Mags not seating easily into my Knights lower

[amac]

Ran a multi gun match today and the last stage required 3 mag reloads. Each one resulted in multiple push-pulls until eventually I slammed the bottom of my mag to lock into my lower. :fie: This is no bueno.

After the match I began to investigate the issue, with the help of some other shooters. Here's what I've got...
1. I am running a Knights lower, Vltor upper and LMT BCG.
2. I am loading 28 rounds into each mag.
3. I primarily use PMAG's. Tested were new/old, windowed/non-window.
4. All mags inspected for wear and dirt in mag catch portion of Pmag.
5. I have installed Magpul Ranger plates on each mag.
6. Also tried various aluminum mags, including a Fed Marshall's mag (better results initially, but lock up issue eventually showed up).
7. Changed from my personal rolled ammo to factory ammo.
8. Tightened down the mag release button to ensure good tension.

What I've come up with is that I can't "slam" in a mag. My mag advances to the point where the rounds are pressing underneath and I need about 1/8 or so of an inch to reach the positive click. With firm, steady pressure, the spring will compress and the mag will seat.

Anyone have an answer? This is driving me crazy! :suicide2:

[Iraqgunz]

Based upon some issues I have seen lately (not with those brands in particular) there is a tolerance issue between the upper and lower receivers which is causing this.

This is simply based upon some recent observations, but the symptoms seem the same.

[amac]

Based upon some issues I have seen lately (not with those brands in particular) there is a tolerance issue between the upper and lower receivers which is causing this.

This is simply based upon some recent observations, but the symptoms seem the same.

I have two setups just the same. The problem appears in both. If what you say is the case, then I feel the need to switch out either the upper or lower and see what happens. Is that about it?

[mtdawg169]

I run an MUR on an SR15 lower and don't have any issues. Do you have any issues inserting empty magazines?

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[Magic_Salad0892]

I have an MUR on SR-15 lower as well.

Make sure the magazine button isn't screwed in too tight or something.

[Iraqgunz]

I would attempt to use a standard upper first and see what happens. Like I said earlier. I recently saw some issues with some standard uppers and lowers being out of spec and not allowing magazines to seat.



I have two setups just the same. The problem appears in both. If what you say is the case, then I feel the need to switch out either the upper or lower and see what happens. Is that about it?

[amac]

It doesn't feel like the mag release is preventing the seat. I have no problems with empty mags, only mags with rounds. I will further experiment with various numbers of rounds. It feels as though something is pushing back - there is to much pressure to seat the mag. As IG suggested, it may be a tolerance issue. The question is, which component is slightly out of spec?

[Magic_Salad0892]

I wonder if it's the feed ramps, or maybe the bolt catch.

I'd call VLTOR, and KAC, then see what they have to say about the issue.

They're both forged, and shouldn't have any issue. I know my MUR-1S is fine.

... Which reminds me. Earlier MURs were billet. You might wanna check yours. When did you buy it?

[amac]

My MUR is relatively new - probably less than a year old. With the bolt locked back, mags seat up with no problem.

[amac]

I went over to a friends house and swapped out uppers, lowers and bcg's. What I thought was a problem is simply a tight tolerance. In fact, my friend wasn't aware of his own tolerance until I pointed it out. Oops! A slight change of mag reload technique and I'm good to go.