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Alstone · Moderator & Site Supporter

Managed to get a shot string finished today, I was looking for 500fps average and got 506 with the power adjuster turned right down so pleased with that, turned right up I was getting 565 so plenty in reserve.

One thing I’m not sure about is the string started in the 480s crept up to the low 500s then dropped back towards the end, why it started low I’m not sure, maybe if rsterne is about can give me some idea ? The sweet spot seems to be around 500fps with most of the shots within 20 fps of each other, and I did get 77 usable shots out of one cartridge.

Slavia Cheers for the idea for cutting the grips should make it a lot easier, any idea how you do diamond hatching that looks neat and if so what tool do I need? One other thing I was going to ask you a while back you posted a photo of a modded trigger for a 22xx, well the small icon photo is still there but no link to the full size photo, do you still have a copy you can post.

Mar nice idea but the cost of shipping would be more than a new one over there.

Al

rsterne · Moderator

The shape of that shot string would suggest to me that as the CO2 cools and the pressure drops the velocity increases (the opposite of CO2s usual performance).... That would indicate that the hammer strike is too light.... Think of it like the bell-curve in a PCP.... Even the spike in velocity at the end (before the final drop) would indicate the same thing.... as the pressure declines (as the last of the liquid CO2 is evaporating) the velocity goes up until it really starts to drop when the cartridge is nearly empty (ie no liquid left).... Rolling Eyes

If you do another shot string with the hammer at maximum, I'm betting it will be "normal" for CO2.... initially high, dropping as the gun cools, then a plateau, then a final plunge.... If that is the case, then it's just a matter of finding a setting in between where the string is virtually flat from the beginning to the final plunge.... Cool

When I am testing CO2 guns I actually count out 30 seconds between shots to remove the cooling variable as much as possible from the results.... You will still get the initial cooling, but it stabilizes better.... The peak in the middle of your shot string may have been nothing more than you firing more rapidly during that section.... Once you find the ideal hammer setting, the rate of fire will hardly effect the velocity at all.... What will happen is that the faster you fire (or the lower the ambient temperature), the fewer shots you will get.... Shocked

If when you find the balance point for the hammer spring setting you are over your 6 FPE limit.... then make up a smaller transfer port.... or use one of Crosman's detuning tricks and put a very thin washer under the seal with a smaller hole in it.... You may have to tweak the hammer setting a bit to get it perfect again.... Once on the plateau, your shots are actually within about a 15 fps range, so that shows a lot of promise right there.... The optimum setting may also change slightly with pellet weight, I don't know.... Wink

Bob

Alstone · Moderator & Site Supporter

Cheers Bob for the pointers on Co2 pressures I can go to 560 fps with a 7.2 grain which leaves me with a decent margin for safety, so I do have a bit to play with. Cool

The temperature was 60*F and I just estimated the dwell between shots so that could account for the erratic figures, also I turned the power down to maximise the shot count, I’ll be a bit more careful for the next string and turn the power up to maximum, which should be the same as when new, as for the shot count that is not important a but a stabilised fps would be nice. Smile

Al

Slavia · Moderator

Alstone · Moderator & Site Supporter

Thanks Slavia, first sorry for making you loose the ball out of the safety, also the first thing I did when separating the trigger unit from the action, only I didn’t know I had lost anything until I put it back together and wondered why the safety was wobbling around.

The first trigger unit seems complicated and I’m not sure how the second stage works, so I’ll leave that alone.

The second custom sear looks promising I may make one and see how it goes.

As for checkering, I have seen tools advertised in the State's but taken no interest until now, whatever you buy from Brownells cost $35.00 for shipping, as far as I can make out is the they are not available over here.

So it lucks like I’ll have to have a go at making a double cutter for diamond checkering.

I got this 2240 for something to do over the winter but the way it’s going it’ll be two winters.

This is where I am at the moment, I drilled out the pivot hole in the trigger to 1/4" and fitted a bush the correct width, this stopped it wobbling also fitted a trigger shoe and spring guide, this makes the whole lot smoother.

Al

Slavia · Moderator

Nice job on the safety cross-bolt, too.

I didn't go as far as 1/4", but I did bore out the pivot points to slightly oversized. I made the replacement pins from the smooth shaft of the same drill that made the holes.

Now is the time for the overtravel limiter:

Alstone · Moderator & Site Supporter

Slavia · Moderator

Alstone · Moderator & Site Supporter

rsterne · Moderator

Alstone · Moderator & Site Supporter

To late Bob I have allready fitted an adjusting screw. I did see a write up on your idea but couldn't find it at the time. But like you say extending the nylon saddle would have done the job anyway Rolling Eyes

Had another play with the crony trying to improve the shot string, The temperature was low at 50*F so using 7.2 grain .177 Hobbys I shot 5 Co2 cartridges playing around with the power adjuster as recommended by you until I got a decent setting also 30 seconds between shots, I was pleased with this one. Smile

Put the trigger stop on today Slavia, it does make a difference. Thumb Up!

Al

Slavia · Moderator

How close are your tolerances between the barrel and the brass breech? I've read about guys dispensing with the barrel band when they have metal breeches (free floated).

Alstone · Moderator & Site Supporter

rsterne · Moderator

Excellent string, Al.... It will be interesting to see what results you get at different temperatures.... You will definitely get more shots at higher temps.... I tuned for the flattest string at 60*F.... At 46*F the velocity tailed off just slightly towards the end of the string.... and at 75*F it had a slight increase at the end (from a ~10 fps lower midrange plateau)....

When you consider all the shots between 46*F and 75* F were within about a 35 fps range.... whereas a stock gun had over 100 fps variation over that same temperature range (and less than half the shots).... tuning for the "self-regulating" range made a HUGE difference.... Wink

When you consider that the pressure of CO2 at 40*F is only about 600 psi while at 75*F it is about 900 psi.... it's pretty cool to be able to accomplish this.... Cool

Bob

Slavia · Moderator