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Posted by Frank (Member # 6) on March 28, 2014, 02:47 PM:
Just got done shooting the lasts few rounds in the 7STW.
It should be noted the 89.5gr line really has no data because I didn't shoot anything. The data was filled in with a split difference between the prior load and the following load. This data point can be ignored. All it does is fill in the spreadsheet to make the data look somewhat normal.
Judging from what I see it looks like the 88.5 grain point is worth loading up and down in 10th grain increments. With the once fired brass now available, I'll load starting from 88.0 to 89.0 in 10th grain increments. The brass will have 1/2 the neck sized. That should aid in bullet alignment with the bore.
Here's the resulting data and graphs:
[ March 28, 2014, 02:49 PM: Message edited by: Frank ]
Posted by Fur_n_Dirt (Member # 4467) on March 28, 2014, 04:28 PM:
Frank,
So, what is your yardage again?
Seems you have slightly hotter/colder velocities at 84 and 87 ..
I am wondering if 5 shots is enough to estimate a good group average..
Seems a second string to verify would validate your conclusions..
[ March 28, 2014, 04:38 PM: Message edited by: Fur_n_Dirt ]
Posted by Frank (Member # 6) on March 28, 2014, 05:07 PM:
Yardage? It was 150 steps. My steps equal about 27.7 inches per step. That came to roughly 120-125yds from muzzle to paper.
I'm glad you mentioned the hot and cold points at 84 and 87. I don't know how to explain that other than consideration to a few points:
1) This was virgin brass, 8mm Rem Mag necked down to 7mm. 7STW has slightly less taper to the case than 8mm Rem Mag so there is a bit of fire forming that's taking place. It may account for the velocity spreads and the high/low peaks at 84 and 87. For the 87gr line/third shot, if you remove the 3745fps aberration the remaining data points are in line with each other. A smallish case?
2) This is a new barrel so it was 5 shots and clean, five shots and clean, 5 shots and clean.
On this second go around, I'm thinking of bumping the lands. I've got once fired brass with 1/2 the neck sized so it makes sense to give it a try within the 10th grain incremental loads.
[ March 28, 2014, 05:15 PM: Message edited by: Frank ]
Posted by KaBloomR (Member # 4252) on March 28, 2014, 06:00 PM:
quote:
2) This is a new barrel so it was 5 shots and clean, five shots and clean, 5 shots and clean.
This may be the culprit in regards to fliers and shitty groups.....
Posted by Frank (Member # 6) on March 28, 2014, 06:26 PM:
KaBloomeR
I thought about cleaning having an effect as well. That's why the removal of flyers from the data. I know some are loath to do that but if you're looking for trends this can give you an idea of where to load when you might have otherwise rejected a possible accuracy velocity. I figure since this is a 7STW with short barrel life I'd try and get as much data from the start as possible. I suppose a reduced loading just to set the cases might have been in order...ahhh 20-20 hindsight ![[Smile]](smile.gif)
What is interesting is how the groups for three, four, and five shot groups "track" each other. The measurements were made without regard for point of aim as being a reference for the measurements. The group size measurements were strictly in relation to each other i.e. you look for the greatest spread between holes with 5 shots, four shots, and then three shots. I wasn't aware of this kind of behavior in group size until now because I never plotted the multiple, resulting traces before now.
I was, just today, starting to correlate velocity with where the bullets were hitting. Since there's so much variance in velocity (because of virgin brass?), I could see the flyers were mostly due to velocity spreads even though the loads in a string had the same charge weight. Kind of makes sense when you think about it.
[ March 28, 2014, 06:38 PM: Message edited by: Frank ]
Posted by Leonard (Member # 2) on March 28, 2014, 07:25 PM:
quote:
Since there's so much variance in velocity (because of virgin brass?), I could see the flyers were mostly due to velocity spreads even though the loads in a string had the same charge weight. Kind of makes sense when you think about it.
Are your cases weighed and segregated?
