Keeping E.S. under 20fps.

[moosehunter]

For you select few out there who can manage to keep your E.S. under 20 fps., what do you attribute this to. I am going the whole case prep gambit and am ashamed to tell you what my E.S. is. The only variable I can think of at this point is the primer. I am using Fed. 210M. What is the primer of choice for you elite who can keep the small spreads?

 

[Guest]

I will list things that contribute to extreme spread becoming smaller.

1) Sorting bullets ogive to base

2) Properly reaming flash holes

3) Controlling neck tension

4) Precise powder measurement

5) Proper bullet seating INTO THE LANDS

6) Proper brass sorting

7) Proper barrel cleaning procedure

8) Consistent primer strike @ right depth

 

[Boyd Heaton]

9)CHANGE TO WLR PRIMERS...

 

[Boyd Heaton]

10)Weigh them.....5.2gr

 

[Michael Eichele]

Everything mentioned so far will help you with your mission, the only other thing I have found is using the proper powder for bullet weight and barrel length and also a slightly compressed load, NO air space inside the loaded round.

 

[bgordon]

All the items mentioned by S1 are necessary to obtain extremely low velocity spread amongst a group of loaded cartridges, but I have found that a couple of specific things must happen even after paying attention to the things previously mentioned.

The first has to do with brass. The following method is one which seems to work to get a few excellent groups of brass which will work to get consistent velocity from. AFTER doing all the requisite preparation steps to get a good group of brass, load up a pile of ammunition with a good proven load using proven components. I normally do between 50 and 100 rounds at a time but you can do more or less, depending on how much brass you wish to end up with. Next shoot all the loaded ammunition across a chronograph using the method mentioned in the second important item and make sure to use a black marker to write the chronographed velocity on each piece of brass. After all the shots have been fired sort the brass by velocity and group it in groups of 10 pieces based upon velocity. When doing this, often I can get 4 or 5 pieces of brass which will give identical velocity for the initial firing. In general, I get between 30 and 50 fps spread across 100 pieces of brass (depending on brass quality) but after they are sorted from lowest to highest velocity I can often get one or two groups of ten which have less than 10 fps spread. If you wish to be really picky, repeat the procedure and fire the brass across the chronograph a second time to verify the consistency of velocity. Again, the quality of the brass will determine how well the first velocity relates to the second velocity. The two times I tried doing a group of 50 cases twice across the chronograph ALMOST all of the brass showed consistent performance by staying in the same position in line. I say almost because both times there were a few cases which simply did not give consistent results and both times I tossed those pieces in the trash. What I did end up was two different boxes of 40-45 pieces which can be counted upon to give less than 10 fps spread for each group of ten pieces of brass as well as less than 30 fps spread amongst the entire box. Once I sort the brass in this manner each piece of brass stays in the same spot in my ammunition container from that point forward until I toss the entire lot as being worn out.
Note that the velocity from the first firing will probably NOT match the firing from the second firing due to external changes such as temperature, powder lot, primer lot, etc. What will remain consistent (except for the bad brass) is the relative position of each piece of brass in line and a low velocity spread when testing loads. It gives you the confidence to test other components and know that you have minimized the effect of brass in the loading process.


The second item has to do with the specifics of chronographing a load. There are probably many ways to get consistent results but this is how I do it.
Try to shoot all loads being compared at a single setting to minimize changes in external conditions. A load shot at a lower temperature will usually chronograph slower than when the temperature is higher.
I shoot a couple of initial shots thru the rifle in order to get the barrel and action up to the temperature which the chronographed loads will see. I normally touch the barrel with my finger and verify the temperature as being slightly warm to the touch. If you take a long enough break to allow the barrel to cool completely make sure and fire a warming shot before re-chronographing.
I fire one shot each several minutes as consistently as possible and feeling the barrel between shots to make sure it has the correct temperature. I only do this when the weather is cool because if the temperature is 100 degrees in the shade the barrel simply wil not cool down sufficiently between shots, which will give bad chronograph readings.

As I mentioned, there are probably many ways to get low velocity spreads but this is one method which works extremely well for me.


Oh yes, one thing to make sure and do to give yourself a better chance to get a load which has a low velocity spread is to use proven combinations even if they are not what you intend to end up with. For instance, one time I bought 5 boxes (100 loaded shells) of Federal Gold Medal 308 loaded ammunition and shot it all across the chronograph in order to give me the best possible chance to come up with some good brass. I know that buying brand new ammunition and shooting it at paper simply to come up with good brass is very expensive but it does give a consistent starting point.

[ 06-09-2003: Message edited by: Bruce Gordon ]

 

[Boyd Heaton]

3,4,6 and 7 in S1's post is all I do...Seems to work o.k.

 

[Brent]

Bruce,

I have been keeping track of velocities and numbering rounds like you for a little while now, with the 300 Ultra anyway. I haven't seperated any out or sorted them but, I do note what number cases I'm shooting on the target with their MV. It's organized better than it sounds.

I use the MTM 50rd boxes and each round gets put in the box in the same spot and stays in that hole. Looking at the open box, I number them 1-10, left to right, 11-20, 21-30, 31-40, 41-50... front row to back row, five rows in all. The next cartridge box is labled (51-100) and is 51-60, 61-70 and so on... I don't mark the cases themselves as it always comes off, I do however take great care to only remove them one at a time or keep them in order in the loading block when prepping and loading etc... I don't feed mine from the mag, but if I was going to then I'd mark them all real well.

Only thing I've really zeroed in on so far is one case out of the 100, #35, and it's been 20 fps faster and 3k psi higher on two occasions now, much farther than any of others which are holding about a 30 fps spread right with this load. I'm shooting it again tomarrow and will weigh it after if it shows up fast again. I still want to go back and look more at how consistant the others have been on seperate loadings. I definitely seen a spread of 10-15 fps with the same case when looking over ten to twenty that seemed higher or lower than the average MV.

Just reloaded some cases, #1-10, that I had done some MV and psi testing using Retumbo... all but two were "almost" too loose to hold primers now. That was only the second loading on these cases too! Pressure never went over 63k psi on the Oehler, but ejector marks and stiff extraction were still seriously evident. So, at this point I know I'm doing better MV wise with RL25 and it isn't thrashing my cases all to hell either, I have some at over 5 loadings so far and primer pockets are still tight, some of these loads were pushed "alot" higher than wih Retumbo too.

Looks like I'll have to do some testing to see what level I can get to with Retumbo and keep these cases alive for a while, doesn't appear that even 63k psi is going to work that well.

 

[AJ300MAG]

Boyd, S1, would you care to elaborate the process you use to evaluate and then control neck tension? How much difference does say .001 in neck size (I.D. of neck before seating bullet) effect group size? Do you use neck bushings alone or do you use an expander after?

Thanks