Grendel LMG

[stanc]

I haven't fired a Grendel, but I have fired (back to back) HK 416 guns in 5.56mm and 6.8mm Rem (which has a very similar recoil impulse to the Grendel). I also fired a 7.62mm HK 417 in the same session. Unfortunately I wasn't allowed to fire them on full-auto but I did get a good impression of how the recoil compared (that was why I was testing them).

If you calculate the recoil energy, the 6.8mm sits half-way between the 5.56mm and 7.62mm in similar guns, but since the HK 417 is noticeably heavier than the HK 416 (thereby reducing the recoil) I would have expected the recoil of the 6.8mm to feel closer to the 7.62mm than the 5.56mm. In fact, the opposite was true - the kick of the 6.8mm felt much closer to the 5.56mm, the recoil of the 7.62mm was a much bigger step up.

That's what the guys on 68forums have said. I don't understand how the calculated recoil can be so much greater, but perceived as not significantly different.

Interestingly, there's a contrary view at the end of this video; the felt recoil of 6.8 SPC is rated as equal to that of 7.62x51.

[video=youtube;nKy3930MO2k]http://www.youtube.com/watch?v=nKy3930MO2k[/video]

This ties in with the MURG tests which compared 5.56mm with 6.8mm and concluded that there was no difference in the practical rate of aimed fire or the hit probability.

This suggests to me that there is a kind of recoil threshold below which most people can control the gun, but above which they can't.

That sounds plausible.

[stanc]

You're going to love this guys...

http://www.army.mil/article/67318/_Ironm...ttlefield/

I'm not sure who did it first though....

Maybe Gene Stoner? Check 4:34 in this late-1950s film:

[video=youtube;iTeMU61qKGY]http://www.youtube.com/watch?v=iTeMU61qKGY[/video]

It took only half a century for the idea to be implemented...

[LRRPF52]

I will have to do your cinder block test with the 100gr NBT's at 2700fps MV to see what happens, or maybe find another 100gr bullet that closely resembles an FMJ or M855A1. Maybe a Barnes 100gr TSX?

[stanc]

I don't know how penetration capability of a NBT or TTSX might differ from that of an FMJ. But, a 100gr FMJ is available.

http://www.midwayusa.com/product/142377/...box-of-100

[RangerRick]

Maybe Gene Stoner? Check 4:34 in this late-1950s film:

It took only half a century for the idea to be implemented...

I like how he turns around and sweeps the cameraman with a big grin! LOL!

RR

[LRRPF52]

So I walked up to DSA's booth today at SHOT, looking to float the 6.5 Grendel/RPD conversion, when they told me to go look at the gun on the counter. It was chambered in 6.8 SPC, with plenty of rounds in the non-disintegrating links from 7.62x39. That would provide some advantage over 7.62x39, but I think we can all agree that the Grendel would give the gun a true 800m beaten zone capability that is superior to the 6.8 SPC, and would provide better penetration within 500m on barriers with higher sectional density bullets too.

I spent some time talking with one of their engineers about the project, and ironed out what he needs to make it happen. Since the RPD has 4 gas settings already on the gas block/regulator, we could use a large gas port on a test barrel and mitigate with the existing block as-is, since their is a wide spread in ga sport diameters in the regulator. Grendel fits in 7.62x39 links already as we have seen, so all we need is a barrel and we're on the way. I have to tell you... that RPD with a 100rd SAW nutsack and the 6.8 linked is really lightweight. It would make an awesome LMG to have everything in that weight & length profile, since the gun is something like 14lbs. The bolt will take high pressures too.

[stanc]

So I walked up to DSA's booth today at SHOT, looking to float the 6.5 Grendel/RPD conversion...

I spent some time talking with one of their engineers about the project, and ironed out what he needs to make it happen. Since the RPD has 4 gas settings already on the gas block/regulator, we could use a large gas port on a test barrel and mitigate with the existing block as-is, since their is a wide spread in ga sport diameters in the regulator. Grendel fits in 7.62x39 links already as we have seen, so all we need is a barrel and we're on the way.

Did he give you any feeling that DSA might pursue this?

[LRRPF52]

Did he give you any feeling that DSA might pursue this?

If I push it, he seemed open to doing it actually. He would need gauges, a reamer, NO-GO/GO, etc.

I talked with another major industry figure and his son about the concept. I think the important thing to push is how this is a major game-changer for small arms development when it happens, from a historical perspective. Getting rid of the 5.56 LMG and 7.62 GPMG in one system that is half the weight of most belt-fed guns is truly a game-changer.

[stanc]

If I push it, he seemed open to doing it actually. He would need gauges, a reamer, NO-GO/GO, etc.

So, are you gonna push it?

[LRRPF52]

I learned recently that there is an 07 FFL holder in my area who does modifications on existing machinegun designs, to include an HK fire control group/grip on SAW's, Mk46's, Mk48's, etc., as well as caliber conversions on them. I think they would be the best route to take with this project.

I was looking at old pics of guys in SOG who carried the RPD for its lightweight, compactness, and firepower.

[stanc]

I learned recently that there is an 07 FFL holder in my area who does modifications on existing machinegun designs, to include an HK fire control group/grip on SAW's, Mk46's, Mk48's, etc., as well as caliber conversions on them. I think they would be the best route to take with this project, compactness, and firepower.

Sounds promising. I wonder if they can give a cost estimate?

[LRRPF52]

I have to tell you how impressed I am with the handling and balance of the RPD. It's been a while since I played with one, and it is very slim, light, and about perfect for an LMG.

I also saw something really cool from Tango Down...an AK quick barrel change system with an interrupted thread system, and a detent protruding out of the barrel trunnion. It would be cool to use that design on the RPD so it has a barrel change feature.

[LRRPF52]

Check this out:

[video=youtube;yL2Wd-nuiZ4]http://www.youtube.com/watch?v=yL2Wd-nuiZ4&feature=player_embedded[/video]

[bwaites]

Interesting. Sounds suppressed, intergral suppressor maybe? But that's a lot of rounds to carry and expend! Very nice.

[BjornF16]

Check this out:

[video=youtube;yL2Wd-nuiZ4]http://www.youtube.com/watch?v=yL2Wd-nuiZ4&feature=player_embedded[/video]

Did we lose the video file?

[bwaites]

Did we lose the video file?

Still works for me.

[BjornF16]

OS X update...had to reboot. All works now...LOL. Thought the spammers had struck again...

[stanc]

Interesting. Sounds suppressed, intergral suppressor maybe?

Nah, just poor sound reproduction. That's quite common in videos such as this.

I'd like to see the negative characteristics of these back pack systems. They never show us that.

[txgunner00]

I'd like to see the negative characteristics of these back pack systems. They never show us that.

+1 I bet it's heavy as hell.

Cool concept though.

[BluntForceTrauma]

I coulda sworn there's a video of Gene Stoner himself, from the '50s, wearing an ammo backpack and firing an LMG in exactly the same way. OK, hell, gimme a sec to Google it. . . . OK, got it.

Link: http://www.youtube.com/watch?feature=pla...VKHBQ9YpNs . Start at the 6:00 mark.

John