9mm Guard Barrel and BCG working with Colt mags (Page 1 of 2)
Posted: 12/23/2017 10:46:30 AM EDT
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For those of you with SBRed standard lowers with mag blocks, it is possible to get those Colt pattern mags to feed a Guard Barrel and BCG.
Will get some pics. |
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Looking forward to seeing how it goes! Curious...you didn't have to tweak the feed ramp at all? With mine I found the top was interfering with the bottom of the BCG a little. Hope all goes well with testing; if all this conversion takes is an adjustment to the mag catch notch then that's going to make lots of people very happy! |
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Originally Posted By 60-Driver:
Looking forward to seeing how it goes! Curious...you didn't have to tweak the feed ramp at all? With mine I found the top was interfering with the bottom of the BCG a little. Hope all goes well with testing; if all this conversion takes is an adjustment to the mag catch notch then that's going to make lots of people very happy! Have a couple of pics but photobucket sucks. |
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Originally Posted By badkarmaiii: So far, nothing done to AMM mag block feed ramp, removed ejector from block, raised mag notch .080", rounded front of mag follower. Have a couple of pics but photobucket sucks. |
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Originally Posted By 60-Driver: Ok cool interested to see your modified followers. I've tried Promag, Uzi, and C-Products so far, all with unmodified followers. Of the three, the plastic Promag followers have been the best at letting the bolt slide over top an empty mag but the orange C-Products are a no go; bolt hangs up ever time. C-Products orange follower... |
Here's mine so far, it's a work in progress. Rock River PDS upper/lower, Promag mag block with ramp walls milled down, chopped up eBay forearm, VZ.58 folding stock, Guard barrel turned down and re-threaded 1/2-28 with a ILWT 3-lug adapter, bolt carrier chopped to work with PDS recoil system:
It works, at least with the limited testing I've done. I shot a few mags of 3-5 rounds then a mag of 15. All suppressed using the same converted Uzi mag. 1 or 2 jams but nothing I would classify as a persistent problem. Will need to take it to the range to try different types of ammo/mags to get a better idea how it works. |
 Franken-Guard: CMMG Guard 9mm barrel and BCG with Colt mag and block |
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Originally Posted By badkarmaiii:
Franken-Guard: CMMG Guard 9mm barrel and BCG with Colt mag and block 
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Finally got out to the range myself to try a few different mag configurations and ammo types. I tried Promag Colt SMG, Uzi, PPS-43, and Sterling. I tack welded temporary 'blocks' onto the PPS, Sterling and one Uzi to seat them in front of the magwell:
In the gun: 
Uzi was an obvious choice since it's already used in other Colt-style 9mm's, but I also wanted to try Sterling and PPS. Sterling mags are just awesome and PPS-43 conversions to 9mm seem to do pretty well even though the rounds are too short for the 7.62x25 mag. However they load almost as easy as the Sterling and none of the rounds seemed to 'walk'. As a bonus, the PPS mags are supposed to hold around 17 rds of 45. That will come in handy when I start tinkering with the Guard 45 setup. Ammo was 115g Blazer Brass, 124g ZVS (Slovakian), 147g Freedom Munitions, and 147g Speer Lawman. All were round nose except for Lawman which has a truncated nose. On the first shot of FM, the case separated; clean cut right in half. I've had a rash of this happening recently with their new manufacture ammo. I've had good luck with FM before but know this is a documented issue. Rather than pressing my luck, I put the FM away and shot the other stuff. Everything else fed well but I did have a few FTF's with the Lawman. I blame the bullet's shape. Mag wise, I hate to say Promag and Uzi gave me the most trouble. I was hoping they would be best since I could readily use them with existing mag blocks but I started having issues if I loaded more than 5 rounds. At that point, they had trouble stripping from the feed lips. I did get one string of 10 shots without issue though. Next round of testing will include C-Products and Metalform mags. The Sterling and PPS did surprisingly well. Lawman again had a few FTF's but all the RN ammo was fine. I'd say the PPS mag prob did best of all. Will end up making an actual magblock for it eventually. I was also using a barrel from an old project gun. The bottom lug on the extension is completely ground off which I think allows for smoother feeding. When I was doing my initial testing, it seemed like the lug on the Guard barrel was causing some rounds to hangup & jam. Has anyone else run into this issue? |
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Originally Posted By 60-Driver:
Haha we'll see....still trying to find a way to get this thing to work with a Lightning Link! Tranferred a lightning link that cost the customer $14k. Crazy! |
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I've done some work on my PSA lower as well. Have not had a chance to test fire yet, but...
Mag height. I did not alter the notch on my mags. Too many to do & I like the idea of any colt mag working. Any metalform mag anyways. I notched the mag catch instead (about .090")  The feed ramp on the PSA appears to be from some other application. The body is short & they put this spacer thing in there. You can see the mag stop on the feed ramp as well.  Turns out that's not such a bad thing. The spacer is symmetrical so I reversed it & trimmed a bit & it gave me a new mag stop .090" lower than the original one.  New mag stop / height  I had to lower the feed ramp inlet & ears, and made the vertical & horizontal angles much shallower since the chamber is now a half inch further forward. The shallower angle seems to make the rounds strip off easier/cleaner as well. Did this with a carbide bit in my die grinder. 
