Complicated length question

[Bbowl1]

Ok, everytime I try and ask someone they either don't understand what I'm asking or I get different answers.

.308
I have many different boxes of 168smk bullets, each a different lot. What I have found using the hornady OAL gauge is that each box touches the rifling at different lengths. As measured with the hornady ogive caliper attachment.

Example: box A touches at 2.232 and I get good results with 2.215 OAL ogive length. Box B touches rifling at 2.200, would you just subtract the same .017 off making box B Ogive OAL 2.183? The question is how do I go from box to box and compensate for the differences.

I have been told:
Just use the same length
Length load develop each new batch (with only 100, by the time I do that they are gone)
Buy a bunch of the same lot!! (I wish I did)
And, huh?

 

[ShtrRdy]

I've noticed this same thing. For cartridges I'm really trying to build consistently, I will buy several hundred bullets of the same lot code. Then I start from scratch and see where the bullet touches the rifling, and measure this length with a ogive comparator. I'll then reference any bullet jump from this length.

 

[Captain Kirk]

I understand the question, and I have seen significant variation in lot to lot OAL length in many "match grade" factory loaded ammo. There is some variation in lot to lot OAL of bullets as well, but this is more rare. Your listing some significant changes in OAL, you may want to contact theammo maker and get their take on it.

 

[waste_knot]

Are we talking ogive length or over all length.

 

[Bbowl1]

I understand the question, and I have seen significant variation in lot to lot OAL length in many "match grade" factory loaded ammo. There is some variation in lot to lot OAL of bullets as well, but this is more rare. Your listing some significant changes in OAL, you may want to contact theammo maker and get their take on it.

Every box i have checked is different however the main 3 are 2.232, 2.222 and right around 2.200. Also I have some at 2.237. They are Sierra match kings but every other bullet brand I have tried varies significantly Lot to lot as well. Within the box though they are all very consistent so I know it's not my own measurements that are varying.

 

[Bbowl1]

Are we talking ogive length or over all length.

Those would be some pretty short .308s if I was talking OAL. Every number example I said is made with a hornady ogive comparator.

I understand the only purpose of a true OAL measurement is for fitting in a magazine.

 

[BobinNC]

Yes, lot to lot bullets even with quality match bullets vary. Pick a seating depth far enough (0.020"-0.030") off your lands to cover (that is seat far enough off for the longest lot if your loading near the lands) and go shoot. SMK's in general are very tolerant about seating depths, and deliver sparkling accuracy even in Rem factory rifles that the lands are almost out of reach. Just look at how many rifles Federal GMM rounds deliver fine accuracy in, and are built with the same varying SMK's.

Comparator tools can be a great asset, until you realize how uneven your bullets actually are, lot to lot. Then you worry and get wrapped around the axle about a few hundredths of an inch difference, here or there. In the end, shooting more and measuring less can be a great comfort.

 

[Bbowl1]

I've noticed this same thing. For cartridges I'm really trying to build consistently, I will buy several hundred bullets of the same lot code. Then I start from scratch and see where the bullet touches the rifling, and measure this length with a ogive comparator. I'll then reference any bullet jump from this length.

Like what I said about just taking the reading from the OAL gauge and subtracting .17 to make my jump? Sounds like the best solution but I find my groups suck unless its the 2.232 loaded at 2.215. 2.222 at 2.005 for example I don't get the same results. All other factors remain the same besides minor temp changes of course.

 

[waste_knot]

Did you measure from the base of the bullet to the ogive and find the same variation across the lots or do you think this is coming from the way the freebore lead is cut?

 

[40xs]

It is generally accepted that smk's do not like to seated into the lands, so, unless you want to segregate all those bullets into different piles and have to reset your die for each group just use the longest measurement and go with that. As mentioned previously smk's are fairly forgiving on the actual measurement and like to be jumped a little, unlike Berger which shoot great soft seated into the lands. My .02 worth.

 

[Deadshot2]

Yes, lot to lot bullets even with quality match bullets vary.

And there can even be variations within the lot. This makes a good argument for buying bulk and then measuring and sorting into your own uniform batches. I focus on base to ogive measurement. My seating dies use only the ogive area to seat the bullet, not the tip, and since this is the actual dimension that matters when the bullet starts it's trip down the bore, that's where I place my focus. Unless I were to trim meplats and re-point, I can't see worrying a lot over OAL as measured to the bullet tip.