I THINK I Can Make This

[gitano]

http://thehunterslife.com/forums/showthread.php?t=15614
Drop down to post #32 to see the appropriate pictures.

And I'm going to give it a try.

But not in .22 RF.

At the moment, I'm thinking .25 Hornet or .25 Remington Jet. Why .25 caliber you ask? Because I have a 21.5" barrel stub left over from a "gov't project". (Project halted by me because of stupid moron gov't reps.) That barrel stub has all the 'meat' necessary at the breech end from which I can machine the "receiver".

Why those cases? Because I'm looking for a reloadable cartridge with ballistics - both internal and external - on the order of a rimfire cartridge; ala the .22 WMR. This is a 'spiffy' little action, but it's not a STRONG, spiffy little action. .22 RF chamber pressure standard is 24kPSI. Both the Hornet and the Rem Jet chamber pressure standard is ~40kPSI, BUT... I don't HAVE to load to that pressure.

I am certain I can make every component, except one: The hammer. I have taken the "action" apart into its elemental pieces, and the hammer is the only piece that looks like a real challenge. The shaping isn't too intimidating, but the placement of the holes for the pins is extremely critical. Just not sure I can get that right the first - or even third - time. Maybe. Maybe not.

Another component that would be difficult for me to make would be the hammer kocking spring. However, there are lotsa black powder folks "out there" that can do that, and I will have one of them make it for me. It's possible, (I haven't checked yet), that Track of the Wolf (TotW) might have one in stock that I might be able to use or modify to use. At any rate, concern for getting that spring pales in comparison to the concern over making the hammer.

Not sure I'll make a trigger group. I was initially thinking I'd just use the existing group and the stock. However, if I'm going to the trouble to make the "barreled action", I might just go the whole nine yards and make a whole new rifle. Have to wait an see on that front.

I'm trying to think of ways to beef that breech up. As designed, the rearward thrust is held by the two screws in the 'ears' of the 'trapdoor-type' breech block. Larger screws and beefier 'ears' will offer some improvement. I can, of course crunch some numbers on 'bolt (breech) thrust' and get a mechanical engineer to provide specs based on screw diameter and ear thickness. But... I might just 'wing it'.

Anyway, I'll post everything about the build here in this thread.


Paul

[gitano]

https://www.trackofthewolf.com/Categories/PartDetail.aspx/0/1/LOCK-LR-1100-MS


Looks like TotW may indeed have something I can use. Keeping my fingers crossed.


Paul

[gitano]

The diameter of the rim of the .22 Remington Jet is 0.440". (Radius of 0.220".) Therefore, the area of the head is pi*0.220"*0.220" = 0.152 square inches. The SAAMI max pressure for the Jet is 40,000 PSI. Therefore, the MAXIMUM thrust on the breech face is 0.152 square inches*40000 pounds per square inch=6082 Pounds. So the design of the breech will have to be such that it can withstand 1.3*6082 Pounds=7906 Pounds. (SAAMI design specs require an action to withstand, without deformation, the max pressure PLUS 30% .) I'll round that to 8000 pounds. That is if I end up using the Jet case.

Doing the same math for the Hornet case, I get: 5442 Pounds of MAX thrust on the breech. Hmm...

Doing the math in the .22LR, I get: 1893 Pounds of MAX thrust on the breech.

So the original breech can absolutely handle something slightly less than 2000 Pounds of thrust. The Jet represents a 4-fold increase over that.  Hmm...

That is if I choose to load to max pressure. Which I never do.


Paul

[gitano]

Hmm... Been down this road before. "It's" coming back to me.

The. 25-20 is likely the perfect choice for this project. Its MAX breech thrust is 6655 Pounds.

Using the Hornady 75-grain V-Max, I can deliver 575 ft-lb, at an impact velocity of 1860 f/s, to 150 yards at a breech thrust of 4520 Pounds, with a trajectory of plus and minus one inch. That's 'only' 2.5 times what the .22 LR 'pushes' on the breech. The .25-20 is The One.


Paul

[gitano]

I'm getting carried away. Again. I need to put some design constraints on this thing in order to keep my eye on what I want this rifle to be. Namely: A reloadable, QUIET, 'garden gun'. I neither need, nor want, "maxes". So...

I think a 60-grain, Hornady FlatPoint is fine!
I think a .22 RF muzzle velocity in the range of 1200 to 1500 f/s is fine. Maybe, if I can pull it off, something subsonic like 950 f/s too.