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(wow. my "new" account has a character limit. never realized)
With this, the bolt (when testing with a standard 5.56 carrier/bolt) still drags on the follower as it's retracted. This isn't a problem with the CMMG carrier/bolt though. The CMMG bolt does not project forward of the carrier as far as a 5.56 bolt does. When retracting, the carrier body holds the mag follower down until the bolt lugs are over top of the follower as well so it doesn't catch the front of the follower like the 5.56 bolt does.  The bolt stop can still work, but it will need a modification. A hooked end to compensate for the lower mag position. It looks like it might, kinda, sorta work now, but won't likely be reliable. --Dan |
| Awesome job! I like the work on the feed ramp. Need to do the same...I've been having feed malfunctions where the front edge of the case neck will catch on the front of the feed ramp and hang it up. I think I may try lowering the feed ramp entirely which should help that out. |
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Turned out nice! Forgot to ask...
-After chopping the barrel, which buffer did you end up using? Any tuning weights? -Any FTF/FTE issues come up in various configurations? (suppressed vs unsuppressed, semi vs auto, super vs subsonic, etc) -Which can were you using? |
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-After chopping the barrel, which buffer did you end up using? Any tuning weights? H2 buffer, no tuning weights -Any FTF/FTE issues come up in various configurations? (suppressed vs unsuppressed, semi vs auto, super vs subsonic, etc) Had one FTF with the subs, which are 135gr and below 125 power factor. -Which can were you using? Griffin Armament Revolution 9mm. |
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NEW YOUTUBE VIDEO
Omega 9K with 5.9oz Armament LARB buffer and slightly softer-than-standard spring. Ammo was some cheap factory relaod stuff my buddy brought. I sold him my upper so now I gotta build another one. 
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I was able to mod a bolt catch and Colt style mag block to work with my CMMG Guard upper. It feeds and ejects dummy rounds 100% (so far). The rounds, however, look really beat up.
I am using PSA mags and the bottom lug on the bolt doesn't hang but does make solid contact with the metal follower - I wonder if this will be a problem long term? |
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Originally Posted By badkarmaiii:
The sharp back side of the bolt lugs are tough on ammo and brass but it works. I ask because I've been messing around with my 45ACP franken-Guard and experienced a couple of split cases so far. One of the lowers I'm testing feeds from HK USC mags and I noticed the lugs were getting hung up on the neck of the brass when I pulled the charging handle back. I would have to release the magazine to get the bolt back then reinsert to chamber a round. Best I figured, under normal cycling the lugs are scoring the brass badly enough to create a weak point that was failing under pressure. |
I'd probably keep it manual with a jewelers file. A few strokes should do it. If I broke out the dremel, I'd use a felt polishing wheel at most. I've gotten a little too froggy with the dremel in previous projects and ended up removing way too much material than originally planned, even with something as 'light' as Cratex  That's just me.
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| Did a quick couple of passes with a file then finished up with some fine grit sandpaper. Huge difference! Bolt is going back easy now, no longer catching on the rim. It's still putting decent scratches in the bullet/brass but a huge improvement from before. I think I may do a little Flitz polish next and hit the lugs and bottom of the carrier to smooth things up even more. |
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Originally Posted By 60-Driver:
Did a quick couple of passes with a file then finished up with some fine grit sandpaper. Huge difference! Bolt is going back easy now, no longer catching on the rim. It's still putting decent scratches in the bullet/brass but a huge improvement from before. I think I may do a little Flitz polish next and hit the lugs and bottom of the carrier to smooth things up even more. Most of the work in a reliability package involves making parts smooth, or so my dearly departed mentor taught me. |
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Yeah I finished up with polish on the lugs and bottom of the carrier. Night & day difference when manually cycling now. It is super smooth with zero binding. Plus the lugs are no longer gouging the bullet/brass. I definitely think it will make a difference in reliability & longevity. Will do a live fire test tomorrow. Granted this is with the 45 but I'm sure it'll also help the 9mm when I get back to testing it... |
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I was able to take my modded mag catch/Hahn mag block out over the weekend. It ran in semi & full-auto. A few observations: 1. Because the slot in my mag block was filed to lower its overall height in the gun I found it best to insert a mag on a closed bolt. This kept the block from moving upward as the mag was inserted and from having the block's feed ramp from interfering with the Guard bolt. 2. Because I modded the mag latch to allow the Colt Mags to sit lower in the gun, I could not swap on my 5.56 upper and have it work properly. The modded mag latch allowed the 5.56 mag to sit too low and would not reliably strip and chamber rounds. Thus, while the gun is very soft to shoot (mith my A5 system and A5H2 buffer) the modded mag catch is not a long-term solution for those who want to be able to swap pistol/rifle calibers. My thoughts are that the only viable solution would be to mod the mag catch slot on the Colt mags OR wait for someone to provide a Glock mag block that has the height of the mag lowered a few millimeters to account for the altered feed height in the Guard system vs. the blowback system. |
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Originally Posted By cbecker333:Thus, while the gun is very soft to shoot (mith my A5 system and A5H2 buffer) the modded mag catch is not a long-term solution for those who want to be able to swap pistol/rifle calibers. My thoughts are that the only viable solution would be to mod the mag catch slot on the Colt mags OR wait for someone to provide a Glock mag block that has the height of the mag lowered a few millimeters to account for the altered feed height in the Guard system vs. the blowback system. Swapping a mag catch takes less than a minute to do and is by far the cheapest and easiest conversion.
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Originally Posted By jreinke: WTF dude! Swapping a mag catch takes less than a minute to do and is by far the cheapest and easiest conversion.
ETA - Video |
9mm Guard Barrel and BCG working with Colt mags (Page 1 of 2)
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