Shifting groups, Air Arms TX200

[Savhmr]

It's been a year or two since I dusted off the TX200 for anything but a recent spate of rat control necessitates using the air rifle so I check that all action mounting screws and sight mounts are all tweaked up ok, and armed with a tin of Air Arms Diabolo Field, set about zeroing for 15 yards, using the chrony and working out the trajectory for the 2nd point of zero etc etc.

 

I get the thing punching one hole on top of another at 15 yds with the odd flyer, probably due to deformed skirts. Upon trying a group of 3 at another target a few inches away (5 bull standard target with one inch centres), the shots suddenly all start group 1.5 inches low. Puzzled, I adjust the sights and try another target. Still low. Go back to the first one, all shots now high. Can't get my head around this. The only thing to change was where the front of the stock was resting on the Caldwell shooting bag...possibly 4 or 5 inches difference from the first group.

 

I chrono'd the rifle using the Diabolos and get a very consistent result after firing a string of about 15 shots. Average = 574 fps (equating to 11.71 ft-lbs energy at the muzzle) , SD of 2fps and ES of 12fps. That's not half bad for a spring rifle which hasn't seen any use in over a year so probably doesn't explain the shifting poi between groups.

 

So now I'm left with two possibilities:

 

1. Where the front of the stock rests really does have this drastic effect on POI as recoil is happening before the pellet leaves the muzzle or;

2. Its down to a dicky scope which doesn't like recoil

 

2) seems unlikely as the groups are consistent in each case and it'll shoot a 5p piece every time from 15 yds until targets are swapped, when it'll miss....but group into a 5p piece within an inch and a half away!

 

Any ideas folks?

Edited July 20, 2016 by Savhmr

[FalconFN]

A problem with the scope is the most likely cause. Do you have another scope you could try?

[Savhmr]

I do, and will probably swap it over to a fixed 4 x 42 scope but just curious to see if there's any mileage in the recoil/rest point theory.

[Walker570]

Yes, I would check out the scope first. With regard to the stock position, I always try and shoot with my hand under the fore end. Having witnessed so many misses where clients insist on resting their deer rifle on a fence post or rail or even a granite rock, I now insist that the fore end is supported by the hand as this is consistent and not going to cause the rifle to bounce. Final zero the same way always.

Hope this helps.

 

I had a Dutch client who insisted in pressing his top of the range PLUS, Blaser, gold inlay and all, into a granite rock and then wrapping his hand over the barrel to hold it down. He missed the first three animals. Eventually I got through to him and managed to insert my pack under the fore end and he started collecting trophies.

[robbiep]

Yes, I would check out the scope first. With regard to the stock position, I always try and shoot with my hand under the fore end. Having witnessed so many misses where clients insist on resting their deer rifle on a fence post or rail or even a granite rock, I now insist that the fore end is supported by the hand as this is consistent and not going to cause the rifle to bounce. Final zero the same way always.

Hope this helps.

 

I had a Dutch client who insisted in pressing his top of the range PLUS, Blaser, gold inlay and all, into a granite rock and then wrapping his hand over the barrel to hold it down. He missed the first three animals. Eventually I got through to him and managed to insert my pack under the fore end and he started collecting trophies.

I would second that. Surprising how the rest point under the barrel can change things on a springer. I had the same issue with a HW77k.

Edited July 20, 2016 by robbiep

[timmytree]

I always use the forward stock bolts on the PS as a reference point for resting, that keeps the balance consistent. Don't vary your hold or position or POI will alter.

[bruno22rf]

You are, actually, left with 3 possibilities, .....you are a worse shot than me

[Savhmr]

You are, actually, left with 3 possibilities, .....you are a worse shot than me

 

 

LoL! Quite true, and quite possible, if by a bad shot, I am not paying enough attention to how a springer is supported.

 

I never hold or interfere with the barrel in any way shape or form and always have the forend supported either by a bipod or quad sticks or with my left hand lightly holding the underside of the stock at the same point. The only other rest used is a rice filled shooting bag. Barrel harmonics come into play for all rifles and I remember my own teaching well when I started out.

 

My gut feeling is that it is directly related to where the forend is resting so I'll shoot some more groups this evening and see what difference moving the rest point makes. Whilst it could be the scope, the fact that I can get consistent groups when switching between targets, just differing POIs tends to rule the scope out I'd have thought. Never really given a lot of thought as to how sensitive a springer might be to altering the rest position but the more I consider it, the more likely it is to directly affect POI, unlike a PCP air rifle.

Edited July 20, 2016 by Savhmr

[Walker570]

New to the TX200 and 27 magpies later, with three known/admitted complete misses. I am beginning to appreciate even with all that weight you stillneed to concentrate on doing the job. I'm beginning to think your on the right track by making sure you have the rifle held absolutely the same every time. The misses I had where all on targets where I had to stretch at an awkward angle to get on and so did not have the normal control.

[stutieb]

Had similar experiences check my post out ,switched to hn field target trophy ,,,so far so good was on aa Diablo field ,must of been a bad batch utter trash by comparison ,even changed my scope at one point because it wouldn't hold a zero and thus was a brand new gun with one and a half tins of pellets through it

Edited July 20, 2016 by stutieb

[Savhmr]

Well, an evening with the TX200 proved me right. Supported in the same place, it put one pellet on top of the other with the odd flyer without the shifting groups. What improved precision was taking a very loose grip on the semi-pistol grip, only to support it from underneath really with most pressure acting on the trigger finger for consistent trigger pulls. Technique plays a large part in this air rifle's consistency. Not impressed with so many deformed skirts on the diabolos so ordered some Accupels instead as they ought to group in the same spot being almost identical in mass and also sharing similar BC. The're slightly lighter so perhaps 580fps would be about right for them (I'll dig the chrony out when they arrive). For now, enjoying the TX as it's a good way to improve technique even for the CF rifles but a damned sight cheaper to shoot! Good stuff. Now for some rat bashing.