Sunday, 13 October 2013

Testing the SMK B45-3 for Improvement.




Now the .177 SMK multi pump is up and running i find myself getting to really like it, and as it's a pretty light rifle i usually take it as a 2nd rifle when i go down the woods for practice. I know it's not the nicest looking rifle by a long shot, but once you get to know it;s many little faults you can compensate.

SMK multi pump as i like it.

It can come apart and be put back together in 20 minutes, so replacing things like inlet valve seals is no problem. Also the magazine works if you load and feed twisting it down and away from the loading port, though it still doesn't like some pellets all the same.

Start loading with red marker in this position so it lets me know when to stop when it reaches the barrel.



2nd pellet loads turning the magazine down and around, avoiding the ball bearing between the barrel and loading port.

Solid harder pellets like Crosmans work well, and the Premier heavies at 10.9 gr and only just fitting never fail. Air Arms diabolo's with their soft skirts deform easily, and H&N Field Trophies are a happy compramise.

When i tested the rifle with the chronoscope i discovered that after 8 pumps the power didn't go any higher, and that it stayed nicely within the UK legal limit of 12 ft/lb.

 
.177 pellets currently in favour.

At 8 pumps.

Crosman Premier Heavies   10.9gr         11.8 ft/lb

Air Arms Diabolo's               8.4gr         10.4 ft/lb

H&N Field Target Trophies  8.65gr         10.5 ft/lb

H&N Barracuda Power       10.19gr         10.8 ft/lb

It doesn't like wadcutters because the flat nose prevents them from loading well, so i didn't bother testing them at all. But on a string of 10 shots each there was no more than 12 FPS variation, and only 8 FPS variation with the Crosman Heavies. This was one of the reasons for being forgiving with this air rifle.

Pellet on the left has the tip worn, this is caused by the tight fit in the magazine.

But the main reason i like this rifle is that it is pretty accurate for what it is, and i can easily hit the hole in my field target rat at 35 to 40 yards. With it having an exhaust valve the trigger is fairly heavy on 8 pumps, but if i squeeze it at the tip it's a lot lighter. The trigger is also the sear and is pivoted at the corner of a rough L shape, remembering how levers work this could easily be redesigned to be lighter. The trigger blade even drops down through a fair bit of stock so there is room to design a trigger with a couple of sears in it, there are plenty of proven designs i could base this on.

Direct trigger and sear, fairly heavy pull at 8 pumps.

The elevation screw on the rear open sights had snapped off, but the two windage grub screws either side of the sight blade will still hold any adjustments made. 

Adjusting grub screws for windage, elevation is achieved by loading thin washers then tighten the grub screws.

 With open the sight's square notch and post it is accurate, however there is a small dove tail on the action for a scope. First i tried the generic 4x32 scope and was very pleased with the results, this only just fitted on as the rear open sight stops any further forward positioning. 

The 4x32 scope fits nicely and is easy to shoot with.

When i tried the AGS 3-9x40 i had to set it back a bit on the dovetails, but it still fitted and accuracy improved no end. 

The 3-9x40 AGS scope can't be moved forward because of the rear sight.

To make this better i would either need higher mounts, move or remove the rear open sights, or extend the shoulder stock by two inches.

This is the butt  being too short if i relax my neck when sighting with the AGS scope.

With a scope mounted on the multi pump i am limited in places to hold the rifle when operating the pump, i can do 8 pumps holding the stock at the rear of the action. Less tiring is supporting the rifle with the side of my palm on the rear sights, though this digs into my hand if i'm taking a lot of shots. If i could extend the pump arm in some way, pumping would be easier and i could support the rifle at the back of the action.

'Ee by gum', it's still a fun little air rifle though.

One way of sorting out most of these problems would be to make a new stock for it, this is something i have often thought about doing. It wouldn't have to be anything fancy, and this air rifle would make the perfect donor for a first attempt. The stock as it is at the moment is pretty naff so i'm sure i could improve upon it, after all i have plenty of bits and bobs in my shed for this project.

Looks like it's time for taking a shufty through the internet for some insperation, there's nothing like a good bit of pluagerism to achieve ones goals.

TTFN

Best wishes, Wing Commander Sir Nigel Tetlington -Smythe

4 comments:

  1. Very interesting Pumper Sir Nigel. The magazine design is interesting, the way it encircles the pump tube. I would like to see more of the internal workings of this air gun. I'll be following your Blog.

    ReplyDelete
  2. Thanks Rick, there will be more on this little air rifle so i will be able to show more detail. The valve body is machined into the compression tube and it keeps chewing up seals on the air inlet valve, but as it only takes 5 minutes to strip that end i will keep on till i find a design that works. This it seems is a problem with all these SMK's, research tells me they were sold with spares and instructions on how to take them apart in Chinese and diagram form.

    ReplyDelete
  3. I have one of these from many years ago in my mis-spent youth. A short cylinder of soft steel/iron in the mechanism kept spreading on one end and I got fed up with filing it back to the right shape. It's been rusting quietly in the loft for 20 years but I'd like to have a go at restoring it now. I look forward to your next article on tinkering with this interesting gun. BTW, why not just fit a ventilated recoil pad to increase the stock length? You could get an extra 3 or 4 cm this way.

    ReplyDelete
  4. Good idea but i built a new stock for it instead, there is a blog entry somewhere around here about it. Heavily influenced by the Air Arms s410 which i eventually got one of recently.

    ReplyDelete