Testing Fast 7mm 168s

[AlanF]

Yesterday at the club shoot over 600yd I decided to try a couple of fast loads in my usual 7 Shehane chambered 34" Bartlein "blunderbuss". Loads were 59.6 and 58.5gns 2213C. I decided to measure velocities with my old F1 Chrony and see what effect velocity variation had on elevation, mainly in response to our earlier forum discussion about high velocities being less susceptible to velocity spread vertical.

Well, the faster load averaged about 3175fps, and in general it held X-ring elevation, except for one higher velocity flier that went over 3200fps and that was 12 o'clock in the 6 ring. The slower load averaged about 3150fps and with no velocity fliers all shots held the X-ring vertically. At those velocities I'm expecting case life to be short, but the cases had already done about 10 reloads, and no primer leaks. I will investigate this further.

[AlanF]

At this time there have been nearly 100 reads of this post, presumably including a good number of 7mm F-Open people. On reading my velocity figures, some would have immediately doubted them, but were too polite to "rain on my parade". I have an admission to make - when those figures started coming out of the chrono on Saturday, I immediately decided that some checking with another chrono would be a good idea, so brought the club's Magnetospeed home to do that. I had single leftover rounds from each of two loads. As expected, the velocities came out much lower, to be precise 3046fps for the higher charge, and 3003fps for the lower. The reason for not revealing the this earlier is that I hoped those higher figures would get a lively discussion going, but alas you've all got better things to do.

My concern is, as far as I know, in Australia at present, there is no way of accurately checking chronographs. We can compare them with another one by setting them up in series, and extend that to several others for greater confidence, but the fact is that no-one can prove that a particular machine is accurate (in absolute velocity terms) to any particular figure.

In our sport, this is of particular concern to F-Open, F/TR and possibly Match Rifle, whenever we are shooting on ranges with energy/velocity restrictions both in Australia and when preparing for overseas competitions. We need to have the confidence that both our own personal chronographs, and those used for testing at competitions, are sufficiently accurate that limits are rarely exceeded.

If my chrono figures at the range were correct, they represented muzzle energy of up to 3840 ft-lb, well above the 3500 allowable limit. As it turns out, they were almost certainly less than 3500, but the truth is I don't know that for sure, because there is no way of accurately testing the Magnetospeed. And what if my F1 Chrony had been used to check velocities at a prize meeting???

The obvious answer to this is for the NRAA to come up with a method for checking Chrono accuracy to a standard that will satisfy requirements, and to offer a testing service for both personal and "official" chronographs. Unfortunately, in its current state of funding and human resources I would doubt the NRAA would be keen to do anything, particularly as in practice, this issue only affects those F-Class categories mentioned above, being about 20% of the membership. Maybe we need a group of F-Class shooters to step up? Funding could come from either donations, or possibly some sort of shareholding, and the testing task run by some willing F-Class group who would charge for the service, with part of the income going back to cover equipment purchase costs.

Thoughts?

Alan

[Antony Cave]

Perhaps all clubs could purchase a Magnetospeed to keep everything the same. They are easy to set up, and going of Bryan Litz extensive testing of quite a few chronys they are very accurate when it comes to Velocities.

http://www.longrangehunting.com/forums/f19/chronograph-performance-review-148450/


There is also the Lab Radar as long as people arent using lead based projectiles. They are another viable option and can test more than one shooter at a time.

[Matt P]

Hi Alan
This is very important issue, IF State Ass start to actually check MV.
I have been doing some limited testing comparing the Labradar and the MS, and they are reading with-in 10 FPS of each other (and calculated come ups agree with the MV), and this slight variation maybe due to where the MS is placed. IMO these 2 chronographs are the bench mark for accuracy and precision.
I think I remember reading that Gary Costello (in the UK) was able to supply a "verified" MS, which is what will be used at the FCWC next year.
Matt P

[Norm]

Alan, BMT in Melbourne have a certified chronograph used for industrial testing of ballistic components.
The testing laboratory provides testing services of armour and impact resistant products used in military and civilian situations for compliance to international test standards.
This is the only such testing facility that is certified to international test standards in the Southern Hemisphere.

So if you want to test a chronograph, this is the only place where it can be done in Australia that I know of.

http://www.armourtesting.com/

[AlanF]

Some good comments there.

The BMT service sounds very promising, although cost would need to be investigated if they normally sell to the military.

So I guess a requirement could be made where any Chronograph to be used in testing at NRAA affiliated shoots needs to comply in terms of accuracy with a certain standard which hopefully BMT could verify. And this verification process would need to happen periodically for each unit, in case their calibration drifts. And for personal chronographs, most owners would probably be satisfied just checking in series with a verified chrono.

[Steve N]

One problem I had with my F1 Chrony was the variation in readings that occurred from day to day or even on the same session if overhead conditions changed. Changes of up to 100fps would not be uncommon. I think it would be a waste or time to have one of them checked for accuracy.
Steve

[Brad Y]

I've got access to a magneto speed that consistently reads about 70fps slower than my one and other peoples ones. Not sure what is up with that.

Alan, if this is the case with the two velocity readings, does that mean the load you had success with earlier in the year in that same barrel was below 3000fps?

[AlanF]

Alan, if this is the case with the two velocity readings, does that mean the load you had success with earlier in the year in that same barrel was below 3000fps?

The faster load is the same as I used in the Vic Queens Brad, but temperatures are about 10 to 15° lower now, so at Bendigo the velocity may have been running at about 3050 to 3060 fps (just under 3500ft-lb) if the Magnetospeed is to be believed, and well over if the latest F1 Chrony figure are correct. I had checked the speed prior to Bendigo with the F1 Chrony at 3020 fps. I think the Magnetospeed is much closer to the truth, particularly because the Chrony has given velocities 150 fps different for the same load on different days.

[Brad Y]

Years ago I accidentally shot my f1. Possibly the best thing in hindsight.

I will be revisiting the 168's soon when I open a new batch maybe this weekend. I have them tuned them in the past to run just under 2900 for short range shooting but they don't hold up at long range with a poor spread and SD. Have shot a 60.10 at 600 with them but at 800m they start to open up in group. Maybe I will take a look at my tuning targets and find something over 2900 that will be a little more suitable for holding up at long range when it's not windy enough to justify swapping barrels and running 180's