Advice about pressure signs

[fdbyrne78]

I have a strange problem. At least I think it's strange. I worked up a load for one of my rifles. It's amazingly accurate. It's easily .4" to .5" 5 shot groups at 100 yards. It's a moderate load with moderate velocity but the gun is chewing up the brass. Ejector marks can be seen on every piece of brass with some having raised burs. Primers look OK.

Since the load data isn't particularly hot I assumed the marks on the brass were from the gun being over gassed. I turned down the gas until the BCG would barely lock back. I swapped in tungsten buffer weights until the buffer weighed almost twice as much as a stock rifle buffer and the marks only got a little better. I rounded the edge of the ejector as well.

I have a load for 90gr TNTs with benchmark that shoots good and the brass looks great.

Does my load data seem hot enough to cause the results I'm having?

Load:

26.6gr AR Comp
Hornady brass (1x)
#41 primers
123gr ELDM
Mag length (not into the lands)
2500 fps

Gun:

20" Satern cut rifled barrel
Rifle gas
Rifle lower

[StoneHendge]

Turn the gas off completely. If you still get marks, it's pressure. If not, it's timing or excess gas.

Without digging into my notes, mid 26's is my max with AR Comp and 120/3s in my tight chambered 22" JP barrel. It's right around 2500.

[Klem]

78.

Yes, that is hot load - beyond SAAMI.

Suggest 25.8 max, or SH's 26, but no more.

[fdbyrne78]

Hmm. Fair enough I guess. Bummer though. It shoots so well.

[Rosecrans1]

Agreed with these guys that is a hot load. You stated it was a moderate load and I'm wondering where you got that?
I'll go to 26.4 in my bolt and below 25.8 in my AR using AR-Comp and 120-123gr anythings.

[myrifle]

I have a strange problem. At least I think it's strange. I worked up a load for one of my rifles. It's amazingly accurate. It's easily .4" to .5" 5 shot groups at 100 yards. It's a moderate load with moderate velocity but the gun is chewing up the brass. Ejector marks can be seen on every piece of brass with some having raised burs. Primers look OK.

Since the load data isn't particularly hot I assumed the marks on the brass were from the gun being over gassed. I turned down the gas until the BCG would barely lock back. I swapped in tungsten buffer weights until the buffer weighed almost twice as much as a stock rifle buffer and the marks only got a little better. I rounded the edge of the ejector as well.

I have a load for 90gr TNTs with benchmark that shoots good and the brass looks great.

Does my load data seem hot enough to cause the results I'm having?

Load:

26.6gr AR Comp
Hornady brass (1x)
#41 primers
123gr ELDM
Mag length (not into the lands)
2500 fps

Gun:

20" Satern cut rifled barrel
Rifle gas
Rifle lower

Mag length( not into the lands) tells us nothing.

Have you measured too be sure you are not into the lands?

I had a satern barrel once. Got rid of it because I had the same issues yours is showing only it did it with factory amax and eld-m ammo. Turns out it was short throated.

[lazyengineer]

78.

Yes, that is hot load - beyond SAAMI.

Suggest 25.8 max, or SH's 26, but no more.

Where do you get this SAMMI data? (this is me asking; not challenging)

Threads like this
https://www.65grendel.com/forum/showthre...ght=ARComp

imply going 27gr and beyond is OK with this powder that weight class bullet. I ask because I have a lot of confusion as well on just what is the appropriate max with this powder and Grendel - as Alliant doesn't have any official ARComp data that I can find for Grendel. I have personally run it 26.0 (2422fps), 26.5 (2462 fps), and 27.0 (2507 fps) gr in some ladder testing in a 20"; but I mostly just made that up based on other people's posts here. Hornady lists factory ammo with this factory loaded ammo in 24" BBL as 2580fps. Of course, with a tail wind and some kind of greased barrel brand new BBL, as we well know, and with tuned powder. But to me, a 20" going about 2500 fps isn't an automatic alarm bell.

FWIW, my worst accuracy was with the hottest loads, so I'm likely going to settling on the 26.0 gr charge, which seems OK in my rig (and gave me a strikingly remarkable 0.5MOA group). Perhaps a mistake?

