Interesting discovery when loading a tight necked chamber

[AZShooter]

I have to make a correction on the neck wall thickness of the 308 brass. The .0105 thickness is with the 30 BR brass. I never changed the setting on the K and M neck turning tool so I figured the 308 would turn to the same thickness.

I measured many loaded 308s this morning with both a micrometer and a dial caliper. OD was .331". This makes the brass neck wall thickness .0115". Checked the reamer print and the neck is .332" making the neck release .0005" No wonder the springback yielded some inherent neck tension.

I now am wondering how the K and M neck turning tool would cut the brass thicker. I did the cut in one pass using the lathe in back gear. Thought about this and have two possible explanations:

Lapua 6mm BR brass necked up for 30 BR has a thinner neck wall to start. The thicker 308 lapua brass caused a difference in the material removed possibly due to flexing of cutting tool or maybe more heat generated.

Or the four times fired 308 brass is flowing into the necks.

I guess I could try to turn a few necks and see if more material is removed. BUT would it actually prove the brass is flowing? Or would this second much smaller cut remove some material because of less stress/heat?

Regardless of why, this stuff is fun and great brain exercise. Hope some of you readers are getting something out of this as well.

Ross

 

[Canadian Bushman]

A lot of times cutting more or less material than a tool was set up cutting will result in a different finish size as well as the temperature of the brass and metal composition. Running the brass at different speeds can also have similar effects.

I always neck turn brass twice on my mill at home and typ. between 800-1000 rpm.
I also put one of my indicators in my k&m tool because i dont trust a micrometer for brass necks once they are removed from the mandrel.

 

[Mikecr]

.001" for total release is interesting. I have to keep up with an carbon buildup on the necks and clean the chamber neck carefully. Any there any special techniques you use?

I clean EVERYTHING in my guns before they go back in the safe. Some may see that as 'special'. To me it's simple respect for firearms.

Do you end up with any brass flowing into the necks after a few firings so you have to turn them again? Bet you have designated your neck turning tool for just that cartridge!

I have ~30+ reloading cycles on cases that were initially prepped and no further maintenance is needed. There is no 'flow' of cartridge brass in my 6.5WSSM. I don't FL size or have to further trim cases with reloading. I don't have to anneal necks to keep same tension, because I'm never adding energy to them.

Is your 6.5 WSSM a target rifle? What is the measured OD after firing and then with a loaded round?
Finally what will the next cartridge be that will have a 40 degree shoulder?

My gun is built as a more or less standard Williamsport IBS LG(16.5lb). But I don't compete.
I'm running 1/2thou interference fit(.2895 OD), and springback after firing brings necks back to .2895. Ready for bullet seating. My dies are custom Wilson, and JLC precision.
My next barrel/chamber for this one will have a 45deg shoulder.

If you wanna talk about tight,, my throat is cut at .2645" which only leaves ~.00025 theoretical bullet bearing clearance. I'm able so far to keep my loaded TIR off bullets at or very near this. But if I had higher runout, I could technically reduce it with a cycle through this chamber.
I haven't yet determined if this is good or bad for the mix. But the gun will shoot 1/4moa to 300 using 139 Lapua/3025fps with this. I am under SAAMI max for pressure.

 

[AZShooter]

Thanks MikeCR very interesting stuff.

I went out again yesterday and the rifle repeated its very accurate performance.

It seems when I think I have done it all in handloading a new wrinkle shows. Stuff like this keeps it fun and challenging.

 

[TracySes23]

It sounds like a viable way to maintain accuracy throughout a barrels life. I dont think that im good enough at controling neck tension to pull it off though. It also seems you wouldnt want to remove a loaded cartridge from a rifle you were soft seating with.

AZ shooter, right after you anneal, are you still able to load your rounds this way?

You're correct about, using chambering a round as a means to seat the bullet. I got a bad batch of Remington 9 ½ Magnum primers & had about 18 misfires from 3 boxes of ammo. When a round didn't fire, I ejected the round pulling the bullet out at the same time. Powder went everywhere. After that I seated bullets .030" off the lands. It's a horrible mess to clean-up ball powder from your action. Fortunately I have a well equipped machine shop at home. 80 psi with a small diameter extension got it all out, but it still took longer than I expected. One box had 7 misfires on the first try. I had another 3 that finally fired off after 2-3 attempts. Frustrating to say the least. Especially when I drive 95 miles round trip to the range & back. Now I'm back to using either Fiocchi or Winchester primers & no more misfires.

 

[Canadian Bushman]

You're correct about, using chambering a round as a means to seat the bullet. I got a bad batch of Remington 9 ½ Magnum primers & had about 18 misfires from 3 boxes of ammo. When a round didn't fire, I ejected the round pulling the bullet out at the same time. Powder went everywhere. After that I seated bullets .030" off the lands. It's a horrible mess to clean-up ball powder from your action. Fortunately I have a well equipped machine shop at home. 80 psi with a small diameter extension got it all out, but it still took longer than I expected. One box had 7 misfires on the first try. I had another 3 that finally fired off after 2-3 attempts. Frustrating to say the least. Especially when I drive 95 miles round trip to the range & back. Now I'm back to using either Fiocchi or Winchester primers & no more misfires.

It does suck to clean powder out of a rifle. Thats an awful lot of misfires.