Velocity/pressure vs. neck tension?

2

280rem

Guest
Is it normal for velocity to go down when neck tension is increased? I load into the lands and I loaded some rounds that had .001 more neck tension then what I normally use. I expected more pressure with the greater tension but I lost about 60 fps. Is this normal? I could not detect anymore pressure than in my other loads. The only difference in the 2 loads was neck tension. Everything else was the same. Thanks, John.
 
My suggestion is that something other than nt was the cause of the velocity loss. IME velocity is not really affected by neck tension. My proposal is that you loaded the two groups of cartridges on different days and that your throwing technique changed a little....... this is just a SWAG :)

If you're weighing your charges to the kernel then you can start to see changes resulting from seating depth but I've never noticed a measureable change from nt.

al
 
Thanks, Al. I said the loaded rounds were the same but in retrospect, I started a new box of bullets(same kind) on the rounds that turned in a lower velocity. Both groups of loads were loaded on different days but I use a balance beam. Could be a slight difference in setting up the scale maybe? John.
 
I've chronographed loads that should have produced very similar results, cases, bullets, primers, and powder all from the same lots or even same boxes/cannisters, but loaded on different days or even the same day and fired on different days that produced different velocities. Not just slightly different, but 50 or 60 fps like was noted. Assuming that the average MV was ~2800 fps a 60 fps variation is ~2.1%. Temperature variations could cause that much difference, or maybe it's gremlins, bore condition, or? Beats me, but it's nothing to worry about IMHO.
 
Statistically speaking

When testing a "load" shooting it once does not give accurate results. Statistic teaches us that you need to test several times under several conditions to be able to reach an accurate (no pun intended) conclusion. Too often I think one sample at the range tested once is used to set data for the gun. As once I mean never checked again or at least several times to comfirm results.
 
This load was developed for a live varmint gun about 4 years ago and the one thing that it has been is consistent. I have used several boxes of bullets, probably 3 different lot #'s of powder and the same carton of primers. I can count on only about 20-25 fps difference over the last 4 years according to my notes. The change I made was going from a Lee collett die to a custom FL bushing die. The bushing I got sizes the case down about .001 smaller than the Lee. I figured on a little higher pressure but if it's there, I can't detect it. Oh well, not really a big deal as accuracy has stayed about the same but I am a little puzzeled. Thanks for the responses. John.
 
Any pressure or velocity variation caused by .001" reduction in neck tension from one batch of cases to another probably gets lost in the noise of other variables. Unless so loose that primer force can move the bullet prior to powder burn, or unless the bullet is cold welded or sealed to the case neck, I doubt that neck tension is a factor in pressures. Most likely, due to chamber pressure being much higher than that required to forge brass, the neck of the case opens up to fit the chamber wall prior to any bullet movement, so neck tension is moot.

Scott
 
Lynn, with all due respect to the other responses, that is absolutley the most plausible one yet. Makes perfect sense to me. Thanks, John.
 
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