Saturday, October 10, 2009

BAM B3-1 Tune Up Part 5

Still going....

With the barrel epoxied and pinned back into the breech block, I was finally able to begin reassembly. For the most part, it's just a reverse of Part 1 found here.

Started by smearing a thin film of moly grease on the inside and outside of the sliding compression chamber. I used Honda moly 60 grease. Look for it at motorcycle shops near you. It's used to lube driveshafts.

The slot in the compression tube accepts the front of the anti-beartrap safety. You'll figure it out.

Piston also gets a thin coat of moly--inside and out.

Not really shown here: From part one, the pin at the rear of the anti-beartrap mechanism was reinstalled and peened.

After installing the piston, I used a dental pick to align the holes for the cocking lever.

Like so.

Spring and spring guide? Yep, moly'd--then they took a ride in the spring compressor.

Trigger and sear got the treatment, too. Moly for everyone!

Started the multi-purpose retention pin. It holds the endcap, trigger, and sear in position.

Inserted an appropriately sized transfer punch from the opposite side through the trigger blade and sear.

Tapped the pin through. Not shown: Peened the end of the pin so it won't vibrate loose.

Moly on the cocking lever at the contact points.

Fit the end into the piston first, then the pivot at the rear.

And grease the pivot pin. Tighten snugly.

Trigger spring is a direct action against the sear. Fit the spring into the rear of the sear then hook the rear over the metal "V" shape formed into the endcap.

Like so. The trigger dropped over 2 pounds of pull weight from simply polishing and greasing the trigger, sear, and piston rod's cocking notch surfaces.

Another view.

Reinstall the two M6 stock attachment bolts.

About time. Mounted the modified Weaver base from Part 3.

Installed a spare red dot sight from buddy Joe.

Another view or three

This is a bit out of sequence, but I wondered if using a rubber bushing between the action and the stock would affect accuracy?

Removed the stock and installed a 0.125" rubber washer. The mounting bolt runs right through. This isolates the breech/barrel assembly slightly. Helpful? Who knows?

Mentioned in an earlier post that I'd free-floated the barrel. A sheet of paper just fits between the barrel and the forend. Again, is this helpful to accuracy? Dunno yet. I've changed and altered so many aspects of this gun... I can say with absolute certainty that the gun now has a much smoother firing cycle than before and it hasn't lost any power.

I fired about 100 shots then set up the chrony.

Here's the 10 shot string with .22 cal RWS Hobbys

So the velocity is still ridiculously consistent. Truthfully, if I saw this shot string posted for a BAM B3-1, I'd think the guy's chrony was broken or he'd been drinking heavily while posting. I fired 4 other guns across the chrony and they all posted appropriate numbers.

It's really interesting to me that both pre and post tune, the gun was shooting almost identical speeds (There's a pre-tune up 10-shot string in part one.) -- especially considering I used a different mainspring. I gained smoothness, lighter trigger pull, and a very slightly tighter velocity spread (only 4.5 fps from highest to lowest). How can this cheap spring gun have this kind of shot-to-shot velocity consistency? I wish I had some kind of wisdom to impart about this, but I'm just as surprised.

One more post to go on this gun. Gotta take care of that muzzle.


Anonymous said...

Hello Derrick, from what I understand, the application of lubricant used in motorcycle paid off, cool! I believe she may become even more soft and quiet if you replaced the original piston seal for a polyurethane ... Once again he excellent work, man you are becoming master of this air gun, congrats! Sincerely, JV ADSUMUS.

derrick38 said...

I considered a new seal, but this one sure isn't broken. I think the seal is a polyurethane. Look at that consistency--is it worth the risk of losing all that to change it?
The B3-1 is pretty quiet--it's only a 550 fps gun after all. I'm sort of embarrassed that I've got so many blog posts about this gun. I think I've written more about this gun than most anything else I've owned. Of course, most of that has to do with this particular gun having so many issues.
Remember the idea here is to see me butcher perfectly good airguns. said...

Dear Derrick, I have learned enough about the changes you have made in their B3-1.This making changes in my well, installed a muzzle break and pistol grip Archer and now I'm thinking of changing the spring by a stronger and sleeve for a polyurethane (those with yellow hole for the screw in the center). I honestly do not know why I have invested in this gun, pressure must be crazy! Here in Brazil that type of rifle is still not widespread and is found very little information about it .You're being modest, has made great changes and have learned a lot from their good ideas! Congratulations for the work, soon I'll post the changes I have in mind, but first I need to get a new spring ... comprensor Sincerely ADSUMUS JV.

derrick38 said...


Obrigado. You are too kind. Mantenha-me informado on your B3-1.
Good luck!

Unknown said...
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Unknown said...

it was a bit pointless re drilling the end cap to fit a button head ! the end cap has a stock attachment bolt through it, it won't be going anywhere. I've replaced the original pin with a stainless steel clevis pin. its a lot easier to remove and replace.