Can changing primer lot change group size

[Retired2021]

I have been developing a load for a 7RM using Norma brass, H4831, Nosler 150BT and CCI #34. I had a consistant velocity of 2974 with single diget ES and SD and group of 3/4 MOA. I ran out of the CCI #34 and opend a new brick of CCI #34 (differnt lot) and my group went to 1 1/2 MOA, velocity remained around the same (2985) but ES was 29 and SD 13.5.

I am fairly new to percission reloading, so I don't know if the different lot of primer caused this, or should I look for some other problme.

Help please.

 

[Dmagna]

I guess it could but I have never had a primer change it that much unless I was switching between LR and LRM primers

 

[Critter Picker]

I've never had a primer change double my group size. 99% of shooters can't hold tight enough to tell @ 100 yards.

 

[RegionRat]

I have been developing a load for a 7RM using Norma brass, H4831, Nosler 150BT and CCI #34. I had a consistant velocity of 2974 with single diget ES and SD and group of 3/4 MOA. I ran out of the CCI #34 and opend a new brick of CCI #34 (differnt lot) and my group went to 1 1/2 MOA, velocity remained around the same (2985) but ES was 29 and SD 13.5.

I am fairly new to percission reloading, so I don't know if the different lot of primer caused this, or should I look for some other problme.

Help please.

Yes, primers do account for "part' of your velocity and the statistic.

I'm not sure how many shots you used to get your stats when you got a single digit ES/SD, but it probably wasn't very many if the ES was single digit. A better than average 7 RM runs an ES of about 30 and less on a rare occasion, but I am talking about well populated sample size, not 3 or 5 shot values and more like at least 15 to 30 shots. That said, a 7 RM doesn't miss a kill zone on account of this till we get out past where the time of flight gets long for killing.

It is also possible that many other parameters caused you to loose the tune, but you should be able to get it back with a little adjustment on your current component lots.

You just missed a drop of Federal 215M primers that were grabbed up within an hour today. Those would have been worth a try, but there was nothing wrong with your CCI #34 either. The #34 is known to be reliable and also good at hot/cold temps since it must pass Mil-Specs.

 

[hesse]

Simple answer is yes. I would say try another lot number and see what happens

 

[cohunt]

Yes

 

[FEENIX]

I have been developing a load for a 7RM using Norma brass, H4831, Nosler 150BT and CCI #34. I had a consistant velocity of 2974 with single diget ES and SD and group of 3/4 MOA. I ran out of the CCI #34 and opend a new brick of CCI #34 (differnt lot) and my group went to 1 1/2 MOA, velocity remained around the same (2985) but ES was 29 and SD 13.5.

I am fairly new to percission reloading, so I don't know if the different lot of primer caused this, or should I look for some other problme.

Help please.

Q: Can changing primer lot change group size?

A: Yes!

 

[stazmania]

That is a big difference. You might have been right on the edge of a node, or did environmental conditions change? Was/is the gun finicky to load for/slight change in charge weight or seating depth making a big difference in group size?

 

[FireFlyFishing]

When you developed the load, were you using virgin brass? Did you reload the brass, use new primers, and have worse results?

 

[MagnumManiac]

Yes it can, just the same as testing primers will change loads.
If you adjust powder, you may fall back into the next node.

Cheers.

 

[Stang66]

Yeppers that can happen even …if same powder lot, bullet lot, and seating depth were the same. In competition long range shooting primer brand, and/or lot numbers can make a difference. Also same with powder and brass. As suggested above drop back your powder charge to the velocity you were shooting well and see if that makes a difference. Basically do a fine powder test of five shot groups. That may resolve your issue. Best of luck. If you still have sone of the old priners May even do a weight comparison.
Best of luck…you will get it.

 

[blvette75]

I have not had it happen to that much of a difference when I have changed to a different primer lot. But will remember this if it happens, just have to buy in bulk more anyway these days, put primers in the same category as powders.

 

[Beluebow]

I have been developing a load for a 7RM using Norma brass, H4831, Nosler 150BT and CCI #34. I had a consistant velocity of 2974 with single diget ES and SD and group of 3/4 MOA. I ran out of the CCI #34 and opend a new brick of CCI #34 (differnt lot) and my group went to 1 1/2 MOA, velocity remained around the same (2985) but ES was 29 and SD 13.5.

I am fairly new to percission reloading, so I don't know if the different lot of primer caused this, or should I look for some other problme.

Help please.

Sounds like a new load work up is in order.

 

[Culpeper]

Explain 3/4 moa. Was that your smallest group or your average group. Same thing with 1 1/2 moa with the next lot of primers. Nobody is going to be able to answer your question without estimating inevitable dispersion. I doubt it is changing lot number. Chances are it is something else in the process.