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billydjann

Member
Jun 3, 2015
461
13
New York, United States
Got my Mrod out today....177 Gen. 1 ----------- 10.5 boxed crossman.
The gun is shooting awful for some reason.... have no idea why.. used to shoot pretty good...
Yes... I went right in a cleaned it very well....seemed to be clean....

I can place 5 or so shots perfect then all of a sudden it goes all over the place.... no rhyme or reason for this ...
... I did not sort pellets....

Here is the chronagraph of the rifle.... 3 shots did not read..
I started off at 2800 psi...

Any ideas what I need to adjust.... or do...

 
Thank you very much... I appreciate the great advice...

I am shooting at 35 yards right now....
As you see I do have the chrony .... but I do not understand yet what to do with the info once gathered...

This will help me very much....this info will help tremendously 
I did size my pellets last night and they are all over the place... I am placing order today for some JSBs

 
Upvote 0
Apart from the spread and SD in velocity, you also ideally want a bell curve to your shots: From your fill pressure velocity should go up to a maximum and then come down again to the velocity you started at.
The difference between the bottoms and the top of the curve is up to your preference, I choose about 30 fps for my shooting.

To determine the curve you fill too much pressure in your gun, so that velocity will be too low due to high pressure. Then shoot over the chrony and record velocities until the velocity is too low again but now because the pressure is too low. For example 890 fps to 950 fps down to 890 fps again.
Then you look at the curve and choose what your preferred lowest velocity is, for example 920 fps for a maximum difference of 30 fps.

The estimated pressure where your velocity was first 920 fps is your fill pressure and the amount of shots past the peak to the second 920 fps is the amount of good shots per fill.

If you knew all this already then my apologies and quickly unread this post.
 
Upvote 0
 Alright you have a chrony, have you downloaded chairgun and looked at these numbers on the graphs/chart?
In .177 a 20fpe ES would be about where you want to be. Thinking you are filling to or near the recommended max psi you may want to back off the hammer spring tension or shorten the striker travel length, you could also adjust the transfer port screw but be gentle with that screw and use a new allen wrench, try getting it down to 900 or so.
Keep us posted.

John
 
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