Grendel and 5R Rifling (Haters gonna Hate)

[XcountryRider]

Woohoo is all 5 alarm of this issue over at the 6.8SPC forum. He goes by constructor over there. This isn't about who's wheener is longer its about seeing the results of a comparison. My statement still stands "One things clear the 6.8SPC no longer always going to be faster out of the gate. It depends on what type of barrel being used." I think that is a completely accurate statement.

[KentuckyBuddha]

I was just kidding and trying to deescalate, good luck on the prop bet and do let us know the results either way.

[joker31]

I think the development with CFE223 is really whats making it a closer argument, if the CFE or other High Velosity, lower pressure per payout technologies come available the two rounds will seem more and more alike, then its more of a preference thing than anything.

The 6.5 has an edge because the high BC Bullets and the technology push with the PPC crowd.
The 6.8 has the initial advantage because of Freedom Group and The military's 5 minutes evaluating the round.

Dont get me wrong, I load for both and have shot both but went to Grendel because of Hornady's interest and the "Real Standard" that is backing the 6.5. I read alot about the 6.8 and did a ton of research on it when I was recovering in Germany. The 6.8's Spec bull$h.. is what turned me off and then the primer confusion (Large/Small) just Pissed me off. I really truely and honestly wanted to see the 6.8 make it as an End User. But damn, pick a poison, drink it and stop all the lawyer derived neutering of the cartridge and it might float.

Mostly its Freedom groups crap of loading it with a primer size that they knew would weaken the cases' head and keep from getting more life out of their cases. Thats why everyone avoids the remington brass like a plague, if it weren't for SSA the 6.8 would have been dead when remington tried the whole forget the 6.8, here's something better, faster,and cheaper with the 30 Remington AR.
The fact is Remington bought into the 6.8 to push development of the 30 Rem AR down the Military's throat because the 6.5 and 6.8 didn't represent to those who make decisions in purchasing for the military a "Markable Clear Advantage over the 5.56"

They must have been smoking crack if they thought the military was going to give Privates two different 7.62's and let them sort it out. Not going to happen, when that was even hinted at, anyone with even a Basic Graduation Certificate shook their head is disgust because yet again nobody cared about Soldiers, Marines or Airmen that actually use the stuff.
SOCOM operators were pretty clear about the 6.8 before when they said that the 6.8 wasn't enough of a difference to make any change even on a small level like theirs. Compared to big Army, SOCOM and SOCCENT are VERY small end Users. They may seem cool to the outsider who watches it on TV but when the Berets get left behind, the BS does too. Historically small buisnesses were approaching big Army through using SOCOM as a proving ground because if privates and the old man command saw SOCOM use it, it has to be good. Its also why in Afghanistan I had 3 Beowulf uppers in my office with no ammo to be found. On paper everything was great in reality theres unforseen things like muzzleblast you can see on paper and sometimes dumb privates and NCO's who want to look cool in front of them do stupid crap like clearing a small space with one and it blinds everyone trying to just do their job. I asked over and over for 50 Beo ammo and we were told by the supply wizards that all of it was pulled from the system. I know that in the real world 10" barrels are needed for some jobs and other times a 20 is needed and right now the 5.56 has more use in both than the 6.5 or 6.8 will sadly ever see. So the Army will stay with the 5.56 and step the ammo up when its needed. (Although I wish the would get away from the tree hugger ammo, it sucks at everything)

But I could be wrong, either like it or don't.

Sidenote: Please oh please god, let some Civilian Impaired person talk crap about wound channels with 5.56 and 7.62x39. So I can show the channel cut down my right arm, the entry and exit holes on my legs and point out that I know of at least one 7.62 that didnt help its owner delay his meeting with Allah. I dare you.

I'm so sick of this topic and those who try to ruin two good forums about two good rounds.

Anyway, rant over for me, I'll just sit back and watch this thing burn.

