Grendel as a Universal Infantry Cartridge

[stanc]

I did a quick perusal of the JBM length tables (http://www.jbmballistics.com/ballist.../lengths.shtml) and found several in the range of 5.4<L/D<5.8 so it would appear that L/D = 5 is not a hard limit.

Okay, but don't forget the tracer.

Tracer projectiles (for rifle/m.g. cartridges) are nearly always -- if not always -- signifcantly longer than ball bullets. If you make the ball round 5.8 L/D, what will a matching tracer be? 6.8? 7.8?

Another thing to consider: Bullets of <5.0 L/D already eat up substantial powder volume in the Grendel case.

Increase L/D to 5.4-5.8 and capacity will be cut even more.

[LRRPF52]

I've discussed this issue at length with Bill Alexander and several other AR guys. They all are in agreement that if you beef the bolt up, you'll create a failure somewhere else, and that failure might be much more dangerous to the user than a bolt failure. As it is, when the bolt fails, any damage tends to go out the bottom of the mag well, which is a generally safe place to go, versus back toward the user, or out the sides towards friendlies.

I have yet to see an AR-10 that has kaboom'd, and I've been shooting them for a while now-several variants from original Dutch AR-10's, Modern Armalite's, and DPMS-based models. Most have never seen factory ammo and have been loaded for by a lot of very young, brave guys. The GAP DPMS .308 I had built has a very tight bore Obermeyer, and it shoots factory Lapua hunting ammo making the brass completely useless after 1 firing. I even tried googling AR10 kaboom and couldn't find anything.

LRRPF52

[bwaites]

I have yet to see an AR-10 that has kaboom'd, and I've been shooting them for a while now-several variants from original Dutch AR-10's, Modern Armalite's, and DPMS-based models. Most have never seen factory ammo and have been loaded for by a lot of very young, brave guys. The GAP DPMS .308 I had built has a very tight bore Obermeyer, and it shoots factory Lapua hunting ammo making the brass completely useless after 1 firing. I even tried googling AR10 kaboom and couldn't find anything.

LRRPF52

Interesting. That's good info. Lots more beef all over there, though, not just in the bolt.

[LRRPF52]

You can put an AR10 bolt face and lugs, as well as the appropriate size barrel extension in the AR15-size platform, although it does require a new bolt carrier and upper receiver as Remington did with the .30 RAR. That uses a .473" cartridge base, but you don't need to go that far, as AR Performance has proven with their 6mm BR bolt and barrel extension combo. The 6mm BR also is a .473" cartridge base. Since the Grendel is smaller, that would just give us more beef, and no more shorn lugs.

LRRPF52

[stanc]

Does anyone know the basis for the L/D = 5 being a practical length limit?

That's a good question. I'm surprised that I didn't ask it, since I normally question everything.

I...found several in the range of 5.4<L/D<5.8 so it would appear that L/D = 5 is not a hard limit.

Yes, that does seem to be true. Some of the CETME bullets we discussed elsewhere had a 5.7 L/D.

Perhaps the 5.0 "limit" came about back when conservative tangent ogives were used pretty much exclusively?

[JASmith]

If I had to guess, it may have had something to do with the then-standard twists on barrels.

Stabilization can also get a little more dicey if the pill is long enough that it can vibrate like an arrow.

The long nose and boat-tail keeps the mass near C. G., so it shouldn't a big issue.

[stanc]

Well, here is the chance for 6.5 Grendel to become 6.5 NATO.

http://www.militarytimes.com/news/2011/07/army-sets-its-sight-on-its-next-carbine-070911/

Only 234,000 rounds of ammo must be supplied for the tests.

[Tony Williams]

I like this bit:

The winning carbine will face off against the improved M4A1 in a battle to become your next weapon. But that point may be moot, as Army officials have said it is highly improbable that the M4A1 will stand a chance against a new carbine.

If I were a betting man, I'd put my money on the conclusion being something like this:

"Winning carbine X is clearly better than the M4 in all respects. However, the improvement programme to the M4, with a heavy barrel, auto switch, and gas piston system among other things, greatly improves the performance of the M4. While it still isn't quite as good as carbine X, the differences are too small to justify the cost of change."

[JASmith]

Got it in one!

[LRRPF52]

I like this bit:



If I were a betting man, I'd put my money on the conclusion being something like this:

"Winning carbine X is clearly better than the M4 in all respects. However, the improvement programme to the M4, with a heavy barrel, auto switch, and gas piston system among other things, greatly improves the performance of the M4. While it still isn't quite as good as carbine X, the differences are too small to justify the cost of change."

Adding an op-rod driven system to the AR only makes it worse, not better. That has been the result time and again with the HK416, POF, ARES kits, etc. Bad news all around, plus more weight where you don't need it, and now you really need to clean carbon off the piston to make the gun run, whereas carbon build-up on the AR increases gas system seal, and does not induce malf's contrary to gun rag propoganda.

I think the defense contractor world is really fretting hard to try to come up with a better design than the direct impingement AR15, and they are failing consistently. No weapon so far has proven to have better muzzle control, as there are no off-axis reciprocating parts in a DI AR15. Reliability is a gun rag fantasy perpetuated for decades now, claiming "piston" systems are superior somehow, when in fact, it is very difficult to match the AR15/M16/M4 reliability record. Sure, they can rig tests in favor for whichever contractor greased the committee of the day (XM8, SCAR, etc.), but you still end up with guys who cling tighter to the M4, especially seasoned veterans in Special Operations units who have more clout than a young soldier who is dazzled with something new and sexy.

FN has been pushing the SCAR for years now, and it still is in the teething stage, with an inferior operating system compared to the M4, a totally unacceptable line-of-sight above bore height, and even magazine incompatibility issues with lot-to-lot. That is a big indicator of QC failures, and the AR18 design never caught-on with anybody other than limited use with the IRA.

