Penetration: weight vs. diameter
 

It has long been established that, all other factors being equal, a heavier arrow is going to out penetrate a lighter arrow. But it is also widely asserted that a small diameter arrow is going to out penetrate a fatter arrow - all other factors being equal.

I'm wondering how these two factors compare when considering penetration on big game animals. On one extreme, I have some carbon express Terminators that weigh 507 grains with a 100 grain Montec. But they are kinda fat. I have some ST Axis arrows that weigh about 25% less; but are also about 16% slimmer. How much weight can you give up by going slimmer withoutlosing penetration? Is the 9.0 gpi Axis slim enough to make up for its lack of weight, in comparison to the 11.0 gpi Terminators?

RE: Penetration: weight vs. diameter
 

Yikes! You pose a difficult question. I don't have a pH.D in physics, but I do have some experience in the subject. That said, I have no idea what the relationship between arrow diameter and weight realtive to penetration is. Intuatively I would say that mass is a more significant contributor to penetration than arrow diameter, but even if that is true - by how much? I dunno!!!

RE: Penetration: weight vs. diameter
 

Probably not. But you can also add weight, like a couple strands of weedeater line, to the Axis and have the smaller diameter plus weight.

RE: Penetration: weight vs. diameter
 

Ashby's studies on diameter was in relation to the diameter of the broadhead ferrule. It was not small diameter vs large diameter. Penetration was very high on large diameter shafts, as long as the broadhead ferrule was even larger. He hasn't compared the two to each other, but I suspect that weight is far more important. It's easy enough to pick a broadhead with a larger ferrule, no matter what the weight.

Arthur, the nice thing about the Axis shafts is that they are fairly heavy for a carbon shaft. I just built some this past weekend. I put 220 grain tips on an Axis 300 (10.7 gr/in). I ended up at almost exactly 600 grains. FOC was about 19%. They flew just wonderfully with broadheads. Just so you know, the 300s come in a 32.5" length - almost long enough for you to shoot. ;)

RE: Penetration: weight vs. diameter
 

I'll have to check into that then, SA... I've got my rest set back far enough into short overdraw position so I can shoot 32" arrows.

RE: Penetration: weight vs. diameter
 

SA

What heads are you using?

I have been testing the Muzzy Phantoms without the bleeder blades sothey come in at 200gr.

The only problem is I cant find 200gr field points[:@]

RE: Penetration: weight vs. diameter
 

Try 3-rivers archery for 200 grain screw in field points. You could also get brass or steel inserts.

RE: Penetration: weight vs. diameter
 

Thanks Bob

RE: Penetration: weight vs. diameter
 

I've managed to get quite a few quys at my local shop to use the heavy tips, so the owner stocks the 200 grain tips. Like Bob says, 3-Rivers has them.

I'm also using the Muzzy Phantoms and got them flying great with the bleeders. I'm not bothering to try matching the field tips exactly, since they fly very well at 200 grains, causing a slightly stiff arrow. With field tips, this makes no difference.

RE: Penetration: weight vs. diameter
 

I done a test yesterday at 40 yards with mine.
I have them on Beman 400's 28" with 4x2"Predator vanes, The other arrow I used as a comparison was a Easton AC Super Slim 27.5", 3x4" Dura vanes with the Muzzy 100 3 blade.

It was a brand new broad head target the Phantoms penetrated a good 8" more and to my surprise 2" higher than the lighter AC Super Slim.

The 2 arrow weights are the Beman 494gr while the AC is 410gr, both broad heads where brand new out of the packet.

The arrow flight I got the the Phantom was perfect and it did hit the target with a THUMP;)

The difference in FOC is Beman 24.8 and the AC 12.6

RE: Penetration: weight vs. diameter
 

It seems like you have multiple variables in your test . . . . would it be possible to shoot each arrow with the same head? Or to test each of the two heads attached to the same arrow? Also, I'm not convinced that the penetration an arrow displays on a broadhead target necessarily indicates what could be expected on game; since almost all of these targets stop the arrow by exerting friction on the arrow shaft. Got some hogs in your neighborhood :)?

RE: Penetration: weight vs. diameter
 

I just weighed my 29" Axis FMJ 340's today. Slim arrow and weighed in at 496 with a 100 grain point.

RE: Penetration: weight vs. diameter
 

In an animal if your broadhead is 1" wide, what difference is it going to make if the arrow is 1/4" or 3/8"? It will be going thru a 1" hole!

Just seems like common sense to me.

Now in a broadhead target I can see a slimmer arrow penetrating better. The foam heals much faster than flesh.

RE: Penetration: weight vs. diameter
 

The arrow folks seem to be convinced that slim arrows penetrate better. Or at least that is their marketing ploy. Other than flesh and blood targets,it's hard to come up with an artificial medium to quantify penetration. I haven't shot enough game to come up with any meaningful comparison on this issue . . . .

RE: Penetration: weight vs. diameter
 

Yep. I have to admit I long held onto that point of view myself. But according to the arrow lethality studies on live game and dead animals that Dr. Ashby has done, smaller diameter arrows really do penetrate better, all else being equal. Heavy arrows penetrate better than light ones. High FOC arrows penetrate better than low FOC arrows. I have to go with the data over gut feeling. So, it looks like if you want maximum penetration you want a heavy, small diameter arrow with a very high FOC.

