Time to chat some BR

L

Lawrence W.

Member
A couple of weekends back we were shooting the SW Regional 5 shot Unlimited in Visalia, CA. Lou Murdica was kicking our butts by playing with his tuner. I don't have a tuner on my rail gun so I could only play with powder and seating depth. The video below shows the dramatic impact that playing with your seating depth can have on your groups.

http://qik.com/video/41832090
 
Lawrence,
Good video and excellent point. You used pre-weighed powder charges. How much powder charge adjustment did you end up using, and what was the temp. range within which this was done?
Boyd
 
Lawrence W. said:
A couple of weekends back we were shooting the SW Regional 5 shot Unlimited in Visalia, CA. Lou Murdica was kicking our butts by playing with his tuner. I don't have a tuner on my rail gun so I could only play with powder and seating depth. The video below shows the dramatic impact that playing with your seating depth can have on your groups.

http://qik.com/video/41832090
Click to expand...

Nice video and it proves, IMO, that seating depth is much more critical to tune than powder. This is explained in Tony's book very well.

I think one of the things that discourages some new shooters and makes them give up the sport is they have not had this explained to them. Most new shooters are told to seat the bullet to a "certain mark" and then adjust the powder to finish the tune whereas many times 0.003" change in seating depth will have much more effect in tune than +/- 1 grain of powder.
 
Boyd Allen said:
Lawrence,
Good video and excellent point. You used pre-weighed powder charges. How much powder charge adjustment did you end up using, and what was the temp. range within which this was done?
Boyd
Click to expand...

My go to load for the rail is 29.4 gr. of N133 lot 222/07. I tried 29.0,. 29.3, 29.6 & 29.9 all to no avail. All 5 targets were shot with 29.4 gr. BTW that is Bart's double ogive BT.
 
I dont understand this " just touching the lands thing." How do you determine were the bullet just touches the lands? I have always found my max jam or the maximum i can seat a bullet out before the bolt forces the bullet to be pushed back inot the case. From there i work backwards. I read a lot and it does seem that quite a few guys use this " just touching the lands" as there base, or starting point. How do you determine this? I have a pretty general idea, but none the less i would like to discuss this a bit. Good video by the way! lee
 
I use the Stoney Point bullet seating gauge to insert the bullet into the throat so there is enough tension to hold the bullet but not enough to put any marks on the bullet. I call this "just touching" and the beauty about this method is that it is very repeatable giving you the same reading to .001 each time. A great article on the device and how to use it is at: http://www.6mmbr.com/catalog/item/1433308/977259.htm.
 
Skeet, one word, 'Silver Sharpie'

You color those bullets silver and you can see "just touching."

All the tools designed to "aid" in this endeavor are a complete waste of money.

IMO

al
 
Personally I tried the black sharpie but it never worked quite right for me.
I went to using a candle and sooting it and it worked great.
Just me though.
 
Just a quick question.
If I seated the bullet way long and let the chambering of the round set it further and then measured the height of the land marks and set my seater that much further in I should be right at "just touching" shouldnt I?
 
No, because different ogives will be marked different lengths when seated the same distance into the rifling. (Smaller ogive numbers (blunter bullets) have shorter marks, than larger ogive number bullets in the same throat.) One of the reasons that some benchrest shooters work off of jam, for a starting place, is that is so easy to find, and you only have one direction to go from there.
 
With the barrel off a sure way to get the exact tangent point (ogive curve tangent to the leade ramp) is to f/l size a case and then measure its base as you would a headspace gage. Then seat a bullet long, hand seat it in the chamber, measure to that case base again, and take the difference in those two measurements. Then set your seater stem out by that additional amount, you then have the exact tangent point.

To satisfy youeself that it is the exact contact point, just set the seater stem out 0.005" less than the difference above. You will find that the original measurement to the original case base and the now bullet seated base differs by 0.005".

 
Boyd I was referring to a complete hard jam and certainly it would be different for each make of bullet.
 
What I have used

is polishing the bullet every time before it goes into the chamber. By polishing the bullet one can see the faintest land marrks. I have called this my "Kiss". When one starts from there, there is always a benchmark to work from. Kiss needs to be re-confirmed on a regular basis.

With the 30's I shoot and have shot, over the years I have found most often, the best accuracy @ .006 into the lands from my Kiss so I think that shows some consistency with using Kiss, at least.

Looked to me like there was stll a bit of vertical in those groups. Perhaps another thou would have taken it out. Yes, .001 do make a difference as well. The question becomes how fine does one want to slice the Frog Hair I guess.

One problem we all face is seating stems are made wrong. All of them should touch the bullet just above where it will kiss the lands. That way, we wouldn't need to be concerned about varying Ogive lengths. Nobody is listening to this one yet but someday folks will, just like they finally have to weighing and using seating depth. It is a rare batch of bullets that won't have varying ogive lengths.
 
That verticle in the pics will be ok for group shooting, but probably would not cut it for score.

Later
Dave
 
Dave Coots said:
That verticle in the pics will be ok for group shooting, but probably would not cut it for score.

Later
Dave
Click to expand...

Hello Dave.

I beg to differ. If I had been shooting score and as I had less than 1 bullet in vertical, I would not have played with the seating depth and I would have centered the vertical over the dot. The tune in the 1st group would have been sufficient to shoot a 250-25X with somewhere around 10 wipeouts. The final tune would have produced a 250-25X with around 15 wipeouts.
 
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