Tuning Tuning Tanto Install on an HW98

I've been shooting this HW98 for several months now. It is a fine rifle. The trigger is excellent for a bone stock Rekord. It is a two stage with a clean pull to a second stage which creeps a tiny bit but breaks around 20 ounces. All in all quite manageable.

The rifle has a "muzzle weight/break" on a long threaded section (about 3/4"). It shot well with that weight just snugged up right against the shoulder on the barrel. I have often thought I might shim that interface between the muzzle weight and the barrel and thereby tune the harmonics of the barrel. 

I had a Tanto from Donnie FL in .25 caliber. I decided to mount it and tune the harmonics at the same time. I printed several shims on my printer.

hw98_shims.1632713496.jpg


The one making the shadow is 7 mm thick and mates the barrel to the Tanto making a smooth transition. The other washers are each one mm thick and were used in the test to find the optimal engagement of the Tanto on the barrel.

hw98_threads.1632713418.jpg


hw98_tanto.1632713635.jpg


To find the best location for the Tanto, I shot ten shot groups (numbered 0 thru 7). The first group "0" was shot with no shim. Then each group after that through "7" was shot with one more shim than the previous group. Finally I shot two more 10 shot groups on the lower right of the target after selecting the optimal number of shims, which in this case proved to be 1 shim.

hw98_harmomic.1632713840.jpg


To test my theory I measured the groups in my On Target software and got the following data, which I graphed.

Harmonic-Graph.1632713926.jpg


Finally I shot the last two groups shown above lower right circled and collected that data into the aggregate below.

1mm-shim-aggregate.1632713994.jpg


In this test pellets were not sorted or selected in any way. When entering the data into On Target I tossed one flier from each group. So the data shown represents 9 shot groups, except in the case of the aggregate where I also tossed one shot but there were twice as many shots in the aggregate -1 (nineteen shots).

It never was a loud rifle, and at 750 fps with H&N FTTs one wouldn't expect there is any real need for a moderator. It was just a lark, but TBH it is so quiet now that I am thinking of having it tuned just to reduce the spring "buzz" on firing. There is literally no noise escaping the muzzle of the rifle now. It is shooting as good as it ever has and now mounts the Tanto.

Works for me.
 
I am skeptical that shooting a single group is the final answer on any particular pellet or rifle configuration. Especially with a springer. Of course it would need a test of some sort to validate my skepticism, such as shooting 5 groups per configuration and then looking to see if all 5 groups were within the tolerances of the first group shot for that config.
 
I am skeptical that shooting a single group is the final answer on any particular pellet or rifle configuration. Especially with a springer. Of course it would need a test of some sort to validate my skepticism, such as shooting 5 groups per configuration and then looking to see if all 5 groups were within the tolerances of the first group shot for that config.

No disagreement there. Just did not have time to shoot that much that day. I opted for one ten shot groups and a look at the trend line, which certainly isn't perfect ...

Some data is usually better than no data. Maybe I can run that test again in a day or two.

Thanks for the feedback