New bullet lot issues

[CShooter92]

I switched to a new lot of 105 hybrids in my 6 dasher last week. I did not change anything else in my load. I took my newly loaded rounds to the range and I’m experiencing pressure that I’ve never dealt with before. I chrono’d the rounds and I’m up from 2920 to 2950-60 now.

I’m running 32.2gr of Varget, 3x fired Lapua brass, CCI 450’s. Gun was just cleaned and patched dry so I know that’s not an issue, even checked for carbon ring and there isn’t one.

I’m just curious if a new lot of bullets can affect the load that much? I did pull some bullets and compare to the old ones and the new bullets are 0.040” shorter overall and 0.030” shorter from the base of the bullet to the ogive. Is the easiest solution to just reseat the bullets, or to drop my powder charge a bit? I have a match this weekend and don’t really have time to do a full ladder of load development.

 

[nn8734]

Drop charge incrementally by .2 grains in three or four separate test groups, keep jump the same and test them at 100. see how they print. Roll with whichever charge weight shows no pressure while still holding a tight group, similar MV. Measure your cases for each test group above the extractor groove before and after firing and compare the numbers. Growth in excess of .0005 indicates
over pressure is present.

I’ve personally never seen a simple lot change of bullets (all other things equal) impact chamber pressure like you described but doesn’t mean it can’t happen.

I’d also check the rifle over completely again if you haven’t already done so

 

[cruze5]

do they weight 105?

 

[CShooter92]

Yup they do.

 

[ShtrRdy]

Same lot of powder? Did you recently get more powder out of a 8 pound jug?

 

[CShooter92]

Same lot of powder? Did you recently get more powder out of a 8 pound jug?

Or leave your powder in the hopper?

Powder was the same lot. 1 lb containers, dumped it in and loaded within 2 days. I didn't leave it sit in the hopper any longer than maybe 24 hours. The lid was on and I have a climate controlled room that's very dry.

 

[Govt Mule]

Reloading Tip: Bullet Bearing Surface and Pressure « Daily Bulletin

Photo 1: Three Near-Equal-Weight 7mm Bullets with Different Shapes TECH TIP: Bullets of the same weight (and caliber) can generate very different pressure levels due to variances in Bearing Surface Length (BSL).

bulletin.accurateshooter.com

Based on what you mentioned with the lengths of the new lot of bullets, this may be playing a role in your increased pressure. You may want to back off the charge a bit with the new lot, and work your way back up.
Cheers

 

[CShooter92]

Powder will speed up when it dries. I know I sound ridiculous but I found out the hard way. Left powder in the hopper for 3 months and a Dasher load that was supposed to go 2940 was going 3020. A year later I switched lots of powder in a 6BR and the new lot was going 2725 instead of 2800. It had pressure at 2725 when the old lot didn't at 2800. And it was less accurate. I left it out for 24 hrs by pouring it in a large glass casserole dish and it sped up 60fps. After another 24 hrs it gained another 10fps. Pressure dropped and accuracy returned.

I know that sounds like crazy town. I posted a thread on here. You can search it. "Drying out powder".

Whatev's. Hope you get it figured out. Happy shooting.

That’s actually quite interesting. I’ve never experienced that before but I’m not doubting that it could have some effect. I would’ve assumed that the powder would collect moisture in the air rather than drying out but who knows. Guess it would all depend on the room

 

[samb300]

My powder seems to collect moisture and slow down due to being in a basement in the midwest.

If you have a dial micrometer, measure the pressure ring on the bullet near the boat tail. Bergers can have pressure rings much larger than 0.2430", I've seen some lots at 0.2437".

Do you have a 0.236" or a 0.237" dia bore on your barrel? A 0.236" combined with a 0.2437" lot of bullets could be a contributing factor.

 

[CShooter92]

My powder seems to collect moisture and slow down due to being in a basement in the midwest.

If you have a dial micrometer, measure the pressure ring on the bullet near the boat tail. Bergers can have pressure rings much larger than 0.2430", I've seen some lots at 0.2437".

Do you have a 0.236" or a 0.237" dia bore on your barrel? A 0.236" combined with a 0.2437" lot of bullets could be a contributing factor.

I bet this is my issue. I just measure a couple bullets from my old lot and they’re right around .2415. The new lot are .2425-.2430.
My barrel is .236 bore.

 

[samb300]

I bet this is my issue. I just measure a couple bullets from my old lot and they’re right around .2415. The new lot are .2425-.2430.
My barrel is .236 bore.

Are you doing this with a dial micrometer? Or just a digital caliper? A regular caliper won't accurately get you to the 0.0001"

I doubt your first lot is less than 0.2430"

 

[MilSpecOkie]

Are you doing this with a dial micrometer? Or just a digital caliper? A regular caliper won't accurately get you to the 0.0001"

I doubt your first lot is less than 0.2430"

About a year or so ago another guy had .241” 105 hybrids too. Everyone said he was crazy and not possible. Then he showed about 4 other brand bullets measured with the same caliper and they all read .243” while the hybrids read .241”. I remember because I thought he was wrong too.

 

[Feniks Technologies]

.236 bore + *possibly* larger bullet could be your issue.

Try to use a .237 bore on barrels going forward.

(Just realized his is a slightly necro thread)

 

[Feniks Technologies]

About a year or so ago another guy had .241” 105 hybrids too. Everyone said he was crazy and not possible. Then he showed about 4 other brand bullets measured with the same caliper and they all read .243” while the hybrids read .241”. I remember because I thought he was wrong too.

That doesn’t mean generally speaking it works enough to be a good idea. His individual calipers along with how he handled them that day worked. Doesn’t mean everyone else’s will or his will every single day.

Also, not implying he did this, but anyone can make calipers read the same and then put just a little more pressure on them and make them show .002 smaller.

 

[rustyinbend]

I switched to a new lot of 105 hybrids in my 6 dasher last week. I did not change anything else in my load. I took my newly loaded rounds to the range and I’m experiencing pressure that I’ve never dealt with before. I chrono’d the rounds and I’m up from 2920 to 2950-60 now.

I’m running 32.2gr of Varget, 3x fired Lapua brass, CCI 450’s. Gun was just cleaned and patched dry so I know that’s not an issue, even checked for carbon ring and there isn’t one.

I’m just curious if a new lot of bullets can affect the load that much? I did pull some bullets and compare to the old ones and the new bullets are 0.040” shorter overall and 0.030” shorter from the base of the bullet to the ogive. Is the easiest solution to just reseat the bullets, or to drop my powder charge a bit? I have a match this weekend and don’t really have time to do a full ladder of load development.

I wonder what would happen if you switched to non-magnum primers ... might be worth a try.

 

[MilSpecOkie]

@Feniks Technologies

I get what you are saying. He posted 5 different bullet pictures that day and only one was different, I’d say he was using the calipers pretty equal per bullet.

 

[Feniks Technologies]

@Feniks Technologies

I get what you are saying. He posted 5 different bullet pictures that day and only one was different, I’d say he was using the calipers pretty equal per bullet.

Again, that’s a single person. As well as anyone can do that. I could post pics of my calipers doing that if I wanted. Doesn’t make it the right tool for the job and doesn’t mean I didn’t cherry pick pics.

Everyone posts pics of .2 groups. That doesn’t mean they are .2 shooters.

 

[MilSpecOkie]

Of course anyone could do that. But why would he? The fact that he is a single person who had these bullets doesn't mean it didn't happen nor was he incapable of running his calipers. He was trying to figure out why things weren't going well during load development. He measured checking for a pressure ring and discovered that. I shoot with him and he's a friend. He wasn't trying to mislead anyone I can promise you that.