Velocity question

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XB I GO
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Velocity question

Post by XB I GO » Fri Mar 02, 2018 4:10 pm

Does the difference between one crossbows velocity compared to another stay constant? For example if one bow says 305 fps and one says 355 fps is there always a 50 fps difference assuming the same arrow weight?

To try to be clear, lets say a bow marked 305 fps shoots 275 fps with bolt X, then does the bow marked 355 shoot 325 with bolt X? And will the 405 shoot 375 with bolt X?

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Re: Velocity question

Post by SEW » Fri Mar 02, 2018 4:47 pm

No. It’s not that exact. Good question though. First off, the numbers aren’t that exact. Secondly, even if the bows were rated that accurately and each model would shoot a 350g arrow at their advertised speed, once you go above that speed, the numbers will start to close. Additionally, there’s draw length. The longer the draw length, the faster , all else equal, the xbow will shoot a heavier arrow compared to the shorter draw length bow. BUT, the differences will be negligible . If a 405 shot a 350g arrow 405 and a 330 actually shot a 330’/sec, then you shot 450g arrows thru them, the differences would likely be a little closer.
The real differences in draw length show up dramatically between the nearly identical velocities M380 and BD400 when shooting a nearly 500g arrow. The difference with a 350g arrow is 5’/sec whereas the 500g arrow(actually test arrow was 486g) is closer to 8’/sec difference due to the extra draw length.

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Re: Velocity question

Post by XB I GO » Fri Mar 02, 2018 4:57 pm

So are you saying the 380 and 400 velocities are really only 5 fps different with 350 grain arrow no matter what they say on them (380 and 400)? And with your heavier arrows they are only 8 fps different? Where did the 20 fps between them go that is marked on them for 350 grain ? I'm still confused. If the 380 is 380 with a 350 grain and the 400 is 400 with 350 grain how are you saying they are only 5 fps different? I'm sorry I don't get it but thank you for trying to explain. Maybe you or someone could be more clear?

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Re: Velocity question

Post by Normous » Fri Mar 02, 2018 5:19 pm

Each individual bow will have a sweet spot for efficiency with a certain grain arrow that cannot be compared to a bow of a different poundage because the sweet spot of efficiency will be different using the same grain arrow.
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Re: Velocity question

Post by xcaliber » Fri Mar 02, 2018 7:53 pm

Normous wrote:
Fri Mar 02, 2018 5:19 pm
Each individual bow will have a sweet spot for efficiency with a certain grain arrow that cannot be compared to a bow of a different poundage because the sweet spot of efficiency will be different using the same grain arrow.
That's the best description out there. It's all about efficiencies.
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Re: Velocity question

Post by Arrowflinger » Fri Mar 02, 2018 8:49 pm

Say what????? :?: :?: :?:
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Re: Velocity question

Post by Boo » Fri Mar 02, 2018 10:40 pm

No, primarily because of limb deflection. The limbs are handmade and like anything handmade, there will be inconsistencies. Also, the glass bundles and resin batches vary. So the bottom line is that each bow is an individual and you switch limbs on one bow will often mean different velocities. Most times that difference isn't large but sometimes it can be significant.
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Re: Velocity question

Post by SEW » Fri Mar 02, 2018 11:11 pm

397g arrow
Blue MD string (99g)

Clean bows : no DB killers, no Air Brakes, all same DM strings,

M380 - 363'/ sec
BD400 - 369
M405 - 375

Ok. This is what I’d recorded with the middle weight arrow. My memory wasn’t perfect.
I used the same string, same limbs and same arrow on each of the 3 xbows. So, no limb variances, string weight/composition,
Etc differences would come into play. The string was exactly 2” off the riser/rail junction on the BD400 and just against the string bumpers on the 2 Matrixs.

Things aren’t always as they seem. Advertised speeds of xbows are just approximate at best. Usually, they are a bit optimistic.
Strangely, the M350SE/LE is usually a few feet/sec faster than the M355. Likewise, the early Micro 335s are/were reported to be faster than Gen 2 Micro 355s.

It’s generally accepted that the BD400 is appx 5’/sec faster than the M380. The 397g arrow had 6’/sec difference. I didn’t record my 351g arrow difference but remember it was 5’/sec different.

Life just isn’t as simple as we’d like it. 😉

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Re: Velocity question

Post by SEW » Sat Mar 03, 2018 9:22 am

Duplicate post
Last edited by SEW on Sat Mar 03, 2018 9:30 am, edited 1 time in total.

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Re: Velocity question

Post by SEW » Sat Mar 03, 2018 9:24 am

SEW wrote:
Sat Mar 03, 2018 9:22 am
SEW wrote:
Fri Mar 02, 2018 11:11 pm
397g arrow
Blue MD string (99g)

Clean bows : no DB killers, no Air Brakes, all same DM strings,

M380 - 363'/ sec
BD400 - 369
M405 - 375
—————————————————————————————————————————————-
Ok. This is what I’d recorded with the middle weight arrow. My memory wasn’t perfect.
I used the same string, same limbs and same arrow on each of the 3 xbows. So, no limb variances, string weight/composition,
etc, differences would come into play. The string was exactly 2” off the riser/rail junction on the BD400 and just against the string bumpers on the 2 Matrixes.