[Klem]

Lazy,

I understand.

Quickload.

26.5 AR Comp lists 56,700lbs at that load at 'mag length', which is 2.283" for a Grendel SS mag. Used the program's default case capacity 35.99gns of water.

QL outputs 2,518fps for a 20" barrel, which is as close to the OP's stated velocity as it gets.

Given velocity is a proxy for pressure I am very comfortable saying it is over SAAMI. Note, given the sensitivities regarding QL on the Forum lately I did not state the predicted pressure. I Just said that it is a hot load over SAAMI. Plus the ejector swipes which are also indicator that it is too hot.

[lazyengineer]

Lazy,

I understand.

Quickload.

26.5 AR Comp lists 56,700lbs at that load at 'mag length', which is 2.283" for a Grendel SS mag. Used the program's default case capacity 35.99gns of water.

QL outputs 2,518fps for a 20" barrel, which is as close to the OP's stated velocity as it gets.

Given velocity is a proxy for pressure I am very comfortable saying it is over SAAMI. Note, given the sensitivities regarding QL on the Forum lately I did not state the predicted pressure. I Just said that it is a hot load over SAAMI. Plus the ejector swipes which are also indicator that it is too hot.

I haven't run QL, but I when I ran Gordon's, it worked fine in most calibers, but in 6.5 Grendel it was claiming common loads as way WAY over max. Maybe QL is better, but aside from freaking me out, I lost confidence in the modeling software when it comes to 6.5 Grendel. That said, you seem to run it a lot, so perhaps in your own experience you have more faith in QL matching your own observations?

[Klem]

Lazy.

You have to admit, the OP's 2,500 fps is pretty close to 2,518.

2,500 is pretty coincidental so I suspect the OP is rounding here.

I use QL in all calibres because, among other things, it is conservative. So while the predicted velocities are never exactly what the chrono measures it gives me confidence it is safe. I compare QL against manufacturer's tables and start 10% low. I think the loads on this forum tend to be hot so don't pay too much attention to what others do here. Plus the recent criticism of it here was undeserved.

[Zeneffect]

Any criticizim of QL being a optical media only product is well deserved. Either the German government is stuck in 1996 or we are being lied to and the developers don't care to implement things like activation keys or other form of intellectual property protection/licensing.

[lazyengineer]

Lazy.
.... I think the loads on this forum tend to be hot so don't pay too much attention to what others do here. ....

To be honest, I think you're right on that part.

[Klem]

Any criticizim of QL being a optical media only product is well deserved. Either the German government is stuck in 1996 or we are being lied to and the developers don't care to implement things like activation keys or other form of intellectual property protection/licensing.

Zene,

Absolutely - No arguments from me. It is just crazy they are using disks and the postal system in 2022.

[VASCAR2]

Speer online reloading data for 6.5 Grendel with 120 grain Gold dot list a start load of 22.8 grains of AR Comp max load 25.3 using Federal GM205 Match AR primers. Speer uses a 24” universal receiver for testing and only show 2418 FPS. The 120 grain Gold Dot is a bonded core bullet and might build pressure quicker than a cup and core bullet.

The Speer reloading data is the only data I’ve seen published for AR Comp. It is common to see forum members load higher charges of AR Comp than listed by Speer with 6.5 Grendel. I really wish Sierra or Hornady would test AR Comp in the 6.5 Grendel. I think AR Comp has a lot of potential in the 6.5 Grendel since it is a temperature stable powder. I’ve contacted Alliant and they said they might eventually do more testing with AR Comp in 6.5 Grendel but directed me to Speer’s data.

[fdbyrne78]

Lot's of good questions. I'll see if I can provide some answers.

I don't have my data with me but I'm not into the lands. My satern barrel had a short throat but it's not that short any more. The rounds drop free from the chamber when inserted by hand. I have measured the jump but don't have my numbers with me.

As for me calling it a moderate load, that was probably a poor choice of words. I don't remember where I got my original load data but 26.6 is a grain less than what many on this forum use all the time. My other Grendel can go higher without signs.

