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TAC 15/15i Basic Unpublished Information

 
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  #64  
Old 03-25-2011, 06:11 AM
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Join Date: Feb 2011
Location: SW virginia
Posts: 82
Re: TAC 15/15i Basic Unpublished Information

Jon, there are a few things I wold like to speak about here.

First, I personally have never gone by the fraction as a way to measure a shafts OD. Many time the fraction is not the OD of the shaft, but actually the inserts outer edge. Sometimes the inserts outer edge has a "flare" to it to make it ever so slightly larger than the shaft. Then the point needed to match that "flare" will be what the manufacturer recommends such as 11/32 or whatever so that the field point or broadhead does not hang over or be smaller than the insert.

All shafts are measured in their spec sheets in decimals such as the ID of .300 and OD of .375. This gives you an idea of how many layers the shaft wall is made up of if the shaft is wrapped. Since PSE is a filament wound shaft, you would just know the overall thickness of the wall of the shaft. If you notice, the insert protruded ever so slightly past the shafts outer wall. Take a caliper or micrometer and check this and you will see the edge of the insert is 11/32 and the shaft wall is slightly less.

This OD number does not correlate with the spine deflection. The fact that at times they do end up the same is mere coincidence. Here is a chart for a Carbon Express arrow called the blue streak.

SPECS - Maxima Blue Streak™ Select

Model GrainsPerInch Spine Diameter
250 7.4 0.413" 0.290
250 7.4 0.413" 0.290
350 8.3 0.347" 0.295"
350 8.3 0.347" 0.295"
Notice how the spine and OD are very different.

The other thing is most people consider a shaft to be extremely straight at .001. Trophy Ridge has a Crush arrow that is in such high demand I cannot get any till close to Fall. They have a straightness tolerance of .0008 and are a smaller diameter shaft with a half in/ half out insert which makes it much wider in diameter than the shaft itself.

Just some observations on my part. Nothing set in stone of course. And I will volunteer provided we get within acceptable and comparable specs to the TAC shaft.

Last edited by Super 91; 03-25-2011 at 06:19 AM. Reason: fix chart alignment
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  #65  
Old 03-25-2011, 11:25 PM
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Join Date: Dec 2010
Posts: 391
Re: TAC 15/15i Basic Unpublished Information

Hi All,
I have a great deal of new information to provide on this thread, but unfortunately I won't have time to do it all tonight. It might need to wait until tomorrow or until I can speak with Super 91 and have him verify my current findings.

For now, what I can tell you is that nobody in the industry currently makes a shaft that can supplement for the TAC15 Arrows.

The spine on these arrows is in fact a .140, therefore the length and stiffness is not possible to reproduce with anybody's existing shafts, so it's a matter of making the best with what we have until somebody comes out with a shaft to meet the crossbows spine requirements.

As Super 91 pointed out in his previous thread, the point .250 would most like not come out of the bow in the direction you wanted it to.

The next area of information should help anybody who wishes to get that last bit of exceptional accuracy out of their shooting, so stay tuned.

Jon
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  #66  
Old 03-26-2011, 06:24 PM
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Join Date: Aug 2010
Location: North West Washington
Posts: 80
Re: TAC 15/15i Basic Unpublished Information

Hello All,

Well, barring another shaft manufacturer jumping into the TAC arrow market, I think we will continue to be forced to deal with the equipment at hand. That is not intended as a negative but statement of fact.

In our search for optimum accuracy obtainable in the TAC system, we must follow the same rules that have produced success with other archery projectiles of the past:

Wall concentricity
Straightness standards
Weight standards
Spine standards
Spine orientation
Squareness of nock and point ends of the shaft
Center shot adjustment
Arrow rest fit
Nock to string fit
Experimentation with fletching rate of twist

In the case of the TAC system we should also be interested in the quality of trigger pull (i.e. crisp break and little over travel), quality of optics, correct secure mounting of optics and mating of the bow assembly to the lower receiver of the AR platform (if one is using the AR).

We may be able to live with relatively wide tolerances with one or more of any of the above listed; however, ignoring all of the above will certainly lead to disappointment.
In my opinion, to extract the maximum accuracy from this system today, particular attention will have to be paid to each specific item listed above.

Just remember to have fun!
Konrad
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“The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter can not be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles.”

Col. Jeff Cooper
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  #67  
Old 03-26-2011, 06:29 PM
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Re: TAC 15/15i Basic Unpublished Information

Quote:
In my opinion, to extract the maximum accuracy from this system today, particular attention will have to be paid to each specific item listed above.
Konrad, that sounds just like the recipe for precision rifle shooting.
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  #68  
Old 03-26-2011, 11:59 PM
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Join Date: Dec 2010
Posts: 391
Re: TAC 15/15i Basic Unpublished Information

Hi Konrad,
This is a great recap of the corner stone standards for shooting accuracy with a bow, but it's concise and totally factual. These elements are not up for negotiation or compromise, since they are long established laws of physics and arrow flight.