& How are you weighing your powder?
I don't see virgin brass, per se, being responsible for wide fluctuations in velocity. As long as you are not processing your cases and shooting them in groups, you can expect similar results with fire formed reloads.
Good hunting. El Bee
Posted by Fur_n_Dirt (Member # 4467) on March 28, 2014, 08:26 PM:
Think about kaboom's response..
Some say maximum group consistency does not come from the first shots after the barrel is cleaned well..
[ March 28, 2014, 08:40 PM: Message edited by: Fur_n_Dirt ]
Posted by KaBloomR (Member # 4252) on March 29, 2014, 05:08 AM:
Exactly. The 8 upper holes in this target are all from the same proven load from my 7mm Mag. I started on the right hand side with a squeaky clean bore and fired the first 4 shots. Numbers 6,7, and 8 on the left are the nice tiny cluster. I keep this rifle clean due to seasonal use, and I never have a clue as to the POI on the "clean bore" shot. Some of you guys probably experience better consistency from the get-go with your customs, though. What you invest in barrels buys me a complete rifle.....LOL
Posted by Frank (Member # 6) on March 29, 2014, 08:00 AM:
Leonard, that's a good question.
I bought the premium cases from Hornady. They're pre-sorted by weight, flash hole deburred, etc. Expensive little buggers! I measured a few at random for case length and uniformity was good.
All in all it was nice looking brass. I didn't go too far in case prep at the start since it was being necked down to 7mm and had yet to be fire-formed.
I ran the case into a stock RCBS 7STW full length die such that when chambering the case there was ever so slight resistance to closing the bolt. This was because of a small "bump" at the beginning of the neck/shoulder junction.... a remnant of the 8mm neck if you will. Here's a pic to help explain:
The STW is belted so I figured this sizing technique would bring the neck into alignment with the bore i.e. the cases are undersized and might otherwise lay in the bottom of the chamber. The slot was cut to determine bullet seating depth when bumping the lands.
Weighing the powder was done with an RCBS scale. I dump a charge from the measure just below the desired weight then trickle in the remainder. The trikling is done so as to keep the beam moving up until the pointer hits the mark. A very repeatable method I've used for years.
[ March 29, 2014, 01:49 PM: Message edited by: Frank ]
Posted by Leonard (Member # 2) on March 29, 2014, 08:40 AM:
Frank, I am unfamiliar with Nosler's presorting by weight? Maybe your internal volume is close to the same, and maybe it isn't? At this point, you are probably stuck with the randomness, such as it is.
But, with a case that size, your volume/weight could range as much as three grains of water, worst case. You have to find a powder that burns consistently and meters accurately. Is the "magnum" powder extruded? I suspect it is?
I'd say you are done with breakin, a long time ago and the crew is quite correct in pointing out that every group contains one round fired through a clean barrel, therefore, for purposes of recording accuracy potential, you haven't much to build on. Benchrest people clean between 15/20 shots and even then, there is a separate target for sighters, for that clean bore shot. Well, they all have their MOJO but they don't clean every five rounds during competition. Nor will you when hunting dangerous songdogs. (I hated typing that word)
One consideration more. If I were you, I would move the goal posts. If this is to be a moderately long range rig, there is merit in testing at realistic distances, like (oh, say) 350, or so? Bullets that group well @100 yards sometimes do not fly equally well, out yonder. Now, you will see a real world example of your talent for busting coyotes. I usually figure there is about 4 1/2" between a coyote's eyes. If you can center your groups in 3" @ 350yds. you have a killer in your hands. Personally, I dial my stuff to be dead nuts at 430 yards.
Good hunting. El Bee
Posted by Frank (Member # 6) on March 29, 2014, 01:48 PM:
Whoops, I meant Hornady cases, not Nozler. I'm shooting a Nozler bullet, sorry. I went ahead and corrected the post above.
[ March 29, 2014, 01:49 PM: Message edited by: Frank ]
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