[woohoo]

Yes I would say everyone here knows I am Constructor. Seems like I was banned here as Constructor several years ago but I like to read some of the military topics Stan gets into so I came back.
Is the only way you can be faster is to do it unfair? Why did you bother posting? Lets use a heavier bullet in the 6.8 or lets use a 5R 6.5 barrel verses a conventional rifled barrel how about a Corvette VS a VW bug? Apples to apples, oranges to oranges.
When you can get a 123gr bullet up to 2700 out of a 16" barrel let me know, I want to watch.

[XcountryRider]

Yes I would say everyone here knows I am Constructor. Seems like I was banned here as Constructor several years ago but I like to read some of the military topics Stan gets into so I came back.
Is the only way you can be faster is to do it unfair? Why did you bother posting? Lets use a heavier bullet in the 6.8 or lets use a 5R 6.5 barrel verses a conventional rifled barrel how about a Corvette VS a VW bug? Apples to apples, oranges to oranges.
When you can get a 123gr bullet up to 2700 out of a 16" barrel let me know, I want to watch.

. I'm not saying the 6.5mm Grendel is always faster than the 6.8SPC. I'm saying that it depends on the barrel and that sometimes the 6.5mm is going to be faster than the 6.8SPC depending on the barrel type. Thats a true statement. You are saying the 6.8SPC is always going to be faster and thats not true at all.

[XcountryRider]

Even still, guys have maxed out with the 120gr SST in the 6.8 SPC with the ARP chamber inside of 2500fps, like in the mid-2400's. Hornady's factory load is a very good velocity-producing load if it registers at 2460fps.

Look at Accurate's loading data for the 6.8SPC. They are using a 20in barrel for the data. Now look at the velocities for the 120gr SST for the 20in barrel. None of the velocities are even getting what i'm getting with my 18in barrel with FACTORY Amax or SST.

[Tedward]

Yes I would say everyone here knows I am Constructor. Seems like I was banned here as Constructor several years ago but I like to read some of the military topics Stan gets into so I came back.
Is the only way you can be faster is to do it unfair? Why did you bother posting? Lets use a heavier bullet in the 6.8 or lets use a 5R 6.5 barrel verses a conventional rifled barrel how about a Corvette VS a VW bug? Apples to apples, oranges to oranges.
When you can get a 123gr bullet up to 2700 out of a 16" barrel let me know, I want to watch.

Stop comparing a 357 to a 38. Two different calibers, cases and everything. Even a 223 and a 556 are different in some ways and use the same case but more similar than a 6.5 and a 6.8.

[woohoo]

Stop comparing a 357 to a 38. Two different calibers, cases and everything. Even a 223 and a 556 are different in some ways and use the same case but more similar than a 6.5 and a 6.8.

I didn't start this VS thread.
I thought we had all dropped this stuff back around 2008 and decided to choose the one that fits our intended purpose best. I have more than a few of each as personal rifles. I don't have time to get into this today, I am way behind on shipping product.

[XcountryRider]

I didn't start this VS thread.
I thought we had all dropped this stuff back around 2008 and decided to choose the one that fits our intended purpose best. I have more than a few of each as personal rifles. I don't have time to get into this today, I am way behind on shipping product.

I think you did actually.

[bwaites]

I didn't start this VS thread.
I thought we had all dropped this stuff back around 2008 and decided to choose the one that fits our intended purpose best. I have more than a few of each as personal rifles. I don't have time to get into this today, I am way behind on shipping product.

Actually, although others were discussing the two, you started the "us vs. them" portion.

I missed most of the this thread so I had to catch up, because I have a real life I have to deal with, but if it doesn't get back on topic and stay there, we'll be done with it real quick.

[woohoo]

I wont argu the performance further, we wasted 2 years and most of us that were there have chosen which cartridge we want to use for what task for whatever reason...personal choice.
There is no doubt some have found performance they like in 5R barrels.
What was the title of this thread...Grendel and 5R Rifling (Haters gonna Hate)?
I've been producing 264LBC barrels with 5R rifling. I don't hate them as a matter of fact they shoot pretty well.

[XcountryRider]

I think we agreed something is more goimg on with the libery barrels than just 5R. Not sure what .

