A Low Pressure Cartridge ?

[EigerWand]

There has been some advice here that the Grendel might not show pressure signs until it's too late.
Primers might look fine, case bases don't expand I suppose, whatever ...
Add to that 8208 powder is said to spike pressures with small increases in load.
Some say you should use a chrony instead to judge whether you're near max load.

Having had difficulty getting 120 Nosler BT to expand and using only a 16" barrel, I was starting to think that unlike other cartridges there could be some advantages to loafing the Grendel as hot as I could. In fact it seems quite hard to fit a book max load in behind a 120 projectile while staying inside magazine length and SAAMI COAL. Has anyone here actually blown up a bolt action Grendel through overloading ?

With a bolt action and good Lapua brass, couldn't it go to similar pressures to the 308 ? I know the SAAMI spec is lower. Is that something to do with the number of 5.56-spec ARs it's used in ?

So, it it really a "low pressure cartridge" and why ?

[Klem]

Not sure what you mean by 'low pressure' with SAAMI spec for Grendel at 52K lbs. .223 is 55K which is not much more. You can run calibres like 223 hotter and the military do this with 5.56NATO at 62K. The new Grey Tip ammo is even hotter than the M855 and all this gives better results down range but the cost is that guns wear out and break down quicker. The reason Grendel is slightly lower is related to the larger surface area of the case pushing back on the bolt, which is hardened but still will crack eventually.

I used to run 223 in a Rem700 bolt action at about 90K lbs, which is way more than SAAMI. We all did, and is the only way you can get a 80gn .223 bullet to 1,000yds with any hope of being accurate. Barrels are changed every year after about 1,000rds and cases last about half they would otherwise. The action is big, strong and chunky. The barrels thick at the chamber. The bolts were after-market with smaller .062" firing pins and tighter firing pin holes to prevent donuts breaking off the primer, which is also a thick magnum CCI450. All this makes it safe. You try that in an AR and it will blow up on the first or second round, maybe in your face.

The 120Nosler BT: although they claim is a varmint bullet is slow to expand, even at higher velocities. They call it "Controlled expansion". It does not matter how fast you send it into flesh from a Grendel it will still slowly expand, and that may be what you want - greater penetration, less disintegration. If you want more expansion then maybe a different bullet is the go, or at least the lighter and therefore faster 100NBT.

Yes, you need a chronograph when loading. The more information you can glean when load testing will make it safer and more efficient.

Nosler recommends 27.5gn of 8208 as max for 120NBT's (@ 1.243OAL). You can free up some case space by making the OAL slightly longer and still fit in a SS mag but you are risking much. At 27.5 the case is full. Add any more and you get into a compressed load. Compounding this is that 8208 is fast compared to other popular powders used in Grendel. This means a steep weight/pressure curve suddenly gets even steeper once you compress it. Manufacturer tables are conservative so you can squeeze a little more in but if you don't have a good handle on internal ballistics you won't be respecting your gun, and if you miss the signs you will be dribbling all over your bib in the hospital.

The Grendel is a relatively slow calibre, just accept it. The case is not big enough to push these big rounds at the optimum speeds they were designed to expand. Add to that the length of the barrel (16") is not conducive to high velocity and you are stuck pushing a heavy bullet at slow speed. If you want speed and not range then you need a different calibre.

So, if you load hot with 8208 you will break the gun. If you want speed go a lighter bullet and/or a longer barrel. If expansion results are still not good enough go a larger case 6.5 of which there are plenty of options: Creedmore, 260Rem, 6.5*47, 6.5*55, 6.5PRS or 6.5*284. If you want that in an AR it will have to be a bigger action - an AR10. Unfortunately there is no slack left at the raggedy edge of a calibre designed to be at the edge of what an AR15 can handle, and no margin for error when dealing with high pressure.

Let me sum this up in one word...

KABOOOOM!


(I use a slower powder with the 120NBT: H4895, using 8208 for lighter bullets).

