NECK TENSION AND ACCURACY This story is embarrassing; but I learned from it. I wish I would learn earlier/easier. In the Savage .223 Rem. I use range pick up brass segregated by headstamp; my groups don't yet warrant using better brass. The cases are trimmed, mouths chamfered, primer pockets and flash holes uniformed for no particular reason. I deprime cases and clean primer pockets at the range, during target changes, using a Lee decapping rod and base and mallet. The loads are low and slow, 7/IMR4227 is typical. Some cases have been tight on the Lee decapper, because, I thought, the pressure was too low to expand the case mouths. All cases are full length sized and “M died” each time. Yesterday I had poor results with a previously fair load, and thought the wind-fierce-was the culprit. Other loads, later, were much better. I got up at midnight, fiddled with the cases and checked my book on this rifle. Only cases headstamped “GFL” were tight on the .222” Lee decapper, those cases were the poor performers yesterday, and the book showed that those cases had performed very poorly for the past five reloadings. I don't know if or when the necks thickened, but the cases are on the way to the recycler. The message is, to me, now clear. Tight case necks, and probably variable neck tension, hurts accuracy. Another argument for having only the gas check/base in the case mouth.
NECK TENSION AND ACCURACY
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- Last Post 02 January 2014
Joe, An excellent lesson for us all, and the learning is that unless you keep good records, you are going to repeat the same errors. Ric
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"The message is, to me, now clear. Tight case necks, and probably variable neck tension, hurts accuracy” How tite? How much tension? If those case necks were so tite as to change the diameter of the bullet when it is seated, or the tension being widely inconsistent, then I “might” agree with your statement. But, excluding the above, just concluding that the tight necks on these cases are causing the accuracy problem, I am not so sure. There are a number of other things in play here at the same time with regard to those cases. some of which we can control and some not. And before being in a hurry to have someone turn them into brass door knobs, it would be interesting to try and find out if the neck tension on those cases is the sole culprit or not. RD
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I read this a mixed lots of cases in the same set of groups being the issue.
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"The message is, to me, now clear. Tight case necks, and probably variable neck tension, hurts accuracy” How tite? How much tension? If those case necks were so tite as to change the diameter of the bullet when it is seated, or the tension being widely inconsistent, then I “might” agree with your statement. But, excluding the above, just concluding that the tight necks on these cases are causing the accuracy problem, I am not so sure. There are a number of other things in play here at the same time with regard to those cases. some of which we can control and some not. And before being in a hurry to have someone turn them into brass door knobs, it would be interesting to try and find out if the neck tension on those cases is the sole culprit or not. RD
I'm not claiming that neck tension is important for everyone-under normal circumstances I'd have sets of bought-new cases completely prepped including turning necks. I'm telling this story because I think that neck tension CAN be important in some cases-like the one described. Maybe always important-I don't know. What I do know is this:12/4/13 a given load other cases 5 groups avg 1.515"12/18/13 same exact load GFL cases 5 groups avg. 2.8"11/19/13 GFL cases, “NO GROUPS"10/30/13 GFL cases “HORRIBLE"10/14/13 GFL cases “HORRIBLE 100 Yard"10/14/13 another load, GFL cases “HORRIBLE"That's all the times I've shot these cases. I measure and record ALL group sizes unless there are no discernable groups, the groups are Horrible.So, this is what I know, the cases are history. That's my story, and...
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i'm new to cb but very good at physics. people here seem to worry too much about dynamic friction which is a fraction of 1% of the force that a bullet sees. higher bullet pull on the other hand, holds the bullet in place longer, building higher pressure which causes powder to burn faster. that causes pressure up...etc. bullet pull is effected by neck thickness and hardness bullet/neck fit, neck to chamber fit and static friction (much higher than dynamic) etc. if i had what looked like serviceable brass throw a known good load all over, i'd be HAPPY cuz i'm gonna figure out what my rifle is telling me to pay more attention to. make the new ones more like the old ones ONE CHANGE AT A TIME. kinda like marriage .... just doing something u think is nice doesn't make it nice.
bob
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Has anyone tried an experiment of loading 50 bullets and randomly PULLING 25 of them (measuring the tension required to pull) and shooting the other 25 for a group?
Might be enlightening.
Might lead to determining how to predict neck tension with the components at hand.
