Opening up primer flash hole????

[762willdo]

I have read that some users of the 6X47 lapua are opening up their flash holes and getting better results on the chrono (ES/SD) and better results on paper at 600/800 in terms of more consistent grouping and better elevation.
anyone have any thoughts or experience with this???
I know on my brass my flash holes are very small to the point that every 10th one (or so) will grab my decapping pin, in fact the holes in my lapua .223 brass are bigger.

 

[camac]

I know two guys that swear by opening up the flashholes a bit for 6*47 Lapua. Exploring hotter primers may help too. Others have gotten this caliber working fine without doing it. I feel the 6*47L is just a little harder to tune than the 6 BR, BRX , Dashers and the like. Once you get the right charge, neck tension, seating depth, primer etc some perform very well. Primer holes as far as I can tell are still a little bit of an unconfirmed (at this stage) claim by a few. It may well turn out correct but I would suggest it just helped them "tune" their particular loads so that their powder charge burned correctly.

Lapua 223 doesn't have small flasholes (should be 78-81 thou) but does have small primers. But 6.5*47 Lapua brass does (should be 58-61 thou). If your decapping pin is catching I would say you have the wrong decapping pin and may have already "punched" the primer holes larger anyway. If it is only catching 1/10 then it may be around 58-59 thou and is "uniforming" them a little for you. Just make sure you debur inside and outside afterwards. It may well be much larger though. If you have a mic, check the size.
If you go down the path of enlarging the holes for a trial I would recommend you only do it on 10 shells. I also like using tapered pin reamers as they do a better job of reaming out flasholes more evenly than anything else I have seen

 

[RDavies]

I have had a bad run with my 6x47s, 2 barrels, 3 rechambers on one. Sometimes it was great, but then, the odd dropped shot. I have an internal flash hole deburrer which takes the flash hole out to about .068" I think. When I get time, I will ream about 10 cases and compare it to the std flash holes and post the results. I have always used AR2209 (H4350) powder, but I am also going to play with some other powders to get the ES down.

 

[762willdo]

went to the range today 5 new pieces of brass with the primer flash hole factory
5 new pieces of brass with the hole opened up
load: 115 DTAC 39.0 RE-17 cci450 seated 5into the lands (my goto load for this rifle)
5 unopened holes fps avg.=3035 SD11 ES19 (normal)
5 opened holes fps avg.=3054 SD 7 ES14 (group was tighter)
groups were shot at 100yds across the chrono tomorrow will shot the same brass at 300yds to see whats what.

 

[coupalr]

762, What size did you open the flash hole to?

 

[762willdo]

5/64

 

[in2deep]

Camac,
could you please elaborate on the tapered pin reamer please like what brand/size/who sells them?
thanks.

 

[camac]

Thanks 762willdo. Figures look like you would expect. With that slight rise in velocity (as expected) it may need redeveloping the load to keep you in the node.- Would be keen to see if you have an easier time of tuning/load development. Keep up the reports, thanks.
I am very much sitting on the fence here and have a reamer plan drawn up with steeper shoulder angle ready for some more good reports..................

Tapered pin reamers - http://www.victornet.com/subdepartments/Taper-Pin-Reamers/2548.html but there are plenty on the market just type in for a search. a 7/0 reamer put right through would give a primer flash hole size in the middle of large and small. A 6/0 taken to end is about a large flashhole size (0.081 thou). You can make a depth stop to experiment at different diameters. I would advice building one anyway as a lot of the reamers have no definitive stop area. I built my depth stops from the brass light fitting wire attachment and a float stop machined down. I will get a photo and post. A good quality reamer will not need this though.

 

[762willdo]

Ok heres what i have figured out. by opening the flash hole to .0781(5/64th's) i have removed 98% of the vertical from my 300M groups, however the downside is that my pressure increased.
Prior to opening, my load of 39grn's RE-17 and a 115dtac with a 450 primer was able to be fired at 90 degrees with no pressure signs, however today it was 76 and my bolt lift was firm(not hard) as well as a slight shine to the ejector area, i already noted a 30+- fps increase over the chrono so now i will drop my load 1/2 grain and shoot over the chrono as well as 300m to check grouping.
all this being said it is well worth it to loose the vertical from my groups.

 

[camac]

You would expect a substantial increase in velocity (and pressure) with opening up the flashole. This is because you are getting a better ignition initiation in your powder. This is the result we were chasing so well done (although I should have warned you to back the loads down when opening up flasholes), Try another load development and let us know how you go. Great news.