Why do Rem. 6BR brass have a flash hole twice as large as my Norma 6BR brass?? The Rem. show pressure signs even on 30g Varget loads I think it is because the bigger flash hole allows more pressure to get into the primer pocket. Any info is much appreciated. Thanks.
Why do Rem. 6BR brass have large hole...
- Thread starter redfeather
- Start date
Forum Boss
Administrator
Gunamonth is right. Here's the deal on Lapua flash-holes. The factory spec is 1.5 mm. That works out to about .059".
If you get the CORRECT decapping pin with your 6BR Redding die all is good--it will be .057" and it will work. Same deal with a Harrell's Precision "semi-fitted" die. Some of the other die makers ship their dies with a std 1/16" or .625" decapping pin. If you are stuck with that, you can ream the flash-holes from the OUTSIDE with the Sinclair tool, item 07-3000. This tool makes a pretty clean hole because it indexes off the primer pocket.
Some people feel that reaming from the INSIDE,and slightly chamfering the inside edge of the flash-hole) aids accuracy. In our tests it did not. Moreover, cases with reamed flash-holes showed higher ES and SD than untouched flash-holes. However, we used a K&M tool which was slightly over size,common problem) and cut the hole to about .067".
If you get the CORRECT decapping pin with your 6BR Redding die all is good--it will be .057" and it will work. Same deal with a Harrell's Precision "semi-fitted" die. Some of the other die makers ship their dies with a std 1/16" or .625" decapping pin. If you are stuck with that, you can ream the flash-holes from the OUTSIDE with the Sinclair tool, item 07-3000. This tool makes a pretty clean hole because it indexes off the primer pocket.
Some people feel that reaming from the INSIDE,and slightly chamfering the inside edge of the flash-hole) aids accuracy. In our tests it did not. Moreover, cases with reamed flash-holes showed higher ES and SD than untouched flash-holes. However, we used a K&M tool which was slightly over size,common problem) and cut the hole to about .067".
NorCalMikie
Gold $$ Contributor
My RCBS "special Ordered" dies came with the larger decapping pin.,the smallest they make) I ordered the small pin assembly from Sinclair and it fits in my RCBS dies so I can do Lapua, Norma and Remington brass. Sometimes mix and match works best.
Forum Boss
Administrator
Ray,
You raise a good point. It could be that the tool used, and the skill of the operator make a difference. As noted, the K&M tool we used is supposed to leave an 0.0625 hole. In fact, it reamed larger than that. When we mic'd the cutter tip on the tool, it was, in fact larger than spec.
What I encourage people to do is prepare a dozen cases or so with and without reamed Flash-holes. Go out and test with a known good load over a chron. If reaming the flash holes appears to work for you, go ahead. If it doesn't, then you've saved a bunch of time.
The primers you use may make a difference in results. Recent tests by German Salazar,see www.shootersjournal.com ) show dramatic differences in the flame front and flash "reach" between one brand and another.
Primer Flash Photos: http://www.6mmbr.com/PrimerPix.html
You raise a good point. It could be that the tool used, and the skill of the operator make a difference. As noted, the K&M tool we used is supposed to leave an 0.0625 hole. In fact, it reamed larger than that. When we mic'd the cutter tip on the tool, it was, in fact larger than spec.
What I encourage people to do is prepare a dozen cases or so with and without reamed Flash-holes. Go out and test with a known good load over a chron. If reaming the flash holes appears to work for you, go ahead. If it doesn't, then you've saved a bunch of time.
The primers you use may make a difference in results. Recent tests by German Salazar,see www.shootersjournal.com ) show dramatic differences in the flame front and flash "reach" between one brand and another.
Primer Flash Photos: http://www.6mmbr.com/PrimerPix.html
Red
I assume your using bullets in the 105 to 107 grain range. If so, 30 grains of varget is a fairly hot load. I know theres alot of data on the net about loads alot warmer but powder lots vary. Alot of guys use CCI primers when using hot varget loads due to the thicker cups.
As far as oversized decapping pins. I spin them in a drill and turn down about half the stem leaving the other half to still fit in the threaded rod.
Jeff
I assume your using bullets in the 105 to 107 grain range. If so, 30 grains of varget is a fairly hot load. I know theres alot of data on the net about loads alot warmer but powder lots vary. Alot of guys use CCI primers when using hot varget loads due to the thicker cups.
As far as oversized decapping pins. I spin them in a drill and turn down about half the stem leaving the other half to still fit in the threaded rod.
