Hotter loads in a bolt gun?

[jason miller]

I just acquired my first Grendel- a Howa Mini. I plan on plinking at extended distances with this rifle, so max BC and velocity will both be helpful. My understanding is that the max pressure for load manuals is kept at 50K psi. I'm assuming this is due to the fact that the Grendel is predominantly a gas gun cartridge.

First question: Is it safe to assume that the brass for this cartridge can handle more than 50K psi? Hornady makes lots of ammo that they load to 60K or more, and Lapua brass is known for being the toughest available. Can both or either makers' brass handle the 60-65K psi that other bolt-action cartridges are loaded to? Or do they make this Grendel brass less robust for some reason?

And if the brass can handle higher pressure, does anyone know what kind of velocity gains should be achievable? Simple extrapolation makes it seem like another 100-150 fps could be on the table just by running up to 60K psi. I wish I had quickload so I could plug some numbers in and see whether a 123 scenar catches a 107 smk and at what range that might happen when both are loaded to their full potential.

[Kilco]

From my experiences, I've been able to run a gas gun at simliar pressures as any bolt gun of equivalent cartridge. Some gas guns (I'm thinking AR-10 chambering primarily) require specific charge weights in order to function properly. With the 6.5 Grendel, I can run loads just as warm as a bolt gun if not warmer with no I'll effects. Same development as a bolt gun, work up slowly and watch for signs of excessive pressure.

Oddly enough, from all youtube, and written reports with the Howa Minis thus far, they seem to run 50-100 fps slower than aftermarket AR barrels of equivalent length. I have no idea why, and this might very well not be the case with all Minis and barrel lengths offered. Yours might be different.

I would just work up your own loads, and not pay attention to other guns and what they run for velocity/charge weights. Work up slowly, and find where YOUR gun limits out and shoots accuratly. Either 107 or 123 will get you way out there respectively. Keep us posted!

[LRRPF52]

Depending on the action diameter and bolt dimensions, you'll want to keep things under control. The mini or micro actions don't have the same wall thickness or bolt lug engagement as a short or long action, and I remember someone here saying their brother loaded too hot and ate a bolt through his face with another cartridge in a bolt gun.

Bill A. said when working with Lapua, the Lapua brass was rated to 60ksi. I talked with the Lapua engineers and test team at a gun show in Finland once, and they had a bolt gun in Grendel that they had pushed way farther than you would ever consider, but trashed the brass with one firing.

Grendel case capacity will keep you limited to more sane pressures, unless you want to test fate and run faster-burning powders with heavier bullets, just to see if your infraorbital foramen and zygomatic arch can sustain an incoming bolt body after lug failure.

I will also remind anyone that velocity is your sign of excessive pressure usually. If you want speed, use CFE223 and LeveRevolution.

I would consult with the manufacturer as to what the working pressure limitations are of their particular action, since bolt dimensions, steel alloy used, and action diameter will play a big role in that.

[BluntForceTrauma]

In my limited study of the issue, I tried to derive some patterns and ballpark figures. What I came up with is that as a rule of thumb about 5,000 psi extra pressure gives you an extra 100 fps. Way too many variables to nail down something, but it's a very rough estimate.

So if your gas gun gives you 2500 fps at 50,000 psi, then a bolt gun at 55,000 psi might give you 2600 fps.

And my figures are entirely debatable, but I seem to remember it was something like that.

Each gun owner has to decide for himself if the juice is worth the squeeze.

Bottom line: Practice safe and sane reloading. Keep your body and your equipment in one piece.

[LRRPF52]

Looking at my numbers from actual pressure trace that Joe did, it's looking more like 7,000psi to gain 100fps with CFE and 123gr.

Each powder/projectile combination will have a different conversion rate.

I think Matt from LSI covered down on this once here. Maybe he can pipe in again here on pressure limitations of the Howa Mini after consulting their engineers.

[SDguy]

No personal experience with the Howa. My bolt action experience with the 6.5 Grendel has been with a CZ 527 with a 24" LW 1 in 9 twist barrel.

I chased the velocity envelope this fall with Hornady 123 grain A-max & SST's & 129 gr SP with CCI BR4's and Leverolution as a propellent. I have more confidence in the strength of Lapua brass than any other by a fair margin. I have not found a better propellant to push the velocity in the 6.5 Grendel.

Do not care to encourage you to pursue a given charge weight or velocity though I will say I experienced much greater velocity than I expected with a compressed load of LVR. I have no way of clearly measuring or quantifying pressure, though I am confident experimental loads exceeded 60,000PSI based on reaching pressure signs. Surprisingly primer pockets held together relativly well.

Interesting experiment Is the most Ill say for that experience. My best accuracy was achieved with a slightly compressed load that I would guess hovered right near 50,000 lbs

The beauty of the 6.5 Grendel IMHO is her efficiency. Offering fairly substantial velocity / punch with a very moderate powder charge. With the moderate powder charge and in turn moderate pressure, brass life is very efficient as well. Make no mistake when you start pushing pressure your brass life will deteriorate.

Many have stated if you want more velocity then choose a larger case like the 6.5 Creedmoor or the 260 Rem. They do have a point. That being said it is interesting to say the least, to see how much the 6.5 Grendel may be pushed.

For some reason Hodgdon does not encourage or offer load data for the 6.5 Grendel with either CFE 223 or Leverevolution. Still both propellants are very popular here.

