Modify poly AICS mags for CRF?

gnochi

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I recently got and have started playing with a Nucleus action, and saw a few recommended tweaks in various threads:
  • Gentler extractor entry
  • Beveled shroud locking pin
  • Cut back magazine feed lips
Those first two items are easy enough, but I only have @MDT_OFFICIAL polymer magazines (308, 10rd, shooting 6.5CM), and I’ve only seen those modifications on steel feed lips.
  1. Has anyone cut back the feed lips of their polymer AICS magazines (ideally MDT) to a bit behind the cartridge shoulder for the Nucleus, or other actions with some style of CRF? What issues, if any, did they encounter on that action?
  2. Has anyone then used these magazines without issues on push-feed actions? (Savage 10 in my case)
Thank you!
 

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I recently got and have started playing with a Nucleus action, and saw a few recommended tweaks in various threads:
  • Gentler extractor entry
  • Beveled shroud locking pin
  • Cut back magazine feed lips
Those first two items are easy enough, but I only have @MDT_OFFICIAL polymer magazines (308, 10rd, shooting 6.5CM), and I’ve only seen those modifications on steel feed lips.
  1. Has anyone cut back the feed lips of their polymer AICS magazines (ideally MDT) to a bit behind the cartridge shoulder for the Nucleus, or other actions with some style of CRF? What issues, if any, did they encounter on that action?
  2. Has anyone then used these magazines without issues on push-feed actions? (Savage 10 in my case)
Thank you!

Yes, we've had some customers modify our polymer magazines 223 for CRF rifles. However, we haven't had much feedback with CRF and 308 polymer magazines. If they require it should be evident right away. However, if you haven't tried it yet don't make any modifications until you can confirm it is necessary. One thing to note, although the polymer magazine has a 10 round body we do list them as 8 round magazines as this is where they work best.

Our polymer magazines work great with Savage short actions; we produce some of the polymer magazines for Savage!
 

gnochi

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Yes, we've had some customers modify our polymer magazines 223 for CRF rifles. However, we haven't had much feedback with CRF and 308 polymer magazines. If they require it should be evident right away. However, if you haven't tried it yet don't make any modifications until you can confirm it is necessary. One thing to note, although the polymer magazine has a 10 round body we do list them as 8 round magazines as this is where they work best.

Our polymer magazines work great with Savage short actions; we produce some of the polymer magazines for Savage!

It looks like I will need to futz with the magazines; I’ll start with one, then, and report back to y’all. I was mostly worried about feed lip pressure, etc., for the Nucleus - and the magazine still running fine if I need to use it in my Savage, let my BIL with a Bergara use a mag, etc.

I have 5 and until now have been running them in my Savage with zero issues of any kind. Excellent product!
 
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MDT_OFFICIAL

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Sounds good! If you need any help feel free to PM us here, on facebook/IG or send us a message through our support portal! We are always here to work with our customers! Any modification you make shouldn't affect the Savage too much.

Thank you for your kind words and believing in our products!

 
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gnochi

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Mostly because I’m trying to make it work with 6.5 Creedmoor - MDT users have apparently successfully modified their 223 magazines for controlled round feed, but they don’t have customer info on modifications to their other magazines.

I don’t shoot a lot of 223; are the feed lips on the 223 Accurate Mags cut far enough back that the next case body can push the case that’s being fed up, or does the shoulder or neck do the pushing?
 

LawnMM

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    Not sure where I missed that (6.5cm) but I did.

    Why not use regular AI, AW, Accurate, or MDT metal magazines?

    Seems like more trouble than it's worth to convert a polymer mag when metal ones already work? You also risk destroying the polymer mag so it doesn't work at all with anything.
     
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    gnochi

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    Not sure where I missed that (6.5cm) but I did.

    Why not use regular AI, AW, Accurate, or MDT metal magazines?

    Seems like more trouble than it's worth to convert a polymer mag when metal ones already work? You also risk destroying the polymer mag so it doesn't work at all with anything.

    That’s a very good point... chances are decent I’ll go that direction instead. There’s a lot of feedback suggesting even metal feedlips need to be adjusted excepting ARC mags - which have other issues that I don’t want to deal with.

    Grumble grumble.

    Separately I’m probably going to rebarrel my Savage into 223 so those accurate mags look like an excellent option, thank you!
     

    LawnMM

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    I have a CRF Bighorn and its fed without issue from AI/Accurate/AW/ARC

    The arc mags shit the bed when they get dirty and the AWs would occasionally cause a weird jam but none of that had anything to do with CRF.

    CRF isn't much different than push feed as they both push rounds forward out of the mag. Push feed just doesn't actually grab the case till you rotate the bolt closed. CRF scoops it as it pops free of the mag.

    Bottom of a CRF bolt is open so the rim can slide up the face as it pops loose from the mag and the extractor retains it.

    Edited to add, don't overthink this. I've modified mags and was never happy with the result. If the polymer mags don't work with your Nucleus get a metal mag that does. AI is the benchmark, if those don't work you've got other problems.
     
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    gnochi

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    I did end up literally hacksawing one of my poly mags, image below.
    • It’s a bit harder to load; I tend to get the case head stuck on the (no longer smoothly tapered from the front) mag lips.
    • It is *much* easier to run the bolt, to the extent that I now notice the hang from the unmodified poly mags when the cartridge is at its maximum angle during feeding.
    • The controlled part of CRF seems slightly better in general, but doesn’t immediately engage on the final round.
    • I did a couple 3ft drop tests (aka bench) onto every face of the magazine and it didn’t lose any cartridges.
    I’ll probably grab a bunch of metal mags soon enough; the better feeding feel alone is worth trimming the lips a bit, and though I’ve tested it I’d prefer the slightly more preload-adjustable metal lips for cartridge retention.

    EFA0B5FA-56A1-4F5E-B92D-A20862A30E96.jpeg
     
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