let's talk neck tension.

[runfiverun]

with my j-words i usually run @.002 tension
i have also been shootin for this with my cast, however i have been re- thinking
this lately
how much difference does it make?
talking rifles here. :Fire:[smilie=1:

[felix]

Depends entirely upon ignition characteristics. ... felix

[wmitty]

felix, please elaborate on this. Should the boolet be crimped if using a very light neck tension or is seating the nose touching the lands preferable?

[felix]

Touching the lands is preferable to a crimp of any kind when the neck tension is too loose for shooting off of the lands. However, there must be enough neck tension to withstand magazine shenanigans. ... felix

[44man]

As long as the boolits are hard, stay with good tension. The important thing is to have the same tension from case to case. BR shooters sort cases by how they group and shoot the same ones over and over. They say it is because internal dimensions are the same when it is really that the neck tension is the same.
Crimp will NOT help correct the problem of different tensions.
If tension is even it will not matter if you are off the rifling or against it. It will help for the different tensions by seating into the rifling though.
Felix is right in that a very slow powder or one that is hard to ignite will need more tension or the boolit jammed into the rifling to initiate a good burn.
Remember that loose tension can allow the primer to blow the boolit some distance into the barrel before the powder even gets going right. Trying to correct it by making the crimp harder can ruin accuracy in itself by sizing the softer boolit as it leaves. You can see this on fired brass that still shows signs of a closed crimp.
Revolvers and lever guns need a crimp to hold boolits in place under recoil. Any gun that has boolits move in a magazine will need crimp but only enough should be used to hold the boolit in place. Don't depend on it to make powder burn better.
I am convinced that the case that varies in tension from all the others you shoot will be the flier. The brass itself is the biggest impediment to perfect groups.
Now maybe we should discuss the cast boolit with lube that lubricates the brass when we want the boolit held tight! :mrgreen:

[felix]

Agreed. Neck tensions consistency is more important than internal case capacity uniformity. For this statement to be a truism, however, start with cases that weigh the same to the nearest grain if possible. The only positive that is guaranteed is that the cases must shoot into the group, no matter what the case parameters are. ... felix

[JSnover]

Thanks. I was taught uniform tension and a light crimp to control ignition. So it didn't make sense to me when the local pros all agreed on the lightest possible tension (thumb seat), no crimp, seat to the lands. Now I see. It takes the case neck out of the equation.
Some days I feel like one of the monkeys in "2001; A Space Odyessey" getting a jolt from the monolith......

[danski26]

Runfiverun,

Only you can answer your question as to how much neck tension matters. As far as bottle neck rifle cases go every variable can change the outcome. What I mean is, your rifle, your brass, your brass prep, your primer, your powder, your powder charge, your boolit and your rifle may or may not be sensitive to more or less neck tension. I think everyone agrees that consistant neck tension is always important but as to how much.......gotta try it in your setup.

[JeffinNZ]

Agreed. Neck tensions consistency is more important than internal case capacity uniformity. For this statement to be a truism, however, start with cases that weigh the same to the nearest grain if possible. The only positive that is guaranteed is that the cases must shoot into the group, no matter what the case parameters are. ... felix

Ditto. My Lee Enfield No4 MkII is VERY fussy about neck tension and if I fail to anneal the necks about every 5th load 'she' sprays bullets right, left and sometimes centre. Keep the necks soft and 'she' will shoot better than me.

[leftiye]

So, on a single shot with the necks maybe unsized even, or sized to just enough drag to hold the boolit from moving, and the boolit against the lands is as good as it gets.?. Then if the powder doesn't ignite reliably go to more powder, or a faster powder.?.

[felix]

Depends on boolit speed desired. If slower, go to a faster powder. If boolit needs to be faster, then go to a slower powder and more of it. Slip boolit fit is the best case tension, but is not practical except for all out competition guns, like breach seating. ... felix

The cheapest way to approach this slip fit business, is to turn the brass necks, and increase the boolit diameter to compensate. If you like the idea and you find satisfaction at the target, then it is time to get a tight neck barrel, use longer necked brass to seat out any longer boolits after the throat enlongates. The idea is to increase pressures to 40K or above, so you can use just about any powder and obtain a valid burn, while keeping the velocity within the boolit's capabilities. ... felix

[runfiverun]

the burn characteristics is what got me thinkin on this one
but more specifically, primer bump
i was workin a load over and i noticed that i had some unburned powder in the bbl.
but with a hotter primer it went almost completely away.

however, when i measured the inside of the fired necks of a sample of cases
i had 8 that were 312 id and 7 that were 315 id
which led to the idea of neck tension as a load tuner.

[HeavyMetal]

Neck tension is a huge issue when seeking accuracy.

The most important part is to select a specific system , loose necks, seat to rifling, what ever and stick to it without mixing the systems!

For maximum accuracy you should get cases from a specific Lot, and brand, sort them as needed by neck diameter and keep them seperate forever! Particularly during reloading!

[44man]

The "thumb seat" thing comes from black powder rifles. Most BPCR shooters do that or use very little tension so as not to size the soft boolits. Since black ignites very easy and fast most work is done with powder compression and boolit selection.
A fast smokeless needs less tension but it should still be as even as you can get.
I get good revolver groups but I could most likely cut them way down by shooting and sorting every case by where it shoots into the group. I just can't afford all the components plus I am lazy! [smilie=1:
Those BR shooters are smart but it costs money, a lot of time and shooting to do it right.
Annealed brass, kept constant is also good but just won't work with heavy revolver loads. Boolit creep is as bad as primer push and soft brass increases primer push too. There is nothing in a revolver to hold back a boolit and is the main reason they are hard to get good groups with. Just changing the brand of dies can have a profound effect on groups.
Some guys really into IHMSA use new brass for every shoot (Expensive) but I find just as much difference in new stuff as I do with old stuff.
I know for a fact that when I shoot way under 1" at 50 yd's and the next group is 2", that it is the brass. Brass difference can make you miss a super load too by passing it up as too large. It will even make you think the boolit is not good.
My neck tension tests with revolvers has shown the POI change between a loose case and a tight one can approach 10" at 50 yd's. Does THAT open some eyes? :Fire:

[danski26]

Not only BPC shooters use "thumb seating". Many high power long range competitors use almost no neck tension. Just enough so the bullet does not fall out of the case when it is tipped over. Seated into the lands as the bolt is closed.

[44man]

I can see it working fine in a single shot. One variable to get rid of. A bullet seated just off or touching the rifling will do it. Just need the right powder.
Not a good idea for a hunting rifle or magazine fed.

[Baron von Trollwhack]

Make sure the 25-20 guys get the word about annealing necks and neck tension. It will reduce the whine and cheese party flyers with the 257420 and that great new 6-banger groupie caster. BvT