The reality is that it is going to take a major leap in firearms design to out-do the AR15 Family of Weapons. Right now, I see nothing competitive, and I attend as many trade shows as possible year-to-year, work with organizations all over the place, and try to keep up with the latest and greatest. What I see more and more is adoption of M4-type carbines as a given, with very few exceptions that seem to be more based on national pride for home-stolen designs (Sweden with the AK5, which most of them don't even realize is a licensed copy of the FNC, a sub-standard design by modern paradigms, the FAMAS, L85, AUG, etc.) Don't even get me started on the G36...

Even some of those countries have had their Special Operations units using AR15's since the early 1960's before the regular US Army even did, and prefer M4's or Diameco Carbines to this very day.

As I've mentioned before, when you see some of the most influential figures in several of the current contenders to the AR15-guys who have been closely or directly involved with the development of the HK416 and ACR, still using AR15/M4 carbines in their classes, that speaks volumes...painful volumes for those looking to break into the market that has been dominated by the AR since 1963 in the US military. There have even been scathing reports from former CEO's of certain divisions from one of the companies involved with the impetus for the Masada-now-ACR, citing serious QC problems and issues that make that system an albatross, and that company still runs its carbine courses with DI AR's religiously.

[stanc]

An interesting post. How would you rate the odds of getting a manufacturer to produce an "AR-12.5" for use with intermediate-size cartridges like Williams' 6.5x45 and Murray's 7x46? Or are we forever limited to just the large-receiver AR-10 and small-receiver AR-15? Would the 6.5x45 and 7x46 lose some of their appeal if they have to be used in large-frame rifles and carbines?

[LRRPF52]

Stan,

I've been turning the gears over this AR12.5 receiver set for a while now. There is one option that might not require that route, using existing AR15 receivers, and that would be with the MGI system and a new magwell. I see more hurdles with the magazines than I do the receivers, really. MGI was working on a 7.62 magwell for their Hydra that used M14 mags, but couldn't get it to run reliably. They did fit a 7.62 magazine into an AR15 lower profile, using their modular mag well lower, but lost the space for a bolt catch.

We know the upper will accommodate a 2.5" cartridge I think, although I wonder about live round ejection and clearance. The next option would be to fabricate a billet set from scratch around these new intermediate cartridges, and make mags for them. Using as many existing AR15 small parts, and an enlarged bolt, costs could be kept under control. The bolt carrier group would need to cycle a bit more rearward than a 5.56 though. I think it's very doable. I would propose a magazine that is no taller than a 30rd 5.56 mag, but uses a semi-coffin shape to hold 30 rounds. This would make a great SASS rifle, but I think I would still prefer and "M4A2" (SOPMOD II) for most riflemen.

A 6.5 or 7mm DMR/Sniper SASS with significantly less weight than an M110 would be great, but in the end...what performance advantages will we gain over a 5.56 SPR with 18" pipe pushing 77gr SMK's? It would have to be significant enough to overcome the benefits the SPR currently has with ammo compatibility, lightweight, and mag capacity-per-volume.

This makes me look at these new intermediate cartridges as proponents for 7.62 NATO replacement if they can match the ballistics.

LRRPF52

[stanc]

I've been turning the gears over this AR12.5 receiver set for a while now. There is one option that might not require that route, using existing AR15 receivers, and that would be with the MGI system and a new magwell. I see more hurdles with the magazines than I do the receivers, really. MGI was working on a 7.62 magwell for their Hydra that used M14 mags, but couldn't get it to run reliably. They did fit a 7.62 magazine into an AR15 lower profile, using their modular mag well lower, but lost the space for a bolt catch.

We know the upper will accommodate a 2.5" cartridge I think, although I wonder about live round ejection and clearance. The next option would be to fabricate a billet set from scratch around these new intermediate cartridges, and make mags for them. Using as many existing AR15 small parts, and an enlarged bolt, costs could be kept under control. The bolt carrier group would need to cycle a bit more rearward than a 5.56 though. I think it's very doable.

Thanks.

A 6.5 or 7mm DMR/Sniper SASS with significantly less weight than an M110 would be great, but in the end...what performance advantages will we gain over a 5.56 SPR with 18" pipe pushing 77gr SMK's? It would have to be significant enough to overcome the benefits the SPR currently has with ammo compatibility, lightweight, and mag capacity-per-volume.

Concur.

This makes me look at these new intermediate cartridges as proponents for 7.62 NATO replacement if they can match the ballistics.

Matching trajectory and wind drift appears to be doable. In fact, the chart for the 7x46 w/130gr bullet shows a somewhat flatter trajectory than for 7.62x51.

http://www.thefirearmblog.com/blog/2010/04/07/7x46mm-uiac-universal-intermediate-assault-cartridge/

And the SPC guys are getting close with 6.8x43 loaded with long-ogive bullets, although it sounds like chamber pressure may be on the high side. Also, they are talking about making a "stretched" 6.8x46, a la Tony Williams' proposal.

http://68forums.com/forums/showthread.php?21686-Optimized-Caliber-Proposal/page5

(P.S. Note that 68forums is way ahead of the 65grendel forum in regard to their avatart. )

[stanc]

I would propose a magazine that is no taller than a 30rd 5.56 mag, but uses a semi-coffin shape to hold 30 rounds.

Something like the new SureFire mags?

http://www.youtube.com/watch?v=QfFluT6hYys

(P.S. Note the iron sights on the carbine are on crooked! )

[bwaites]

(P.S. Note that 68forums is way ahead of the 65grendel forum in regard to their avatart. )

I see that they have plenty of "tarts" in their avatars if thats what you mean!