Grendel and 5R Rifling (Haters gonna Hate)

[Tedward]

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.

Thank you for putting it in layman's terms, got it.

So that being said, wouldn't a smaller diameter bore with a same weight bullet then have a longer bullet and be more stable. It might be a little slower but stay more on course longer being more accurate in the smaller diameter?

[XcountryRider]

No ones Liberty rifles have went boom so far we have only seen higher velocoties woot woot!

[Drifter]

Thank you for putting it in layman's terms, got it.

So that being said, wouldn't a smaller diameter bore with a same weight bullet then have a longer bullet and be more stable. It might be a little slower but stay more on course longer being more accurate in the smaller diameter?

The smaller diameter bullet of the same weight (and of similar design) will likely have a better ballistic coefficient. It might start slower, but will retain velocity better and be less affected by wind. A couple of hundred yards or so out, the slower high-BC bullet's speed will surpass the faster low-BC bullet. Ballistic coefficient, barrel twist, velocity, etc factor into the accuracy equation for long-distance shooting. Generally speaking (again), that's what makes the 6.5 popular.

My own perspective views a larger bore as possibly having an advantage in terminal hunting performance at shorter distances (<200 yds), with a midrange area (200 to 300 yds) being relatively equal between two bore sizes (with similar bullets), and the smaller bore showing an advantage at longer distance (>300 yds). There are certainly other factors, such as bullet selection, factory ammo selection, etc.

When bore sizes are close and the differences subtle, a case can be made for either as having the advantage based on a particular viewpoint. Consumers and end-users arguing over which is better is rather silly. Simply pick the one that is perceived to be best for the planned application, and respect someone else's decision to do the same. In most cases, the target will never know the difference.

[Ridgerider]

Think most are missing the point and we can all argue which is which but don't think one person has mentioned a little thing called density altitude. Temp.etc.etc or that the Grendel is just better at doing what it does.

[XcountryRider]

Its interesting the number of people in this thread that work at or paid by companies in the AR industry. Only a few of us actual just regular shooters that aren't biased financially in this discussion.

[bwaites]

Its interesting the number of people in this thread that work at or paid by companies in the AR industry. Only a few of us actual just regular shooters that aren't biased financially in this discussion.

The only ones here that get paid, that I know of, are WooHoo (AR Performance) and Bill Alexander. Anyone else?

[XcountryRider]

The only ones here that get paid, that I know of, are WooHoo (AR Performance) and Bill Alexander. Anyone else?

Ridgerider for Quality Arms in Idaho is another......

[bwaites]

Ridgerider for Quality Arms in Idaho is another......

Ah...thank you, didn't realize that.

Anyone else?

[XcountryRider]

To show how close these MV are to the 6.8SPC look at these 6.8SPC chrony data from a magno speed from Stag 7HL upper (20.77" barrel). We are getting a little slower MV for the SST than the Amax. Somewhere around 2645-2640ish fps. Assuming a 20fps drop in MV per inch that puts us really close to the velocity he's getting with his 6.8SPC. So close the difference is completely meaningless. Especially considering the higher BC bullet would take over so quickly. His are magno speed velocities which are about 10FPS higher than a F1 Master Chrony would be measured 10ft from the muzzle. In other words the Liberty barrel has pretty much erased the advantage the 6.8SPC has enjoyed at least in this example. I'm sure someone can find a different example but that proves the point. It can no longer be said in general that the 6.8SPC is faster at the muzzle. It may or may not be depending on the barrel. Of course all things being equal the 6.8SPC will be faster but in the real world they aren't equal with different people using different gear getting different results.

Hornady 120gr SST Shots: 5
Min 2594 Max 2615
Avg 2607.8 S-D 8.58
ES 21
Series Shot Speed
2 1 2615 ft/sec
2 2 2613 ft/sec
2 3 2594 ft/sec
2 4 2612 ft/sec
2 5 2605 ft/sec

http://68forums.com/forums/showthread.ph...r+velocity

[XcountryRider]

Here's another example 120gr SST shot from a 18in PSA barrel. Hes getting 2525 fps (27.5gr AA2200). Compare to my factory 123gr Amax from my 18in Liberty/AR Stoner barrel at 2560fps. I'll need to drop that MV a bit for SST compared to Amax and you get the idea. Could he load a hotter load sure but it proves the point again that we are now in 6.8 starting gate territory and with the higher 6.5 BC its a different discussion than it has been.

http://68forums.com/forums/showthread.ph...Velocities

[LRRPF52]

Anything an amatuer like me can measure?

