Reading tea leaves on target

[Pathfinder76]

I shot some loads over the chronograph yesterday with the intent of just getting some velocity numbers. But, I decided, at the last minute to throw them on paper despite a full value 30km/hr gusting cross wind. Here are the non scientific results. I had five runs of loads in 1/2 grain increments in both new cases and once fired cases. Interesting (though not totally unexpected) that the once fired cases produced consistently higher velocities.

[kujoseto]

Nice stuff.
I’m just about to run some reloder 16 loads for 165 gr in a 30-06 with 25” Jury barrel. This is encouraging to see.

I think a reasonable conclusion is when you get to testing with less wind, you’re gonna have something great for big game. Although, do you ever have less wind than that down there?

How did those velocities compared with where you expected them to be?
What’s the rifle?

[Pathfinder76]

The rifle is a custom Model 70.

Often fired cases will produce less velocity because of greater case capacity. I think in this case, capacity is similar but the fired cases have a bit more neck tension. That raises pressure a bit.

[Deer Hunter]

Originally Posted by chuck

Often fired cases will produce less velocity because of greater case capacity.

Does case capacity or chamber capacity determine the pressure/velocity?

[Pathfinder76]

It absolutely can, yes.

[no-regard]

Interesting test, thanks for posting. Neat to see the pattern in velocity increase as they all walk up the target, as well as the repeatable velocity change between the cases.

[Deer Hunter]

Originally Posted by chuck

It absolutely can, yes.

So your essentially saying new brass is smaller, has less case capacity therefore increases pressure and velocity compared to fireformed brass. That’s a new one for me.

[Deer Hunter]

Originally Posted by chuck

capacity is similar but the fired cases have a bit more neck tension. That raises pressure a bit.

1 thou increased neck tension is responsible for higher pressure and velocity? That's incredible.

[Pathfinder76]

Originally Posted by Deer Hunter

1 thou increased neck tension is responsible for higher pressure and velocity? That's incredible.

Quit trolling me and actually look at the velocity numbers in my post. Man this is getting real old.

[Deer Hunter]

Originally Posted by chuck

Quit trolling me and actually look at the velocity numbers in my post. Man this is getting real old.

I am not trolling you. I am discussing your findings. And reasoning. If you don't care to discuss it with me fine, but no need to take your ball and go home.

I have seen no velocity differences in varying neck tension. Crimps included.

[kujoseto]

What do you use for sizing that makes the neck tension greater? What did you use for new brass load? How did the two differ?
Sounds like a nice rifle. Is that the one you have posted pictures of that has the brown synthetic (McMillan?) stock?

[Pathfinder76]

It is, yes.

Once fired brass is harder and has more spring back. Even with the same expander mandrel run through the neck, it had 10 thou more tension.

[Deer Hunter]

Originally Posted by chuck

It is, yes.

Once fired brass is harder and has more spring back. Even with the same expander mandrel run through the neck, it had 10 thou more tension.

10 thou more neck tension must make it hard to seat bullets.

[Pathfinder76]

Originally Posted by Deer Hunter

10 thou more neck tension must make it hard to seat bullets.

Sorry. one thou.

[Nyksta]

8, 9, 10, 11 if you find it repeats itself

[kujoseto]

Originally Posted by chuck

It is, yes.

Once fired brass is harder and has more spring back. Even with the same expander mandrel run through the neck, it had 10 thou more tension.

Ah, okay. I would say I’ve noticed that from time to time when loading some rounds but wasn’t certain as to why.
Sometimes I use rcbs FL, Lee collet, Redding bushing, or CH bushing dies. So far, I can’t say one is head and shoulders above the other.
Knew you meant 1 thou as well.

[kujoseto]

The experience of many here is congruent with Chuck’s. Increased neck tension holds that bullet for pressure to mount just enough to increase his velocity by 9-25fps in this case. No pun intended.
And you’re making arguments against the recorded data posted above for you to see. He stated the facts of the situation and it’s for you to interpret, but you can’t say that’s backwards when his data is sitting right there.
I do wonder if energy is lost at all reforming the case in the chamber. So new brass or re-sized smaller may make enough difference to shave 10 FPS but I don’t have enough experience to know.

[kujoseto]

When you load up more of those upper end charges and get out for some more shooting, it would be great to hear an update with some more pics

[Pathfinder76]

Will do.

[kujoseto]

Ok that’s just friggin sweet you went and tested some rounds already. Makes me want to do the same.

