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Neck tension, crimping and pressure/velocity? #14203901 10/15/19
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Rodell Offline OP
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I have occasion to make up some more 300 Weatherby loads. I have a "tried and true" recipe developed but was running low. This time, though, I annealed the brass using an AMP annealer. Using the same lot of IMR 7828SSC, I saw a 200+ fps drop in velocity (Labradar, shot old and new at the same session). I certainly wasn't expecting that and the accuracy wasn't good at all, which isn't surprising given the velocity difference.

I applied a light crimp with a Lee FCD and the velocity came up, but just a little. The bullet is a 168 TTSX and the length is such I'm not where I can crimp into a groove.

I'm not sure I can get enough powder into the case to get my velocity back. I could run more neck tension (I was using .002" measured) but could easily bump it up) or apply a heavier crimp - would that make enough difference?

What's the writer.wisdom on the effect of more tension and crimping on velocity?


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Re: Neck tension, crimping and pressure/velocity? [Re: Rodell] #14204336 10/15/19
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Jim_Knight Offline
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I hear a box of new brass...calling your name! smile I use new brass to start, and I "always" use the FCD. Whether it is Barnes or a Hornady, it gets crimped! Now, I can get anywhere from 1/2" to 1 1/2" five shot groups, and I just shoot rocks and Coyotes at any distance and big game only out to 375 or much closer. I would load ammo a whole lot differently if I was a bonafide, Long Range Shooter. IOW, I don't sort cases or bullets by weight, only my powder!. smile I don't check for runout, case neck thickness, tension, nor do I anneal. I "do" use quality brass and I always deburr the flash hole and uniform primer pockets. I use a Lee Case Trimmer, when they get too long, zip and I'm done. I do caliper each round for proper seating depth ( that I have established via measuring prior) I also use a Sinclair VLD inside case mouth deburrer.

Now, many guys here anneal, and hopefully they can help you keep what you have...but Life is so short...new brass is out there...:) Come on...you need at least two new boxes....:) Ha Just messing with you...Have a ball.

Last edited by Jim_Knight; 10/15/19.
Re: Neck tension, crimping and pressure/velocity? [Re: Rodell] #14204350 10/15/19
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John55 Offline
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Interesting for sure. I anneal after every 3rd shot and never see any speed differences. I also use gauge pins to set neck tension, prefer 3 thou for hunting ammo. Never crimp anything except big bore loads like 416 or 450. Is your powder from same can or just same lot?

Re: Neck tension, crimping and pressure/velocity? [Re: Rodell] #14205344 10/16/19
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nighthawk Offline
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In my Super Blackhawk using slow powders without a heavy crimp would really drop velocity and leave a lot of partially burnt powder. Pressure = heat, so it appears the extra pressure generated more heat on initial ignition (powder burns exponentially faster with pressure) before the bullet popped, firing up the powder more completely. Guessing a soft neck after annealing does the same thing. Powder burns up more slowly, bullet goes further down the barrel before the powder all burns, more volume for gas to fill. Maybe a slightly faster powder or don't anneal so soft?


The key elements in human thinking are not numbers but labels of fuzzy sets. -- L. Zadeh

Which explains a lot.
Re: Neck tension, crimping and pressure/velocity? [Re: Rodell] #14205835 10/16/19
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alpinecrick Offline
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Pressure rise.
A faster pressure rise theoretically burns the powder more efficiently, taking advantage of the energy stored in the powder earlier in the pressure curve. It also can help with accuracy. A lot of BR shooters seem to subscribe to this idea.

With slower burning powders this has generally been my experience too. Not every time but usually. Went through this last year with RL-26 while messing with LCD dies. Bought LCD dies for 4 different cartridges and none of them would size the neck enough to hold the bullet. I could pull the bullet out with my fingers. So happened I bought extra standard diameter mandrels in 270. While waiting for undersize mandrels to arrive I sanded down one of the spare 270 mandrels. More than I intended........ended up at .2727 according to my mic. What the heck, I'll give it a try. I was already making straight ammo with my old method, but the tight necks (which I like for a hunting round anyway) produced more velocity and better accuracy.

Also, I will almost always get a velocity drop from new brass to fired brass, most likely because of the higher volume of fired brass creating less pressure rise.

Although 200fps is a lot, and I don't think it all can be attributed to less neck tension, especially because you did crimp the ammo.


