Some thoughts on assessing your choice of shotgun for use with a Chaszel(or other) adapters or insert

A customer once asked
While I have your attention, perhaps I can ask for your opinion / expertise. My plan is to use the insert in a Mossberg HS 12. This firearm is Turkish made. I’m aware there’s about 12k psi difference between .44 mag and .45-70. Do you think it is smarter / safer to go .45-70 instead? And do think Turkish made shotguns are capable of handling the insert?
My response
Hi Customer
Wow, that is a way more complex question than it seems on the surface. 
I started to respond and realized that I had answered similar questions a # of times with people asking about different firearms.  I think that I will consider you the first reader of this response and will publish it on the website for others to chew on. 
Chaszel makes very specific recommendations on their website in regard to their recommended choice of firearms to use their inserts in.  That information is the only reliable advice that NINE35 can endorse.  It is strongly encouraged that the suggestions of Chaszel, especially in relation to remote firing to test a firearm are followed.  Since NINE35 has no control over the condition of the firearm or ammunition used, no liability is accepted in selection of appropriate firearms for use with shotgun caliber conversion inserts.
 The following information is presented in order to provide anecdotal information in order to help understand some of the considerations of why I think Chaszel made their recommendations.  
Factors to consider.
1st/ What is the condition of the firearm?  Is it new and tight, or worn out, have any parts started to fatigue?  What is the headspace condition?  While this is not mentioned by Chaszel, the obvious course of action would be, do not use any firearm that is not in safe condition, even if it is on the recommended list.
2nd/ What is the design? For instance, a question regarding the quality of Turkish (insert any brand or country here) manufacture was raised.  In my opinion the design is as important.  Is a Turkish, fold in half, single shot, as strong a design as an over/under? I do not think so but it could be.  To do the assessment we need to look at things called load paths and sizes of components such as the hinge pin dia. frame dimensions, materials used etc. and how the force is applied.   For instance, in an O/U which may have lower lugs engaging the frame, the force between the breech face and the locking bolt/frame lugs are likely at a better mechanical advantage than the top barrel enjoys.  Many rifle shotgun combos have the rifle barrel located on the bottom, could it be for this reason?  This does not discount the fact that the upper barrel is still designed to handle the forces involved in firing a shot shell.  The upper barrel is in a similar position relative to the hinge pin and lower bolt as many single shots such as a Cooey or similar firearm.   
Although it is not possible to cover every design, one problematic issue has been clearly identified and that is the issue of the size of the firing pin hole relative to the primer.  With a rifle the pin and hole are relatively small, effectively supporting the primer as best as can be.  Typically, this is not so with shotguns, they operate at lower pressures where this is not as much of a consideration.  There is (or was) an internet video where the author describes how the primer ruptured and blew the firing pin out the back of the firearm (Turkish made folding shotgun).  It pushed past the hammer becoming lost forever.  Fortunately for the owner it was being remotely fired at the time.  For this reason, shotguns that have been factory designed to handle centerfire rifle and pistol cartridges, as well as shotshell cartridges, are clearly a better choice.  Examples are H&R/NEF, SB1 (lower power calibers) and SB2 frames, TC Encores and some of the later Rossi's that came as multi barrel firearms (the models which included high power rifle calibers) from the factory,  I also like the Baikal firearms as the seem to share the same frame as the single shot rifle.