The sequence of priorities can be argued to some degree if anyone wants to get political, but the elements are all there and as stated some may have more importance than others, but all are need to be checked and verified or adjusted to achieve optimal shooting performance.

I believe we learned years ago that spine alignment, shaft deflection, shaft straightness and shaft weight / F.O.C. were the four big critical factors affecting arrow grouping and flight performance, but these only become critical after the others you've listed have been set up and tuned during the initial bow set up sequence.

I like to equate these items as similar to what a "Long Range Precision Shooter" does. Let's face it, he's probably not going to be able to walk into a store and by a stock rifle that's going to give him the type of accuracy and performance that he's looking to achieve.

Like wise, store bought ammo isn't going to give him the type of consistent pin point accuracy that he's looking for either, so what does he do? He customizes his gun in many different ways to get it shooting the way he ants it and he may hand load special ammo with different powder measurements and different bullets until he has just what he wants and needs to provide the accuracy that few others ever attain.

We are chasing the same type of special accuracy, just with a slightly different type of shooting instrument, so it takes some customizing of both the weapon and the ammo to achieve the highest level of performance possible with today's components.

We'd love a straighter shaft if one was available, but in light of what we have available and can do, we can do quite well with today's materials.

I think all TAC15 owners will be pleasantly surprised within the next week or two once we complete our research and we publish the findings and how-to's.

Collectively, we have gone from knowing almost nothing about these crossbows and their arrows to knowing almost everything there is to know in a very short amount of weeks. Thanks to everybody's intellectual input and help, we've unraveled a great deal of information. Much has been tested, thanks to Super 91 and a great deal of technical know how and engineering data has been brought to the table by yourself (Konrad and a few others).

I'd like to say more, but I dare not, since the actual verified bare facts come from somebody else who's compiling and crunching the data.

Stay tuned over the next few days!

Jon
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  #69  
Old 03-27-2011, 07:45 AM
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Join Date: Aug 2010
Posts: 21
Re: TAC 15/15i Basic Unpublished Information

this info is getting better every day, i love it when i shoot compound bows
20 yards or 100 yards fletching contact was a major concern. dont yo think
shooting thru the wisker bisket is causing problems at longer ranges? i always used a fall away. i know the speeds are faster here, but there are
rest that still have less contact???
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  #70  
Old 03-27-2011, 12:09 PM
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Join Date: Aug 2010
Location: North West Washington
Posts: 80
Re: TAC 15/15i Basic Unpublished Information

Hello Everyone,

For all intents and purposes that list is indeed straight from a precesion gun makers “to do” list for accuracy.

I liken center shot to verification of chamber axis to throat/barrel bore axis and squaring of the bolt face to same.

No precesion rifle marksman ever succeeded using poorly balanced or unmatched weight projectiles. “Center of Balance” fore and aft is a large part of bullet stabilization along with jacket concentricity. Bullet base squareness produces evenly applied gas pressures to the bottom of the bullet as it exits the barrel in the same way squared nock ends of an arrow distribute the driving force of the string evenly to the shaft. Weight variables affect time of flight (velocities) and as such produce vertical stringing issues. Thankfully, most custom bullet manufacturers have eliminated those issues all together.

Fletching type and twist are exactly the same as matching the rate of rifling twist to velocity and projectile weight.

Limb to riser to human fit is the same as barreled action to stock to human fit. A poorly bedded action will never “settle” into the stock. The microscopic movements between the two components affect force distribution differently with each shot. A poorly fitting stock promotes shooter error because he is constantly trying to compensate for the poor fit as consequently never gets the shooting platform into the exact same position before firing the next shot. Once again, inconsistent distribution of recoil forces negatively affects point of impact and group size.

Poor optics and/or poorly mounted optics are a subject on its own. Much has been written and the fact remains that if the internal mechanism shifts between shots or the mating between the optical device, the mount and the shooting platform changes, point of impact changes.

And then we come to triggers…
Even were all of the above perfect, a horrible trigger pull will destroy accuracy potential. Dragging a harsh, heavy sear across an engagement face disturbs even the best aiming concentration and position. An excessively long trigger over-travel allows for platform disturbance after primer ignition but before the projectile leaves the barrel.

The first time I dabbled in custom “tuning” was when I began weighing stones for my Wrist Rocket on Mom’s kitchen scale.
But that is a story for a different day.

In short (he said as he rambled on), I stand guilty as charged in “borrowing” from my firearms experiences.

I eagerly await the upcoming testing reports.

Thanks for all of the kind words,
Konrad
__________________
“The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter can not be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles.”

Col. Jeff Cooper
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