Flash hole diameter preference

[BuffaloBill]

I’ve recently begun loading for a new 6BRA build. The flash holes as they come out of the box (see post #4) I opened (Lapua 6BR Norma brass) have about 40% looking like the one on the right. Those will pass 0.069” gauge pin. The other 60% (as shown on the left) will pass only 0.062”.

I’m tempted to drill them all 0.070”. Or am I better off using only those as shown on the left because a larger flash hole somehow hurts grouping? I hate to set aside 40% of them. Powders I foresee using include Varget, H4895, N540.

I’ve been reloading since 1980 but hadn’t been uniforming flash holes. For this project I’d like to go after details like this in an attempt to further improve group size.

What do you recommend?

 

[Coyotefurharvester]

Keep them separate and see if it matters, best case it doesn't matter(no extra work).

 

[fisherman987]

It totally looks like the one on the right has had a uniformer ran through it because the edges of the hole are beveled.

 

[BuffaloBill]

It's my fault. I figured it out. Yes these were unfired, but not exactly as they left the box. I had primed these earlier, then deprimed them (those having the larger hole). My sizing die has a 0.054" decapping pin. But I'd used the universal Lyman decapper. I punched those flashholes out myself......grrrr. It's 40% or so of half a box.

 

[fisherman987]

Alex wheeler and the crew at Deep Creek did some experimenting trying different flash holes drilled to different sizes and I'm pretty sure they found no meaningful difference all the way to .080 like Alpha brass has.

 

[rjtfroggy]

I drill all mine out to .071 before I do anything else. Never saw a difference.

 

[Fire Dog]

It totally looks like the one on the right has had a uniformer ran through it because the edges of the hole are beveled.

That definitely looks to have been “tampered” with… Are you sure that it was an “Un-Opened Box”?
The photo clearly shows a shiny bevel around the flash hole in the one on the right.
I have KM flash hole uniformer/de-burring tools but they are suppose to go into the case to remove any swarf left behind when the flash hole is drilled or in lesser brass, punched.
I have never seen it done or have used it from the primer side…
Quality brass such as Lapua, Peterson {I’ve used both} or any to several brands I have found that it is a waste of time as on inspection {with a bore scope} of the inside of the case that the interior area of the flash hole is clean and unless you want to enlarge the flash hole {which should be 0.062”} you defeat what you paid for, ie. a “small” flash hole.
I used my .080”{I also have the .062” and they now make one designated for 6PPC that is .059”} for a friend that had a 6PPC and wanted to see if having a larger flash hole would help ..,,, The net result was he no longer could get groups any where close to what he had previously… Wound up scrapping 50 cases!

 

[bozo699]

I’ve found mine works best unmolested
Wayne

 

[WSnyder]

That definitely looks to have been “tampered” with… Are you sure that it was an “Un-Opened Box”?

It's my fault. I figured it out. Yes these were unfired, but not exactly as they left the box. I had primed these earlier, then deprimed them (those having the larger hole). My sizing die has a 0.054" decapping pin. But I'd used the universal Lyman decapper. I punched those flashholes out myself......grrrr. It's 40% or so of half a box.

 

[MikeRu]

I drilled the small flasholes in my 6.5 Creedmoor brass using a 5/64” bit, they shoot just fine

 

[Jason D Hostetter]

Highly unlikely you'd ever be able to shoot the difference, and .007" or .0035" per side, likely won't change your ES or SD, it might make a difference if you were using some of the suitable slower burning ball powders, but not with the 3 that you mentioned. Plus, I'd assume you're using Fed205Ms or BR4s, which are fairly mild, so it'll make even less of a difference. If you were to use Staball 6.5, Staball Match, PP2000MR, CFE223, or Ramshot Biggame, I'd say use Remington 7 1/2s or CCI 450s and drill them all to .080" to get the best ignition. However, I've had no problem lighting 37grns of Staball 6.5 under a 109 Berger in a straight 6br, with untouched Lapua brass.

 

[BuffaloBill]

Thanks for the replies everybody. I’ll keep them segregated, load the two groups the same, and see if they shoot or chronograph differently. I’d posted this pic in a thread in the gunsmithing section yesterday. It was the first outing on a new build and so far so good. Pic shows the first three shots after an initial two to obtain that zero @100yds.

I’d read a few times on this forum how fireforming new brass seems to often yield good groups. This is my first time experiencing this.

 

[ASbobcat]

I drilled the small flasholes in my 6.5 Creedmoor brass using a 5/64” bit, they shoot just fine

Big difference in powder volume between PPC/BR and Creedmoor.

