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Tac15i accuracy and consistancy problems

 
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  #57  
Old 01-16-2012, 12:21 AM
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Join Date: Dec 2010
Posts: 391
Re: Tac15i accuracy and consistancy problems

Hi Okiebowie,
The issue of arrows hitting higher at higher elevations above sea level is almost always due to the fact that as one gets further above sea level air becomes thinner, thus increasing the ambient pressure within an arrows shaft. This increase in pressure causes an arrow to fly flatter for a much longer distance before it begins to drop.

I've watched archers out in the western U.S., in the Rocky Mountain States easily taking shots at large Jack Rabbits at 90 and 100 yards. because their arrows would carry flat so much farther than they would at lower elevations.

It's somewhat similar to the extra arrow elevation that we get during the hot summer months, but even more so. Heat will also account for additional pressure build up within an arrow shaft, so this causes a raise in impact points from when the crossbow or compound bow was initially sighted in at sea level or during cooler temperatures.

Xbow755
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  #58  
Old 01-16-2012, 07:38 AM
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Join Date: Jan 2011
Posts: 55
Re: Tac15i accuracy and consistancy problems

PURVIS6 -

I've lived your pain. Last fall I had the same thing happen to me. The consistancy with the Tac-15i was not there !! I cannot place an exact fix that happened, but I am finally getting solid 2" groups to 60yds and 3-4" groups at 90yds. There was a time when I was getting tight groups, but out of 6 arrows I would have 2 separate groups 6" apart. I think this was from a little extra pull on the string. One of the people I spoke to recommended that when you are cocking your Tac to back off on the crank handle about 1/8 of a turn after the carrier locks into place. You must do this with the clicker button depressed to allow the spool to go backwards. (CAUTION: Be sure you have a good hold on the cocking handle before you do this just in case the carrier pops out). I have not had the carrier pop out on me, but I was careless once while cocking and had the cocking handle slip out of my hand and when it backspun it busted up the back of my hand pretty good. After I started doing this, I have not had the separate groups !!

I also had one limb separate. PSE replace all limbs and since it has been shooting very nice.

If you look at some of my other posts here, I used to have a clunking sound while cocking and that was caused by the string not moving correctly over the spool when cocking. To mitigate this, I pull the string to the left when i start cocking it.(for the 1st 2-3 turns of the crank handle)

WildWillie

Last edited by WildWillie; 01-16-2012 at 08:33 AM.
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  #59  
Old 01-16-2012, 08:16 AM
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Join Date: Aug 2010
Posts: 21
Re: Tac15i accuracy and consistancy problems

Dear purvis6
i know your frustration.i have been struggling with mine for a year
and a half.i have had 3 different bows and lost 2 hunting seasons.
I am sending it back again today.i talked to the engineers again and it is not us,its the bow.the problems are exactly the same on every bow thats having problems. Ill keep you posted,i know how aggravating it is.
Ron
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  #60  
Old 01-16-2012, 01:58 PM
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Join Date: Aug 2010
Posts: 154
Re: Tac15i accuracy and consistancy problems

Quote:
Originally Posted by jon.henry755 View Post
The issue of arrows hitting higher at higher elevations above sea level is almost always due to the fact that as one gets further above sea level air becomes thinner, thus increasing the ambient pressure within an arrows shaft. This increase in pressure causes an arrow to fly flatter for a much longer distance before it begins to drop.
I can assure you that arrows hitting higher at higher elevations has nothing to do with the "ambient pressure within an arrows shaft". If that were the case, then we would all be pressurizing our arrow shafts from compressed air bottles. Along with having to replace O-ring seals on the point & knock ends. This would of course lead to over-pressure, super-pressure, hyper-pressure arrows, and tweakers in E.R.s from exploding shafts.

The reason arrows (or bullets) fly further at high altitudes vs. sea-level has to do with the air being thinner. Thinner air, less resistance, slower decline in arrow's velocity.
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  #61  
Old 01-16-2012, 02:47 PM
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Join Date: Dec 2010
Posts: 391
Re: Tac15i accuracy and consistancy problems

I knew the thinner air played a big role in arrows flying flatter for a longer distance at higher elevations, but didn't realize internal pressure wasn't the main factor. Your explanation makes logical sense, so I'll have to remember it.

