Kinetic Energy vs. Momentum for CROSSBOW HUNTERS!

A Friend of Bunjie asked "Can you give a dumbed down video on what exactly slugs are? Explaining kinetic energy would be good too. I get both a little bit,but you go into depth when you explain things, and when I trysearching things, I get a crazy range of opinions and not much fact."
Well, I can give you BOTH crazy opinioins AND fact, how about that?
This channel is about my love of the crossbow, hunting, and the outdoors. I hunt exclusively with the crossbow. I love it and I aim to help you love it, too!
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Now, I am not sponsored by anyone. I am a free agent. I experiement with different types of gear, but I'll tell you my honest opinion about everything out there. I am not sponsored by Excalibur or Scorpyd...read on:
Bunjie (The O.B.) is a 2010 Excalibur Axiom Crossbow. After a decade of killing deer, hogs, squirrels--you name it!--with the "stock" 20" Easton Firebolt arrows, Bunjie experimented with heavy arrows during 2020 but has since decided to hunt with 20" ProFlight arrows from Easton, for a total arrow weight of just under 400 grains when tipped with a 100 grain Rage Crossbow Hypodermic Broadhead. This keeps ol' Bunjie around 300fps. Is Bunjie retired as of 2021?
Bunjie, Jr., is my daughter Genevieve's crossbow, an Excalibur Micro Suppressor 355. She also shoots ProFlights (16.5" variety) with a 150 grain Rage Trypan Crossbow Broadhead, for a total arrow weight around 415 grains. This crossbow was a much appreciated gift from a Friend of Bunjie, and it changed Death by Bunjie forever by inspiring Genevieve to become a part of it as a second-generation crossbow hunter, and it also convinced me there is a benefit to a newer, faster crossbow (see our 2020 Maryland Doe Hunt).
Bunjie III (or Bunjie '21, Bunjie 3.0) is a 2021 Scorpyd Deathstalker, the result of trying various models and looking at dozens of them online for characteristics I liked. It is, in fact, another gift from a different Friend of Bunjie, which goes to show how important Friends of Bunjie are to this channel and what an impact they can have. Although I really liked what I saw online, I would not have even tried a Scorpyd given that no shops near me carried them. This was sent to me new, free of charge...with the only stipulation being that if I didn't like it, I would send it back to that FOB. After spending some time with it, I am convinced it is, in fact, the right crossbow for me in 2021, and I look forward to showcasing this crossbow in future videos.
So, I am not sponsored by these companies. I am sponsored by Friends of Bunjie! (I'm not asking for gifts whatsoever--please don't feel like you should send me stuff! But I do appreciate the support I've received over the years! I'm just trying to express my appreciation for that.)
Once again, this channel is about my love of the crossbow, hunting, and the outdoors. I hunt exclusively with the crossbow. I love it. Sure, like a lot of kids, I started hunting with a good ol' Model '94 Winchester .30-30 back in the 80's, but drifted away from hunting when I went off to college, law school, and started a family. As my daughter got older, I regained my interest in the outdoors, and I consider myself lucky to hunt on the same property today that I hunted on as a kid. I got the Excalibur Axiom crossbow in 2010 and I haven't looked back. This channel is the result of combining my interest in filming and hunting...
...and music, too! My related channel, Yankee Militia, showcases my music. Some of the music is hunting-related, so check that out, too! The soundtrack for this channel is provided by my band, so the two are intertwined. The albums "Live Free or Kill" and "Zombies Gotta Eat, Too!" are available on Amazon.com and elsewhere. A third album is in the works.
All Hail Bunjie!
--Rich Wilson, Death by Bunjie

[@tythomps]

Energy upon leaving the bow is kinetic energy, as is energy at the point it gets to the target is still kinetic energy. Momentum is actually not energy at the target. Think of momentum more as an object in motion's ability to resist having its velocity changed. THAT is why momentum has a much bigger effect on penetration than kinetic energy does.

[@Ganjaseed]

This is correct.

[@JohnTomasella]

Watching a lawyer try to explain a dumbed down version is something to behold. You did a great job.

[@Deathbybunjie]

🤣 made my day thanks

[@beearcher36]

Cannot remember what I had for dinner yesterday but I do remember kinetic energy formula. Velocity x Velocity X Mass (arrow weight) Divided by 450,240.0 (EXAMPLE) 410fps X 410fps X 400w = 67,240,000/ 450,240 = 149.34 ft lbs of kinectic energy. Enjoy this channel a lot. Tell Bunjie high.

