Help Troubleshooting Velocity anomolies

bsnedeker

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So I'm testing some loads for my 270 and my 300 WM and I'm having trouble getting consistent velocities...hoping someone can give me some tips on what to check.

I feel like I'm being VERY meticulous about my process: tracking number of times fired for brass and always using the same batch for each test, cleaning, prepping, and measuring cases before loading, measuring powder with my beam scale and checking on a (cheap) digital scale, seating all bullets to a consistent CBTO (within 1 thousandth) and yet I get this inconsistency.

Example: Last night I took the 270 to the range with my chrono. I had four 3-shot groups to test different CBTO. On every group I would have two shots that grouped almost touching with a velocity difference of less than 20 FPS, but I would have one shot in the group that would be (on average) about 1 inch away from the other two, and the velocity on this "flier" would be off by almost 100 FPS (2 shots at appr. 2650 FPS grouping together, one shot at 2550 FPS about an inch away). That said, I'm still at around 1 MOA for the total group so it might be acceptable I've just seen that most people who hand load are able to get velocities within 10% and I'm not getting that every time.

I'm getting the same thing on my 300 WM for which I use a different powder and bullet obviously. I am using the same primers on both rounds (winchester WLRM's) so I'm going to do a test this weekend with some different primers, but other than that the only common factor is me and something I'm doing wrong. If anyone has any advice or other things I can check I would really appreciate it!
 

Rob5589

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Curious why you double check with the cheap digital? Do you not trust the beam scale? Do you find yourself increasing or reducing the charge often after checking with the dig scale? If both guns are having the same issue, I would be looking at my scale/s.
 
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bsnedeker

bsnedeker

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Curious why you double check with the cheap digital? Do you not trust the beam scale? Do you find yourself increasing or reducing the charge often after checking with the dig scale? If both guns are having the same issue, I would be looking at my scale/s.

Yeah, it's a trust thing. A month ago I realized my beam scale was not giving me consistent results. There was some gunk built up in the pivot point and if I would bump the scale the pointer would go to a different spot. I cleaned it really well and put a couple drops of oil in it so it now gives me consistency, but I like to check with my digital scale just to make sure it isn't creeping again. My digital scale is accurate to within +/- .02 grains in theory so I like to check it against that every load just to make sure I'm taking that factor out.

That said I've been seriously considering updating my powder system to one of the RCBS chargemaster systems as I've heard they are great at giving consistent loads.

Edit: Oh, and no, I don't find myself having to add or remove powder when I check on the digital. It's just a checklist item for me mostly.
 
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Are you seeing any pressure signs with the faster loads?

Assuming your powder charges are consistent, I think the most likely culprit is a powder/primer combo that doesn't work well together. It could also be a neck tension issue, or a dirty barrel with a carbon ring.


It could also be that your velocities are fine and your chrono is being affected by muzzle blast. What type of chrono do you have, and where is it located relative to your muzzle?

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bsnedeker

bsnedeker

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Are you seeing any pressure signs with the faster loads?

Assuming your powder charges are consistent, I think the most likely culprit is a powder/primer combo that doesn't work well together. It could also be a neck tension issue, or a dirty barrel with a carbon ring.


It could also be that your velocities are fine and your chrono is being affected by muzzle blast. What type of chrono do you have, and where is it located relative to your muzzle?

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No pressure indicators that I can see...primers look the same and the cases all measure the same post-firing.

I just cleaned the crap out of my 300 so I know that thing doesn't have any carbon built up...haven't cleaned the 270 this year.

How would I check neck tension? Measure ID of neck before seating? I usually only measure the OD. After I trim and camfer/debur the neck I do clean the inside of the necks with a cotton swab to make sure I get any case-lube out of there, but that's all I do.

I did consider an issue with my chrono and muzzle blast. I'm using the new caldwell chrono (the upside-down one) and it probably is a bit closer than it should be as the range I shoot at is underground so there is only about 12 feet between the end of my barrel and where I can set up the chrono. However, the fact that every round that had a different measured velocity also had a different POI made me think the chrono was accurate. That said, another test I'm planning on doing is shooting some rounds into a berm in my backyard with my chrono about 20 ft away to see if the muzzle blast was affecting things. I just can't check my group size this way as I don't have a 100 yards to shoot on my property without scaring the neighbors!
 
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I have the ced chrono, which looks to be a right side up Caldwell and I can't get readings that make sense until I'm 25' from the muzzle. Can you set your chrono up at the target, or do you shoot in a 12' long underground range?

To measure neck tension measure the neck od before and after seating bullets, a good number is 0.003." In your case we are looking bto see if whatever measurement you get is exactly the same shell to shell. If you're using a bushing neck sizer and not turning your necks you will have inconsistent neck tension unless your cases are manufactured perfectly.