[jason miller]

I'm not looking to go overboard. But there is no sense leaving free performance on the table. Pressure has nothing to do with capacity, as 5.56 loads go up to 63K, and I would bet money that there are guys running over 70K with their PPC's. But the point about less lug engagement may hold some validity, although I highly doubt a well-designed bolt action like the Howa with modern metallurgy would have any problem with 60K psi. And I would tend to agree that it takes more than 5K to get an extra 100 fps- especially in this application. It's also hard to apply a rule like that, because 100 fps is a greater percentage of 2500 fps than it is 3000 fps; but 10k psi is the same percentage of 50K psi no matter what the velocity is. And I won't be trying faster than normal powders. That's not how one safely gains velocity. For example, if you want to run a 6.5x55 up to more modern pressures in a modern rifle, the same slow-burning powders that make the most velocity at lower pressures are the ones that produce top velocities at higher pressures. Although I understand this Grendel might run into problems with getting enough of the slower-burning(relative to its size) powders in the case. I'm hoping my 2.33" magazine length helps with that.

As suggested, I plan on working up carefully with my chrono. Just thought it would be nice to see if anyone else has any experience/insight to lend. Thanks for the replies so far.

[LRRPF52]

Another forum member achieved considerable velocities with his Savage Grendel, but it has a larger action than even a Rem 700 SA.

[Klem]

We used to deliberately load over SAAMI in .223 to reach out to 1,000yds in F Class competition. That was possible using 30 inch barrels and solid actions like the Rem700SA. Also helping are smaller firing pin holes and pins, with magnum/thick primers to minimise primer piercing. Plus Lapua brass is used exclusively with the compressed loads. According to Quickload peak pressures are approaching 90K. No discernable damage to the gun or brass and this goes on every weekend. Bear in mind however the .223 in an 8kg F Class gun has a lot of metal around it. Big solid actions with heavy Varmint/Palma barrels.

No doubt the smaller Howa action will take higher than recommended pressures, until it doesn't. It will also manifest in other symptoms like short brass life and pierced primers.

The Grendel case has 37.5grains of water capacity while the 6.5*47 has 48grains. if you are chasing another 100fps above SAAMI's recommended safe limit you could simply use that calibre and be done with worrying about when you're going to eat your bolt and lose your eyesight.

[jason miller]

Howa sells these things in .204, which I believe has a max SAAMI pressure of 60K psi. I'm not going to eat my bolt by running my Grendel to that pressure.

[nuthead]

I haven't been able to get more than 2540fps with a 123gr amax and 8208 out of mine before getting a sticky bolt.

However my brass might have grown a bit too long when I measured it... I've trimmed it all back now though so I'll give it another go. The accuracy node should be close to 2580fps with that powder/bullet combo

[Klem]

Howa sells these things in .204, which I believe has a max SAAMI pressure of 60K psi. I'm not going to eat my bolt by running my Grendel to that pressure.

Maybe not, but with such confidence in an unknown you might end up eating your words as well as your bolt.

The SAAMI spec for .204 is 58,740lbs based on a cartridge that has more support than the Grendel with the same chamber OD (9.14mm case base diameter compared to the Grendel at 11.15). Might not sound like much but these differences are taken into account by the SAAMI engineers. Also, the .204 burns less powder than the Grendel at 31gns of water case capacity compared to the Grendel's 37.5. Like I said, your Howa should tolerate more pressure than SAAMI, but then so should all our guns. SAAMI is based on the lowest common denominator plus a margin for safety. Hopefully the excessive pressure will manifest itself in early symptoms like pierced primers and sticky bolts.

[Von Gruff]

If not using factory ammo then having my Grendel-Max chamber gives me 2700fps for the 123gn A-Max/SST and 2950fps with the 100gn in a 21 1/2 in barrel.
I set my max pressure (through QL) at 57k psi so havent gone overboard chasing velocity

[JASmith]

Howa sells these things in .204, which I believe has a max SAAMI pressure of 60K psi. I'm not going to eat my bolt by running my Grendel to that pressure.

There are two critical issues to consider when looking at pressure:

First, at what pressure does brass start to flow? If your primers get loose after even five shots, you are in danger of sending brass and hot gas through your action!

Some brass is softer than other brass, even different lots from the same manufacturer.

Second: bolt thrust. The reason Bill A uses 50,000 psi for recommended max working pressure in the Grendel is the difference in area of the base of the cartridge. That area times the pressure yields the thrust that must be resisted by the lugs. Early Grendel shooters pushed the pressure envelope and broke bolts. Current Grendel shooters have learned that little is gained by pushing the pressure envelope.

The same is true of a mini/micro bolt action designed and tested for cartridges like the .204 Ruger and .223 Remington.

Further, Bwaites and LRRPF have correctly captured the potential gain from going up by the 5-10 ksi folks think about. Fifty to 100 fps out of about 2500 buys very little in terms of reduced wind drift or drop.

Klem has it right, if you want to boost velocity, work with a larger capacity case. Very easily done with bolt guns, especially if one is willing to go with the 6.5 Creedmoor length of cartridge.

[jason miller]

Yeah, but it could mean being supersonic at 1,000.

Thanks for all the safety concerns, but I've pretty much had my fill and don't care to argue. I've already weighed the risks and rewards and made my own decisions. Looks like I'll find my own conclusions in the coming months.