Author Topic: Re: Bam B50 9mm build (75yds) (Read 22769 times))

wildman510 · « **Reply #20 on:** March 04, 2014, 02:40:38 PM »

The shoulder on the barrel will be a weak spot but since I dont use my guns as golf clubs and with a barrel band I shouldnt have any trouble.

wildman510 · « **Reply #21 on:** March 05, 2014, 10:03:18 AM »

Ruff drawing on what need done to breech and barrel. I dea is to keep gun looking as close to stock as possible.

toine · « **Reply #22 on:** March 05, 2014, 04:37:11 PM »

On the off chance you haven't seen it, I have a site I've used to archive posts and info B50/51 related.

https://sites.google.com/site/b50tuning/

Mostly links to older GTA and posts from other forums. as well as some pictures and a copy of a community made book of info.

wildman510 · « **Reply #23 on:** March 05, 2014, 06:03:14 PM »

Quote from: toine on March 05, 2014, 04:37:11 PM

On the off chance you haven't seen it, I have a site I've used to archive posts and info B50/51 related.

https://sites.google.com/site/b50tuning/

Mostly links to older GTA and posts from other forums. as well as some pictures and a copy of a community made book of info.

Thankyou very much for the link. Ive been taking measurements all day and getting plans drawn up. Had to purchase some reamers and other odds and ends to make a new valve stem. Its all coming together on paper hopefully I can start making some actual progress tommorow evening.

wildman510 · « **Reply #24 on:** March 07, 2014, 01:28:00 AM »

Made some progress on the breech tonight. Milled the loading area out, Bored for new barrel and bolt, recessed screws enough to let bolt pass. Also milled the riser out. Tommorow ill work on the valve.

Monkeydad1969 · « **Reply #25 on:** March 07, 2014, 02:10:39 AM »

Where did you get your barrel from (& cost) and what is it's OD going into the breech (is it 1/2")? How long is it, too?

Joe

wildman510 · « **Reply #26 on:** March 07, 2014, 08:19:38 AM »

Barrel is a Lothar Walther blank 28" $145 shipped. O.D, going into the breech is 17/32 or .531".

wwonka · « **Reply #27 on:** March 07, 2014, 09:41:03 AM »

Quote from: wildman510 on March 07, 2014, 01:28:00 AM

Made some progress on the breech tonight. Milled the loading area out, Bored for new barrel and bolt, recessed screws enough to let bolt pass. Also milled the riser out. Tommorow ill work on the valve.

What sort of mill/lathe are you using? Thanks.

Monkeydad1969 · « **Reply #28 on:** March 07, 2014, 12:06:24 PM »

Quote from: wildman510 on March 07, 2014, 08:19:38 AM

Barrel is a Lothar Walther blank 28" $145 shipped. O.D, going into the breech is 17/32 or .531".

Thanks, Josh.

wildman510 · « **Reply #29 on:** March 08, 2014, 03:31:53 PM »

Quote from: wwonka on March 07, 2014, 09:41:03 AM

Quote from: wildman510 on March 07, 2014, 01:28:00 AM
Made some progress on the breech tonight. Milled the loading area out, Bored for new barrel and bolt, recessed screws enough to let bolt pass. Also milled the riser out. Tommorow ill work on the valve.

What sort of mill/lathe are you using? Thanks.

South bend lathe prolly about 40yrs old, and the mill dont know off hand its old also.

wildman510 · « **Reply #30 on:** March 08, 2014, 03:33:22 PM »

Worked on the valve. Port has enough meat to go up to 9/32 but opted for a 7/32 right now. Throat was opened to 9/32 for now. Cut an extra groove for a oring on the valve. Ill get some pics up tonight.

wildman510 · « **Reply #31 on:** March 10, 2014, 10:15:09 AM »

Made a new valve stem using a piece of round stock, 1/8 drill rod, and teflown oring. Opened the throat to 9/32 and the port is 7/32. Reassembled the airtube last night and pressurized to 3000ps1. So far has held air. Did some test firing this morning WOW is this thing loud. This project seems to be coming together.

wwonka · « **Reply #32 on:** March 10, 2014, 11:11:14 AM »

Nice going... You're really making this happen. I'll bet it was an anxious night waiting to check the pressure in the morning. Look forward to seeing the strings...

wildman510 · « **Reply #33 on:** March 13, 2014, 01:27:43 PM »

