INCONSITANT VELOCITIES

[rtc111]

hello,

When I chrony my reloads im getting velocity differences of 40 FPS. I know the powder is the same because i double check each powder load on two scales before i put it in the case. The guy at hornady said that it could be because i have defference in my neck tension (bullet release). How can i fix this? Im using an RCBS FL sizer die.

I've also heard it could be because weight and volume of my brass, i check for weight but not volume, should I and how?

Let me know what you guys think please

[24Sailor]

hello,

When I chrony my reloads im getting velocity differences of 40 FPS. I know the powder is the same because i double check each powder load on two scales before i put it in the case. The guy at hornady said that it could be because i have defference in my neck tension (bullet release). How can i fix this? Im using an RCBS FL sizer die.



I've also heard it could be because weight and volume of my brass, i check for weight but not volume, should I and how?



Let me know what you guys think please

Straight wall or bottleneck?

VOLUME: Fired and resized case....seat a spent primer....weigh case......fill with H2O till it crowns over the neck.... weigh again..... repeat on several cases. Rather time consuming but I can't think of any other answer.

Are you uniforming your flash holes and neck turning? If not that may be another factor

[ronas]

It might be helpful if you could give.
bullet brand
type of bullet and grs.
primer type and size
brand of brass
is all brass the same brand
weight of each casing from group you fire the group with 40fps variation
has all brass been fired same # of times
if rifle what is loaded round ogive?
powder brand and grs.

[Fjold]

40 fps isn't bad for a high power rifle cartridge, it's more of a concern of you are loading for 45 ACP.

We'll need more information.

[rtc111]

Okay I'm using 225 gn Hornady SST bullets. All seated to the same depth by foster competition die, and checked by Hornady base to ogive. Using 72.2 gn of RL 15, 40 FPS using beta alpha chrony.

Brass all fired the same time, and Remington brass. Not crimped but possible thinking about using LEE factory crimper. My FL die is RCBS. This is a BRowning bAR .338 WM (semi auto)

[rtc111]

RL 19 powder not 15

[24Sailor]

Ok now the real question......What kind of groups are you shooting? If you're happy with the grouping, fretting over a 40 fps inconsistency is silly. I don't shoot competition but I do try to achieve the most accurate loads for my old rifles I have a pair of 1960's era Remington 700's that are shooting sub MOA with 80 - 100 fps readings between high and low. I've yet to get a 40 fps bracket with a 10 shot sequence.

Remember also barrel temperature is a factor...With lightweight sport rifle barrels, when they heat up you may find your POI walking up the page....you may or may not see a change in velocity.

I saw a suggestion from the CF rifle forum to check case volume on a fired shell. That is incorrect. They need to be fired then resized as individual pieces of brass will expand differently even at identical pressures. If you had a bolt action and were neck sizing only you would still need to fire the cases more than a couple of times to get all of them uniformly fire formed (thats pretty much when they're stuck) to your chamber.

[gau17]

Depending on how many times the brass has been cycled, you might need to anneal them. 40 FPS isn't bad. Most Chrono's lie. See how the rounds groups at 200 or 300. Don't get too caught up on the 40 FPS.

[NotEnufGarage]

To get the best consistency, everything has to be consistent. Check bullet weight, powder charge and case weight. A 1 or 2 grain difference in case weight can be a significant enough difference in case volume to throw off the velocity. I've seen case weights for large rifle cases vary by 10 grains within a single batch (same headstamp).

For 5.56 match loads, I separate my cases into batches down to the 1/10th of a grain by manufacturer (LC). I don't worry so much about the year, since LC is LC. In theory their cases are made to the same specs every year. To get any more accurate would require measuring the actual case volume of each case before loading. That would be very time consuming and messy. For .308 and .30-06 I try to keep them within 1 grain.

You might also be fighting a resonance issue with your barrel. Each barrel is different and "likes" particular velocities and "dislikes" others. This usually shows up in accuracy more than in velocity, though.

Just for grins, buy a box of match ammo that uses the same bullets and chrono it for comparison. I'll be you'll find some variation.

[rtc111]

I'm shooting a .9 inch group at 100 Y which is good I think for a large caliber semi auto hunting rifle. It's not powder I double check each powder charge before I put them in the case. Bullets are all seated the exact same based in ogive. I guess we're just going to have to step back a little more and see what happens.

[rtc111]

I'm also going to anneal the cases, should I anneal them before I resize them? That's what a Hornady worker said.

[gau17]

Correct. Anneal > Size.

This should make the neck tension more uniform. If you are not familiar with the process click on the link below. I like DeSimone's procedure toward the bottom of the article. This is how I started. Now I just look for the color changes on the brass. You have to find which procedure works for you. There are many opinions out there. Good luck. Be safe.

http://www.6mmbr.com/annealing.html

[Sunwolf]

Let me get this straight...you are worried about 40fps difference out of a gas operated semiautomatic rifle?There are bigger things to worry about...like what`s for lunch!

[wtkaiser]

You are already shooting a sub MOA group. Assuming a whole bunch of other stuff, you should be good for 400-600 yards (on a deer-sized target). Perhaps I am over-simplifying this, but why all the fuss? The gas system itself could account for the variations.

[Fjold]

40 fps is not important. If they were all exactly 20 + fps or 20 - fps off the average velocity. Your standard deviation would be less than 3 fps.