Does Jamming negate neck tension?

[noload]

I been thinking alot about neck tension lately. I think from a physics stand point that a jammed bullet.... lets say .010-.015" will pretty much negate many neck tension inconsistancies. I believe the force required to move the bullet caused by the jam overcomes any neck tension issues. Basically the neck will blow off the bullet (regarless of tension) before the bullet starts to move down the bore. Hence every bullet starts its travel with the same force applied. Hence MV should be the same if the jam is the same on all the bullets. I use very light tension and just touch the lands with VLDs. It works well with all the barrels I've tried it the last 3 years. But years ago I though I had to jam a VLD... maybe cause my necks were much tighter. just throwing it out there. Pat Lundy

 

[vtmarmot]

Not sure how we'd know unless we ran a test - maybe two five shot groups each with lots of brass sized with .001 progressively smaller bushings. Start with .001 tension and go up to .005 tension. Seat all bullets to the same depth (maybe .005 jam) and compare results. 50 shots, 10 groups. Anyone tried this?

 

[Immike]

Excellent question.

 

[savagedasher]

Wouldn't neck tension have a effect on how far you can jam? Larry

 

[Erik Cortina]

There is no cure that I know of for inconsistent neck tension. Tighter neck tension will allow a bullet to jam further in the lands than one with light neck tension.
I have seen seating depth changes of .003" take a good load and scatter it, so I would think that inconsistent neck tension would allow at least that much inconsistency in seating depth.

 

[noload]

Eric, I agree on everything you said. I think we agree on he fact that the jam force will overwelm the neck tension. I sort my loaded cases with all kinds of info when I practice. I look for a different POI when I shoot 4 light tension necks, and then a hard one , suprisingly the hard seated bullet will still hit the group like it belonged there. Granted 90% of my practice is at 300yds ,but after seeing that a number of times I've concluded there is no garantee that you will shoot a bad group with 1 hard seated bullet in the bunch.

 

[artbosco]

No. First you work up the load then fine tune with both seating depth and neck tension.

 

[LHSmith]

No. First you work up the load then fine tune with both seating depth and neck tension.

I agree. If one looks at short-range BR competition, the is an awful lot of imperical evidence that jamming does NOT negate NT. Consider that N-133 almost universally requires heavy NT for best accuracy, while LT-32, H-322, and 8208 work best with lighter NT (when all use the same bullet jammed).
Beware of running limited testing. Fitted necks (virtually no NT) at one time were used by some competitors because they had the potential to shoot extremely small groups, yet in the grand scheme of things ( the AGGREGATE), at the end of the day very few matches were won using this method.

 

[fguffey]

*****


I been thinking a lot about neck tension lately. I think from a physics stand point that a jammed bullet.... lets say .010-.015" will pretty much negate many neck tension inconsistencies.

I can not measure neck tension, I do not have a gage that measures in tensions. I have micrometers that measure interference/crush fit and I can measure bullet hold, bullet hold is measured in pounds.

As to the other part, jamming into the lands, that works for everyone but me. I want my bullet to have a running start, I am the fan of allowing the bullet to have jump. I do not want my bullet setting at the at a dead stop when the pressure starts to build.

F. Guffey

 

[Joe Salt]

I'm with Outdoorsman On this, once I got a load that is close, now I play with seating depth, Then neck tension. But only one thing at a time or you will be chasing your tail. I know there will be disagreement with one thing at time, but when you change just one you can go back if needed.

Joe Salt

 

[Shynloco]

As to the other part, jamming into the lands, that works for everyone but me. I want my bullet to have a running start, I am the fan of allowing the bullet to have jump. I do not want my bullet setting at the at a dead stop when the pressure starts to build.

F. Guffey

F, you aren't the only one who has experienced the notion of a jump requirement versus a jam. But that very much depends on what the rifle/chamber requires and means knowing your rifle. I've had a .308 that shot beautifully with a jump (.020) and was absolutely horrible with a jam. When I changed out the barrel and went to a match barrel chamber, that same rifle now loved the jam.

And as to this entire issue of neck tension negated by a jam. Personally, I cannot see tension changing once you've sized the neck of a casing regardless of the amount of tension applied. Now there certainly can be inconsistency involved in terms of the neck tension if you aren't checking (measuring) your necks once sized. But even with jamming, you can only jam so far before you run into the "immoveable object" theory which I why I set my seating depth to just touching the lands. I worry about potential inconsistent "seating depth" if you aren't measuring your bullets and using non customized bullets to insure each bullets as identical as possible to each other in the batch. That to me is a variable that cannot be overlooked if you are serious about accuracy and consistency in your cartridges. Just my thoughts.

Alex

 

[rcw3]

If you're "jamming" .015", I dare say that it's likely when you close your bolt the bullet is being pushed back into the case some. I do think jamming can negate some of the ill effects of wide variances in neck/bullet tension - - no definite proof of this but just impression based on all the tinkering, loads and shooting I have done over the years. FWIW, for loadings requiring the best accuracy I typically jam if I can as I feel I get better and more consistent results from that.

