Making 70 to 75 grn 6mm Bullets on .825 Jackets

[RGRobinett]

As a pretty loose guide-line, I can point to some results which one Greg Sweezey, if not THE best, certainly, one of the ALL-time best Hunter Rifle competitors, having ammassed nearly double the HoF points of the second place points holder, and his experience using the BIB thirty Cal./123 Gr. fill vs. the "normal" 112 Gr. fill (.925" jacket length).

During 100 Yd. competition, over about a two season span, alternating between the two weights/fills, there was a marked difference in his 100 Yd. aggregates. Typically, with the the 112-7 ogive, Greg would garner 19-21X (10 Lb rifle, 6x scope, 1/16th" X-dot) - rarely less than 18X, which he considered as having had, "a bad day".

When opting for the 123 Gr. sibling, his X-count dropped to 16-18X . . . for most of us mortals, still, "not too shabby", but for Greg, measurably weaker scoring. That said, he told me that the 123s were slightly more advantageous at 200 and 300 Yd., where even on one's good days, the [1/16 MOA] Xes are more a matter of luck, but there was enough precision that the slightly extra BC kept the wide shots on the ten-ring. Greg's fellow competitors were/are a pretty tough crowd even on his bad days, he won/placed/showed. RG

 

[jackieschmidt]

Here's a chart from an example I ran that's probably a bit more clear. It's interesting that there is a minimum theoretical sensitivity (maximum accuracy potential), but that tends to be below the pragmatic limits of core weight. Note that this presumes an optimal twist. If you limit yourself to available twist rates, there are some jumps in the green curve when you hit a point where there is a better available twist.
View attachment 1471522

Great info. however, I am going under the thought, (which can be dangerous) that when shooting N133 in a 6PPC, the optimum tune window might be, (another dangerous thought), better with a little more bullet weight in the same length jacket as the 68 grn bullet.

I have been shooting the 6PPC for decades, and have always thought that on paper, it is really a tad slow for the combination.

I am relating this strictly to a 6PPC in the configuration that we use in Short Range Benchrest, with N133.

I have everything on hand to see if I am out to lunch or not. I can even take a 13.5 twist barrel and switch it out for a comparison.

If it proves to be futile, I will just toss the idea into that bucket of things that didn’t work.
It’s getting pretty full.

 

[gunsandgunsmithing]

Great info. however, I am going under the thought, (which can be dangerous) that when shooting N133 in a 6PPC, the optimum tune window might be, (another dangerous thought), better with a little more bullet weight in the same length jacket as the 68 grn bullet.

I have been shooting the 6PPC for decades, and have always thought that on paper, it is really a tad slow for the combination.

I am relating this strictly to a 6PPC in the configuration that we use in Short Range Benchrest, with N133.

I have everything on hand to see if I am out to lunch or not. I can even take a 13.5 twist barrel and switch it out for a comparison.

I like the logic and I agree with you on it. The difference might be so small that it's hard to realize it's benefit or lack of. Gets back to, ya gotta be able to shoot the difference for there to be one, but I think it's a step in the right direction. Magic bullets can happen for a combination of reasons. This might well be but one of those. At the very least, if you see no improvement in group sizes, it still makes life easier to handle cases that powder is not falling out of, kinda full. Much like blowing the shoulder forward only a little bit but met with much less criticism. Lol!

 

[Nader]

Jackie,
I've made up to 72.5 gr bullets on a 7-3/4 flat base and 69.5 gr on a 8-1/2 boat tail. They were both shootable but nothing to be gained over 68gr. Same results with anything under 65gr.
Mostly N133, four different BR guys shot them in good rifles, same results, nothing to be gained in competition.

 

[dcali]

Great info. however, I am going under the thought, (which can be dangerous) that when shooting N133 in a 6PPC, the optimum tune window might be, (another dangerous thought), better with a little more bullet weight in the same length jacket as the 68 grn bullet.

I have been shooting the 6PPC for decades, and have always thought that on paper, it is really a tad slow for the combination.

I am relating this strictly to a 6PPC in the configuration that we use in Short Range Benchrest, with N133.

I have everything on hand to see if I am out to lunch or not. I can even take a 13.5 twist barrel and switch it out for a comparison.

If it proves to be futile, I will just toss the idea into that bucket of things that didn’t work.
It’s getting pretty full.

That's the *all else equal* bit. finessing the weight to hit the perfect sg, at the spin used, at a good powder node is (I think) an under appreciated skill. Let us know how it goes.

 

[jackieschmidt]

I cut some cores and made up some bullets that came out to 69.8 grns.
I made it to the range this morning, got there early and set up before the 100+ degree heat came in.

It took me a while to find the tune window I wanted withe 69.8 grn bullet. I set my Ohler 35 Chronograph up to get the velocities.

The barrel on my LV 6PPC is a 13.5 Krieger, shooting over my usual 4 flag set.

One thing I found was anything over 3400 shot really bad. The tune window came in pretty good with 30.3 grns of 133, yielding an average of around 3370 fps. 3400+ is simply too hot.

Shooting in a straight across right to left orange condition, I shot these six 5-shot groups. It was ebbing and flowing, that .300 group gives you an idea how much. I had four knotted up pretty good, lost one of the shots when I just missed the tails coming up.

I’m not real sure how to interpret my results. I think the 69.8 grn bullets shot about as good as this barrel is capable. The load window dropped enough to making getting the powder in easier. 3440 fps is the sweet spot with this same bullet in 68 grns. That is using 30.6 grns of 133.

Here are the 6 groups for record. Not a bad day at the range.

 

[RGRobinett]

Jackie, per advice provided by [the late] Dan Hackett, based upon percentages, of the comparative powder charge weights : bullets weights, your [tune window] result, "falls right into place". RG

 

[Infrequent Shooter]

We have historically made 66 and 68 grn 6mm bullets on .825 J-4 Jackets.

I have about 10,000 71 grn cores left over from when I was attempting to make a decent 103 grn bullet.

Right now, I am making a 68 grn FB bullet on J-4 .825 jackets, which I have about 16,000 of. I also have access to a double radius BT die set.

I was thinking about cutting some of these cores and squinting them with enough weight to make a 70 to 75 grn bullet. I would have to try a different weight core to see how far the lead comes up into the bullets tip to arrive at a weight. With a 68, there is still quite a bit of air between the top of the core and the metplate when pointed up.

Any of you bullet makers ever did this? Going under the assumption that just about everything imaginable has been tried with the basic 6PPC, I figure somebody has.

I’m sure everybody is thinking…...”Why”?

I have always thought that 133 was a little slow in burn rate for our typical 6PPC. I was thinking that adding a few grns of weight to the same length bullet might be a better match. Everything else would stay the same.

I would probably be looking at around 3370 fps as the upper load window, as opposed to the 3430 I shoot now.

this is how much air gap is in my 68 now.View attachment 1471461

best shooting site on the internet

 

[JPB3]

Going at your idea another way, run your reamer in an additional .020'' for 133

 

[gunsandgunsmithing]

Going at your idea another way, run your reamer in an additional .020'' for 133

That would be very near a 6 ARC. My 6 Grendel is the same but .070 longer than a ppc. But yes...same principle. .070 sounds like a lot but it's not and there's isn't much difference between it and a ppc in real world testing. A little more capacity and a little more speed, if you step on the gas a bit. The key is good brass. The Lapua Grendel brass is same quality is the 22r brass. If Lapua were to make ARC brass of the same quality, it would make a lot of sense and would essentially do away with fire forming if people went with the ARC chamber. I feel very certain it would be better accepted if it were called a .045 long ppc than what it is...a 6 arc, though.