6.5 Cartridges

[bsumoba]

[LynnJr]

Russ69
Ignore the Troll his only claim to fame is that he can crack corn.

[longrange1]

6.5 Cartridges

I still don't know what you are going on about?

[ar15barrels]

Tight chambered necks help locate the bullet in the center of the bore.

If the clearance is just right (under 0.002" total), it also makes it so that you do not need to resize the case to be able to seat a bullet.

But can also cause pressure issues.

Only if there is too much variation in neck thickness, causing the neck to be binding in the chamber.

[Jimmy's]

The 3 mouse kateers.

[longrange1]

And the one big red floppy clown shoe


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[TMB 1]

If the clearance is just right (under 0.002" total), it also makes it so that you do not need to resize the case to be able to seat a bullet.

Start it with your fingers and they seat perfect every time you close the bolt.

[russ69]

Russ69
Ignore the Troll his only claim to fame is that he can crack corn.

Was it wrong to laugh really hard at that one?

[bsumoba]

Only if there is too much variation in neck thickness, causing the neck to be binding in the chamber.

I've had numerous discussions with my smith (who shoots with Larry Costa, a world class BR shooter, and shoots on his personal range on his property) about various aspects of short range BR and which processes I can adopt into the F-Class game.

One thing they are starting to do more is to run more neck clearance. They do turn necks, but they don't typically weigh brass which is something I would have thought they did. Go figure...

[LynnJr]

I think what Eric was asking is if the thickness matters.
6PPC brass that goes into a 0.262 tight neck chamber is 262-243 for the bullet then another 0.001 - 0.002 of total neck clearance so the cases neck is 0.009 thick.
If we shoot a 6 Dasher with the same 0.243 bullet in a 0.268 neck chamber with 0.002 total clearance the neck is 268-243-2=0.013 thick.
If we now shoot a 243 WSSM the brass in the neck is as thick as a 50 BMG tight neck chamber at 0.020.
All of these cases will be centered in the bore due to the neck turning but the 243WSSM will group worse than the Dasher which will group worse than the PPC.

[eric n]

I think what Eric was asking is if the thickness matters.
6PPC brass that goes into a 0.262 tight neck chamber is 262-243 for the bullet then another 0.001 - 0.002 of total neck clearance so the cases neck is 0.009 thick.
If we shoot a 6 Dasher with the same 0.243 bullet in a 0.268 neck chamber with 0.002 total clearance the neck is 268-243-2=0.013 thick.
If we now shoot a 243 WSSM the brass in the neck is as thick as a 50 BMG tight neck chamber at 0.020.
All of these cases will be centered in the bore due to the neck turning but the 243WSSM will group worse than the Dasher which will group worse than the PPC.

I guess I was asking...Does chamber diameter matter?
Will a .268 neck agg as well as a .262 in a ppc? Are guys running .262s because of the thin neck sako brass and stuck with it because it works or is there a reason that .262 gives peak accuracy?
After a little research, the .268's win as well it seems.
I was asking because I'm going to build one and the thought of turning lapua down to .009 makes me cringe. How many passes do you take?

Brian- I've ran 3 barrels with .001 neck to chamber clearance. (.0005 per side) 2- 223s and a 6br. Never had unexpected pressure or weird fliers but I clean after every range session. With that said, I can't see any difference between .001-.004. I will never run a tight neck again.

[bsumoba]

Brian- I've ran 3 barrels with .001 neck to chamber clearance. (.0005 per side) 2- 223s and a 6br. Never had unexpected pressure or weird fliers but I clean after every range session. With that said, I can't see any difference between .001-.004. I will never run a tight neck again.

It can definitely be done, but there is always the risk of excessive pressure. In F-Class, we almost all run about 0.004-0.005 neck clearance, the goal being to get a clean bullet release. We have seen accuracy issues with less neck clearance but almost no accuracy degradation with more clearance. The negative to excessive neck clearance is that one must size the necks down quite a bit when reloading. This may lead to other issues such as neck splitting, etc.

[pennstater]

Thanks again to all who intelligently replied to my OP regarding the different 6.5 rounds. Man, some differences to be sure. Like I mentioned earlier, I didn't really have a grasp on all of them and said applications. Pretty interesting to have you guys take the time to explain all this. Appreciated.
I just skip past the kid.

[ar15barrels]

I guess I was asking...Does chamber diameter matter?
Will a .268 neck agg as well as a .262 in a ppc? Are guys running .262s because of the thin neck sako brass and stuck with it because it works or is there a reason that .262 gives peak accuracy?

I think the thinner necks would give you less DEVIATION in bullet-pull pressure.

More stuff to consider...

Be careful in comparing different neck thicknesses as you have to take into account how the people are loading.
BR shooters will often breech seat.

(the explanation below is more for people not aware as I think you are well aware)

To breech seat, you load to a very low neck tension (or bullet pull if you will) and then you let the barrel seat the bullet.
This allows your bullet to always be seated at the same tension into the lands IF your bullet pull (neck tension) is consistent.
Doing that makes it so you do not have to chase the lands as the throat wears because the bullet will simply move forward into the throat automatically.

Varmint or field shooters would not want to breech seat if it is important for them to be able to extract a live round from the chamber without firing it.

So if you are NOT breech seating, then you are loading to a fixed length off of the lands, you would adjust your seating length every couple hundred rounds to keep your ammo in the sweet spot.
If you are not breech seating, you can get away with thicker necks and the difference in bullet pull will not be quite as important compared to the breech seating example.

That's not to say that thinner or thicker necks are better in general, just that thinner necks are probably more appropriate for breech-seating.
You could probably run thin or thick necks if you are loading to a fixed seating length and not see as much variation in group sizes as a breech seating shooter would see from the thicker necks.

[LynnJr]

The problem with too much clearance is overworking the brass and creating the need to anneal it constantly.
The problem with thick necks is they can't be loaded down without the risk of collapsing the case. The 243 WSSM if loaded any way other than full pressure will collapse the brass.
You eliminate that problem by ordering a custom reamer and turning the necks.

Eric
The PPC uses very fast burning powders and uses the thinnest necks. The 6BR and Dasher use slower powders and thicker necks. The 50BMG uses the slowest powders and has the thickest necks.

If you use flatbase bullets you need more necking down of the brasses neck because the pressure ring expands the brass as the bullet is seated. If you don't size it down enough it will allow a jumped bullet to wobble in the cases neck.
I can literally pull the bullets out of my 300 WSM by hand at the line and put them back in. They "Click" into place when the pressure ring finds its seating depth as the brass already has it memorised.
The thickness is less important on the bigger volume cases because most of the larger volume cases are used with boattail bullets and require less tension/necking down.