[Bill Alexander]

The velocity of a projectile is a work function. Constraining the variables associated with the volume, expansion ratio and powder burn rate, velocity becomes directly proportional to the mean pressure during the bore time.

Faster from the same known standard loaded round can only result from more pressure. This is a bad thing.

Variables within a barrel can increase the pressure and it is well known for people to have barrels that are faster than others. This generally results from a tight major diameter, high aspect ratio or error in the throat.

5R rifling has by design a lower aspect ratio. It will typically lower pressures and directly lower velocities. This can be compensated by bringing the load up to the original pressure which will normally allow a slight increase in velocity. This same effect may be seen in the use of MoS2 on bullet jackets.

There are techniques that can be applied to gain velocity. The reduction of engraving forces by lengthening the throat or an increase in throat diameter can be used. They usually magnify the throat erosion and can create secondary detonations in extreme cold climates. It is rare to find a cartridge that has the volume to benefit.

By simple physics ( or complex pressure breach work) the 6.8 SPC will allow for an increase in velocity between 30 and 90 fps over a Grendel when both are loaded with identical projectile weight and constrained to the safe limits of the weapon. The SPCII throating drops the pressure slightly as above and can be compensated by the addition of charge weight. It will yield around 30 fps.

There is no magic in internal, external, intermediate or terminal ballistics. If you see something extraordinary hope that you can find the instrument error before something disassembles itself.

[XcountryRider]

Anything an amatuer like me can measure?

[XcountryRider]

One observation that points to increased presure is that the Aa2520 powder loads from Alexander Arms are to high for us with the liberty barrels. Our max loads are more in line with hornadys recommended loads. When i loaded 30.2 gr of AA2520 for barnes 120grtsx i was at 2820fps out of my 24 in. barrel. In other words we are getting more velocity with less powder.

[Tedward]

The velocity of a projectile is a work function. Constraining the variables associated with the volume, expansion ratio and powder burn rate, velocity becomes directly proportional to the mean pressure during the bore time.

Faster from the same known standard loaded round can only result from more pressure. This is a bad thing.

Variables within a barrel can increase the pressure and it is well known for people to have barrels that are faster than others. This generally results from a tight major diameter, high aspect ratio or error in the throat.

5R rifling has by design a lower aspect ratio. It will typically lower pressures and directly lower velocities. This can be compensated by bringing the load up to the original pressure which will normally allow a slight increase in velocity. This same effect may be seen in the use of MoS2 on bullet jackets.

There are techniques that can be applied to gain velocity. The reduction of engraving forces by lengthening the throat or an increase in throat diameter can be used. They usually magnify the throat erosion and can create secondary detonations in extreme cold climates. It is rare to find a cartridge that has the volume to benefit.

By simple physics ( or complex pressure breach work) the 6.8 SPC will allow for an increase in velocity between 30 and 90 fps over a Grendel when both are loaded with identical projectile weight and constrained to the safe limits of the weapon. The SPCII throating drops the pressure slightly as above and can be compensated by the addition of charge weight. It will yield around 30 fps.

There is no magic in internal, external, intermediate or terminal ballistics. If you see something extraordinary hope that you can find the instrument error before something disassembles itself.

So your saying you get more velocity out of a 6.8 with the same powder and same weight bullet than a 6.5? Or the 6.5 needs less powder to compare the two rounds safely??? I do not understand why the 6.5 needs limited load to compare it to the 6.8. That makes no sense. If they both have a 120gr bullet and the 6.8 can only handle X amount of powder and the Grendel can handle X+1 safely, then the Grendel has better velocity period.

Sort of like if you put a 100 hours power engine, 4:10 gears and the same transmission in a VW Bug or a Heavy Chevy, the VW will be faster, there's no magic in that either..

Maybe I'm missing something but why are we comparing the 6.5 and 6.8? I thought the topic was about 6.5 with 5R rifling and maybe another 6.5 type of rifling. That would be nice to discuss.

