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Tack-Driving Loads for 9mm CMMG Guard RDB PCC?


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I have a pair of 16" PCCs built around the CMMG Guard RDB system. They run 100% reliably, but accuracy is mediocre. So far, nothing I have tested shoots 10-shot groups smaller than 3" at 50 yards, and many loads look like a buckshot pattern. Has anyone found a load that is a tack driver in this platform? Bonus points for power factor <140 and/or 115gr bullets, but if I have to go hotter or heavier that's not a problem.

Edited by StealthyBlagga
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Two questions.  Of the loads you have tried, what was the most accurate?  What is an acceptable group, in your opinion?

I've never tested my CMMG for 50 yard groups, since we don't usually have access to that range for the USPSA matches that I shoot.

So, if I dare leave my house (thanks CoVid) and test at 50, I'll let you know if mine does any better.  I'm thinking, that my red dot sight may be a limiting factor., so a third question.  Are you using a magnified sight?

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Are you using a magnified sight?

 

That was my question too. I see so many people on forums asking about accuracy because their rifle won't group rounds on top of each other. But they are usually just using a red dot and I'd bet one with a 6 or 8 moa dot. THAT is the limiting factor in accuracy, not the gun or load.

Also, if you want real accuracy get a gun designed for that. Most PCCs are for close range games or home defense, not longer range target shooting.IMO

 

 

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Mine shoots 1.5” at 25yd with a 124gr precision delta JHP running around 140pf. Benched in. With a 4x scope.

 

All the ammo I typically run through it for my USPSA use? That’s more like a 3-4” and is all I need at my local matches. It doesn’t make sense to pay the premium for that bullet for 97% of the shots you take with a rifle in a USPSA match.

 

<edit> oops, Hollowpoint, not fmj.

Edited by MemphisMechanic
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1 to 1 1/4 in groups at 50y

3.8 to 4.0 gr Sport Pistol

124 JHP   

1.100 length

I am a 3gun shooter so my pcc is set up just like my 223    1 to 6  vortex pstII

Now the reason for the 3.8 to 4.0 powder charge. there are 5 of us that shoot together.

The different buffer systems and barrels has an effect . One has a JP 14in Barrel. One has a MPX.

Two have PSA barrels. And one has a Lead Star(over priced PSA🤣) I had a cmmg .

so if you can not get yours to shoot you may wont to look at your buffer system.It may

be too light for longer range accuracy.

 

Load #2 is not as universal

2in groups at 50 yards

3.0 sport pistol

135 gr RN   SNS coated

1.125 

 

 

Edited by AHI
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Thanks everyone. I am running a red dot, but am a long-time Limited Division 3-gunner so am very used to shooting tight groups with a red dot. It sounds like my 3" groups at 50 are not unusual. I will look at Sport Pistol to see if ti tightens things up. If I find a tack driver, I will post it here.

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Precision Delta 124gr JHP, 4.0gr of N320, 1.135" OAL. IIRC I got 1.7" group at 50, and I'm a mediocre shooter as you know 😊, so I'm sure it's capable of better than that. This is with a JP barrel, not sure if that length will fit a CMMG barrel, but if it will, and we ever have matches again 😀, let me know if you want to try some.

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41 minutes ago, Southpaw said:

Precision Delta 124gr JHP, 4.0gr of N320, 1.135" OAL. IIRC I got 1.7" group at 50, and I'm a mediocre shooter as you know 😊, so I'm sure it's capable of better than that. This is with a JP barrel, not sure if that length will fit a CMMG barrel, but if it will, and we ever have matches again 😀, let me know if you want to try some.

I don't think it's just the barrel, but, the entire RDB system. I don't think it's reached it's full development yet. 

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Check this thread to see what I did to make my CMMG more accurate. I think the feed ramp and the sloppy fit between the barrel and reciever are the biggest problems for CMMG accuracy. Mine runs the Glock mags.

 

My CMMG 16" Resolute 200 likes the Frontier 121 gr FP bullet the best of every bullet I have tried, it has a little harder and thicker plating than most plated bullets. I use the Frontier bullet with 4.8 gr of N340 or 4.0 gr of N320 - haven't settled on a winner there yet. I've had 10-shot groups measure 0.8" center-to-center at 27 yards (25 meters) with this load. LOS 123 gr FP over 3.9 gr N320 is my practice load, it groups 1.5"@27 yards. Factory Geco 124 gr FMJ also run accurately in mine, but they are a litte hot at 156 PF.

 

Generally, my CMMG seems to like medium weight bullets around 120-125 grains loaded to 140-145 PF.

 

Edited by mrd
added info
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MRD, it was interesting that you brought up the whole dinging thing with your system, because when I had a loose ejector on one of my regular/blowback PCC's, it would sometimes alter bullet feed from mag (Glock mag) and rounds would get dinged on the way in, or just have feeding and ejection problems.  That was remedied by tightening and loctiting the ejector blade.

