mechanical broadheads

[pilsbury38]

Has any one ever tryed useing them with a low poundage bow? I have a Mathews z7 set at 52lbs and have been useing 100gr hellrazors. I would like to try 100gr grim reapers but am a little concerned about the low poundage, any thoughts? Does anyone know the formula to figure out kinetic energy? Thanks in advance.

 

[chaded1]

Here is a calculator that you just plug your info in and will give you FPS and Kinetic energy. This is very accurate and is always within 1-2 fps with my set-up and when I run it through a actual chronograph. http://www.backcountrybowhunting.com/articles/calc/

Now, if you want my personal opinion I would probably shy away from a mechanical broadhead with your set-up. I would guess with your set-up you are going to be in the low to mid 50's of Kinetic energy. But that of course is a very rough estimate since I don't know your draw length, arrow weight, etc. If you do decide to go with a mechanical my advice would be to go with a broadhead that has a small cutting diameter and uses the least amount of energy to open the blades, i.e. a rear-deploying head. Also, keep your shots very close and do your best to put it where it needs to go. Stay away from the shoulder or your in trouble. Hope this helps as it is all I can think of at the moment.

 

[pilsbury38]

Thanks, you confirmed a lot of my thoughts, guess I just wanted to here it from someone else. Think I will stick with my fixed hellrazors

 

[Thunder53]

Well, for what it's worth, using chaded's calculator I have 55-57 lbs of kinetic energy.

65 lbs Matthews bow with a long draw.

I have shot Spitfire 100's, a mechanical broadhead, for years without any problems and they generally blow through any deer I shoot.

I think the Spitfires blade retention set up puts enough pressure on the blades to prevent premature opening and yet they have opened everytime for me on shooting.

The last 4 deer I have shot with this set up all dropped within 50 yards of the hit.

Just sayin'.

I'm sure the archery website may have better intel than me.

 

[exMember]

I like fixed broadheads my self. I dont trust those little rubber band deals

 

[chaded1]

Well..Thunder, you have him by over 10 pounds of draw weight and possibly more draw length so I'm not really surprised with your results. :lol: What kind of Mathews bow do you have? I would think your bow produces more KE than that but I may be wrong. I have a 61 pound with 28.5 inch draw and mine produces 69-70 pounds of KE. Which is also less pounds and probably a less draw but my bow does have aggressive cams which could be the cause. The OP could very well use a mechanical and be successful but in my opinion I don't believe it would be the best set up for him.

 

[chaded1]

I like fixed broadheads my self. I dont trust those little rubber band deals

Actually, there are many now that don't use the rubber bands. Here is one that I shot last year. Redhead Gator 2" cutting diameter. Takes very little energy to open the blades.

Right behind the shoulder, double lung, deer down in 20 yards and done.

 

[Thunder53]

You'd probably be right with a newer Mathews, mine is an older LX model.

65 lbs., 31" draw, 450 gr arrow.

The Spitfires don't use rubber retainers, just internal spring steel pressure.

ALSO, mine actually does chronograph at about 20-25 fps faster than the caluculator showed.

 

[chaded1]

Thunder, I believe you have a miscalculation. I just ran your setup and its giving me 79 ft of Kinetic Energy. The LX has a IBO rating of 317 fps if I recall correctly? Now this is with the 20 grains on the string but you could have a loaded string and it still wouldn't bring you down into the 50's.

 

[Thunder53]

Thunder, I believe you have a miscalculation. I just ran your setup and its giving me 79 ft of Kinetic Energy. The LX has a IBO rating of 317 fps if I recall correctly? Now this is with the 20 grains on the string but you could have a loaded string and it still wouldn't bring you down into the 50's.

Well, I didn't really know the IBO, so I used 275 thinking as an older bow it would be about there.

Actually re-running the calculator using 317 IBO (and 10 gr on the string) I got 81 lbs.

I have the absolute correct calculation in my bow case (from the proshop) but it's at my lake house up north (400 miles away), but I'm going up this weekend and if I remember, I'll check.

Never thought it wouod be that high of an IBO!!

I can say that my cousins wife uses a bow with a draw weight of 45 lbs (don't know her other stats) and she shoots the Spitfires and hasn't had an issue.

I'd actually use a cut on contact head (I like the Slick tricks), but my best accuracy has been with the Spitfires.

 

[chaded1]

I figured something was off because that calculator shouldn't be that far lol. I have had mine at the Pro shop a couple of times and its always really close to what I get on that calculator. Mechanicals and low poundage will work just not ideal to me, a COC style head is better at penetrating which can sometimes be an issue. I shot mechanicals last year and did fine. I shot the G5 T3 and the broadhead shown above. This year I have the Slick Trick Grizztrick 2's in my quiver. I always broadhead tune my bow for the fix blades so there is no problem with accuracy.

 

[Minnesota]

I was shooting a 2 blade rage out of my 2005 Hoyt Vtech, 28" draw set at about 52 pounds. The one and only deer I have shot at with this set up perfect pass thru, and he went about 50 yards and piled up. Blood was just pumping out of him!

 

[inline50]

For those of you that use mechanical broadheads, do they all lock in place after they open-up :?:

 

[chaded1]

No they don't all lock in place. Some do but some don't.

 

[Slitrik]

Even with my short draw length of 27", I still get 74 ft/lbs. I shoot a strother sx-1 at 67 lbs.
And you might want to remember that kinetic energy is not a good rating for bows. Yeah, it helps to give a general idea of its power, but momentum is a better way to go.

And the formula for kinetic energy is (Weight of projectile in grains divided by 7000) x (velocity squared) divided by 64.32.
Make sure you do it in that order. I'll do a sample problem.(250 grain bullet, 2000 fps)
(250 divided by 7000) = .0357142 x( 2000x2000)= (142856.8 divided by 64.32)= 2221 ft/lbs of energy.

 

[chaded1]

Slitrik is right about momentum but KE is a good reference point to go by. Here is a good Momentum calculator. http://archerycalculator.com/archery-kinetic-energy-and-momentum-calculator/

 

[Thunder53]

Slitrik is right about momentum but KE is a good reference point to go by. Here is a good Momentum calculator. http://archerycalculator.com/archery-kinetic-energy-and-momentum-calculator/

When it comes to bowhunting, I long ago decided to just use my "dead deer calculator" since I just get confused with all the "purdy nummers"!! :lol!:

 

[pilsbury38]

I think I am doing something wrong. I have a Mathews z7 set at 52lbs 28.5 inch draw shooting a 340gr arrow with a 100gr broadhead and I keep coming up with 71 kinectic energy. I don't think that's right.

 

[chaded1]

I think I am doing something wrong. I have a Mathews z7 set at 52lbs 28.5 inch draw shooting a 340gr arrow with a 100gr broadhead and I keep coming up with 71 kinectic energy. I don't think that's right.

I'm getting 58 lbs of KE for your set up. What are you putting in for IBO speed rating? Also, is your arrow 340 grains total or 340 grains plus 100 giving you a total of 440? Which Z7 do you have? I used the Z7 extreme specs which has a IBO speed of 330.

 

[pilsbury38]

Total weight 440. The original z7. 58 seems more realistic thanks