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bsnedeker

bsnedeker

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I have the ced chrono, which looks to be a right side up Caldwell and I can't get readings that make sense until I'm 25' from the muzzle. Can you set your chrono up at the target, or do you shoot in a 12' long underground range?

To measure neck tension measure the neck od before and after seating bullets, a good number is 0.003." In your case we are looking bto see if whatever measurement you feet is exactly the same shell to shell. If you're using a bushing neck sizer and not turning your necks you will have inconsistent neck tension unless your cases are manufactured perfectly.

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My range is a 100 yard underground range, so it has a bench, about 12 feet of floor space, and then a long tunnel that I can't get into with the target at the end. I'll try the test this weekend with the chrono 25 feet away and see what I get.

I use a full size RCBS die and I don't do anything special with the necks. I've never measured the OD after seating so I'll give that a try as well.
 
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It seems like the problem is chrono placement or primer/powder interaction then.

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bsnedeker

bsnedeker

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It seems like the problem is chrono placement or primer/powder interaction then.

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Thanks, I hope you're right as I can test both of those things this weekend. I just did some googling on neck turning and that is a rabbit hole I don't think I want to go down if I don't have to!
 

MTbow

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Are you seating real close to the riflings? bullet ogives vary. A spread that large could indicate 2 being just off the rifling and the third just touching(for instance).
 
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bsnedeker

bsnedeker

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Are you seating real close to the riflings? bullet ogives vary. A spread that large could indicate 2 being just off the rifling and the third just touching(for instance).

The closest I get to the lands is .025" so I don't think that's the issue. The last test I ran I did tests at .025, .030, .035, and .040 off the lands and I had this issue with all of those CBTO measurements. I'm trying to be overly conservative on chamber fit since these rounds will be for hunting which is also why I FL size every round.
 
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Great point by MTbow, that's very true.

Neck turning is a rabbit hole, and really only matters if you're outside neck sizing with a bushing die.

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ckleeves

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Couple things I would check.
Chronograph, if you have access to another one see if they agree with each other. Some really aren’t that accurate, even a 1% swing and your off 50 FPS. (+25 one way -25 the other)

If your beam and your digital agree with each other every time then a chargemaster isn’t going to do you any good. A good beam will weigh “finer” then a chargemaster will. So I doubt that’s the problem.

I would try a variety of primers. Sometimes it’s as easy as that and you clear up some big ES’s.

Depending on the brand and number of firings on the brass you may have some pretty good work hardening going on. You can usually feel it either in bullet seating or if your using a expander ball when you pull it thru.

Not sure what powder your using but even if it’s a published load there are probably powders listed that the burn rate is not quite ideal which can lead to pretty big spreads.






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bsnedeker

bsnedeker

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Couple things I would check.
Chronograph, if you have access to another one see if they agree with each other. Some really aren’t that accurate, even a 1% swing and your off 50 FPS. (+25 one way -25 the other)

If your beam and your digital agree with each other every time then a chargemaster isn’t going to do you any good. A good beam will weigh “finer” then a chargemaster will. So I doubt that’s the problem.

I would try a variety of primers. Sometimes it’s as easy as that and you clear up some big ES’s.

Depending on the brand and number of firings on the brass you may have some pretty good work hardening going on. You can usually feel it either in bullet seating or if your using a expander ball when you pull it thru.

Not sure what powder your using but even if it’s a published load there are probably powders listed that the burn rate is not quite ideal which can lead to pretty big spreads.






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Unfortunately this is the only chrono I have access to at this time. I'm hoping the primer test will be informative for sure.

I was considering starting over from scratch and trying a different powder, at least on the 270. I'm using IMR 4831 in the 270 and Magpro in the 300. I did burn-rate comparisons when I selected the Magpro for the bullet I'm using, but I honestly picked the IMR 4831 out of a hat as that was the first load I ever developed and I didn't know anything about powder burn rates.

Edit: Oh, and I do anneal my cases between reloadings. I don't have a fancy annealer so I just do the method of putting the case neck to a torch until it gets hot then I douse it in water to cool it...probably not ideal but I'm not ready to invest in an annealer at this time.
 
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Your annealing technique could be the culprit too, there's a lot of room to introduce inconsistencies with your method. Fiddle with primers first though, that's cheap and easy to test, neck hardness is pretty difficult to measure at home.

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Try different primers, I'd start with 215M (wm) 210M (270) if you can find em.

If weighing each charge I would avoid using ball powders. They seem significantly more difficult to get consistent velocities from.
 

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