I think that you are all correct. That load MAY be safe in some guns... but not mine apparently.

[JASmith]

Lazy,

I understand.

Quickload.

26.5 AR Comp lists 56,700lbs at that load at 'mag length', which is 2.283" for a Grendel SS mag. Used the program's default case capacity 35.99gns of water.

QL outputs 2,518fps for a 20" barrel, which is as close to the OP's stated velocity as it gets.

Given velocity is a proxy for pressure I am very comfortable saying it is over SAAMI. Note, given the sensitivities regarding QL on the Forum lately I did not state the predicted pressure. I Just said that it is a hot load over SAAMI. Plus the ejector swipes which are also indicator that it is too hot.

The QuickLoad user manual says do not use the results to infer safe pressures.

My own experience confirms that the advice is sound.

[Klem]

78,

'Safe' is a relative term.

In bolt guns there is more latitude to go higher than SAAMI. When I was shooting F Class all the .223 shooters could not compete out to 1,000yards without deliberately loading hot. Strong actions and chambers, plus magnum primers and smaller firing pin holes contained the pressure so you can do this for the life of the action without issue.

SAAMI limits are based on the lowest common denominator of likely action, plus a further margin of safety. Unfortunately, AR15's are about the most fragile actions you can buy. Grendel on the other hand with its same AR size bolt but wider diameter case makes it even more susceptible to pressure. Add to that loaders pushing boundaries and sooner or later one of those lugs is going to fail - it's the weakest link. Might not be immediate - might be in 1,000 rounds of constant hammering. Also depends on the quality of that bolt and how the lugs share the load with that barrel extension. This is a controversial statement but maybe you can be comfortable that it will fail sooner rather than later with a spare bolt at hand. Thinking of bolts as consumable items like we do barrels is one way of loading hotter than SAAMI - obviously not too hot but just over and carry a spare bolt.

It is the Forum's understanding that when you start to see typical overpressure signs on spent cases it is already over SAAMI. Your load is 103% full and that is compressed. Pressure climbs steeper once the case becomes compressed.

[Klem]

The QuickLoad user manual says do not use the results to infer safe pressures.


My own experience confirms that the advice is sound.

JA,

I am surprised QL doesn't warn against turning on their program. Their warnings against using their own program read like a life story. Indicative they are conservative by nature and frightened to death about liability. As I said, I am happy using QL because it is so conservative that even if the pressure outputs are incorrect they are likely to still be on the safe side.

[LRRPF52]

JA,

I am surprised QL doesn't warn against turning on their program. Their warnings against using their own program read like a life story. Indicative they are conservative by nature and frightened to death about liability. As I said, I am happy using QL because it is so conservative that even if the pressure outputs are incorrect they are likely to still be on the safe side.

They both vary 9,000 to 20,000psi over and under actual pressure test breech readings. They aren’t consistently-under SAAMI MAP. That’s the problem.

You could take Hodgdon’s and Western Powder’s cumulative data and enter each combination into QL to compare against their measured pressure test breech numbers if you have a lot of time on your hands.

You will see numbers all over the map relative to the real-world numbers.

[LRRPF52]

Speer online reloading data for 6.5 Grendel with 120 grain Gold dot list a start load of 22.8 grains of AR Comp max load 25.3 using Federal GM205 Match AR primers. Speer uses a 24” universal receiver for testing and only show 2418 FPS. The 120 grain Gold Dot is a bonded core bullet and might build pressure quicker than a cup and core bullet.

The Speer reloading data is the only data I’ve seen published for AR Comp. It is common to see forum members load higher charges of AR Comp than listed by Speer with 6.5 Grendel. I really wish Sierra or Hornady would test AR Comp in the 6.5 Grendel. I think AR Comp has a lot of potential in the 6.5 Grendel since it is a temperature stable powder. I’ve contacted Alliant and they said they might eventually do more testing with AR Comp in 6.5 Grendel but directed me to Speer’s data.

Yes. Gold Dot builds pressure faster than most cup and core bullets from what we’ve seen so far.