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I’ve never really been that happy with Prime’s magwell. It’s always seemed a bit off Systema spec to me. I remember asking Tac about it, when he fitted my first Prime lower. The answer I got was that it was a known problem. How widely known, I don’t know, because I never found anything in the literature about it and I felt slightly mad in banging on about it. I put it down to an acceptable quirk.

A few years later and I’m glad to see I’m not the only one who wasn’t happy about it. I’d never really noticed that Prime’s magwell is wider. I use Tac’s Pmags, which have sprung inners – so wobble isn’t a problem. However, Tosh from SGT explained to me that it’s actually this additional width which was causing the issues I’d encountered – to do with the mag catch.

Now, if you have a first gen SGT lower, you will have a Prime spec magwell. Prime used to be SGT’s OEM. The good news is – and another reason to buy – SGT’s gen 2 lowers are SGT’s own spec.

Tosh tells us more:

“Our 1st gen M4 Lower’s magwell was on the looser side of the tolerance, although, that data was never ours to begin with.

Our 1st gen M4 was milled by Prime (through Andaxworks), we gave our data, beginning with the motor grip area where Prime had problem with their own. The flush dummy pin data was incorporated to differentiate our lower to theirs (or so we thought…). We also initiated to give the magwell data but they told us it was too late…so what we ended up with was 70% of SGT data built into Prime’s problematic lower. We were assured they were 7075 aluminum, we had them tested and were astonished to hear that it was actually 6061.

So what was the 30% data that they were missing? For obvious reasons we can not divulge those areas (since I’m sure they’d love to copy it), but some of that was the magwell.

I too, never liked Prime’s magwell data, and I’d surely would have loved to incorporate ours into theirs, perhaps we were lucky that we did not because they do not know PTW, nor AR really. We would have just handed over our fuit of loom to them for free.

So we started the 2nd gen 7075T6 M4 lower last summer, of course, never through Prime again, and this time we spent literally incredible amount of time trying to perfect the data to make it as close as RS spec.

T6 means it is tempered at certain temperature to increase and maximize strength and hardness. You can always tell Prime’s a 6061 since they weld the milling center point right in the magwell, you can’t weld for 7075 and that is a giveaway. I put up the comparison photos (below), SGT Gen1 M4 which Prime is using currently, still without compensating us for its use, is exactly same as what Prime is selling.

For more information about difference between 6061 and 7075, here is a good link….

Prime magwell.

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SGT magwell.

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You could see that the large space between the magazine and magwell wall compared to SGT Gen2 M4. Now, don’t get me wrong, I expressed it as “on the looser side of the tolerance”, meaning it still will work with PTW’s without a problem, but for my taste, Prime is too loose. Please do understand that RS magwells are never made for perfect fit either, they need to drop for quick mag changes. As you can see from the pic, mags are never perfectly rectangle either, and all mags have differences, so you need some play to accept various tolerances.

Three receivers in comparison.

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Gen1 M4, Prime is same as ours.
Gen2 M4, SGT data.
Gen2 416, SGT data.

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See the difference between the top one and the lower two?

Since we’ve been talking about the magwells, let me further add that the underside magwell cosmetics of Prime isn’t what it should look like. Albeit many RS AR’s out there, Prime’s magwell is too rectangular… forged receivers tend to be more rounded, like ours. The cut out at the bottom too, has more angle to let magazines slip into the magwell.

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The cutout ramp for the magazine insert.

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You know, 6061 is much easier to mill than 7075, plus, its a cheaper material. We go through all these millings to make it in ‘relentless pursuit of perfection!!!’

FYI, our 416 magwell has same dimensions as our Gen2 M4 as well.”