SO, HAVING USED THE SAME STRING, SAME LIMBS, SAME ARROW, SAME CHRONOGRAPH WITH THE ONLY DIFFERENCE BEING THE BASIC XBOW DESIGN: RAIL LENGTH AND RISER DIFFERENCE BETWEEN THE BD VS THE 2 MATRIXES. SO THE DIFFERENCE SHOWN IS WITH EVERY VARIABLE REMOVED. EVEN THE BRACE HEIGHT WAS THE ONE ON EACH XBOW THAT YEILDS THE HIGHEST VELOCITY.

Things aren’t always as they seem. Advertised speeds of xbows are just approximate at best. Usually, they are a bit optimistic.
Strangely, the M350SE/LE is usually a few feet/sec faster than the M355. Likewise, the early Micro 335s are/were reported to be faster than Gen 2 Micro 355s.

It’s generally accepted that the BD400 is appx 5’/sec faster than the M380. The 397g arrow had 6’/sec difference. I didn’t record my 351g arrow difference but remember it was 5’/sec different.

Life just isn’t as simple as we’d like it. 😉
The above is a revised version of the above.

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Re: Velocity question

Post by SEW » Sat Mar 03, 2018 9:26 am

Duplicate post

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Re: Velocity question

Post by janesy » Sun Mar 04, 2018 6:56 am

The "335" or "380" is a name and nothing more. There is a post on here somewhere when questioned by someone why the supressor doesn't hit 355, they said " well we had to call it something!"

What you can be confident in is that as the name goes up so does the speed. But they are hardly consistent with each other , at the end of the day it doesn't matter. Most people don't know what a chronograph is, let alone how fast their crossbow actually is. For the vast majority that I have ran over the chrony, most are up or down only 5 fps. So its pretty close. Not close enough to worry about it.
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Re: Velocity question

Post by SEW » Sun Mar 04, 2018 8:59 am

SEW wrote:
Sat Mar 03, 2018 9:24 am
SEW wrote:
Sat Mar 03, 2018 9:22 am
SEW wrote:
Fri Mar 02, 2018 11:11 pm
397g arrow
Blue MD string (99g)

Clean bows : no DB killers, no Air Brakes, all same DM strings,

M380 - 363'/ sec
BD400 - 369
M405 - 375
—————————————————————————————————————————————-
Ok. This is what I’d recorded with the middle weight arrow. My memory wasn’t perfect.
I used the same string, same limbs and same arrow on each of the 3 xbows. So, no limb variances, string weight/composition,
etc, differences would come into play. The string was exactly 2” off the riser/rail junction on the BD400 and just against the string bumpers on the 2 Matrixes.

SO, HAVING USED THE SAME STRING, SAME LIMBS, SAME ARROW, SAME CHRONOGRAPH WITH THE ONLY DIFFERENCE BEING THE BASIC XBOW DESIGN: RAIL LENGTH AND RISER DIFFERENCE BETWEEN THE BD VS THE 2 MATRIXES. SO THE DIFFERENCE SHOWN IS WITH EVERY VARIABLE REMOVED. EVEN THE BRACE HEIGHT WAS THE ONE ON EACH XBOW THAT YEILDS THE HIGHEST VELOCITY.

Things aren’t always as they seem. Advertised speeds of xbows are just approximate at best. Usually, they are a bit optimistic.
Strangely, the M350SE/LE is usually a few feet/sec faster than the M355. Likewise, the early Micro 335s are/were reported to be faster than Gen 2 Micro 355s.

It’s generally accepted that the BD400 is appx 5’/sec faster than the M380. The 397g arrow had 6’/sec difference. I didn’t record my 351g arrow difference but remember it was 5’/sec different.

Life just isn’t as simple as we’d like it. 😉
The above is a revised version of the higher above.

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Re: Velocity question

Post by XB I GO » Sun Mar 04, 2018 9:02 am

I am curious what difference in Bolt speed makes a difference. A difference that happens over and over again. Like if one bolt at a certain speed has X energy, X drop at say 40 yards, X amount of penetration - what does it take to increase the X with the same Bolt? I think even 1 FPS makes a mathematical difference but how much makes a difference that matters for real? 10%? 20%? I’m trying to do a report for school about significant and insignificant changes in value. We can use our hobby as a topic. My brother is doing basketball. Someone has golf, cars, etc. I may have to do some test myself but right now we only have one crossbow. Thanks

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Re: Velocity question

Post by papabear1 » Sun Mar 04, 2018 9:45 am

Arrowflinger wrote:
Fri Mar 02, 2018 8:49 pm
Say what????? :?: :?: :?:
X 2 :roll: :lol:
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