Apples to oranges.

 

[Laurie]

Alex wheeler and the crew at Deep Creek did some experimenting trying different flash holes drilled to different sizes and I'm pretty sure they found no meaningful difference all the way to .080 like Alpha brass has.

That depends on the case / charge size. Alpha and David Tubb (among others) have decided that in larger cartridges, there may be benefits in the standard (2mm) hole diameter. (Or even in David Tubb's case with the 6XC, using the large primer.) Conversely, a great deal of experimentation has been done over the years by serious benchrest competitors on PPC / BR size cartridges and written up in places like the old Precision Shooting magazine. Without exception, it was found that increasing the flash-hole diameter to much over 0.070-inch had adverse effects on ES values and group size in these cartridges.

 

[Fire Dog]

That depends on the case / charge size. Alpha and David Tubb (among others) have decided that in larger cartridges, there may be benefits in the standard (2mm) hole diameter. (Or even in David Tubb's case with the 6XC, using the large primer.) Conversely, a great deal of experimentation has been done over the years by serious benchrest competitors on PPC / BR size cartridges and written up in places like the old Precision Shooting magazine. Without exception, it was found that increasing the flash-hole diameter to much over 0.070-inch had adverse effects on ES values and group size in these cartridges.

That is what my friend found out when I drilled out his 6PPC brass…. Just could not get a decent group… Not even a “3 shot” one….much less 5-10 shots.

 

[Fire Dog]

Thanks for the replies everybody. I’ll keep them segregated, load the two groups the same, and see if they shoot or chronograph differently. I’d posted this pic in a thread in the gunsmithing section yesterday. It was the first outing on a new build and so far so good. Pic shows the first three shots after an initial two to obtain that zero @100yds.

I’d read a few times on this forum how fireforming new brass seems to often yield good groups. This is my first time experiencing this.
View attachment 1674898

With that result, I’m curious why you didn’t put another 2 shots down and go for the “one hole” group? Three is promising, five is confirming…

 

[jackieschmidt]

That is what my friend found out when I drilled out his 6PPC brass…. Just could not get a decent group… Not even a “3 shot” one….much less 5-10 shots.

One of my favorite Benchrest stories involves the late Larry Baggett and Flash Holes.. I know it is true because I was there to see it.

We were at Kansas City for the NBRSA Group Nationals. The last yardage of the event was the HV 200 Saturday Morning.

Larry, who was a great shooter, was having vertical problems with his 6PPC and 133. Sometime Friday he went to a local store and bought a pound of 4895 and small drill around .070 inch.

He drilled out the flash holes in some cases, and basically filled the case full of 4895.

So what did he do? Not much EXCEPT go out and win the HV 200 width a bunch of nice round .350 to .500 groups .

Larry was known for doing some unorthodox things. But he always proved that there was a method behind the madness.

 

[BuffaloBill]

With that result, I’m curious why you didn’t put another 2 shots down and go for the “one hole” group? Three is promising, five is confirming…

I maybe should have. I was curious how much copper was in the freshly-chambered barrel, and cleaned it after the five total shots. There was some deposited about half way down the tube.

 

[M-61]

I do not touch the flash hole, other than a very light pass to clean any burr out that may be there. Yes Lapua occasionally has a burr. Don’t care if they may drill them or punch them. There’s the occasional burr. That’s a one time deal. Burr’s do not reappear. Now I really prefer small flash holes. years ago I bought PMC small rifle primer brass for my 22-250. Obviously not a bench rifle or cartridge. (Colt-Saurer)
Only people who made it to the best of my knowledge. Using that small rifle small flash hole primers reduced my groups about half the size.Three shot groups only as it’s a varmint barrel burner and this rifle is really a fine piece of jewelry. Now I only shoot 100 yard bench rest. 6BR, 6.5br, 30 br. All small flash holes. Most accurate rifles I’ve ever owned. My 30br has shot in the ones for me. That small flash hole experience years ago has never left me. Small or large flash holes or large or small primers to me has always been a bit of a mystery as to what’s really going on. I use what works for me and write only what I personally have done, I recommend nothing to anyone.

 

[SeabeeKen]

Alex wheeler and the crew at Deep Creek did some experimenting trying different flash holes drilled to different sizes and I'm pretty sure they found no meaningful difference all the way to .080 like Alpha brass has.

I found a govt study done on flash hole size a while back. After reading thru the 100 plus pages, they found larger flash holes were 20% more accurate with regard to precision. I posted it somewhere but don't recall where