Enlarging brass flash hole?

[STS]

Agree Alex. There are so many different variables that it would take exhaustive testing to have a conclusion that would stand up to a statistical evaluation. My Mickey Mouse 20 round test isn’t worth much. All I learned was that the rifle would fire as expected, and without any crazy chronograph surprises or degradation of accuracy at 400 meters.

 

[Mulligan]

Tom and I did test flash holes in Alpha BRA brass. They sent me brass with no flash holes. I drilled and reamed them. We went from .050 to .080. It was a hard choice between. 050 and .080. .060 was good, .070 was not. I didn't expect results like that. Probably why you will hear people say not to open them up. Your much better off at .060 than .070. But if you go past that to .080 it's good. I would not assume the same results in all cartridges or even in the same with different powder or primer combos.

Did you see any increases in pressure as the flash holes were opened up?

I remember Dan Dowling trying larger flash holes on a PPC. I think he went well above .080”, but I’m not sure of that. I do not recall him having issues at all.

Just curious
CW

 

[Alex Wheeler]

I'd have to ask Tom but I don't remember any real difference there. We just looked at how they printed in and out of tune at 1k.

 

[Ned Ludd]

I'd have to ask Tom but I don't remember any real difference there. We just looked at how they printed in and out of tune at 1k.

Thanks for sharing the results of the flash hole tests, Alex!

I'm also curious about pressure/velocity as a function of flash hole diameter with a given primer/powder/bullet combination. I started using Alpha munitions SRP brass in a couple of my .308 Win F-TR rifles last year. Unlike Lapua, Alpha uses a 2mm flash hole in their .308 Win SRP brass. Using Varget and 200.20Xs, I end up with very similar loads in either brand of .308 Win SRP brass. In other words, the slight difference in case volume and 1.5mm vs 2mm flash holes don't seem to create large differences in tuned loads. If you and Tom ever do any similar flash hole testing in the future, perhaps you might get the chrono out and record velocity as well. I understand that may not the typical practice with load development, but it might provide additional insight into how flash hole diameter affects grouping, or at least what changing flash hole diameter is not doing.

Greg Taylor

 

[Brians356]

MAY BE improved by UP TO 20%.

Translation: No correlation.
-

 

[Alex Wheeler]

Thanks for sharing the results of the flash hole tests, Alex!

I'm also curious about pressure/velocity as a function of flash hole diameter with a given primer/powder/bullet combination. I started using Alpha munitions SRP brass in a couple of my .308 Win F-TR rifles last year. Unlike Lapua, Alpha uses a 2mm flash hole in their .308 Win SRP brass. Using Varget and 200.20Xs, I end up with very similar loads in either brand of .308 Win SRP brass. In other words, the slight difference in case volume and 1.5mm vs 2mm flash holes don't seem to create large differences in tuned loads. If you and Tom ever do any similar flash hole testing in the future, perhaps you might get the chrono out and record velocity as well. I understand that may not the typical practice with load development, but it might provide additional insight into how flash hole diameter affects grouping, or at least what changing flash hole diameter is not doing.

Greg Taylor

We always have the crony out. He has that data. I just dont remember any big difference. @tom would know

 

[tom]

Greg, Clay,

I didn't see any velocity difference, and if I did the average was within the expected ES with the larger on the higher end. The tune windows indicated no changes when running ladders on the same range session as well. I thought 50s 60s and 80s were all very tunable and for whatever reason 70s stunk 2 for 2 trips. Not dissimilar to some spring and tip diameter stuff we did last off season where I would see it go from horizontal favor, to diagonal, and to vertical. Having drew a moose tag, and struggling by the way, I missed this year's off season to do any follow up stuff. I did have Alex stress relieve my barrels by hauling them to Florida and back though!

Tom

Edit to add this. Some of the more impressive days I had working with 50s were on our coldest days...approaching zero, so that didn't seem to matter. And the numbers were normal.

 

[22BRGUY]

Translation: No correlation.
-

WRONG
The article I was referring to said essentially the same thing as the last paragraph
of the Masters Thesis link John Weigel posted.

 

[Mechdraw]

Hi Butch
Sorry about delay in reply.
The test was done due to bad timing in bolt cycling in defence semis. It was found that reducing firehole size changed port pressure in a favourable way but reduced velocity about 30fps.. I was involved in the resting.
Regards

 

[Mechdraw]

Port pressure was the main concern, velocity change was secondary

 

[Steve Donlon]

I sized some Lapua 6.5 Creedmoor SRP brass with my regular 6.5 Creedmoor RCBS sizing die for LRP brass. It opened up the primer hole bigger but not as much as the hole in LRP brass. When I shot these loads I made I compared them to the exact same load that I did not enlarge the hole. The ones I made bigger shoot 1/2 MOA higher at 500 yards and 1/2 MOA higher at 1000 yards. They are also more accurate. They are faster and more accurate. After I saw the results I took a RCBS neck sizing die and put a LRP pin in the die and opened the hole on all my Lapua SRP brass. I used already sized brass and did not have to lube the brass to do this. It was very easy. After I enlarged the holes I used a Lyman small primer pocket uniforming tool to remove the small lip on the edge of the hole from enlarging it. The load is 40.9 grs of RL16 @ 2775 FPS with CC! 450 primers. This load now shoots 1/2 MOA groups at 1000 yards on a good day with no wind. It shoots exactly the same point of aim as 40.5 grs. of IMR 4350 with Lapua LRP brass and BR2 primers. Elevation is 23.5 moa at 1000 yards. At 6500' elevation. I also shoot 42.3grs. of RL16 with the same 147gr Hornady bullet at 2850 FPS using Hornady brass that is just as accurate but was looking for a accurate load that was at a lower pressure. I could not get the same velocity from Lapua brass without pressure signs so I found a load that was just as accurate but less dramatic.

 

[markm87]

Have done it. Works fine. This was some of that .059 flash hole creedmor brass I opened up just enough to work with my decap die.

 

[MikeRu]

I used a drill press and ran a 5/64” (0.078”) drill bit into all my 6.5 Creedmoor SRP cases after some testing indicated better groups. Primer is Fed 205M. No ragrets.