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Fla mac
05-13-2009, 09:50 AM
Ok here is my question. If you load a round into the lands does the neck tension have any effect on the velocity of the projectile? I would think by the time the bullet starts to move the case and the neck has expanded so the tension on the bullet would have no effect on the velocity. Tell me if I am right or wrong. I know the OAL has an effect in the case pressure.
Fla mac

Louis Boyd
05-13-2009, 03:46 PM
I would expect that it would have little effect in the situation you describe. It would be simple to test by loading a few rounds with loose and tight tension and shooting them over a chronograph.

Joe S
05-14-2009, 01:01 PM
Hmmmm, The bullet having a bit of freebore allows it to engrave with the rifleing easier which reduces pressure some.

Added case volume will lower pressure

The bullet up against the lands will require more pressure to engrave the bullet and get moving.

Neck tension from what I`ve been lead to believe doesn`t take much pressure to overcome. I "think" brass starts to expand at ~600psi

Velocity is the result of pressure on the bullet over time.

I`d suspect the added pressure required to overcome the rifleing would cause the bullet to under go a higher psi during the beginning of its travel and possibly show a higher velocity. I don`t know if the added pressure would be enough to show a gain though or if it would be lost to other conditions and fall within the extreem spread of the load.

Short answer: I don`t know:D

alinwa
05-14-2009, 01:08 PM
Having fired tens of thousands of rounds over the chronograph I've never found a correlation between neck tension and velocity.

I've also never crimped my necks.

al

Randy J.
05-14-2009, 01:18 PM
How far into the lands affects the pressure curve which may in turn affect velocity. As neck tension is important in maintaining how far into the lands you want the bullet to be ((too weak the bullet is pushed back into the case (unless it is a compressed load) and you won't be into the lands much as you think you are)), I would say yes it affects velocity but only slightly. A tighter neck tension may also assist in preventing a canted bullet in the bore so tension affects accuracy in some systems. Whether it affects velocity can only be determined over a chronograph. If you have one, try it and get back to us. Randy J.

Donald
05-14-2009, 03:48 PM
I was testing some load in my 6ppc the other day over a chrono. Basically jammed hard into the lands and just off the lands. Five shots each. There was almost no difference in the velocity. Something like average of 3325 jammed and 3318 average off the lands. Almost in each case, 3 different loads those off the lands had much more verticle than those jammed.