Flash hole diameter preference

[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

 

[Fire Dog]

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

I would think that any government study would involve military brass rather than any of the smaller bench rest calibres but saying that, I personally have found that moving to “Palmer” small primer/small flash hole brass in my 308W increased the accuracy of my Steyr hunting rifle.
I did need to use a faster powder {4895} and magnum primers but at 100 meters {328 feet} I put 5, 168gr Hornady into a 4 in one hole with the 5th just touching {last shot nerves}.
Previously I had been using LC match brass {Lg primer/Lg flash hole} and had never been able to get a group as good as that.
There is a reason that the US Military rifle team use this small primer, small flash hole brass and that is improved accuracy…
Perhaps the study that you read was conducted by the very companies that make the ammunition that the government buys?
I leave it to the more knowledgeable experts but depend on personal experience in the end.
What shows up on the target is what finally counts…

 

[JFrank]

I’ve found mine works best unmolested
Wayne

I’m convinced that Lapua knows more about brass than I do, I don’t mess with flash holes.

 

[Kracken McGraw]

I’m convinced that Lapua knows more about brass than I do, I don’t mess with flash holes.

I recently bought one of the K&M flash hole deburr tools that fits the Lapua brass. So far it has does nothing, that’s how good most of the brass is.

 

[M-61]

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

Yeah, I’d like to read that if it’s ever found. I’d like to read what they wrote not what you posted. Maybe they put come some MilSpec number next to their study to really make official.
Now when you say “ 20% more accurate with regard to precision “ what Exactly does that mean? Do I think you read through 100 pages to find that out? You bet I do. 100 pages … KITDFOHS

 

[M-61]

As far as ‘studies’ go. They show whatever the person paying for the study wanted it to.

 

[M-61]

I’m convinced that Lapua knows more about brass than I do, I don’t mess with flash holes.

I reached that conclusion with every single manufacturer of brass from day one. Doesn’t mean they do it. There’s always an accountant in the end that will determine exactly what will be done. There is no country on earth that can produce brass better than the USA. However the American companies don’t happen to because the bottom line is not correct. Lapua has no special skills at all, they merely are happy with their bottom line.

 

[Bob3700]

When the AMU was still shooting the M-14, they purchased a quantity of Remington 308 BR brass that was thin n had the small primer pocket. They used that brass for their 1000 yd matches. I shot matches with them at Oak Ridge n they even collected the fired brass ( orders from their NCOIC). I asked what load they were shooting n the only answer I could get was IMR 4064 n REM 71/2 primers. I believe that brass also had small flash holes ( not 100% sure about that though). It certainly worked for them.

 

[SeabeeKen]

Think this is it. It came from this website

https://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=8415&context=masters_theses

 

[Kracken McGraw]

I reached that conclusion with every single manufacturer of brass from day one. Doesn’t mean they do it. There’s always an accountant in the end that will determine exactly what will be done. There is no country on earth that can produce brass better than the USA. However the American companies don’t happen to because the bottom line is not correct. Lapua has no special skills at all, they merely are happy with their bottom line.

I don’t know about that. Lapua must know their metallurgy pretty well.

 

[Laurie]

When the AMU was still shooting the M-14, they purchased a quantity of Remington 308 BR brass that was thin n had the small primer pocket. They used that brass for their 1000 yd matches. I shot matches with them at Oak Ridge n they even collected the fired brass ( orders from their NCOIC). I asked what load they were shooting n the only answer I could get was IMR 4064 n REM 71/2 primers. I believe that brass also had small flash holes ( not 100% sure about that though). It certainly worked for them.

That was Remington's '308 Competition', also known as 308 UBBR (Unformed Basic Bench Rest) brass. It was made for reforming into the various versions of the BR Remington which had only just been introduced sometime in the 1960s. Hence the unusually thin walls to facilitate reforming. Back then, you had to buy form-dies to make your own BR cases as Remington didn't produce any or loaded ammunition (nor anybody else for that matter). (In fact, they never did other than for a period many years later when 7mm BR Rem became a popular metallic silhouette / single-shot pistol number and was offered as a factory ammunition product.) As you say, they not only had small primer pockets, but the smaller diameter flash-hole.

Naturally, many keen shooters learned about these cases and tried them in the 'basic' 308 Win form or in various wildcats based on the 308 case. The primary attraction wasn't the small primer ignition, rathe the thin walls which gave the case an unusually large capacity. As a rule, it didn't work out well for most who tried this, apparently through inadequate ignition - large ES spreads, hang and misfires were widely reported. Many users drilled the holes out to standard size and obtained an improvement.

