Well, let's see if I can get the old photobucket kicking. I made the heavy vs light video. It is semi-scientific, and can be debated for accuracy.

If I wasn't lazy, (or if I would have thought of it at the time....) I should have used the same gun but switched the bolts.
It's possible one spring has more tension than the other, or the bolt slides better in one receiver than the other, etc.

BUT..... the fact the lighter bolt actually travelled further (I'm guessing around 2" more) than the heavy bolt, YET the heavy bolt took more time to travel the shorter distance it travelled, should say something too.

By the distance the heavy bolt travelled, I would say adding more weight would start creating problems. I'll have to find my scale and weigh each bolt and report back.

Heavy bolt: 168 g
stock: 145 g

No damage yet....

In the back of my mind I know the designers of these guns at Marushin were no fools, and I have to wonder what not-leaving-well-enough-alone can do. I am a notorious tinkerer and have a "even the best designs can be improved" philosophy.. hehe There's my struggle...

I am in the middle of another test to clarify the results in this video. I've already shot a video of the heavy bolt firing 3 rounds in full auto. (both MP40s are working perfectly now! ) I figured there were too many what-if's by only shooting single rounds and in two separate guns. Now that I shot the heavy bolt MP40 footage, I will put the stock bolt in the same gun, shoot the three rounds and that should clear up some of the questions. I hope I'm not going to start boring people with all these drawn out tests hehe.

I've confused myself regarding slowing down the videos multiple times, and how to convert the figures back to real time numbers. It's not so much the math, but whether WMM (Win Mov. Maker) converts the footage accurately 2x, 4x, 8x etc. Perhaps you can help clear the confusion..

Real time is 30 FPS
I film at 300, so I'm starting out 10x normal speed
Then I half-speed it three instances: 20x -- 40x -- 80x
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Now, let's say we take the cycle time of 12.80 (at 80x speed-- IF 80 is the correct number at all)
Divide 12.80 by 80= .16 seconds
That is where I have to wonder if my numbers all jive or not.
.16 seconds seems too quick.

I need to film a stopwatch to check my figures I think.

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Yes, it's wild seeing how everything seems to flop around. The barrel is wagging, the receiver seems to be flexing in the middle, and the magazine looks like a clanger on a bell! I thought I had that pretty snug too!
I saw a video on a guy shooting a pellet gun with a steel barrel, and that barrel wagged around quite a bit.

Ok, did the stopwatch calibration test. I won't bore you with the video from it. lol
I can tell you it is more exciting than my "Watching Grass Grow" mini-series.


At 300 FPS, it took 50 seconds for the second hand to move 5 seconds. 10x is correct

I "slow down, half'd" it 3 times. So the equation is 10 x 2 x 2 x 2= 80
It took 400 seconds for the second hand to move 5 seconds.
So it seems the camera is accurate, and WMM is actually doubling the time correctly for each "slow down, half".

400 divided by 80= 5 seconds real time.
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Sometime I will try to take a slow motion video, and then speed it up to show what it looks in real time.
I now see that I was off a little. At 10x, if I double the speed THREE times, I end up at 1.25x and not 1x.
Close enough I guess.

I'm guessing that you guys calculate your cyclic rate by seeing how long it takes to fire 30 rounds.
If it takes 10 seconds, your ROF is 180 RPM.

60 divided by time it takes to fire x number of rounds fired.

Does that seem correct?

Not the huge numbers we wanted to see, but a change nonetheless.

Heavier Bolt Final Video

Excellent tests and even better to see what is going on and I reckon you calculations are spot on.

8ace

In the first video I said I added "a couple ounces", but it was only 0.8 ounces. I think we all knew more weight would slow the ROF down though. The change is pretty minor and would be difficult to notice in your gun I think. I've seen some videos of real MP40s and it seems their ROF is around 3-400 RPM. The information I found said they fire at 500, so I don't know what to believe.