[Bubba FAL]

Ok, this has burned me in two consecutive matches...

I am suddenly experiencing FTF (failure to feed) malfunctions with previously reliable 25rd mags. Issue occurs when feeding the second to last round from the mag during the rapid-fire stages - end up with a bolt over base condition. This has cost me over 30 points in each of the last two matches and I'm getting irked.

The mags in question are CPros of various vintages. Two have the black Magpul follower and the third had the brown unmarked follower (but has been retrofitted with CS spring and olive Magpul follower). I've used them in various matches over the past year with no trouble. Two 15rd PRI mags have also been used without a problem.

I've used the same mags in slow-fire stages and they reliably actuate the bolt hold open, so I'm thinking it's not a short-stroking issue.

Load in use is 28.0gr H322 under 115gr SMK in SSA brass. Primers are Wolf SRM. OAL is 2.255". Ejection (with case deflector in place) is 2-3 o'clock. I've used this load in competition for over a year, with no problems 'til now.

I am unable to duplicate the problem when hand cycling dummy rounds. Upper is CMMG with M4 cuts.

Only thing that's changed recently on the rifle is the replacement of the original 6-position M4 stock with a Magpul CTR stock. Overall the rifle has ~2,500 rounds through it.

Any ideas on what's going on?

 

[paulosantos]

How many rounds through those mags? I'd replace the magazine springs on them with ISMI or SSS Springs.

 

[Bubba FAL]

I replaced the spring on the oldest mag at the same time I replaced the follower. This was about 200 rds ago. One of the mags is fairly fresh (black follower), maybe 100-200 rds thru it. The one that seems to be holding up the best right now has the most rounds through it - maybe 500-600. This is what's confusing me...

 

[paulosantos]

I replaced the spring on the oldest mag at the same time I replaced the follower. This was about 200 rds ago. One of the mags is fairly fresh (black follower), maybe 100-200 rds thru it. The one that seems to be holding up the best right now has the most rounds through it - maybe 500-600. This is what's confusing me...

It alomost sounds like the magazine springs aren't strong enough and that is causing the problem, or it can also be a followerproblem. Have you taken them apart and cleaned them?

 

[Bubba FAL]

Mag springs were my first thought, but it's odd that I'd have multiples go Tango Uniform all of a sudden. I checked cleanliness after the first occurrence. Two mags have CS springs in 'em, the third has an aftermarket spring. I have a bunch more 25rd mags to try out in order to determine if the issue is limited to the ones in question. I hate the thought of wasting a bunch of valuable reloading components running trials, but ya gotta do what ya gotta do.

 

[Test_User]

If by CS springs you are talking about the POS ones CP uses they are cheap Chinese made very low quality.

The issue with finding the issue with these mags is hard. They are cheaply made mags with cheap parts. It makes tracking down issue difficult. With the two mags they both have the same issue with the last rounds correct?

You said you changed the spring and follower out in one why? Because of this issue ir before this happened? If before why?

What spring aqnd follow did you use for replacement? CP SSS ISMI?

If you swapped out for new CP follower aqnd spring adn the other one having the issue seems to alos have fairly new soring and foillower I woudl say that is the common point. THe SSS springs are the best and will last the life of the mag. The fact you have another mag that work good rules out other area for issues.

 

[Bubba FAL]

Tim,

Tried to answer your questions as best I could...


If by CS springs you are talking about the POS ones CP uses they are cheap Chinese made very low quality.

I replaced the original springs with Brownells CS springs (not SSS or ISMI) over a year ago. There are exceptions - three of my mags have SS springs (again, from Brownells). One of the mags in question has this spring in it. This was done as a preventative measure, not because of functional problems.

The issue with finding the issue with these mags is hard. They are cheaply made mags with cheap parts. It makes tracking down issue difficult. With the two mags they both have the same issue with the last rounds correct?

Yes, and they had been reliable in use for over a year until now.

You said you changed the spring and follower out in one why? Because of this issue ir before this happened? If before why?

I replaced the follower in the one mag due to initial problems a couple years ago. I put a Magpul 6.8 (olive) follower in it and it gave no problems after that - til now.

What spring aqnd follow did you use for replacement? CP SSS ISMI?

I have now replaced the original brown follower in the one mag with a Magpul. All springs are now either Brownells CS or SS. I have not had an opportunity to do more testing with other mags, so I can't say for sure that the issue is strictly mag related. If I see similar problems with other mags, I suspect the buffer spring - since my rifle has recently passed the 2500 rd. mark. I plan to measure the current spring just to satisfy my curiosity. The buffer spring in my Colt HBAR made it 7,000 rounds but it had shrunk to ~11" free length by that point (and was quite weak!). The buffer spring in a 6.8 seems to take a bit more abuse than in a 5.56. Guess I'll just have to bite the bullet and get some SSS mag springs.

If you swapped out for new CP follower aqnd spring adn the other one having the issue seems to alos have fairly new soring and foillower I woudl say that is the common point. THe SSS springs are the best and will last the life of the mag. The fact you have another mag that work good rules out other area for issues.

 

[Bubba FAL]

Measured the buffer spring - 10.6875". Still within spec (10.0625 - 11.25 for carbines), but maybe worth replacing since I'll be ordering mag springs anyway ...

 

[Renegade360]

Measured the buffer spring - 10.6875". Still within spec (10.0625 - 11.25 for carbines), but maybe worth replacing since I'll be ordering mag springs anyway ...

going a different route, you said you replaced the stocks recently, did you also replace the buffer tube? if so, maybe you want to check and see if the two are drilled to the same depth.

That being said, try swapping a spring/follower from troubled mag to a working mag and see if the same issue occurs with either one. that should eliminate either the mag body or follower/spring as the culpret and point a finger at the offender.

 

[Bubba FAL]

Negative on the buffer tube, simply slid the original M4 stock off and slid the Magpul on...
Range tests to take place this week (weather permitting).

 

[shooter_gregg]

If I understand you correctly, the mags all have different components inside. Did this problem occur after the change out or before? If the ftf is with a variety of mags it would tend to eliminate them as the cause. Since it only happens during rapid fire it might be a heat issue. Could it be something in the bolt, say the gas rings or the key getting restriction inside. Would something in the bcg delay the timing enough to cause this condition? I am by no means an AR expert, but have some troubleshooting experience.

Tim???
Harrison???

 

[Bubba FAL]

You understood correctly - the mags were reliable in use for over a year. So - either the mag springs have failed at the same time or there is another cause. As you noticed, this is happening during rapid fire, which has me thinking the buffer spring has gotten weak.

 

[Bubba FAL]

Post-range visit Update

Well, made it to the range today. No malfunctions whatsoever with the same mags that previously gave me trouble. All I can figure is that the follower and spring swaps have cured the trouble. I tried both my match loads as well as some old SAAMI loads (26.1gr H322 under 115gr. FMJs) - no difference in operation. So...either the problem is solved, or the +35 degree temperature difference took care of the problem.

Of course, guess what was waiting for me when I got home from the range - package from Brownells with SSS action spring and SSS mag springs! Installed the action spring - big difference! Another range trip is mandated to verify reliable operation...