Air Arms S410 Carbine - Randomosity

[davhill]

Hi, new boy here with my first post.

My S410 Carbine has just had some TLC but it's still causing me frustration. Here's the lowdown.

This .22 rifle has a walnut thumbhole stock and a factory silencer. I use it at my local range to shoot NSRA 10-spot targets at 25 yards
from a benchrest setup. Using the club's Model 1813 Anschutz (.22 LR with Match barrel), my average hovers around the 96 mark, using the rifle's rising cheek piece and a butt hook (Oooh, Matron).

The AA, on the other hand is less co-operative. I found the bolt was jamming and this led me to do a stripdown and fix as follows...

Degas, remove silencer, stock and indexing mech, bolt housing and pressure chamber.

Lightly stone burring from the forward edges of the T-shaped slot under the bolt housing.

Find the dog pin loose and the sleeve canting, clean up and refit the pin with Loctite, ensuring the sleeve is still rotating.

Clean everything and reassemble with new seals but left the trigger housing on, left the barrel attached
and left the hammer strictly alone.

What's happening now? Here we go.

I found the gauge reading 50 bar when the chamber's empty. Hardly a capital offence but weird.

The bolt action is still a bit baulky and it takes quite a pull to take it to the fully open (click/cocked) position.

The mags seem to index well enough and a new clip has stopped them falling out when cocking.

But - and here it is. The pellet strikes are all over the place. Tonight, I put two in the ten ring but the next three
scarcely hit the black. There's no specific direction, it's truly random.

Just to clarify, I use a Caldwell iron rest (as with the Anschutz). I fitted a canvas butt sleeve/cheek piece (the rifle's nosebag) and this
improved mounting and cheek weld. So on a good night, I can group well enough. I'm using a seriosuly powerful Hawke sidewinder scope and heavy field ammo which the gun seems to like - it hates Milbros.

So it's tuning time and I'm wondering where to start. Any suggestions therefore gratefully accepted.

[TenMetrePeter]

I would have polished the hsmmer rail with brasso and kept it either dry or with dri-slide dry moly treatment.

If the variation is vertical only then hammer rail or piwer can be a cause. If it’s all over the place then try without the moderator first of all then check the mag isn't clipping pellets. Cleaning the barrel with s pull thru is wise but will take time to re-lead so check out the pellet damaging parts first.

Some people recommend stripping out the moderator baffles, popping in a velcro hair curler or similar and opening out the exit hole.

[tonyc]

Random shot distribution is unlikely to be power but I'd still check with a chrono (preferably with moderator removed) to confirm power is consistent. Are you sure your scope is okay and is mounted securely, and your barrel is secure? After removing and refitting the cylinder I take care to ensure the barrel band isn't applying pressure to one side of the barrel.

It could just be a mismatch with your pellet choice. Try JSB-manufactured pellets; finding the best match for the barrel can take time but at 25 yards I'd not expect to see much variation.

[davhill]

Well, thank you gents, suggestions taken on board.

It occurred to me that if the bolt action isn't smooth, it could be one of two things.

Either the mag isn't indexing correctly, making for a foul between the probe and the mag.

Or, because the cocked position takes a big pull to find, the hammer/rail could need attention.

I assume drawing the bolt back all the way makes the hammer engage with the sear?

What I do know is that a gunsmith did a service but didn't touch the hammer assembly or the trigger mech. This was on account of Loctite having been used on the fixings.

In any case, it's time to get another seal kit.

[Dreamer_UK]

If your shots are random, check that the moderator is fitted precisely in line with the barrel. When I first got my second-hand S400 the mod "looked" fine, but I found that it was misaligned very slightly. meaning odd shots would clip the end just the tiniest amount, throwing off the pellet. Mine was caused by using a Rowan Engineering slip on mod with a barrel end that had lost some of it's paint cover, allowing the mod to move slightly on tightening, as it only had one grub screw to center it.

[davhill]

The plot's thickened somewhat and a decision has been reached.
My AA is a pre safety catch model and a mate and I did a bit of testing.
I had my mate shoot five pellets into a target at 17 yards, resting the gun
on a post. Then, he shot twenty more pellets, ten from each magazine.

The results were easily interpreted. The randomness is markedly in elevation
and it was easy to see that what haappened at 17 yards would clearly occur on the range
at 25 yards.

Now suspicion has fallen on the hammer, the plan is simple in that I'll strip this and the
trigger assembly and service these areas.

However, although the windage results were acceptable, the action was still notchy. So, I intend
to treat the rifle to a new generation indexing plunger device from AA. Then, we'll see,

So thanks again, I'll keep you informed.