Peak Weight Measuring Lower than Expected

[Mighty Mouse]

I finally got around to building a draw board and used it today to map the draw force curve of my Mathews Heli-m. Peak weight measured 60.1 lbs on a LCA 2.0 digital scale, and a Weston spring scale gave similar results. This surprised me because the shop I bought it from advertised it as a 70 lb bow and there's a 70 lb sticker label on the lower limb. Limb bolts are tightened all the way down. Is there any possible explanation other than that the shop misled me and the sticker is wrong? String is 3 years old, cable is 2 years old, original 26.5" cam was swapped after purchase for a 28" cam.

 

[joshdidthis]

Check your ata to make sure it's in spec or close.

Sent from my SM-G950U using Tapatalk

 

[Mighty Mouse]

Check your ata to make sure it's in spec or close.

ATA measures 30-3/8" vs. spec of 30".

While I was at it, I measured brace height as well: 7-1/8" measured vs. 7" spec.

Would you consider those measurements acceptably close to spec?

 

[Brendan]

So, draw weight shouldn't be off that much with that measurement.

Possible that the limb is labeled wrong, or check your scale.

I don't know the Heli-M at all personally, but I did a quick search and found something that said wrong limb turrets could do that and have draw weight running low

 

[*zap*]

I bet you have 50-60# limbs. If the info is on a sticker I would not trust it.

Elite sent me a replacement set of limbs for my GTO a few years ago. Crackers put them on last week when I went to see him for new strings, my old limbs were 40-50# the replacements maxed at 64#. Backed off one turn they were 61#. One turn left to back off and I guess they will be 56-58# or so. So the limbs are 56-64#. Quite a jump from 49# for my shoulder especially with the GTO cams. I need to adapt or drive back to Cameron , Missouri and have him swap the limbs back. Start doing some exercises for building up my draw muscles this week.....talked to someone who said drawing with the elbow up and rotating the shoulder back uses more back and less deltoid. Will try that also. I need to get this worked out since I hunt in pretty cold conditions.

 

[Mighty Mouse]

Possible that the limb is labeled wrong, or check your scale.

I don't know the Heli-M at all personally, but I did a quick search and found something that said wrong limb turrets could do that and have draw weight running low

My spring and digital scales are giving the same results and both scales check out with a 50 lb sandbag, so I'm pretty confident that I'm getting accurate draw weight values.

Thanks for the suggestion on limb turrets. I found an old Archery Talk thread mentioning turrets as a possible culprit. I'll try to do some more research on that theory.

 

[Mighty Mouse]

I bet you have 50-60# limbs.

That seems to be the most likely scenario. I can't see how else I would be 10 lbs off with all other measurements in or close to spec. I added a few twists to the cable yesterday and got the peak weight up to 63 lbs, but I don't know how far I should push it since I suspect mislabeled limbs. I'm planning to visit a nearby Mathews dealer this week and have him look it over.

 

[OR Archer]

Look at the cam. There’s a 1/4” cut out on it. The buss cable should run through the middle to outer half. If it isn’t you need to add twists to the buss cable until it does. Once you get the cam rotation correct then remeasure the peak weight.
If the string/buss are that old you should replace them.

 

[Marble]

Are there deflection numbers on the limbs like a Hoyt?

 

[Mighty Mouse]

Look at the cam. There’s a 1/4” cut out on it. The buss cable should run through the middle to outer half. If it isn’t you need to add twists to the buss cable until it does. Once you get the cam rotation correct then remeasure the peak weight.
If the string/buss are that old you should replace them.

I added as many twists to the cable as I could without a press and got the peak weight up to 63#. The cable is running pretty much dead center through the timing hole on the cam. I think I'll order a new string and cable today like you suggested and see if that helps. It was about time for a new set anyway.

Are there deflection numbers on the limbs like a Hoyt?

The only identifying mark on the limbs is a sticker with "70/26.5" (the supposed draw weight and original draw length before I swapped the cam) printed on it.

 

[*zap*]

You might check Carters archery for strings, send bow and an arrow and he will also properly tune it. Mike knows his stuff.

 

[Marble]

I added as many twists to the cable as I could without a press and got the peak weight up to 63#. The cable is running pretty much dead center through the timing hole on the cam. I think I'll order a new string and cable today like you suggested and see if that helps. It was about time for a new set anyway.
View attachment 112609


The only identifying mark on the limbs is a sticker with "70/26.5" (the supposed draw weight and original draw length before I swapped the cam) printed on it.
View attachment 112610

So I get that it's just like mine. I have a sticker on my bow too. But on the end of my limbs (Hoyt), where they go in the pocket, there are deflection numbers that will really tell you what limbs are on your bow. I hope you are able to get it fixed with what you got, but it's way off. You could have the wrong cable on there or the wrong limbs or IDK.

I would probably take it to a shop and go through it to see what the heck is off.

 

[Marble]

I just did a quick google search and it seems the Mathews limbs have deflection numbers. If it were me I would go to the shop, explain, and then let them check it out. If it is off Mathews should take care of you.

 

[Mighty Mouse]

I just did a quick google search and it seems the Mathews limbs have deflection numbers. If it were me I would go to the shop, explain, and then let them check it out. If it is off Mathews should take care of you.

Unfortunately I can't find any clues on the limbs themselves other than the sticker. The only place deflection info could be hiding would be on the area of the limb that bears against the riser, which I can't access without taking the limbs off.

I just ordered a Twisted X string/cable set and plan to visit the bow shop soon. Thanks for the suggestions, hopefully I can get this figured out.

 

[Brendan]

In my experience with mathews, deflections are not visible until you pull the limbs.

Have the shop check if you're having strings done.