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  1. #1
    User
    Join Date
    Aug 2015
    Location
    Cape Town
    Posts
    159

    Default BAM B40 Upgrades

    In July 2016 I acquired a BAM B40 which had a damaged barrel. There were flat spots inside the barrel and the rifling was damaged. I decided to turn it into a project rifle and replace the barrel and at the same time upgrade a few other parts. With only a portion of the upgrades done I have been using the rifle as my primary HFT rifle and I have been very happy with the results so far. I have already seen a big improvement. I have won a few league shoots with the rifle and it keeps up with the high end springers fairly easily.

    The project rifle is a BAM B40 in .177 caliber. As most of you know it is a copy of the Air Arms TX200. Most of the TX200 parts are a straight fit in the B40 without any modifications required. The build quality of the BAM isn’t nearly as good as that of the TX200 but it still makes a very good platform to start from. When I got the rifle it was shooting 867 fps average using 8.44 grain JSB 4.52mm pellets at sea level.

    Here are some photos of the rifle before I starting working on it.









    After shopping around a bit I found a brand new HW100 Carbine barrel at Rosenthals. The old barrel is held in place with a lock nut and some epoxy. To remove the barrel the epoxy needs to be heated enough to let go. In this case it had to be heated quite a lot and the heating ended up damaging the bluing so I had to re-coat the rifle as part of the upgrades.


    This is the barrel as it arrived from Rosenthals




    Nick (Scout Sniper on the forum) machined and threaded the new barrel to fit the B40 action. In this photo the original shroud was already back in place.



    After the new barrel was fitted the rifle averaged 850fps with the 8.44 grain 4.52mm JSB pellets. My plan was always to drop the power output to below 12fpe so that I could use it for HFT. The original stroke length on the B40 is 96mm which is very long. From the little past experience I have of dropping the power on long stroke springers I know that the rifle will become very hold sensitive when the power is dropped to 12fpe levels. That is also one of the reason why so many TX200 MK3 competition shooters short stroke their TX200's. Therefor I decided to short stroke the rifle when dropping the power. I settled on a TinBum short stroke adapter and also decided to replace the piston seal with a 25mm Weihrauch piston seal. This shortened the stroke from 96mm to 83mm.


    TinBum kit took 1 month to arrive from the UK from date of order. Was small enough that it was sent via normal post directly to my post box.



    Before installing the kit I had to sort out the damage to the bluing and instead of having the rifle re-blued I decided to go with a gun coat instead. I just wanted to try something different. I sent the gun to Powerkote in Montague Gardens in Cape Town.

    I can't find any photo's of the rifle before sending it in for coating but this is what it looked like when it came back.




    Piston fitted with the TinBum short stroke adapter and the Weihrauch 25mm piston seal.




    The original top hat is a heavy steel top hat weighing 25 grams and it was also very thick adding 12mm of pre-load. The steel top hat also wasn't a very good fit. I removed the top hat and even though I haven't done so yet I plan on replacing the top hat with a better fitting Delrin top hat. The new short stroke adapter and piston seal added 14 grams to the weight of the piston assembly so it was a nett loss of 11 grams overall. I will also be replacing the steel rear spring guide with a better fitting derlin spring guide. I didn't do any of this initially as the waiting period at the airgunsmiths I usually use was to long and I was impatient. I wanted to get the gun back together and see how the consistency was and I wanted to put some lead downrange so the new piston seal could break in so to speak.

    After assembly.




    After assembly I only managed to shoot 3 shots as a quick test and the results were 760 fps, 757 fps and 760 fps. I knew I couldn’t judge the consistency over 3 shots so the first chance I got I shot a 16 shot string with a low of 750 fps and a high of 773 fps giving me a ES of 23 fps. This is what the string looked like:

    758
    752
    770
    750
    754
    762
    762
    773
    760
    751
    750
    756
    755
    772
    763
    755

    I wasn’t happy with that but the rifle was dieseling a bit and I knew once the new piston sealed settled and the rifle stopped dieseling the consistency would improve. I am not 100% sure how many pellets I put through the rifle after that but at that stage I was actively shooting HFT with the rifle and practising with it. At one of the HFT shoots I manged to do another 6 shot string and it looked like this:

    755
    755
    759
    757
    756
    761

    At this point the rifle was no longer dieseling at all and since that string every string I have shot and every chronograph test before HFT league shoots have yielded a 4 – 8 fps spread. That is on par with my HW97 in terms of consistency.

    The rifle is also deadly accurate with the new HW100 barrel and it is easy to shoot accurately as well. I can’t see a difference in accuracy between my HW97 and the B40 shooting at 30 and 40m. Sometimes I shoot better with the HW97 and sometimes I shoot better with the B40. It all depends on how I am shooting on any given day.

    I recently bought a new HFT scope for my HW97 so the HW97 will soon do duty as my primary HFT gun which means I will have all the time I need to have the parts made to complete the B40 upgrades. They would be as follows:
    • Delrin top hat.
    • Delrin rear spring guide.
    • PTFE piston sleeve.
    • Button the comp tube. Does nothing for performance but it does smooth out the cocking cycle and the cocking cycle isn't as smooth on the B40 as I would like it to be.



    I will post another update when the remaining upgrade parts are ready to be fitted.

  2. #2
    User
    Join Date
    Sep 2014
    Location
    Johannesburg
    Posts
    238

    Default Re: BAM B40 Upgrades

    Very nice!

  3. #3
    User
    Join Date
    Aug 2015
    Location
    Cape Town
    Posts
    159

    Default Re: BAM B40 Upgrades

    The weather in CT was very nice yesterday so I shot a few groups with my HW97 en my B40, not necessarily to directly compare but more to fine tune their zero. However I did end up doing a bit of a comparison. I am not 100% sure how many groups I shot in total but it was about 10 or so combined between the two rifles. These are my 3 best groups out of the lot. Both rifles are capable of a lot better groups at these distances but I am not shooting particularly well of late. Even so, seeing as I shot both at the same time under the same conditions is still at least proves that the B40 can keep up with my tuned HW97 if I do my part.

    All groups are 5 shot groups shot with JSB Exact 8.44gn 4.52mm pellets. All groups were shot in the HFT prone position from a peg.

    HW97 @ 41m

    Click to see full size image

    BAM B40 @ 41m

    Click to see full size image

    BAM B40 @ 25m

    Click to see full size image

    I am a bit disappointed about pulling that one shot in the 41m group with the BAM B40. It could have been a much better group.

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