Jeff
gaintwist
Silver $$ Contributor
This is an interesting thread. I found similar on BR central. Here is a quote from "Joe" on his test of different flash hole diameters similar to the moderator's suggestion.
-----------------------------
All groups were 5 shots @ 100 yds
Temp was about 35 degrees, very slight breeze.
Test #1
.058" Flash hole
Group size .190"
Avg. Velocity 3204 fps
Extreme Spread 49 fps
Standardd Deviation 20 fps.
Test #2
.068" Flash hole
Group size .156"
Avg. Velocity 3215 fps
Extreme Spread 31 fps
Standardd Deviation 15 fps.
Test #3
.078" Flash hole
Group size .125"
Avg. Velocity 3202 fps
Extreme Spread 18 fps
Standardd Deviation 8 fps.
fyi,
gt
-----------------------------
All groups were 5 shots @ 100 yds
Temp was about 35 degrees, very slight breeze.
Test #1
.058" Flash hole
Group size .190"
Avg. Velocity 3204 fps
Extreme Spread 49 fps
Standardd Deviation 20 fps.
Test #2
.068" Flash hole
Group size .156"
Avg. Velocity 3215 fps
Extreme Spread 31 fps
Standardd Deviation 15 fps.
Test #3
.078" Flash hole
Group size .125"
Avg. Velocity 3202 fps
Extreme Spread 18 fps
Standardd Deviation 8 fps.
fyi,
gt
Forum Boss
Administrator
Joe's Test appears to be with PPC or other cases based on the velocities. But this just points to the importance to do you OWN testing using match loads.
With new 6BR cases, using Norma 203B, our ES with unreamed Flash Holes averaged 8.5, with average SD of 3.95, Average MV of 2921.,This was tested with 3 5-shot strings).
Same load,30.3gr N203B), with large flash holes,reamed to .067"), showed Average ES of 17, average SD of 6.225, Average MV of 2927.
With 30.8 IMR 4895, unreamed,small) flash hole loads averaged 9.9 ES with 4.4 SD, while large,.067") flash hole loads averaged 20.0 ES and 10.4 SD.
YMMV. A lot depends on the consistency with which you can ream and chamfer the flash-hole.
You really need to test for yourself. But I can say this, if you start with small,unreamed flashholes) and are seeing ES under 13 with good accuracy, you probably won't do any better.
With new 6BR cases, using Norma 203B, our ES with unreamed Flash Holes averaged 8.5, with average SD of 3.95, Average MV of 2921.,This was tested with 3 5-shot strings).
Same load,30.3gr N203B), with large flash holes,reamed to .067"), showed Average ES of 17, average SD of 6.225, Average MV of 2927.
With 30.8 IMR 4895, unreamed,small) flash hole loads averaged 9.9 ES with 4.4 SD, while large,.067") flash hole loads averaged 20.0 ES and 10.4 SD.
YMMV. A lot depends on the consistency with which you can ream and chamfer the flash-hole.
You really need to test for yourself. But I can say this, if you start with small,unreamed flashholes) and are seeing ES under 13 with good accuracy, you probably won't do any better.
Okay, what you guys are saying is that the bigger flash hole sometimes produces a better ES and groups?? Is my theory flawed when I say the larger flash hole allows more pressure to reach the primers causing pressure problems?? I am still studying all this info on flash hole sizes. I am trying to figure out why everyone does not use the same flash hole size on 6BR brass?? Does one 6BR brass maker know something the others do not?? Thanks.
Forum Boss
Administrator
I've talked to Lapua's engineers. They basically went with the small flash hole because of the proven success of the small flash hole with the 6PPC.
With their new cartridge, the 6.5x47 they went with a large rifle primer and large flash hole. They claimed accuracy was slightly better. But no data has been released.
Another factor I noticed with a reamed flashhole in the 6BR--I got slightly more velocity but the cases showed pressure signs, particularly stiff bolt lift, earlier. I attributed this to the fact that the bigger hole lets more of the charge push back on the primer. Just a theory though.
With their new cartridge, the 6.5x47 they went with a large rifle primer and large flash hole. They claimed accuracy was slightly better. But no data has been released.
Another factor I noticed with a reamed flashhole in the 6BR--I got slightly more velocity but the cases showed pressure signs, particularly stiff bolt lift, earlier. I attributed this to the fact that the bigger hole lets more of the charge push back on the primer. Just a theory though.
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