Brass inconsistency phenomenon

[DTF370]

Hey guys,

I believe I am experiencing some sort of phenomenon, voodoo curse, or haunting (surely it’s not operator error, right?). If you have any ideas how to diagnose this issue please chime in.

I recently acquired a GA precision built 308. I began load development and when I hit the range to begin the shoosting I noticed that my loaded rounds chambered inconsistently. Some rounds allowed the bolt to close with no resistance, some has a bit or resistance, and others would have taken force to chamber. In my moderate experience, I believe this is a sizing issue.

I’m using FGMM brass. I’m using Redding full length sizer on a T-7 press. On this lot of brass I fully processed and prepped a batch about 8 months ago. I just pick from the fully prepped brass and go straight to loading. I know without a doubt that each round was sized.

My question is, would there be such a significant spring back on the brass if it has sat for 8 months? I’ve never had this issue but I also have historically just loaded to the demand of ammo I have been using. Or is there some phenomenon I could be running into?

Thank you in advance.

 

[nn8734]

Brass (esp softer brass) does spring back. What is your shoulder bump relative to the chamber length? What is the length of your fired cases, on average? Do you have a chamber drawing or know the length of the chamber?

If your clearance real tight (.001 or less) then some cases may not have had their shoulders pushed back far enough while others have. This is due to slight variations in the brass cases themselves. There is always a small sub population with variance from your shoulder bump/die setting.

 

[straightshooter1]

This ^^^^^^^^

I've used FGMM brass in my .308 a lot and whenever I had hard bold closing, it was that shoulder was not bumped back far enough. Since I started annealing after every firing, that issue doesn't come up any more.

 

[FLIGHT762]

If you don't have a way to measure shoulder bump, you're just guessing where you're at. Inconsistently applied case lube can result in inconsistently bumped case shoulders. I've seen this over and over.

You need to find the bump threshold where your cases chamber smoothly into your chamber. I like using a type of comparator / gauge that shows a number. It makes it very easy to see that any case over .XXX" will not chamber.

 

[DTF370]

Prior to this load, I have no idea how far the brass was bumped. I do have a comparator and can bump compared to my newly fired rounds. The brass was prepped for another rifle. I do not have chamber drawing or anything. These were just rounds used to sight in and start development. I do have the means to properly size brass to my chamber’s preference, I was just a bit more alarmed at the inconsistency of my brass. It worries me that the brass of the same lot that I prepared was so inconsistent that some wouldn’t even chamber while others were fine.

Annealing is something I could defiantly try. I typically do, but this had not been annealed yet. I hate myself for not using Lapua, but for a field rifle I kind of hated to spend the extra money. In the end I have always regretted not going Lapua...

 

[918v]

Brass (esp softer brass) does spring back.

Soft brass springs back less than hard brass.

 

[918v]

Prior to this load, I have no idea how far the brass was bumped. I do have a comparator and can bump compared to my newly fired rounds. The brass was prepped for another rifle. I do not have chamber drawing or anything. These were just rounds used to sight in and start development. I do have the means to properly size brass to my chamber’s preference, I was just a bit more alarmed at the inconsistency of my brass. It worries me that the brass of the same lot that I prepared was so inconsistent that some wouldn’t even chamber while others were fine.

Annealing is something I could defiantly try. I typically do, but this had not been annealed yet. I hate myself for not using Lapua, but for a field rifle I kind of hated to spend the extra money. In the end I have always regretted not going Lapua...

You should always check a new chamber before loading up a bunch of ammo. The ones that don’t chamber can be made to chamber and will provide a reference for your new die setting.

Yeah, brass that sits around for a long time will spring back to different degrees depending on the hardness. But I would never anneal once or twice fired brass. I would just use it till the pp went, especially FGMM. Annealing that is just dumb.

 

[FLIGHT762]

Well, if you have any more of that brass, it's easy to take your comparator and measure the bump and take any brass that's bumped over .XXX" and take that brass and repair it (re bump). I use a Redding body to do that.

What case lube were you using? Hornady One Shot? Different MFG's of brass will bump differently and work hardened brass will spring back differently. That's why some of us use the Redding Competition shell holders to bump more or less without having to re-adjust the sizing die for whatever brass were using at the time.

That's why I use a comparator and measure.Aany shoulders over .XXX" get re-bumped.

I just did this yesterday. I was sizing some Speer Nickel 223 cases. They were not bumping back as much as some brass WCC 5.56 was. Had to re-adjust for that. After the adjustment, brass bumped perfectly.

 

[Snuby642]

Apparently your new chamber is slightly smaller than the old one you set your die too.

You may have to bump more maybe just one thousands worth.

 

[nn8734]

Soft brass springs back less than hard brass.

Thought it was the other way aroundL, thanks for the clarification.

 

[Snuby642]

He is right soft metals (annealed) spring less.

Hardening slightly more each time worked will change the ammount.

 

[Jordanwickham]

Try as I might I can't get less than 1-1.5 thou variance in my bump dimension. Your new chamber could be right in the middle of the variance of your old chambers bump dimension which is giving you some that are smooth, some that are firm, some that are hard to close the bolt. I also have never sized brass then had it sit around for 8 months so there could be some slop there too.
Typically when I get either a new gun or new barrel, new brass is also part of the package.
If you are intent on using the FGMM brass I'd give it all a couple thou bump and start from there getting a new sized dimension.
If you have the means to get new brass I'd go that route.