More detailed comparison and testing
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Since I do not have an original VSR for testing, the cross compatibility test is done using a T10 and some spare parts I have in hand and might be slightly (but not significantly, probably) off.
Receiver compatibility
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While the receiver is on-spec in terms of seating in a stock, due to the narrow stock width a bull barrel cannot be used. It's likely that a tapered VSR can seat into this stock without issues but I cannot verify.
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Remember I said about the trigger not being compatible……well it turns out
I lied instead. Although the threads are not the same compared to standard VSRs (M2, compared to the M3 of the T10, and M4 of the SSG10), provided you have compatible screws or use the stock screws you can actually attach an aftermarket trigger onto it and it functions entirely A-OK.
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However due to the trigger box design if the Fieldcraft, it seems that the stock Fieldcraft trigger couldn't fit into other rifles like the AACT10, even though you can attach the trigger onto it like normal. Anti parts scavenging much? (If you used a regular trigger you can fit the whole receiver into the T10 as usual)
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A hex screw slipped during the process of attempting to detach the outer barrel from the T10……rip, good thing I have kept the spare barrel somewhere handy though
As seen in here the receiver thread part is significantly wider, you cannot fit an aftermarket bull barrel onto it at all (not that you can given the stock dimensional limitation). Good thing the receiver is VSR compatible though.
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A CYMA 50rd mag and a regular TM mag has been used to check magazine cross compatibility.
While the stock magazine is a snug fit and can enter and leave the mag well effortlessly, the other two mags couldn't fit in properly, and will get stuck even if you managed to brute force it in, you will have to disassemble the gun to get it back out. (In comparison, the T10 doesn't have any of these issues and all mags can be used pretty much normally)
It turns out the stock magazine is about as wide but is slightly shorter than the others (the CYMA is notably longer than a TM one by a really small margin), hence the jammed mags problem. By filing the magwell slightly with a chisel (as seen in here - it was a flat reflective surface), while the stock mag is now a bit loose (but still comfortably tight) while the others now fit snugly.