Velocity increase on 6 month old ammo

[pdogger]

I had maybe 30 extra rounds from hunting season last year....i hadn't shot that gun since then until a week ago, and had put it away clean. To my surprise, velocity jumped from 3010 avg to about 3070 avg. i cleaned the rifle again and used simichrome to check for carbon ring (there was none). I loaded down a grain with the same jar of powder (N560), same primers (F210), same brass, etc. temp wasn't really any different from my sessions last fall - all in the 60's and 70's at the same location.

Today I worked back up and got 3020 with the same powder charge on ammo that was loaded yesterday...I also shot 2 more of the old ammo and got 3070 again. No pressure signs the other day or today so I felt comfortable with those old rounds.

My guess is that brass springback is what led to the velocity increase...I go .003 under with a FL bushing and then .002 with a neck turning mandrel, so it could come back tighter over time. I anneal with AMP after each firing so the brass isn't worked hardened.

Nothing else changed...could it be springback? Or could it be bullet and neck getting sticky? I tumble with STM and then coat with graphite powder prior to neck expanding and thought that would cover any metal stickiness issue.

Gun is a 280AI with 168 hunting VLD's. Ammo has been kept inside where temp range is normal with heat and AC.

 

[pdogger]

Temp. change...

 

[JASmith]

Yup!

I could not find an indication of temperature for eother check of velocity.

That, coupled with normal variation in small sample sizes, could easily show a 60 fps change on velocity.

 

[The Oregonian]

Temp. change...

The ammo from last year was 3070 and ammo I loaded yesterday at the same powder charge was at 3020. The temp difference between last year and this year was about 10 degrees.

 

[DSheetz]

Could carrying ammo around and the movement of the powder granules rubbing on each other cause the powder to begin to cause the powder to break down and thus affect feet per second velocity to change by causing a burn rate change ?

 

[SpeedGoatShooter37]

What type of chrony were you using? What was the sun condition of the times you tested?

 

[Will D]

Cold welding. I almost gaurantee it. If you try to seat your bullets deeper or pull them with a hand puller, you will feel them "pop" when they break free. This extra pressure that it takes to break them free increases chamber pressure, thus increasing velocity.

If you want to get rid of this issue, the best option is to HBN coat your bullets. You can clean your necks, use different lubes, it wont really change it. Using HBN coating on your bullets will get your ammo consistent shelf life and also likely lower your e.s., that has been my experience.

Please tell me what HBN is.

 

[Deputy819]

Please tell me what HBN is.

https://www.bulletcoatings.com/product/reloading-bullet-tumbling-boron-nitride-hbn-powder-kit/

 

[The Oregonian]

What type of chrony were you using? What was the sun condition of the times you tested?

LabRadar used for all of the velocities last fall and now...range shooting benches are in the shade but don't think it matters for labradar. And the last fall 61.4 and the two days ago 61.4 were shot within a few minutes of each other and still gave me 50 fps difference. I'm almost positive it was cold welding but will be able to pull bullets today to see.

 

[Ckgworks]

I had cold weld on some 6.5x55 loads after about 6 months. It's the only time in many years it has happened to me. I wrote it off to the combination of brand new brass, and bullet combo......I could really feel when trying to pull the remaining bullets. It hasn't happened since with fired brass, and I don't really clean the inside neck out.

 

[Calvin45]

I have also experienced this cold welding effect when when pulling bullets after being stored for extended periods. Another remedy is to not clean the brass to the point that the "inside of the case is brought bare metal........leave a carbon film on the inside of the case. When cleaning my brass, I use corn cob with no additives, and tumble/vibrate just long enough to completely clean the outside of the case, but leaving a carbon film on the inside. This also has eliminated the long term cold welding issue for me. This carbon film seems to also aid in consistent seating pressure, velocity, and low ES.

Another case of excessive cleaning being unnecessary and possibly detrimental. This makes sense. I've never experienced this issue, and while I do tumble my brass I've never got it like-new shiny, nor have I in any way cleaned or brushed in inside of the neck.

 

[DSheetz]

Will D. it's hexagonal Boron Nitride other then that it's supposed to reduce friction kind of like waxing your aircraft I guess .

 

[Chase723]

My experience with HBN has been just the opposite. I quit using it. Currently, all the ammo I load without HBN has an ES somewhere between 10-15fps. I didn't see any benefit to it whatsoever over standard reloading practices and all it did was create more expense and time for me.

Furthermore, every bullet I pulled that was coated with HBN was destroyed because it took extreme clamping pressure to get ahold of it to pull it out with the collet bullet puller. Also, it seemed like the tiny HBN particles would lock the bullet into the case mouth because, well, it's a small particle tightly interposed between two surfaces. This was confirmed by the fact that when I pulled the bullets they were all scratched.

 

[DSheetz]

I use a kinetic bullet puller that way the bullet isn't damaged . I don't pull a large number of bullets at any one time . Also if I happen to seat some too deep I can knock them out a little with out pulling them all the way out and seat them to the right depth this would loosen the bound up bullets and allow you to reseat them to the correct depth wouldn't it? I don't think it would affect the neck tension .