6.5 Grendel Blowing Up Guns?

[HoustonHipster6.5]

A guy at the range was telling me why he doesn't use 6.5G. He's an ex-SWAT guy and an avid reloader. He was trying to sell me on the 25-50 Sharps. He said that the way 6.5G seats into the rifling of the barrel in an AR or other semi-auto causes a pressure spike at the throat of the barrel and causes guns to explode. He's a smart guy, but that sounded like horsesh*t.

Anyone know anything about this issue? Any validity to it?

Thanks in advance.

[grayfox]

Sounds like a moron walking, to me.
He needs some elementary instruction in what happens during the first few microsec after striking the primer. Note that for QL and Grt one typically winds up accounting for a larger "case volume factor" since when the bullet obturates into the rifling it leaves some chamber volume behind, which adds to the case volume and then becomes the chamber in which the gas pressure builds.
The method of bullet motion and seating in a grrr is the same as for any AR style barrel, I would dare to say the same as for any barrel, except for those where the bullet is jammed into the lands from the first.
Maybe his experience comes from such land-jamming, or from a gross overpressure - kaboom style - of a large overcharge??
He is welcome to his opinion but literally thousands of shooters and millions of rounds would argue against him.

[stonehog]

It sounds like he's trying to sell you something.

[biodsl]

Please...please ignore that guy.

He is welcome to his opinion but literally thousands of shooters and millions of rounds would argue against him.

What grayfox said.

[kmon]

It sounds like he's trying to sell you something.

I think you are right. Also involves something I shoveled a bit of when showing bulls in the FFA years ago.

Per QL in most the highest chamber pressure happens very close to the time the bullet has fully been engraved by the rifling which in the Grendel is more gradual progression to the rifling in from throat to full rifling in the barrel is more gradual. Peak pressure generally occurs just after the bullet is fully engraved with the rifling and fully fitting the bore. The Grendel is also a lower pressure round than most used modern cartridges. 4 to 10 thousand less PSI in the Grendel than other rounds, I would want to hear him explain how less peak pressure leads to more blown up barrels.

If he blew one up that way properly loaded the bullet does not engage with the lands until it has moved some overcoming the neck tension resistance and started moving. Perhaps he was loading long jamming into the lands and using the extra powder volume in the case hot rodding for all possible velocity. if you want more velocity get a bigger cartridge. I will take the Grendel and enjoy it and if I want more velocity I will go to a larger cartridge with more powder space and higher standard pressure in say an AR10.

[JASmith]

The compound throat has confused a lot of would be smart guys.

The interesting thing is that the compound throat and short cartridge in the Grendel actually reduce peak pressures from what QuickLoad and GRT predict. There are two primary reasons for this:

First, the gentle taper in the throat reduces the initial engraving force.

Second, the primer charge slaps the back of the longer bullets before the main powder charge gets into its burn. That results both in a larger case volume and more initial movement than are modeled in the predictors.

Both are difficult to model in either QL or GRT with the core math model they use.

[lazyengineer]

The compound throat has confused a lot of would be smart guys.

The interesting thing is that the compound throat and short cartridge in the Grendel actually reduce peak pressures from what QuickLoad and GRT predict. There are to primary reasons for this:

First, the gentle taper in the throat reduces the initial engraving force.

Second, the primer charge slaps the back of the longer bullets before the main powder charge gets into its burn. That results both in a larger case volume and more initial movement than are modeled in the predictors.

Both are difficult to model in either QL or GRT with the core math model they use.

Thanks for that. GRT way overpredicts Grendel, and this is the first good explanation I've seen on why that might be.

[VASCAR2]

Sounds like the guy is confusing 300 Black Out with 6.5 Grendel. Very common to blow up an AR-15 mixing ammo in 300 BO in 5.56 AR-15. The only AR-15 I ever saw Kaboom was using hand loads where the person inadvertently mixed pistol and rifle powder loaded into 5.56. Fortunately no one was seriously injured but sure ruined a very nice AR-15.

[grayfox]

It sounds like he's trying to sell you something.

Definitely a "Music Man" scene "yes there's trouble, right here in River City...!!!"
JA's explanation was what I was trying to get to as well... his is more to the point technically.

