Sunday, September 13, 2009

BAM B3-1 Tune Up Part 1

Nick sent this to me several months ago in a box that must have been wrapped in about 1200 feet of clear packing tape. I'm still not sure if he was trying to make the box airtight or protect me from the interior contents. He remains silent on that question. Inside I found an AK-47 lookalike BAM XS-B3-1 air rifle from Xisico.



Depress the button at the rear of the receiver...

And the stock pivots to the right and locks securely in place.



It cocks via a sidelever located on the right side. Push the latch downward and pull completely to the rear. The entire compression chamber retracts in the same manner as the just slightly more upscale HW-77/97s and TX-200's.

Pellets load directly into the exposed breech. The first pellet loaded fell right through the barrel to the ground. What? As did the second. It finally occurred to me that this was a .22 cal and not a .177. Takes me a while sometimes...

Anyway, before I tear into it and screw it all up, I tried thinking ahead for a change and shot it over the chrony with .22 cal RWS Hobbys.
Here's the shot string:
555.2 fps
552.9
555.0
554.3
555.1
553.0
557.6
558.6
558.1
559.7... The max velocity spread was 6.8 fps for 10 shots. ??? I wondered momentarily if Nick or another previous owner had tuned the powerplant, but no, the shot cycle was too brutal. The gun was gritty, rough, and noisy in no particular order. Then there was the vibration and recoil--all the more pronounced because of the steel buttplate. Oddly, the velocity numbers were not only very consistent, they're also anywhere from 50 to 140 fps faster than the gun is rated depending on where you find the data.

The single-stage trigger pull weight varied from 8.5 to 9.5 pounds. It builds, peaks, then drops almost a full pound as it goes through the rest of the travel before firing at an indiscriminate point. It is perhaps the worst trigger I've ever shot in an adult air gun. Oh, the front sight also pivots on the barrel with each shot and the rear sight moves randomly.

Of course, Nick also mentioned that every time he fired the gun he envisioned the steel endcap blasting out the back of the gun and into his skull. Yep, this one's a real confidence builder.

So I've got all that going for me. It's probably no big wonder that it stood in the corner next to the workbench for several months while I wondered what to do with it.

I've got the time to get to it now and I'd like to smooth out the powerplant, get the trigger under 5 pounds and come up with either a way to secure the sights or mount a low powered scope or dot sight. While I have no doubt that all this can be done, I may also throw it in the recycling bin out of sheer frustration.

So, uh, here we go.

I believe that I swapped the top allen bolt shown here when the gun arrived. It was probably a phillips head. Either way, it's an M6 x 1mm thread.

Here's the front stock securement screw and the screw cup previously blogged in August.

Removing the two bolts allows the action to separate from the receiver.

I decided to take the rear sight off as well. One bolt at the rear and a cross bolt up front. Comes right off, really.

The ramped sight blade is then pulled out.

Used a dental pick and fished out the trigger return spring. Note: The stock spring is likely black color. I previously swapped to this spring in an attempt to lighten the trigger pull as it was over 10 lbs. Note: it worked! I got the pull down to 9.5 lbs. Release the doves!

Unscrewed the pivot pin for the cocking lever.

The lever with some struggle, pulls out of the endcap at the rear and can then be unhooked from the sliding compression cylinder up front.

Like so.

Safety first. Dropped it into my medieval spring compressor.

Punched out the trigger pivot pin. This proved to be problematic. Both ends of the pin were slightly peened and the pin did not want to push through the holes in the sheet metal trigger blade. Eventually, it came out, but it was a real pain and left some lovely marks on the trigger blade.

Trigger pin, blade and the sear. I may get a replacement blade, maybe not. It cleaned up later and looks OK. More importantly, the sear is perfectly fine, so I'm not concerned.

Unhooked the spring on the anti-beartrap mechanism.

Stuck the end of a 10" crescent wrench into the endcap slot and gave it a few twists to loosen it. It's not threaded, just stuck. A couple twists and it popped loose.

There's the spring preload. Looks like under 2"of free travel. Pretty minimal.

Spring guide is a piece of rolled sheet metal. A tight, press-fit in the spring. Appears to be about an inch too short to properly support the spring. Note the spring is slightly canted at the left-most end.

Then the piston can be slid out.

Piston seal is unscarred. I'll check the seal against some others in my parts box. Maybe Crosman uses a gun with the same seal. That could be helpful info for sourcing a replacement.

The rear pin on the anti-beartrap mechanism was also peened on both ends. Punched it through slightly, then used a small file and removed the peen on exposed end. Reversed the direction on the punch and it came right out.

The anti-beartrap catch drops into a slot in the sliding compression chamber, holding it open when the cocking lever is pulled completely to the rear. Don't retract the cocking lever partially and attempt to load the gun--or you have defeated this safety feature.

There's the slot. It's pretty substantial, given the relatively low power the rifle generates.