Bams held air for a few days now. Im planning on fitting the barrel this weekend. So hopefully I can start getting some shot strings by monday. The lothar blank seems to have a very tight bore and is very nicely rifled.

wildman510 · « **Reply #34 on:** March 15, 2014, 10:29:27 AM »

Got the gun assembled this morning its only shooting 500fps with 78gr jsb's. Im thinking I need a heavier hammer spring. The pressure went from 3000 to 2700 after 8 shots. Any thoughts appreciated. Will a heavier spring help keep the valve open longer?

rsterne · « **Reply #35 on:** March 15, 2014, 12:30:09 PM »

Yes, you're experiencing partial valve lock.... You need a much stronger hammer spring, a heavier hammer, more hammer travel, or some combination of the three.... Welcome to the world of modding PCPs to Big Bore.... With the increase in the valve throat you need a 45% increase in hammer energy just to crack the valve off the seat.... Then you need enough extra hammer energy and momentum AFTER that to produce enough lift and dwell to propel the 3-4 times heavier pellet.... which basically needs 3-4 times the amount of air to reach the same velocity.... If it needs 4 times the air, that means twice the lift and twice the dwell, which requires twice the energy, times 1.45 for the energy to crack, so you need roughly 3 times the total hammer energy....

Bob

wildman510 · « **Reply #36 on:** March 15, 2014, 04:45:47 PM »

Ok Rsterne for a quick try I dropped a lock washer over the spring guide, added a 1/4" stroke using the stroke adjustment. 720fps ears are ringing now. Heres a couple of pics. After everything is adjusted the way I want it Ill blue the reciever and blacken the riser.

rsterne · « **Reply #37 on:** March 15, 2014, 05:40:17 PM »

720 fps, not too bad for early trials, that's 90 FPE.... That's about what I got at 1800 psi with my first 9mm Disco.... As I gradually went through making a heavier hammer and fitting a stronger hammer spring it went from there to 107 FPE at 2400 psi, and got to 127 FPE at 3000 psi with 78 gr. EunJin pellets.... I tried 132 gr. cast bullets at that point, but it was only marginally better at 138 FPE.... Once I fitted the double tube (250 cc of air) and tuned it for a proper shot string I got 8 shots at 117 FPE average from 3000 psi down to 2000 with the pellets and 9 shots from 2800 psi down to 1700 at 127 FPE with the bullets.... Those figures were achieved with a 7/32" transfer port, and a rear-cocking 90 gram hammer with a very beefy spring.... My new .30 cal Disco Double has been tried in a .9mm version, and ends up at the same kind of string, although with a PEEK valve and an even heavier spring and more hammer travel it has produced as high as 192 FPE for one shot at 3000 psi with a 132 gr. bullet.... still running the quite restrictive 7/32" porting....

Seeing what is possible when converting a .22 cal PCP to Big Bore is a lot of fun and very rewarding and educational....

Bob

wildman510 · « **Reply #38 on:** March 15, 2014, 06:48:29 PM »

My throat is 9/32 and my port is 7/32. Made the transfer port out of teflon. Im happy so far. Im already looking forward to building one for myself as this ones going to be my fathers. I may settle on a velocity of 800fps or a little less depends on the shot count I end up with. The bam only has 196cc resevoir but keeping the gun looking close to stock was the goal. At the distances the gun will be used at I dont need super velocity. Thankyou Rsterne for your valve specs it saved me alot of time. So far my valve stem seems to be holding up.

wildman510 · « **Reply #39 on:** March 21, 2014, 09:53:40 PM »

Ok 200 pellets later and a lot of pumping and tinkering. I finaly got a usable string. Ive got a low of 728 and a high of 754 for seven shots. 190 bar to 140 bar for six shots. Or 2755psi to 2040. Im still using the factory spring and hammer. I drilled the hammer out and tapped and put mu own recessed striker in it. I also dropped the transfer port size from 7/32 to 3/16. Hammer spring i shimmed about an 1/8 inch. Stroke with recessed striker is 1/4 inch recessed from nose of hammer. Power can be increased by dropping in a larger transfer port. and striker adjustment. Obviously with less shots. Im using 78gr Jsbs. Anything over 800fps drops my shot count too 2 or 3 aaccurate shots.

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Re: Bam B50 9mm build (75yds)

Author Topic: Re: Bam B50 9mm build (75yds) (Read 22769 times))