[TomSawyerNW]

First I ever heard of this after many years of being in forums for guns of all types. I imagine he has some hard evidence? And if he doesnt...well....

[Old Bob]

I had a kaboom once. In a 3 gun match I was shooting re-manufactured 5.56 NATO ammo that was made by a local outfit here in Albuquerque. I had a round rupture on me. It blew a hole out the side of the case, jamming a section of the case head into the bolt face where it is permanently stuck. The escaping gasses blew the magazine out of the receiver, scattering magazine parts & remaining ammo everywhere. The bolt face & the carrier were both cracked with some parts sheared off & lost it the dirt where I was shooting. The receivers, after a thorough exam, were deemed still functional. Except for a little lost dignity, I was unharmed.

I took what was left of the ruptured case & the remaining ammo back to the maker & showed him what happened. I've known the guy for years & was good friends with his daughter & SIL. He expressed his surprise & offered to buy back the remaining ammo, an offer I accepted. I was surprised as well 'cause I know he took great pride in his products. Crap happens sometimes even when you take care to do the best you can.

[StoneHendge]

Last month, a guy at the range told me that ammo is expensive because manufacturers are hiding it in secret warehouses instead of selling it. You can learn lots of interesting things from guys at the range.

[Double Naught Spy]

The only time I have heard of a Grendel kabooming was with handloads during rapid fire with a squib.

[BluntForceTrauma]

last month, a guy at the range told me that ammo is expensive because manufacturers are hiding it in secret warehouses instead of selling it. You can learn lots of interesting things from guys at the range.

Ha!

[LRRPF52]

The only major catastrophic failure I recall being mentioned here on the forum over the years was the guy who loaded 140gr on top of a really fast powder well outside of the powders used for Grendel. Yikes!!!!

I think he just sheared a lug or two, nothing crazy. My memory may be wrong though.

I just used the CSE and found 2 instances:

1. Young’s MFG bolt failed on first firing.

2. Reloaded steel case

Grendel operates in the 49-51,8ksi working pressure range, which is really nice for safety, hand-loaders, and ammunition manufacturers.

No need to push pressures when the projectile BC does so much work for you.

[LR1955]

John Paul also reported a Grendel blowing up. This was when he first started making Grendel uppers. He attributed it to Wolf 123 grain Soft Points when they were the only commercially made Grendel ammo. This ammo was notorious for gross copper and carbon fowling and apparently it so clogged the barrel with crap that it created a bore obstruction and blew the upper apart. If I recall correctly, he also said the guy was doing a lot of rapid fire so was going through a bunch of ammo.

LR-55

[Fess]

Thanks for that. GRT way overpredicts Grendel, and this is the first good explanation I've seen on why that might be.

The poor pressure prediction of QL for the Grendel created a big ruckus in the first few years after the cartridge was introduced. IIRC, QL was predicting well over 60K psi for loads that had been pressure tested at below 52Kpsi. I recall that Marty ter Weeme (458 SOCOM and Teppu Jutsu) was credited at the time for coming up with the idea that the case volume was changing quickly because the primer started the bullet moving prior to main powder ignition. A few years ago, I asked if QL has fixed the problem for the Grendel and never got a satisfactory answer. I think that some advanced users just used a larger case volume to get closer to the correct answer.

[HoustonHipster6.5]

I love the musical theatre reference in a gun forum!

[JASmith]

Gotta love the musical theater!

The poor pressure prediction of QL for the Grendel created a big ruckus in the first few years after the cartridge was introduced. IIRC, QL was predicting well over 60K psi for loads that had been pressure tested at below 52Kpsi. I recall that Marty ter Weeme (458 SOCOM and Teppu Jutsu) was credited at the time for coming up with the idea that the case volume was changing quickly because the primer started the bullet moving prior to main powder ignition. A few years ago, I asked if QL has fixed the problem for the Grendel and never got a satisfactory answer. I think that some advanced users just used a larger case volume to get closer to the correct answer.

That might partly explain the default volume in QL now being 37.5 gr, when few or no cartridges have that much space.

And, yes, QL seems to do much better with standard weight bullets these days.