Can anyone explain whats going on

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I have worked up a couple of loads for my .308win and was getting 1/2 to 3/4" groups @100, that was until my wife picked me up a flash hole deburring tool and I used it on some of the brass. That is where the problem came into play, groups went down the can. :confused: I think I know why, but wanted some seasoned knowledge to confirm my reasoning. Load is 168 SMK over 43.2g H4895 Lapua brass.
 
If the tool was only deburring, there should be no change in group size. The only reason I can think of is that the flash hole is being enlarge a little; that is if the deburring has anything to do with it at all. You also don't mention what size groups you're getting now.
 
The groups are 1.75 to 2". I know it has nothing to do with loose scope mounts or action screws because I can shoot known accurate ammo in the rifle and get consistent groups.
 
Lapua brass has drilled flash holes they don't need de burred. I think you changed the angle of the flash hole thus giving a different ignition flash to the powder column.

Lupua is outstanding brass, no prep needed, just load and shoot. We all learn from our mistakes don't get bothered by it learn from it and keep chasing them little bitty groups.

If you want to play with brass prep get some winchester, rem, even federal lol or some mil spec and play with brass prep. Keep some as factory, and change one thing at a time. When deburring flash holes the weight of the tool should be enough to remove burr from cases with punched flash holes. It doesn't take much, and any altering to the depth, angle etc will diminish accuracy.

edit to add= mark or trash the brass that you altered so far with flash hole tool, and make the mark permanent. Can you imagine chasing fliers from a few of those dropped in a pile of brass ? A fellor would be cussing up a storm !!
 
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I think it was on the 6mmBR site that I saw a test with standard flash holes and then flash holes nearly twice the size. If I recall correctly there was no change in accuracy.

I think something else has changed coincidently along with the deburring process. Think carefully, new batch of powder? See if you can think about any changes, you did, different batch of brass?
 
I've never done any extreme work on flash holes, other than just minor uniforming when the need is obvious. But never noticed any change in accuracy.

Maybe you've enlarged the the flash hole, or too much, and it's changed ignition, maybe it's igniting quicker, or the flash depth into the charge is deeper? Like I said, never had a problem with this.

I think Andrew has a good angle, look carefully at everything your doing, and then try to find that one little thing you might be doing different, different primers, powder lot, check the charges to make sure they're what you think they are.

GS
 
Many times a modification and/or change in components will affect accuracy. Many manuals warn about that.

If groups have opened up, and the sole change you've made is deburring, stop deburring. If you stop and groups don't go back to where they were, you've introduced some other variable that's changed something.

I'd allow that deburring has simply put you back to square one working up to your gun's "sweet spot" with respect to accuracy .
 
I've tried deburring from time to time and can never recall a time when it made any detectable difference in accuracy either for the better or the worse.
 
Lapua brass has drilled flash holes they don't need de burred. I think you changed the angle of the flash hole thus giving a different ignition flash to the powder column.

Lupua is outstanding brass, no prep needed, just load and shoot. We all learn from our mistakes don't get bothered by it learn from it and keep chasing them little bitty groups.

If you want to play with brass prep get some winchester, rem, even federal lol or some mil spec and play with brass prep. Keep some as factory, and change one thing at a time. When deburring flash holes the weight of the tool should be enough to remove burr from cases with punched flash holes. It doesn't take much, and any altering to the depth, angle etc will diminish accuracy.

edit to add= mark or trash the brass that you altered so far with flash hole tool, and make the mark permanent. Can you imagine chasing fliers from a few of those dropped in a pile of brass ? A fellor would be cussing up a storm !!

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Last edited by Clint M; Yesterday at 11:01 PM.
These were my suspicions as well. I am using the same 20 brass so no other changes were made. Same bullets out of the same box, and same pound of powder, same primers. I have plenty more unfired brass from the same batch that has nothing done except trimming so I will load some of them and see what happens. Thanks for all the replies.
 
Flash hole deburring

th_B4Deburr4B.jpg
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th_10thouDeburr001A.jpg
[/URL][/IMG] If you changed the diameter to a larger hole, that may be the problem?? Not Lapua in photo.
 
Flash hole deburring

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If you changed the diameter to a larger hole, that may be the problem??
The flash holes look like the pic on the right. I used the lyman tool and only took .010 out. Would you suggest changing brass??
 
Are you asking to change brass brand or just the brass you have deburred ? Lapua is the best brass made by far, it's so good many BR shooters now shoot it right out of the box with no prep work, some will do minimal prep work of primer pockets, many many no neck turn chambers now from reading, and that is saying something to the quality of Lapua brass !!
 
In your OP you stated that :

"I think I know why, but wanted some seasoned knowledge to confirm my reasoning. Load is 168 SMK over 43.2g H4895 Lapua brass."


What do you think it is??
 
How many times have those pieces been fired
I have fired those 20 around 7 or 8 times. I anneal after the third firing and neck size until the shoulder needs to be set back, then I set them back .003.
[What do you think it is?? /QUOTE] I am thinking the same thing Clint M Is thinking. I think I changed the ignition flash to the powder column, thus causing different burn rate and changing things enough to affect accuracy. I plan to load 5 of the same brass along with 5 fire formed brass that I have not used the flash hole deburring tool and see if I get different results from the two. I had never used a deburring tool on brass before this so it kinda stumped me when those small groups opened up after using it on these brass. Glad I didn't use it on all my Lapua brass cause I don't have a lot of hair to pull out trying to figure out the problem.:banghead:
 
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