Cracked bolt lugs using naked eye sight. I think you just have a barrel with a tight bore or strange throat and bore that builds pressure differently, yielding higher mv. My 16" Grendel has spit out factory 123gr Scenars at 2583fps before, which told me something is wrong, as great as it would have been to have that speed. Temp sensitive powders can do that to you. When I clocked that load again during cooler weather, I had 2450fps with 7fps ES, & a nice grouping gun.

[XcountryRider]

Cracked bolt lugs using naked eye sight. I think you just have a barrel with a tight bore or strange throat and bore that builds pressure differently, yielding higher mv. My 16" Grendel has spit out factory 123gr Scenars at 2583fps before, which told me something is wrong, as great as it would have been to have that speed. Temp sensitive powders can do that to you. When I clocked that load again during cooler weather, I had 2450fps with 7fps ES, & a nice grouping gun.

I've cronyed 3 Liberty barrels so we can move past they discussion that something is wrong with my barrel. Soon others on here will crony theirs as well.

[lilharcher]

What I don't understand, why the fixation and need to go on every different shooting community to blab, including throwing it in other site's face? I understand discussing it hear since this a Grendel site, but why the need to thread crap at other sites?

Your enthusiasm to prove you are right is getting in the way of a good initial topic.

[Drifter]

I've cronyed 3 Liberty barrels so we can move past they discussion that something is wrong with my barrel.

I hope you are right, for your own safety (and anyone else around when your weapon is discharged).

But be sure to reference Bill A's previous post from a page or two back, especially the last sentence:

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]

First some of you were telling us ar stoner barrels were made in PI sweet shops and now your saying they are going to explode?

[XcountryRider]

What I don't understand, why the fixation and need to go on every different shooting community to blab, including throwing it in other site's face? I understand discussing it hear since this a Grendel site, but why the need to thread crap at other sites?

Your enthusiasm to prove you are right is getting in the way of a good initial topic.

woohoo or constructer or H what ever his handle is posted on the 6.8 forum not me.

[DW61]

I ordered a chrony last night. I'm curious to see what my 18" Stoner is putting out using factory loads. Now the next step is reloading equipment..

[woohoo]

I ordered a chrony last night. I'm curious to see what my 18" Stoner is putting out using factory loads. Now the next step is reloading equipment..

One thing to remember. All chronographs don't read the same. The shorter cheaper versions are usually more erratic than longer versions like the CED and Oehler.
Great tools to test one of your loads against another though.

[lilharcher]

woohoo or constructer or H what ever his handle is posted on the 6.8 forum not me.

Must be a different XcountryRider from Pine Valley then. Not sure why you needed to post this to a thread specially about a 270 wildcat AR. I am a supporter of the Grendel but I don't know why you feel the need to go on other sites and talk chit like you are some expert. To each their own. Funny you claim to be so inocent. Here is your initial post that started all your issues with Constructor, who I don't even know BTW, but loved how he called you out and you didnt even take him up on his bet:

Here is your exact post:
I got access to a chrony last week and clocked some grendel loads i'm using and found out my velocities were pretty high. I'm getting 2820fps on Barnes 120gr TSX loaded with 30.2grs of AA2520. 28.3gr of AA2520 is getting me 2500FPS from a 140gr Nosler BT Hunter. The factory Hornady Amax 123gr is going at 2650fps from my barrel as well. The 270AR is going to deliver more performance but probably not enough better to have me switch. Good luck i hope your successful but I've decided to stick with my grendels.

Top two velocities are 120 barnes TSX.



140gr Nosler BT velocity testing with Accurate 2520 powder. 28.5gr MV 2525fps, 28.7gr MV 2540fps, 28.9gr MV 2560fps.

[LRRPF52]

A 123gr Hornady factory load going 2650fps from a 24" makes perfect sense. A 120gr TSX from the same barrel going 2820fps does not make sense, other than a significantly over-pressured load. A load like that is going to break your bolt lugs, crack the cam pin hole, or worse.

The 120gr TSX should be going slower, and loaded with less powder due to its start pressure and bearing surface. I think that's the 3rd time I've mentioned this in this thread.

2560fps with a 140gr NBT from a Grendel? Holy crap! The velocity curve is consistent. What are your primer pockets like?