6mm Grinch case capacity

C

cbrewer

New member
Does anyone know the case capacity (grains of water, cubic inch, cubic cm) for the 6mm Grinch? I am developing loads for mine (1:12) using N133. Would like to know so I can calculate potential loads. At the moment, 28.0 N133 produces a nice results at 3113 fps as does 28.2 N133 at 3143 fps.
 
A friend (scientist) measured five of my fire-formed cases and determined their capacity as 36.59 grains of water. This volume can be used to calculate and develop loads for many rifle powers. The process requires some calculations but are not difficult. Subtracting the case neck volume (~4%) by using solid geometry (or using more sophisticated software) with the weight of the N133 (as published) determines the 100% case rifle powder capacity without compression.
Moving forward on the load developments.
 
I measured case volume of H2O by seating a bullet in a fired case and filling it with water. The best way I found was to use a Little Lindy Worm Blower. It's a fishing accessory that has an angled needle tip. The trick is to put a drop of food coloring in the water to keep air bubbles from forming on the inside of the case that rob you of the real volume of water. I found that out working on racecars when CC'ing cylinder heads. Then just weigh the case as normal. The water won't spill out the primer hole, so it's easy to do.

I will keep an eye on your progress as right now, I'm having a 1-12" barrel chambered in 6BR. If it shoots well enough, it may go on my HV rifle. What bullets are you using?
 
My scientist friend calculated the case capacity to 30.90 grain N133 at the neck junction. My calc was 31.66. But I probably have the Shoulder Frustrum Volume off. I will use his as it is lower and he has infinitely better math skills than I do (plus access to some really cool measuring instruments/machines).
I am using 68gr HPFB made by Ammerman Arms and have five loads of five rounds each to try soon. The loads to be tested are: 27.7, 28.0, 28.3, 28.6, 28.9 of N133. All at 2.280 OAL which is 2.827 BTO using my comparator. At 100 yards using N133 25.2 @ 2925fps with same OAL/BTO produced one group 0.46/0.42MOA and another at 0.18/0.17MOA. At 25.8 @3021fps one group was o.35/0.33MOA and the other 0.15/0.14MOA. I have a long way to go to improve my ability and consistency. Soon to have a 45x scope which will be a major improvement and am hopeful it will help me improve.
 
cbrewer said:
My scientist friend calculated the case capacity to 30.90 grain N133 at the neck junction. My calc was 31.66. But I probably have the Shoulder Frustrum Volume off. I will use his as it is lower and he has infinitely better math skills than I do (plus access to some really cool measuring instruments/machines).
I am using 68gr HPFB made by Ammerman Arms and have five loads of five rounds each to try soon. The loads to be tested are: 27.7, 28.0, 28.3, 28.6, 28.9 of N133. All at 2.280 OAL which is 2.827 BTO using my comparator. At 100 yards using N133 25.2 @ 2925fps with same OAL/BTO produced one group 0.46/0.42MOA and another at 0.18/0.17MOA. At 25.8 @3021fps one group was o.35/0.33MOA and the other 0.15/0.14MOA. I have a long way to go to improve my ability and consistency. Soon to have a 45x scope which will be a major improvement and am hopeful it will help me improve.
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A 6 Grendel is essentially a .070 long 6 ppc and holds a bit more powder than the ppc. A grinch is a Grendel with the shoulder blown out from 30 to 40 degrees, adding a tad more capacity still.

I say all that to say this..the loads you plan to test are light to moderate in a ppc. Lapua Grendel brass is the only brass I've found to hold up at br pressures
 
I finished testing loads for now. My Grinch (12:1, .268 neck) likes 29.1 - 29.2 N133 with the 68gr HPFB by Ammerman. Best group so far is 0.110 (5-shots) with others about 0.120-0.140. Using a Sightron III 45x45 with dot. It seems there is no difference in group size between 004 off, touching, and 002 into lands at 100 yards, 3310 fps. +/- 8 fps (SD). Interesting rifle cartridge.
 
cbrewer said:
I finished testing loads for now. My Grinch (12:1, .268 neck) likes 29.1 - 29.2 N133 with the 68gr HPFB by Ammerman. Best group so far is 0.110 (5-shots) with others about 0.120-0.140. Using a Sightron III 45x45 with dot. It seems there is no difference in group size between 004 off, touching, and 002 into lands at 100 yards, 3310 fps. +/- 8 fps (SD). Interesting rifle cartridge.
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FWIW, I am using 30.6gr of n133 and a 68 gr fb bullet in a straight 6 Grendel. Shoots tiny and no pressure signs at all in my rifle. It's a little below the case mouth without a drop tube, dumping charges straight from the powder measure. You should have a tad more capacity in that Grinch. Maybe or maybe not enough more to reach a node above what I can in a Grendel but you're still mild, imho. Nothing wrong with that if it shoots small but it kinda does away with the reason to do a Grendel or a Grinch if you're just gonna use mild to moderate ppc loads in it. Step on the gas a little and I bet she comes to life.

My logic for a straight 6 Grendel is in part the simplicity of it. Just neck it down and shoot it...no fire forming and a tad bit more horsepower, as well as not having to fight to get powder in the case to meet and beat ppc speeds. No doubt, it shoots and made sense to me. I haven't been disappointed with any of them. I've had a couple of dozen 6 Grendel bbls and chambered them for others as well, so I'm trying to speak from experience to you. It's up to you of course, how you load and proceed.
 
I have shot the grinch cartridge a good bit and have always used 80 gr bullets and 12 twist barrels. I like to load mine at around 31.0 with 8208 pulldown powder and have gone as high as 31.5 with good results. I have also found LT-32 to work but at a lower change weight.
 
Thanks for info. 8208 seems scarce just now, as can't find any. Would like to use it if I get some 80gr. Your recipe is one of the better ones.

