Could this be the "Matrix Ibex" Draw Weight?

[JT of PA]

I was looking over the specs on the back page of the catalog and wondered if I could use the Matrix 380/355 values to propose the draw weight of a Ibex type Matrix would be.

Here goes.

Matrix 380
260 lbs. draw weight / 380 fps velocity = 0.68 something

Matrix 355
240 lbs. draw weight / 355 fps velocity = 0.68 something (huh, they match)

Ibex
175 lbs. draw weight / 305 fps velocity = 0.57 something

My Takeaway - The Ibex limbs don't store as much energy as the Matrix limbs. So, if I take the 0.68 from the Matrix limbs times the 305 fps velocity of the Ibex I should get a rough guess of a "Matrix Ibex" limb weight.

0.68 x 305 fps = 207 lbs. draw weight.

The current Ibex 175 lbs. draw weight would creep up to 207 lbs. at a shorter Power Stroke of unknown length. (Roughly 20% less draw weight of the Matrix 380 - I'm very interested in a Matrix Ibex with a non-camo, aluminum rail!)

Any folk who can fix my rough math above ... have at it please.

Note:
None of the above takes into account the Power Stroke measurements of:
13.12" - Matrix 380
12.25" - Matrix 355
14.50" - Ibex.

[Species8472]

Crossbow physics are essentially the same as the physics of a spring. I am not sure but I believe the limbs on a 355 and a 380 are identical - the only real functional difference between the bows is the power stroke. Looking at the draw- weight compared to the power stroke yields a ratio of 19.6 lbs force per inch of draw on the 355 and 19.8 lbs force per inch of draw on the 380.

If the limbs acted as perfect springs the above ratios would be identical but they are not. This is likely because as a spring gets close to the maximum amount it can be extended the force per inch required creeps up until the spring fails - read limbs snap or splinter.

If you could somehow mount the matrix limbs to an ibex and maintained the power stroke at 14.5 inches the draw weight would actually exceed the draw weight of a 380. Using 20lbs per inch for that last 1.38 inches would add about 28 lbs to the draw weight. This would bring the draw to somewhere between 285 and 290 lbs and quite probably cause the limbs to fail. Not something I would try.

The ratios that you calculated are actually a measure of the efficiency of the bows. The matrix series needs 0.68 lbs force per ft/s of velocity developed. The Ibex needs 0.57 lbs force per ft/s of velocity developed. This tells us that the Ibex limbs are actually more efficient as they need less force per unit of velocity. The ratio for the ibex limbs cannot be applied to the matrix limbs as the ratios are limb specific. The value you calculated would be the draw weight of Matrix 305 - i.e. a bow with matrix limbs that fires at about 305 ft/s. The power stroke for such a bow would be about 10.5 inches using the ratio of 19.6 lbs force per inch of draw (207/19.6=10.56 inches).

[awshucks]

I think he's trying to figure out the draw weight of a future short limbed xbow, w/ shortened rail that will produce around 305 fps.

I'd just wait for the ATA, lol.........p.s. One can bet Excal is already on this........

[JT of PA]

I'd just wait for the ATA, lol.........p.s. One can bet Excal is already on this........

Awshucks ... Your words made my night.

[JT of PA]

Species8472,

Thank You for the response and your in-depth input. Math is not my strong point and I appreciate when other's with a higher intellect in this area help out.

I chuckled a bit to myself when I was typing the original post and my wife asked me what in the world I was typing ... she said, "That doesn't sound like a What's the difference between a Flemish and Endless loop string question!"

All the best.

[Species8472]

So I think I misunderstood your question. Your math is correct a Matrix 305 (if there was such a thing) would need a draw weight of 207lbs to develop a velocity of 305 ft/s. Power stroke would be somewhere around 10.5 inches.

Sorry I thought you wanted to mount matrix limbs on an ibex and pull them 14.5 inches.

[JT of PA]

So I think I misunderstood your question. Your math is correct a Matrix 305 (if there was such a thing) would need a draw weight of 207lbs to develop a velocity of 305 ft/s. Power stroke would be somewhere around 10.5 inches.

Sorry I thought you wanted to mount matrix limbs on an ibex and pull them 14.5 inches.

10.5" Power Stroke ... I'll have to trim my beard ...

No more, "Duck Dynasty" look for me.

Seriously though, I wonder how short a Power Stroke you can go before it becomes too short and doesn't balance right?

[ldock]

I sent you a private message . The gentleman I told you about has cut several matrix bows for lower draw weights smaller shorter bows and sells them as fast as he posts them.

[Species8472]

So I think I misunderstood your question. Your math is correct a Matrix 305 (if there was such a thing) would need a draw weight of 207lbs to develop a velocity of 305 ft/s. Power stroke would be somewhere around 10.5 inches.

Sorry I thought you wanted to mount matrix limbs on an ibex and pull them 14.5 inches.

10.5" Power Stroke ... I'll have to trim my beard ...

No more, "Duck Dynasty" look for me.

Seriously though, I wonder how short a Power Stroke you can go before it becomes too short and doesn't balance right?

No idea, but when i stated your ratios were a measure of efficiency this was only partially true as the power stroke does play into the efficiency calculation. No point going there as the physics get too boring.

Regarding the minimum PS. I suspect you could go pretty low if the limbs, when at rest with the bow stringed, were under a decent amount of tension.

[JT of PA]

Good point. It's not like a shotgun blast going off 12" from your face, it's an arrow. A "Twang" ain't as bad as a "BANG".

[robertyb]

I sent you a private message . The gentleman I told you about has cut several matrix bows for lower draw weights smaller shorter bows and sells them as fast as he posts them.

You talking about Danny cutting the rails down?