Savage 720 (licensed A-5 copy) locking block question

[MJD]

Short story and question: I am investigating a double-fire malfunction in a relative's 16 gauge Savage 720. After disassembly, I found out the locking block rail sheared (red circle in attached image). There is only one channel in the locking block for the rail to ride (it seems there could be one or two channels depending on manufacturer and time period).
Does anyone know if the locking blocks are the same dimensions across Browning A5/Savage 720/Remington M11, and/or if they are the same dimensions across 12/16/20 gauge?

This link from an online store indicates 20 and 16 gauge might be interchangeable...but having a little more trouble finding that clarity with a Savage-specific part since parts aren't apparently known to interchange easily between Savage/Browning/Remington.

https://www.midwestgunworks.com/page/mgwi/prod/B1111261

This is my first go with an A-5 derivative, so any insight is appreciated!

Edited to add - I believe the double-firing was caused by the sheared locking block rail jamming up the works, causing the firing pin to be stuck forward and striking the primer of the fresh cartridge....but that's just my hunch. Could also have been the 70 years of gunk from salt water and thick brush.

 

[Rudolph31]

I’m guessing you went to Numrich Arms and found that they have the part, but don’t specify the gauge. I’d call them.
https://www.gunpartscorp.com/gun-manufacturer/savstevspgfld/shotguns-sav/720-2

 

[MJD]

Thanks @Rudolph31, I did find the parts diagram on Numrich pretty quickly, but had a heck of a time getting someone on the phone, so I thought I'd try here first.....but I'll give them another ring.
Ebay had a lot of 12 gauge parts, but I am going to do a deeper search tonight.

I notice you and @Sovblocgunfan were big contributors to this great forum thread, it was a good read:

https://www.thehighroad.org/index.php?threads/looking-at-a-savage-720.850665/#post-11115830

 

[Rudolph31]

I’m glad you dug that thread up — I’d forgotten I knew all of that! Sovblocgunfan and I go back years on Shotgunworld. He was making a Browning/Remington Frankenstein. I’m not sure how that turned out; but if he says a part fits, you can believe it.

I’ve had the locking block rail break on an Auto-5. In that case I had a FTF and found the firing broken as a consequence. The narrow rail locking blocks are scarce, so I had to look on eBay. You’ve got to be careful there as sellers often don’t know what they have. I almost bought a part, then found the rail was on the wrong side. Eventually I got lucky. I hope you do too.

 

[MJD]

I was able to get on the phone with someone at Numrich and they indicated that since the part wasn't delineated as a specific gauge on the website schematic, it would likely fit.

I might just go ahead and order it, see if the dimensions are the same, and return it if not....the CS rep indicated they had a pretty good return policy on parts that weren't actually used.

I'm also going to go ahead and order a new friction ring, springs, etc....might as well give it an update!

 

[Rudolph31]

Good luck. And be sure to tell us what you find out.

 

[entropy]

I'm fairly certain it's on the 12 gauge frame. Whether Browning parts work or not, that I don't know.

 

[MJD]

So, an update.

I still have not found a definitive source to determine if the overall bolt assembly and/or locking block is different between gauges for the Savage 720/726/745/775/etc, nor do I have buddies with a veritable library of shotguns to get a few samples, tear down, and break out the micrometer

I have seen numerous listings on Ebay and Gunbroker that break these out by gauge, though as we established further upthread, Numrich does not.

I got a new locking block from Numrich. On this new piece, it appears the "locking" part of the block that interfaces with the barrel is a bit larger than on the original piece. That appears to be the only dimensional difference other than a (very) slight difference in machining on the back end of the block. In the attached photo, I've circled the part of the block slightly larger than the original piece.

I did verify there is no damage or peening to the part of the barrel where the locking bolt locks up with the barrel. So my general thought is that there could be
A) a dimensional difference between gauges in the locking block for the Savage, and/or
B) a change in part dimensions over the production run of the Savage A-5 licensed copies from 1930-1960s, or
C) I am completely out of ideas.

As I see them, my options here are to:
A) send the part back to Numrich with their refund policy, and try to get a part off ebay/gunbroker/the interwebz that is advertised as 16 gauge, and roll the dice it's actually the right size, and in okay shape.
B) say the hell with it, and try to slowly and lightly reprofile the locking bolt so the portion that is oversized is ground down such that it allows the locking bolt to correctly get into position with the barrel cutout. I'll be out 70ish bucks if I screw this up, but that's part of the game messing with these older, out of production guns. Other than that one bit I circled in the attached pic....the remaining portions of the locking bolt are dimensionally the same as the original piece.

If nothing else, this has been an outstanding opportunity for hands-on practice for multiple iterations of assembling/disassembling the A-5 type shotgun as I've gone through this process.

 

[MJD]

An update. I chose option B above. I lightly filed the locking block until it was able to fully engage the barrel.

Plenty of BLO on the stock and I think this one will continue to be in the family for another generation anyways.