190gr Sub-X cycling issue

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BrianT
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190gr Sub-X cycling issue

Post by BrianT »

My Novel, thanks in advance to anyone that reads all of this, and for your help. Also, please let me know if I have this in the wrong place.

Rifle- 16” CMMG Barrel, Carbine Length gas, gas port was .110”, now .123”, Odin Works Low profile gas block.
Sprinco White Standard carbine buffer spring, or Sprinco Yellow Reduced power spring, 3.0oz and 4.75oz buffers
All Unsuppressed. Shoots Supers from 110gr thru 150gr no problem.

When I first started shooting Subs with this rifle, 208gr Hornady BTHPs and Berry’s 220gr Plated SPs, I had a few Fail to Ejects and No bolt lockbacks, only with Lil Gun and CFE BLK, so I put in the Reduced Power spring, and haven’t had any more issues. 1680 was never an issue.

Then I started trying to shoot the Hornady 190gr Sub-Xs. My first load of 5 rounds, 11.2gr A1680 @ 2.070”, all shot, ejected, and locked the bolt back, but were slow, about 930fps.
I jumped up to 12.2gr, which was over the 1050fps I am looking for, and the first 2 rounds shot ok, but after the 2nd round the bolt caught the 3rd round just forward of the base of the case, instead of the base itself, and wedged the round into the feed ramp/lugs.
I cleared this, shot the 4th round, and had the same issue/problem with the 5th round being wedged between the bolt and the feed ramp/lugs.

I stepped down to 12gr, which gives me the velocity I’m looking for, but still got cases not feeding right.

I tried going back to a standard carbine spring, and then went to the 4.75oz buffer, no change same problem.
All cases land at about 4:30.
I ASSumed I was undergassed a little.

I pulled the gas block, and measured the gas port, which was .110”, so I opened it up to.123”.

I shot 5 of the 190gr Sub-X rds thru it, all good velocities, no failures, thought I had it licked.

I then tried to shoot these same 190gr Sub-X rounds thru my 10” BA barrel, pistol length gas, which up to this point has shot everything I have loaded in it, from 110gr thru 220gr, with no failures, and had this same feed failure, after the second round.

I cleared this, and put the remaining 2 rounds in this magazine, in my 16” rifle.

I had the feed failure after the 1st round.

Why am I having these issues with these 190gr Sub-Xs, or is it something I'm missing with the rifle?

I also tried 9.6gr of H110, 190gr SUB-X, 2.050”, over 1100fps, but none fed the next round, and no bolt lockback…This was with the standard buffer spring and 3.0oz buffer.
Augenblick
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Re: 190gr Sub-X cycling issue

Post by Augenblick »

If you didn't see any signs of gas leakage when you addressed the gas block i wonder if you problems are more mechanical in nature? I say this because I have loaded the sub-x 190 with h110,cfe blk and 1680 and had full function in a sig rattler 5.5" and a PSA 16" pistol length. It seems with those loads and especially in your 10" pistol length gas that you should have plenty of gas with those powders to cycle. From what I have read the 16" carbine gas barrels are going to be harder to work with in general.

Make sure your gun is clean and well oiled.

What brass are you using?

One of the things l have learned is that different cases have different capacities. What might be a full powder load in one case may be compressed in another case with a different head stamp. Without the right neck tension a compressed load may grow in length.

Do you have a case gauge/ammo checker? If not it might be helpful to figure out what is going on.

Check you COAL the next day to see if those loads grew on you if they were compressed. I'm not sure they could grow enough to cause magazine feed issues or not but maybe?

That's all I can think of this late. I'm also really new to this so hopefully some of the more experienced guys here will weigh in.

Might be helpful to list you magazines too.
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dellet
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Re: 190gr Sub-X cycling issue

Post by dellet »

On paper no reason that load should not work in your rifle.

If it truly is only the 190 sub x bullet, check the diameter, maybe it’s undersized.

It was not clear to me if after having the problem with the 190’s, you switched back to the 208’s and solved the problem. Trying to narrow down load or rifle problem. That might or might not have been proven when the load was tried in the pistol gas rifle.

