Need Help: Random ‘slow’ rounds

[JollyRoger]

Hi all,
I’m looking for some expertise or help on something I noticed yesterday while shooting. I am very new to reloading (about a month in) but have been having consistent and fantastic results. SDs for the last 400ish rounds have been under 10, accuracy is sub 1” per 10 round groups.

My set up:
Redding T7 Press
Redding Premium dies
RCBS chargemaster

Norma 6.5CM brass (1x fired)
Federal 210 primer
41.5gr H4350
140gr ELD-M
Average MV is 2745

Rifle:
Accuracy International AT 24” barrel with CGS Hyperion
Nightforce 5-25 F1 Mil-C

While shooting yesterday I had 4 rounds that were much slower than normal… like 2590 and another at 2640 I think. My average is 2745. After 3 slow rounds I weighed every single remaining round I had and they were all within just a few grains of eachother, which I believe to be variance in brass weight since I weighed them all with powder but before seating the bullets. Even after weighing them all I had another round that was close to 100fps slower than normal.

If my powder charges are consistent at 41.5gr, and everything else is in line, what could cause my slow rounds? Is there anything else I’m missing??

 

[Formidilosus]

Hi all,
I’m looking for some expertise or help on something I noticed yesterday while shooting. I am very new to reloading (about a month in) but have been having consistent and fantastic results. SDs for the last 400ish rounds have been under 10, accuracy is sub 1” per 10 round groups.

My set up:
Redding T7 Press
Redding Premium dies
RCBS chargemaster

Norma 6.5CM brass (1x fired)
Federal 210 primer
41.5gr H4350
140gr ELD-M
Average MV is 2745

Rifle:
Accuracy International AT 24” barrel with CGS Hyperion
Nightforce 5-25 F1 Mil-C

While shooting yesterday I had 4 rounds that were much slower than normal… like 2590 and another at 2640 I think. My average is 2745. After 3 slow rounds I weighed every single remaining round I had and they were all within just a few grains of eachother, which I believe to be variance in brass weight since I weighed them all with powder but before seating the bullets. Even after weighing them all I had another round that was close to 100fps slower than normal.

If my powder charges are consistent at 41.5gr, and everything else is in line, what could cause my slow rounds? Is there anything else I’m missing??

What is your chrono?

 

[JollyRoger]

What is your chrono?

Garmin Xero.

 

[Formidilosus]

Garmin Xero.

Hmm.

In those 400 rounds that you have chronoed- there have been no slow rounds? If you didn’t chrono those 400 rounds, what’s the largest shot group size that you have chronoed at once? I.E., it’s real easy to have good ES with 5-10 rounds, when done for 30+ shots- it’s also quite common to have a 80-120fps ES with a lot of combos.

The slow rounds, did they hit within the group?

 

[Truck24hr]

Are you trickling every charge?

 

[Fireflyfishing]

Same lot for all reloading components?

 

[JollyRoger]

Hmm.

In those 400 rounds that you have chronoed- there have been no slow rounds? If you didn’t chrono those 400 rounds, what’s the largest shot group size that you have chronoed at once? I.E., it’s real easy to have good ES with 5-10 rounds, when done for 30+ shots- it’s also quite common to have a 80-120fps ES with a lot of combos.

The slow rounds, did they hit within the group?

I haven’t chronoed all of those 400 rounds… that probably sounded misleading. But results at distance have been consistent. Meaning I may have had slower rounds but didn’t hear the difference or see rounds fall way short.

Largest sample size I have chronoed is 12 rounds.

Yesterday I was shooting at distance and the rounds did not fall within the cone of the rest of my rounds. I could hear the difference and didn’t see my impacts which is when I looked at the chrono

 

[JollyRoger]

Same lot for all reloading components?

Yes, same lot for all components. Except the brass which was factory Norma ammo I’d shot previously

 

[JollyRoger]

Are you trickling every charge?

