Optimal Hunting bullet for 18in Grendels.

[LRRPF52]

One of the biggest considerations with the solid bullets like the Barnes TSX/TTSX or Hornady GMX is that your start pressure needs to be accounted for. The solids resist being swedged into the lands of the rifling more than a thin-jacketed cup and core bullet, so they will spike on you much faster with the pressure.

The short story is that you can't extrapolate load data based on bullet weight. Jacket construction, bearing surface length, then weight are the factors to consider. Not only do the solids have more resistance to being forced into the rifling, but they tend to have longer bearing surface for their weight, which increases pressure more quickly.

With the 120gr TSX, you'll notice in the 6.5 Grendel Reloading Handbook that AA's data using BL-C(2) is about the same for the 129gr SST, both showing speeds of under 2500fps from a 24" barrel as mseric pointed out. All it takes is pressure to generate velocity, and an immediate house call from Mr. Murphy.

[XcountryRider]

AA used a 24 inch barrel, you are matching his velocity of 2650fps with an 18 inch barrel? Your 6 inch reduction in barrel length should net you a velocity loss of about 150fps +/-, about 2500fps.

Although AA does not list 2520 in his 120 TSX data he does list a Max velocity of 2503fps out of a 24 inch barrel.

Hodgdon lists a Max velocity for their powders tested at 2419fps out of a 24 inch barrel.

Either your Chrony was off or your load is HOT.

The same load from my 24in Barrel is 2820fps measured in two separate chronys and magno speed and a speed chrony F1 master. You'll notice all my velocities are higher than AA speeds. I'm getting 2650fps from factory Amax for my 24in barrel and 2560fps from my 18in barrel. I'm pretty sure the AR Stoner/Liberty barrels are fast maybe the 5R rifling? Not sure what Hodgdon velocities have to say about it when i'm shooting 30.2gr of Accurate 2520. I'm sure its a little hot and needs to come down its already under tha max loaded listed in the forums reload data page. Here's a thread i started on the subject.

[LRRPF52]

2620fps makes sense for the Hornady factory 123gr A-MAX from a 24" barrel. 5R could account for increased velocity, as the .308 gas gun I had built with a 22" Obermeyer 5R barrel would match 24" barrel velocities with the exact same load, but that is only 2" difference, with way higher pressures using 47gr of N150.

I get 2460fps from my 16" using the Hornady factory load. 2 of the last 5 I chronographed were actually 2470fps.

[JASmith]

We really do need to connect with what the primers tell us.

When we see signs indicating that we are on the edge of being too hot, we ARE TOO HOT for long term reliability of the AR-15 rifle chambered for the Grendel.

Further, the added range for terminal performance plus reduction in drop and wind drift are rather small when considered in terms of what one enjoys with standard pressure loads.

When you get velocities of 100-150 above standard, you know that the chances are excellent that you are either too hot or there is a chronograph calibration issue. Test the chronographs by lining two up in tandem -- easy to do if one of them is a Magnetospeed -- and see what velocities you get with each shot. If the two velocities for each shot are within 25 ft/sec, the chronographs are most likely both in calibration. If that velocity is 100 - 150 ft/sec above standard velocity for your barrel length, you are probably well above SAAMI-specified pressures.

The best advice is then to back off a few per cent in powder even if your inspection of the cases suggests that the load was safe. It not likely good for your even though it might be OK for the brass.

[XcountryRider]

2620fps makes sense for the Hornady factory 123gr A-MAX from a 24" barrel. 5R could account for increased velocity, as the .308 gas gun I had built with a 22" Obermeyer 5R barrel would match 24" barrel velocities with the exact same load, but that is only 2" difference, with way higher pressures using 47gr of N150.
. I get 2460fps from my 16" using the Hornady factory load. 2 of the last 5 I chronographed were actually 2470fps.

I'm getting 2650fps from factory Amax from my 24in. Could the 5R rifling benefit the longer Grendel bullets even more than the 308 bullets? I really wish someone else would chrony there AR Stoner barrels so we get another data point.

[XcountryRider]

We really do need to connect with what the primers tell us.

When we see signs indicating that we are on the edge of being too hot, we ARE TOO HOT for long term reliability of the AR-15 rifle chambered for the Grendel.

Further, the added range for terminal performance plus reduction in drop and wind drift are rather small when considered in terms of what one enjoys with standard pressure loads.

When you get velocities of 100-150 above standard, you know that the chances are excellent that you are either too hot or there is a chronograph calibration issue. Test the chronographs by lining two up in tandem -- easy to do if one of them is a Magnetospeed -- and see what velocities you get with each shot. If the two velocities for each shot are within 25 ft/sec, the chronographs are most likely both in calibration. If that velocity is 100 - 150 ft/sec above standard velocity for your barrel length, you are probably well above SAAMI-specified pressures.

The best advice is then to back off a few per cent in powder even if your inspection of the cases suggests that the load was safe. It not likely good for your even though it might be OK for the brass.

