[prairierast]

anyone seen or shot a 5/35SMCc? case some were between a 204 Ruger and 22-250.

 

[Rocky Raab]

I didn't understand the second sentence, but I am shooting a 5/35 SMc. The cartridge is a reformed 6 BR, with a specifically-designed elliptical shoulder. The shoulder shape and position is designed to focus primer shock waves back into the propellant, and also to contain the propellant within the case. The physics behind it are complex and far beyond me to explain, but it was desgined by rocket motor engineers to take advantage of solid rocket propellant knowledge.

It is (from the name) a 5mm (.20-cal) round with a case capacity of 35 grains of water, designed by "By" Smalley and "Mic" McPherson.

One of the chiel difficulties with the round is the problem of bullet disintegration at the velocities the round is capable of producing. In my tests, Hornady bullets remain intact but are less accurate than Sierra bullets. The Sierras, however, concistently blue-streak above 4300 fps, sometimes as low as 4100 fps. Moly-coated Bergers stay together at even higher speeds, By tells me, but I haven't shot any of those. He also loads to hotter levels than I do, but he doesn't have a Pressure Trace system hooked to his barrel, and I do.

I hope to complete an article on it with load and pressure data this summer.

 

[Ackman]

There've been some articles about the cartridge. A couple were "hunt" articles that were nothing more than thinly disguised self promotion for the cartridge. Also ther'es a website with all kinds of stuff that's mostly BS. It's just a BR case necked down to .20 cal.......nothing more than a .20BR with the shoulder bulged out a little. To prove how wonderful the whole thing is, it's compared to a .22-250 but never to a .20BR.....hmmm, why do you suppose that is? I know two guys on this board who shoot the .20BR, and with the same bullet they're getting the same velocity with accuracy at least equal that 5/35 SMc. The guys who created it may work on rockets, and they can hype it all they want, but it's all a bunch of BS.

 

[NYCSTRIPES]

Friend of mine is a retired engineer from Savage Arms, still does some work for them and was the original designer of the Model 10/110 action family. I asked him about his thoughts on the cartridge and he was unimpressed. He suggested the 20BR instead. Recommended that I stay away from it, more hype than capability. I would like to hear about your findings Rocky.
Ken

 

[Ole]

ALRIGHT ACKMAN!!!! I did talk to one guy with a .20BR and in less than 600rds his barrel was toast, junk in other words. Can't see where this other case would be any different, to much powder to small a hole.

 

[glenn asher]

I always thought it was a bit of "overthinking" the problem. Still do. I suspect that in twenty years, we will have forgotten all about the hemi shoulder.

 

[GLWenzl]

ALRIGHT ACKMAN!!!! I did talk to one guy with a .20BR and in less than 600rds his barrel was toast, junk in other words. Can't see where this other case would be any different, to much powder to small a hole.

FWIW I built my 20 BR with the thoughts of it not lasting because I *knew* it was OB...

I now have just over 600 rounds through it and can not set the bullets out any farther than I could new. The gun smith (Weaver Riffles) sent a couple inches of the barrel he cut off and chambered it so I would always know what my new chamber dimensions were; I think he calls it a critter.

At any rate I am re-thinking my original OB thoughts and will know more after another year of PD'n but as of right now it is the best long range ratsmack’n PD getter I have! One example; 5 shots at 494 yards range at PDs and ended up with 5th shot a miss and the other 4 one-shot kills. (20 BR = too much fun!)

That said I have a 20 BR barrel a friend built and is trash at 600 rounds. I have the barrel and sectioned it to look at the damage. It still shot his 39 gr bullet accurate however it started copper fouling…. Some say it was the combo of the thin skinned 39s and the R-10X powder he used (I used to 40 v-max and Ramshot Tac). I have no ideal what is happening just my experience is all I have to go on but for now this 1-11 twist pacnor super match stainless steel barrel is holding up well, I have no intentions to ease up on’r yet and from what I have seen is no worse barrel life than either my 22-250 or the 22-250 AI that I had and being able to see hits, less wind-drift and unbelievable accuracy with any powder combo has made this the most awesome PD riffle I have.

So not encouraging anyone to run out and build a 20 BR thinking that it will last forever however I would not call em a barrel burner just yet nor would I discourage anyone from having too much fun!!!

 

[GLWenzl]

I hope to complete an article on it with load and pressure data this summer.

I am interested in your results/article. FWIW I shoot a 20 Habu Shrew (20-221 Imp) that has both radius shoulder and a bud that has a std 20-221 Imp. Although it is not a scientific test from as near as I can see there seems to be very little if any difference between the radius and non radius shoulders. Same components = near the same velocity. Both of them get an unbelievable velocity and accuracy with the 32 v-max making it a better high volume PD round than my 20 BR

 

[AVanGorder]

20ppc

A shooting buddy of mine has a 20PPC on a Nesika action. It will shoot 4600fps, I've seen it myself. Not all the bullets will make it to the target at that speed. There are no signs of pressure, and, it shoots great!

 

[NYCSTRIPES]

I am looking forward to testing my 20 cal wildcat later this year

Hearing your friend's 20PPC is getting that velocity is encouraging. I have a chamber reamer from Dave Kiff for my 204 Russo-Varminter which is identical to the 22 cal variant I made a year earlier.
With the added case capacity of the PPC based case I designed, I should see some excellent velocity from my wildcat with the 20 cal shooting 40gr bullets.
Depicted in the picture are the 220 Russo-Varminter, 22PPC and 220 Russian parent case.
Ken