The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > Handloading, Reloading, and Bullet Casting

Reply
 
Thread Tools Search this Thread
Old December 23, 2008, 07:57 PM   #1
tools
Senior Member
 
Join Date: October 13, 2006
Posts: 124
Gauging flash hole?

Hi all. Does anyone out there bother to gauge the flash hole in their brass before reloading? (Note I am NOT talking about chamfering the flash hole here, that is something I always do.) Basically what I am wondering about is the size of the flash hole (its diameter) -- does it matter if it gets bigger than spec?

Context: I shoot alot of long range and am trying to build the most accurate handload I can. I haven't seen flash hole gauges being sold in the precision shooting shops, so I am guessing someone along the way proved it is not necessary, but I don't know for sure.
tools is offline  
Old December 23, 2008, 08:28 PM   #2
Loader9
Senior Member
 
Join Date: July 29, 2008
Posts: 949
I do on brass that I expect target accuracy out of it and that includes long range hunting loads. I size mine to .081 EXACTLY. I have the tools to do it so why not. Even running a drill bit in the flash hole of the appropriate size can help in accuracy. The primer and the how that flash of energy gets to the powder makes all the difference in the world.
Loader9 is offline  
Old December 23, 2008, 08:40 PM   #3
jaguarxk120
Senior Member
 
Join Date: February 28, 2008
Location: Michigan
Posts: 2,618
How interesting, same size as the pilot drill on a #2 center drill.
jaguarxk120 is online now  
Old December 24, 2008, 10:07 AM   #4
tools
Senior Member
 
Join Date: October 13, 2006
Posts: 124
Are the flash holes the same size on all calibers? Or is it two sizes -- one for small rifle and one for large rifle?
tools is offline  
Old December 24, 2008, 11:16 AM   #5
amamnn
Senior Member
 
Join Date: May 13, 2006
Location: WA, the left armpit of the USA
Posts: 1,323
Flash holes are not necessarily all the same size. There are certain match cases, especially those used by BR shooters, but not exclusively BR brass, that are quite a bit smaller than standard brass. There is quite a bit of evidence from testing as far back as the Frankford Arsenal tests in 1923, that a milder flash results in better accuracy. This is so for a number of reasons and is the basis for the smaller flash holes. Taking this further, it would then stand to reason that you would not want to make your flash holes bigger than they come from the case maker. You can buy flash hole reamers that are cartridge specific, which will aid in keeping the proper diameter of the hole.

All this being said, there is not much, if anything to be gained by diddling with flash holes if you are shooting a factory off the shelf rifle. There are many more important to accuracy issues with those chambers and bolt faces you find there. Even if you shoot a nice, tight, blueprinted custom gun it would be more profitable to address primer seating uniformity problems before worrying about flash holes.

Among the other benefits of using premium brands of brass is the fact that their flash holes are drilled rather than punched, which means the holes will be much more likely to be round and the right diameter. This does not mean they are perfectly clean and that deburring will not be necessary.
__________________
"If the enemy is in range, so are you." - Infantry Journal
amamnn is offline  
Old December 24, 2008, 12:27 PM   #6
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 21,022
Lots of interesting odds and ends to mention here. It is correct that milder flash promotes accuracy. A few years back, RWS put out a particularly mild lot of primers and the benchrest crowd bought that lot out faster than you can sneeze. The reason for this is primer seating, cartridge headspacing variance, vent (flashhole) size and shape and other factors alter ignition, introducing inconsistencies in the ignition energy and its distribution in the powder. The less significant that inconsistent primer energy is made to the whole load, the more the pressure curve in the chamber is controlled by the powder charge. The loader controls the powder powder charge, so that minimal primer contribution puts him in better control of shot-to-shot performance. At 100 yards the error is usually hard to see, but at 300 yards and beyond it is pretty apparent.

It is not true that a factory gun will never see the error. When I was loading Accurate 2520 for my M1A, I found my best 168 gr. SMK load went from 1.25 moa at 100 yards to 0.75 moa when I deburred the vents in my cases. That is an unusual degree of difference, but was partly the result of lighting a ball powder charge that didn't fill the case well. This was with Federal 210M primers. With stick powders, like Varget, the vent deburr made no visible difference at 100 yards from that gun. The fact ball powders are harder to light (due to the decreased space between grains for the flame front to travel through) made this factor significant.

The smaller flashholes are desirable from the above standpoint, but I think a consistent flashhole is generally more important than size. The .30-06 casehead vent size is nominally 5/64" (0.078" -0, +0.004"; Hatcher's Notebook, p.27, '61 ed.). Reaming to 0.082" (#45) is thus in spec, even though having an 0.067" (#51) would be nice, there isn't an economical way to get there.

One problem that arises is fine ball powder, like Winchester 748, can fall into the vent and around the primer anvil affecting ignition consistency. Some folks have experimented with cutting discs of wrapping tissue, newsprint, or even toilet paper and dropping those in over the vent before charging with powder to prevent that. At the same time it mitigates the flash intensity some. You might want to experiment with that?

By the way, if you've looked at "green" ammo, the non-toxic primers require even larger vents to prevent blowing themselves backward out of the primer pocket and piercing and mushrooming. I've only found them in pistol cases thus far, but if you find any "NT" rifle caseheads in the future, they will not be for accuracy loads.

As to measuring the vents, this is done with what are called pin gauges. If you own numbered reamers or drills, though, you can check by dropping them in. For the drills your will also need an OD thimble micrometer with 0.0001" graduations to verify the drill's actual diameter, since they are often a couple thousandths undersize.

The premium cases typically have no burr to remove. Lapua .308 cases had a small burr in one lot a few year's back and they got enough complaints that they fixed it. If you look with a magnifier they appear to have been ironed or stamped out, though it may just be they use an anvil that prevents their formation in the first place? As to drilling, I don't know about that? Lake City cases are all drilled per military requirement. They still have burrs, and you see a lot of slightly (and sometimes not-so-slightly) off-center vents in them. I don't see anything off-center in either the Lapua or Norma cases I have. Whether by drill or by punch, I believe the tooling can be designed to make vents consistent. It is just a matter of how much you spend on it.
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member and Golden Eagle
Unclenick is offline  
Old December 24, 2008, 12:54 PM   #7
WIL TERRY
Senior Member
 
Join Date: July 6, 2000
Location: BLACK HILLS
Posts: 1,322
How Many Of You Whippersnappers Have A Herter's Flashhole Guage ??

OH...you weren't even around then ?? Sorry 'bout that !!! It measured 'em to the last .001" slick as you please. The first million dollar USPS money order gets mine .
WIL TERRY is offline  
Old December 24, 2008, 03:12 PM   #8
jaguarxk120
Senior Member
 
Join Date: February 28, 2008
Location: Michigan
Posts: 2,618
I've got one and it works great.

Picked it up at a gun show, the guy selling it didn't know what it was. I think I paid an outragious sum of $1 for it.
jaguarxk120 is online now  
Old December 24, 2008, 05:36 PM   #9
tools
Senior Member
 
Join Date: October 13, 2006
Posts: 124
Can anyone with the Herter's gauge take a picture of it and send measurements? Maybe I can make one.
tools is offline  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 07:41 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2021 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Page generated in 0.08950 seconds with 10 queries