I hauled the mighty Anschütz 520 out this afternoon for its first proper test fire and after confirming zero at 25m which was good we moved to 45m and then onto 100m in the tunnel range.
Ammunition is CCI HP Subsonic and rifle is a Anschütz 520 with barrel cut to 12.5" with unknown sound moderator, Harris type bipod and a Simmons 2.5-10X 'scope. The results were not great with a 10 shot group after zeroing of 1.72MOA wide by 3.24MOA high. Obviously the next job is to try some another type of ammunition. It must be expanding and subsonic, other than that I have an open mind.
My question is regarding the vertical dispersion which is virtually twice that of the horizontal. Everything is tight and as it should be with the sound moderator correctly fitted and tight. My initial thought is it could be down to the bipod attachment as the barrel is not floated in anyway so the weight of the rifle might be causing some flex on the barrel leading to the verticals however I could be very wrong as I have not shot a short barrelled semi auto rimfire at 100m before.
Thoughts anyone?
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Could be lots of things... Try a back-to-back comparison without the moderator to eliminate any issues there before you go too far into the investigation :)
I ran out of time and ammunition so will return with a range of different types of ammunition and a couple more sound mods and do some more extensive testing. I did not shoot the rifle before I chopped it so I have no idea of how it performed before nor what to expect with a short barrel.
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You have to exclude all the variables one by one.
I would start with no moderator, no bipod (front and rear sand bags instead) and standard velocity Eley or RWS.
I'd think the vertical dispersion is coming from inconsistent velocities of the CCI subs, I'm using them just now, haven't chrono'd this batch but previous lots have shown extreme spreads of 74fps. Eley and RWS subsonic HP's have been much more consistent velocity wise for me.
farmer7 wrote:I'd think the vertical dispersion is coming from inconsistent velocities of the CCI subs, I'm using them just now, haven't chrono'd this batch but previous lots have shown extreme spreads of 74fps. Eley and RWS subsonic HP's have been much more consistent velocity wise for me.
I think this is your best starting point - by and large I find all longer range groups with a .22lr show vertical dispersion. 50 fps difference in the same box is not particularly unusual - even "match" ammunition isn't as consistent as you might imagine.
50fps is about 5% at subsonic speed - You would be a bit miffed if your centrefire ammo had the same 5% ES at around 150fps.
In this short video I tried 6 types of .22lr ammo at 65 yards - when all the shots were plotted they showed a definite vertical group, even though it was a bit breezy. All of the 30 consecutive shots would have hit a golf ball.. Tenex was certainly the best but at three times the price of most.
A good real life review Alan. At exactly 45 metres it grouped at around 1.2" vertical and 0.5" inch wide so the verticals were already evident. One thing that is niggling me is the trigger pull which is quite heavy in comparison to the other rimfires we have here so as well as ammunition testing some trigger work would not go amiss.
the 520/525 trigger is a drop out affair and was only flushed during the rebuild as opposed to be stripped so a closer inspection may reveal something, unfortunately I cannot find any notes on the triggers so it will be interesting...
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