Could be digital scale issue. ALWAYS weigh an item of known weight on your scale to check calibration/accuracy before each loading session. Takes one second and eliminates one variable in the puzzle...
Dramatic drop in velocity with exact same components - strange! Ever seen this??
- Thread starter nimrod_gn
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before you go through a long list of eliminating all the variables I take your chrono and a friends and shoot through both for comparison or shoot a friends reloads of which your friend is confident on what velocities should be and shoot through your chrono and see.
I second the new brass vs. once fired aspect.
Other things I would check.
Get a borescope and look at your barrel. Shooting 3400 to 3500 velocities w copper bullets means you might need a good copper cleaning w Boretech CU2+ or Montana Extreme in addition to carbon cleaning sequentially as it layers up, carbon, copper, carbon, copper, etc.
Check your scales. N570 is very notorious as being a chunky monkey powder and does not always meter well for me. Anytime I throw N570, I weigh it on both a balance and an electronic scale until they both agree its exact.
Was there any difference in your neck tension or crimp possibly?
Did you lube necks or bullets w graphite or other dry lube one time and not the next when seating?
How do you measure seating?
With caliper or w adjustable seating die?
Though you state temperature was not a factor, did you cool the barrel between shots any differently?
Ammo can really be affected by sitting in a hot chamber vs. a cooled one.
Good luck on solving the mystery.
Other things I would check.
Get a borescope and look at your barrel. Shooting 3400 to 3500 velocities w copper bullets means you might need a good copper cleaning w Boretech CU2+ or Montana Extreme in addition to carbon cleaning sequentially as it layers up, carbon, copper, carbon, copper, etc.
Check your scales. N570 is very notorious as being a chunky monkey powder and does not always meter well for me. Anytime I throw N570, I weigh it on both a balance and an electronic scale until they both agree its exact.
Was there any difference in your neck tension or crimp possibly?
Did you lube necks or bullets w graphite or other dry lube one time and not the next when seating?
How do you measure seating?
With caliper or w adjustable seating die?
Though you state temperature was not a factor, did you cool the barrel between shots any differently?
Ammo can really be affected by sitting in a hot chamber vs. a cooled one.
Good luck on solving the mystery.
JKPhoto
Active Member
I think that the only things that would result in this level of change would be the fouling issue and the weight of the charge. One or the other. Just my $0.02
muleystalker
Well-Known Member
While shooting the first session were you placing a round in a heated barrel and then taking your time to shoot, it's real easy to cook a round with a hot barrel. While shooting F-Class where we are shooting 20 rounds at a time you can experience this if you camber a round in a hot barrel and then try to wait for a wind condition.
Are you using a beam scale, if so it's real easy to bump one of the weights one notch and not realize it.
Are you using a beam scale, if so it's real easy to bump one of the weights one notch and not realize it.
Paulstarr
Well-Known Member
Butterbean has the right idea, do another batch and see what happens, sometimes chrono's fib the megnetospeed fits to the barrel and with most rifles has an effect on resonance.I use one and although I trust the velocities but in most cases it can have effect on the P.O.I.I take it the primers were for the same batch and the ambient temperature was around the same, if so,Mystery to solve.
And before the OP has a chance to verify here we are
Carbon Ring, Y'all forgot to tell him to check for a carbon ring, Break out the bore scope, Or wait, Maybe He didn't use an AMP annealer, I bet that's what it is, Yep I'm sure that's the problem
Carbon Ring, Y'all forgot to tell him to check for a carbon ring, Break out the bore scope, Or wait, Maybe He didn't use an AMP annealer, I bet that's what it is, Yep I'm sure that's the problem
You Funny… Hand held drill and socket should do it! LOL…
Doom2
Well-Known Member
Got to be humidity. That powder sucked up some moisture!
nimrod_gn
Well-Known Member
Station pressure almost identical. Air temperature and temperature of ammo almost identical. Case length, neck tension same. I even weigh the brass. Humidity very similar. Use digital scale that I calibrate before each use. All of this is still leading me to believe it must have been something up with the chrony.
Jer2170
Member
Absolutely love it B.B. you the man!!!
You can get scale calibration weights online from several sources. They can be used as a "sanity check" for the scale after calibration.
Doom2
Well-Known Member
I was kidding about the humidity. Barometric pressure has almost no effect on chronograph readings, especially for the MS. For optical chronographs its on the order of 1/2 fps on a 55gr 223 round @15 ft from the muzzle for 1/2" mercury. For heavier bullets its less.