Yessir. If it’s over or under once it beeps I dump it and try again

 

[Truck24hr]

Yessir. If it’s over or under once it beeps I dump it and try again

Any possibility you have a scale issue? I use an old school RCBS, and haven't tried an electronic one.

Do you have a scale you could verify with?

 

[JollyRoger]

Any possibility you have a scale issue? I use an old school RCBS, and haven't tried an electronic one.

Do you have a scale you could verify with?

It’s the only scale I have, and brand new so hopefully that’s not it. I could find a manual scale to double check

 

[Fireflyfishing]

Couple of thoughts:
Perhaps your scale is floating. You may want to invest in a check weight set. My gut is telling me this isn’t it though.

Run us through how you prep your brass.

Could be primers…

Are you shooting in drastically different temperatures?

 

[JollyRoger]

Couple of thoughts:
Perhaps your scale is floating. You may want to invest in a check weight set. My gut is telling me this isn’t it though.

Run us through how you prep your brass.

Could be primers…

Are you shooting in drastically different temperatures?

Brass prep:
I’ve got a box full of once fired Norma brass. It started life as Golden Target ammo that I fired through this rifle.

Lube. Run through full length sizing die and deprime. Next I trim to 1.910” I believe (I don’t have the book in front of me currently). After that I do a quick de-burr on the inside and outside of the neck. Then I do a few scrapes in the primer pocket, until it’s shiney.

Once it’s all trimmed, deburred, and clean I prime them. I’m using a Lyman hand primer tool. Generally I squeeze until it feels seated and it’s either flush or slightly sunk in.

I don’t currently anneal or have a brass cleaner/tumbler.

The temperatures… I’m not sure how much of a change in temp would make a difference? I’ve only been doing this a month or so, so temps have been in the 20s up to maybe 50°.

They are Federal 210 primers

 

[Carl Ross]

I have had bad batches of primers before that gave similar symptoms. Switching to a different lot of the same model primer solved the issue.

My other thought is if you over-bumped the shoulder and have excess headspace that can cause ignition issues, but I don't think they symptoms match that as well.

 

[Fireflyfishing]

I’ve got a box full of once fired Norma brass. It started life as Golden Target ammo that I fired through this rifle.

Did you have any funky results with this ammo when originally shot? Did you get velocities when shot?

Lube. Run through full length sizing die and deprime. Next I trim to 1.910” I believe (I don’t have the book in front of me currently). After that I do a quick de-burr on the inside and outside of the neck. Then I do a few scrapes in the primer pocket, until it’s shiney.

How do you have your resizing die set up? How much are you bumping the shoulder? Do you have a headspace comparator?

Is there a way you can separate the cases that produced the low velocity shots from the loads that shot “normal?” You could measure a couple of things like H2O volume or weigh them against the other cases and see if there is a big difference from the average of your “normal” cases.

I don’t currently anneal or have a brass cleaner/tumbler.

You’ll want to get something to clean your brass eventually. Not an issue for your current problem though.

The temperatures… I’m not sure how much of a change in temp would make a difference? I’ve only been doing this a month or so, so temps have been in the 20s up to maybe 50°.

Not seeing an issue here

They are Federal 210 primers

This could be the culprit? It sucks having to try different primers if you don’t have a stock pile of different brands with the current market. This may be it though.


How are you seating your bullets relative to the lands?

 

[HuntHarder]

I would get another scale and verify your chargemaster is weighing accurately.

 

[JollyRoger]

Did you have any funky results with this ammo when originally shot? Did you get velocities when shot?

How do you have your resizing die set up? How much are you bumping the shoulder? Do you have a headspace comparator?

Is there a way you can separate the cases that produced the low velocity shots from the loads that shot “normal?” You could measure a couple of things like H2O volume or weigh them against the other cases and see if there is a big difference from the average of your “normal” cases.

You’ll want to get something to clean your brass eventually. Not an issue for your current problem though.