[@johnbarron4265]

This was a pleasure to watch. Your grasp of the underlying physics is on-point. I think I'll hang up my crossbow and take a bowling ball into the woods in the upcoming season. Hopefully I don't spook the deer with my fancy wind-up. In all seriousness though, you've brought to the surface another factor that is equally important to both KE and MO: projectile surface area. The more surface area on the shaft and fletchings, the harder the arrow has to work to plow through a deer and the more momentum is robbed that could have instead been used by the broadhead to slice farther through the animal. In theory, an arrow even just 20% smaller in diameter with the same broadhead can achieve a pass-through with a lot less KE and MO, which could be an advantage for crossbow hunters who want a faster arrow rig but don't want to sacrifice penetration capability.

[@Deathbybunjie]

You must be looking ahead in the script haha...I agree and broadhead choice is HUGE in my book, will talk about soon

[@James28R]

except its fairly wrong..

[@crickratcrossbowhuntingand9321]

Very good and informative video! I agree that these numbers sometimes blind us as hunters from what is most important. Scouting, tuning and accuracy.

[@delmisbrown9675]

I like that velocity square part.

[@bokkenwielderful]

Thank you! this has stimulated a lot of thought. Introducing bowling ball ballistics dropped in a missing piece in my understanding. I have not been this excited about bowling balls in ages.

[@Deathbybunjie]

😅

[@jasonoutdoors175]

Awesome video tutorial, thank you professor Rich.

[@exman05]

Of the odd questions I nerd-ed out about over the past few years... this one piques my interest. I dug into speed vs weight last season. This helps.

[@mikeguy9668]

Weight kills

[@twdaugherty1]

Love your videos. You explain things in laymen terms easy to understand. Thank you for being so informative. Keep them coming.

[@Deathbybunjie]

You're welcome thanks for watching!

[@matthewlyness8161]

Great video I shot a 405 grain bolt out of my Excalibur mag340 and it loves it deadly accurate!!! Keep up the good work October 2nd is just around the corner for Pennsylvania opening day I'm sure you and Genevieve are very excited for that

[@Deathbybunjie]

Oh, yeah, good luck out there 👍

[@driftlesshunter9200]

Would you please share what broadheads you plan on using with your Mag 340? I am compound bow hunter fighting some shoulder pain that lingers on this channel. I really like the simplicity of the Mag 340, & it remains on wish list. I just haven't pull the trigger on getting a crossbow yet. I love input from Mag 340 owners.

[@matthewlyness8161]

Swhacker 150 3 inch its amazing accurate nice and light I love the crossbow definitely recommended!!!

[@frederickbierweiler8020]

this was super infomative video!

[@dr.froghopper6711]

Sensei? Well yeah! Heck Rich, I watch your old stuff like crazy. I’m not new to archery or hunting. But I’ve never hunted using archery, only rifles. And, while I’ve had Multiple Sclerosis for 10 years or more, I haven’t hunted at all, mostly especially with a crossbow. I’m coming back from being an incomplete quadriplegic. It’s not fun but it qualifies me as mobility impaired with a permanent degenerative disease. That, in turn, means that I can use my crossbow as a legal sporting weapon in any hunting season except those designated as “Bow ONLY “. And I can shoot from a vehicle, though I’d prefer a ground blind that I can stand up in. Leg cramps make a tree stand unlikely. Anyway, I’m learning a ton and I appreciate your time and effort in producing your videos.

[@scottlemee4986]

Nice explanation. The only thing that most don't understand and that you have said before, there is a sweet spot between weight, speed and accuracy.

[@Deathbybunjie]

Yep all trade-offs

[@jheckert1]

the best way to see how number affect the outcome, set up an excel spreadsheet where you calculate out KE and Momentum. For one table keep mass the same and change velocity through a range. Then do another table where you change mass but keep velocity constant. Compare the numbers and you can better see how changing one or the other affects the outcome.

[@leveraction767]

You made a great point and why manufactures started hyping K.E.. you either have to lighten the arrow (loose M.O.) or buy a new bow. Which would you do? I would just bump the arrow weight and take a couple of steps forward to the target, to save trajectory.

