Flash Hole

[Homerange]

Partially tapered flash hole with the larger diameter on the inside of the case.

OK, thanks. So how would/could inside flash hole chamfering fit into any possible venturi action ?
I don't see it could, would you agree ?

My understanding of venturi action is a tapering orifice speeds up volume flow then just past the tightest restriction where a vacuum is formed additional volume is sucked into the flow to provide a greater overall volume quantity.
I don't see any possible advantage in any ordinary rifle case from this.

I'm a chamferer and my research has me believe it has the greatest effect on consistency of ignition by removal of any flash hole burrs that could affect the primer blast dispersal and also by bringing a small part of the charge closer to the primer which helps ignition spread.
Years back when I first got a press after some decades of just using a Lee Target model handloader set I stumbled on a great novice loader thread where a poster with decades of experience stated quite categorically that the one case prep tool he couldn't live without was an inside flash hole chamfer tool.
I've had the Mk2 Sinclair tool since and use it on all calibers.

 

[Jeff A]

If you are talking about .308 Win. Palma cases with small rifle primer pockets, definite con. SR primer cups are about .020-.022 thick. LR cups are .027. By enlarging the flash hole diameter you would be allowing more gas pressure volume against a thinner cup. Pierced primers by firing pin is a possibility.

CCI 450 and BR-4s and Remington 7 1/2 primers all have cups of .025". These are all Small Rifle Primers.

 

[Dusty Stevens]

OK, thanks. So how would/could inside flash hole chamfering fit into any possible venturi action ?
I don't see it could, would you agree ?

My understanding of venturi action is a tapering orifice speeds up volume flow then just past the tightest restriction where a vacuum is formed additional volume is sucked into the flow to provide a greater overall volume quantity.
I don't see any possible advantage in any ordinary rifle case from this.

I'm a chamferer and my research has me believe it has the greatest effect on consistency of ignition by removal of any flash hole burrs that could affect the primer blast dispersal and also by bringing a small part of the charge closer to the primer which helps ignition spread.
Years back when I first got a press after some decades of just using a Lee Target model handloader set I stumbled on a great novice loader thread where a poster with decades of experience stated quite categorically that the one case prep tool he couldn't live without was an inside flash hole chamfer tool.
I've had the Mk2 Sinclair tool since and use it on all calibers.

If it works for you by all means keep doing it. Its a detriment to most

 

[bobm]

CCI 450 and BR-4s and Remington 7 1/2 primers all have cups of .025". These are all Small Rifle Primers.

True...but others that might find their way into a small primer pocket have thinner cups. See the chart I was referencing from. I should have said "some primers"

https://www.google.com/search?q=primer+cup+thickness+chart&tbm=isch&source=iu&ictx=1&fir=2PfaYGeMWD08JM%3A%2CwVIT3ftnxTXt3M%2C_&usg=__VsDw2Ki1PvV3Fa-rJcRUGFTk8K0=&sa=X&ved=2ahUKEwiVgZaW98XcAhUk44MKHcKNCYQQ9QEwAXoECAMQBA#imgrc=2PfaYGeMWD08JM:

 

[Homerange]

If it works for you by all means keep doing it. Its a detriment to most

You know only too damn well the variation in internal flash hole burrs. Not everyone uses or can afford drilled flash hole brass. The little bit of 308 Lapua brass I have gets chamfered too and 6fps ES is the result.

 

[Macropod]

OK, thanks. So how would/could inside flash hole chamfering fit into any possible venturi action ?
I don't see it could, would you?

You are right. It isn't a venturi as such nor does it act like one, but somehow it has acquired that description in common shooter's language.

My experience with long range 308 shooting shows it hasn't been at all detrimental to grouping or waterline at 1000yds. Possibly it has improved elevation consistency at longer ranges a little. This is with LRP Lapua brass though. The object was have each case identical and the K&M tool used helped in that respect.