With the rear pin removed, the lever can be pulled out of the notch freeing the compression chamber. The compression tube then slid right out.

Compression tube, piston, mainspring and the spring guide.

and the endcap, too...

Up top, a better pic of the slot the anti-beartrap lever sits in.
Middle, the piston has some scuffing from contact inside the compression tube.
Bottom, the spring has a slight cant.

Cocking notch on the piston is rough. This will get polished in an effort to smooth and lighten the trigger pull.

Sear goes inside the trigger blade like this.

Sort of how it all interacts. Trigger sear holds the notch on the piston rearward when cocked. The spring guide and spring will be installed inside the piston which sits inside the silver compression tube. Ah, I'm getting ahead of myself. These parts all need some clean up and fitting first.

Removed the piston seal. This was a surprise that the end of the piston was a bolted on flange. I expected it to be turned as one piece. The seal was a very loose fit on the piston. I'm considering tightening the fit.

Polished the ends of the piston body on a buffing wheel. Also polished the cocking notch for the sear as well as the sear itself.

The rough inside edge of the square hole in the compression tube could potentially damage the piston seal on reassembly.

A cratex rubberized wheel on a Dremel tool made the burr removal effortless. Be careful to not remove metal any deeper in the compression tube.

More to come in a few days...

15 comments:

Carlos said...

Was going through your B3-1 post. Try a spring and seal for the TX-200. I use one mine about 8 years ago.

Anonymous said...

The culprit on such wonderful replica air rifle is that there is no sight rails on it. The sights are mounted with two silly screws, mounting a scope or red dot is useless as it is to flimsy for the two screws to hold them in place under recoil.

Besides that this rifle is great, very similar to the XS-B8-1, in fact even better as the B8-1 front barrel grip is plastic.

Anonymous said...

i welded mt rail to the gun, has held zero for 11 yrs, otherwise , yes, the rail is useless.

jimmy62alan said...

Hi there, I realy want one of these quirky b3-1's the write ups have me wanting one everytime I read one. Its been said that the bam is a low powered gun but a bit of tweaking and the uk power limit of under 12 ft lbs is very much called for if any one is needing any tuning tips drop me a line at my email address boyle1962@yahoo.co.uk
If theres a Bam .22 for sale please contact me as well.
One thing I would mention is that no ones mentioned fitting s piston sleeve which does transform the loading and firing could be worth a go guys.
cheers for now
ALAN
Sheffield/England

derrick38 said...

Alan,
Not sure I'm following about a sleeve transforming the loading and firing? Sleeving the piston really has two uses. Primarily, its a band-aid when the desired tolerance fit doesn't exist between the spring and piston. On some guns it also can eliminate contact noise between the cocking lever and mainspring. Neither was an issue on this gun.

jimmy62alan said...

Hi Derrick, as I mentioned I havent got a BAM yet but still looking but I have got a similar loading chinese
rifle I pickup some time ago and fitted the sleeve to that and it did improve things, as well as giving the gun an upgrade in power with further tweaking it has became a nice little gun.
I can't wait to find a Bam I just love the look of it and can't to get my grubby paws on one lol.
ALAN

Anonymous said...

I have a bam b 3 for sale in .177 if anyone is interested email me at maddoghoughton@hotmail.co.uk
Thank
Matt

Colin Johnston. E-mail- colinjohnston1961@me.com said...

I have just acquired a BAM XS3 and I want to renew the mainspring and seal. Can anyone tell me where I can buy these parts?

Colin Johnston. E-mail- colinjohnston1961@me.com said...

Does anyone know what the published specs are for the BAM XS-B8-1. I am about to strip mine and I'd like to know what power I can expect to obtain after renewing the mainspring and seals and polish up the compression chamber. Cheers guys!

Anonymous said...

Archer Airguns is where I got mine

Skillet

Anonymous said...

mine was stolen a few months ago and I cant find anywhere to order one, if you have one you will sale me please email messygiuseppe@yahoo.com I am in the U.S in Oregon

Anonymous said...

mrodair has recently gotten a shipment of the newest prodution of this gun which claims better internals.. they have .177 and .22

mike oxbig said...

mrodair is either in prison or dead. I've tried to contact him a few times via his website using his email address, but I've had no response.

Anonymous said...

Hello Congratulations on the site, I have a 5.5 k xisico here with the name of AR + b5, installed a spring Hatsan 125 and installed a locking pin thicker, the shot was almost as strong as my rifle nitro six cbc. (80 kg gasram) remains to be seen if the trigger myself and the rest of the rifle is not broken.

Anonymous said...

Hello Derrick38 ; I read a comment on the exchange spring of AR + by Hatsan spring 125. I decided to take the test to be able to increase the power . The Spring Hatsan 125 has greater width , so it does not enter the piston ! Dismounted mine and was a waste of time ... Now I have to have manufactured a stronger spring personalized ... I wonder what was the magic that this fellow did? Thank you for your attention and good shots ! Adsumus Brazil .