I do know that pressure inside the hollow of an arrows shaft changes with the heat of a day an will account for elevation differences on the face of a target, especially during the summer months. In competition we often would need to make adjustments for these temperature variations between 7:00 AM and noon because of the 20 degree shift in temperature.

Typically, your arrows are sealed, just not using o-rings. Your seal comes from the glue holding your inserts in the front of a shaft and the glue holding your nocks in the rear. This is a much more prevalent condition with aluminum arrows than with carbon arrows, but it can and does occur with carbon as well.

Regards,

Jon
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  #62  
Old 01-18-2012, 12:22 AM
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Join Date: Aug 2010
Posts: 154
Re: Tac15i accuracy and consistancy problems

Quote:
Originally Posted by jon.henry755 View Post
I do know that pressure inside the hollow of an arrows shaft changes with the heat of a day an will account for elevation differences on the face of a target, especially during the summer months. In competition we often would need to make adjustments for these temperature variations between 7:00 AM and noon because of the 20 degree shift in temperature.
I do not believe that changes in the air pressure inside an arrow shaft as a result of ambient temperature change has any noticeable effect on an arrows flight path.

What the change in ambient temperature will have an effect on is the arrow's ballistic coefficient (air resistance / drag). Which can result in arrow hitting higher or lower than the conditions the X-bow (or bow) was sighted in for. If you take a look at various ballistic calculators, they usually take into consideration air density (atmospheric pressure [altitude & barometric], temperature, and humidity).

See "Correction Factors" at Hornady's External Ballistics for examples of deviations from norm due to Higher Temperature, Higher Barometric, and Higher Altitude: External Ballistics - Hornady Manufacturing, Inc

You can see the effects of making such changes using Hornady's Ballistics Calculator: Ballistics Calculator - Hornady Manufacturing, Inc


Solely for interest:
When talking Extremely Long Range ballistics there are also these effects on a projectiles path due to variations in gravity (flight path**, position latitude, spin of earth), earth's rotation (time in flight and direction), projectile spin (with wind - pressure difference up/down), and few others: External ballistics - Wikipedia, the free encyclopedia

** This might help explain one of the subtle effects due to gravity: The most detailed view of Earth's gravity from the GOCE satellite | Earth | EarthSky
The "force of gravity is slightly stronger at the poles compared to the equator".
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  #63  
Old 01-18-2012, 11:14 PM
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Join Date: Dec 2010
Posts: 391
Re: Tac15i accuracy and consistancy problems

Hi Okie,
While your explanation might be scientifically correct the fact of the matter is that temperature and altitude Do play a role in affecting the flight characteristics of an arrow and therefore need to be checked or accounted for when we're isolating these types of problems.

I'm not Bill Nyes the science guy, so I'm not in a position (nor do I want to be) to isolate the specific science behind the reasons that air temperature or elevation cause flight differences and need to be checked. My experience comes from over 40 years of competitive archery shooting experience, coupled with an engineering background that allows me to understand and apply some of the basic principles learned to help solve certain problems or improve functional performance of others.

I will say that although I understand the merit behind your explanation as it applies to ballistics and bullet flight, it is in direct opposition of the common cause and effect beliefs in the field of archery as it applies to the flight of a hollow projectile.

The reasons I have given are based on the age old established beliefs amongst competitive field archers that have been around for the past 3 or 4 decades. That doesn't necessarily make them technically correct, but I haven't the time or inclination to validate every nuance in the industry. It's sufficient to say that any changes in either elevation or temperature could and do account for flight deviations and need to be checked for accuracy.

I personally have a great deal of experience with the affects of temperature changes on the change in arrow elevation as temperatures increase. This change becomes more and more exaggerated as you reduce the velocity of an arrow by shooting a lighter bow.

Regards,

Jon
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