Case Neck Tension Change Over Time?

[Guns&Bows]

Hey guys. So, I worked up a load a couple months ago for my 300 RUM using H1000, new norma brass, CCI 250 primers and Berger 200.20X bullets. I had loaded 40 rounds two months ago after my load workup and I was averaging 3125 fps and an ES of about 30 fps.

Fast forward. I loaded up an another 20 rounds using the EXACT SAME component lots, sizing process, CBTO etc. Went shooting 3 days after loading this new batch. I started my session with the 2 month old rounds and my average was down to 3085 fps with an ES of about 20 I think. Thinking that was odd I switched over to the new reloads and I was back up to an average of 3120 fps with an ES of about 40 fps.

Nothing has changed in components or process regarding these two lots. Is it possible that the brass changes over time? Maybe neck tension decreases a little reducing velocity?

 

[Wedgy]

What chrono ? If not MS or Labradar it's within the error
What temperature outside ?
Rounds laying in the sun ?
Have you cleaned the barrel ?
Assuming brass has been equally annealed.

 

[antelopedundee]

Brass can spring back over time. When you size/resize your cases try leaving the case in the sizing die for 15 seconds before pulling it back out.

 

[Guns&Bows]

What chrono ? If not MS or Labradar it's within the error
What temperature outside ?
Rounds laying in the sun ?
Have you cleaned the barrel ?
Assuming brass has been equally annealed.

Magnetospeed sporter chrono.
Temperature was 55 degrees but that shouldn't matter because this was seen in the same shooting session.
Sun wasn't out and was under a covered shooting area.
Barrel was not cleaned.
Brass was all new norma which I ran all through my Redding sizing die.

 

[Guns&Bows]

Anyone else have any insight? Thanks!

 

[fmuguira]

Anneal to keep the cases in consistent condition regarding neck tension.

 

[codyadams]

So rounds you already had loaded, that were shooting 3125, changed down to 3085, with the only variable being 2 months time. The freshly loaded ammo is up to 3120, as your 2 month old ammo was, 2 months ago. The brass used in all of this is all new, unfired but sized brass.

How is your ammo stored?

 

[aushunter1]

I believe there is such a thing as case weld which develops between the projectile & the brass case over time.

How this influences actual FPS & accuracy 12 months later is up for debate.

I think keeping handloads as 'fresh' as possible is the key to keeping all things equal.

 

[Alex Wheeler]

Its very normal to see a velocity difference between virgin and reloaded brass. It will stabilize now that its been fired and resized. Velocities change daily as well. If this is a new barrel, theres a good chance load preference and velocities wont settle down until 200 rounds or so. Its not the neck tension. Also keep in mind that different lots, even different boxes in the same lot may not be the exact same. Re check your tune any time you change anything.

 

[codyadams]

Its very normal to see a velocity difference between virgin and reloaded brass. It will stabilize now that its been fired and resized. Velocities change daily as well. If this is a new barrel, theres a good chance load preference and velocities wont settle down until 200 rounds or so. Its not the neck tension. Also keep in mind that different lots, even different boxes in the same lot may not be the exact same. Re check your tune any time you change anything.

From my understanding, the brass is all the same, all unfired, new, only sized brass, not some of it fireformed and other new creating different velocities. I very well may be wrong, but that was my understanding from what the o.p. wrote....

 

[FURMAN]

I believe there is such a thing as case weld which develops between the projectile & the brass case over time.

How this influences actual FPS & accuracy 12 months later is up for debate.

I think keeping handloads as 'fresh' as possible is the key to keeping all things equal.

I have heard reports of this. I typically do not load much more than I plan to shoot so I have not experienced it but may be something to consider.

 

[kiwikid]

Just like codyadams I'd like to know where your ammo was stored. Norma tested the effects of relative humidity on 30-06 ammo velocity. Most powder has a RH of 40% to 50% when we buy it but when they stored the loaded ammo at 86% it lost around 30 fps after 60 days. It gained velocity when the ammo was stored at 20% RH. They stored samples at both RH levels for 600 odd days firing samples at set intervals.
Bullet weld theoretically should increase the velocity not decrease it.

 

[can1010]

it might not be your ammo. I have used the mag sport for years and one thing that is critical is that it don't slide on barrel while shooting.
when I mount mine I put the extra rubber spacer on top of barrel then strap it tight.
I also take a measurement from mounting block to muzzle and record it, for me I use two and a half inches because of muzzle brakes and use it on all guns.
use a wood or plastic tape or unplug unit if using metal or it screws with the bayonet.
if it moves even a 1/4 inch will change velocity more than you would expect