65 Receiver Set with Polymer mags from PF (HOPEFULLY)

[Nukes]

Since the MDR and MDR-C are designed to accept both M16 and SR25 magazines (already planned to accommodate 5.56, .300 BLK, 6.8 SPC, .308, and 7.62x39), it seems to be a more flexible platform for the Grendel magazine project.

http://deserttech.com/mdr.php

[cory]

Since the MDR and MDR-C are designed to accept both M16 and SR25 magazines (already planned to accommodate 5.56, ,300 BLK, 6.8 SPC, .308, and 7.62x39), it seems to be a more flexible platform for the Grendel magazine project.

http://deserttech.com/mdr.php

I think we'd all agree with this. However, there won't be a lot of us that can afford that option.

[LRRPF52]

If you really want to make a polymer mag, use the Colt 901 lower receiver and a new upper. You could use a 2.5" COL if you really wanted to. It'll be a one-off, needing a different reamer.

[cory]

I didn't see anywhere that I could buy a stripped receiver set. By the time I bought the rifle and built it to what I want, I'd be $3k+ into it before glass. That's just not feasible.

[PrecisionFirearms]

The 68 Mag for the LWRCI will not work for the Grendel. It has a wider body that allows the Grendel to jam against the body walls. Loaded 25 rounds into it and the top 5 flopped around. No way.

[cory]

So an optimal polymer mag for the Grendel would need to be wider, correct?

[PrecisionFirearms]

No I think it should be narrower to prevent the rounds from forcing themselves against the side walls. A straighter stack would help with side wall stress and also align the bullets to the ramps better. The closer together to center line of mag the more upward pressure and less side wall pressure. It's a matter of fulcrum points.

[stanc]

No I think it should be narrower to prevent the rounds from forcing themselves against the side walls.

I can't imagine how you reach that conclusion. The SPC case is smaller diameter than the Grendel case. To achieve proper stacking, a Grendel mag would have to be wider, not narrower.

[PrecisionFirearms]

The wider the body, the more force there will be on the side walls as the fulcrum point shifts more to side to side versus up and down.

[ATTACH=CONFIG]5976[/ATTACH]

As you see the figure above. Upward Spring pressure will be divided about evenly vertically and horizontally in the left example. The second example shows that more pressure would be transferred vertically due to vertical center line of stack of circles (the Fulcrum Point) has moved closer together. Points of contact that create the triangle (or Diamond, which is just a double triangle) are the important angles resulting in force applied.

BTW Loading 6.5 Grendel in the 6.8 PMag took considerable more effort than loading 6.5 Grendel in a regular Pmag. That was my first clue that this was not going to work. It jammed up and the last 5 rounds were very sticky. Stripping off the first rounds on top required tapping the mag to get the next one to move up. Much worse than even a regular Pmag. The side to side pressure was just too great and causing too much drag. Wider would have made it worse. Case in point is my 300 Win Mag has a narrower body in ratio than my Pmags. Disadvantage is a longer mag for the same round count.

[PrecisionFirearms]

Yes and no.

Wider would do it but it would have to be quite a bit wider. I am thinking in terms of using existing mags or mag wells. Not creating a whole new mag well AND Mags. If the mags were narrow enough the force vertically would be greater creating less tension on the side walls. That is the issue with trying to use standard mag bodies now. Too much pressure on side walls because the contact is side to side and not equal in up and down too. The rounds are not touching vertically, just horizontally creating a jamming effect. If we make that angle steeper the force would be directed vertically and not so much horizontally.



I may not be explaining it so you guy can understand it, its too late at night.

[cory]

Yes and no.

Wider would do it but it would have to be quite a bit wider. I am thinking in terms of using existing mags or mag wells. Not creating a whole new mag well AND Mags. If the mags were narrow enough the force vertically would be greater creating less tension on the side walls. That is the issue with trying to use standard mag bodies now. Too much pressure on side walls because the contact is side to side and not equal in up and down too. The rounds are not touching vertically, just horizontally creating a jamming effect. If we make that angle steeper the force would be directed vertically and not so much horizontally.



