B40 owners a little input please (HELP!)

[DMikeM]

As most of you know I recently purchased a BAM B40 from Mike Melick. It came undamaged except for a small dent in the stock, and the button on the bottom of the shroud broke off after about 100 shots.

Loading this gun with Crosman Premier Lites was a real pain so I spun a cone shaped grinding tip in the port a little with my fingers and it help. The Breech opening is very wet with oil and I have wiped it out several times. The trigger adjust screws came out on me so I Teflon taped. It shoots ok but not near as expected with the CPLs flying all over the paper like a shotgun blast at all distances even down to 8 yards. I have borrowed a Chrony from a friend and the numbers on this gun are terrible. 650 with CPLs, 740 with RWS Super HP(6.9?), and 615 with Crow mags. Compared to all the reports I have seen on this gun from other users I am wondering if I got a bad seal or bad spring. I have not opened it up as I have not seen any info on the proper way to break it down. I am wondering if it is my altitude (6,800 ft above seal level) that is causing the low numbers or is it just taking a long time to settle in, I already have about 500 shots through it with several types of pellets. A breakdown or tune guide for this or a TX200 would be ideal as I have been unable to find one yet.

I copied this from my post in the other thread as I don't think many will see it buried there.

As an update I am still disappointed with the B40. The FPS after a few hundred shots barely breaks 650fps with a CPL 7.9 gr. The RWS Super HP will go 740 average and group well. The CPL will not group less than 1 inch CTC even at 8 yards. Crow Mags seem to group the best but only give me about 615 FPS.
The trigger settings just flat suck. I ended up drilling a hole through the guard so that I could get to the screws better. I added some Teflon tape to the screws to keep them in place, then actually added a little weight to the trigger as it was at about 4 ounces or less to pull. Also the loading port/breech is full of oil of some sort that I and clearing out about every 30 shots. I like the scope, much more clear than the leapers or Barska scopes and it has not budged even a little since I mounted it.

[Walt]

Wow! I haven't heard anything like this about a B-40. The one I owned was trouble free very accurate and seemed to be of  good quality. I  got mine from Best Air Guns a couple of years back and as I recall the factory lube left a bit to be desired but it was easy to take down and responded well to a de burr and lube home tune. I did nothing to the trigger it was very nice the way it came. I did the same thing you did to the breach and that fixed the only operational problem I had with the gun. http://www.xisicousa.com/files/B40diagramlist.pdf This might help for a tear down and IMO that is where you need to start.
W

[DMikeM]

Hey Walt,

Thanks for the reply.
I have looked at the diagram a few times and am assuming that the #41 screw holds the action in place. I would like to have a look in it to see if I have a bad seal or something else is going on. Oh and BTW is that a Simmons scope on yours and what model is it?

[speedturtle]

Mike, try this link: http://www.severi.be/airgunning/TX200%20strip.htm

Hope this helps. My suggestion... consider tuning it yourself if you can. If it can't really group well you might have a bad barrel to start with. Good luck.

[DMikeM]

Thanks ST this is exactly what I had been looking for. I will check it over before attempting the tune. If it is damaged I will contact Mike before doing anything. Do you have any knowledge of where others were adding a pair of o-rings?

[shady816]

good luck with the AG Mike i know apsolutly nothing about the b40 but i have noticed alot of china gun owners poping up with problems with the most recent purchased models i hope this trend comes to an end soon.

[bcshooter]

Hi Mike, I added two orings to the cocking lever to replace the rubber dot that came off after about 100 shots thru the B 40 and my TX200. I used a #10 oring from Lowes or Home Depot, haven't had a problem since the were installed. The orings fit in the two grooves at the end of the cocking lever. Stay with it, the B 40 is a excellent shooting platform, a good cleanout,debur and lube is all it really needs at this stage. Shoot Safe and Enjoy......Bill

[DMikeM]

shady816 - 5/24/2010  1:56 PM

good luck with the AG Mike i know apsolutly nothing about the b40 but i have noticed alot of china gun owners poping up with problems with the most recent purchased models i hope this trend comes to an end soon.

Thanks Shady, Mike responded to my post on the yellow Chinese so i think i will tear it down tonight and see what I can see. My .177 B26 is shooting pretty darn good these days. Still deep into it with my .22 though.

[DMikeM]

bcshooter - 5/24/2010  2:15 PM

Hi Mike, I added two orings to the cocking lever to replace the rubber dot that came off after about 100 shots thru the B 40 and my TX200. I used a #10 oring from Lowes or Home Depot, haven't had a problem since the were installed. The orings fit in the two grooves at the end of the cocking lever. Stay with it, the B 40 is a excellent shooting platform, a good cleanout, debur and lube is all it really needs at this stage. Shoot Safe and Enjoy......Bill

Oh I totally understand what you are talking about now. Makes perfect sense. Thanks.

[fisherdude]

I have two thoughts to share on your situation.

1. The seal may have been damaged during assembly.  Seals are very frequently damaged by burrs not removed before inserting the piston by the manufacturer. Damaged seals do not shoot well!  The solution is to disassemble the rifle and use wet/dry sand paper, needle files and/or dremel tool to remove all burrs and reassemble with a new seal.

2. From your description, it sounds like there may be oil getting into the compression chamber (possibly from a damaged seal).  This can cause irregular velocities and poor accuracy.  Although some manufacturers actually recommend that you oil the compression chamber from time to time, most tuners on this web site - including myself - recommend that the compression chamber be completely dry when reassembling.  Oil inside the compression chamber causes dieseling.  I never use oil either inside or outside the compression cham ber.  Use just a LITTLE  molly lube on the outside of the seal when reassembly.  Then use spring tar on the spring and reassemble.  This should clear up variations in velocity due to dieseling.  There is more information in the library on this site on tuning.

Keep at it, tuning your rifle is a wonderful learning experience.

[Walt]

The scope is a BSA air gun rated 3-12X44AO I sold it with the gun. Natchez now has the new version of this scope for $45 and on the new one the AO works from a side wheel. I put it on a Gamo 220 reman' and am quite pleased. Has about 200 rounds through it.
W

[DMikeM]

Update,
 I found the spring to be kinked and the breach seal was not seating, and the piston screw was dinged up. Mike is sorting this out for me so it should be up to snuff in no time.
On a side note I was able to grind out the o-ring groove well enough to use it and installed a second ring up near the flat side of the screw top. Got a washer under the breach seal and straightened the spring out by hand.
While I had it apart I polished the cocking slot and deburred whatever I could fine. Polished the top of the trigger group and the spring ends. Cleaned it all up and lubed as needed. It shoots pretty good now 850 to 870 FPS with cpl but I want to put in the new parts Mike is sending and see if it will come up over those numbers.
Also all the pellets I shoot out of it will group tight now.

[itsnotom]

your not gonna get much more(if anything) than you have now

[Jaymo]

I put rubber O-rings in the 2 grooves in the front of the cocking lever. They do a nice job of replacing that little rubber button.