[grayfox]

^^^ This. +1.
Listen to Klem, save your face.

[grayfox]

The 120 class bullets have harvested lots of game, deer etc. We have a thread on here with numbers and graphs. There are other powders more suited to the 120's IMO, but keep in mind your barrel needs to tell you what it likes.
One of our members has taken literally hundreds of hogs with the 90 gr Tnt bullet. So there's plenty of capability in the Grrr. You do need to stay within reasonable bounds however.
But you should be doing that regardless of which rifle you have in hand.

[1Shot]

If you are using a bolt rifle you will experience hard bolt lift and primer failure before you blow up a rifle no matter the caliber if you are using powders suitable for it. Depending on the bolt rifle it may never blow up but you may weld the action shut from flowing brass. Test have done this with the old Japanese WWII rifles which are some of the most robust of actions ever built. As has been said the AR is not meant to handle anywhere close to that pressure.
If you can't get the 120 BT to expand like you want change bullets. If you want to run a 120 gr get some Speer Gold Dots or Sierra Pro Hunters. They will expand at lower velocities. I love the 120 Gold Dot, cheap, accurate and DEADLY.

[Jakal]

Every factory Hornady round that I have shot in 5 different Grendels all have flatter primers than what I load too. I mean flat, all the way to the edge. I get better performance, consistency, and accuracy with handloads. Some run faster some run slower but always tighter.

Look at the 129 grain Nosler ABLR, lower MIOV (minimum impact opening velocity) or the Barnes 100 or 115 grain TTSX.

[Klem]

If you are using a bolt rifle you will experience hard bolt lift and primer failure before you blow up a rifle no matter the caliber if you are using powders suitable for it. Depending on the bolt rifle it may never blow up but you may weld the action shut from flowing brass. Test have done this with the old Japanese WWII rifles which are some of the most robust of actions ever built. As has been said the AR is not meant to handle anywhere close to that pressure.

1Shot,
Reminds me of watching a mate accidentally load a heavy bullet used for subsonic on a column of powder used for supersonic, in Blackout. We were at the range and had brought scales and press to load test. He was using a 16" Rem700 put together by AA. There was an almighty bang and a huge amount of smoke out of the action, but you are right, the action held firm. Apart from the stout recoil he was fine, if not a bit shaken.

We could not prise open the bolt and needed to head back and use a breaker bar and hammer. The bolt was stuffed with the case welded into the face. We couldn't get it out. Never seen anything like it before. The gun had received a 'proof' load and needed to be retired.

In a light-weight AR it would have been a grenade.

You live and learn.

[EigerWand]

Hi Klem,

Thanks for your detailed and informative reply.

I've tried 123gr ELD-M factory ammo and although its sold as a target round, it got much more the sort of terminal ballistics I'm looking for.
So, I'll do some reloading with it and see if that's confirmed with more use.

I'm using 27.5gr of the 8208 and I reckon even that's compressed.

I have a ladder of higher charge weights loaded up for future testing but after reading your advice think I'll just pull them all and put the time into setting up a load with the ELD-M. Cut my losses. Hopefully I'll get the expansion with more modest powder charge and don't really need the velocity if I can make proper use of the KE I have.

[Klem]

Eiger,

I'd be careful of ADI's powder chart where 8208 is concerned. They list 29.8 as the max load for a 107SMK but according to Quickload that is 106% of the available case volume. Around 27.5 - 28gn is where the case gets filled to 100% when using 8208 and 58mm OAL.

I use 8208 for bullets up to 120 and 2206H for 120 and above.

[1Shot]

Now were people really can get into trouble is by listening to people that don't know what they are talking about and not checking with proper data and information.

