Little things...

[M14AMU]

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

Yep!

 

[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.

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!

Understand and I am in no way criticizing, just the opposite. It is rare that we have a condition in which only one parameter is changed and we get such a dramatic result. In this case you have two small five shot groups separated by eight inches. I think you have an excellent opportunity to repeat the test, maybe even with more shots and see if this is repeatable. If so the next step would be for someone else to attempt to conduct a similar test to see if again there is a similar outcome. I am not sure exactly what we would do with the result but you never know when something like this will be useful down the road. Respectively, Clyde.

 

['Freak]

With a .012” neck wall thickness the case neck to chamber wall clearance is ~ .004” total so .002” on each side and probably enough so for a clean bullet release.
Then with neck wall thickness increased to .013” the case neck to chamber wall clearance is reduced to ~ .002” total so only .001” clearance on each side and now possibly impeding the bullet’s release to the point that there’s increased pressure so also increased velocity resulting in the eight inches higher impacts, ya reckon?

 

[M14AMU]

With a .012” neck wall thickness the case neck to chamber wall clearance is ~ .004” total so .002” on each side and probably enough so for a clean bullet release.
Then with neck wall thickness increased to .013” the case neck to chamber wall clearance is reduced to ~ .002” total so only .001” clearance on each side and now possibly impeding the bullet’s release to the point that there’s increased pressure so also increased velocity resulting in the eight inches higher impacts, ya reckon?

That's one of the things I'm attempting to find out! ;D ;D

 

[noload]

rmulhern, the groups at 800yds ....are those pigs knuckles or people knuckles , I amazed a 308 can shoot that good, especially 2 groups. Hell I'm ammazed any gun will shoot that good. I don't mean to be a wise guy but ..Maybe I'm missing something???

 

[M14AMU]

rmulhern, the groups at 800yds ....are those pigs knuckles or people knuckles , I amazed a 308 can shoot that good, especially 2 groups. Hell I'm ammazed any gun will shoot that good. I don't mean to be a wise guy but ..Maybe I'm missing something???

You need to come spend a day with me and I'll be glad to show you!!

 

[noload]

I congratulate you on your small groups. I guess I would not be concerned about the neck thickness if they both group well. Seems you could pick either neck wall and go with it. Your test about nk wall was enlightening, and I am envious of your shooting bench and range.

 

['Freak]

With a .012” neck wall thickness the case neck to chamber wall clearance is ~ .004” total so .002” on each side and probably enough so for a clean bullet release.
Then with neck wall thickness increased to .013” the case neck to chamber wall clearance is reduced to ~ .002” total so only .001” clearance on each side and now possibly impeding the bullet’s release to the point that there’s increased pressure so also increased velocity resulting in the eight inches higher impacts, ya reckon?

That's one of the things I'm attempting to find out! ;D ;D

Though all were recently similarly annealed, thinkin’ the thicker neck would still be a tad more resistant to relinquishing its grip on the bullet, so hanging onto it a tad longer, and increasing pressure by just a tad. But, I don’t figger that’d be enough all by its lonesome, to account for the pressure/velocity increase it’d take to move those impacts the eight inches higher. Thinkin’ there’s something else additional to a tad increase in neck ‘tension’, therefore the theory of ~ .001” clearance on each side of the neck wall to a .308 caliber’s chamber wall may well be bordering on an overly crowded case neck additionally impeding the bullet’s release? I dunno, therefore the use of question marks.

FWIW, I fed ShootersCalculator a BC of .510, 185 gr. bullet, 200 yd zero, and etc. Muzzle velocity had to increase from 2500 fps to 2545 fps to have the thing move impacts at 800 yards, 8 inches higher.

 

[Joe Salt]

Maybe I'm miss reading as usual! If you used the same bushing or FL.die, you just changed your neck tension. Like Jim said. To do it right you need to go a thou. tighter for the .12 than the .13. My two cents!

Joe Salt

 

[M14AMU]

rmulhern, the groups at 800yds ....are those pigs knuckles or people knuckles , I amazed a 308 can shoot that good, especially 2 groups. Hell I'm ammazed any gun will shoot that good. I don't mean to be a wise guy but ..Maybe I'm missing something???

noload

I shot these five shots for you from 800 yards this morning:

Untitled by Rick Mulhern, on Flickr

Top shot is cold barrel!

Most folks don't have a clue....as to how great a well built rifle/load will perform!! It appears I need possibly a 1/4 MOA up.

 

[SmokinJoe]

I think you probably have two things working together to produce a little extra velocity in the .013 neck cases. As has been mentioned, bullet tension would have to be a bit higher if both the .012 & .013 necks were sized using the same bushing. But also, when you reduce the neck to chamber wall clearance, the case will seal off any escaping gases just a tad quicker thus giving slightly more pressure. You can really see this when shooting small stuff like Hornets where case capacity is so small that any little thing makes a fairly big difference.

 

[noload]

noload

I shot these five shots for you from 800 yards this morning:

Untitled by Rick Mulhern, on Flickr

Top shot is cold barrel!

Most folks don't have a clue....as to how great a well built rifle/load will perform!! It appears I need possibly a 1/4 MOA up.
Maybe I should get me one of those 308's. Very impressive group for sure.

 

[M14AMU]

.308 aka 30/06!

It's just a worn out old cartridge!!

No fancy name, not Creedmoorish, belted case, or the latest 'whizz-bang special' necked down to whatever name!