why am i having abnormally low velocity?

[Blazer-6]

I shoot an HK USP tactical 40 in IPSC Major - 4.9" polygonal barrel. My chrono readings don't look right at all. I failed in different chronos with loads that pass with friends' para ords. I loaded 1.150" w/ 4.8 N320 and 180 gr. moly and got only 919-920 FPS (targeting 950 fps for 170PF). quickload already calls that overpressure.

Then, i loaded JHPs for carry and worked up my load from the VV N340 start load from their manual. I continued to work up from the max published load of 6.1 gr because the primers were still very healthy and i'm loading to a non standard 1.150" anyway. I got to 7.5 grains before any sign of primer flattening and cratering! i made some 7.2 grain loads and the primers were quite healthy, chronoed them @ 1100 FPS. quickload already places that load at 1290 fps and something like 60000+ psi pressure. im getting 1100 fps and normal primers with a 7.2 load! VV limit is at 6.1, sierra at 6.3 grains!

what is this? Is my barrel leaking or something?

[CocoBolo]

Crono's can vary so try another crono. On the loading side make sure that you are not over crimping, too much crimp can knock off 60 fps. Your load isn't very long I load them 1.185 in my STI with 4.5gr I get 172pf.

You should not be using reloads for carry, speak with your attorney about this.

[Glockman1000]

That is pretty weird, try Coco's suggestion of using another chrono, other than that maybe it's the different rifling used between the Para & your HK.

CocoBolo, factory ammo is hella expensive in the PI, as is owning a gun & competing in IPSC for that matter. If I remember correctly, you have to have a permit to own a loading press. Last time I was there, .45 brass sold for $1.25 a piece US. VV powder is very reasonable though. They sure can throw a match though, you will actually get every piece of brass that you fired out of your gun. They can have a field course ready for another shooter in 30 seconds or less. You will always have some one to attend to you along with awesome Philippine cuisine & let's just say that after the shooting day is done, the nightlife is just well, very interesting.

[Dennis (CT)]

You may also want to check the height the bullet is passing over the chrono sensors.

If it is too high (6"-8"), you will get slower readings, I have experienced this. From a solid rest, while aiming no more than 3" to 4" over the sensors, try some of your current left over, slower rounds . You will see a big difference in speed. Don't know why, but closer to the sensors seem to give more accurate readings.

Good Luck.

[Blazer-6]

factory ammo is sure expensive here, the handloads i make are from new shells. im military btw. the matches here are frequent, and convinient, the night life - phenomenal. guns cost 200-250%

[Glockman1000]

The PPSA have always hosted excellent matches. Never been to Mindanao, only matches in Luzon. My friend's family is inviting me over next time to stay in Bohol, Cebu for a few days, just planning right now. Their little girl calls me Tito Troy!

[Justsomeguy]

You also might consider where the sun is when you take your chrono readings. I have gotten weird results when the sun shines into the sensors. I solved this by taping a standard IPSC target or some other piece of cardboard over the sensor baffles/reflectors when the sun is shining into the sensors. That is... you gotta shade those sensors!

[RePete]

I've run 4.6gr/N320 w/180gr CMJ and got 978fps (PF 176) from my STI Trojan but only got 940fps (PF 169) from my Glock 35.

The difference is the polygonal rifling, which the HK has too.

I think Glockman1000 hit it for you.

[leas327]

You also might consider where the sun is when you take your chrono readings. I have gotten weird results when the sun shines into the sensors. I solved this by taping a standard IPSC target or some other piece of cardboard over the sensor baffles/reflectors when the sun is shining into the sensors. That is... you gotta shade those sensors!

I have also had issues with the position of my chrono relative to the sun. If I try to chrono too late in the day it will give me false readings. I try to chrono between 2-6 p.m. with the sun directly over the sensors. If the sun is low and angling in, my chrono will read fast.

Also put a fresh set of batteries in or recharge it. Low Bat will cause it to do funky stuff.

These two things and rereading the instrucions have turned my chrono from a waste of money to a valuable tool. Mine is a Alpha Chrony I think. It gets a bad rap but my ammo chrono'd 168-170 multiple times through it and chrono'd 168 at the Ohio Sectional and 169 at Indiana last week. I will bet there was 25 degrees difference between the temperatures of those matches.

ETA for spelling...it sucks being dumb...

Edited August 16, 2012 by leas327

[jmbaccolyte]

You also might consider where the sun is when you take your chrono readings. I have gotten weird results when the sun shines into the sensors. I solved this by taping a standard IPSC target or some other piece of cardboard over the sensor baffles/reflectors when the sun is shining into the sensors. That is... you gotta shade those sensors!

I have also had issues with the position of my chrono relative to the sun. If I try to chrono too late in the day it will give me false readings. I try to chrono between 2-6 p.m. with the sun directly over the sensors. If the sun is low and angling in, my chrono will read fast.

Also put a fresh set of batteries in or recharge it. Low Bat will cause it to do funky stuff.

These two things and rereading the instrucions have turned my chrono from a waste of money to a valuable tool. Mine is a Alpha Chrony I think. It gets a bad rap but my ammo chrono'd 168-170 multiple times through it and chrono'd 168 at the Ohio Sectional and 169 at Indiana last week. I will bet there was 25 degrees difference between the temperatures of those matches.

ETA for spelling...it sucks being dumb...

My son is very smart, but dyslexic. He can't spell well either.

Edited August 19, 2012 by jmbaccolyte