Effects of flash hole size in ballistics and precision

[Bryan Z.]

 

[marchx]

Another great video Bryan. My intuition tells me that many people could be dissapointed that part of their routine turned out to be "statistically insignificant" in terms of impact on accuracy.

 

[mongo chicago]

I always felt that some of the "must do" beliefs of shooters are in the "old wive's tales" catagory. Then again if someone truly believes that doing something will help, then psychologically it will.

 

[Big Mc]

If you get a warm and fuzzy feeling, go for it. Tommy Mc

 

[Doom]

I always felt that some of the "must do" beliefs of shooters are in the "old wive's tales" catagory. Then again if someone truly believes that doing something will help, then psychologically it will.

Unfortunately you are correct that many of the must-do's are based on a one time test and now oftentimes based on sample test statistics without any analysis other than what a chronograph spits out.

Fortunately, there are folks out there that are beginning to take the time to demonstrate (as Bryan did here) how statistical testing can be used correctly and effectively.

 

[Ned Ludd]

A couple years ago, I purchased some Alpha Munitions SRP .308 Win brass, which uses the larger (2 mm) flash hole. If anything, my ES/SD values are even slightly lower with Alpha brass as opposed to Lapua SRP .308 Win brass, which uses the smaller (1.5 mm) flash hole. So in my hands, the difference in flash hole diameter is pretty much a wash in .308 Win. However, it's worth noting that the difference in flash hole may be significant in other cartridges. For example, the relatively .223 Rem case uses the larger 2mm flash hole. ES/SD values with tuned .223 Rem F-TR loads are typically about twice as high as for tuned .308 Win F-TR loads, and one of the potential causes or contributing factors in that difference could be the flash hole. That's really the only way it can be obtained so there is no good way to test/compare. Nonetheless, any differences caused by flash hole diameter might tend to show up in smaller cartridges where almost everything seems to have a greater effect on velocity stats.

 

[mikecr]

Does weighing powder even matter for whatever that is?
What cartridge and approx load pressure?

 

[JimSC]

great video.


What I was taught was that the smaller flash hole and small rifle primers permitted hotter charges without blowing primers. Not sure if that was back of the gunshop wisdom or based on facts

 

[markm87]

Very cool. I remember reading about opening up the Lapua Small primer 6.5cm brass that comes with a .059"ish flash hole to accommodate existing decap pins. The vast majority of guys said it was the end of the world to do this.

Only one reply was from a guy who'd actually done it and found no difference in performance as well.

 

[jackieschmidt]

The one instance where I saw a shooter drill out flash holes in a 6PPC (in conjunction with a different powder), was Larry Bagget at a Nationals in Kansas City in the mid 2000’s.

Larry had been fighting vertical, and decided for the last 200 yard Sat morning in Heavy Varmint, he would try something. He went to a local hardware store and got a drill to drill out the flash holes to a larger size. I can’t remember the exact size, but I think 5/64.
He then found a one pound jug of 4895 at the local gun shop.

The next morning he went out and won the HV 200. He didn’t shoot anything really that small, just five nice round “threes, fours, and fives” in some switchy conditions and got the job done.

I have never tried it myself. But at least I got to see a world class shooter think out of the box and come up with something.

 

[Gargoyle]

Well my flash hole reamer still clears the tumbler media...

 

[Dusty Stevens]

The ppc inventors drilled them all the way to .080 and decided they needed the small hole. This is why they went to the 220r case to start with or it woulda been a br

 

[Doom]

Bryan has run one test on one cartridge with one powder, one bullet, one brand of brass, etc. While it possible to speculate that that this is proof we really need to have other tests done on these and other components and cartridges to draw general conclusions.

 

[Bryan Z.]

Bryan has run one test on one cartridge with one powder, one bullet, one brand of brass, etc. While it possible to speculate that that this is proof we really need to have other tests done on these and other components and cartridges to draw general conclusions.

Let’s see some data from other tests!

 

[Goodcat]

Very cool. I remember reading about opening up the Lapua Small primer 6.5cm brass that comes with a .059"ish flash hole to accommodate existing decap pins. The vast majority of guys said it was the end of the world to do this.

Only one reply was from a guy who'd actually done it and found no difference in performance as well.

I decap before sizing with a Lee recapped. I just shaved down the decapping pin on it. Ha

 

[Bryan Z.]

The one instance where I saw a shooter drill out flash holes in a 6PPC (in conjunction with a different powder), was Larry Bagget at a Nationals in Kansas City in the mid 2000’s.

Larry had been fighting vertical, and decided for the last 200 yard Sat morning in Heavy Varmint, he would try something. He went to a local hardware store and got a drill to drill out the flash holes to a larger size. I can’t remember the exact size, but I think 5/64.
He then found a one pound jug of 4895 at the local gun shop.

The next morning he went out and won the HV 200. He didn’t shoot anything really that small, just five nice round “threes, fours, and fives” in some switchy conditions and got the job done.

I have never tried it myself. But at least I got to see a world class shooter think out of the box and come up with something.

Cool but unknown what had the effect, flash hole size, powder change, or both. This is why I test isolated variables.

 

[SeabeeKen]

Did not Norma or Lapua test flash holes and find smaller holes showed a difference? I recall reading something about it yrs ago

 

[Bryan Z.]

Did not Norma or Lapua test flash holes and find smaller holes showed a difference? I recall reading something about it yrs ago

If anybody has a reference to the test(s) or the actual results, please post that here for us to see.

 

[Liven The Dream]

I picked up some Winchester .284 Brass in the red/black bags.
The Flash Holes look like key holes.
The stuff shoots well ?

 

[CharlieNC]

Too bad not many here understand basic statistics. When discussing the SD and ES results which were "not statistically significantly different" at the "industry standard .05 level", the more appropriate statement is the P = .08 result means there is a 1-.08 = 92% chance that there IS a difference; how different is that than the 1-.05=95% chance there is a difference threshold? In other words there is a much higher probability the results are different than that they are not. And the SD does not follow a normal distribution and the proper test for significance is a F-test, what did that show?