Grendel LMG

[RangerRick]

Perhaps "effective range" was not the best term to use. What I'm thinking is that the trajectory should be at least as flat as for 7.62x54R.

The challenge will be to design a FMJ bullet with BC good enough to achieve that trajectory, when launched at a MV for which the cartridge is capable.

Good question. I don't know if there is a generally accepted definition.

Maybe it'd be best to just show gel tests comparing wound channels of 6.5 Grendel and 7.62x54R?

The old gel test of the Norma 120gr FMJ does look very similar to Fackler's wound profile of 7.62x54R. It's conceiveable that a FMJ bullet optimized for 6.5 Grendel could do significantly better than 7.62 at closer ranges. At long distances (over 400 meters), Gary Roberts says there's no real difference between different calibers.

The data I've found suggests that the service round projo is 148 grains at 2723 fps. The cartridge seems to be capable of more than that, but maybe that's only in modern bolt actions and not military weapons. The Sellier & Bellot 150 grain FMJ goes 2840 fps out of a 28 inch barrel. That's very similar to the 7.62x51 and we know the Grendel comes close to matching those ballistics.

The Hornady .312, 150 grain FMJ only has a BC of .361, their 150 grain boat tail FMJ has a BC of .398, so we have them beat there for lead cores. Steel cores of the same weight would almost certainly have higher BC's because of the length.

That looks to be the biggest advantage of the x54: lots of room in the case for long bullets because of fairly low powder loads relative to case size.

With the higher sectional density we may be able to make up what the bullet lacks in weight to get similar penetration capability, particularly at longer ranges.

I have a buddy with a Mosin Nagant I could probably borrow to do tests, but my range only goes to 300 yards.

At what range do we need to demonstrate plate penetration?

[JASmith]

Isn't it interesting that the US managed to duplicate in 1955 the performance of a round developed in the 1890s?

[RangerRick]

Looking at the picture of the belt it looks like the tab by the bullet with 7.62x39 rounds may be there to guide the head of the case as it is stripped out of the belt, not the neck.

It clearly doesn't touch the 7.62x39 case neck.

If that's the case, it bodes well for smooth functioning with Grendel cartridges.

Rick

[RangerRick]

"Isn't it interesting that the US managed to duplicate in 1955 the performance of a round developed in the 1890s?"

Yes, but it's in a case 2/3 the length, allowing shorter actions and vastly simplifying gas operated systems, which means lighter guns. Compare the Browning 30 to the M-240 or M-60.

Rick

[RangerRick]

Bill A interested in this?

I wonder if Bill A would be interested in this? I'm sure he'd like to see the Grendel Cartridge in a belt fed system.

Demonstrating that the relatively straight walled cartridge works in a belt fed system would be a plus for him.

If nothing else, maybe we could get him to let us use some of his test facilities.

Rick

[JASmith]

"Isn't it interesting that the US managed to duplicate in 1955 the performance of a round developed in the 1890s?"

Yes, but it's in a case 2/3 the length, allowing shorter actions and vastly simplifying gas operated systems, which means lighter guns. Compare the Browning 30 to the M-240 or M-60.

Rick

Your point is well-taken. The rim also complicates feeding in automatic weapons. Your observation helps illustrate why we need to avoid a one-dimensional focus on any one characteristic.

It also helps show how things can get complicated real fast.

The way development folks deal with the complexity is to write a list of characteristics the new thing needs to have to be useable as a replacement for the old thing. That list, when formalized, becomes a requirements document.

Cheers!
Joe

[stanc]

The data I've found suggests that the service round projo is 148 grains at 2723 fps. The cartridge seems to be capable of more than that, but maybe that's only in modern bolt actions and not military weapons. The Sellier & Bellot 150 grain FMJ goes 2840 fps out of a 28 inch barrel. That's very similar to the 7.62x51 and we know the Grendel comes close to matching those ballistics.

The Hornady .312, 150 grain FMJ only has a BC of .361, their 150 grain boat tail FMJ has a BC of .398, so we have them beat there for lead cores. Steel cores of the same weight would almost certainly have higher BC's because of the length.

http://7.62x54r.net/MosinID/MosinAmmo.htm shows MVs and BCs for various 7.62x54R military and commercial loads in different barrel lengths. Not sure how the BCs were arrived at (Perhaps they used two chronographs?), as some seem ridiculously low, while some others look excessively high.

I have a buddy with a Mosin Nagant I could probably borrow to do tests, but my range only goes to 300 yards.

At what range do we need to demonstrate plate penetration?

I think it'd be good to do it at 100, 200 and 300 yards, if the 7.62 ammo has boat tail bullets, like 150gr Wolf Gold and Prvi http://7.62x54r.net/MosinID/MosinAmmo029.htm

If you use ammo with flat base bullets, like the 148gr Wolf load http://7.62x54r.net/MosinID/MosinAmmo017.htm , perhaps only 100 yards, since it'd lose velocity too rapidly at the longer ranges.

