Range Report Contaminated Flash Hole - Test

[tnichols]

Ever wondered if all the fussing over primer pockets and flash holes is worth your time? I always tumble my brass after all the prep work for a half hour or so just to get rid of shavings and what not. I always check the flash holes for tumbling media before priming, except I forgot the other day and started priming. I caught my error early in the process, but ended up with 5 that had seated primers with a piece of tumbling media lodged in the flash hole. I decided to go ahead and load them and next time I chronoed to see if it made any noticeable difference. Here are the results:

Load: 77 gr. SMK over 24.6 grains of RE15 in new, prepped LC09 brass, and a Federal GM205M primer.
Base to Ogive Legnth: 1.859
OAL: 2.255 - 2.260
Gun: Bushy Varminter
Barrel: 24" 1:9
Temp: 39F
Humidity: 66%
BP: 30.23

First String: Above load - Clean Flash Hole
1. 2800
2. 2799
3. 2790
4. 2783
5. 2793
Average: 2793
ES: 17
SD: 5

Second String : Contaminated Flash Hole
1. 2723
2. 2760
3. 2788
4. 2763
5. 2770
Average: 2760
ES: 65
SD: 21.1

A couple of things I forgot to mention. All charges are thrown with a CM1500. Chrono is a CED M2. Looks to me like the prep work IS worth it. I didn't put these on paper, just ran them across the clocks. Thought you guys might find it interesting.

 

[aggiesig]

Re: Contaminated Flash Hole - Test

I would be interested in the group size difference, but seeing how different Standard Deviations, I would assume that the groups would be proportional to the SD.

 

[Rob01]

Re: Contaminated Flash Hole - Test

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tnichols</div><div class="ubbcode-body"> Looks to me like the prep work IS worth it. </div></div>

No, looks like you shouldn't leave media in your flash holes is all.

Been in a discussion on another forum about deburring the flash hole and I have tested with and without and found no difference in velocity, ES, SD or accuracy.

 

[9H_Cracka]

Re: Contaminated Flash Hole - Test

AWESOME and thanks dude!

Would still be in the group at 200-300, but something that would sure make a dent in your score at 600 on back.

 

[tnichols]

Re: Contaminated Flash Hole - Test

I agree with Rob01, don't leave media stuck in your flash holes. I just thought this is something that if it goes unchecked can make a difference. I deburr, uniform, etc... and I guess my point was, if you don't check for media, it could certainly have an effect on that rounds performance. At 100-300 yards, no big deal, but beyond, judging by the SD, I'm thinking it would certainly make a difference.

 

[azimutha]

Re: Contaminated Flash Hole - Test

Just goes to show those media flash holes are not straight shooters.

 

[Creature]

Re: Contaminated Flash Hole - Test

My guess is it effects the way the primer ignites the powder.

 

[Grump]

Re: Contaminated Flash Hole - Test

I seem to remember that someone ran a similar test (similarly small-sample too) with a .308 maybe a year ago...



...and the results were BETTER with a chunk of walnut shell in the flash hole.

But I think he reported accuracy too.

 

[Unknown]

Re: Contaminated Flash Hole - Test

As long as flash holes are the item of discussion: When examining new lots of Lapua 6.5 Grendel brass, I noted that a one sixteenth drill bit would pass through about 60% of the flash holes, and would NOT pass through the other 40%. So, now when I get a new lot of brass, I uniform the flash hole sizes to all be one sixteenth of an inch. I haven't tested whether it makes a difference, but common sense tells me that different sized flash holes will certainly not help accuracy. Making them all uniform can't hurt.

What really surprised me was that this was from Laupa brass.

 

[damoncali]

Re: Contaminated Flash Hole - Test

Interesting test, but be careful - that's no where near enough rounds fired to come to any useful conclusion.