Two questions I have from that test:
1. Does this prove Chuck’s data wrong or does it more likely imply the Lee factory crimp die may impose inconsistencies and neck tension is better created with a bushing die or the Lee collet die?
2. What is the consistency of the load without the additional factors of crimp die imposed? (Baseline of the same 5 loads first would help... instead of only one round fired without the variable of crimp imposed) I know Chuck’s data didn’t have that as he was increasing charges, but in trying to prove whether an outcome is repeatable, it would help if we minimize how many factors are introduced.
I think it would be better if several of us could test a tried and true load as is, then duplicate it with the one factor changed being neck tension. Maybe some common methods of creating the neck tension could be used too. List whether tension adjusted by:
1. Factory crimp die
2. Bushing die
3. Collet die
(Bushing die could just be rcbs fl sizer instead... either way the 1F can be tighter because work hardened slightly after firing and pulling the expander ball through doesn’t open it up as much)

Kinda thinking out loud here when I’ve got insomnia and shouldn’t be putting thoughts in writing.

[DLab]

Also,if DH neck sized only then crimped ,his base to datum measurement wouldn't be as consistent adding slight changes to volume compared to a bushing fl. sized case.
How many times were the .308 cases fired?
Too many added variables for a fair comparison.

Chuck,
I was going to comment earlier how rounds 8-11 on your test target looked similar in results to load testing using Scott Satterlee's Ladder method that I've tried with .5 grain increases,although the brass would be the same of course,where you see a similar POI at a velocity plateau within a .5-1.5 grain load difference with a horizontal stringing effect with minimal vertical.
Also easy to find max or close to max, load limit at the same time.

[Pathfinder76]

I agree on 8-11. I was very pleased with that.

[Pathfinder76]

Originally Posted by DLab

Also,if DH neck sized only then crimped ,his base to datum measurement wouldn't be as consistent adding slight changes to volume compared to a bushing fl. sized case.
How many times were the .308 cases fired?
Too many added variables for a fair comparison.

Chuck,
I was going to comment earlier how rounds 8-11 on your test target looked similar in results to load testing using Scott Satterlee's Ladder method that I've tried with .5 grain increases,although the brass would be the same of course,where you see a similar POI at a velocity plateau within a .5-1.5 grain load difference with a horizontal stringing effect with minimal vertical.
Also easy to find max or close to max, load limit at the same time.

You are on to something. :-)

[kujoseto]

Completely agree way too many variables introduced.
Gonna go look up that ladder method you describe. I’ve been following the Optimal Charge Weight stuff which appears to be similar based on what you say here and looking at Chuck’s data

[CBR]

Reading this thread reminded me of an article I had found on the Peterson Cartridge website a few years back that is relevant to this subject. I copied the link below. You guys might find their data to be of interest.

https://www.petersoncartridge.com/te...eated-firings/

[Pathfinder76]

It definitely does. It’s easy to measure that, but you can also feel it when seating bullets. Re velocity. I would suspect any increase in velocity would likely be deemed statistically insignificant, and it’s increase would not be linear.

[CBR]

Yeah I thought this article would be of interest as it seems to disprove the theory that increased neck tension from fired brass is responsible for increased pressure and hence velocity, which seemed to be the hypothesis from earlier in this conversation, and is something I had been curious about before as well. The Peterson findings seem to corroborate with Deer Hunters experiment (tough to tell exact numbers from their chart but velocity looks remarkable consistent) and my own findings from back when I was playing around with it. Interesting subject and good conversation.
Chuck - just curious, have you seen increased velocity related to increased neck tension from prior testing previously as well? Does anyone know of another study/data that links this relationship? I would be curious to see more data on this subject if guys are seeing different results. Thanks

[CBR]

Hey guys, I've been digging into this subject a little more for my own education and found a few things. There's a pretty cool thread on an american forum some of you may be familiar with that is also super relevant to this discussion that I thought I would post here:

https://www.24hourcampfire.com/ubbth...pics/7609943/1

specifically the quote by author John Barsness: "pressure will be the same with either new or used brass of the same lot. This has been proven umpteen zillion times in pressure labs"

I've also been reading the book "Interior Ballistics: How a gun converts chemical energy into projectile motion" by E.D. Lowry and they touch on the subject with similar findings as well. It's getting a little old but that's a great book if you can get your hands on it. Anyways it's an interesting subject and gets addicting once you start going down the rabbit hole.