From data collected , most of the negative performance of these adapters is with arrows exceeding 700 grains which have encountered heavy bone as associated with water buffalo and cape buffalo. It is not commonly reported on deer size animals although I personally experienced the problem after hitting a white tail high in the spine area.
This bending problem is also not just isolated to the adapters used in glue on style broadheads .It is also documented with screw in style broadheads in which the screw post is part of the broadhead. This bending in also not just isolated to adapters made from tool steel but also shows up in aluminum and stainless steel adapters. That brings us to the “Weak Link” which is the screw post its self.
The standard female insert for all arrows aluminum and carbon is a NC 8-32 thread. The standard male thread consist of a threaded section which has a rough diameter of .158 inch or about 5/32 inch. It is almost exclusive in adapter failure to find this 5/32 diameter threaded post bent. There are several suggested solutions to this problem that range from hardened steel, synthetic materials and alloyed steels as material for stronger adapters. All have and will only be methods to strengthen the flimsy 5/32 diameter screw post.
There are options that skirt around the standard adapter and that is a one piece glue in insert adapter combination. These adapters/insert, (one style )can be seen at
http://www.vintagearcheryco.com/shop/. eliminate the post and connection point between arrow and adapter. The strength comes from diameter of the insert .The diameter is only restricted by the arrow size. For example a 5/16 carbon arrow has approximately a .249 inch inside diameter and a 9/32 arrow has an approximate ID of .204 dia. At this date for all big game hunts and until the bending of screw in adapters can be completely solved this is the safest method to potentially eliminate the “weak link”.
Titanium is a strong alloy and seems to be everyone’s panacea for the problem. Titanium has superior strength compared to it weight. But most grades do not have much more strength than carbon steel. If ones objective is to go light but stronger than aluminum than titanium is a good choice. When shopping for titanium adapters match the grade of the titanium to the game hunted. Most metal charts will show that grade 5 is superior to all others. It is extremely hard to machine the threads in grade 5 and to this date we have not been able to produce a grade 5 adapter that can be produced economically. I am however encouraged as just to day I was put in contact with a machinist that says he can make it. Our proto type will weigh 75 grains. It is solid in the 5 degree taper and the taper is to the max length at 1 inch.
Grade 5 titanium has a yield strength or tensil strength of 120,000 psi this is about twice the strength of mild tool steel and more than two times the yield strength of lower grade titanium
http://www.onlinemetals.com/titaniumguide.cfm While the adapter/insert combination has had no known failures and is stronger than most other adapters ,or screw on broadheads, it is not as handy as a screw in adapter. However, an archer can solve the problem match with different insert weights and adapter weights so the can replicate the weight of a adapter/insert. Use the screw in set up for practice and the adapter/insert for their hunting arrow. Titanium in the right grade may be a decent alternative.
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