After getting my BR99 modified to the level I wanted AND running reliably (with birdshot and slug cartridges) I coincidentally shot a match which used buckshot and that showed up that the magazines with standard springs did not like long cartridges. Effectively the bolt return spring ran out of steam due to the friction of the hard magazine spring and extra length of the cartridges I was using.
It seemed quite common on the US forums to chop mag springs to get over this (although these were MKA1919 springs). With no point of reference I decided to cut my mag springs…. Initially I just cut off one coil and this seemed to make next to no difference so I went to two. I tested this for one practice match and the gun works fine with normal cartridges but was still a bit sticky with buckshot. (I only fired 20 buckshot cartridges so not exactly a thorough test mind). That being the case I went ahead and cut off another coil (total 3). Again I tested this and it seemed to do the trick. It also allowed me to put 11 cartridges in magazine, not that I ever did that as the whole point of the exercise was to easy tension on the carts, not increase capacity (further IPSC rules prevent you having more than 10 carts in a mag at the start of a stage anyway). After a couple more tests and a few matches I cut 4 magazines by 3 coils.
3 coils cut;
The gun was happily running for a good 3-4 matches but then started to really badly jam, typically the jamming started on the first big PSG match of this years calender and has completely buggered any chance of a decent placement this year
;First jam stage @ 0:43 Second straight after @ 1:29
Note the jam manifests itself by not only jamming the action, but also locking the magazine into the gun which takes some heavy-handedness to remove
. It was noted on all occasions that the jam occurred on the second from last cartridge.After finally getting around to some proper testing I’ve discovered its apparently due to the magazine spring not pushing the cartridge up fast enough to coincide the timing of the bolt and the the way the cartridge rim is supposed to work with the magazine lips.
It’s a lot harder to explain in words than it is through a live demonstration. Basically as the cartridge is stripped from the mag, the mag spring should push the cartridge rim up clear of the mag lips before the rim gets to the front section of the magazine. With my now worn and cut springs this just isn’t happening fast enough and the cartridge rim is getting wedged into the front part of the magazine. This means that the nose of the cartridge is in the chamber, but the rim is stuck in the magazine, which is why the mag locks into the gun when the jam occurs, and why you can’t just bang the cartridge in using the cocking handle.
Sort of explaination/demo;
Slow-mo normal cycle;
Slow-mo jam;
Fortunately I’ve only cut the 3 coils off the 4 magazines I mainly use for competitions. I also carry 2 spares with me but have only taken 1.5 coils off them, and I have 2 more in the house that I’ve not touched at all. As a double check I’m transplanting the untouched/1.5 coils removed springs into the 4 comp mags and testing them on Sunday. If all goes well it looks like I’m going to need to buy 4 replacement springs, or perhaps put some blocks in the bottom of the magazines to get the needed spring pressure back. So once you're moved in properly Overpaa, i'd appreciate it you could chase those springs up!
CONCLUSION: Don't mess with mag springs!! If you get issues with long cartridges, buy shorter ones!!!! I've used RC4 buskshot in unchopped mags and they work fine.
Just thought I’d post this in case someone else is thinking of getting the Dremel out soon…
Oh and I managed to capture one of those freaky chamber flame outs you only seem to get with gas operated guns
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