Other problems with the load could be loose neck tension, not being sized correctly, oversized expander.

My 16” carbine uses a FA carrier, standard spring, H (3oz) buffer and .097” port. Subs without a suppressor are not a problem with 1680 and bullet weights down to 175 grains. So if it’s a rifle problem, I would suspect something binding, heavy trigger springs can cause the hammer to put more pressure on the carrier and slow it down and such. Same load on different rifles, different lowers kind of rules that out.

In a 16” barrel, rule of thumb numbers with 1680, would be 1 grain equals 100 fps. With your numbers pressure is either not developing, bad powder, or leaking. Two different barrels points to not developing, assuming velocity was also lower than expected.

New brass might be an indicator, open a new can of powder if you have it.

If you wet clean the brass, make sure it’s dry.
300 Blackout, not just for sub-sonics.
BrianT
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Re: 190gr Sub-X cycling issue

Post by BrianT »

First, thank you both for your replies!
As to your questions:
Definitely no leakage anywhere around the gas block, I verified it is aligned correctly, and the hole in the gas tube is the same as in my barrel, .123”.
I almost don’t call the failure with the 10” barrel a failure, because the velocity of the 2 rounds that fired averaged 913fps. It has always cycled rounds down to the low 800fps range, but…I guess it’s a question.

Rifle was clean and well oiled.

All of these test rounds were Win 300 BLK brass, which I had shot once previously.

They are sized correctly pass the Sheridan gauge, and measure correctly with the Hornady comparator.

They are not growing, not compressed, and remain at 2.070”, ±.010” for the plastic nose.

I measured the diameters of the 190s, the 208s, and the 220s, at .308.

Neck tension seems good, the same for all 3 bullets, with a very light crimp.

When I experienced the problem during the last test session, I loaded up some 220s, and those 5 shot fine. But, I’m thinking now of loading maybe 20 of the 208s and 20 220s, and just shoot them to make sure I don’t see any similar issues, with more than 5 rounds loaded.
I’ve only been loading 5 rounds trying to find a starting load, velocity and stability, for when my suppressor shows up. Then these subs will most likely only be shot with the suppressor...

I’ll verify my FCG setup, it’s a BCM PNT FCG, with Kaw Valley lighter springs, pull averages 4lbs.

I’ll try a new bottle of 1680, and I don’t think the brass can be wet, but I’ll confirm.

I’m also going to try different brass, and possibly swap out the BCG, maybe this one isn’t as efficient as it should be…

I appreciate your help, and I’ll post back what I find, either way.
BrianT
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Re: 190gr Sub-X cycling issue

Post by BrianT »

All mags are 300 BO PMAGs.

Tried a new bottle of 1680, no change.

Tried LC brass, no change.

Swapped BCG, same issue.

Swapped complete Lower, same issue.

I’m going to load up some 208s and 220s, more than 5 each, and test again.

I’m also going to try loading these 190 Sub-Xs a little longer, and try 5.56 mags.
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dellet
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Re: 190gr Sub-X cycling issue

Post by dellet »

If you had a load that was on the edge, changing seated depth, might solve the problem and still might solve the immediate problem here. But........

If the action would not cycle with 12 grains of 1680, there is a much bigger issue.

The loads that have worked for thousands of people, failed multiple rifle configurations and barrels. Unless you can find something in common with those rifles, it’s the load.

About the only thing left is the primer.

Low velocities indicate low pressure. If the bullet fits the barrel, then it’s burn rate of the powder. Loose neck tension, wet brass, contaminated powder seem to have been covered. About all that is left is ignition.

Other indicators are failure with CFE BLK. It’s only redeeming quality is that it will reliably cycle an AR, no matter how screwed up the load or rifle is. Yet it failed.

A different lot or brand of primer, even a small pistol primer in a pinch. Anything to induce a change. This load is low pressure enough that it’s not a problem. What you can do if a slam fire is a worry is load no more than two rounds at once. All you need to see is if the second round chambers. Worst case is a double tap.

If that bothers you, then make a dummy round to be the second one in the magazine. Just use a spent primer and no powder.