 

But with my CMMG RDG upper, I use CMMG P-mag inserts and a mil spec lower, and have found the feeding to be very smooth and reliable.  So maybe that contributes to why I haven't seen deviations in grouping like others have noted, less or no dinging.

Edited by MoRivera
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Sounds about right, MoRivera.

 

The dinging was not my own idea, I read about the feed ramp dinging the bullets somewhere. I remember someone posting a picture with bullets that had indentions in the lower part of the nose from the edge on the lower part of the feed ramp. My bullets did not get dinged that bad, but I could for sure see markings and scratches on my bullets after ejecting unfired rounds. If dinging was part of the problem it would also explain why accuracy was more improved with softer bullets, like plated, than with FMJ's.

 

But considering how sloppy the barrel to reciever fit was, I think this was part of the problem too.

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6 hours ago, mrd said:

Sounds about right, MoRivera.

 

The dinging was not my own idea, I read about the feed ramp dinging the bullets somewhere. I remember someone posting a picture with bullets that had indentions in the lower part of the nose from the edge on the lower part of the feed ramp. My bullets did not get dinged that bad, but I could for sure see markings and scratches on my bullets after ejecting unfired rounds. If dinging was part of the problem it would also explain why accuracy was more improved with softer bullets, like plated, than with FMJ's.

 

But considering how sloppy the barrel to reciever fit was, I think this was part of the problem too.

Ah I see.  Thankfully, the 8" RDB barrels I have are pretty snug to the receivers I'm using so far.  Yeah, some dings on my other PCC that had feed/eject problems were more like gashes.  Especially with rounds like Blazer Brass which has a pretty think copper plating.

Edited by MoRivera
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  • 3 weeks later...

I this was my AR15, I would weep. But well, this is my "tack driving load" for my CMMG...

25 m = 27.3 yards

19 mm = 0,75 inches, center to center.

8-shot groups, shot rested with bean bag in front of receiver, scope with 20x magnification

I have better scope and mounts now, will test at 50 and 100 meters when opportunity presents.

 

20200504_222719.thumb.jpg.87302165aa3e7ee8245172fedbfc6818.jpg

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  • 4 weeks later...

After some testing and load development, this is what I have come up with:

 

147gr Blue Bullet Round Nose

2.8gr WSF

CCI SPP

Mixed brass

 

This load is VERY soft shooting, makes a 133 power factor, uses powder I have a lot of, and is relatively inexpensive. The 10-shot group below was shot today at 50 yards with a Trijicon MRO red-dot optic. The cluster is 8 hits in one ragged hole - the one high hit out on its own is a mystery, and this is what I have come to expect from both my Guard PCCs...  a reasonably tight group and then one or two wild flyers.

 

uaBSLCO.jpg?1

 

 

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3 hours ago, rondog said:

How does wsf compare to titegroup?   I need to find a good load for a pcc that’s on loan to me for a future match.   

 

Rondog... I use 2.7 grains of Titegroup with a 147 grain coated bullet to get a slightly higher PF as noted by Stealthy above.  Loaded to 1.148 OAL, I get 980 fps with a 16" barrel.  Stealthy used my "formula" as a basis for his test.

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Something I have always done to save frustration with a gun that is going to be used primarily for speed/competitive type shooting is to first figure out what the inherent accuracy of the firearm is.  Mount a magnified optic.  If you are a reloader go through the process of working up a load. If not, see which factory ammo you are willing to feed it on a regular basis is most accurate.  Shoot from a very good rest and figure out what the accuracy potential of the gun is.  At least then you have a base point to base performance with something like a red dot on.  If your gun can shoot 1" at 50 yards with a good rest and magnification, you have an idea what to expect from the gun.  If you put an 8 moa dot on a gun and it shoots 5" at 50 yards you have no idea if that's as good as the gun may be capable of.  Of course you aren't going to be as accurate with a dot as a magnified optic, but only experience will tell you what kind of difference to expect for you. Starting with a new gun, putting a 8 moa dot on it and just shooting doesn't tell you anything. It could be your technique, a gun that just isn't accurate for whatever reason, or a combination of the two.  

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2 hours ago, drysideshooter said:

Something I have always done to save frustration with a gun that is going to be used primarily for speed/competitive type shooting is to first figure out what the inherent accuracy of the firearm is.  Mount a magnified optic...  

