Re: Bam B50 9mm build (75yds)

[wildman510]

Anyone ever converted a bam b50 to 9mm.  I just ordered one and a barrel from lothar walther. 

[wildman510]

Ive owned numerous marauders and sold them went back to springers.  Tired off pumping and no local fill station.  I figure if Im gonna have a pcp it might as well be a a big one.  The bam b50 looks like a good platform to use.

[grumpy]

Don't know of anyone who made a .357 but Bruce here on GTA did a very nice .308 B50. Search out his build thread in the big bore forum. Bet theres some great info that can be applied to your build. Keep us updated.

[wildman510]

I definetly keep everyone updated.

[rsterne]

I would suggest before you start you decide if you want to set the gun up for pellets and roundball (68-78 gr. and therefore 100-160 FPE).... or if you want to go to cast bullets of 100 gr. and up (and therefore 200+ FPE).... It makes a big difference in the decisions you make on the build....

Bob

[wildman510]

I would suggest before you start you decide if you want to set the gun up for pellets and roundball (68-78 gr. and therefore 100-160 FPE).... or if you want to go to cast bullets of 100 gr. and up (and therefore 200+ FPE).... It makes a big difference in the decisions you make on the build....

Bob

Looking right now to shoot jsb's 78gr around mid 800's.  Purchasing 2 the second one may be headed for something setup for 115gr

[wildman510]

Ill make sure to take pics Im gonna start teardown tommorow. if the wife allows

[rsterne]

I would recommend at least 7/32" ports or the equivalent area straight through for 125 FPE average in a string starting at 3000 psi.... You can reference the performance of my Disco Double in .357 cal, that is what I'm running in that gun.... Here are what the strings look like with 250cc of air available....



You may want to run 1/4" porting, but the larger valve throat will require more hammer to knock it open, but it has the ability to deliver more power if you can do that.... It will likely require a PEEK valve poppet if you do, however, Delrin may not be up to the job at 3000 psi with the throat size required to supply 1/4" ports.... The maximum you can run for a round port in a .357 barrel is about 9/32" without loading problems....

Bob

[wildman510]

Thankyou for that info rsterne.  Im thinking of just opening it up too 1/4 inch then making different size transfer ports to get the final desired flow.  Fitting the barrel and making a new bolt, and other odds and ends I can do.  With 2 young kids and working swing shift I greatly appreciate any advice to knock some time off this project.  Some pics will come later tonight.

[rsterne]

At 1/4" you may have to drop the fill pressure below 3000 psi, depending on how everything flows air, or your velocity may be more than what you want with the 78 gr. pellets.... If that is the case, you can either leave it that way, or fit a smaller transfer port and lean on the hammer spring preload to get the fill pressure back up.... Lots of flexibility with 1/4" ports I would think.... Don't forget to allow for the valve stem area when calculating the throat diameter.... It doesn't hurt to have the actual area of the throat (seat minus stem) slightly larger than your 1/4" ports, but it doesn't buy much (if any) performance.... For example, if the stem is 1/8", you could use a 9/32" throat, which would result in an area the same as a 1/4" port.... or you could go up to a 19/64" throat (or even 5/16") but don't forget that as you increase the seat diameter the force to crack the valve at a given pressure (and hence the required hammer strike) goes up by the square of the increase in diameter.... Eventually you will run out of hammer strike....

Bob

[wildman510]

If I have too Ill build a new hammer.  The valve stem is something ive never attempted to make been brain storming on this for 2 days.   I figured on making a few different sized transfer ports to fit between the breech and air resevoir to fine tune the final flow.  Pardon me if my wording isnt exact im not always good at wording what im thinking about.  Being im also into electronics ive contiplated an electronic solenoid valve and programable timer for a valve idea but im not big on a battery powered gun maybe something to play with down the road.

[wildman510]

They are very nice rifles for anyone who has never seen one.  Looks like Im gonna have to definetly raise the breech.  Ill have to order some 1" 1/4 id tubing to cut a spacer out of.

[wildman510]

Finally got the gun tore apart this morning.  The throat of the factory valve is already .234 or 15/64.   Stem is 1/8". 

[wildman510]

Valve pics.

[wildman510]

The valve spring is sure a heavy one.  As for the valve stem im thinking of using some drill rod, brass,  and maybe a teflon sealing surface.

[wildman510]

Not much else I can do today except polish some stuff.  I wont be back to the shop till thursday.

[wildman510]

Barrel pulled from breech rather easily with a little heat.  Taking care not to damge anything cause the barrel may be used for another project later.

[rsterne]

Looking forward to seeing how much you can hog oyut that valve, as right now the ports are too small for even a good .22 cal....

Bob

[wildman510]

Looking forward to seeing how much you can hog oyut that valve, as right now the ports are too small for even a good .22 cal....

Bob

Like you stated before theres plently of material to hog out in there.  After pulling the barrel from the breech I had an eeeek moment.  Theres not much materail on the stock breech to bore out and fit the new barrel.  After some quick measurements though the new barrel will fit once a shoulder is turned down and bore the breech out a little.  But this pretty much scraps my idea of floating the barrel.  For strenght reason Ill have to make a new barrel band also.  The equipment I have to work with is old and making a new breech would be a very lenghty process.  Looks like 9mm is the absolute maximum caliber you could stuff in the factory breech.  The barrel inserted into the breech is only gonna have a 2mm or .078" thick wall left.

[wildman510]

I may want to find someone to discuss making a new breech with.  But for now ill work with what I got.