Neck tension problem

[Sgt_Jamez]

Im trying to achieve a .002" neck tension using some FC M1A .308 brass. It's been neck turned to .013" and then run through a .332" bushing Type S die. At this point the case mouth inner diameter was too tight for my .304" trimmer pilot to fit inside. My understanding is that .013" x 2 + .308 = .334" - .002" = .332" for bushing selection. So where did I go wrong? I measured the case mouth ID but I didn't write it down. It was something like .298". Sub .300". The Redding bushing, marked as .332" actually has an ID of .330".

I'm guessing the brass isn't springing back as expected, so annealing is in order. But where else have I missed the boat. Any light you guys can shed is appreciated.

 

[gau17]

Re: Neck tension problem

Can you tell me what your loaded round measures? loaded round - .002 should be your bushing size. Let me know if it = .332. Your neck thickness could be inaccurate.

You can always trim prior to sizing the neck.

 

[MitchAlsup]

Re: Neck tension problem

Well, 332 - 2*013 = 306 so a 304 pilot should fit. If it does not then:
A) the bushing is not 332
B) the pilot is not 304
C) the neck walls are not 013
or
D) the bushing is not round (and thus the neck is not round after)

There aren't any other ways the math can work.

 

[gau17]

Re: Neck tension problem

My money is on "c"

 

[jetsurgeon]

Re: Neck tension problem

Measure the case mouth diameter (outside dimension) after you've seated a bullet. Subtract .002" from that overall case mouth dimension, that then will be your needed bushing size.

Hope this helps....

J

 

[Dusty]

Re: Neck tension problem

I have been experimenting with bushings lately and have found out, that if you size down very much at one time, you will end up with a neck diameter smaller than the bushing. For example when I size Winchester .308 brass that is .345 neck diameter with a .339 bushing I will get an OD of .337. So I go down the first time with a .336 die and then follow up with a .331 for the final neck diameter I end up with a .332 OD.

Btw. Sinclair recommends that if you are going to size down thin neck brassin one operation, fired in a chamber with a loose neck to use a bushing .001 larger than the OD of a loaded cartridge. I thought it was a misprint at first, but after a little experimenting I found that they where correct.

 

[ksthomas]

Re: Neck tension problem

Funny thing about Sinclair . . . those guys usually know what they're talking about!

 

[Ring]

Re: Neck tension problem

question... if you use a collet die "lee" that squeezes the next around the mandrel then it dont care how thick or thin the necks are since it cant get any smaller then the mandrel....

and since you can make the mandrel thinner then spec if needed and the die only cost like 20$ and you dont have to buy 100$ neck turners or the time to turn, how are bushing dies any advantage?

 

[gau17]

Re: Neck tension problem

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ring</div><div class="ubbcode-body">question... if you use a collet die "lee" that squeezes the next around the mandrel then it dont care how thick or thin the necks are since it cant get any smaller then the mandrel....

and since you can make the mandrel thinner then spec if needed and the die only cost like 20$ and you dont have to buy 100$ neck turners or the time to turn, how are bushing dies any advantage? </div></div>

You can Choose how much of the neck is sized.

 

[Sgt_Jamez]

Re: Neck tension problem

So a loaded round measures .332".

Why do all my Redding bushings measure .002" less than what they are marked for?

I am measuring neck wall thickness with the Insize neck wall gauge. Measurements ranged from .0125" - .0130". Is this considered thin? The rifle is a Rem 700 5R. Is that considered loose?

I guess I need to measure the neck OD after being fired?

I am getting more confused. Seems like it should be simple, but somehow I am screwing it up.

 

[remaction]

Re: Neck tension problem

I haven't noticed where you've indicated that the pilot is in fact .304, as Mitch mentioned, be sure to check that.

I suspect Dusty may be on the right track. .013 necks will probably give you short brass life (due to necks splitting) as I see that you are shooting a 5R. I just checked and SAAMI spec for a .308 neck dia. is .3435. If yours are .332 when loaded, that is .0115 under the chamber size. In other words, a lot of expansion and resizing is done with each load cycle. I just checked my loaded rounds (lapua brass) and they are at .337-.338 after I turned the necks enough just to clean them up (knock down the high spots).

 

[SONIC SAAMI]

Re: Neck tension problem

Why the neck turn job for a factory 5R?

 

[oldfatguy]

Re: Neck tension problem

Some people neck turn brass to make the thickness more consistant. I have had 260 Rem Lapua range from 0.015" to 0.017" neck thickness on the same piece of brass.

OFG

 

[Sgt_Jamez]

Re: Neck tension problem

I did re-check the pilot and it is .304". And I turned these cases just to uniform the thickness. The whole process was intended as an experiment to see if uniforming the necks would help make more consistent ammo. Maybe I am just introducing problems.

 

[gau17]

Re: Neck tension problem

If your loaded rounds are measuring .334, then your neck thickness is .012 not .013.

.012 + .012 + .308 = .334 - .002 (desired neck tension)= .332 (bushing size)

 

[YAOG]

Re: Neck tension problem

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sgt_Jamez</div><div class="ubbcode-body">Im trying to achieve a .002" neck tension using some FC M1A .308 brass. It's been neck turned to .013" and then run through a .332" bushing Type S die. At this point the case mouth inner diameter was too tight for my .304" trimmer pilot to fit inside. My understanding is that .013" x 2 + .308 = .334" - .002" = .332" for bushing selection. So where did I go wrong? I measured the case mouth ID but I didn't write it down. It was something like .298". Sub .300". The Redding bushing, marked as .332" actually has an ID of .330".

I'm guessing the brass isn't springing back as expected, so annealing is in order. But where else have I missed the boat. Any light you guys can shed is appreciated. </div></div>

You may have multiple issues working against you here. First brass headstamped with FC is Federal brass which has issues with soft primer pockets. Full pressure loads will kill the brass in just one or two reload cycles. The soft pockets are made worse by doing the usual primer pocket uniforming. When using FC brass don't take any material out of the primer pockets and use only moderate pressure loads. But chances are you will still have to toss the FC brass in just a few reloading cycles.

It is well known that when neck sizing more than about 0.004"-0.005" you will tend to oversize the case neck and get a smaller than marked case neck OD. This is true for any brand of neck bushing not just your Redding neck bushings. German Salazar published some very good articles documenting this and offered a solution, two-step neck sizing which yields reliable neck tension as long as your brass is not work hardened excessively. You can also try to use a bushing that is larger than your target neck OD but this is not particularly reliable and you will get significant variation in neck OD depending on how hard your case necks are. See this link: <span style="font-style: italic"><span style="font-weight: bold">The Rifleman's Journal</span></span> for an index to his articles.

As to the Redding bushings being undersized it is commonly believed the Ti coated Redding bushings are 0.001" undersized. This is sort of true. I have eight or nine Redding Ti coated bushings and they seem to average 0.0005" undersize. I do not know how you are measuring your bushing ID but you cannot use calipers to measure bushing ID and get good measurements for the same reason you cannot use calipers to get a good case neck thickness measurement. You need to use a small hole gauge to get reasonably good measurements of neck bushings or you will see incorrect measurement numbers.

Hope this helps!

 

[YAOG]

Re: Neck tension problem

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DaveD</div><div class="ubbcode-body">Why the neck turn job for a factory 5R?
</div></div>

Good question. As good as my own 5R milspec is there seems to be little practical performance advantage to be gained from neck turning for a factory chambered barrel. Again this was covered by German Salazar in some of his blog's questions and testing. If you yout ammo and your rifle and are shooting under 1/2 MOA with a factory chamber and barrel there will be nothing to show for neck turning.