I'm posting this both here on the varmint forum and then on the reloading forum, for those who might be interested...

This is for those who are interested.. not an invitation for debate and argumnent with those who don't think Blue Dot should be used in varmint cartridges.. we've hashed that over so many times, it is ridiculous...

per request, I went out and chrono'ed these.

Temp: 108 degrees
Rifle: Model 70 Varmint 26 inch barrel.
Primers: Rem 9 1/2
Cases Used: Winchester

Load 1: 18.5 grains of Blue Dot
a). 40 grain Sierra HP: 3558 fps, 3559 fps
b). 36 grain Barnes Varmint Grenade: 3680 fps. 3700 fps
c). 30 grains Berger Varmint: 3515 fps, and 3515 fps

Load 2: 19 grains of Blue Dot
a). 40 grain Sierra HP: 3619 fps, 3627 fps

Load 3: 19.5 grains of Blue Dot:
a). 40 grains Sierra HP: 3660 fps, & 3675 fps

Load 4: 20 grains of Blue Dot
a). 40 grain Sierra HP: 3668 fps & 3715 fps...

What I left out of the above was the results out of an inital cold barrel. These were fired during 2 sessions. Both times the temp was in the the 108 degrees range.

Both loads were with a 40 grain Sierra HP.. With an 18.5 grains of Blue Dot charge, the intial MV was 3918 fps.. and with a charge of 19 grains of Blue Dot the inital MMV was 3957 fps.

the second shots were having MV in the range of the 3550 fps range.for the 18.5 grains and 3600 fps for the charge of 19 grains of Blue Dot. This presents an interesting scenario. Is blue dot NOT temp sensitive, or considering the results, does its velocity actually speed up as the chamber is cooler and then slows down as the chamber heats up?

cheers
Seafire

quote:

Originally posted by seafire2:
19 grains of Blue Dot the inital MMV was 3957 fps.

The results you got (all of it) was totally interesting. The initial 3957 fps says that the energy contribution to bullet velocity from 19gr. of Blue Dot was equivalent to 41.5gr. of H414. That is amazing !! roger

Roger,

I wasn't trying to equal H 414 velocities with Blue Dot, all I was showing is where the velocity parameters were with that powder and those bullet weights....

all I am trying to figure out is why the first bullet is giving me 3900 fps plus and then settling down to 350 fps less on the second and subsequent shots..

this is not with a clean barrel.. only a cold barrel...

this is also noted only so far on days like this one when the temp is 108 degrees....

That makes no sense at all,
If anything,you should see a decrease with the
cold bbl shot.
How far are you from the 1st sensor?
I take it you have plenty of chrono experience, and aren't measuring muzzle blast?
Sounds like an anomaly,
i'd retest.

17 Rem,

you are exactly right.. it is an anomoly.. that is why I am reporting it... to open it up to maybe other forum members have observed similar anomolies in other stuff...

I did go out and retest it.. at first opportunity... twice even.. got the same results...

It should be just the opposite.. and I made sure it was with a dirty barrel.. not a clean one...so it couldn't be blamed on a lubed barrel...

all I can figure out is the first shot is out of a cold tight chamber... the first round heats it up enough and the high temps.. 105 to 108 that we have been having... expands the chamber enough to dramatically lower the pressure...

I'd even thought that maybe on the first one I had accidently put more of a charge in there, or a freak but potential problem I have seen before,is that some tumbling media was left stuck in a case and that plus the powder,will result in a higher pressure...

I am sure there is an explanation, but right now it is not presenting itself...

Firing one round, or even dozens of rounds, is not going to appreciably expand anything.You may see
.0002/.0003" if your lucky,that's not going to change chamber pressure for squat.
Must be something else quite strange occuring.

Well with process of elimination, the reason will eventually show up...

might give the ballistics guys over at Nosler a call tomorrow.. maybe they can shed some insight onto it..

funky huh?

I have seen this first shot the fastest condition quite often but just shined it on. Some were over 100 fps so this did not surprise me. The amount of energy transformed into bullet velocity from a light charge of powder was a shocker.

I doubt there is enough gas generated or pressure wave from the Blue Dot to give an erratic gas chrono reading.

Could be wrong but ponder as you might the """proff derived answer""" to this phenomina may be hard to come by. roger