Velocity spreads and neck turning??

[BML]

Shooting a factory Savage LRH 6.5x284 with Norma Brass

Have a question regarding neck turning. I've heard with custom builds it's almost always a necessity to neck turn, however with factory rifles it's not as big a deal.

What exactly would be affected by NOT neck turning my brass? Velocity? Accuracy? Both?

I have a specific issue that I am looking for an answer, but don't really know if it's caused by not neck turning. I did some velocity testing last weekend using 12 brand new pieces of brass and different powder weights. I did all the brass prep except neck turning. My best velocity group was 2791, 2796 and 2796 with 48.4 grains of H4831SC and 140g AMAX. My group wasn't stellar at .952

I loaded those same 12 pieces of brass all with that same combo and performed exactly all the same brass prep. Again, not neck turning. I shot them today, shooting 2 six shot groups. Both group sizes were over an inch and speeds were far less than last testing. Here's the speeds:

First group in order of shots:
2655
2666
2698
2689
2671
2678

Second group in order:
2684
2692
2684
2710
2695
2711

I'm trying to understand how my velocities could be so much lower this time around as compared to last time around when the loads are exactly the same. Conditions were nearly exactly the same both days.

Anyone have any ideas?

 

[Mikecr]

I've heard with custom builds it's almost always a necessity to neck turn, however with factory rifles it's not as big a deal.

This is wrong. While neck turning may be required for a tight neck chamber, that chamber is always a choice. And anything that is 'not a big deal' with specific regard to factory guns, is probably hog wash.. It often takes way more tricks in the bag to get factory guns shooting well.

What exactly would be affected by NOT neck turning my brass? Velocity? Accuracy? Both?

Both can be affected, but indirectly from neck thickness. Given this, there is more than one way to skin the cats. Also, some choose to turn necks as a matter of basic reloading/sizing plan.
Velocity: All else equal thinner necks springback with less force causing lower bullet grip(tension). This lowers velocity a tad and is countered elsewhere in load development. But it also has the benefit of reducing ES in many cartridges(and will not raise ES). This because lower springback forces mean lower springback force variance -to affect MV.
Accuracy: Accuracy is a matter of what you can repeat in the long term(not a wallet group).
While neck turning does greatly reduce runout, accuracy gain from this could be beyond your proving. An easier to see benefit comes down to exact control & consistency w/regard to chamber fit and minimal sizing, so that you get nice long runs of great performance from your brass, before needing to mung it all up with annealing(for rising ES).

I'm trying to understand how my velocities could be so much lower this time around as compared to last time around when the loads are exactly the same

Simple case capacity change from new to fireformed. You should never waste time load developing with new brass.
This is not a matter related to neck turning.

 

[BML]

That's great info. Thank you!

 

[Rusty54]

What Mike said, plus you must realise most of us don't use premium brass. Personally almost everything I use is range brass, so I do everything within my ability to uniform them and neck turning is one of the most important steps.
Your Norma brass is likely very uniform but this is not so with most other types, and without getting too specific, commercial brass neck thickness on, lets say 30-06 can run anywhere from .011 to .016 and an individual piece of brass may be very thick on one side of the neck and near minimum on the other and the mouth of a neck may be very thick where the base is thinner or vice versa.
Next time you run a velocity test you'll also get a more reliable result if you shoot 10 or even 20 of the same load if you really want to test that load, though that has nothing to do with your question.

 

[Timber338]

The guys above are all right.

Specifically relating to neck turning, you don't need to turn your necks unless there is a .002" or larger variation in neck thickness. I typically like my brass to be .0015" or better and Norma and Nosler brass is typically within .0010". So I never turn my Norma/Nosler brass.

My Winchester brass, on the other hand, usually sucks. Less than 1/2 of the brass have necks within .0015". most fall around .002 to .003 variation. And I'll get a few brass necks that vary by as much as .006".

My premium brass usually has a nominal neck thickness of .014" and varies +/- .0005".

To get my Winchester brass within .001", I have to turn the necks and remove brass from about 3/4 (radially) of the necks. If you remove brass all the way around the neck they will get too thin. I end up with a nominal neck thickness of .012" which is pretty thin.

Also, a general rule of thumb is that any variation in the thickness of the neck will also be present in the body... which you cannot fix. So all in all, you need to shoot good brass to get the most out of your gun.

 

[paphil]

Chronographs can cause more frustration than any other thing I do in the workup process. Different time of day with different angle of light and differences in cloud cover seem to give me fits with my PackII chrono. I rely more on vertical spread at 1000 yards and click count. 150fps difference could give up to 2 moa difference in spread at 1000 yards so I always try to shoot a few downrange to verify the same hight of impact. Did you use a different bottle of powder the second day? I have gotten differences like that with the same H4831sc from different lots! Neck turning helps to center the bullet in the bore but it is relative to chamber size. I like my loaded neck to be about .003 under chamber size. As mentioned in a previous post, an even thickness all the way around is important. Too much trimming when turning can make the loaded neck be undersized which is not good either. They will still fire but can cause premature neck splitting due to excessive streatching each time you fire and then resize.

 

[BML]

Thanks again for all the tips. Shooting conditions were nearly exactly the same both days. Same time, weather, wind and temps.

Powder was the same tub however the primers were a new batch.

I was curious as to if it could have been the difference between new brass and once fired brass. Sounds like that is the culprit.

I have a neck turner on order. I'll be more diligent in the future in regards to measuring neck thickness and turn if necessary.