Velocity increase over time?

[NYDAN]

It seems as if some loads that I have shot before are running faster now than a year or two ago. I would guess that a barrel would NOT change characteristics from wear to yield a faster round. What are the major factors that would make a load change velocity? I can think of the following considerations. Are there other factors:

1. Ambient Temperature
2. Different powder lots
3. Brass that has been reloaded a few times without annealing?

 

[MAinAR]

Mechanical bond of bullet to neck?

 

[NYDAN]

Mechanical bond of bullet to neck?

MAinAR thanks for that thought. Are you referring to neck tension?

 

[Dwh7271]

Different primers or a primer change
Crimped vs not crimped(pretty much what MA said)
Different brass or brass capacity

 

[MAinAR]

Mechanical bond of bullet to neck?

MAinAR thanks for that thought. Are you referring to neck tension?

Not really a neck tension change so much as copper tends to "bond" to brass when in tight contact with brass, the way to test is to take a loaded round and "reseat" bullet just a touch deeper like .002-.003 and you will hear and feel a slight pop as it breaks this mechanical bond. If it does the slight pop velocities will come back to original.

If no pop loose then something else is going on.

Freshly loaded rounds usually are a bit slower than rounds that are even a month old due to this. Something to consider when loading max velocity / pressure rounds.

 

[NYDAN]

Mechanical bond of bullet to neck?

MAinAR thanks for that thought. Are you referring to neck tension?

Not really a neck tension change so much as copper tends to "bond" to brass when in tight contact with brass, the way to test is to take a loaded round and "reseat" bullet just a touch deeper like .002-.003 and you will hear and feel a slight pop as it breaks this mechanical bond. If it does the slight pop velocities will come back to original.

If no pop loose then something else is going on.

Freshly loaded rounds usually are a bit slower than rounds that are even a month old due to this. Something to consider when loading max velocity / pressure rounds.

I understand. Thank you and Dwh7271. Those are things I wasn't thinking of.

 

[Horsethief]

Silly question, but is it the same bullet? One with a higher BC would have a higher velocity with all other things being equal. Differences between chronographs or the sensing level could be at work. The most likely causes for a velocity increase have been mentioned.

 

[NYDAN]

Silly question, but is it the same bullet? One with a higher BC would have a higher velocity with all other things being equal. Differences between chronographs or the sensing level could be at work. The most likely causes for a velocity increase have been mentioned.

All the components are the same. Depending on the load, differences could come from different lots of bullets, different lots of powder, different lots of primers. Different variables for different loads. Also, the brass has been reloaded up to 3 times now.

 

[DrMike]

Lot-to-lot variation in powders/primers and even in bullets and brass, can account for considerable variation in velocities. However, I have witnessed on several occasions barrels that yielded increased velocity with time as the break-in proceeded. I have a Model 70 chambered in .280 that is yielding velocities that are almost 200 fps faster now than what I observed for the first 200+ loads. It was a rough barrel with a rough throat. As that has been broken in, velocities have increased and copper deposits have become less of a problem.

 

[Bonz]

Bonding of jacket to case neck is your culprit as was shared. It bumps pressures in my 35 Whelen AI so each year I "crack" the seal by running the rounds into the seating die. Never affected accuracy and pressure comes right back to normal.

 

[salmonchaser]

Amazing what a guy can learn.

 

[Vince]

Amazing what a guy can learn.

Yup.
This place springs forth as a fountain of information. I'm going to test this for my own curiosity but I'm inclined to believe it as I've not gotten bad info here.

Vince

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