Dusty Rounds Moving Faster

[jrock]

I've been tracking a phenomena in my reloading lately. I will load up a test the day or two before I shoot it. I pick a load I like, then load up 50. I pull them off the shelf 4+ weeks later and notice the velocities 100+ fps faster with ejector marks and hard bolt lifts. I have not seen this with anything I have previously worked on.

The chamber is a 6.5 GAP 4S neck turn, 28" 5R barrel, H1000 out of an 8 lb keg, and Norma brass. I've see this phenomena with two bullets I've tested. Therefore, it doesn't appear to have anything to do with the bullet. Since the powder is coming out of an 8 lb keg, I don't think it has anything to do with lot variance. It is my first time playing with imperial dry lube on the necks, both inside and out with a bushing die.

- I've heard humidity during reloading can be an issue. I have a home humidifier that keeps it within 5% so that doesn't seem likely.
- Since I'm using a bushing die, I wouldn't think the necks are relaxing to increase neck tension. I've heard that may occur over time with expander use.
- I've heard bonding of the bullet to the neck over time may be an issue but its just 4 weeks. I haven't had any issues with other guns and ammo I reload.
- I've tried tests with clean and fouled barrel conditions with no fix to the issue.

Maybe I need to avoid loading up tests right before I shoot them.
Any suggestions will be appreciated.

 

[Dean2]

Are you making compressed loads, have you measured COAL when first made and then after sitting for a couple of weeks, have you tried pulling a bullet to see if neck tension is the same as first loaded, how close to the lands are you seating the bullets, is there lube on the inside of the case neck from the resizing operation. All of these things can cause the issue you are seeing.

 

[jrock]

Load is not compressed. Probably 90 to 95% full.
I've recently pulled bullets 2 times and the tension is pretty close. Obviously subjective but its not noticeably harder.
I'm jumping 20 thou.
I'm using imperial dry lube and I do not wipe it out before seating bullets. I've read in places that leaving the dry lube on the inside of the neck can help with ES. Part of the reason I'm trying it out. I always wipe out wet lube

 

[Dean2]

Then the only other thing I can think of is temperature. 100 FPS swing is pretty large for the same load over a few days. I am presuming you have the Chrony setup right and aren't getting variation from shooting across the screens at different angles. If it isn't temp or Chrony error and Chrony seems unlikely since you are also getting pressure signs, I have not further advice.

 

[jrock]

Temps were within 10 degrees of each event. H1000 is "supposed" to be stable. I have a Chrony so there could be some number mess ups for one reason or another. I believe it to be right as I'm out of the accuracy node and getting bright ejector marks and hard bolt lifts. I'm baffled. I've already checked all the brass dims after the first time it happened, and annealed the cases but it didn't make any difference.

Two more things I think I can try
- No dry lube, clean necks.
- Additional 0.001" of neck tension.

 

[Gord0]

Take one and put it in the seating die and seat it a little deeper very slowly. Listen and try to feel if there is any pop. If there is, you're getting cold welding.

 

[The Oregonian]

Take one and put it in the seating die and seat it a little deeper very slowly. Listen and try to feel if there is any pop. If there is, you're getting cold welding.

Cold welding is my guess too. But a month seems like a short amount of time for that to happen. I dry lube the inside of the case necks before I load - graphite powder seems to help according to folks that would seem to know. I don't think it can hurt so i do it. I also don't load more than I am going to shoot fairly soon due to cold welding potential.

 

[Gord0]

Cold welding is my guess too. But a month seems like a short amount of time for that to happen. I dry lube the inside of the case necks before I load - graphite powder seems to help according to folks that would seem to know. I don't think it can hurt so i do it. I also don't load more than I am going to shoot fairly soon due to cold welding potential.

I know some people load and seat long if their ammo will be sitting for any length of time. They just seat it to the depth they need right before using.

 

[jrock]

Thanks for the suggestions. I'll play with seating some more.

 

[del2les]

Also, did you clean your rifle before these latest shots? Lubes and some solvent films left in the chamber can cause a load to increase back thrust into the bolt head and cause pressure signs. In my earlier days of loading, I saw this a couple of times.

Then there are the rare times when a clean barrel increases pressure until sufficiently fouled.

 

[jrock]

Originally, the barrel had ~50 rounds down it. I pulled all the bullets, dropped a grain of powder, and cleaned the barrel. I do swab the chamber out. Next time out, I fired two shots and velocity and pressure were still too high. I did see 30 fps more speed on the first shot with a clean bore, which I have mapped to be normal for a clean bore first shot.
I pulled bullets, and dropped 0.5 grains which I think will get me into the velocity pressure range I'm looking for. If it proves good, then whatever is happening is causing pressure signs equivalent to 1.5 grains over pressure!

 

[MagnumManiac]

Have you developed the load with new brass then loaded up once fired brass?
If so, once fired brass will often increase velocity and pressure over max if not adjusted from new brass. The reason is that new brass runs lower pressure due to the case being blown out, thus doesn't happen with once fired and pressure can exceed max...ask me how I know this?!

Cheers.

 

[jrock]

Good thought. The recent load development and dusty rounds have been on the third firing. I annealed the brass after the second firing. I'll go back to my records and see if it may have been part of the initial issue.
I try to do my final load testing on once fired brass because of that reason. I have noticed that brass fired twice seems to be slightly more stable than once fired. I bump 2 to 3 thou.

 

[MagnumManiac]

For hunting I use a load developed on twice fired brass, but actually use new brass to hunt with.
For my comp guns and varmint/LR rifles, I use thrice fired brass for load development and use whatever round count brass for hunting cuz it all gets annealed after every firing, so it's fire formed and stable throughout usage.
I once used to load and travel to a range to test loads, then I had the fortune of shooting on my own private range, however I soon discovered that the travel had somehow 'settled' my rounds and I had pressure excursions during a match.
I discovered that the packing scheme of the rounds made a HUGE difference if not all the same. So, I discovered the 'swirl charge technique', which is pouring the powder in using a funnel so that the powder swirls like a tornado into the case. The difference in powder height is significant and it flattens out pressure/start pressure/velocity improving both ES & SD. Give it a try, it works very well.

Cheers.