Not seeing an issue here

This could be the culprit? It sucks having to try different primers if you don’t have a stock pile of different brands with the current market. This may be the it though.


How are you seating your bullets relative to the lands?

Oh yeah that factory ammo was terrible lot to lot as far as velocity consistency. It’s initially what got me to start reloading.

Resizing die: I set this up to bottom out with a slight cam over. I do have a headspace comparator but don’t remember the measurement off the top of my head, and I’m not at home currently. I can look this afternoon. I think I’m using the Hornady 400 gauge though and things have measured consistently.

I should have kept those pieces separate but didn’t. I will say I was measuring every case with powder and primers in and they were all between 201 and 206 grains.

The primers came in a box of 1000. Maybe I have a box in there that’s not as good? I don’t have any others but could easily try some.

Bullet seating: I used the Hornady OAL measuring tool about 7 times, took the average and then subtracted 0.030 from that for my depth (to the ogive). That measurement is 2.314” for everything I’ve loaded.


Thanks for everyone’s help so far, definitely appreciated

 

[Fireflyfishing]

Resizing die: I set this up to bottom out with a slight cam over. I do have a headspace comparator but don’t remember the measurement off the top of my head, and I’m not at home currently. I can look this afternoon. I think I’m using the Hornady 400 gauge though and things have measured consistently.

You want to find the size of your chamber using your headspace comparator and fire formed brass from your chamber. Only size 0.002” max shoulder bump. This will elongate the life of your brass relative to “full length” resizing to SAAMI spec. This should help with overall consistency of your loads…although I don’t think this will solve your current issue.

I should have kept those pieces separate but didn’t. I will say I was measuring every case with powder and primers in and they were all between 201 and 206 grains.

Try again; see if you have some low velocity loads. If so, separate the brass of those loads and try again. This would isolate bad brass.

The primers came in a box of 1000. Maybe I have a box in there that’s not as good? I don’t have any others but could easily try some.

This is what I would try first.

Bullet seating: I used the Hornady OAL measuring tool about 7 times, took the average and then subtracted 0.030 from that for my depth (to the ogive). That measurement is 2.314” for everything I’ve loaded.

No problems here! As long as it chambers and is grouping on paper well.

 

[JollyRoger]

You want to find the size of your chamber using your headspace comparator and fire formed brass from your chamber. Only size 0.002” max shoulder bump. This will elongate the life of your brass relative to “full length” resizing to SAAMI spec. This should help with overall consistency of your loads…although I don’t think this will solve your current issue.

Try again; see if you have some low velocity loads. If so, separate the brass of those loads and try again. This would isolate bad brass.

This is what I would try first.

No problems here! As long as it chambers and is grouping on paper well.

Got home and did some measuring.

Once fired brass is averaging 1.526 using the D400 headspace comparitor. My die is set to do about 1.515 but I have seen some slight variation of up to 0.002”.

Making sure I understand what you’re saying… I should set my die to get me to ~1.524” for headspace? Rather than the 1.515 to 1.517 I’m getting now?

 

[Fireflyfishing]

Got home and did some measuring.

Once fired brass is averaging 1.526 using the D400 headspace comparitor. My die is set to do about 1.515 but I have seen some slight variation of up to 0.002”.

Making sure I understand what you’re saying… I should set my die to get me to ~1.524” for headspace? Rather than the 1.515 to 1.517 I’m getting now?

Correct. Every time you size your brass, you’re working it way too hard. You only need to size your brass 0.0015-0.002” so it properly chambers smoothly and consistently.

When you size your brass excessively, the brass must go somewhere. It goes to the neck, and you will need to trim…a lot. Meanwhile, your brass will get thinner at the web and eventually you will have case head separation. An exception to what I wrote above is when you need ammo that chambers in any rifle.

For proper load development, you will want to start testing with the fire formed brass, not brass sized at the max sized/min headspace dimension.

Another benefit to this is more volume in your case to put more powder to run higher velocities in your load. Provided you’re not having pressure issues.