 

[Laurie]

The LItz tests showed neither benefits or disbenefits from bevelling (let's forget the common 'venturi' term) flash-holes. Bryan's take on the possible benefits was that of a reduction in the length of the flash-hole passage as it could conceivably abstract heat / energy from the primer eject passing through. He therefore bevelled one end and both ends in the tests, but neither made any difference over and above the effect of a simple deburr on the internal (exit) end - which gave major ES/SD reductions. As with the many handloading practice tests in Modern Advancements Vol 2, results were on the basis of chronograph results, not groups.

 

[Macropod]

So getting back to small/large flash hole debate, ignition should be better under cool/cold conditions with a large flash hole. This would be particularly so with slower or harder to ignite powders.

I just can't see why a small flash hole would work in a 308 case any better than a large flash hole. I know the rationale behind the srp usage and lower es and sd numbers and this has been demonstrated often enough. I suspect there are limitations with effectiveness when a certain combination of case capacity, ambient temperature and powder type is met. My feeling is a large flash hole helps mitigate issues when running close to the edge of the above conditions. One of our club members did considerable experimentation on this and confirmed (at least in his mind) the benefit of the srp/large flash hole combination.

Yet another thing to experiment with...

 

[avidflyer]

The LItz tests showed neither benefits or disbenefits from bevelling (let's forget the common 'venturi' term) flash-holes. Bryan's take on the possible benefits was that of a reduction in the length of the flash-hole passage as it could conceivably abstract heat / energy from the primer eject passing through. He therefore bevelled one end and both ends in the tests, but neither made any difference over and above the effect of a simple deburr on the internal (exit) end - which gave major ES/SD reductions. As with the many handloading practice tests in Modern Advancements Vol 2, results were on the basis of chronograph results, not groups.

My take away from this is, its better to use a tool that deburrs froms the inside then one like the sincliar that works from the outside. Although I do like the sinclair since it indexes off the promer pocket. I’ll take 15 pieces of brass and try no deburr, inside, and outside and see what I come up with. Easy enough to run over the lab radar

 

[johara1]

You know only too damn well the variation in internal flash hole burrs. Not everyone uses or can afford drilled flash hole brass. The little bit of 308 Lapua brass I have gets chamfered too and 6fps ES is the result.

Lapua isn't drill either..... look in at it the flash holes on BR. brass. ... jim

 

[cw308]

It won't hurt to deburr the flash hole , will give a more uniform burn to some degree , I'm sure you could chronograph 10 of the same reloads 5 deburred . I deburr and uniform primer pockets on all new brass .

 

[Ccrider]

What is the best tool to debur and uniform.

 

[avidflyer]

for deburring check

It won't hurt to deburr the flash hole , will give a more uniform burn to some degree , I'm sure you could chronograph 10 of the same reloads 5 deburred . I deburr and uniform primer pockets on all new brass .

check out the sinclair tool for deburring indexes off the pocket

 

[Homerange]

What is the best tool to debur and uniform.

For consistent depth internal flash hole chamfering the Sinclair Gen 2 tool:
https://www.sinclairintl.com/reload...ersal-flashhole-deburring-tool-prod34127.aspx

Not to be confused with earlier versions that didn't have wings on the cutter that stop the chamfer at always the same depth.

 

[cw308]

Ccrider
I use the RCBS flash hole deburring tool , it is set after trimming your cases to the same length ,adjust cutter off the case mouth . Uniformer is also from RCBS . They all work the same , every company sells them , there all good , I just like RCBS.

 

[Macropod]

I like the K&M deburring tool as it indexs off the inside of the case negating the new for consistent 'trim-to-length'.

 

[Ccrider]

Thanks. I have a pick set that I use to get media out of flash holes after tumbling. While doing this I noticed that the holes are not the same size in Lapua 6mm brass. Not sure if it matters but would like to uniform them and see.

 

[cw308]

I use a #45 drill bit to uniform my flash holes on 308 & 45acp's found some smaller holes on both calibers , if I remember right they were Winchester brass . On all my new brass I will uniform the primer pockets an deburr an chamfer the flash holes , only has to be once . Makes seating an bottoming primers trouble free . I can't remember off the top of my head what the measurement of the flash hole should be , wouldn't be hard to find . Then get he bit to fit.