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i'm new to cb but very good at physics. people here seem to worry too much about dynamic friction which is a fraction of 1% of the force that a bullet sees. higher bullet pull on the other hand, holds the bullet in place longer, building higher pressure which causes powder to burn faster. that causes pressure up...etc. bullet pull is effected by neck thickness and hardness bullet/neck fit, neck to chamber fit and static friction (much higher than dynamic) etc.
if i had what looked like serviceable brass throw a known good load all over, i'd be HAPPY cuz i'm gonna figure out what my rifle is telling me to pay more attention to. make the new ones more like the old ones ONE CHANGE AT A TIME. kinda like marriage .... just doing something u think is nice doesn't make it nice.
bob I wonder if/how much breech-seating = no-neck-tension contributes to accuracy. I have used step-necked cases in tight-chambered guns with the bullet loose in the case neck, stopped by the step. Pretty good results.Is neck tension variation important? How could we find out?
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I wonder if/how much breech-seating = no-neck-tension contributes to accuracy. I have used step-necked cases in tight-chambered guns with the bullet loose in the case neck, stopped by the step. Pretty good results.Is neck tension variation important? How could we find out? This has already been researched by Jerry Bottiger in Fouling Shot #224 with the conclusion that there appeared to be no significant difference between .005” neck tension and .003". At least in his case. If I were to explore the neck tension question, this is how I would do it. !. Cases -- same lot, weighed to within the same range, all fired same # of times in same rifle, uniformed and annealed. Necks reamed and turned to same thickness. And then once fired after annealing with full power load. Indexed to same spot when chambered and fired in rifle.
Bullets -- same lot of alloy, weighed to within same weight range, indexed the same when sizing and loading, seated to align with index mark on case. Chambered with index marks aligned to same position in chamber. Cases either neck or full length sized with neck bushing sizing die. Use different size bushings. No expanding.
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Could someone please do that,,, so I don't have to!
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Yes, I too wish some one would.
Forgot to add in the element of concentricity. Every time I try to edit. the narrative is all squashed together.
So, one more thing--
Concentricity -- concentricity of empty case necks are checked after sizing. Then loaded round after bullet is seated. If each of the above does not fall within a range that was decided on, the case and/or loaded round is eliminated.
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I really like your analysis. Although I'm a chemist in my career, I've done quite a lot of applied friction research. I puzzle over things like bullet seating into the throat that would increase the force to start the projectile movement vs frictional drag of neck tension. I Usually seat into the throat with just enough interference to push my bullet into the neck about another 0.001 inches while closing the bolt. I like the slight compression fit. I don't Have a good visual image of the force to overcome frictional drag versus the change in neck diameter as pressure increases. Is the projectile already in the barrel before there is much neck expansion. Too many questions!
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I really like your analysis. Although I'm a chemist in my career, I've done quite a lot of applied friction research. I puzzle over things like bullet seating into the throat that would increase the force to start the projectile movement vs frictional drag of neck tension. I Usually seat into the throat with just enough interference to push my bullet into the neck about another 0.001 inches while closing the bolt. I like the slight compression fit. I don't Have a good visual image of the force to overcome frictional drag versus the change in neck diameter as pressure increases. Is the projectile already in the barrel before there is much neck expansion. Too many questions!
I agree Loren and that's what make cast bullet shooting more interesting than other shooting disciplines where everybody does the same things. Shake and bake reloading seems boring.
John
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R.D - Let me try to understand what you're measuring. Concentricity by definition means to two features having the same center. Co-axiality refers to two features having the same axis. (see ANSI Standard Y14.5M) Can I ASSUME you are measuring runout or total runout, as with a dial indicator and rotating the case. Runout is an indication of ROUNDNESS, but takes into account variation in whatever supports the feature being rotated (bearings, vee block etc.)
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I read this a mixed lots of cases in the same set of groups being the issue.
Years ago, I walked into a local gun shop that also offered custom reloading. A customer was dropping off his brass the be reloaded. I stood there looking at his box of mixed headstamp brass, and the guy behind the counter finally asked me what I was looking at. I told him “2-1/2 inch groups". I was pretty well known there, and he looked in the box and agreed with me to keep me quiet.
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TRK: “Concentricity -- concentricity of empty case necks are checked after sizing. Then loaded round after bullet is seated. If each of the above does not fall within a range that was decided on, the case and/or loaded round is eliminated" By checking the concentricity of both the empty case neck and bullet after it is loaded, I am measuring how true both are to the center axis/ centerline of the cartridge case so that the bullet can be introduced into the throat as close to the bore centerline as is possible. And as a normal step in loading, especially when using new brass the first time, I also check the concentricity of the case neck after the first firing. Just to see if there are any naturally crooked cases. It's not unusual to find some that no amount of sizing or firing will straighten out.
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