.357/9mm marauder build

[shorty]

The build has begun and I can use some help/information on some stuff. The barrel liner is very poor quality. It came in slightly bent and since it is such a thin wall thickness it is easy to bend. One end is concentric to the bore and the other end is way off. I figured just go with it and if it works I can always get a better barrel or barrel liner.

The conversion is from a 22 synrod and the purpose is to see if I can do it, along with being able to put it back to stock configuration if it doesn't work. And not get hurt.

I turned down the concentric side of the barrel to match the breech and extended to the stock shroud holder.
I turned set screw placement holders in the barrel liner to match breech set screws.
I turned down the other end of the barrel to match the stock shroud "end cap". Not sure what its called.
Opened the exit of the "end cap" to .40"
Drilled .187" barrel transfer port.
Made a bolt sleeve to accept oring. Set screwed to stock bolt.

Everything fits, and when completely assembled with shroud it looks stock.

The easy stuff is done. Now for the hard stuff or just the stuff I am not sure with and can use some advice.

What size should I lead the barrel?
How far should the lead be past the transfer port?
What pellets or round ball or combination of should I get to experiment with?

Pretty fun stuff and challenging. Here are some pictures.

[oldpro]

 I think you are going to have some serious issues. One the barrel is way to thin and not sure if you can use set screws from breech to hold it in you might have to epoxy it into receiver. Second that large a bore requires a ton of air to push a slug to a point it will be stable. I doubt you will be able to get more than 1-2 shots before it falls off the pressure required to push a huge slug at speed unless tethered you only have 213cc to play with and to get a .357 to stable speeds will require 70-100 psi per shot depending on tune. Im not trying to burst your bubble but a .257 or .30 cal would be a much better suited bore for a M-rod.

[shorty]

Oldpro,
I completely agree with everything you mentioned. I am currently into the build and "for me" I have to see what's going to happen. It has only cost me $23 bucks for the liner along with some "fun/learning" time on the lathe.

For me to go forward, I can really use some advice with:
What size should I lead the barrel?
How far should the lead be past the transfer port?
What pellets or round ball or combination of should I get to experiment with?

Almost there to see "what's going to happen".Too me, it doesn't matter if the barrel comes flying off or if I get 2 inch groups at 30 yards. These and those things are learning experiences and helps for improvements.

[shorty]

Forgot to mention that valve stuff has already been worked on so 50 to 100 psi per shot does not seem to be an issue when using the .22 configuration.

[shorty]

This is what I was looking for in my build. This is the only 9mm/.357 marauder I have seen on the net. Not much to go on but very sweet.

http://www.network54.com/Forum/79537/thread/1354240289/Sigamander%27s+9mm+Mrod+%26amp%3B+***Graphic***+kill

[oldpro]

77.62 grain slug at 800fps=110fpe thats what he was lobbing the slug out of his barrel at. This is dreadfully slow and will have the slug shooting in a rainbow arch. Though I know that that slug can be fired at a much higher velocity with a little more work than he did but the price of the build will go up quite a bit. Still it can be done. Look at my .257 179fpe marauder build and you will get some idea what its going to take. Its in this forum ill see If I can find a link.

[shorty]

I know you and others do great work on these types of guns and that's why I am asking for some advice on the barrel lead size/ length and what pellets to start out with. Even if I am doing everything wrong I still would like some advice on this.

 I just don't want to guess right now because I know this is most likely the most important part of the build to actually "lob" a pellet out. Believe me, I would take 100 fpe for 6 to 10 shots on a 3000psi fill.

I would actually be very happy to get that 800 fps for my very first big bore gun build that I know nothing about.

[Nomadic Pirate]

800 fps and less is what RAW .357 is shooting those 81gr JSB pellets and there's already many happy customers out there, if you can get her to shoot 750 fps you should be very muck ok and a happy camper

[oldpro]

 Shorty you selling yourself short you can get that baby to hum im sure of it. Give me a ring at the shop and ill look up some specs for you and see If I can get you some solid information backed by real world numbers. Glad to help in any way. I can give you some valve specs also I have saved from some big bore projects.

[shorty]

Thank you for the offer to call and talk. If it's not one thing it's another. Just getting ready to get into the build again and here comes little sis with brake problems. Of course big brother has to stop working on fun stuff to mend a sticking caliper.

So caliper was fixed this am and and back to work on the gun. Since there was no advice to the lead in dimension and length, I decided to ream at .356" and approximately .25" past transfer port.

I also didn't have any pellets or slugs so I took 2 flat pieces of aluminum, pined them together and made a mate shift pellet mold with a head of .354" and skirt area of .357"/.358". Slugs weighed out to 8 grams on an old pot baggy weighing thing from the 80's ( I have no idea why I had that thing). So about 124 grains.

I had to make a new transfer sleeve (shorter) because I did not put a flat on the barrel at the barrel port.

Put everything together and dry fired at 0 HS with a tissue on the receiver to check for leaks. 2 dry fires and no leaks.

Turned HS up to 6 turns (49fpe with .22/25.39gr at 2800psi), loaded a slug, put safety glasses on, and shot through the chrony.

Boy I wished I had a video camera at the time. That thing was loud. Real loud.

Chrony registered at 400 fps. Yea I know it was low but, there was a reason. That "dang" oring on the bolt disintegrated and pushed the sleeve on the bolt back.

Well, I can't say it was a failure and the barrel did not move or fly off the gun. Projectile came out of barrel. If that "dang" bolt sleeve and oring didn't blow out, there should have been alot of potential there to get to the 100 fpe potential.