I may not be explaining it so you guy can understand it, its too late at night.

You're coming in loud and clear Mark.

It seems the ideal mag would be so wide that we'd need a magwell wider than any current AR, correct? So then would the ideal mag be so wide that it'd affect reliable feeding with the center line of the ammo being shifted so far to the outside? At least with the standard bolt and extension.

Then could what your suggesting have a the inverse problem?

[montana]

I would tend to think a new Grendel mag wouldn't need to be any wider than any of the current 7.62X39 AK mags. Measure any AK mag , steel or plastic and see what mag well width is needed.

[stanc]

It seems the ideal mag would be so wide that we'd need a magwell wider than any current AR, correct?

Correct. For a 6.5 Grendel PMAG, the mag well would have to be wider even than the LWRC SIX8 mag well.

So then would the ideal mag be so wide that it'd affect reliable feeding with the center line of the ammo being shifted so far to the outside?

I don't see why. AFAIK, the stainless steel mags currently used achieve proper stacking. The centerline of the cartridges in a "SIX5" PMAG would not change; only the external width of the magazine would.

Then could what your suggesting have a the inverse problem?

Yes, indeed. Doing as he suggests would result in shifting the centerline of the rounds inward.

[cory]

I would tend to think a new Grendel mag wouldn't need to be any wider than any of the current 7.62X39 AK mags. Measure any AK mag , steel or plastic and see what mag well width is needed.

Good point! I didn't even think about that. It's nice having people here smarter than me who can point these things out.

Does anyone have one they can try filling with Grendel ammo? If not I'll order one from Joebob.

[stanc]

Good point! I didn't even think about that. It's nice having people here smarter than me who can point these things out.

Does anyone have one they can try filling with Grendel ammo? If not I'll order one from Joebob.

Save your money. It's been done.

[video=youtube;GhAcUNjBrNE]https://www.youtube.com/watch?v=GhAcUNjBrNE[/video]
https://www.youtube.com/watch?v=GhAcUNjBrNE

[PrecisionFirearms]

Curvature of the AK mags doesn't work well in 30 round configuration. Up to 15-20 rounds they were fine, after that it jammed badly due to curve of mag that was done to work with the tapered case 7.62x39 cartridge.

We tried it.

[PrecisionFirearms]

I starting to lose the point of this thread. Wasn't this thread started in order to find a polymer mag for the Grendel and not to redesign a metal mag? I for one use ASC 6.5 and PRI 6.8 Mags with no problems at all. Personally I like the PRI Mags the best and never had a malfunction with one in over 5,000 rounds fired using 15 round PRI mags.

[montana]

I starting to lose the point of this thread. Wasn't this thread started in order to find a polymer mag for the Grendel and not to redesign a metal mag? I for one use ASC 6.5 and PRI 6.8 Mags with no problems at all. Personally I like the PRI Mags the best and never had a malfunction with one in over 5,000 rounds fired using 15 round PRI mags.

There is no 30 round plastic or metal mag for the Grendel. If some billionaire wished to make one they could take the width of the AK mag and design it to the Grendel case taper. If a lower could be made with the new mags and match the AR platform then it would be feasible, but then it would only work with the new Grendel mags. All of my older AA magazines have functioned flawlessly in my rifles but a strong 30 round P-mag would be nice . If a dedicated 6.5 Grendel rifle were built with new mags it would be another choice for for Grendel owners to argue about pros and cons LOL.

[PrecisionFirearms]

Sometime when I nothing better to do, I'll design and machine a billet Aluminum 7075T6 Grendel mag. Wonder how the feed lips would last?

But it would be a pretty mag. Machine each half and then weld them together and machine the weld line smooth. Machine the follower and floor plate.

Hmmm What Time?

[stanc]

I starting to lose the point of this thread. Wasn't this thread started in order to find a polymer mag for the Grendel and not to redesign a metal mag?

Not exactly. According to the OP, the purpose of this thread was to convince Precision Firearms to offer a receiver with wider mag well which would accept a 6.5 Grendel PMAG, a la the LWRC SIX8.

So, are you convinced?