Speaking of neck tension (IF)

[justinp61]

I read through the other thread and didn't want to run it off in a ditch by asking questions on it. I'm working on loads for my recently rebarreled 22-250. With my RCBS standard and competition dies and a Redding neck size die the cases only have .001-.0015" IF measuring after sizing and after seating the bullet. With a Redding bushing die with a .246" bushing the rounds have .005-.0055" IF. I have on order a Redding full length bushing die and a .247" bushing. The cases are Winchester with Sierra 55gr boat tailed Game kings, the bullets probably have about .100" bearing surface i the case. Not counting the boat tail of course.

I've shot test loads with both IF's. The loads with the very light tension grouped just under .6" C/C at 200 yards. The groups from the bushing die were about 1.5" vertical and probably 1/2 horizontal. Everything other than the IF was the same.

So how would one compensate for the vertical? Increase powder charges? Reduce powder charges

The rifle is a carry around, magazine fed about a 8 1/2 pound coyote/groundhog rifle so I need to be able to load/unload, take bouncing around without worry of the bullet moving in the case.

Thanks, Justin

 

[Seabeeken]

If I understand it all, it sounds as if you need to re develop your load. A new ladder or OCW test would seem to be in order. My neck tension tests showed that .001-.0015 was best is all my rifles that I tested and it seems your rifle likes it also. With a new barrel, I'd redevelop the load, perhaps working in .2 gr increments on either side of the current load if pressure signs permit it. I'm sure there are others with more experience in this and I hope they chime in. Keep us posted on your results whatever you decide.

 

[dok7mm]

I would try seating depth testing first, especially if there is little difference in velocity between previous loads.

 

[cdherman]

You mention that your seating depth has only .100 shank in the case. I'd don't see how you are going to get by with that long term, especially in a magazine fed, working rifle. Typical rule of thumb is to have the neck contact be at least the same as diameter of the bullet. Now, I get it that rules of thumb are meant to be broken or fudged, but .100 shank is really too little in most every bit of reading I've done. Especially for you application. Might work in a single shot bench gun....

 

[Mikecr]

A lot of cartridges do not provide a full cal length of neck.
.100" of grip on the shanks will work fine with a lower recoiling cartridge (like a 22-250).

OP if you're doing better with 1-1.5thou IF, then you kind of answered your own question.
Order a bushing to provide ~2thou IF after spring back, and mandrel pre-seat/expand to 1-1.5thou IF.

 

[justinp61]

I checked the bearing today, .020" off the lands is .090-.100". the rifle showed promise at .085" from the lands, that'll put the bullet around .160" in the case. More testing will come.

Thanks guys.

 

[LaHunter]

A lot of cartridges do not provide a full cal length of neck.
.100" of grip on the shanks will work fine with a lower recoiling cartridge (like a 22-250).

OP if you're doing better with 1-1.5thou IF, then you kind of answered your own question.
Order a bushing to provide ~2thou IF after spring back, and mandrel pre-seat/expand to 1-1.5thou IF.

If he would end up with .001-.0015 i.f., why would he need to go .002 i.f. with a bushing, then go to .001-.0015 with a mandrel?
This sounds like that would put him back where he is now?? Which may be where you feel he needs to be.
I am new to the 'bushing die world', so I am working on getting a solid understanding of this.
Would the OP be better off getting 2-4 bushings to achieve various neck tensions / I.F. within a given range and see how well the loads shoot?

 

[slikmrc]

With the .0055 NT you may be getting some bullet distortion when seating the bullet. Chamfer and lube inside case necks might help.

 

[Mikecr]

If he would end up with .001-.0015 i.f., why would he need to go .002 i.f. with a bushing, then go to .001-.0015 with a mandrel?
This sounds like that would put him back where he is now?? Which may be where you feel he needs to be.
I am new to the 'bushing die world', so I am working on getting a solid understanding of this.
Would the OP be better off getting 2-4 bushings to achieve various neck tensions / I.F. within a given range and see how well the loads shoot?

He only needs one bushing. Tension adjustment is with LENGTH of neck sizing(springback force against an area of bearing gripped (PSI)).
Expansion(bullet pre-seating) is important. It drives thickness variance outward -away from seating bullet bearing. It establishes counter energy to last added, which after expansion, will be a latent inward spring back (instead of outward). So tension does not decrease over time/storage.
And if you set the final interference, after inward springback, to no more than you have anyway (after bullet seating), you'll reduce seating forces so it's not a big battle to get the exact CBTO desired.
Bullets make terrible expanders

 

[PddPdd]

OP, is there a reason you wouldn't want to try .002" or .003" IF? Most posters seem to utilize the .001 - .004" IF range to find what their rifle prefers.

Note: I'm assuming IF = interference fit

Also, how are you measuring your neck ID after sizing? Pin gauges or ?

It might be interesting to see what your neck ID is after pulling a bullet on one of the .005" IF rounds.

 

[ntsqd]

OP, thank you for using Interference Fit (IF) instead of the misleading and incorrect "neck tension".

Regardless of which type of mandrel expander you get you should be able to buy the mandrels in .0005" increments for, in the big picture, not a lot. I'd get the range of expander pins that takes you from .0005" IF out to .004" or .005" IF and then test them all.

 

[Mikecr]

It might be interesting to see what your neck ID is after pulling a bullet on one of the .005" IF rounds.

Neck ID will spring back ~1/2thou under cal.

 

[PddPdd]

Mikecr,

Follow up clarification, so any neck IF over .001" will result in .0005" IF after bullet is seated? I'm assuming this is for annealed brass and that work hardened brass might have more spring-back?

Just trying to learn from your experience.

 

[Mikecr]

The bullet will expand necks to cal diameter(from whatever they were).
When the bullet is pulled, the neck springs back around 1/2thou from that cal, with small variance tied to a few neck attributes.

Also, work hardened brass springs back less(either direction), but with more force. This is due to granular structure breakage with heavy working/yielding.
Broken grains are shorter and resist slipping by one another. This resistance in play increases force(tension).
Process annealing lengthens the grains so they'll slip by easier, reducing tension forces, while increasing ductility(spring back).

You will not know what your neck tension actually is until there is a way to measure it.
But for sure, the less you change it, the less variance you'll cause in it.
It's amazing that so many who chant about consistency are often more 'consistent' with mutating their brass in all directions.