Modern Sporter builds Q&A

I’m reading lots of complaints about mag compatibility. How common an issue is this?

I’d planned to use Gen 3 PMAGS, and the metal 10/30 mags S&J have/had. Maybe the Canadian made pistol mags too.

Is the mag issue something the end user can fix?

I've tested steel GI mags, gen 2 pmags, ATRS 10 round pistol mags, LAR - 10 round pistol mags, even Black Dog 22LR mags for my 22 conversion, all work and cycle fine, the pmags were a bit tight inserting and did not drop free without a little pull.
 
I’m reading lots of complaints about mag compatibility. How common an issue is this?

I’d planned to use Gen 3 PMAGS, and the metal 10/30 mags S&J have/had. Maybe the Canadian made pistol mags too.

Is the mag issue something the end user can fix?

It is not common, there were some uppers made (slick sides) that had an issue with the dimensions at the front. We caught this caught this fairly quickly and thought we had stopped any from getting out... It appears that a box (20-30) clearly made it through and got past us. So of the thousand or so receivers currently out in the public, it's a very small chance, and we are happy to correct it, if given the opportunity.
 
It is not common, there were some uppers made (slick sides) that had an issue with the dimensions at the front. We caught this caught this fairly quickly and thought we had stopped any from getting out... It appears that a box (20-30) clearly made it through and got past us. So of the thousand or so receivers currently out in the public, it's a very small chance, and we are happy to correct it, if given the opportunity.

I messaged you guys about my one set. The other set with just the pivot pin installed works fine.
 
Anyone else having their rear-fixed pin start rotating in the receiver?
My buddy's build has some upper/lower play and the rear pin is spinning. Im not sure what to do to fix it, since he had me assemble it for him.
 
Out of curiosity, how is the barrel receiver extension to upper fit on these? What is the measurement ATRS is opening their receivers up to to accept the barrels?

I have installed 3 barrels into 2 receivers. I took measurements but don’t recall them. All three barrels needed one complete wrap of 0.001” shim stock for a nice fit. Having said that I’ve only seen one barrel/receiver interface that didn’t need any shim stock in about 10 builds so this isn't out of the ordinary imo.

The barrels were:
BSF
Faxon
Custom lilja from ATRS(don’t know who’s extensions they use).
 
I have installed 3 barrels into 2 receivers. I took measurements but don’t recall them. All three barrels needed one complete wrap of 0.001” shim stock for a nice fit. Having said that I’ve only seen one barrel/receiver interface that didn’t need any shim stock in about 10 builds so this isn't out of the ordinary imo.

The barrels were:
BSF
Faxon
Custom lilja from ATRS(don’t know who’s extensions they use).

I'm about to help my gun buddy from Canmore with an ATRS build. It will be my first. He's going with a BSF barrel.

So what is "Shim Stock"? A quick google suggests it wraps around the barrel for a tighter fit - is that it?

Where can a guy lay their hands on some? I dont imagine there is a great selection around Canmore so it might be an internet thing. I looked around a little and it seems like it comes in a bunch of different materials (aluminum / brass / steel) and thicknesses / widths.
 
I'm about to help my gun buddy from Canmore with an ATRS build. It will be my first. He's going with a BSF barrel.

So what is "Shim Stock"? A quick google suggests it wraps around the barrel for a tighter fit - is that it?

Where can a guy lay their hands on some? I dont imagine there is a great selection around Canmore so it might be an internet thing. I looked around a little and it seems like it comes in a bunch of different materials (aluminum / brass / steel) and thicknesses / widths.

It's just a sheet of stainless steel that's 0.001" thick, comes in a roll, 6" wide, however long. I think I got mine from amazon but not sure could have been Acklands.

I just cut a strip as wide as the extension, then cut it so it doesn't quite wrap the whole way around. Trim a bit for the feed ramp and some for the aliment pin if needed. It cuts like paper with normal scissors.

It can be a PIA sometimes, if it crumples while trying to slide the extension in the receiver its usually best to just start over with a new piece. A little Aeroshell grease helps but just a thin film. If its really tight I will add some heat to the receiver with propane. If it still wont go with one full wrap just trim it a bit so their is a gap at the top.

I'm not a expert, just my experience. Feel free to PM m if you have any questions or can't find any shim stock.

This is the stuff I used but any would work I'm sure.
lfP5f7M.jpg

TxnOs1s.jpg
 
It's just a sheet of stainless steel that's 0.001" thick, comes in a roll, 6" wide, however long. I think I got mine from amazon but not sure could have been Acklands.

I just cut a strip as wide as the extension, then cut it so it doesn't quite wrap the whole way around. Trim a bit for the feed ramp and some for the aliment pin if needed. It cuts like paper with normal scissors.

It can be a PIA sometimes, if it crumples while trying to slide the extension in the receiver its usually best to just start over with a new piece. A little Aeroshell grease helps but just a thin film. If its really tight I will add some heat to the receiver with propane. If it still wont go with one full wrap just trim it a bit so their is a gap at the top.

I'm not a expert, just my experience. Feel free to PM m if you have any questions or can't find any shim stock.

This is the stuff I used but any would work I'm sure.
lfP5f7M.jpg

TxnOs1s.jpg

Thanks for the pointers. I`ll get some ordered as a first step but your explanation makes perfect sense.
 
Ive read in this thread that lapping the receiver is not required and is not recommended by ATRS.

For those that have completed builds how does the receiver to barrel fit seem and has anyone needed to lap?
 
Hi all this is my first build and so far all is going well except my bolt catch retaining pin won’t seat flush, am I using the wrong pin or is it a part of the design? Other pics I’ve seen of finished builds have the pin being flush
 
It's just a sheet of stainless steel that's 0.001" thick, comes in a roll, 6" wide, however long. I think I got mine from amazon but not sure could have been Acklands.

I just cut a strip as wide as the extension, then cut it so it doesn't quite wrap the whole way around. Trim a bit for the feed ramp and some for the aliment pin if needed. It cuts like paper with normal scissors.

It can be a PIA sometimes, if it crumples while trying to slide the extension in the receiver its usually best to just start over with a new piece. A little Aeroshell grease helps but just a thin film. If its really tight I will add some heat to the receiver with propane. If it still wont go with one full wrap just trim it a bit so their is a gap at the top.

I'm not a expert, just my experience. Feel free to PM m if you have any questions or can't find any shim stock.

This is the stuff I used but any would work I'm sure.
lfP5f7M.jpg

TxnOs1s.jpg

I just ordered some stainless 0.001 stock from Amazon.

I probably got enough for 100 builds but its not expensive.

Been reading up on it a little and it certainly seems like a better bet than just Loctite to bridge the gap (which is what a lot of folks seemed to be using)
 
Hi all this is my first build and so far all is going well except my bolt catch retaining pin won’t seat flush, am I using the wrong pin or is it a part of the design? Other pics I’ve seen of finished builds have the pin being flush

Could someone please give me some insight into this before I get frustrated and do something stupid lol
 
Could someone please give me some insight into this before I get frustrated and do something stupid lol

So are you saying that your bolt catch roll pin, is sticking out from both sides on the lower? A picture might help us if that's an option for you, as I'm trying to picture what you mean and why you can't just tap it in further.
 
Anyone happen the know the size of the ball bearing early lowers use for the safety? The guy I sold mine to lost it swapping safety levers...
 
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