We have 3 possibilities one two chronys are off only when chronying Rifles with AR stoner 5R rifling barrels but not other rifles. Very unlikely!!. My loads are hot BUT when shot from other grendels have at least 100 or more FPS slower velocities. Also very unlikely. They could be and probably are a little hot and need to come down but that's not the whole story because they are significantly slower out of other rifles. The third possibility is something about my rifles that both share the same barrel bolt combo is making them faster. I think its a combo of a little hotter loads and faster barrels possibly. The only way to be sure is if someone else with factory ammo and a completely different chrony takes measurements.

[Drifter]

My loads are hot BUT when shot from other grendels have at least 100 or more FPS slower velocities.

This might have been covered before, but in case it wasn't... Have you checked your particular chambers / barrels for max COL? Whether factory or reloads, if you're jamming the lands, pressure and velocity will be higher when compared to barrels that have more freebore. Just a thought...

[LRRPF52]

We have 3 possibilities one two chronys are off only when chronying Rifles with AR stoner 5R rifling barrels but not other rifles. Very unlikely!!. My loads are hot BUT when shot from other grendels have at least 100 or more FPS slower velocities. Also very unlikely. They could be and probably are a little hot and need to come down but that's not the whole story because they are significantly slower out of other rifles. The third possibility is something about my rifles that both share the same barrel bolt combo is making them faster. I think its a combo of a little hotter loads and faster barrels possibly. The only way to be sure is if someone else with factory ammo and a completely different chrony takes measurements.

Since nobody owns your barrels, their barrels will have different characteristics, unless you suspect the 5R rifling to be involved. I'm still interested in who is making barrels with 5R rifling that are button-rifled.

[XcountryRider]

Since nobody owns your barrels, their barrels will have different characteristics, unless you suspect the 5R rifling to be involved. I'm still interested in who is making barrels with 5R rifling that are button-rifled.

I doubt i got lucky with 2 fast barrels by chance i think something else is at play like the chambering or more likely the 5R rifling. Maybe a combo of both?

[joker31]

I'm thinking Liberty are 5R buttons, I could be wrong though. My Satern is cut 5R that I know.

[mseric]

The same load from my 24in Barrel is 2820fps measured in two separate chronys and magno speed and a speed chrony F1 master. You'll notice all my velocities are higher than AA speeds. I'm getting 2650fps from factory Amax for my 24in barrel and 2560fps from my 18in barrel. I'm pretty sure the AR Stoner/Liberty barrels are fast maybe the 5R rifling? Not sure what Hodgdon velocities have to say about it when i'm shooting 30.2gr of Accurate 2520. I'm sure its a little hot and needs to come down its already under tha max loaded listed in the forums reload data page. Here's a thread i started on the subject.

Factory Ammo chronys at 2650fps, your handloads chrony at 2820fps, doen't that tell you something? Tells me that your handload is "Hot".

Carry on.

[XcountryRider]

I'm thinking Liberty are 5R buttons, I could be wrong though. My Satern is cut 5R that I know.

Yes they are.

[XcountryRider]

Factory Ammo chronys at 2650fps, your handloads chrony at 2820fps, doen't that tell you something? Tells me that your handload is "Hot".

Carry on.

Tells me two things my load is hot and my barrel is fast. My same load out of a friends gun is going 2700fps not my 2820fps. Here's my current thinking. Velocity is a factor of the pressure from the powder and the resistance of the barrel working against it. If 5R rifling gives less resistance the bullet will travel faster. The grendel is a long bullet which means more surface area touching the rifling causing more resistance. If 5R rifling has less friction and resistance to the bullet we'd would expect longer bullets like the 6.5mm to get more benefit from 5R rifling compared to non 5R than say a 308 which is shorter and fatter with less surface area.

[Drifter]

Tells me two things my load is hot and my barrel is fast. My same load out of a friends gun is going 2700fps not my 2820fps.

If you're jamming the lands and he isn't, the extra speed is potentially the result of extra pressure.

All I'm saying is that, in the interest of safety, be damn sure of what your max COL is for any particular bullet in your own chamber. If excessive pressure is repeatedly applied, sooner or later, something's gotta give.

[XcountryRider]

If you're jamming the lands and he isn't, the extra speed is potentially the result of extra pressure.

All I'm saying is that, in the interest of safety, be damn sure of what your max COL is for any particular bullet in your own chamber. If excessive pressure is repeatedly applied, sooner or later, something's gotta give.

If i was jamming the lands would i not be seeing scratches on my bullets? That would also mean i'm jamming the lands on two separate rifles that both came as a bolt barrel set.

[rickOshay]

By the way, that "friends gun" was a standard 24" Satern heavy barrel with 1:8.75 twist.

XCR's gun does appear to get higher velocities. But his loads are too hot, and he has posted pics of the cases that show significant extractor marks and flattened primers. He has been urged to back off on those loads and work up again with close attention to pressure signs on his brass.

