Ultimate reloading Mystery

[Robrex]

Shooting a 6BRA in NBRSA 600 and 1000, IMR 4895, and 103 Vapor Trails, neck turned to .0114 on an .269 necked chamber, annealed every time seated .010 of jam. The reamer is shared with 3 men, and I’m the only one that anneals. The first two firings the necks grow and then need to be trimmed, after that they shrink and they settle about .005 under trim to length. After 11 firings I decided to re-analyze a piece of brass in the AMP annealer and it posted a much higher setting…I re-verify…same higher setting. I measure the necks and the turned necks have grown to .0119 to .012, that’s where the length shrinkage is flowing. Lot’s of flyers! Both my friends who don’t anneal, necks remain the same thickness, and their cartridges don’t shrink. Is annealing making the cartridges shrink and the neck thicken…!

 

[hunter67]

What a great question! I am making popcorn.

 

[Fire Dog]

Shooting a 6BRA in NBRSA 600 and 1000, IMR 4895, and 103 Vapor Trails, neck turned to .0114 on an .269 necked chamber, annealed every time seated .010 of jam. The reamer is shared with 3 men, and I’m the only one that anneals. The first two firings the necks grow and then need to be trimmed, after that they shrink and they settle about .005 under trim to length. After 11 firings I decided to re-analyze a piece of brass in the AMP annealer and it posted a much higher setting…I re-verify…same higher setting. I measure the necks and the turned necks have grown to .0119 to .012, that’s where the length shrinkage is flowing. Lot’s of flyers! Both my friends who don’t anneal, necks remain the same thickness, and their cartridges don’t shrink. Is annealing making the cartridges shrink and the neck thicken…!

I had heard that from a gunsmith that I have used and he was saying that some brass the he had annealed in an AMP machine had shrunk.
I have been using an AMP Mk1 {now loaded with the Aztec code} for years and had never seen that happen to any cases that I have been using.
Your experience may explain why he found the shrinking cases…
It was a 300 Winchester and whether or not he turned his necks did not enter the conversation. Perhaps just the fact that the neck is short means it has less resistance to the body brass flowing.
I have checked my cases, 6BR, 280AI, 308 Palma and Lapua 6.5 necked up to 7mm and not found any such thing happening but none are neck turned.
I can only speculate that by thinning the neck that leaves an area for the brass in thicker areas some place to flow whereas an unturned neck resists that flow effect.

 

[Straightshooter1]

Shooting a 6BRA in NBRSA 600 and 1000, IMR 4895, and 103 Vapor Trails, neck turned to .0114 on an .269 necked chamber, annealed every time seated .010 of jam. The reamer is shared with 3 men, and I’m the only one that anneals. The first two firings the necks grow and then need to be trimmed, after that they shrink and they settle about .005 under trim to length. After 11 firings I decided to re-analyze a piece of brass in the AMP annealer and it posted a much higher setting…I re-verify…same higher setting. I measure the necks and the turned necks have grown to .0119 to .012, that’s where the length shrinkage is flowing. Lot’s of flyers! Both my friends who don’t anneal, necks remain the same thickness, and their cartridges don’t shrink. Is annealing making the cartridges shrink and the neck thicken…!

No, not normally. . . depending on your process.
Hmmm???Something else is going on. Do I understand you're trimming before you anneal? Are you sizing your brass with the expander ball in the sizing die?

My current box of Lapua .308's and 6.5 PRC's have their necks turned to .014" and both still measure .014" thick after both have been fired 17 times and and annealed after every firing. When I trim them with my 3-way trimmer, the only cutting I detect is some cleaning of the chamfer and trim lengths remain the same. My trimming operation is the very last in my whole brass prep.

Similarly, in my firsts two firings of the brass I find that they grew in length by ~.004 and then the growth stopped. I attributed that growth due to the fire forming process and once fire formed their dimensions have been stable.

I anneal my cases the very first thing after decapping, then clean them up before sizing with a Forster FL sizing die. Once the lube is removed by way of dry tumbling, I then run a mandrel through the necks to get the "neck tension" I'm after. 3-way trimming then follows.

If you're running an expander ball in your sizing die, then yes, that could result in what you're describing as the ball can draw brass up (like that donut portion that tends to form). Then yes, the annealing can make it easier for that expander ball to draw the softer brass up than the harder necks from repeated sizing that haven't been annealed.

 

[tommeboy]

Every time you size the body the brass grows. Only place for it to go is the neck.

 

[fisherman987]

How far back from the end of the chamber do you trim your brass back?

 

[NZ_Fclass]

I would second the expander ball issue. I gave up using them on all competition brass. I use Alpha and Norma BR brass and Alpha Dasher with an AMP annealer and have seen no growth in neck thickness or length. Norma BR brass is over 20 firings, Alpha, 5.

 

[Robrex]

No, not normally. . . depending on your process.
Hmmm???Something else is going on. Do I understand you're trimming before you anneal? Are you sizing your brass with the expander ball in the sizing die?

My current box of Lapua .308's and 6.5 PRC's have their necks turned to .014" and both still measure .014" thick after both have been fired 17 times and and annealed after every firing. When I trim them with my 3-way trimmer, the only cutting I detect is some cleaning of the chamfer and trim lengths remain the same. My trimming operation is the very last in my whole brass prep.

Similarly, in my firsts two firings of the brass I find that they grew in length by ~.004 and then the growth stopped. I attributed that growth due to the fire forming process and once fire formed their dimensions have been stable.

I anneal my cases the very first thing after decapping, then clean them up before sizing with a Forster FL sizing die. Once the lube is removed by way of dry tumbling, I then run a mandrel through the necks to get the "neck tension" I'm after. 3-way trimming then follows.

If you're running an expander ball in your sizing die, then yes, that could result in what you're describing as the ball can draw brass up (like that donut portion that tends to form). Then yes, the annealing can make it easier for that expander ball to draw the softer brass up than the harder necks from repeated sizing that haven't been annealed.

 

[Robrex]

Thank you for all the help. Just to clarify some of your questions. Lapua brass after initial fire forming, all subsequent firings, I de-prime, anneal, full length size with a custom bushing die, set the neck tension with a Cortina no-lube mandrel and die, tumble in medium rice to remove Imperial wax, then trim if they need it, and light chamfer. I seat with an AMP press and usually get a dreamy line that looks perfect. All that said if the necks thicken I lose too much clearance, chamber becomes too tight, and I get flyers…pull out my hair. I’m going re-turn my brass as a last step before chamfering and see what happens. Every day a mystery or two at the range.

 

[Robrex]

Mystery diagnosed but not solved! Just to let you know, I've traced the thickening necks to a newly sharpened reamer. There are three rifles (one is my light gun) and none of them are exhibiting the neck thickening. The reamer we've been using successfully for some years, had an issue and we sent it back to be sharpened/reconditioned. The first and only barrel cut with the new reamer is my heavy gun and it's the one exhibiting the neck thickening the entire length of the neck. Both my rifles use brass annealed every time with an AMP annealer, and even though the chambers should be exactly the same, I use two completely different sets of 100 pieces of Lapua 6MM Norma. The light gun necks measure exactly on the money the same as when I first turned them to .0114, the heavy gun has grown to .0123...both have 11 firings. I'm going to purchase a new duplicate reamer set the Bartlien back and see what happens.