Equipment: RimX .22LR, WOOX Exactus Stock/chassis, Mueller Works 24" bull barrel, Trigger Tech Diamond, Eley Tenex, Randolph Machine Front Rest, Protektor Rear Rest. I've been reading a little on barrel harmonics, specifically looking for understanding of the sinusoidal wave and its characteristics in regard to projectile behavior on muzzle exit and ways of influencing.
There are a few reports and articles, some written with a decidedly technical engineering style, some with readily understandable basic fundamentals. Then there are available products offering a means to manipulate the harmonics for a beneficial response.
One person posted a video on the $2.00 solution. He was using a shaft collar. I viewed it. It had inherent logic, and his methods were reasonable.
I measured my barrel diameter (1.21") and the nearest size shaft collar (1.25"), and decided to give it a try. It is a 2 part unit (no harm to the barrel), quality stainless, appears semi-polished. A little gun oil on the inner wall and off to the range.
(I noticed my Anschutz target rifle has the muzzle end of the barrel diameter at 1.00" for 2+ inches from the end, tapered to a 0.92" remainder barrel length. With slots machined in, the end is apparent design for front site placement. However, (I'm thinking) the wider 2+ inch length of muzzle end might just affect barrel harmonics in a positive accuracy way. (?).
More encouragement to try the shaft collar idea on the RimX.)
So, back to the shaft collar. With zero engineering or mathematical rational I decided to place the collars at 1/2" from muzzle end to start, with the rear collar 1/2" from the front collar. Again, no scientific justification. I thought if a touch of a stock can upset a free floating barrels accuracy (most agree on this point) by disturbing harmonic resonance (?), then collar on the barrel can affect the frequency characteristics (?). (My apologies to engineers, gunsmiths and mathematician's sensibilities who continue to read this after the first sentence). Again, with no particular mathematical model in mind, I decided on 1/2" increments of movement for the test. I had just over 8" of distal barrel length to work with up to the stock forend.
Group patterns initially showed no obvious pattern to my untrained eye, but it looked like target 3 and 6 ( 1.5" and 2" from muzzle) almost wanted to form, then began to spread. Likewise target 13 (5.5" from muzzle) looked good, excluding the flyer, and my attention was starting to wander, so almost stopped there, but was close to the end of the length so kept shooting.
That led to target 16 (7" from muzzle) and 17 (7.5" from muzzle). In retrospect I'm pretty sure I can see slowly forming circles in groups 13-14-15, culminating in 16 and especially target 17! Continuing to target 18, which is at 8" from muzzle end, it appeared to me the wave was oscillating out of its maximum 'best'.
Settling (a surprise indeed!) on target 17, (which was 7.5" from muzzle end with the front collar at the 7.5" mark), the group measured 0.19" CTC.
Not wanting to let this go, with temperature 34*F, and ammunition out in the cold for 1-2 hours at this point, I shot two additional 'collared' groups on target 22 and 23. These two groups of 5 rounds measured 0.25" and 0.24" respectively. This definitely had my attention. So, I needed a control group(s). I removed the collar. All other variables were unchanged. Same weather, Eley Tenex, rifle, time of day, cold hands, shooter, etc.
The two 'non-collared' control groups at target 24 and target 25 differed markedly from the two 'collared' groups immediately prior.
At this point I did shoot some points on the sight-in target which showed well but decided to save an accuracy trial with the shaft collars at 7.5" for another day as I was a bit tired from a long shoot.
One final note: This build has already shown itself to shoot groups with this precision.
This without the collar, using Lapua ammunition which this build was
chambered for.
Desert Precision Gunworks model of excellence!
Just seeing if I could 'Gild the Lily' ; ).