 

[jsthntn247]

I beleive it can negate small differences in neck tension (less than .001) but not larger ones. If your having more than .001 swings in neck tension, you have bigger problems going on anyway.

 

[mikecr]

I agree with OPs notion about jam potentially negating tension variances -given normal bullet grip.
I look at bullet grip and jam engraving as two separate influences to a pressure curve, and I can think of no reason the combination would add.
So if it takes 2xxxPSI to cause a neck to release, and 3xxxPSI to engrave from jam, then 3xxx is dominant to the pressure curve. If you were to raise neck release to 3.5xxPSI, then 3.5xx becomes dominant.
I think ideally you would want the factor -that you can manage- to be the dominant one, AND at a value that produces best results(that's the hard part).

As discussion goes roundy-roundy it's clear that isolation in testing is very difficult.
You can't even test the subject without a means to measure bullet grip, and you have no way to do that right now. Also 6PPC pressure curves won't predict 7WSM pressure curves(totally different tests). And so jam as dominant(like any seating depth) could not be assumed better across a gamut of barrels & cartridges.

Remember when everyone said you had to jam VLDs?
Nothing about that was true.

 

[WyleWD]

No. First you work up the load then fine tune with both seating depth and neck tension.

I agree with this post and Eric's.

Each to their own method, but I start out with at least 2-4 thousandths of neck tension with the bullets just off the lands, maintain that during load work up and then experiment seating depth. After the rifle's preferred seating depth is established then maybe try loosening or tightening the neck tension. JME. WD

 

[fguffey]

can't even test the subject without a means to measure bullet grip, and you have no way to do that right now

Who is

You

and

you have no way

I have a tension gage, it measure tension, it does not measure interference /crush fit. then there are other factors that are always omitted.

F. Guffey

 

[BoydAllen]

This is one of those things that is best answered by careful testing at the range, shooting over a chronograph. I can tell you from experience that with more neck tension bullets will go farther into the rifling before being pushed back, and that being farther into the lands will raise pressure, which should have an effect on tune and velocity. Sometimes these things are more complicated than they first appear to be. The surface finish of the insides of case necks also gets into this as well. If you clean all of the powder fouling out of necks, and compare that with leaving some in there will be a felt difference in seating force, which should also show up in jam length. (old school definition of jam as the maximum length to which bullets can be seated without being seated farther into their cases as the round is chambered)

 

[mikecr]

I have a tension gage, it measure tension, it does not measure interference /crush fit.

Are you measuring actual bullet grip, or seating force?

 

[noload]

As far as bullet grip is conserned. Before I seat any bullets I check my nk bushing size to be sure it will give me enough grip.... but not too much. Case neck conditions change progressively.(fresh anneal to work hardened and any where in between.) I use wilson seaters and a arbor press. I strive for a lightly seated bullet....something tight enough so you cannot pull the bullet out with your fingers. If I have to make special mandrel, or use an E mandrel to get that tension... thats what I do. Over the course of say 50 case necks I have some differences. They will seat mostly the same, but you do have a harder one now and then. (they will turn into expermental or foulers). This is all a feel thing... I mark the press reguired to seat the bullet with a number between 1 and 10. That number gets written down on all the rounds I load. Number 0 represents a loose seated bullet, number 2 I can't move with my fingers, number 3 to 4 is what i strive for, number 5 is probably a .0015" to .002" tension. So number 9-10 is off the charts scaring the bullet when seated. I guess a New untouched Lapua case would rate a number 7. All that said, I do see how I hit on White paper at 300 yards with variety of different neck tensions. I test and practice at 8am when conditions are at their best. Finding out a just touch scenario is a challange in its self, and saying you have a .015" jam is just educated guess. Saying you are pushing a tapered bullet into a 1.5 degree tapered hole is really just a persons feeling...it may only be jamming .010" and marking the bullet the rest. I think every part of shooting, reloading, and machining is a feel thing. I do not have any hard numbers on my neck tension.... but this works for me.

 

[lpreddick]

i'v asked myself this same question for over 2 years, esp if jamming "negates" neck tesion variation and the contriversal "cold bonding". i would work up a load that shot overlapping holes with .020 jump and if these were shot 6 months later...NOT THERE! seated these bullets .005 and some popped, then seated smoothly. not all popped so neck tension was not consistent. started seating .020 into the lands and worked up a one hole combo. one year later and the one hole is still there!!! inadequate and varying neck tension and will allow bullets to be pushed into the neck and this distance could vary, so i use .002 tension( .002 less than loaded neck diameter. my thinking is that a "low" pressure is required to move a jumping bullet while a very much higher pressure is need to move the bullet already in the lands and this pressure greatly exceeds that need to overcome neck tension. why .020 into lands...testing .025+ and bulllet seating into the neck occurs. i'v suspected variations in neck tension is a significant factor in consistent accuracy.