[@Deathbybunjie]

That's one option for sure

[@chucksmith5002]

Well Rich you just managed to Confuse the heck out of me . LOL Enjoyed it

[@Deathbybunjie]

😅

[@HuntStewTV]

I love crossbow application month

[@leveraction767]

Lever Action Oh! #2: 1 slug. ..... 1 slug is the difference between an arrow and a bullet. Slugs are fractional and therefore dont sound scary. Well...they are. Even when in fractions. .040 slugs to 1.4 slugs is the difference of being hit in the head and having that hit go through your head. Dont get hung up on the decimal. Remove the decimal and the K.E. / M.O. are same as far as effect. As I said...This is why K.E. was chosen by the manufactures for sales incitement.

[@rongarofalo3482]

Another great video Rich. Thanks

[@Deathbybunjie]

Thanks good to hear from you Ron

[@leveraction767]

O.K. ... Another Excellent video. Thanks and lets talk about it online! Get that page open bro!

[@moosejcthunter5686]

I 2nd that motion! All in favor.....

[@johnb6084]

The deflection of the bowling ball along the pins reminds me of a quartering deer and reported deflection with broadheads.

[@Deathbybunjie]

If only Swhacker made bowling balls lol

[@johnb6084]

@@Deathbybunjie Haha, that's great!

[@leveraction767]

Oh yeah!

[@frederickbierweiler8020]

Rich there is one more way to calculate your momentum and that is a paper and pencil i know its old school and some may not even recognize the terminology but ive heard that it can also be very accurate. just saying lol

[@dr.froghopper6711]

I concur. They learned me good when I was in college, lol! Calculators were allowed but you had to show each step of your work, on paper. I can honestly say that Physics, the Pythagorean Theorem, and Basic Chemistry have proven to be some of the most useful parts of my education. I’m good at math but I don’t like it. Only if I can use it in a practical sense. But I’m a devout nerd so I’m pretty creative at finding practical uses, lol!

[@rayphillips4514]

I always loved physics; chemistry not so much! Ok, but now I am confused! Should I take my crossbow to the bowling alley with blunt tips or should I carry my bowling ball to the Doghouse blind? Life was so much simpler back in the Bear Razorhead days! In all seriousness Rich another interesting video! Thank you and keep it going!

[@Deathbybunjie]

Lol until Rage makes a bowling ball, haha

[@marky7596]

Interesting topic, and it's cool to hear the math and science behind all of it. All of that been said there's no replacement for shot placement, and having a razor sharp broad head. A rifle depends on the KE and EFP to harvest game that's why there is a huge difference between a 30-30 and a 300 Win Mag both shooting .308 caliber 150 grain bullets. Because the 300 Win mag is going so much faster. As far as archery equipment goes I feel the numbers on a piece of paper are not nearly as important. All archery equipment "ideally" your shot hits both lungs and the heart and the game is incapacitated due to mass hemorrhaging and asphyxiation, not that the arrow is dumping tons of energy into the game. Millions of animals have been harvested over the course of time with bow and arrows going less then 200fps.

[@richardvila1173]

Very well explained Dr. Terminator! Lol

[@Deathbybunjie]

😅

[@oldgrumpyhunter]

Double the weight of the arrow you double KE and double the momentum Double the speed you quadruple the KE and double the momentum. At the Earth's surface, an object with a mass of 1 slug exerts a force downward of approximately 32.2 lbf Where the term "Slug" came from? Well, a Slug and a Snail are both parts of the Phylum Mollusca family and they both move VERY slow. Wait not that type of slug! According to an online source: "The name "slug" was coined before 1900 by British physicist Arthur Mason Worthington, but it did not see any significant use until decades later. It is derived from the meaning "solid block of metal", not from the slug mollusc. A 1928 textbook says:"

[@Deathbybunjie]

I can HEAR you saying this 🤣 that's great

[@oldgrumpyhunter]

@@Deathbybunjie I may already have. LOL

[@one-eyedarcher]

I just watched the video. Guess why I missed it? I was bowling the last night of our summer league! How cool is that?! Bowling is a great way to see the effects of speed and weight differences IMO. A little old lady who throws a 10 lb ball has terrible pin carry. The ball literally deflects off pins. I used to throw a 16 lb ball over around 16 mph and averaged about a 194. A couple years ago I switched to a 15 lb ball and throw it around 18 mph. The pins seem to blow up when I hit the pocket now. I have found the best weight and speed combo for me. My average went up to around a 210. A perfect archery set up for me is a bow that can push a slightly heavier arrow, say 450 to 480 gn in the 400 fps range. Best of both worlds IMO.