I settled (for now) on the 68 Ammerman, over 30.0 N133 @ 3395 fps, .002 off the lands. Had 10 rounds, so I decided to shoot for score. 10 10s 8Xs (5 blowouts). Just practicing but I think it will do for a while. Mike Ezell said to "Step on the gas a little and I bet she comes to life," so I did and the Grinch seems to shoot even better. Wasn't able to evaluate it at 200 because of switchy twitchy winds. Hope to get some more trigger time next week. Fun shooter.
 
SteveH said:
I have shot the grinch cartridge a good bit and have always used 80 gr bullets and 12 twist barrels. I like to load mine at around 31.0 with 8208 pulldown powder and have gone as high as 31.5 with good results. I have also found LT-32 to work but at a lower change weight.
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That's stepping on the gas pretty good in a straight Grendel and there's not much difference between it and a Grinch...fwiw. Is your brass holding up well up there? I run about the same 8208xbr load with 80's and brass life is what I'd call fair. Accuracy is up there with anything, though.
 
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cbrewer said:
Thanks for info. 8208 seems scarce just now, as can't find any. Would like to use it if I get some 80gr. Your recipe is one of the better ones.

I settled (for now) on the 68 Ammerman, over 30.0 N133 @ 3395 fps, .002 off the lands. Had 10 rounds, so I decided to shoot for score. 10 10s 8Xs (5 blowouts). Just practicing but I think it will do for a while. Mike Ezell said to "Step on the gas a little and I bet she comes to life," so I did and the Grinch seems to shoot even better. Wasn't able to evaluate it at 200 because of switchy twitchy winds. Hope to get some more trigger time next week. Fun shooter.
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Yes, 8208 is just hard to find right now. Hopefully it gets better but its been a while. It's at the top of my powder choices for it and the 80's. It'll shoot the 68's well too fwiw. And I think you're now in the right window with 133 and 68's. You might go up a tad depending on your bbl and pressure but I don't think you should have pressure problems with less than about 31.0 gr or so. It should be gettin happy up there now. Keep us posted.
 
mwezell said:
That's stepping on the gas pretty good in a straight Grendel and there's not much difference between it and a Grinch...fwiw. Is your brass holding up well up there? I run about the same 8208xbr load with 80's and brass life is what I'd call fair. Accuracy is up there with anything, though.
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Yes, my brass is holding up for 20 firings or so before the pockets get loose. I also mainly use BR-4 primers and have tried 450's. I am using Lapua grendel brass! My powder is older pulldown powder not the newer stuff.
 
Happy New Year to all!
The 6mm Grinch has performed well. The Ammerman 68s with 30.0 N133 and .002 off in Lapua brass did well at 100 and 200. Hope to start 2024 using some 80 grain Dominators (Bart's Bullets) with 8208. I scored two cans of it. I plan to use SteveH's recipe 31.0 - 31.5 plus Bart's information: 3100 to 3280 fps.
I also anneal my Lapua cases. I have noticed cracks in 4 cases at the shoulder after 15 firings. Have plenty of Lapua brass. Also, Starline has a line of 6.5 Grendel that seems to be very rugged, according to a friend's experiments using it for his wildcats.
Bought a Garmin chrony. So simple and easy to use. Small, rugged, rain-proof, long battery charge-life. Never missed recording a shot. It's what a chronograph should be.
 
Yes. Dominators are back. I'm going to load some with 31.0 of 8208 as per SteveH. I think they will perform well at 100 & 200 for me.
 
cbrewer said:
Yes. Dominators are back. I'm going to load some with 31.0 of 8208 as per SteveH. I think they will perform well at 100 & 200 for me.
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Definitely starting at the top end but if it works in your bbl, go with it. I do think I'd start at around 30.0 though and I'm far from shy about loading hot..
 
Pete Wass said:
Which 6 MM stays in tune the best?
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Lol! Since capacity and bullet weight are factors in choosing the best powders, and the powders used play largely into staying in tune or not(without a tuner)...your question isn't as simple as it seems.

IME, n133 shoots great in a ppc and a 6 grendel but does not hold tune as well as lt32 in either.

A lot comes down to available and suitable powders that can be competitive in a given case and then, how those powders act in those cases.

To simplify...use lt32 if it shoots competitively in your gun and cartridge...with typical 62-68gr bullets. Not much difference in a ppc/grendel/grinch. They're all very close to one another.

The magic is...a load that takes a long drop tube and a slow pour into a ppc fits into a grendel or grinch with a short one. Lol! That's about it!
 
mwezell said:
Lol! Since capacity and bullet weight are factors in choosing the best powders, and the powders used play largely into staying in tune or not(without a tuner)...your question isn't as simple as it seems.

IME, n133 shoots great in a ppc and a 6 grendel but does not hold tune as well as lt32 in either.

A lot comes down to available and suitable powders that can be competitive in a given case and then, how those powders act in those cases.

To simplify...use lt32 if it shoots competitively in your gun and cartridge...with typical 62-68gr bullets. Not much difference in a ppc/grendel/grinch. They're all very close to one another.

The magic is...a load that takes a long drop tube and a slow pour into a ppc fits into a grendel or grinch with a short one. Lol! That's about it!
Click to expand...
Thanks for that. I had come to think there hasn't been the right powder found or created yet for the 6 BR. I have avoided getting involved with 6 PPC's because of their well publicized being finnicky. I have used a tuner on the 6 BR with about the same results as naked but I don't claim to be a Tuner Master. I have been sporadically shooting the 6 BR in Hunter Class Score. It has been either GREAT or a shotgun. When it has shined, it was amazing. My question was to perhaps find a 6 that would be more forgiving than the 6BR.

Pete
 
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