3rd/ What is the period of manufacture and quality?  For instance, the Iver Johnson, Cooey, Stevens 301 and many similar designs, use a 3-sided frame a full width hinge pin with a swinging bottom lug/bolt engagement.  I would put my money on a new Stevens made in China (not a fan of the country or politics, but know many good people from there) over an old cast iron Iver Johnson.  If we look through the lens of #2 (design) I may take a Cooey over a folding Turkish modern.  I have heard of one person who had an issue with a Cooey (it did not fail) but the shell peened itself into a soft breach face.  They had removed the spring-loaded ejector and believe that created a situation where the insert was not held against the breach face.  Not having personally inspected the firearm, I cannot say if there were other issues such as a loose hinge pin or headspace problems (their theory seems to support this).  Do not forget quality of manufacture.  For instance, the Cooey just mentioned, may have had the relatively thin factory case hardening worn through over time, remember the ejector rides over it when closing, or, maybe it was not properly heat treated in the first place.   Technology has vastly improved in both materials and processes so with similar designs, the more modern firearm is likely the better choice.  With the Cooey motioned above, there were no injuries as there were no catastrophic failures even after approx. a box or so was fired through it.  The user did discontinue using it.  I have a customer with the aforementioned Stevens shotgun who has shown me pictures of shell casings showing obvious displacement of the primer into the area of the firing pin hole.   This leads us into #4 
4th/ Operating pressure and choice of cartridge / ammunition.  This is an important consideration as base diameter and operating pressure of the cartridge influence the real forces acting on the firearm.  The pressure and diameter, relate to what is commonly referred to as Bolt Thrust.  In single/double shotguns this is the force exerted between the hinge pin, locking bolts and breach face.   So, although the 44 Mag at 36 KPSI pressure sounds more powerful than a 12 ga at 12 KPSI, the force is less (using .43 dia. and 36KPSI for the 44 Mag. vs .73 dia. and 12KPSI for a 12 Ga. to calculate (pi x r2 x psi) than the 12 ga.  However, the force is more concentrated on a 44 Mag because of the much smaller dia. of the cartridge base.  Remember the peened Cooey breach face mentioned earlier, that is a good example of the wrong cartridge for that individual firearm, I believe the owner was shooting 357 Mag.  If 38 special loads had been used there may have been no issue as the force would be lower due to the lower operating pressure acting on the same diameter base.  This is a good time to remind people that firearm chambers should be dry (no oil) when firing.  The variation in potential ammunition used, also needs to be taken into account. For instance, 45-70 loads can be had in several different pressure levels, make sure you are using the trap door rifle load level cartridge pressures when using an insert, not those loaded to higher pressure for the modern 1885 lever firearms.  Components used in the manufacture of the cartridge have an effect.  As mentioned, we know that the primer/firing pin hole relation is one of the critical areas.  Choosing a cartridge with a harder primer will be better able to deal with the unsupported area.  Hand loaded cartridges are another similar topic as well.  There are so many variables that it is totally, a use at your own risk proposition.   However, if you are going to reload, I would suggest using rife primers in your handgun cartridges as well.
So, in summary
- Only Chaszel recommendations can be endorsed
Things to consider in purchasing a shotgun insert
-Is the shotgun a robust design?
-Overall condition and age of the firearm.  A 22LR may be safe in almost any shotgun, but if there is an excessive gap between breech face and insert and the shell rim ruptures upon firing, it may not affect the firearm but the resulting shrapnel may cause injury or worse.
-Era of manufacture and the potential for poor quality materials being used, it is my opinion that older Chinese firearms (almost any older Chinese manufactured product) was inferior compared to newer Chinese manufacture.  This can even apply to NA products, remember the term "cheap knockoff", looking the same does not = being the same.  For instance, the newer Chinese Stevens look like an SB1 but the larger firing pin hole on the Stevens indicates that it is not exactly the same even if it is robust in manufacture. 
-Design of the firearm related to the power level of the intended cartridge.  Think about if a primer ruptures with 36 KPSI pushing on it, where will the shrapnel or displaced firing pin and escaping gas go?
Specific answer to your question.
Many major brands such as Mossberg use Turkish manufacturers and would insist on the firearm meeting their standards.  So I believe that there are some good Turkish units out there.  As per Chaszel's remarks if it is other than the recommended shotguns listed, caution should be exercised.
Regarding your suggestion of choice between the 44 mag and 45-70 see the comments and calculations above.  The 45-70 has a larger base and bore dia. than the 44 mag and you may find the force exerted is not that great a difference as you may think.  The 45-70 benefits from having a rifle primer as standard, compared to a magnum primer (typically harder than standard pistol).  Will it be safe for the operator, probably, remember the remote firing caution from Chaszel.  Will it damage the firearm like the cautionary tales mentioned above?  It will depend on all the factors mentioned above.
I know that this is not the absolute yes or no you are looking for all I can offer is the following is what I have and use.
In my Turkish o/u and Rossi 20 ga. single, 9mm no issue so far.
In my NEF SB1 single, 357 mag and 357 Max. (custom reamed) , no issue so far.
Ron
This article is provided for information and only you can determine the factors discussed and how they apply to your firearm, no liability is assumed in providing this information.  If you are not sure bring it to a qualified gunsmith.
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