Flash Hole Uniformity


Lord Kimbote
October 15, 2011, 03:19 AM
While I was loading some mixed brand .357 SIG brass this evening, I noticed that the flash hole on Remington brass was considerably tighter than the other brands I was loading (Federal, Winchester and a few Speer).

My question is: how much of an impact would this restricted flash hole have on the load? Should I separate the Remington brass and use different load data?

I am inclined to think that the difference is negligible, but any input from you all would be appreciated.


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October 15, 2011, 04:04 AM
If the flash hole is "considerably tighter" I would think it would make a difference you could see if your gun was sufficiently accurate.

October 15, 2011, 05:59 AM
Good morning
Some years back someone writing for one of the better reloading mags wrote about accuracy in a finely tuned handgun. Flash hole unifornity was one of the items he included. Bottom line was if you can hold a very accurate handgun as well as a Ransom Rest you can see a .2 inch accuracy improvement at 50 yards. Author purposely used about 20 cases per study that were of different manufactures and that displayed a good variance of what we might call a standard flash hole. He also did case length, crimp variation, bullet weight , powder charge and varying primers.
All efforts at uniformity add to accuracy with reloading. Certain special opps groups reload their own entry ammo... not to gain the accuracy edge but to know for sure there is a primer hole, a properly seated primer & powder in the case.
Mike in Peru

October 15, 2011, 06:27 AM
Back when the .357 Maximum was first introduced and Winchester, Federal and Remington all made brass, there was a noticeable difference in the flash hole and in the brass thickness and it made a difference (small but still there) in the maximum level charges.

October 15, 2011, 10:43 AM
Of course one could "Uniform" them. Just find a drill bit that is the same size as the larges flash hole and make them all the same.

October 15, 2011, 01:32 PM
For the "average" shooter it makes no difference. If you're bullseye shooting at 50 yards, then it "might" make a difference.

You'll also run across some Speer 357 Sig brass with a small "s" on the headstamp that has an even smaller flash hole. I load them all together and both of my 357 Sig pistols shoot small groups at 25 yards with mixed brass and a good load.

Hope this helps.


Justin Holder
October 15, 2011, 03:34 PM
If your concerned about having top notch accuracy get one of these.

Lyman Flash Hole Uniformer Tool

October 15, 2011, 04:14 PM
I have a related question: I have a bunch of Aguila .38s with the flash holes off center, as in the attached pic. Federals shown for comparison. Should I keep or toss?

October 15, 2011, 04:23 PM

If you're just loading for informal plinking, etc., then load them up and shoot away. On the other hand, if you're loading for 50 yard bullseye shooting, then don't use them for that, though you would probably not be able to tell the difference unless you're a Grand Master class shooter.

When decapping brass with off center flash holes, it helps to loosen the nut on the decapping stem a little so the decapping pin can move to the hole. Flash holes are punched from the outside, and if the tool holding the brass gets a little worn, or if the punch is slightly out of alignment, then you'll get off center flash holes like the ones you've pictured.

They're really no big deal for most informal shooting.

Hope this helps.


October 15, 2011, 08:04 PM
I've tested loads with varying sized flash holes in my Ransom Rest and I really haven't found a consistent, appreciable difference (+/- .2" at 25yds). For my skill level shooting off-hand at bowling pins and steel plates, +/- .2" will never make enough of a difference for me to start uniforming flash holes. However, if I was competing in 50 yard bullseye I would want every edge I could get.

I do cull the cases with off-centered flash holes. I also square the primer pockets and deburr the flash holes. Since the flash holes are punched from the outside, as ReloaderFred mentioned, they often leave a burr on the inside of a case. Deburring flash holes can make a significant difference.

October 15, 2011, 09:00 PM
If your concerned about having top notch accuracy get one of these.

Lyman Flash Hole Uniformer Tool

That is a flash hole deburring tool, it does nothing to the flash hole itself. It's really a small center drill in a holder.

Lets get the terminology straight here. There's the primer pocket, then the flash hole. There's a flash hole deburring tool often falsely identified as a flash hole uniformer. Then there's a primer pocket uniformer, and primer crimp reamer.

If you want to be OCD about the size of the flash hole itself, then do as amlevin said, find out the largest FH in your brass, then find a drill that's the same size, drill out all to the same size.

October 15, 2011, 10:13 PM
A 5/64" drill bit (or a few of them) and that Lyman flash hole deburring tool will allow you to make them all .080" nominal in size which is the large end of pistol caliber flash holes.
The problem is depriming those cases with the smallish flash holes. (Speer .357SIG)
If you are unlucky enough to find yourself able to force the larger decapping pin into the small holes, three times out of five it will get stuck, and often enough get broken forcing them back out.
Headed decapping pins to fit those small holes without breaking the bank? Lyman replacemnts from MidwayUSA ( less than $3.00/10)

October 15, 2011, 11:57 PM
Snuffy the Lyman "flash hole uniformer" does in fact have cutting flutes on the portion that enters the flash hole. So if you have a case with a tight flash hole it will in fact enlarge the flash hole in addition to deburring the flash hole.

So it does in fact "uniform" the flash holes in that it will enlarge the flash hole on those cases with a tighter flash hole.

If you are talking about something else I'm ready to learn.


October 16, 2011, 12:52 AM
Dentite, you are correct. I assumed from looking at the 2 I have that the drill portion was too small and too short to drill out undersize flash holes. I just measured mine, one is a Lyman, it is .080 and plenty long to go all the way through the FH.

I almost made it through today without making a mistake!:banghead: I hate to spread misinformation, I never want to be accused of bee essing anybody.:eek:

Lord Kimbote
October 16, 2011, 12:53 AM
Again, I am very impressed with the information posted in this thread, thanks very much. I wish I had joined this forum years ago.

For what I am using my pistols for, I am relieved to find that the difference in flash hole size between brass manufacturers will not be a problem. Luckily, my Lee decapping die does not have a problem fitting into the constricted flash holes.

Friendly, Don't Fire!
October 16, 2011, 01:32 AM
This is why I process my brass after the first firing to include reaming the flash hole with a Sinclair Flash Hole tool. It has a green handle and two different size reamers - one at each end.

When people say they never bother with the flash hole and primer pocket, I ask myself, how much of a hurry could one be in to not consider cleaning the primer pocket and quickly reaming the flash hole a twist or two from each end?

I know why I reload, it is for premium ammo at a lesser price than factory. I also enjoy reloading, so time at the bench for me is enjoyable time. I don't look for things to do that don't need doing, however I am a firm believer that the primer pocket and flash hole are both important parts of the overall case component.:)

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