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Not being married to any particular political party sure makes it a lot easier to look at the world more objectively...
Having said that, MAGA.
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Re: Neck tension, crimping and pressure/velocity? [Re: Rodell] #14206122 10/16/19
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Tejano Offline
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I would like to see the numbers on progressively tighter neck tension and velocity. Hard to believe 200 fps is entirely due to neck tension but it's possible. Were there any other changes like primers? Was there a big change in humidity between the two loading sessions. This can play havoc with thrown charges.


"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
Re: Neck tension, crimping and pressure/velocity? [Re: Rodell] #14207588 10/16/19
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HawkI Offline
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Agreed, but I was thinking more along the lines of weighed charges and the possibility of reducing the case volume through the sizing process.

"Tried and true" loads are often verified only by weight, when a volumetric setting (if using the same powder lot) might be better for repeating the original results.

Of course bullet lots can also change things/results too.



Re: Neck tension, crimping and pressure/velocity? [Re: alpinecrick] #14209153 10/17/19
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MuskegMan Offline
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Originally Posted by alpinecrick

. . . So happened I bought extra standard diameter mandrels in 270. While waiting for undersize mandrels to arrive I sanded down one of the spare 270 mandrels. More than I intended........ended up at .2727 according to my mic. What the heck, I'll give it a try. I was already making straight ammo with my old method, but the tight necks (which I like for a hunting round anyway) produced more velocity and better accuracy.


Every single LCD die I've bought has had too little bullet tension for my taste, and like you, some moved just with finger pressure.

I'm going to be going thru the same exercise with a .270 Gay LCD here shortly. As you probably know, that .2727" diameter mandrel won't give .004" of neck tension due to the brass springback after you release the radial force on the collet. Did you actually measure the neck tension that it gave you?

When I start sanding one down (mandrel chucked in an electric drill and using sandpaper) I'm constantly checking the neck tension, looking for 0.003 - 0.035" (or so) of neck tension. I'm curious about other folks approach to this.

Re: Neck tension, crimping and pressure/velocity? [Re: Rodell] #14209575 10/17/19
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Dave_Skinner Offline
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You've got to have the fire burning before the bullet starts to move. You have a magnum, with a mighty primer, and there's a chance that some bullets move with primer firing, that's "upset" and a "variable" that hurts beyond the speed loss. You are on the right track in your thinking.

Mandrel diameter has an effect on your pull, if you have only 2 thousandths, that's on the low end for everyone except benchrest, and THOSE guys put their bullets right against the riflling. Keep in mind that just one thousandth in neck wall thickness is HALF of your total, or TWICE your total "pull." That's why the BR people turn necks.

Further, you've got a kicker, so I have tio wonder if your loads in the magazine are shifting enough to mess stuff up, too.

Either get a bushing necker and the bushings that give you four thousandth's (or so) or buy a couple of extra balls and spin them down to the point where you've got a firm, and CONSISTENT pull. Also keep in mind that more tension is more forgiving than loose necks up to a point.

You should be able to feel pull as you seat, the amount of force, especially if you use your fingertips on the loading lever handle. That has been sufficient for me, if something feels wrong, it usually is.


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Re: Neck tension, crimping and pressure/velocity? [Re: Rodell] #14213382 10/19/19
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Tejano Offline
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At what point is neck tension too much? Certainly if bullets or the case is distorted but before this is their a point it is counterproductive? I usually only do finger tight, about .001, and then jump to .004 and stop there. Am I leaving potential accuracy on the table by not doing increments?

I am cavalier about primers too usually just testing a standard and a magnum only for each load.


"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
Bravo

Re: Neck tension, crimping and pressure/velocity? [Re: Rodell] #14213404 10/19/19
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Mule Deer Offline
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Rodell,

I suspect your AMP annealing was too much for that particular batch of cases, making the necks too soft. I suspect this because I played with an AMP extensively a couple years ago, with generally very good results--except with one particular "brand" of .30-06 cases. I looked them up in the list the AMP people provide, and used the recommended setting. The same load that rifle had shot very well for years results in lousy accuracy.

I contacted AMP and they weren't partocularly helpful, so I figured it out on my own--I think. That particular batch of brass was around a decade old, and the company that sold it was not making their own brass. Instead they were buying brass from some factory, headstamped with their brand. I suspect the batch that AMP listed was from a later batch, which may have even been made by another company--though I have also seen brass made by the same company vary considerably.

Anyway, after that bad first firing, the brass work-hardened up just enough to go back to work very well again. Many factors can affect bullet "pull," and too-soft annealing is one.


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John Steinbeck

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