Many years ago, I shot 1/4", 3/8" and 1/2" mild steel plates at 100 yards, using 7.62x51 M80 and 5.56x45 M193. The 7.62x51 punched holes through the 1/2" plate at that distance, so it seems likely that 7.62x54R also would.

Since I don't know what thickness of mild steel 6.5 Grendel and 7.62x54R will penetrate at 200 and 300 yards, if you decide to test at either of those distances, I'd suggest shooting at 3/8" and 1/4" in addition to (or in place of) a 1/2" plate.

If you feel like it, I'd also like to see a CMU (hollow cinder block) shot at 100 yards with both calibers.

Rick, if you're willing and able to do these tests, I'll gladly pay for the mild steel plates, cinder blocks, and ammo.

P.S. Take good, hi-res photos, please.

[JASmith]

<sigh>

You aren't the only one who I am communicating with in this thread...

[RangerRick]

I think it'd be good to do it at 100, 200 and 300 yards, if the 7.62 ammo has boat tail bullets, like 150gr Wolf Gold and Prvi http://7.62x54r.net/MosinID/MosinAmmo029.htm

Many years ago, I shot 1/4", 3/8" and 1/2" mild steel plates at 100 yards, using 7.62x51 M80 and 5.56x45 M193. The 7.62x51 punched holes through the 1/2" plate at that distance, so it seems likely that 7.62x54R also would.

Since I don't know what thickness of mild steel 6.5 Grendel and 7.62x54R will penetrate at 200 and 300 yards, if you decide to test at either of those distances, I'd suggest shooting at 3/8" and 1/4" in addition to (or in place of) a 1/2" plate.

If you feel like it, I'd also like to see a CMU (hollow cinder block) shot at 100 yards with both calibers.

Rick, if you're willing and able to do these tests, I'll gladly pay for the mild steel plates, cinder blocks, and ammo.

P.S. Take good, hi-res photos, please.

Where is a good source for the plate?

[stanc]

Where is a good source for the plate?

I used to buy them at metal scrap (salvage? surplus?) yards. Check the yellow pages for your area?

[JASmith]

Make sure you use plates from the same sheet.

We had trouble correlating test results with computer predictions on some destructive tests a few years back. I asked for tensile tests for the steel used in the structure. The results showed that the steel had a yield strength about 50% greater than the nominal yield strength for mild steel. The predictions went a lot better when the proper material responses were modeled.

This disparity in yield strength will confuse your penetration results.

I'm assuming you won't want to pay for a test laboratory to assure that the different sheets have the same strength, so getting the plates from the same sheet will at least assure uniform comparisons.

[stanc]

Make sure you use plates from the same sheet.

I'm assuming you won't want to pay for a test laboratory to assure that the different sheets have the same strength, so getting the plates from the same sheet will at least assure uniform comparisons.

A very good idea if more than one plate of a particular thickness is to be used. But, if Rick decides to shoot at only one distance, then only one plate will be needed. OTOH, if he elects to shoot at more than one distance, it'll probably require one plate each of different thicknesses.

I'm thinking that 7.62x54R lead-core FMJ should punch through 1/2" mild steel @ 100 yards, but it may be necessary to drop down to 3/8" @ 200 yards, and 1/4" @ 300 yards, in order to get full penetration.

[JASmith]

Just to clarify: The target plate will likely be about 6X6, 12X12, 18X18, or 24x28 inches, depending on convenience and range.

The parent plate from which the target plate is cut is generally much larger. I have rarely seen them larger than 4' wide, but they can run 8-12 ft long. Longer is doable, but handling the plate gets to be a bit of a challenge.

So, depending on what is found, there is a possibility of getting several target plates from one parent plate. These should have pretty much the same properties. Not always, but usually close enough for our purposes. Yeah, even this gets complicated when you don't want to unintentionally mislead or confuse yourself or your audience.

A RELATED POINT:

As a rule of thumb, try to keep the hits more than 1-inch from the nearest edge. (Three or four times the plate thickness or bullet diameter, whichever is larger)

The metal will have some heat-induced changes in properties near the edge if torch cut. Also, the plate will respond differently to hits near even a saw-cut edge because of edge effects.

[RangerRick]

RPD Belt Photos

Hi Guys,

Got the RPD belts and drum today. Stan, your 10 round section should go in the mail tomorrow.

I put some Grendel rounds loaded with Nosler 120 grain FMJ's in the belt as well as some new IMI 7.62x39 brass.

The belt seems to work great. The link only has a slight taper. This makes sense because the head of the cartridge has to slide through it when loading.

Of course, mechanisms can be boogered up by small changes, so we will have to see.

This first picture shows the loading tab on the right. Moving right to left the first case is a 7.62x39, followed by an empty Grendel case followed by a loaded Grendsel round. The empty slot was because of a bent up link.





These are pics of the belt loaded with a few Grendel rounds and 7.62 cases:







continued in part 2.

[JASmith]

Nice work!

The Grendel in those belts looks like it is at home and positively lethal!