Nock vs. String Failures - The HuntingPA.com Outdoor Community
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post #1 of 18 (permalink) Old 10-15-2017, 10:32 AM Thread Starter
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Nock vs. String Failures

I'm pretty new to hunting with a crossbow, this being only my third season. The hunting part has been no problem, after 16 years of hunting with a vertical bow, adapting to the crossbow went well. Learning the nuances of the equipment is another thing.

So... the other day I had a string fail while shooting at a nice doe. Completely blew up my string and cable set and splintered a limb. Thankfully the event didn't lead to a poorly hit deer. I found the bolt a couple yards short of the deer with no sign of a hit, but with a missing nock. i'm shooting a Mission MXB-360. The specs are: 160# draw weight, 14 inch power stroke and it shoots a 400 grain arrow at 352 fps.

The bow is just over two years old, but only got hunted with one full season in 2015, as last year I had a non-hunting related fall injury and missed almost the whole season. So basically, the bow has seen one full hunting season plus a few hunts between last year and so far this year. The string showed some light fuzziness in the serving at the nocking point, but not to the point that I thought it needed replaced. I was using 22" Victory Decimator bolts with half moon plastic nocks. After the string failure, I was quick to beat myself up for not changing the string sooner. But the fact that the nock was missing bothered me, and the more I thought about it, I'm thinking that the nock failed and the string blew right through it and the wall of the shaft cut the string. My daughter's boyfriend told me that his crossbow shoots at about 350 fps and that he's broken three plastic nocks just target practicing in the back yard.

So after doing some research, I'm finding that failures of plastic nocks are not that unusual. I'm seeing why Mission's bolts have aluminum nocks. I wonder if any of you guys have had similar issues, or know someone else who has, who can share some thoughts. Are you able to swap out plastic nocks for aluminum nocks? Are they readily available? Are there different sizes (weight and diameter)? Have any of you switched out your nocks? I'm getting a replacement limb and string and cable set shipped in, but if this is a nock problem, I don't want a repeat of this snafu.

Any help you can provide will be greatly appreciated.
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post #2 of 18 (permalink) Old 10-15-2017, 11:00 AM
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I highly suspect nock failure. The new plastics or polycarbonates are pretty tough stuff but they are not as durable as aluminum. I also has a plastic nock failure some years ago that resulted in a snapped string but no damage to the bow.

Missions are tough on nocks due to their aggressive cam design but this is mostly a problem with the 400, not the 360. If there was any fatigue in your nock, the aggressive cam turnover of the 360 probably caused it to fail and cut your string.

Aluminum moon nocks are the answer if you want the most durable nock material. Or you can simply swap out your plastic nocks every year to be safe. They are available for .300 ID shafts which are the most common crossbow arrow. I am sure your shop could get them for you if you wanted them as they are standard issue on Mission arrows. Black Eagle also manufacturers aluminum moon crossbow nocks.

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post #3 of 18 (permalink) Old 10-15-2017, 11:17 AM Thread Starter
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Thanks dpms, I figured you'd have some thoughts, and they are appreciated. The bolts didn't have that many shots on them. I'm thinking between 20 practice shots each. Do you think they'd fail that quickly? I saw Black Eagle's nocks on line, but it seems that they were made for a couple of particular shafts. How much do bolt shaft thicknesses vary between manufacturers? I want to make sure they would fit snugly in my shafts.
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post #4 of 18 (permalink) Old 10-15-2017, 11:21 AM
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Originally Posted by WexfordBowhunter View Post
Thanks dpms, I figured you'd have some thoughts, and they are appreciated. The bolts didn't have that many shots on them. I'm thinking between 20 practice shots each. Do you think they'd fail that quickly? I saw Black Eagle's nocks on line, but it seems that they were made for a couple of particular shafts. How much do bolt shaft thicknesses vary between manufacturers? I want to make sure they would fit snugly in my shafts.
You might have just had a bad nock. It can happen with anything. There are some variations between manufacture ID. .300 is a standard but not every manufacturer builds their arrows to this standard. Some are as small as .285.

If you are not sure of the ID of your shafts, firenock and lumenok have some good arrow fitting guides on their website where you can look up the diameter of your arrow.

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post #5 of 18 (permalink) Old 10-15-2017, 11:43 AM
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Are you 100% sure the bolt was back tight against the string? Just a thought? My friend shoots flat nocks in his ten points and the other year he had a problem with his serving being cut, now he ever so slightly chamfers his nocks to make sure the mold didn't leave a sharp edge on the nock.
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post #6 of 18 (permalink) Old 10-15-2017, 12:00 PM Thread Starter
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Thanks. I'm now sure it was a nock failure, I should have done this before, but I went and looked at the shaft and there were two indentations in line with the string. I've attached a pic. I'm sure I had the bolt fully seated, that's always been a concern of mine and I make sure every time I load a bolt in the shooting rail. Based on my research, I'm going to bite the bullet and switch to aluminum nocks. Thanks for the tips for the Firenock and Lumenok sizing charts. That should get me going in the right direction.
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post #7 of 18 (permalink) Old 10-15-2017, 12:40 PM Thread Starter
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Update, it looks like the Black Eagle nocks will work. They run $14.99 for a pack of 12 and small package shipping is $6.25. I ordered a couple of packs. Cheap insurance against a repeat of this failure.
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post #8 of 18 (permalink) Old 10-19-2017, 07:45 AM Thread Starter
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I got my xbow back last night. I switched out the nocks. Had to glue them on place. Looks good though and I'm anxious to get back out this evening.
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post #9 of 18 (permalink) Old 10-19-2017, 07:47 AM
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I got my xbow back last night. I switched out the nocks. Had to glue them on place. Looks good though and I'm anxious to get back out this evening.

Great to hear. Best of luck moving forward!

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post #10 of 18 (permalink) Old 10-19-2017, 05:33 PM
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I broke my new sting and cable after 6 shots. I blamed it on the archery shop. They blamed it on the nock. I got back to the cabin and checked it out. Sure enough, the half moon nock did not line up with the odd feather down. MFG defect. I checked all of the new ones I bought and the rest were good. I'll know to check from here on out.
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