Anyone got some good ideas for the bolt sleeve and oring. I used an oring behind the sleeve and used two 4/40 set screws to the bolt. Hard to believe it all moved back and blew apart the barrel seal oring.

[shorty]

Made a steel sleeve instead of the oring behind the bolt sleeve and replaced the bolt sleeve/barrel oring with a urethane oring instead of a black rubber oring.. Won't have any more time for testing today but all together and breech tissue tested again for a pass.

Here's some pics.

[shorty]

Yeah I know I said I wasn't going to do it again today but the charcole really takes 20 minutes to get hot for hamburgers and hot dogs.

I loaded in the last mate shift slug of 124grains and shot again with the bolt modifications and hit 502 fps. Almost 70 fpe.....

Time to take a break, cook some food and order some pellets or round balls.

So I will try again (since no one had any ideas on the barrel lead and length) What kind of .357" or 9mm pellets would be good for a first try out???

I can't understand why you big bore builders are not helping out here. Travis is the only one that actually reached out.  The trial and error approach is not fun. I am scared as heck to pull this trigger.

I'll tell you what though. It appears as if anything up to .357" can be chambered into the .22 synrod fairly cheaply with the right tools and know how.

[oldpro]

 Its no BB gun LOL! Yea when those big bores go off its a scary thing if your use to normal pellet rifles. To much info to share for me to two finger type but your welcome to give me a ring or text me ill text back.

[shorty]

It was only 2 questions:

Lead in size and length
and
what size pellet or round ball to try out.

Not one person had a recommendation....What's up with that?

I really appreciate the help/offer Travis. I am not going to waste my 1 valuable call or text unless I am truly against the wall to meet a goal.

Too me,
This build is something anyone can do with the right tools and know how. It also shows the limitations and dangers.

This build to me is not only to get a 22 synrod to get (at or over) 100 fpe. It's more than that.

Keep posted because I am ordering round balls and JSB's.....

[Monkeydad1969]

Its no BB gun LOL! Yea when those big bores go off its a scary thing if your use to normal pellet rifles. To much info to share for me to two finger type but your welcome to give me a ring or text me ill text back.

X2 on calling Travis.  It is just to much info to type and then it can get lost in translation, and some things can be forgotten when someone is typing out the big bore bible.  Hey, you can use my 'call a friend lifeline' if need be.

Joe

[rsterne]

We kind of told you that you were venturing into an area unlikely to produce much success, and possibly dangerous, with the extreme thinwall barrel, and the loads on the bolt, which has already failed you once.... Now you are criticizing us for not offering help on a questionable project?....

I rather think that is unfair.... I for one don't want to further encourage you to possibly injure yourself on what I think may be an accident waiting to happen....

Bob

[oldpro]

 Bob Im with you as I stated earlier its a bit sketchy...But I will help out if asked, but still this should be no bigger than .30 cal for safety reasons and in-fact Id personally keep it a .257 to have safety margin to at least 3-1 min. High pressure thin walls and low safety margin equals bad things. You could get and appropriate barrel for less than 1 stitch at the ER just saying!

[crosman999]

Bob Im with you as I stated earlier its a bit sketchy...But I will help out if asked, but still this should be no bigger than .30 cal for safety reasons and in-fact Id personally keep it a .257 to have safety margin to at least 3-1 min. High pressure thin walls and low safety margin equals bad things. You could get and appropriate barrel for less than 1 stitch at the ER just saying!

very well said,the .30 would be very achievable too!!

[shorty]

"We kind of told you that you were venturing into an area unlikely to produce much success, and possibly dangerous, with the extreme thinwall barrel, and the loads on the bolt, which has already failed you once.... Now you are criticizing us for not offering help on a questionable project?....

I rather think that is unfair.... I for one don't want to further encourage you to possibly injure yourself on what I think may be an accident waiting to happen...."



I told myself that I am not going to be a jerk anymore on the forum so I am not. Just a productive member.  I meant not to criticize. I just thought there is just a "standard" or good "go to" numbers for leading and lead length. Your doing the right thing by not encouraging an unsafe act.

Now I am not saying this project was safe in anyway.

Burst pressure on barrel with an .035" wall thickness is between 8000psi and 11000psi (over 3:1 safety factor at 3000psi).
Heres a good table/chart:
http://www.engineeringtoolbox.com/barlow-d_1003.html

Shear/break strength of the 8/32 on the bolt is still a little unknown but from the data on this site would suggest that the 8/32 will fail at approximately 600 to 1200 lbs (minimum 2:1 safety factor).
Here's the site: http://www.derose.net/steve/resources/engtables/bolts.html

The bolt sleeve failed for one reason and 1 reason only. Poor design on my behalf. Should have never used an oring between sleeve and bolt. Easy fix with steel and problem solved.

This project is not a failure. First time on a big bore build and the second shot from a mate ship casted bullet at 70 fpe out of a 22 synrod chassis ? To me, that's pretty cool. A little impressive and for under $30 bucks.

I might try a different caliber next time like the .257 or 30 but I need to finish this first with a shot string and accuracy testing first.

[shorty]

This was an old post from a long time ago.
http://www.gatewaytoairguns.org/GTA/index.php?topic=9585.0

Bob, this was your .357/9mm carbine build. Pretty close in design. Your post from way back in 2011 helped. From my only 2 shots out of the gun looks like it will be comparable.