Projectile RPM limits...

[Con]

Anybody know what the 'rough' limits are on RPM for projectiles?

Have had a bee in my bonnet for years to build a fast twist 22cal with enough case capacity to push the heavies at some speed. Cartridge of choice at this stage looks to be the 22/250 or possibly 22/250AI to cut case stretch out.

Barrel looks like it will be a Bartlein (1:6.5 through to 14" available) or Maddco (1:8"), in Medium Palma contour.

Projectiles of choice ... 69gr TMK, 77grTMK, 69gr/77gr MKs, Berger 80gr as all are available in bulk packs. Would love to try the Sierra 90gr and yet to be released 95gr 22cal ...

However the 77-80gr are really where I want to be, with the 69s for added speed at times.

QuickLoad predicts that the 77-80s will be coming out at around 3200-3300fps, the 69s at just under 3500fps.

Will the projectiles withstand the speed and stresses of 1:8" or possibly 1:7" barrels?
Cheers...
Con

[kickinback]

I’m contemplating the same thing at the moment. It’s a 22x47 with a 1-8. Curious how fast I can push a 69gr before it flies apart. I’ll have a crack on the 25th when I get home.


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[MISSED]

Interesting topic Con

In my little patch of paradise I am launching 40 vmax out of the 20 BR at 4200 fos in a 1-10 twist wonder what revs they are doing

32 gr zmax hang together at 4400fps in a 1-11

[GJS]

Missed, I work it out at 302400 rpm for the 40s.

[MISSED]

Missed, I work it out at 302400 rpm for the 40s.

Wow


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[Tony Z]

Con there was a lot of discussion about this amongst the LR BR shooters here in Aus a number of years back. There were two trains of thought then as there is now. Enough to stabilize and no more. Then there was the spin the freckle out of them group. I had maintained 260,000 rpm was the line of demarcation where once you were beyond that you were in the lap of the gods.
Then a few years later Stecker came out with the same figure and a new release of heavier jacketed Berger bullets that were known to come apart once you spun them too high like the 140 grain 6.5s.
If you look at those that have set records, the ones i know of use SFs far lower than what Litz is currently advocating. Shooters were doing very well at SFs of 1.2 or lower. Even down to 1.0. Litz claims that you require an SF of 1.5+ to maximize BC and has a calculator that gives a drop in percentage of BC for a given bullet once you run below that number. Others maintain you go there and the bullets, unless perfectly made, won't group. So it's a Catch 22.
I reckon if you're field shooting bunnies, BC is less important against grouping capability and a drop in BC is greatly offset by accuracy. If you work in the 1.2 to 1.3 number, the old standard befor Litz, you should be fine. Anything over 260,000 RPM is in the area where jacket material is starting to yield with any 6mil bullet and upwards. With a 22 cal or less i suspect and know 300,000 RPM is sill acceptable. But not with every bullet. It is bullet specific at those RPMs.
Specifically with your 22/250 AI. I did a number of these for the 80 SMK using 8 twist barrels. Life span is in the 800 to 1200 max for FClass or Fly accuracy. Probably the most erosive cartridge after my 7/300 WSM i have come across where when they go, the bullet doesn't hit a six foot square board at 500 metres. For the bullets you mentioned that are heavier than 80 grains you will most likely have to get down to a 7.25 twist like the yanks favour in their rat guns. The 95s will most likely need a 7 twist or possibly faster.

[Con]

Thanks Tony,
Plenty to consider.
Cheers...
Con

[lee_enfield223]

I remember years ago a guy was shooting a 220 swift at the range with sierra 55gr blitz kings(if I am correct) and he was complaining that he couldn't see holes in his target at 100m,, well I was doing range officer duty at the time and stood behind him when he fired, and I thought i saw a ghost!!!!!!!!!! YES about 20m in front of the rifle I saw a grey mist!!!! I got him to fire again, and by this time other guys were watching too, and most of us saw the grey mist, it was the projectiles blowing up, I went into the local gun shop a few weeks later and looked at the box of sierras and it said maximum velocity 3600 FPS. well I guess he was driving it hard as his primers were creeping back into the firing pin hole. here's the max ADI load and I am sure he was way over that !!!!, I didn't ask him what was the twist rate of the rifle as I think safety was more important and we advised him to use different ammo.
55gr AR2208 .224" 2.680" 34.0 3,516 fps 47,000 CUP 36.0 3,645 fps 51,900 CUP

[frl0173]

I have a video and still shot of a friend shooting his 20-250AI shooting 55gn projectiles and watching them turn to grey mist cloud at about the 20m mark.

[Con]

You guys aren't making me feel more confident!

The original idea behind this rig was, and still is, to use it on a property where cross-gully shots are the norm, and the wind generally howls. So cutting the breeze cyclonic winds is important. Shots can range from 100 to 600 yards, missed rabbits before playing with my hunting 308Win at 150yards due to wind drift!

There's also a club that shoots F-class nearby that I didn't know about ( ) so hoping to see some duty there just for the challenge, fun factor and practice, not serious competition.

Thoughts of going a 6mm wildcat (6SLR) are also still bouncing around my head, as is a 6.5mm ... but on a gun to be used on rabbits/foxes and paper I feel like its over-kill going beyond 6mm. Plus the 22cal 77-80gr pills are cheaper in bulk than anything fatter!

Crucial is that the cartridge works 'best' with one of our local powders, no more Alliant and V powders. Hence the 22/250 idea and run heavy projectiles and AR2209.
Cheers...
Con

[Camel]

Just bloody do it Con, and stop worrying about the unimportant details.

[Con]

Just bloody do it Con, and stop worrying about the unimportant details.

Fear not ... this fast-twist causes me some anxiety, but the other that will get put together is a piece of cake in comparison.

Cant just build one now can you?

Cheers...
Con

[Camel]

Mate I am just a bit worried about your sanity, if you leave this much longer you will end up at Johno's age and mind set of "No more builds"

[Con]

Mate I am just a bit worried about your sanity, if you leave this much longer you will end up at Johno's age and mind set of "No more builds"

Fear not, Johno doesn't agree with me on this. When we get agreement, then we worry!! Besides, he's feeling less grumpy and I believe is adding to the stable again... 'But only one!' he protests!!
Cheers...
Con

[Camel]

Mate I am just a bit worried about your sanity, if you leave this much longer you will end up at Johno's age and mind set of "No more builds"

Fear not, Johno doesn't agree with me on this. When we get agreement, then we worry!! Besides, he's feeling less grumpy and I believe is adding to the stable again... 'But only one!' he protests!!
Cheers...
Con

Oh Gawd, here we go again.