If you have read my review on the Cybergun S&W M&P 9c, you’ll know that I like it a lot. It’s a replica I shoot often and it gives consistent groups at six yards (the range at which I most often shoot). However, after a few hundred shots it shoots just over 2″ low using the recommended 0.2g BBs at that range. Now, I find that very irritating. I prefer a pistol that shoots high to one that shoots low, so I wondered if it might be possible to do something about it? The M&P 9c doesn’t have adjustable sights, I can’t easily modify the sights to improve things and I don’t want to fit a laser or some form of optical sight. So why not adjust the hop-up I hear you say? Well, in my experience with GBB pistols, hop-up makes little difference at six yards. It’s not completely ineffective, but I have found that adjusting hop-up will change the point of impact by only ½” or so at this range. Useful for fine-tuning, but not to correct an error of over 2″.
All the targets shown in this article were downloaded from the Umarex Boys Club forum (http://umarexboysclubforum.myfineforum.org/index.php), though I filled in the centre circle in black, just to give a clear and consistent aim point for testing.
Establishing a baseline
There is no point in trying to improve the accuracy of your replica until it is giving consistent results. A combination of the pistol wearing in and you getting used to it is likely to change where your shots are striking over the first few hundred shots. I have now used my S&W M&P 9c enough to be confident that, with 0.2g BBs, it shoots just over two inches low and a hair to the right at six yards. For all testing, I used the pistol rested (to remove as far as possible errors due to my technique) and for each test I fired a string of ten shots with a fresh fill of gas. Although I show only one picture of each set of results below, I shot many, many more in the course of researching this article.
Ten shots, six yards, rested, 0.2g BBs. Group is 2″ and the centre of the group is just over 2″ below the point of aim (centre of the black circle)
So, I have established the problem. But what’s the solution? The first thing to consider is BB weight. The recommended BB for this replica is 0.2g. In general, heavier BBs will lower the point of impact while lighter BBs will raise it. So, the first thing to try is 0.12g BBs to see if that will raise the point of impact.
Ten shots, six yards, rested, 0.12g BBs. Group is 3.75″ and the centre of the group is approximately 1½” below the point of aim (centre of the black circle)
Sure enough, using the lighter BBs has raised the centre of the group by around ½”, but the grouping is much worse. It’s clear that I won’t be using 0.12g BBs in this pistol. Just to check, I also try heavier 0.25g BBs.
Ten shots, six yards, rested, 0.25g BBs. Group is under 2″ but the centre of the group is almost 3″ below the point of aim (centre of the black circle)
As expected, the heavier BBs hit the target even lower, around 3″ from the point of aim. Grouping is good, but using different BB weights doesn’t seem to be the answer here.
So, what is the answer?
Next, time to have a look at the pistol and see if we can find anything that might be causing the problem. It doesn’t take long to find that the inner barrel is a very loose fit inside the outer barrel. With the pistol held level, the inner barrel is actually drooping slightly, which may be contributing to shooting low. The reason is easy to see.
The brass inner barrel is fitted with an O ring near the muzzle end. This is generally a good idea, because it helps to stabilise the inner barrel inside the outer barrel. Unfortunately, it isn’t working at all here.
With the inner barrel in place, the O ring is actually within the wider, threaded section of the outer barrel and isn’t making contact with the outer barrel at all. Hopefully the diagram below explains the problem (sizes and gaps are obviously exaggerated for clarity).
What can you do about it? A suppressor which screwed into the threaded part of the outer barrel might do the trick. If I had access to a lathe, I’d be tempted to cut a new O ring groove on the inner barrel about 15mm to the rear of the existing groove. This would then seat the O ring within the narrower (unthreaded) part of the outer barrel. However, I don’t have a lathe or a suppressor, so I need a simpler solution. The easiest is to add some packing to the bottom of the inside of the outer barrel, which will make the inner barrel sit straighter. After some experimentation, I used two layers of packing, each made up of a 3mm wide strip of duct tape approximately 40mm long, stuck inside the bottom of the outer barrel. Depending on what you use as packing you may need more or fewer layers. You’re aiming to have the inner barrel still able to move freely inside the outer barrel, but to be supported at the bottom. It’s a little fiddly to place the packing precisely, but it’s worth taking time to get it straight as if it’s off to one side, it will push the barrel off-centre.
With the packing in place, I tried shooting some more, concentrating on 0.2g BBs.
Ten shots, six yards, rested, 0.2g BBs, with barrel packing in place. Group is over 2″ but is centred much closer to the point of aim
OK, this is much better. It’s now time to start fine tuning by adjusting the hop-up. Moving one increment at a time, I tested until I was able to produce reasonable groups which are centred for elevation precisely on the point of aim.
Ten shots, six yards, rested, 0.2g BBs, with barrel packing in place and hop-up adjusted. Excluding the flyer on the right, the group is under 2″ and is centred for elevation on the point of aim
Well, that was easy! With a minimum of effort, I have been able to improve the accuracy of my Cybergun S&W M&P 9c. With a three inch barrel it’s never going to be a tack-driver, but at least now I’m consistently producing groups right on the point of aim. The additional packing inside the outer barrel can’t be seen at all, and after around 100 shots is showing no signs of coming loose or affecting the performance of the pistol.
A poor fit between inner and outer barrels is a common issue on GBB pistols. Sometimes it doesn’t cause major problems, though it can contribute to inconsistent grouping. In the case of the S&W M&P 9c, it seems to have been the cause of the pistol shooting low and this simple fix it has increased my enjoyment of this replica.
You can buy the S&W M&P 9c at Pyramid Air here.