Chrony help please...

[shooter3048]

I'm a little new at this reloading thing so bear with me. This morning I loaded some 40cal, 175 SWC with Power Pistol and here are the results from the range: 5.8 grns with oal of 1100-1106 that averaged 1038 fps for ten shots. The Lyman Pistol manual I have says for the 175 SWC bullet at 5.8grns, oal of 1100 should produce 873 fps with that load. Now I have for some reason, that I'm not even sure how to fix, is the bullets are 1100 oal at the start of a session and then some range up to 1106 when the Dillon 550 is fully loaded with shells (all stages occupied). I've looked at the bullet seating die and there is no buildup of lead. So what is the cause of the variance in oals? Is this normal? Why is my bullets chroning at 1038 instead of 873? :???:Any knowledge on the subject would be greatly appreciated.

shooter3048

[freedom475]

A lot of the manuals use a standard "pressure barrel" not a real gun to obtain there velocity info. Also if you'er using a cast boolit your velocities will be higher than those listed if the data was obtained from Jacketed boolits as the friction from the copper j" will slow the boolit considerably.

The chrono is one of the best tools a handloader can have. You can begin working up loads and watch the Pressure spike happen especially with fast pistol powders. A whole gr. increase in powder might only give a few fps increase but the next .2 will give 100fps as the powder reaches its max working pressure.

Also watch those manuals close, I used a starting load from Hornady to ruin a CZ 10mm the load was so hot that it blew both grip panels off and cut up my hand and speckled my face with metal shavings. It also destroyed the magazine as all the presssure went out the bottom. Another manual (Hornady I think) lists a 35rem with a 220gr at 3000fps! I don't have a 35rem but this sure dosen't sound right/safe to me. My 338 won't even do this velocity with 220gr.

Hope this helps

[MtGun44]

Three possibilities.

1- Lead boolits go faster than j-word bullets due to lower friction.
2- you have a tight chamber - this is not at all uncommon. Glocks are reputed to
have very loose chambers, so if yours is something else it may be tighter which
will easily make this much difference. I have seen 125 fps difference with .45ACP
in different bbls, same length bbls, just tight match chambers in the fast ones.
3 - dangerous - possibly the boolits are being pushed into the case due to
inadequate neck tension and/or taper crimp which will push up the pressures.

Rumor has it that pushed in boolits is what is blowing up Glocks. I have no idea
if this is correct, but the .40 is a high pressure round and reduced powder
space does dramatically increase pressures, so the theory passes the initial
reality checks.

Let a few rounds chamber during firing normally and then open the action and
carefully eject to see if the LOA is reduced. This can be very dangerous if it is
happening. Be safe, you shouldn't be able to push the boolit into the case
pushing as hard as you can against a hard surface.

Bill

[dubber123]

Another thought is, if you have a Chrony, (the ones that fold open), and it's not fully opened up, the velocities will read high. Just changing brands of brass can have a huge affect on velocity. For instance, when switching from Federal brass to Remington brass, in my .45 Colt, I have to increase the powder charge a full 1-1/2 grains. The Federal brass is much heavier, (in my lots of it anyways), and equal powder charges go much faster out of the Federal casings. I have heard of Mag primers substituited for standards producing a big velocity jump. At any rate, enjoy the extra speed, most of my guns shoot way slower than the manuals say!

[runfiverun]

as for your oal changing check your sizing die hitting your shell plate
and make sure your shell plate is just loose enough to turn freely to keep it from tilting back and forth.

have learned to check it right off when i set up my 550's

runfiverun

[NSP64]

If your glock has polygonal rifling, that will allow faster loads. My Desert eagle in .357 shot faster (it has poly rifling). The rounds in the mag may be hitting front of mag during recoil, or being shoved in by the feed ramp during cycling.

[twidget]

I had the same problem shortly after getting my chronograph. It turned out to be lighting conditions. If the sun is low and behind you on a clear day it can cause the shadow of the muzzle blast to trigger the skyscreens. It happens only with subsonic boolits and gives a reading near the speed of sound (about 1100 fps). Using the diffusers over the skyscreens helps as does shooting on overcast days. Another cure is to shoot through a hole in a sheet of cardboard in front of your shooting point. I live at 48 degrees north and it happened to me on a sunny day in January when the sun is low even at noon.

[Lloyd Smale]

Its about normal for a chronograph to be a 100fps off. One day we tested 4 differnt chronos of differnt makes and used a ohler as a standard as it has proven to run pretty close to what it should. The Chrony was the farthest off. It was a consistant 125 fps faster reading then the ohler. The owner sent it back and had it reclalibrated. I never consider the velocity given by any chrongraph as written in stone. theres just to many variables and they can vary 50fps with the same load on a differnt day. Angle of the sun, temp and other things effect them. What there good for is getting a ball park idea of what your load is doing as to fps and standard deivation and are about the best tool if your working up loads at the top end of the scale to show pressure problems. But there far from a truely precise instument.

[Bass Ackward]

Well, if a chronograph IS going to be off, I would certainly want it to be high for the safety factor.