Newbie here, well I was around 15-20 years ago but that is another story. I have a .40 SW upper and years ago I remember mating it with my Colt GC lower it used a special forward pivot pin(which I have), but I cannot remember if anything else had to be altered ie the buffer,springs,etc. Anyone got a clue?

Dan O'

No one here has an opinion?

It might be helpful for suggestions if you post more details about your upper. I’m assuming it is blowback and you would probably want a heavier dead blow buffer, maybe ask @Mad-Machinist (Rudy @Macon Armory)

Shoot it as is, then if it has any issues, that's when you address them.

If I was to guess at any issues that you may have......1st is Feeding.....2nd is extraction.......and then maybe play with buffer weight (try a 5.5 oz.....AFTER starting with a std 3.5oz )
With a std length carbine style buffer in a PCC configuration, you should be using a poly/rubber  buffer spacer to create the proper stroke length required for the BCG.
BCG should bottom out about 1/8" back from the bolt catch.

This is how set-up should go....load 1 round in mag, charge weapon, fire weapon.
Verify no feeding or extraction issues.
 If it had an issue, look to a BCG/mag issue. Some BCG might interfere with magazine.
 Some ejectors may need a slight adjustment. Look for any obvious wear lines on the components.
 If these don't solve it, only then would I look at the feed cone of the barrel, or bullet shape.

If it shot the single round OK......

Load 2 rounds -fire-  and then verify no feeding/extraction malfunctions.

Load 5 rounds -fire-  and then verify no malfunctions. If you have zero malfunctions at this point.....I would just go to the 5.5oz buffer to slow it down some and call it good.



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I recently set up a .40.  I used a bolt and buffer I got from Rudy, along with the standard carbine recoil spring.  It cycles great, and works with the occasional light load my press seems to produce for some reason.

Mark

Just me but I would start with a 5.5oz buffer if your upper is blowback. My dedicated CMMG Colt style lower works fine with the 5.5oz buffer but the 40 might need a little more weight. The Macon Armory 9mm buffer is adjustable from 5.5oz to 7.5oz.

I figured that 40 would require a heavier bolt. When I suggested a 5.5oz, that was as a minimum to start with. I would never suggest using anything lighter for a blowback.

I am interested in a 40 upper but would like for it to be able to be fed from Colt style magazines.

That would be awesome. I have loaded my 9mm Metalform mags with 40S&W ammo but didn't care for how they sat with the 9mm follower. Plus the fact that I'm sure the feed lips need to be adjusted to feed 40 vs 9mm