Small flasholes in 6.5x 47

B

Bob Kingsbury

New member
Shooting my 6.5 x 47 today and noticed while making changes in seating depth,
my point of impact changes drastically. Using Vld bullets changes of .005 per
group and spanning .025 total for the day, I can cause my POI to change by
2-2 1/2 inches at 150 yds. I can also return to the original POI by changing
the seating depth back. Just wondering if the 6.5 x47 is at the limit with
the small flashole and If anyone has noticed this. I have thought for some
time that seating depth was related to ignition
 
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I think every .005" deeper you go decreases your case capacity about .07 grains and unless you are already seated through the neck your neck tension changes also, so pressure should increase. Did your group size change as well? - nhk
 
The group size was larger at the extremes. But not by a lot. I have never seen this much change in others that I shoot. Adding
a half grain of powder doesn't bring that much change untill you leave that node. Never seen this before at this level.
 
Bob: I have read a number of times recently wear as a shooter has said he could not get his 6x47 Lapua to shoot good and had rechamberd it
to a different cartridge and swore they would never go back.
Now to switch cartridges for a moment, Dave Tubbs a world class shooter, stated while
working with Norma to develop new brass for his 6XC he tried both small primed and large primed brass. His testing showed that the small primed brass
using H-4350 showed to be very erratic, consequently he requested the brass be made with the large rifle primer and large flash hole. I might remind you that the shoulder of the 6XC is moved forward to hold about three grains more of powder, the acual case is only .050" longer than the 47 Lapua case.

I have just trimmed 100 of the Norma 6XC brass .050" and reformed the shoulder back to fit my 6x47 Lapua. We will see. Also the Norma brass from
Tubbs is about $.40 cents each cheaper than the Lapua. also, I've been entertaining the thought of just drilling the flash hole of about 20 pcs. of the Lapua brass out to a .080" flash hole and staying with the CCI-450 primer. I think that may also get the job done as the 450 primer is a excelent primer.

my 2 cents. John
 
You might have something there; the 6XC (large primer) vs. the 6X47 Lapua (small primer). I developed some loads for a friend's 6X47SM, which uses the large primers, and it shot very well. How is the .308 with the small primer pocket catching on? - nhk
 
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We should consider that there is more to seating depth adjustments than currently understood.
The truth passes all tests. And yet, every notion out there about seating depth fails tests.

Actually, with this cartridge, every 10thou seating adjustment(which is a lot) corresponds to about .07gr of powder.
5thou adjustment is half of that, or .03gr worth of powder. 25thou span is 0.15gr. Would your barrel really shift -so much-(>1.5moa) with these adjustments to powder?
My barrels don't, no way, but they act similar to OPs with seating adjustments.
This tells me that seating is NOT merely a fine adjustment to tune, and probably has nothing at all to do with 'tune'.
It tells me that the best seating(wherever that ends up being) is a prerequisite to best performance, that is not yet understood, or predictable.

So I've gone to finding best seating FIRST(during brass fireforming), before moving on to load development.
Try it & once you have it, notice that you can change loads, powder types, and primers(but not bullets) without the slightest affect to that best seating depth.
Seriously, go back and check it again.
It is what it is.

One day someone will figure out seating. They'll define it & we'll benefit with prediction of it. I HOPE
 
6.5mm = .264"

.264/2= .132" radius

((.132 * .132) * 3.14) * .005" = .0002735568 cubic inches

.0002735568 cubic inches * 16.387064 cubic centimeters/cubic inch = .004482 cubic centimeters

.004482 cubic centimeters * 15.432 grains/gram = .069166224 grains of water

or

.07 grains
 
And .07gr H20 capacity results in a velocity change(2fps) that is compensated for with .03gr H4350 in a 6.5x47L.
This, with QuickLoad
 
I found my 308win palma loads erratic. Been thinkin bout drilling the flash holes out to. 075 for about a year now. Let me know how this works out, I think the CCI 450 is an excellent primer too.
 
Two things come to mind... 1) I think I read some where that David Tubb felt that the dividing point between large and small primers was at about a 40 grain charge. 2) I drilled out some .308 flash holes to 3/32" (I'm not recommending this) and the SD dropped considerably. When I mentioned that to Speedy his comment was that I probably would have had the same improvement if I de-burred the flash holes and made the flash holes the same length, which I may have done unwittingly. Since then I've either used Lapua brass or de-burred the flash holes. My .308 (Lapua large primer) F-class load has an SD of 8 fps. - nhk
 
The seating depth (bullet acting as a piston) can change the displacement and the stroke, which increases the load density. The choice of primer changes the spark and the flash hole meters the ignition, which is now acting on a smaller cylinder, but the same powder charge is now more dense. A .037" increase in seating depth on a 6.5 mm bullet on a .260 Remington decreases the case capacity 1% and increses the load density 1%. - nhk
 
Hell FL sizing leaves more H20 capacity variance that that..
It is not enough volume change to result in >1.5moa shift.
Nor is it a significant neck tension change..
Now off the lands to first contact with lands, can significantly change pressure. That could maybe do it. But that's not what Bob is doing here.

This is a very common scenario with seating depth adjustments. Shooters get changes like this when going from 10thou into lands to 20thou into lands, and that has no effect on velocity at all.
And even a full grain of powder variance would not have so much of an affect on POI at 150yds.

Just sayin, a basis is weak to missing, for primers being the cause of POI shifts -while changing bullet seating..
 
Let me see...if a fellow had a fixture and a vertical mill (or for that matter a lathe), could he open up primer pockets from small to large, and then retest, and then do a series with various flashhole sizes....couldn't he?
 
Last year, I reformed some new 308 brass to 6.5 x 47. Some groups were better, but some not. having thought about this now,
I bet the capacity was not that close. At the time, I should have chrono-ed this, but didn't. yesterday. I reamed flasholes to
.073. It did shoot pretty good, about .3 something at 150 for 3 shots. With no other changes, the primers were flattened
more. This implys to me that more pressure was applied to the cup. If thats true, it also implies that more fire was applied to the
powder, instead of being metered as the small hole would.
 
It could also mean that the % of chamber pressure that the primer pocket sees is increased. The chrono should tell the tale.....I think
 
Boyd, Yes, I'd say thats exactly whats happened, but would think it also works the other way.

Mikecr-- no but I will soon

I could well be all wet here, but for a long time I used one seating depth for a given bullet/barrel. At some point, I
found that a seating depth good for one powder wasn't always the ticket with a different powder. Think neck tension
plays in this as well. This 6.5 x 47 just seems to be an extreme
 
I agree that more than volume change comes into play and a chronogragh may give a better explanation. I would guess the original loads were at the high end of the pressure curve or a spike and sensitive to change. - nhk
 
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