380 chrono much slower than I would like

[Handline]

i bought a chronograph and this spring shot my 380 through it. My last reading was 375fps.

Fast forward to a week ago when I was helping a friend who was tuning his 380. We chrono his bone stock bow with 400 grain arrow and tips at 350+- fps. We also checked DB level on it then added silencing items and rechecked to see what made a difference. Any way we took out 3db and he lost 4-5 fps by what we did.

At the same time when we did his bow I shot mine through the chrono it read 350+-fps. I figured it might be somthing with the chrono. So I shot my micro it shot 334fps and a 330 matrix that went 328fps with in minutes of our 380 matrix

For the fun of it I had my buddy shot a 350 grain arrow and tip and he got low 360s fps.

Today I shot my bow again. 351fps changed strings and got 355fps with a 350 grain arrow.

The micro and 330 matrix shot very well speed wise. What am I missing with the 380s. I mean one was factory not a year old and my bow has air brakes a boo string with whiskers shooting 350 grain arrow and tips. I can't imagion the bows being off the mark that much. If they shot 370fps I would not care but 350fps kinda stinks.

[GrassyKnoll]

Welcome aboard....

So you are saying that your 380 was shooting 375 when you first got the chrono right?

At that same time did your 380 have the air brakes and Boo string with puffs installed when you first achieved the 375?

There are a few things to think about here.

1. where was your brace height at when you initially achieved the 375 fps vs. where it was when you shot the 350 fps?
2. was your chrono level when you shot it?
3. what brand chrono is it?
4. what is the total completed arrow weight you are shooting both times when A: you got 375 fps and B: 350 fps
5. do you use a light it for the chrono and if so was it on during all the test shots including when you got that 375?

These are just a few questions that come to mind.. There are more experienced guys here than me that will help you out too..

[Normous]

I would send the chrono back to be recalibrated. In the spring did you record the temperature, barometric pressure, cloud cover, lighting, etc? Was it used in the exact same conditions recently? Was is stored in a damp basement maybe? Dropped perhaps? The least expensive one are known to be finicky, especially it used under different environmental conditions.

[vixenmaster]

Chrony's tend to burst many ppl's bubbles On the real life side are you happy wid the accuracy ? Its been great fer a yr, don't let that change fer you. I have owned n shot my Vixen's that got 218 fps wid 628gr arrows n was jus tickled wid the accuray n killed many a tick toter

[Handline]

My arrow weight is right at 350 grains from my scale. Has been since day one.

chrono was as level as a table, which i didnt check but nothing leads me to think that it is terrible out of whack. nothing rolls off of it.

this spring when i shot it was about 60 degrees but i was inside using an incandestent light, the other day i was in natural sun light. I did expect variance between the two but 8% seems drastic for a light source change

Main reason i am questioning is because the stone stock 380 shot only slightly faster (which i figured it would) than mine and both were at 350fps mark.

I did not have air brakes on at the spring shoot, but I did have my boo whisker string. When we put the air brakes on my buddies 380 last week we did chrono runs between every item we added and the air brakes lost .5-1 fps, this was with 6 shots through the chrono.

accuracy has been and still is great, no complaints. So please do not take my question as a bashing to the bow, i wouldnt be pooring the money i have in that i did if i didnt like it. In my family alone we probably have had 6 excaliburs. I am questions if my chrono is messed up or im overlooking somthing with the bow. It gets me because the micro and 330 matrix shot at what i expected.

[GrassyKnoll]

Another question...lol

From when the chrono read 375 and your scope setting back then and now as it reads 350, has your scope setting changed as far as yardages and POI? Because if they have not, then the chrono is off.

[Handline]

Also brace heights was maintained from 1-2 string widths from reds all the time. I have owned the bow for 2.5 years

[wildcatter]

I would guess the problem lies in the distance you have the chono from the bow. The only thing I can imagine that makes sense is the Micro and 330 are dead nuts on what I would think is correct!! I have seen others do this, and blame the wrong culprit.

They both have a shorter stroke than the 380's and I believe you are hitting the first sky screen before the arrow clears the string???

