MV & POI Differences ?

[ElmerThud]

Yesterday I checked out with my chrono, two boxes of .25-06Rem. ammo. I had loaded . Everything in respect of case prep, the recipe and the bullet was identical except for one thing. One box was several times fired cases and due to be annealed, the other box were anneald cases.

The anneald cases produced an average MV of 3146fps with 28fps ES.
The not yet anneald cases produced an average MV of 3099fps with 32fps ES

The difference in POI @ 100yds was 1.5" The faster load POI lower than the slower... I was surprised at that, considering were only talking about 47fps difference between the two loads. Obviously this was just a field test using my Chrony, nevertheless it has provided an interesting benchmark.
Has anyone experienced similar or have any comments? ATB ET

 

[DrMike]

I have observed on numerous occasions a load with higher velocities impacting significantly lower than one with lower velocities. It suggests that harmonics are sufficient different to alter the spatial point of exit for the bullet. To be sure, we anticipate that the higher velocity load will impact higher than the lower velocity load; and that is the usual observation. Still, the exception proves the rule, and the exception humbles us.

 

[ElmerThud]

Man alive Mike, shouldn't you be sleeping....you must be at least five or more hours behind UK time!

As you say, sometimes ballistics aren't quite as one would expect. It's rather annoying that there was that much difference though and not a little frustrating I can tell you. :roll: ATB ET

 

[truck driver]

Man alive Mike, shouldn't you be sleeping....you must be at least five or more hours behind UK time!

Us old farts don't need as much sleep to rebuild our energy as the younger ones do since we don't use as much. :roll: :lol:

 

[SJB358]

That's pretty interesting. Any difference in the accuracy between the two?

 

[DrMike]

Rodger is correct. As a certifiable "old fart," I seem to exist on a minimum of sleep. Of course, I do a minimum of work, which helps immensely (conserving energy, you know). Scotty, in several instances (searching my memory banks just so I don't have to walk around and secure my records), when I've witnessed this phenomenon, accuracy was neither significantly degraded nor improved.

 

[nvbroncrider]

I have noticed the in my 338 when I bring a charge up I go high and right. I think a lot of it has to do with sight in as to what the bullet will do on the vertical plane. Harmonics also play a significant role.

 

[ElmerThud]

That's pretty interesting. Any difference in the accuracy between the two?

Not really any difference Scotty, only the POI changed but the groups still held together quite nicely. As I say, frustrating but not insurmountable. Just have to zero each remake of ammo in its own right.

At 100 yds a red hind or stag would have been dead, but a roebuck might have just had the top of it's leg broken and the bullet deflected away from vital organs. At a greater range anything could happen. :?

As for the 'sleep' issue...I'm happy to take as much as I can get when I'm not out playing of course :grin:
Cheers ET

 

[SJB358]

Great info. Thank you fella's. I will have to check it out. I anneal each time now, just so I can get everything to as close to the same as possible.

 

[Darkhorse]

I've seen the same thing in .44 mag pistols and muzzleloaders. In those instances it has to do with recoil and I think the same thing is happening here.
I think the bullet is held tighter and is released a fraction later than the annealed rounds so it exits the barrel higher in the recoil arc. It doesn't take much to make a 1.5" difference at 100 yards. That's my short explanation.
I am in the process of annealing all my rifle cases. When I started working up a load for my 7mag., I took the easy way out. I so-called, sorted my cases by brass hardness when I resized them. Some were obviously hardened, some not so obvious. Anyway, I decided not to anneal. How dumb of me think I could achieve consistency by the feel of a press arm.
I now think the majority of my groups were corrupted by inconsistent brass hardness in the neck. The last 5 shot group I shot were all with freshly annealed brass. Made a real difference in the tightness of the group.

 

[skidmark]

What process and how are you annealing your cases ?
Just curious.

 

[SJB358]

What process and how are you annealing your cases ?
Just curious.

I use MAP gas, a cordless screw gun and a socket that fits the case. Do it in low light and once the case starts to get a red tint, drop it and grab the next one.

 

[Darkhorse]

I use the same procedure but propane instead of map. I try to get the same same flame length each time, then count as I anneal the first one watching both the neck and the heat color working down the case. After the first couple I got the count down and it goes real fast.
I still drop them into water but I know a lot of people don't do that anymore. I take them out and drain them, then blow the case out good with my air compressor. Before loading I let them soak in the sun for several hours to help dry out any moisture. I never anneal the same day I want to load.

 

[Al in SC]

a socket that fits the case ???

 

[salmonchaser]

Put them in the sun, in the northwest you could be waiting months

 

[Darkhorse]

I live in the Southeast. No shortage of sun here.
Use a deep well socket that the case will just barely fit into with a extension. I just cut off an old 1/2 ext. The socket must be tight enough that the case will turn when the drill runs, but not so tight you can't tip it over and drop the case out.
I turn the torch so the flame hits the neck at an angle and doesn't wash over the shoulder and neck at the same time. Angle the drill up so the case doesn't spin out.
Start the drill and place the neck in the tip of the hot inner flame and start counting on contact. The count is not set in stone but is an indicator of when the neck begins to glow and the heat signature reaches the correct point below the shoulder. The count will change depending on the heat of the flame so always set a new count with the first case.
Mainly I drop in water because I want all heating to end right then.
Water quenching will not make your case neck harder. This is brass, not steel. Brass is different.
Repeated sizing work hardens brass which leads to open groups and split necks. Annealing softens brass. And you can overdo it, so when the neck just begins to turn red, stop there. Don't let it really glow bright red.

 

[Oldtrader3]

My guess is that there is a difference in the amount of hoop tension by the case on the bullet with old work hardened cases versus annealed cases.. The tensile yield of the annealed cases is going to be lower than work hardened cases which will hold bullets a smidge longer than annealed cases. This would affect the supersonic gas jet lag and cause a slight difference in muzzle lift time. Plus dielectric bonding will effect the neck tension of the bullets as well with the hard brass having more neck-stiction due to more tensile yield on breakaway force.

 

[Ridgerunner665]

The faster load leaves the barrel sooner....the muzzle has less time to rise from the initial recoil (slight recoil) that is generated when the bullet starts moving (Newtons 3rd law of motion)

Though it often feels like it happens all at once...recoil begins as a slight push, the moment the bullet starts moving...and progresses until the bullet exits the barrel.


Sent from my DROID RAZR HD using Tapatalk

 

[ElmerThud]

I use propane and a dish of water to stand my cases in. Rotate the whole lot on a lazy susan & takes about 14-18 secs to get to the right heat. The water prevents heat getting into the lower case & I knock them over to quench immediately. Dry out in our wet rainy winter weather, blow out with air & stow until I'm ready to load.

I guess I anneal every 5 loadings but never checked out the difference between anneald & not yet anneald performance. I reckon the least scientific explanation is the softer brass case neck/shoulder is sealing in the chamber much faster aiding additional pressure and consequently more fps MV.
Does anyone go with that viewpoint? or is that oversimplified?
Cheers, ET

 

[Oldtrader3]

I guess there are many theories. :<)