Can changing primer lot change group size

I want to thank everyone for the great advice. I received the shipment of 215 primers and did another test. This time the group (three shots) was 1 1/2 inch by 1 1/2 inch in a clover leaf patten at 200 yards. But the velocity was 100 f/s faster than my load I was trying to duplicate. The Norma brass was the second firing for both tests.

From reading through everyone's comments, I think I had a combination of issues. One being the change in primers, and the other is the velocity being out to the "good" node. Another factor might be that the barrel is so new. It now has a total of about 80 rounds down the tube.

I will describe my load process to see if that helps you all advise me. I start out with five or 6 powders with 2 shots each. The bullet I am using is seated to SAAMI depth. I use the velocity of the 2 shot tests of the powder to make adjustments in Quick Loads. After adjusting QL I choose two powders that had the least ES. I test the two selected powders with 3 shost each to fine tune QL and test for which load has the lowest ES. Then I fire 5 shot groups moving seating depth 0.010" closer. In this case I started at 0.096 and did six loads to end at 0.045 off the lands. The groups for 0.076 and 0.066 were both 3/4 inch (in a clover leaf pattern) at 100 yards. So I figured the node was at 0.071. That is when I ran out of the box of primers I was using and switched opened a new brick. I then tested at the seat of 0.071 at 200 yeads and got a three in group. That's what preplexed me and promped the start of this thread.

My next step is the retest with the powder adjusted to match the velocity that was so good on the 0.076 and 0.066 tests.

Thanks again everyone. This forum is a valuable source of informaiton for me. I hope that someday I will enough knowledge to help other like you all have helped me.

Your not going to get a valid es with two or three shots. I do know you can chase your tail a lot by relying on small sample sizes and then not being able to repeat the results. Been there done that got the tee shirt.

cajun said:

Your not going to get a valid es with two or three shots. I do know you can chase your tail a lot by relying on small sample sizes and then not being able to repeat the results. Been there done that got the tee shirt.

Click to expand...

Neither should anyone be judging accuracy by a single group. A single good group is only a "potential indicator" that requires further qualification.

Lots of chatter made about wasting components chasing a load but the fact is that "shooting" is both soort and recreation so bench time is never wasted and is the real arbiter on the accuracy of any load.

Neither is ES. Some wonderful accuracy loads are found to have what we would term excessive ES. We can be too easy criticise a load with higher ES but a tight groupnis a tight group and qualifying with more shooting will teach where as walking away immediately will generate assumption.

Remember, its a very short time ago where benchrest shootersntook their prepped brass to the firing line on a tray and bolted/G Clamped their powder thrower onto the side of the bench and dumped into the case to see what shot best and never ever, was there a chronograph present to measure velocity or Extreme Spread.

Accuracy was a requirement, anything else was irrelevant and absolutely neither the equal of accuracy nor a requirement to know.

AussieWriter said:

Neither should anyone be judging accuracy by a single group. A single good group is only a "potential indicator" that requires further qualification.

Lots of chatter made about wasting components chasing a load but the fact is that "shooting" is both soort and recreation so bench time is never wasted and is the real arbiter on the accuracy of any load.

Neither is ES. Some wonderful accuracy loads are found to have what we would term excessive ES. We can be too easy criticise a load with higher ES but a tight groupnis a tight group and qualifying with more shooting will teach where as walking away immediately will generate assumption.

Remember, its a very short time ago where benchrest shootersntook their prepped brass to the firing line on a tray and bolted/G Clamped their powder thrower onto the side of the bench and dumped into the case to see what shot best and never ever, was there a chronograph present to measure velocity or Extreme Spread.

Accuracy was a requirement, anything else was irrelevant and absolutely neither the equal of accuracy nor a requirement to know.

Click to expand...

I remember those days, they couldn't even tell you what the load was. Just 42 clicks of H322.

Critter Picker said:

I remember those days, they couldn't even tell you what the load was. Just 42 clicks of H322.

Click to expand...

When I used to ask them, back in my youth, they'd most often laugh and say, "who cares", "only accuracy wins the match".

That was true of the short range bench guys but at longer ranges es means vertical dispersion. You're not winning that game with a high es.
As for small sample sizes these days I try and rule out the bad combos quickly. If 2 or 3 shots is 1 1/2" it's not going to get better with more data points. But when you do find a good load you do need multiple groups and data points to get a true picture.

cajun said:

That was true of the short range bench guys but at longer ranges es means vertical dispersion. You're not winning that game with a high es.
As for small sample sizes these days I try and rule out the bad combos quickly. If 2 or 3 shots is 1 1/2" it's not going to get better with more data points. But when you do find a good load you do need multiple groups and data points to get a true picture.

Click to expand...

That's axiomatic.

I recently did a test with a foreign primer against cci br and fed 205.
The fed shot .011 larger and cci shot .088 larger group than foreign. Speeds also varied a good bit but dont have that data with me today

I have a 7 prc that loves n560
But I started using 9.5 mags and then went to 215m
With the 210m went out about an inch with the 9.5m I'm getting .5 to.25 groups

I want to report what I did and make a comment. I switched to 215M primers, and my group tightened up. My comment is there are a lot of very knowledgeable folks on this forum, and I appreciate your willingness to share your knowledge. I am a hunter. I want a decent load that performs dependably. It appears there are a lot of target shooters here. One person commented that any test of a load that was less than 30 was not statistically significant. I used 31 rounds to develop my hunting load, which took 6 sessions. A friend used my rifle to take a deer at 729 yards. All I saw was forked horns and three points, so I did not get to test it for myself. My load development process may not be statistically significant, but if it can hit a deer at 729 yards (I also tested at 600 on steel before hunting), then I don't care what the mathematics of statistics say. Thanks again everyone.

I will say, relying on ES numbers is futile, barrel time is far more important because even low ES can have negative results on barrel time. You want your bullets exiting when the barrel is either still, at the top or bottom of barrel whip, or in the middle.
The only way to know this is to shoot groups WITHOUT using your chronograph, it is just an unnecessary distraction you're focusing on.
Only look at chronograph results AFTER working up loads.
I've never attempted to use QL the way you describe, it seems a waste of time relying on PREDICTIONS for data.

Cheers.

If the barrel is new you cant rely on accurate ES or velocity until the chamber is properly firecracked. If you want to hunt long range you want the lowest ES possible, you need at least 10 rds to measure ES accurately.