I would back up another foot and try it again. Level is the wrong term, the chronograph should be laced parallel to the arrow flight, if your target is being shot with bow pointing 20* down, the chronograph should be also. I think this close but, I would rule out any problem with the chronograph since the 330 and Micro are reading near perfect!

I have been doing this for over 30 years, and temp, humidity, pressure wont make 5 fps difference in any extreme with any bow, air rifle, I have ever used. Now a firearm may as burning rates and batch to batch ammo changes!! The changes on that bow won't make 20 fps difference, I believe this is a case of user error, not the chronograph as they don't change with different bows.

[Handline]

The chrono was set at 40" in front of the arrow tip on the 380 when bow was cocked. This set up included a lead sled for steadiness while shooting, I wanted this testing to be repeatable. So the micro and 330 would be slightly further away because they are shorter.

I would say parallel was close but not perfect. Defiantly not extremely out of parallel.

It just might be the way it is. But it doesn't seem right that both 380s were both at 350ish speed

[wildcatter]

One other thing I always do is shoot 12 shots if I am going to use the reading as a recorded speed. I then throw out the lowest and highest speeds and average the other ten shots, this is what I go by for my speed reference for any setup.

I never shoot just one shot and call it fact?? Just the way I record my results.
Remember the chronograph has to be at least 2' in front of your limbs to the first sky screen.

[wildcatter]

The chrono was set at 40" in front of the arrow tip on the 380 when bow was cocked. This set up included a lead sled for steadiness while shooting, I wanted this testing to be repeatable. So the micro and 330 would be slightly further away because they are shorter.

I would say parallel was close but not perfect. Defiantly not extremely out of parallel.

It just might be the way it is. But it doesn't seem right that both 380s were both at 350ish speed

I thought you said yours was shooting a 350 grain arrow and shooting 350 ish??? if so with a heavier string air brakes, silencers attached and any other this is not normal speed, but if you are now saying both bows having this done to them and shooting 400 grain arrows,,,, I would say the reading is close!!

no way you will get 370 with a 40 strand boo string, (what I shoot) and a 400 grain arrow with nothing else done to a stock bow. I think I am missing something here?

[Handline]

My bow with all the add ins was shooting 350fps with a 350 grain bolt including tip.

The other 380 shot 350 fps with a 400 grain bolt including tip. When he shot the 350 grain bolt his increased to low 360 fps. His bow was at that time 100% factory.

When we added a Flemish string he lost 4-5fps. When we added air brakes he lost .5-1 fps. I would use the logic that my air brake also didn't change bolt speed significantly.

[wildcatter]

I understand your concern now, and yes that is well low of my results and not at all good with the 350 grain arrow. But I don't think the chronograph is the problem with the results of the other two bows, maybe find another chronograph, stop by your local bow shop they should have one set up and see what theirs says for a comparison??? Good Luck,,,,,

[DeathMerchant]

This thread was a great help for me when trying to figure out what was going on with my crossbow speeds. I have two large covered decks on my place, one facing east, the other facing west. I used the east facing one for my first speed checks and using a BE executioner with 125g tip (total 409.6gr), I got an average of 225 from my wife's Vixen II and a very shocking 315 from my Matrix 380. I knew there was something wrong. Reading this thread made me think about distances between crossbow, my Chrony Master Alpha, lighting, etc. I had the Chrony way too close to the bow and the lighting on the east deck in the afternoon was much too low to get accurate readings. So I moved to the west facing deck and placed the Chrony directly under the skylight and placed the crossbow 48" from the Chrony. This time, using the same 409.6 gr bolt, I got the results I was expecting with an average of 259 from the Vixen II and 365 from the Matrix 380. The Vixen is stock and the matrix has dissapator bars on it, everything else including string is stock with about 3/16 off pad BH. Thanks for the information.

[wildcatter]

Good to hear,,, sounds much better, glad you got it worked out. We all learned these things the same way, so you have plenty here that been there done that,,, even when it's wrong, it's the only way I ever learned to do anything right.....

Good luck with two very dependable bows!!