Decreasing velocity???

[Rocken Rod]

Ok first time posting! I have a 243 with a Carbon 6 barrel and have about 100 Shots through as of now. I bought 2 bags of Starline brass and after some brake in shots and cleaning I figured I’d do some powder and seating testing. Gun shoots 3 shot groups around a half inch with a COAL of 2.730. I didn’t hang bullets out farther than that because I’m shooting Nosler 70BTs and was trying to keep close to.243 length in the case neck. So here’s the problem, I’m now starting to reload my once fired brass to hopefully get down to some bug hole groups. I bumped the shoulders back .002 and used the same powder charge combo as before and my group suck. Also something else I’ve noticed is my velocities keep dropping every shot after my initial shot with my once fired brass. And no I don’t believe it’s my chrony cause I shot another gun right after and the velocity held steady.
1st 3727
2nd 3679
3rd 3664
4th 3643
A&D EJ-123 powder scale.
Any suggestions/ help would be appreciated! Thanks

 

[David Christian]

1st shot of a recently cleaned barrel, or first shot of a test string with the barrel already warmed up and any residual cleaning fluids burned out?

Did the brass need to be bumped?

Why are you sticking to a certain coal?

Powder most likely needs to be adjusted between virgin brass and once fired—that is normal.

 

[Rocken Rod]

It was a cold barrel but secondary shoot velocity’s still decreased. Brass was bumped .002 after first firing. I guess I’ll have to do a powder ladder test again, thinking perhaps need more for case fill??

 

[Bill Norris]

Ok first time posting! I have a 243 with a Carbon 6 barrel and have about 100 Shots through as of now. I bought 2 bags of Starline brass and after some brake in shots and cleaning I figured I’d do some powder and seating testing. Gun shoots 3 shot groups around a half inch with a COAL of 2.730. I didn’t hang bullets out farther than that because I’m shooting Nosler 70BTs and was trying to keep close to.243 length in the case neck. So here’s the problem, I’m now starting to reload my once fired brass to hopefully get down to some bug hole groups. I bumped the shoulders back .002 and used the same powder charge combo as before and my group suck. Also something else I’ve noticed is my velocities keep dropping every shot after my initial shot with my once fired brass. And no I don’t believe it’s my chrony cause I shot another gun right after and the velocity held steady.
1st 3727
2nd 3679
3rd 3664
4th 3643
A&D EJ-123 powder scale.
Any suggestions/ help would be appreciated! Thanks

Probably will need to fire the brass more than once to see fps get better. I would not worry about keeping .243 of the bullet in the case neck. Try seating the bullets closer to the lands like maybe .020 OTL and work @ .003 steps away and/or .003 steps closer to the lands.

 

[Rocken Rod]

Probably will need to fire the brass more than once to see fps get better. I would not worry about keeping .243 of the bullet in the case neck. Try seating the bullets closer to the lands like maybe .020 OTL and work @ .003 steps away and/or .003 steps closer to the

 

[Rocken Rod]

Brass now measures 1.628 after second firing which I had bumped it back to 1.626.

 

[Bill Norris]

Looking good.

 

[searcher]

What powder are you using? Those velocities with that bullet indicate you are running a rather warm (if not hot) load with that bullet. As such, I'd be leery of running the bullet to jam without backing off your powder.

Do you have any shoulder-to-base measurements of the brass that you fired the first time - before being fired? If your fired brass has "grown" in length in that measurement, as others noted, it will change the dynamics of your load. I'd be inclined to look in your manual at the powder you are using - and back it off perhaps 2 grains. Nosler lists 3,661 fps as the fastest MAX load in their #8 manual for that bullet, using RL17 powder. They show Varget as their "accuracy" load, though I'd also try Rel 15. Most powders they recommend average a "MAX" load speed of around 3,550 fps, including Varget and Rel 15. Other manuals might show much higher velocities as max in their loads, but I'd probably be inclined to weigh more heavily on the manual that makes the bullet the first time around. You are running your bullets seated out a bit more than the 2.710" recommended length. Longer seating tends to be better than shorter most often - but not always. You might try seating them at the recommended depth just for kicks.

Are you sure you are not running a compressed load? if so, some of those bullets may be backing out after seating, leading to erratic performance. Just a thought.

 

[Rocken Rod]

1st shot of a recently cleaned barrel, or first shot of a test string with the barrel already warmed up and any residual cleaning fluids burned out?

Did the brass need to be bumped?

Why are you sticking to a certain coal?

Powder most likely needs to be adjusted between virgin brass and once fired—that is normal.

What powder are you using? Those velocities with that bullet indicate you are running a rather warm (if not hot) load with that bullet. As such, I'd be leery of running the bullet to jam without backing off your powder.

Do you have any shoulder-to-base measurements of the brass that you fired the first time - before being fired? If your fired brass has "grown" in length in that measurement, as others noted, it will change the dynamics of your load. I'd be inclined to look in your manual at the powder you are using - and back it off perhaps 2 grains. Nosler lists 3,661 fps as the fastest MAX load in their #8 manual for that bullet, using RL17 powder. They show Varget as their "accuracy" load, though I'd also try Rel 15. Most powders they recommend average a "MAX" load speed of around 3,550 fps, including Varget and Rel 15. Other manuals might show much higher velocities as max in their loads, but I'd probably be inclined to weigh more heavily on the manual that makes the bullet the first time around. You are running your bullets seated out a bit more than the 2.710" recommended length. Longer seating tends to be better than shorter most often - but not always. You might try seating them at the recommended depth just for kicks.

