Velocity Issue

[darchell]

I have two questions about velocity. I am loading 35 grain Berger bullets in front of 26.6 grains of benchmark lit by Federal 205 primers. Every loading document I can find shows velocity plus 3700. My average of 18 shots was only 3673? Does this seem right? Even in the favorite load section of this forum I found everyone else shooting with the same and less. According to Berger's information, sent to me upon request, they show 25.5 grains of Benchmark should be pushing the 35 grain Berger at 3775. any suggestions or ideas?
The other question is about the differences in velocity. Of the 18 shots my fastest was 3724 and my slowest was 3633, which I might add registered exactly for four separate rounds. So this would be my most consistent. The variation is 91 fps. Is this normal? This is with the same powder, charge and primer. All the specs. are the same. Any thoughts on this or suggestions of things I can do to shrink the variation a little?
I did learn one thing. I have seen that most everyone is suggesting the use of Redding Bushing Dies be it full length or just neck. I also noticed that no one is recommending RCBS sizing dies. I, of course have RCBS dies. Anyway, I found when loading that some bullets I can start with little issue in the case prior to running the ram. Others I have to fight and claw at to get them in the neck to start them. They then go up into the die at an angle but this is the only way I can get them to balance on the neck. There is obviously a variation in the tension. Seems the thought of not using RCBS sizing dies is coming to light. I am surprised I am getting the average accuracy I am with such a variation. My groups are typically around .5 I get the occasional .2 and the occasional .7 but for the average I would say around .5.

[Rick in Oregon]

darchell: The difference in velocity from the estimated or tested velocity in Berger's test barrel, or those barrels used in the manuals by the bullet makers will almost certainly differ from your actual results. The plain and simple reason is that there are "fast" barrels, and "slow" barrels. Two barrels from the same maker of the same caliber, made on the same day will vary in terms of both velocity and accuracy. Don't fret, it's normal.

As for the dies, for years I also used RCBS like many others, but over time switched to Redding, especially favoring their Competition Seating Dies, which perfectly align the bullet in a sleeve all during the seating process, ensuring perfect axial alignment with the case. This step is critical to good accuracy. RCBS dies are good, don't get me wrong, it's just that most accuracy minded shooters migrate to Redding, both sizing and seating dies. For most shooting in a 204 bolt gun, only neck sizing is required, and in a factory barrel, there's no real need to go to bushing dies unless you neck turn, and that is also pretty much not needed in a factory barrel.

I should also add that Forester dies are very good, and some shooters seem perfectly content using Lee dies. Many stick to the dies they started out with, and if they're getting the accuracy they feel is acceptable, then those dies are perfectly acceptable...to them.

As for the difference in seating pressure required to seat your bullets, that is usually caused by neck thickness variations of the brass that comes to light after sizing. This will cause vertical stringing of your groups on target due to differences in neck tension holding the bullet in the case. More neck tension required will strike differently on the target than light neck tension. To cure that, you'll have to sort your brass by neck thickness using a neck or tubing micrometer. Some lots of brass are good in regard to thickness, some are abysmal in that regard. Lots from the same maker can vary. You may get one lot that only differs about .0015", then another that varies a whopping .002" variance. You just have to check and sort them in lots, then keep them separate to avoid variances in neck tension. The other alternative is to neck turn them all to one thickness, which is alot more work than most shooters want to undertake.

If you are getting half inch groups now, simple sorting of your brass using the dies you have on hand now should provide you with very good accuracy. Many shooters will never get a rifle into the half inch range; you're already there. Sort your brass by neck thickness, use the load that gives you the .5" groups, and you'll most likely find those groups will shrink even more. Good luck, let us know how it shakes out.