So, when the US Palma Teams got together with Lapua back ca. 2008/9 to have a run of experimental small primer / small flash-hole cases made, and range-tested them over a season, the US Palma Teams' Long range Forum was inundated with posts by sling shooters who said it wouldn't work, in many cases from their own experience. Not only did the combination now work, but Lapua put this version into its catalogue and it has been widely used by F/TR, Palma and Fullbore shooters in many countries since 2011 or thereabouts

There is no reason to doubt the experience of the naysayers and their genuine concerns, but it seemed something changed to powders and Small Rifle primers early this century which changed a marginal situation into an acceptable one (with most powder grades anyway). The reason that the Palma Teams decided to experiment was that a team member, whose name I can never remember sadly, collected stocks of the Remington 308 Competition brass and competed very successfully using it over a couple of seasons. He persuaded the team managers to look at the concept, and they in turn involved Lapua to produce experimental brass. (The close collaboration with the Finnish manufacturer is why Lapua was able to subsequently christen its new case model the 'Lapua Palma 308 Win'. The US teams have trademarked the name and guard it zealously. AFAIK, Sierra with its 0.308 155gn MatchKing bullet and Lapua for this single case model are the only commercial companies who have been granted such permission for use on their products.)

There is a surprising number of these elderly cases still in circulation and many are owned by members of this forum. There is at least one forum member who was on the Palma team at the time and knows the entire story in detail.

 

[Bob3700]

Laurie,
U are correct on the thin wall / more powder capacity of the 308 UBR brass. My AMU contact indicated they used Remington 71/2 primers to light off the stout loads of IMR 4064. They also indicated that temps below 50 degrees caused hangfires. Above that temp the loads were ok.

 

[Fire Dog]

That was Remington's '308 Competition', also known as 308 UBBR (Unformed Basic Bench Rest) brass. It was made for reforming into the various versions of the BR Remington which had only just been introduced sometime in the 1960s. Hence the unusually thin walls to facilitate reforming. Back then, you had to buy form-dies to make your own BR cases as Remington didn't produce any or loaded ammunition (nor anybody else for that matter). (In fact, they never did other than for a period many years later when 7mm BR Rem became a popular metallic silhouette / single-shot pistol number and was offered as a factory ammunition product.) As you say, they not only had small primer pockets, but the smaller diameter flash-hole.

Naturally, many keen shooters learned about these cases and tried them in the 'basic' 308 Win form or in various wildcats based on the 308 case. The primary attraction wasn't the small primer ignition, rathe the thin walls which gave the case an unusually large capacity. As a rule, it didn't work out well for most who tried this, apparently through inadequate ignition - large ES spreads, hang and misfires were widely reported. Many users drilled the holes out to standard size and obtained an improvement.

So, when the US Palma Teams got together with Lapua back ca. 2008/9 to have a run of experimental small primer / small flash-hole cases made, and range-tested them over a season, the US Palma Teams' Long range Forum was inundated with posts by sling shooters who said it wouldn't work, in many cases from their own experience. Not only did the combination now work, but Lapua put this version into its catalogue and it has been widely used by F/TR, Palma and Fullbore shooters in many countries since 2011 or thereabouts

There is no reason to doubt the experience of the naysayers and their genuine concerns, but it seemed something changed to powders and Small Rifle primers early this century which changed a marginal situation into an acceptable one (with most powder grades anyway). The reason that the Palma Teams decided to experiment was that a team member, whose name I can never remember sadly, collected stocks of the Remington 308 Competition brass and competed very successfully using it over a couple of seasons. He persuaded the team managers to look at the concept, and they in turn involved Lapua to produce experimental brass. (The close collaboration with the Finnish manufacturer is why Lapua was able to subsequently christen its new case model the 'Lapua Palma 308 Win'. The US teams have trademarked the name and guard it zealously. AFAIK, Sierra with its 0.308 155gn MatchKing bullet and Lapua for this single case model are the only commercial companies who have been granted such permission for use on their products.)

There is a surprising number of these elderly cases still in circulation and many are owned by members of this forum. There is at least one forum member who was on the Palma team at the time and knows the entire story in detail.

A small foot note,
I have some “Palma” marked Peterson brass, it must have been early production as the later case head stamps have .308 Win SRP. No doubt that when these hit the market Peterson’s management received a call/letter from some lawyer to “Cease and Desist” due to copyright violation…
They are the ones that shot so well in my Steyr, and indeed a “stout” load of 44gr of 4895 behind a 168 Hornady + a CCI450 primer but definitely impressive results and I have never thought of waiting by the phone for the International Committee to call and be asked to join the team…

 

[Alex Wheeler]

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.

Tom and I did test flash hole sizes from .050-.080. There was quite a bit of difference. However it most likely only applies to the primer and powder combo used for the testing.

 

[charlie b]

I found the same thing back when I shot cast bullets. DIfferences in powder, charge, bullet weight caused different reactions to flash hole dia. Same kind of thing with large primers vs small primers or magnum vs std. Some combos liked one or the other. Some didn't care.