I agree with JASmith and others who have posted the view that gaining 50 - 100 fps to extend hunting reach is not worth the risk of broken bolt lugs or much worse. There is a nice write up on hunting reach of the Grendel in the Reloading Handbook and on JASmith's nice paper on "Ideal Bullet Weight". Pushing the biggest bullet as fast as possible is not necessary to hunt with the Grendel.

[XcountryRider]

By the way, that "friends gun" was a standard 24" Satern heavy barrel with 1:8.75 twist.

XCR's gun does appear to get higher velocities. But his loads are too hot, and he has posted pics of the cases that show significant extractor marks and flattened primers. He has been urged to back off on those loads and work up again with close attention to pressure signs on his brass.

I agree with JASmith and others who have posted the view that gaining 50 - 100 fps to extend hunting reach is not worth the risk of broken bolt lugs or much worse. There is a nice write up on hunting reach of the Grendel in the Reloading Handbook and on JASmith's nice paper on "Ideal Bullet Weight". Pushing the biggest bullet as fast as possible is not necessary to hunt with the Grendel.

I'm thinking that 29gr range of AA 2520 will be in the right range with plenty of velocity and much safer. I'm thinking that will probably give me around 2700ish for the 24in and 2580ish for the 18in. We'll see. If i get that i'll be really excited!! Where did the loads come from on the site reloading data? It says high load of 30.4gr of accurate 2520 for the 120gr TSX. I'm at 30.2gr and already at 2820fps. Also the 120tsx at 2820fps does not have extractor marks. Thats the 28.5gr of 2520 with the Nosler 140gr. 30.2gr of 2520 with the 120tsx does not have any extractor marks at all but does show primer cratering.

[Drifter]

If i was jamming the lands would i not be seeing scratches on my bullets? That would also mean i'm jamming the lands on two separate rifles that both came as a bolt barrel set.

Here's a simple method to check COL (courtesy of rasp65):

http://www.65grendel.com/forum/showthrea...-amp-crimp

As for two barrels, are they both from the same maker, using the same reamer?

Stay clear of the magwell if you have any uncertainty when shooting those same loads.


If you think I'm attempting to scare you, well... you're right.

When something doesn't add up, it's worth investigating further, especially when it comes to firearms.

A fast barrel is good only if it's safe.

I want your barrel to be fast. And safe. And I want you to be around to tell about it.

[JASmith]

I think we are starting to see the reason that virtually all reloading manuals and sites have the admonition "START LOW AND WORK UP CAREFULLY!" Many of them suggest that the starting load be 10% below the maximum recommended load.

The usual explanation is that every rifle, case, powder lot, etc. is different from others that are nominally identical. These variations WILL affect load performance. Sometimes the effect is reduced velocities and pressures. Other times, like the present case, the velocities and pressures are high. The really lucky ones are those which display nominal results.

[LRRPF52]

Primer cratering is at least the 3rd stage of too high of pressures:

* Stage 1: Erratic velocity jumps from a steady, predictable curve of increased powder charges when running a pressure ladder with the chronograph (This is about when you have exceeded the Maximum Average Pressure by SAAMI.)

* Stage 2: Case head expansion on your brass. Measure before and after.

* Stage 3: Flattened primers start to appear. This is an unreliable method for determining excessive pressure signs because we are way above MAP at this point, and there are varying stages or other causes of flattened primers (self-loaders have more dimensional tolerance, and many production bolt guns have excessive headspace).

* Stage 4: Cratered primers. Now we're really in bad territory. The pressure and heat are so intense, that the primer is transitioning from a solid, into a liquid, and flowing into the firing pin hole. The raised dimple with crater rim is only there because your firing pin kept it from going any farther. Not only is the chamber pressure exceeded, but the rearward force on the primer is hard on the bolt components, often leading to microscopic cracks on the surface of the firing pin's nose.

* Stage 5: Ejector extrusion. This is a small circle that will appear on firearms using a plunger style ejector. As it becomes worse, it will protrude even further into the ejector channel.

* Stage 6: Pierced primers. I've heard figures of being well into the mid-high 60,000 psi territory here, when using the thicker primer cups recommended for high-power rifles.

* Stage 7: Blown primers or black soot flow from around the primer cup, clearly visible on the case head. Loose primer pockets.

* Stage 8: Case failure, usually a case head separation, which causes permanent damage to the AR15 action, including bolt carrier splitting, upper receiver fragmentation, lower receiver warping, bolt fusing, or other catastrophic failure symptoms of extreme damage.

Where are the pressure ladder results with these powder/projectile combos?

Start load = _____fps
next increment = ______fps
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At what point did the velocity jump from the predictable behavior? That is the main question that needs to be answered in your quest. I find it with every load I work up, and then back away from it into the last accuracy node, keeping in mind the temperature.