[darchell]

Rick thanks for the reply. Although I wanted to get another set of dies I was going to hold off for now anyway until I work out everythign else with this rifle. It is very accurate so far and I am going to do what I have learned from past expierence, let the rifle tell me what it likes instead of telling it. Kinda like at home, you know, "Yes Dear" is ussualy much more simple then arguing your point and eventually considing and doing what she wants anyway. But I digress, I appreciate the info and will try the sorting of the brass. I have had a few groups that were strung vertical and horizontal. Still around a half inch but with four or five shots it would cut a line in the paper where the rounds all touched but in a line. The majority of the cases, winchester brass, seem to be the same, tight, and only a few are able to be seated.

[Jim White]

darchell,

You’re doing pretty good compared to mine. I have a CZ-527 American and with the following MAX (near and maybe over) I’m getting the following;

Rifle: CZ-527 American, 22” barrel, 1x12 twist.

Ammo:
- Case: Remington
- Bullet: 39 SBK
- Primer: Remington 7 ½
- OAL: 2.260

Powder:
- H-4895 @ 28.1 grains: 3500 FPS. Hodgdon website (using H-40 grain info) is 3741 FPS (27.7 grains is max).
- RE-15 @ 28.1 grains: 3460 FPS (Sierra reloading manual states 3600 (give or take).
- Varget @ 28.1 grains: 3320 FPS. Hodgdon website (using H-40 grain info) is 3647 FPS (28.1 grains is max).

Chronograph:
- 13’ from muzzle to front of Chronograph

Weather:
- Light: Sunny
- Temp: 50 degrees

* No over pressure signs and all groups are 0.5 MOA or less.

* I've checked the powder scale for accuracy with known calibration weights. Actually I'm .1 grain light @ 28.1 grains.

* When shooting thru the screens its set up where the bullet passes down the center. The only other thing that might make a difference is the direction of light which is slightly FWD of the chronograph @ about 2:00. As the days get longer and the light is more consistent I’ll try again as well as test the loads for pressure signs as the temp increases. Varing the height the bullet passes over the sensors along with passing slightly left or right of the sensors has some effect but not much.

I'm definitely baffled. I can understand a few FPS but 200 to 300 FPS has me scratching my head. I've also checked using another chronograph and the results were similar. Maybe that’s just the way it is but I'm not giving up yet.

* I just got my 700 in 204 back from bedding, crowning and free floating. It to shoots these loads very well with no pressure signs. I'll try and chronograph them soon and see if there is much difference although I do expect some because of the 4" of extra barrel length.

Jim

[darchell]

Jim,

One thing I noticed today when I went out is my tripod is rather cheap. The Chronogragh wobles when the bullet passes. I have it set 10 feet back. I am not sure if this has an effect on the situation as I am sure the bullet is though prior to the rocking but maybe it does. Today I had a 100 FPS spread over 18 rounds.

[Jim White]

Somewhile back, someone posted a conversion chart for chronograph distance to the muzzle. i'll try and find it because mine is quite a way back.

[OldTurtle]

I tend to worry less about velocity than I do about consistent accuracy....Very few if my loads will come anywhere close to the max velocity claimed by the various bullet/powder producers..

Chances are, that your chrono is 'rocking' due to muzzle blast (air disturbance) and you can reduce this by hanging a weight from the tripod that doesn't touch the ground.....how much weight depends on your tripod..

Once you get within the .5" group factor @ 100yds, smaller groups will require judicious applications of minute changes in powder and seating depth and you can only change one factor at a time...It's tedious, but rewarding when you achieve the .25" groups...

I've tried several brands of dies and found the Forster Benchrest series gives me the most consistent groups....

[Jim White]

I have the groups already and you're right, its very rewarding.

Also, that may be all she'll do. I'm also going to try at another firing point on the range and see if that matters. Its not so much the velocity as I want to know what the velocity is (in reality) so I can set my scope turrets acordangly. I'll also check out the weight for the chronograph.

Otherwise, I'll take accuracy everytime and besides, the rifle shoots good and I don't want to burn the barrel out no sooner than I have too...

Thanks for the ideas...