significant enough that it would be worth repeating the test to see if you get similar results. Also it would be interesting to see someone else with a similar set up repeat this test.

T-REX

I had ten rounds loaded....five cases with necks turned to .013" and five cases with NT at .012"! All ten rounds loaded one hour before I shot them. Both five shot knuckle sized groups with one group 8" above the first group fired.

I'm not 'quite' ignorant enough to believe that this is a static condition that would exist in all situations as the test is too limited for any conclusion thereof and I will test further as the weather allows. But....in the event with further testing since accuracy does not appear to suffer with knot sized groups being delivered at the before mentioned distance...the only correction that would be needed would be a change in elevation zero! Initially I commenced this endeavor to find out if there would be any significant change by tighter neck clearance betwixt the loaded round and neck wall and I haven't arrived at a conclusion at this time. I'm NOT convinced yet that it's neck tension because the five rounds fired with thinner neck walls shot the lowest!!

I made a correction in my first post as I typed the wrong dimension as to neck wall thickness!

 

[johara1]

Maybe a rise in pressure with more neck tension? just a consideration …….. jim