MAS-50 pistol grip disintegration.

[Leonardj]

Have any collectors out there fortunate enough to have been able to add a MAS-50 to their collection found that the grips on the pistol are disintegrating, or shrinking at all?

I have what I believe to be one of the very rare "civilian" versions of this air pistol, and this problem may only be specific to the plastic used for the tortoiseshell grips, however, it may also affect the standard black grips.
When I originally purchased it, about 25 years ago, the grips were in excellent condition. This is the condition of the grips back in around 2013, when I took the pics that are now posted on the Vintage Airgun Gallery.

https://forum.vintageairgunsgallery....50-air-pistol/

Imagine my surprise when I opened the box today, and saw this.







I last had the gun out about a year ago, and just noticed very minor deformation of the bottom edge of the RH grip (similar to what is seen currently on the LH grip, but not as bad), but I had no idea that the disintegration as shown could happen within the span of just a few more months.

[Garvin]

Sad to see that, Len. Degrading like the early LP53s, it seems.

[ccdjg]

That is really bad news Len. I have checked my pistol, which has the standard issue black grip, and while there is no sign of cracking (yet) the grips do seem to have pulled back somewhat from the grip frame edges.



I also notice that my grip plates no longer lie flat against the frame and are bowed out slightly. Luckiy l had left the grip screws quite slack when I last took it apart, otherwise there could well have been some cracks developed.

I suspect (but can't be categoric) that the grips were hot pressed from a thermoplastic polymer which contained too much plasticiser (usually butyl phthalate). Over many years this evaporates and the plastic shrinks. The plasticiser loss is accelerated by contact with absorbent materials, so was the particularly bad side the one stored face down, perhaps on cloth?

I have encountered another problem with the MAS 50 - the black finish on the frame fades slowly when exposed to light. The frame is aluminium or aluminium alloy, so it was probably blacked by anodising and dyeing with an organic dye. Such dyes will fade in light, whereas traditional black on steel last forever. Some time ago I decided to display my pistol in a wall cabinet. After about three years later, I found that the exposed side was a significantly lighter black, almost grey, compared to the underside. So, it came off the wall and is now always kept in a drawer.

The MAS is a nice pistol with some interesting features, but was evidently not made with longevity in mind!

[Leonardj]

Sad to see that, Len. Degrading like the early LP53s, it seems.

Hi Danny,
Yes very much the same, except that the LP53 grips just break apart - no shrinkage noted, at least on my early LP53 grips.
These MAS grips have shrunken by over 0.060", which may well be what caused them to break up.

[Leonardj]

That is really bad news Len. I have checked my pistol, which has the standard issue black grip, and while there is no sign of cracking (yet) the grips do seem to have pulled back somewhat from the grip frame edges.

I also notice that my grip plates no longer lie flat against the frame and are bowed out slightly. Luckiy l had left the grip screws quite slack when I last took it apart, otherwise there could well have been some cracks developed.

I suspect (but can't be categoric) that the grips were hot pressed from a thermoplastic polymer which contained too much plasticiser (usually butyl phthalate). Over many years this evaporates and the plastic shrinks. The plasticiser loss is accelerated by contact with absorbent materials, so was the particularly bad side the one stored face down, perhaps on cloth?

I have encountered another problem with the MAS 50 - the black finish on the frame fades slowly when exposed to light. The frame is aluminium or aluminium alloy, so it was probably blacked by anodising and dyeing with an organic dye. Such dyes will fade in light, whereas traditional black on steel last forever. Some time ago I decided to display my pistol in a wall cabinet. After about three years later, I found that the exposed side was a significantly lighter black, almost grey, compared to the underside. So, it came off the wall and is now always kept in a drawer.

The MAS is a nice pistol with some interesting features, but was evidently not made with longevity in mind!

Hi John,
Yes, as can be seen in the pic of the bottom of the grip frame, my grips have "cupped" upwards away from the grip frame as well.

No, the bad side was actually facing up, with the LHS grip resting on the bottom of the cardboard storage box.

No, I was not aware that the anodizing on the frame was adversely affected by light. Thanks for that bit of info.

BTW, absolutely marvellous job you've done on your Webley Mercury pistol build. Congratulations on yet another masterpiece.

[trajectory]

That is really bad news Len. I have checked my pistol, which has the standard issue black grip, and while there is no sign of cracking (yet) the grips do seem to have pulled back somewhat from the grip frame edges.



I also notice that my grip plates no longer lie flat against the frame and are bowed out slightly. Luckiy l had left the grip screws quite slack when I last took it apart, otherwise there could well have been some cracks developed.

I suspect (but can't be categoric) that the grips were hot pressed from a thermoplastic polymer which contained too much plasticiser (usually butyl phthalate). Over many years this evaporates and the plastic shrinks. The plasticiser loss is accelerated by contact with absorbent materials, so was the particularly bad side the one stored face down, perhaps on cloth?

I have encountered another problem with the MAS 50 - the black finish on the frame fades slowly when exposed to light. The frame is aluminium or aluminium alloy, so it was probably blacked by anodising and dyeing with an organic dye. Such dyes will fade in light, whereas traditional black on steel last forever. Some time ago I decided to display my pistol in a wall cabinet. After about three years later, I found that the exposed side was a significantly lighter black, almost grey, compared to the underside. So, it came off the wall and is now always kept in a drawer.

The MAS is a nice pistol with some interesting features, but was evidently not made with longevity in mind!

I would tend to agree that the likely cause is "plasticiser migration" over time & perhaps the cracking is exaxerbated but pressure from the grip screws.... there is unfortunately nothing much that can be done to prevent the process but it might be possible to delay or slow it down slightly. For instance it might be worth considering removing the side plates from the pistol & wrapping them in cling film or putting them in a sealed bag with the air removed as much as possible. Storing away from light & especially excessive heat might help too. I think I would at least slacken the grip screws even if I didnt remove the grip plates but the effect might be marginal. Certainly over tightening would be risky. Its also possible that the colourant to give the veigning might contain a differant ratio of flexibiliser than the bulk material. If so you could speculate that there could be differential losses betweeen the two colours sstting up internal stresses which in turn could be made worse by the non unifom section of the grip ie a hole in it for the grip screw which could explain why the problem seems worse near it at the extremity of the grip.

A great pity.

[ptdunk]

That’s a shame...
Might be worth taking a silicone mould of a decent pair so some replacements can be cast for future use?
(If any decent grips have survived this long)

Tortoise shell effect would be tricky to replicate in resin but something close is probably possible.

Matt

[Geordie]

There's a chap on the AGF who is doing reproduction grips for old Webley and Acvoke pistols - it may be worth dropping him a line to see if something could be done to give your gun a new lease of life:

https://www./community/index.php?thr...acvoke.310593/