RE: Penetration: weight vs. diameter
 

The Axis arrow I'm using are the ST's - they are all carbon and the 400 series weigh 9.0 gpi. Axis FMJ are quite a bit heavier and, although I haven't put the calipers on any yet, don't appear to be as slim as the ST Axis. Minemike out at about .262". The A/C Super Slims are even skinnier at .252".

RE: Penetration: weight vs. diameter
 

I think a heavy arrow would work better than a skinny. Like if I had to choose between a heavy fat arrow and a lighter skinny arrow I think the fat heavy arrow would out penetrate the light skinny arrow providing the weight difference was big enough.

Paul

RE: Penetration: weight vs. diameter
 

I'm inclined to agree with you. I'm sure slimmer could make up for a certain amount of weight, but probably not 100 grains worth. Other factors would, of course, be the surface finish of the arrow shaft and the FOC.

RE: Penetration: weight vs. diameter
 

ROSKOE; I believe a slimmer arrow would get better penetration in a target than a larger arrow of same weight.but once you go from target to animal I prefer a heavy arrow as opposed to a lighter slimmer one,because once your broadhead opens him up it's easy saiing.That just my 2 cents.Anyway I like all the advantages of a heavier arrow.I've heard you comment on how queit your bow is with the heavier arrow many times.As far as the guys at the archery shop trying to sell you on something thats their job,plus have you ever noticed how each shop tend to push a differnt bow,broadhead arrows ect.One shop swears by mathews the next may praise hoyt and so on.

RE: Penetration: weight vs. diameter
 

I have to admit the local shop is big on the Axis - as is one of my hunting buddies. One thing that turned out pretty well in this process is that I was able to swap Whisker Biscuits (large to small) without any change in point of impact. Maybe I was just lucky . . . . . .

Hate to be indecisive, but I'm kinda torn at this point between the heavy arrows and the new Axis. If I was just hunting elk, it would easier - go with the spear. But antelope opens on August 15th and elk on August 25th. Both seasons are rather long and one could conceivably hunt goats on Saturday and wapati on Sunday. For the dual purpose, I would probably lean towards the Axis. And fall turkey opens September 1st. Can't wait :)

RE: Penetration: weight vs. diameter
 

Arthur, Ashby has written so much, it's difficult to remember everything, but I did find this that he wrote.

"Data was suggestive that shaft diameter did appear to be of significance in penetration. When velocity, broadhead and arrow mass were constant, shafts (1) smaller than the broadhead ferrule in diameter, (2) equal to the broadhead ferrule in diameter and (3) larger than the broadhead ferrule's diameter did appear to be a significant factor in penetration. No difference was discernable between shafts of varying amounts smaller than the broadhead's ferrule. If the smaller diameter shafts are assigned a factor of 1.0, then the apparent reduction in penetration was 10 percent (0.9) for shafts equaling the broadhead's ferrule diameter and 40 percent (0.6) for shafts of diameter exceeding than the broadhead's ferrule.

With a quick look, I couldn't find anything else that contradicted this. It appears that his studies had to do with the relationship between shaft size and ferrule diameter. The thing about the small diameter shafts is, it is easy to find broadheads with larger ferrules. In fact, I don't think you can find otherwise.

RE: Penetration: weight vs. diameter
 

Yes I could, but that would open up another can of worms because the arrows are currently spined for the heads and if I swaped heads then I would have one arrow over spined and one under spined;)


That is true and I totally agree but my tests where for mainly arrow flight and to see what the drop was between the 2 arrows I was expecting the heavy head to drop but was surprised when it didn't.Oh and the human element was taken out of the shooting;)

Unfortunately no I dont but I do plan on going after some again when the weather cools down.

RE: Penetration: weight vs. diameter
 

Ashby had posted a preliminary chart in a thread over on Tradgang.com that showed average penetration for a variety of arrows using the same broadhead. I think it was GoldTips he'd weighted up to 600+ grains, to be equal to the larger diameter arrows he was using. Don't remember the brand for sure at this point. Anyway the carbon arrows did penetrate better. Not much better, only a couple of inches, but it was measurable and consistent.

I kinda drew my own conclusions from that. It may well be the shaft dia. vs the ferrule dia. is what makes the difference. I'm not sure Ashby himself has reached a firm conclusion yet. But it's obvious to me from his data that, using the same broadhead, a smaller diameter arrow shaft at the same weight with the same FOC will yield at least somewhat better penetration.

Doesn't mean I wouldn't still poke a hog with a 2315 or a 23/64ths cedar though. They've been doing great for me for a lot of years. It's just that I've still got a lot of crow left to eat over this shaft diameter thing. ;)

RE: Penetration: weight vs. diameter
 

I agree that diameter most likely has an effect. I was just trying to find if there was any hard evidence of it.

I know what you mean. I'm totally convinced on the benefits of extreme FOC arrows, yet I'm going to be shooting some 2018s with only 125 gr on the tip, out of my longbow this fall. 560 grains that flys straight, will still do the job on a deer. I have the arrows and they are too weak for a heavier head, but they have plenty of deer shooting left in them.