OzFclass

I have just built and done load development on a new rifle. Barnard action 1-1/4 parallel Krieger 5 R barrel in a 6" barrel block directly in front of action, Cal. 6.5x55 Rogue using J.L.K.140gr. V.L.D. projectiles. Other barrels I have used shot 44.6g of 2209 or 45.8g of 2209. I tested both loads with .010 into lands,.010, .020..040 and .060 jumps.
I forgot to add that I counter bored muzzle to suit 21st Harmonic for the Purdy Prescription tune method. This gave me a useable barrel length of 29.5"
The results of testing over 3 different times has given me almost identical groups with both loads and jumps within a few thou. The agg.of the 15 groups was .1283. The only difference was that the lower load shot about 1/2" lower than the higher.
Now my question is, do each of these loads represent a separate node, or does the Purdy Prescription tune produce these results? Another question is do I have one of these mythical " hummer' barrels that the short range B/R shooters talk about?
All testing was done at 100yds. I have shot 2groups at 500m 1@ 1.644 the other 1.941 with 1 shot going where I held off for what I thought was a small let off of wind and that is where the 4th. shot went about 1'' away from the others, the 4 went 1.096.
Can someone come up with any info. on these happenings or am I a lucky "B" and fluked everything.
Cheers,
Trevor.

Timely Old Trev, there’s a young man out West who will be interested in this as I have just hurt his head with further additions to the theory of tuning. There is no such thing as pointing someone in the right direction when there is so much to know and build on as you become more sophisticated.

It has been my view for years now that it is the harmonic length that is the group tightener. Its nodal and depends on a strict velocity range, hence why you vary the harmonic input to find the correct harmonic length to get a super node. Despite your the 100 yard test the trends will be evident and can be improved upon with greater test distance. Usually three shot groups have insufficient data. I have come to realize that incremental charge testing does require 5 shot groups as a minimum. Those not so tight groups on the whole trend tell me the harmonic length is wrong if all other preparation and rifle soundness is right. If I am satisfied with the harmonics, I establish the launch angle for a desired tune and fine tune with 3 shots groups doing a seating depth test.

You would have noticed on a previous post how rythmic groups were when a rifle had a tuner attached after it was tuned. The same thing happens when the harmonic length is right. However it is the launch angle as you have indicated by the group elevation points, which remains tight that is the key to further success. Five shot groups will enable you to discriminate for subtle difference as to where a weakness could arise with the pitch of a shot and shooting beyond one hundred removes any suspicion of coning. Goodluck. You still need to verify the results.

I would also add that because you have used a long barrel block you have effectively shortened the fundamental amplitude of the barrel. This reduces the lift that may be desired at long range but at very short range will result in loads appearing to hold similar elevation. David.

Hi David,
Thanks for the input. I was quite happy with the 2-500m. groups. Considering I stuffed up one shot and shooting Townsville range in the middle of the day can be quite a challenge. After the Southern Cross 1000yd. shoot early July at which I shoot a.284 Win. I am going to try the 6.5 at 1000 yd. at Townsville to see how it goes without doing anything else with load development or tuning. To put an adjustable tuner on the 6.5 I would have to remove weight from the stock as the rifle weighs in at 9.55kg.
Cheers,
Trevor.

Sitting here with a head cold and I swear my head just about exploded...

Brad Y wrote:Sitting here with a head cold and I swear my head just about exploded...

I don't have a head cold but there's inopportune swelling of my frontal lobe.