I was at a local open to anybody shooting range set up by the National Forest people. Some fellow shows up with a M1 Carbine and sets up his stuff on a table at the far end away from where I was shooting. All of a sudden I hear what sounded like the time I fired a 7mm STW with a muzzle break out of a shooting house and forgot to put my ear plugs in. I looked over to the guy and he is laying on his back having fallen off the bench. I ran over to him to check him. He gets up and starts to shake his hands but I see no damage. He said they felt like they had been hit by a hammer. I looked at his carbine and it is in pieces. The bolt is missing. I find the guys hat and it has the bill of the hat with a big ripped hole in it. I walk out into the parking lot behind and I find the mangled bolt of the rifle. I start asking questions of where he got the ammo etc. First off I discovered that this guy was not the brightest bulb in the box. He was a new hand loader. He went to a big box store, can't remember which one, to purchase all his stuff. He was told by the person at the store that for his 30 carbine he should use BULLSEYE powder. He said that he did not know there was specific data for powders to load with or how much powder you were supposed to use. He thought you just filled up a case and seated a bullet on top of it and since the fellow at the store told him BULLSEYE was the powder he should use he just filled up the case and seated a bullet. I hope this fellow did not breed. His genes do not need to be in the pool. He was a very lucky idiot that the bolt only went through his hat brim and not his head.

Next time I went to this range as I had just finished shooting and was packing up a car pulls into the lot. Six guys that looked like they came from the movie Deliverance pile out and two throw beer bottles up into the woods. As I was taking my last bit of stuff to the truck I hear them talking. They are going to sight in the new scope for one of them that was just put on a Rem. 742 30-06. One of the fellows walks down to the 100 yard target back and puts up a piece of cardboard with a target on it. I then hear him shout, "shoot one and I will see where you hit". He then proceeds to just walk about 10 feet to the right of the target. As I quickly drive out of the parking lot I hear the rifle fire. That is the last time I ever went to that range.

[lazyengineer]

Eiger,

I'd be careful of ADI's powder chart where 8208 is concerned. They list 29.8 as the max load for a 107SMK but according to Quickload that is 106% of the available case volume. Around 27.5 - 28gn is where the case gets filled to 100% when using 8208 and 58mm OAL.

I use 8208 for bullets up to 120 and 2206H for 120 and above.

Some GREAT replies on this thread sir!

On 8208, that one is interesting. According to Hodgdon's annual load manual (and ADI apparently), you can run 29.8 gr of compressed 8208 under a 107 SMK for 2667 FPS @ 49,300 psi, out of a 24" BBL using the heavy Lapua brass.

In my own experience, I'm running 29.4 gr (so .4 gr below book-max), and am getting some compression. I'd say powder is coming well up into the shoulder. It's clocking 2709 fps out of a 20" with Hornady brass. And I'm .4 gr below book max! (in a world where book max tends to be conservative). Shoots like a dream and gun and brass all seem fine; but yea - I will agree; be careful out there, no way am I going to take that up to the full book value of 29.8 gr.

[Klem]

Lazy,

At 29.4 are you getting that crunching feel when seating a bullet?

I figure up to 103% of available case space is OK given space being filled with powder (especially extruded powder) is more 'elastic' than fixed. We manage this by using drop tubes and vibrating the case to settle powder levels lower and fit more in. But at some point it becomes fixed and you start to break up stick powder and change its burning profile.

I use 28.5/8208 with the 107SMK, 58mm OAL but have wondered about going a little more. It is a really accurate bullet and load.

[jhoyda]

Hi Klem,

Thanks for your detailed and informative reply.

I've tried 123gr ELD-M factory ammo and although its sold as a target round, it got much more the sort of terminal ballistics I'm looking for.
So, I'll do some reloading with it and see if that's confirmed with more use.

I'm using 27.5gr of the 8208 and I reckon even that's compressed.

I have a ladder of higher charge weights loaded up for future testing but after reading your advice think I'll just pull them all and put the time into setting up a load with the ELD-M. Cut my losses. Hopefully I'll get the expansion with more modest powder charge and don't really need the velocity if I can make proper use of the KE I have.