[woohoo]

Several things can be manipulated within the bore depending on what the designer of the button considers important. Bore diameter, bore area and land to groove ratio and all combinations of those to meet the need.
I heard where some famous or maybe infamous project lead had designed a button for a new hopeful military cartridge a few years ago. He wanted more bore area so he simply made the groove diameter larger than the bullet diameter(more than needed for stretch and rebound). If the button maker hadn't caught it the bullets would have rattled down the bore and they would have had blow by at least until carbon built up.
Just an if. If someone designed a button without knowing the stretch and rebound of the barrel material the groove could end up smaller than needed. A little smaller could help accuracy, a lot smaller could increase pressure more than wanted.
A button too large or no stress relief could result in a big sloppy bore, slower velocity with less pressure and poor accuracy.
An air gauge would not map the bore but it could be used to compare the groove diameter between 2 barrels if in this case the 5R rifling was close enough to use the same air gauge.

[Drifter]

So your saying you get more velocity out of a 6.8 with the same powder and same weight bullet than a 6.5? Or the 6.5 needs less powder to compare the two rounds safely??? I do not understand why the 6.5 needs limited load to compare it to the 6.8. That makes no sense. If they both have a 120gr bullet and the 6.8 can only handle X amount of powder and the Grendel can handle X+1 safely, then the Grendel has better velocity period.

Sort of like if you put a 100 hours power engine, 4:10 gears and the same transmission in a VW Bug or a Heavy Chevy, the VW will be faster, there's no magic in that either..

Maybe I'm missing something but why are we comparing the 6.5 and 6.8? I thought the topic was about 6.5 with 5R rifling and maybe another 6.5 type of rifling. That would be nice to discuss.

Generally speaking, I think the point is that bullets of the same weight can be pushed faster through a larger bore, all else being equal.

[bwaites]

So your saying you get more velocity out of a 6.8 with the same powder and same weight bullet than a 6.5? Or the 6.5 needs less powder to compare the two rounds safely??? I do not understand why the 6.5 needs limited load to compare it to the 6.8. That makes no sense. If they both have a 120gr bullet and the 6.8 can only handle X amount of powder and the Grendel can handle X+1 safely, then the Grendel has better velocity period.

Sort of like if you put a 100 hours power engine, 4:10 gears and the same transmission in a VW Bug or a Heavy Chevy, the VW will be faster, there's no magic in that either..

Maybe I'm missing something but why are we comparing the 6.5 and 6.8? I thought the topic was about 6.5 with 5R rifling and maybe another 6.5 type of rifling. That would be nice to discuss.

Tedward,

Think of the bullet as a piston. If the surface of the piston is larger, there is greater displacement as the piston moves, allowing more work to be done by the piston (the same principle of larger displacement car engines), since the "work" of a bullet is unidirectional (and nothing is moved by the gas expansion except the bullet), then that larger piston translates into greater velocity, all else being equal. Modifications of the throat, grooves, etc. all impact that velocity somewhat, but if ALL the things are equal otherwise, the larger diameter bullet will be faster.

However, the drawback is that the larger diameter bullet (of the same weight) will be less aerodynamic, because it has a larger frontal surface area exposed to air, and because it is shorter overall. Thus the BC is lower, and the slightly slower bullet at the barrel will catch and surpass it soon. (Sometimes by 100 yards). That's why the Grendel is such a good cartridge. It allows the use of high BC bullets in AR15's. No other cartridge allows the use of such aerodynamic bullets at these weights.

Finally, velocity is a direct function of pressure. Increase pressure increase velocity. Increase pressure enough....go BOOM!

I have two 5R Grendel barrels, both cut rifled. Their velocities with factory Hornady are within FPS of expected. I suspect that the Chronographs being used on the rifles that seem really fast might be a tad bit optimistic. Thats been discussed elsewhere, since Chrono builders can do that. People don't like to see that their pet loads aren't really as fast as they thought they were, so the calibration at the factory is a bit high.

[DW61]

Well now I have a good reason to order a chrony tonight.. for safety reasons..yeah that's the ticket