You will want to test for lock back with a single round in the magazine at some point any way.

You might also start with a Berry’s bullet. It should be .309” diameter, just to make sure the bore is sealing.

About all I can think of at the moment.
300 Blackout, not just for sub-sonics.
BrianT
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Re: 190gr Sub-X cycling issue

Post by BrianT »

You're right, I haven't tried another kind of primer. I have been using CCI450 SRMPs, I have some others I can try.

One thing I noticed yesterday, when I had the Failure to Feed, I dropped the mag, cycled the bolt, to clear the wedged round, and when I went to put the mag back in the next round was pushed pretty far forward of where it should be, I smacked the back of the mag again, and re-inserted the mag.

I'm just wondering now, what pushed that round so far forward, and is that maybe why they aren't feeding right.
Anyway, I'm going to load up some of the same 12gr 1680 190 Sub-Xs today, and see if I can figure out if it was the failure that caused it to be pushed forward, or if it was pushed forward and caused the failure.

Thanks again for your help!
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dellet
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Re: 190gr Sub-X cycling issue

Post by dellet »

You might try loading a single round, see if it locks back. Then two rounds make sure it feeds.
Then 3-4 rounds.

It was
Common practice to load 28 in a 30 round magazine because of feeding issues.

For what it’s worth, I have never even tried a dedicated 300 BLK magazine. Never modified a 223. Mostly use lancers. Only magazine I ever had a problem with was I think a 2nd generation Pmag. It was a well documented problem at the time. Long ago corrected.

The 450’s should be fine, but maybe a quality issue. Just looking for something to blame.
300 Blackout, not just for sub-sonics.
BrianT
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Re: 190gr Sub-X cycling issue

Post by BrianT »

It does lock the bolt back, once I get to that last round, or load only one.

The only 556 mags I have are the M3 PMAGs, and when I put these 2.070" Sub-Xs in them, they won't even strip the first round correctly. It immediately pushes the nose of the round to the right of the feed ramp, and wedges it in between the lugs and the next round. I should find some other brand of 556 mags, just for instances like this.

As far as I was wondering about that next round being pushed forward, it was the failure causing this. It was not causing the failure.

I loaded some up at 2.150", instead of 2.070", and I put an H2 buffer in it, and all 5 rounds ran correctly.

So, I loaded up 10 more @ 2.150", but put the H buffer back, it failed after 2 rounds, put the H2 buffer back, and it ran the rest correctly, even shooting fast.

I'm going to load some more up and see how short I can go, and still run correctly, and try some different primers @ 2.070".

I also loaded up 20 220gr Berry's 11.3gr A1680 2.220", should put me between 1000-1050fps, and they ran flawlessly in 2 different mags.

Thanks again, I appreciate all of the suggestions.
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dellet
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Re: 190gr Sub-X cycling issue

Post by dellet »

Starting to make more sense.

If you can load one round, and it locks back, it’s not an under gas problem. That really should be the first test run. Load one, load two, load a magazine full and have at it.

Now that I think about it, it might have been a Gen3 issue and I solved it by putting in the gen2 follower. I know I posted about here probably 2013-14.

I also had the stacking problem in the magazine causing a fail to feed when I first started with the cartridge. It was the way I loaded the magazine. Completely for got about this.

If you don’t push the cartridge all the way to the back of the magazine, they stack funny and bind. The key is that the nose of the bullet on the top round stays level or maybe tips down a little bit. The top round needs to point up at maybe a 15* angle. This happens naturally with only one round.

Load a single round, note that position, and make sure each of the next rounds point the same way.

In my case it was absolutely operator error. Sometimes tapping the magazine when full corrects it, but once I figured out what I was doing wrong it was obvious.

It would suck if you’re having that problem this whole time.

The shorter the cartridge length, flatter the bullet nose, the more important this becomes.

Edit to add
The problem with the PMag was the with follower in the rear was too short. What would happen is on last round, it wasn’t able to contact the lever for the bolt catch. No lock back on last round.
300 Blackout, not just for sub-sonics.
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