 

Thanks for the reminder, but that's not my issue. I am a long-time Limited 3-Gunner and know myself to be capable of shooting MOA groups at distance with a red dot. The trick is to size the target so that the dot nests and centers very naturally with a halo of black evenly around it - this way, alignment issues are immediate apparent and easily correctable. In my case I am shooting 3" black rounds at 50 yards with a 2MOA dot turned down to the lowest visible brightness. I shoot for groups with my weak-eye closed. The PCC is supported front and rear with sandbags, which makes for a rock-solid hold. Lastly, I am centering the dot in the tube for every shot to minimize parallax error.

 

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19 minutes ago, StealthyBlagga said:

 

Thanks for the reminder, but that's not my issue. I am a long-time Limited 3-Gunner and know myself to be capable of shooting MOA groups at distance with a red dot. The trick is to size the target so that the dot nests and centers very naturally with a halo of black evenly around it - this way, alignment issues are immediate apparent and easily correctable. In my case I am shooting 3" black rounds at 50 yards with a 2MOA dot turned down to the lowest visible brightness. I shoot for groups with my weak-eye closed. The PCC is supported front and rear with sandbags, which makes for a rock-solid hold. Lastly, I am centering the dot in the tube for every shot to minimize parallax error.

 

I get where you are coming from. You know what you are capable of with a red dot, and are confident with your abilities.  I personally always feel better knowing what a particular firearm is capable of so that I can adjust my expectations, if it lacks accuracy with a red dot. No need to always go there first.  I find it easier to assess what a firearm can do with something other than a red dot, but everyone obviously has their own methods. If two examples of the same rifle are performing similarly, and poorly, it may not be ammo related.   Good luck with getting it resolved.  

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  • 2 months later...

Fesh 16" rdb

Zeroed scope using factory prime ammo.then shot PD hp both 115 and 124

Its pretty abvious barrel likes the lighter 115 better?

Do you guys see anything interesting with the groups? Which load should i re test and maybe tweak a little.

They were all loaded using progressive LNL

All at 50 yards using scope

received_705934779986276.jpeg

received_316699419538000.jpeg

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On 5/4/2020 at 10:38 PM, mrd said:

I this was my AR15, I would weep. But well, this is my "tack driving load" for my CMMG...

25 m = 27.3 yards

19 mm = 0,75 inches, center to center.

8-shot groups, shot rested with bean bag in front of receiver, scope with 20x magnification

I have better scope and mounts now, will test at 50 and 100 meters when opportunity presents.

 

20200504_222719.thumb.jpg.87302165aa3e7ee8245172fedbfc6818.jpg

Nice groups!! Is your OAL 27,0 mm or 27,8? Can't read it well 🙂 I am very interested in the Frontier 121 FP's! What PF do you achieve with 4,0 gn N320? Did you ever try RS12? I switched form N320 to RS12 with a 124 plated bullet and my JP loves it! Best regards!

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Thanks! Oal is 27,8 mm and they were about 145 PF. I have only tried N320 and N340 and they seemed to run better with N320 for me.

 

However, it seems Frontier does not make this bullet anymore. Terrible timing too, I just found this load and was about to order more bullets when I found out. I thought I found 2000 of them at sportshooter.de but they turned out to be .355 instead of the .356 I used, also shape was different and OAL had to be made much shorter. I have not yet shot them in my CMMG.

 

Frontier now makes a new type 121 gr FP, that they offer in both .355 and .356 and this new bullet is supposed to have a thicker coating to simulate a jacketed bullet. It is also much pointier, looks a lot like LOS bullets but with a thicker coating. However, I have not tried them so I can't speak to their performance.

 

I think the CMMG benefits from harder bullets, the bolt is really sharp and is tough on both the bullet and the casing, as is chambering. The bullet needs a harder coating or jacket to withstand the abuse. Softer bullets get deformed in the CMMG, at least in mine.

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4 hours ago, mrd said:

Thanks! Oal is 27,8 mm and they were about 145 PF. I have only tried N320 and N340 and they seemed to run better with N320 for me.

 

However, it seems Frontier does not make this bullet anymore. Terrible timing too, I just found this load and was about to order more bullets when I found out. I thought I found 2000 of them at sportshooter.de but they turned out to be .355 instead of the .356 I used, also shape was different and OAL had to be made much shorter. I have not yet shot them in my CMMG.

 

Frontier now makes a new type 121 gr FP, that they offer in both .355 and .356 and this new bullet is supposed to have a thicker coating to simulate a jacketed bullet. It is also much pointier, looks a lot like LOS bullets but with a thicker coating. However, I have not tried them so I can't speak to their performance.

 

I think the CMMG benefits from harder bullets, the bolt is really sharp and is tough on both the bullet and the casing, as is chambering. The bullet needs a harder coating or jacket to withstand the abuse. Softer bullets get deformed in the CMMG, at least in mine.

Tnx. I just ordered (before I read yr reply) 1000 pcs from sport shooter (I am in NL).... will do some testing and let you know. 

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