Are you sure you are not running a compressed load? if so, some of those bullets may be backing out after seating, leading to erratic performance. Just a thought.

 

[Ned Ludd]

Once virgin brass has been fire-formed/expanded to fit the chamber and re-sized minimally (i.e. ~.002" shoulder bump), the case volume will no longer be the same. In fact, the case volume or some other aspect(s) of the brass can change enough on the first firing/processing to cause the virgin brass load to no longer be optimal. In other words, the load needs to be re-worked once the brass has been fire-formed. This is standard load development procedure, IMO. It might require only a small tweak to restore the velocity obtained in the original virgin brass load, or it might require something more. I would suggest treating the load in fire-formed brass as starting from scratch. If you wish to try something simple to start, just adjust charge weight to re-create the original velocity of your tuned load in virgin brass with the fire-formed brass. However if that doesn't do the trick, I'd start over and do a complete load work-up in the fire-formed brass.

With respect to the velocity decrease, we really don't have sufficient information to address that question with anything more than speculation. Apparent changes in velocity can be frustrating to diagnose over the internet because they often require statistical significance, meaning a LOT of evidence, before any meaningful cause can be determined and corrected. For example, one of my LabRadar units often gives very high velocity values (i.e. by as much as 20-30 fps high) on the first shot of a string. I don't know why, it just does. In such a scenario, the velocity values you listed for #2 through #4 could be such a case if the ES/SD values for that load were only a little on the high side. As such, it's very difficult to offer any potential diagnosis without more information.

 

[Rocken Rod]

Some more information.
Using Staball 6.5 powder max load 49.8g per Hodgon. I worked up to these with no apparent pressure sighs.
New brass has a shoulder measurement of 1.622, first time fired brass at max load was 1.627 so .005 stretch. Again I started at I started at the bottom of powder charge weight. I am .020 of the lands

 

[Rocken Rod]

Once virgin brass has been fire-formed/expanded to fit the chamber and re-sized minimally (i.e. ~.002" shoulder bump), the case volume will no longer be the same. In fact, the case volume or some other aspect(s) of the brass can change enough on the first firing/processing to cause the virgin brass load to no longer be optimal. In other words, the load needs to be re-worked once the brass has been fire-formed. This is standard load development procedure, IMO. It might require only a small tweak to restore the velocity obtained in the original virgin brass load, or it might require something more. I would suggest treating the load in fire-formed brass as starting from scratch. If you wish to try something simple to start, just adjust charge weight to re-create the original velocity of your tuned load in virgin brass with the fire-formed brass. However if that doesn't do the trick, I'd start over and do a complete load work-up in the fire-formed brass.

With respect to the velocity decrease, we really don't have sufficient information to address that question with anything more than speculation. Apparent changes in velocity can be frustrating to diagnose over the internet because they often require statistical significance, meaning a LOT of evidence, before any meaningful cause can be determined and corrected. For example, one of my LabRadar units often gives very high velocity values (i.e. by as much as 20-30 fps high) on the first shot of a string. I don't know why, it just does. In such a scenario, the velocity values you listed for #2 through #4 could be such a case if the ES/SD values for that load were only a little on the high side. As such, it's very difficult to offer any potential diagnosis without more information.

 

[Ned Ludd]

What is the target image shown in your reply to my previous post supposed to indicate?

 

[M-61]

I bumped the shoulders back .002

Why/? Hard bolt closing?
Forget hunting and semi-auto’s
Bumping is to correct a problem,not a mandatory step.
Every time you just bump as a step in reloading that shoulder will blow forward to the datum line when fired. How many times can that brass be needlessly moved?
This has nothing to do with your stated problem but you stated it in your reloading procedure.

 

[K22]

Just some notes to add what has already been offered but focused on consistency of group and group size rather than addressing velocity variation. Speer testing showed that velocities can vary anywhere from 10 to 80 f/s shot to shot aside from temperature affects even in the most carefully constructed reloads.

1. I have shot the 70 Nosler BT in several of my 243 Wins, 10" twist. This bullet is very accurate in my rifles with Varget and IMR 4064. The seating depth that worked best for me was 2.680, which was the depth Nosler tested. Also, I found that the lower powder charges published in Nosler's Manual gave me more consistent groups.

2. Bumping new case is normally not needed and, in my experience, can be detrimental to consistent accuracy. A better approach in my experience is to measure new cases at the datum line. And after the first firing, measure the expanded case. Set your FL die to size the case to that measurement or slightly less, i.e., no bump but make sure you are not extruding the case, i.e., lengthening it. Check in the chamber to verify adequacy of chambering. Then monitor case stretch on subsequent reloading's for chamber fit. You may find that you do not have to bump the shoulder for quite some time. The FL die also size the radial dimension of the case and often this enough to allow reliable chambering.

3. Your shot sequence could also be affecting your groups if you are shooting from an overheated barrel. Your bench technique could also contribute to shot to shot variation.

4. If you are cleaning with aggressive copper solvents, in my experience, velocity will decrease until the barrel is re-plated with copper. In addition, the most stable groups I have obtained in all my rifles and calibers are from barrels cleaned with mild solvents that do not aggressively attack copper. This included clean and cold barrel shot POI consistency.

 

[C.E.Smith043]

Just my opinion, but the powder you are using is on the slow side of the burn chart. I would focus more around Varget burn rates.

 

[jelenko]

Personally, I like to confirm seemingly unexpected results. I'd do another 4 - presumably the velocities would even out.