[@Deathbybunjie]

Wow that's a great example...all trade offs, looking for that sweet spot!

[@leveraction767]

Nobody is speaking to energy loss to the broadhead size/design. I hope thats gonna be a thing! :)

[@Deathbybunjie]

Oh that's big...that's coming for sure

[@abelwalker4396]

I second this motion

[@Dutch.1722]

400 grains is good whitetail medicine. 450 grains buries 2/3 of the fletches into my foam chunk xbow target at 25 yards. 400 grain bolt chrony at 380 fps amped rated at supposed 415 fps.

[@turtleman5111]

That's odd, because most manufactures use a 400 grn bolt as a standard to determine fps. I have 3 Barnetts; they come w/Headhunters which weigh about 412-415. So, rt away, Im not getting the fps as advertised(I mean, its only a couple fps), but thru experience, I'm using 540 grn bolts now. A little slower, but MUCH better penetration+ damage! I've never lost a deer that I hit, since.

[@Dutch.1722]

@@turtleman5111 I nicked one in the jugular because it wasn't where I was aiming at 28 yards when bolt arrived. Xbow is very loud.. As group came in, I shot at one not looking at me when others noticed the odd shape of the bow wrapped around a tree. Everyone jumped.. Not a drop on the broadhead. Rage 2 didn't deploy. Blades were hardly dented. There was white hair on the ground and bright red blood. I followed it till I lost trail. My buddy found it a week later. Shame. I am going back to bow as Its shape is vertical to me and not horizontal. I think a couple figured me out as I was in position when they approached and saw the sideways of the xbow around the tree as they approached. A bow is in line with your body. That being said 2 more deer and a yote last season. 400 grains did the job

[@turtleman5111]

Dutch 1722 Dutch, I REALLY wish that I could read your whole reply, but I get to "as g...Read More, it doesnt allow me to READ MORE, even on my own dam reply! I must hit 'edit' on mine, to see what I said. Idk how to get around it. (This only happens with 'replies')

[@leveraction767]

This week you are putting me to the test. LOL Yesterdays video is a LONG and drawn out response that actually belongs on a facebbook (Friends of D.B.B.) page or a forum. That was not only a good video but one that I could sink my teeth into and that I wish members of the D.N.B. crew could see in real time. This one?... I have far less to attack. You really did a great job in addressing a question and explaining it well. Yes... I have 2 counter points but I cant remember what they were LOL I will have to go back and re-watch and bring them up separately. You REALLY need to get a forum up and running for discussion or at least open that Facebook page up again and just let Genevieve moderate it. JMO

[@Deathbybunjie]

Thanks muchly, not a bad idea on the GKW moderator...I think the hardest part of the week is almost over for you lol

[@leveraction767]

LMAO! :D

[@rayphillips4514]

@LeverAction They say vitamin E is good for your memory but I keep forgetting to take it! Lol

[@huntingscienceexplained9825]

Since we're doing puns, I really hope you get the market penetration you're looking for with this video.

[@Deathbybunjie]

bwahaha i do love puns

[@driftlesshunter9200]

An arrow is somewhere between a bowling ball & a bullet.

[@chrisruzsa2798]

The highest amount of “slugs” I have ever seen I think was 1.5 slugs and that was a 1500 grains bolt for shooting elephants.

[@Deathbybunjie]

That would get the job done!

[@leveraction767]

I am doubling arrow weight. So... when saying we are not adding much. Speak for yourself! LOL

[@charlesmorris6476]

Not all crossbows are suitable for hunting. Recommendations for elk hunting is 65 foot pounds of kinetic energy(this is a conservative value, you can get away with Less). Notice that at 250 ft./s this value cannot be achieved. Even at 275 ft./s you only get close to it at 10 yards out. It’s only from 300 ft./s and up that you get enough kinetic energy at all feasible hunting distances (up to 50 yards) to be able to comfortably hunt elk. As such it is recommended that elk hunters stick to 300 ft./s or more. For Whitetail deer this requirement is lower - any crossbow 250 ft./s and up will be a safe pick. Hopefully you find this information useful in determining what crossbow to buy and how kinetic energy changes based on arrow weight and speed.

