Can a load change its accuracy with time?

[Les in Wyoming]

I read in a book where the author said he had a load that was accurate if you shoot it within a few days. But it sets for a while, the accuracy is unreliable. I have experienced this, but decided it might be temperature and switched my load. But I have suspected this with other loads. I recently tried to pull a bullet out of a cartridge loaded a few years ago. It would not come out. I had to give up. I could probably shoot it, but the neck tension must be incredible. Any input on this phenomena is much appreciated. I have loaded enough 300 WM to last for years of hunting. I hope I did not make a mistake.

 

[Sockeye66]

The term for this is called "cold weld", basically time affecting dissimilar metals to the point that the brass and copper are stuck together. It can have an affect on pressure and accuracy. One way to combat this is using a nylon brush with graphite and scrub the case neck well. I currently have some 6.5x284 loads that are doing this after about a year and those cases were not brushed.

 

[sedancowboy]

It is called cold welding. The bullet adheres to the neck of the cartridge. It is caused by the metals being dissimilar and causing a reaction. To restore the cold welded cartridges simply bump the bullet with your seating die. The accuracy will most likely be restored and you can pull the bullets.

 

[MagnumManiac]

It is not always caused by bullet weld.
I have made up loads and shot them 20 minutes later after completing load development for a comp shoot, which were perfectly fine in those parameters, but after a 4 hour road trip, those rounds changed and on the very first sighter shot I had a locked bolt. It could not be opened at the range, even with a hammer. Luckily I use PT&G one piece bolts because I had to chuck it in the lathe with the brake on and pound it open with a dead blow lead hammer. The case, what was left, was fused to the bolt face.
I removed the barrel and measured lug recesses and all was good. Only real damage was the extractor and ejector and a burn on the boot face where the primer let go.
Don't be fooled, powder settling in a case can change how it burns.
I tested this afterwards, cases charged without any settling and the powder being compressed slightly showed no excessive pressure, charges that were vibrated, with 1 grain less powder showed excessive pressure. I have a theory about this, but the Pressure Trace has not shown a conclusive result yet.
The above charge that was just poured into the case I call fluffy charging.
Cases that have either vibration or swirl charging, I call hard charged, because no more settling occurs even during transport.
Had this happen with RE25 and Retumbo twice now and in 300WM & 338-416 Rigby Improved.

Cheers.

 

[DJ Fergus]

It is not always caused by bullet weld.
I have made up loads and shot them 20 minutes later after completing load development for a comp shoot, which were perfectly fine in those parameters, but after a 4 hour road trip, those rounds changed and on the very first sighter shot I had a locked bolt. It could not be opened at the range, even with a hammer. Luckily I use PT&G one piece bolts because I had to chuck it in the lathe with the brake on and pound it open with a dead blow lead hammer. The case, what was left, was fused to the bolt face.
I removed the barrel and measured lug recesses and all was good. Only real damage was the extractor and ejector and a burn on the boot face where the primer let go.
Don't be fooled, powder settling in a case can change how it burns.
I tested this afterwards, cases charged without any settling and the powder being compressed slightly showed no excessive pressure, charges that were vibrated, with 1 grain less powder showed excessive pressure. I have a theory about this, but the Pressure Trace has not shown a conclusive result yet.
The above charge that was just poured into the case I call fluffy charging.
Cases that have either vibration or swirl charging, I call hard charged, because no more settling occurs even during transport.
Had this happen with RE25 and Retumbo twice now and in 300WM & 338-416 Rigby Improved.

Cheers.

I'm glad you posted this. I have long suspected exactly what you described but never took the time to prove it to myself. If I'm not using a drop tube funnel, I also swirl my powder into the funnel. I've been doing that for so long that its just a habit now. I read along time ago that it would help lower extreme spread. I believe there is some merit to that idea.

 

[DJ Fergus]

As far as cold weld goes, Do you guys think its less likely to happen with new virgin brass? I personally think its less likely, because I haven't noticed much of change with a load in new brass. I never rule anything as being impossible though.

 

[Mikecr]

I believe actual cold welding is a corrosion situation that takes more time than we're talking about here.

I think some of this is sized brass behavior over time.
When we size we add energy, putting the brass in a state that is not it's lowest energy level. All things in nature seek a lowest energy balance.
So you size the case body, it expands a bit when pulled from the die, but that expansion will continue over time. It isn't settled yet.
Hours, weeks, months. I've noticed it can take 4mos to settle.

As case bodies expand to close chamber wall clearance, pressure goes up with firing. This, because the case is absorbing less energy for firing expansion before hitting chamber walls.
It's load developed away from concern by folks who neck size only, but FL sizing people can hit on problem loads with it (over time).

 

[MagnumManiac]

DJFergus,
I find new brass has more neck tension, which I do not like having a tension I do not desire.
I put them all through a mandrel to get MY desired IR. Even then, I notice more resistance seating than on the same brass after the first firing even if I anneal.
I have also noticed that the pressure ring is a lot tighter in the neck/shoulder juncture.
My 25-06's all have SAAMI short throats and all bullets are past the pressure ring. In new brass this area is tighter than a fishes butt, but I can't do anything about it. Even on the second loading it is not as tight.
I know the neck and body expand, but the die puts it back, maybe a little lesser than factory, but it's hard to gauge that area.

Cheers.

 

[philipbrousseau]

Tag

 

[scope-eye]

I have always found that when accuracy starts to fade with the same load, is when the throat starts to erode.

Dean

 

[ShtrRdy]

As far as cold weld goes, Do you guys think its less likely to happen with new virgin brass? I personally think its less likely, because I haven't noticed much of change with a load in new brass. I never rule anything as being impossible though.

I believe it's more likely to happen with new brass. Or brass that has had the inside of the neck squeaky clean.

When there's a layer of firing residue on the inside of the neck it separates the copper from the brass

 

[Chadp82]

This was an interesting post and curious to see what others add.

A couple of years ago I went to the range with reloads and my dad's old rifle. When he was alive, these were his hunting loads. I never shot his rifle much, but decided to take it along on the range trip just for the heck of it.

first shot, stuck bolt. I got it open and wondered what the heck. Decided I shouldn't send any more of these downrange.

I got home and pulled one apart. There was certainly some corrosion around the base of the bullet. I pulled another one, it actually acted as if it was pressurized and popped a little. I was using a collet puller. It too showed corrosion.

I then decided to pull them all and dispose of them due to finding this. I chalked it up to being old. I did pull a bullet on reloads I found dated the same for another cartridge and everything seemed fine.

not exactly sure why they behaved differently. Same powder and load date, but different bullet, but Dad's loads were 300 WM, and the comparison load was 30-06. Both with H4831 but the 300 WM loads had a Nosler partition and the 30-06 loads used a Hornady Interlock. Oh, and the load dates were around 2005 if I recall.

 

[Calvin45]

As far as cold weld goes, Do you guys think its less likely to happen with new virgin brass? I personally think its less likely, because I haven't noticed much of change with a load in new brass. I never rule anything as being impossible though.

I would think it should be the opposite but of course I just don't know. If it really is cold welding that happens the presence of a thin film of carbon, inevitable after it's been fired, should be a good thing, technically maintaining a barrier between the case metal and jacket metal.

 

[Calvin45]

On a less serious note...if you don't drink the same amount of coffee before each shooting session you'll be different amounts of jittery. Don't blame the ammo!!!!