Paul

[gitano]

It's got it's challenges, primarily head/rim diameter too small at 0.307/0.311 for a standard 0.373 bolt face, but the 5.7x28 does have the small RELOADABLE case going for it. Head/rim diameter is a moot issue in a falling or tilting block, OR the "action" I am contemplating making. So... It's between the .25/20, and the 5.7x28 case necked up to .25.

Paul

[gitano]

Some pictures for comparison. I didn't have a clue about the 5.7x28 until I found some brass at the range. (I have a dummy round already necked up to .25.)

Loading to 25,000 PSI (.22LR max pressure), yields MAX "bolt" thrust of 2405 PSI. Better than both the .25/20 and the Jet, even when both are loaded 'down'.

I am of course going to look at using the unmodified (.22 caliber) case. However, I don't imagine that I'll be able to get the MVs down in the 12-15 hundreds of f/s and still keep pressure up over 20,000. The pressure experience has taught that is required for sealing the chamber and getting CONSISTENT ignition. AND... I have the .25 cal barrel in hand.

.22LR, .17HMR, .22WMR, 5.7x28


5.7x28 with .223 Remington


Paul

[Jamie.270]

If you want to reduce the rearward thrust PSI even further, you might consider the .22 TCM casing.
It has a .376 base diameter.

[gitano]

While it seems somewhat counter-intuitive, the larger the head diameter, the greater the bolt thrust. Consider a head diameter of 1 square inch. The max bolt thrust would be equal to the max pressure. Now consider a head diameter of 0.5 square inches; max bolt thrust would be 1/2 the max pressure. Therefore, the larger head of the .22 TCM, (a cartridge heretofore unknown to me), would increase the bolt thrust over the 5.7x28 case, not diminish it.

That said, the "proper" nominal head diameter of 0.373" plus the small size of the case, makes the .22 TCM an excellent candidate for consideration for this project. Now I have to find cases.


Paul

[gitano]

You'll be shocked to find out that I did some number crunching with the .22 TCM. ��

Using a 57-grain Lyman cast bullet and 4 grains of Trail Boss, I get a muzzle velocity of 1400 f/s at a max chamber pressure if 23,000 PSI. That's basically identical to. 22LR internal ballistics. �� Except I don't like cast bullets.

So, using a 60-grain Sierra HP, and the exact same load, I get a MV of 1381 f/s, at a max pressure if 24,700 PSI.

Dropping the charge down to 3.8 grains, drops the max pressure to 22,800 PSI and the MV to 1343 f/s. Perfect! Looks like the .22 TCM might actually be THE cartridge for this build.

Given the 60-grain bullet, it's not exactly .22 rimfire performance, (it's better), but close enough. Change the bullet type to "spitzer" yields a little, (very little), better trajectory and better impact energy and velocity.

In a stronger action, the 35-grain V-Max can be driven to at least 3100 f/s. But... I dont need another "Hornet".



Paul

[gitano]

However! I've been down this 'low pressure' road, and the results were abysmal.

Paul

[Jamie.270]

You'll be shocked to find out that I did some number crunching with the .22 TCM. ��
Paul

Me?
Shocked by you, Mr "Paper Whipper" himself, crunching numbers?


HA!  Nevah!!!

[gitano]

Oh yeah... Forgot, temporarily, about the .25 caliber barrel - in hand. Which would require necking the TCM up.

Paul

[Jamie.270]

Oh yeah... Forgot, temporarily, about the .25 caliber barrel - in hand. Which would require necking the TCM up.

Paul

What is the bullet length/size limit, given this barrel's twist rate and the velocities you're looking for?

[gitano]

I'm pretty sure the twist rate is 1:10. I've been working pretty hard, (paper-whipping all design elements), on getting the velocity down to 1050 f/s. I'd settle for 1500-ish if I can't get slower. 1250 f/s would be OK. (Remember that I need to keep the max pressure down somewhere around 25 kPSI.) So... No trouble stabilizing a 60-grain .25 caliber bullet with a 1:10 twist. I haven't looked/calculated it, but I'm pretty sure I can stabilize an 80-grainer doing 1050-ish at 1:10.

I don't want to go above 60-grains, but I don't have any 60-grain .257 bullets in hand, and because the rat sons of bachelors bullet manufacturers that learned (from Barack Hussein Obama) that they could LOWER production, create the APPEARANCE of shortage, and thereby INCREASE PROFITS, there are NONE OF THOSE, (or any other for the most part), bullets to be had. I have some 75-grainers, and I have a mold that throws a 72-grainer (when gas check is included). You know what I think of cast bullets. :frown However, I think a cast 72-grainer doing 1050-ish might be exactly what I'm looking for. That is if I could hit the broad side of a barn with it. [/SIZE]

Paul