[@Deathbybunjie]

Depends on arrow weight, though. The Original Bunjie, shooting around 300 ft per second with a stock arrow only generates about 72 ft lb of kinetic energy. However, with its current arrow setup, it's around 85. With a proper broadhead, I have no problem killing an elk with that crossbow. I'd even shoot a moose with it. Now, of course, Bunjie the Third would have a much greater selection of broadheads for the job 😆

[@charlesmorris6476]

@@Deathbybunjie Absolutely mass is a necessary component to drive the Bolt further, but at 300 fps or above most hunting bolts are made with enough weight to get the job done. 👍🦌

[@locksbog4270]

👍🤔✌️

[@DanielGarcia-zw8nx]

That's a lot of info. I don't need 😴 just shoot your crossbow and go get your game and cook it👍👍

[@Deathbybunjie]

Well put lol

[@ryand5313]

Bigly

[@leveraction767]

i will have to say that my dumbed down explanation of K.E. is the ability to carry a load at a certain speed. My definition of M.O. is the ability of load to provide work. Work is all I am concerned with until that effort is surpassed. Then I just want to work faster. SO.... When I have enough M.O., then I will focus on K.E.. This is inline with your beliefs Rich. No? Well I will assume yes LOL you believe M.O. for you're bow is sufficient and that NOW you are focusing on K.E.. Yes?

[@Deathbybunjie]

Kind of...once adequate MO is achieved, I'm happy! I'm not shooting through houses LOL

[@leveraction767]

Lever Action Showing how ineffective K.E. is, I will point to the fastest (never released) Ravin 500. Its K.E. stat is 222 and a M.O. of .888 .... Now look at my Excalibur 380 (280 fps) which has a K.E. of only 134 but a M.O. of .957. My bow smokes that worlds fastest bow. Not even a contest. A 400 grain arrow V.S. a 770 grain arrow. Its actually embarrassing for Ravin and that 500, being put up against a recurve that isnt even close to the fastest recurve. ;)

[@Deathbybunjie]

But your fps well under 300?

[@James28R]

And if you put a heavier arrow into the ravin it will 'smoke' your crappy cheap bow.

[@leveraction767]

Gonna have to disagree with you on "once you pick out your bow, these numbers become less relevant" . ... Mainly due to the fact that (every year and year after year) I hear people talking about deer (just deer mind you) running away with the arrows and not penetrating small/thinned game such as deer. Lets not even get into Hogs or Caribou, Elk and the like. Deer. Little wimpy deer. .... People throwing tooth picks at the speed of thunder always seem to have these issues. Nobody throwing freight trains are posting these stories. LOL (You know I love you!)

[@chrisruzsa2798]

In fairness though that’s because a lot of “archers” go way beyond the ethical range (ethical range should always be 50 yards in until arrows and bolts and go the speed of a bullet.) d60-90 plus yards if they had a typical rifle with a much higher powered scope they would be shooting deer 3 miles away and get the same effect.

[@leveraction767]

While I believe there is an ethical range, there is no one distance for all crossbows. There are crossbows from 250fps and all the way up to 480fps. The range is gonna be different for those bows at either end and in between, as to how long it takes an arrow to get to the animal. In polling, the average speed for last years crop of crossbow hunters was 350fps with speeds less than 350 being a higher majority than those over 350fps. 50 yards is a poke with even the fastest bow out there today and certainly 2X the distance that a crossbow specing 250 would be efficient at.

[@chrisruzsa2798]

@@leveraction767 see that’s just it though you could have the world’s fastest most powerful crossbow it could go 100 plus yards accurately even manufactures say “do not shoot at live animals beyond THE ethical range. If your weapon isn’t capable of doing the 50 yard range than you can’t do it if your skill is not able to do it you can’t do it. If you can than you can but you should not exceed the 50 yard range and a many people tend to think crossbows are mor superior to vertical bows they actually are not. A 80 compound with longer draw is more powerful or equal to a 200 lb recurve crossbow. The shorter draw length is a major set back. Also to be fair 50 yards is the max range for another reason too archery it’s a style of hunting that is about being close if you want to take unethical long range shots I would recommend to get a rifle and make those shots then ethical. And the ethical range of 50 yards isn’t just about the animal it also about safety looking through a crossbow scope they have narrower widths than rifle though they look similar, you may see the animal perfectly at 60 plus yards but can you see past it? Can you confirm the rule of “know your target and beyond.” If you can’t tell what’s beyond that shot you by law can’t make it or shouldn’t make it. And this goes into it as well. Now this depends on your elevation. Stand or saddle hunters may not run into this problem but blind and still hunters well they do run into this potential problem.