Do these wide tolerances matter downrange? (Hornady 68 match)

Been reading bad reports by reloaders on the Hornady 68 grain Match BTHP bullet. I happen to have bought 300 of them a while back at a gun show, noting they were much cheaper than SMKs.

Curious, I measured and weighed 10 of a box of 100, a typical 10% inspection of a product. The results (length and weight):

.997/68.1
.997/68.1
.998/68.1
.999/67.8
.999/68.4
.998/68.1
1.000/68.2
1.004/68.3
1.004/68.4
1.004/68.4

I'm focusing on the .999/67.8 to 1.004/68.4 difference, and wondering if this may be the reason reloaders are reporting disappointment with the bullet.

I'm no expert, but I would think diameter anomalies would be more important than length and weight.

Quote:

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Originally Posted by Bang

Been reading bad reports by reloaders on the Hornady 68 grain Match BTHP bullet. I happen to have bought 300 of them a while back at a gun show, noting they were much cheaper than SMKs.

Curious, I measured and weighed 10 of a box of 100, a typical 10% inspection of a product. The results (length and weight):

.997/68.1
.997/68.1
.998/68.1
.999/67.8
.999/68.4
.998/68.1
1.000/68.2
1.004/68.3
1.004/68.4
1.004/68.4

I'm focusing on the .999/67.8 to 1.004/68.4 difference, and wondering if this may be the reason reloaders are reporting disappointment with the bullet.

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The flyer in that group is the 67.8, all of the rest are average of 68.2 -.1 +.2 which seems reasonable. Not sure if even the 67.8 is that far out when it comes to shooting.

The way the jacket is drawn and the way the ''hollow point'' is formed , .005 is not really a concern. Look at a Sierra Match King if ya want to see something.

What rifling twist rate? 68grs need faster twist. Min is 1:8 , but they do best in 1:7

I'm well aware of SMK length variations. In fact, they are the reason I bought the Stoney Point (Now Hornady) gauges. But something about their ogive (I'm guessing), a bit different than Hornady's, seems to be more forgiving of the variations.

SMK's are no better. Some guys swear by Custom Competitions. Some the A-Match. Lots the SMK. My NM AR prefers the SMK. You've got 300 of them, Try them out. If by the end of 300 rds you haven't started zeroing in on a load that you are happy with try something else. That's half the fun. Good luck
As for twist rate, a 9 twist barrel is fine for 68's. My NM shoots 80 grain SMK's just fine to 600 yds with an 8 twist barrel. I believe the "optimum twist" for the 77 SMK is 1:7.7 and while there are some 7.7 NM barrels out there most are either 7 or 8.

Good luck

Yep,half the fun. Just hoping I do a little better than some of those who have tried similar.

What does the cartridge base to ogive datum vary by? Just measuring bullet length with a caliper, or for that matter with a micrometer, means little. The distance from the ogive datum (an imaginary line on the circumference of the bullet where the bullet first engages the rifling) to the rifling is more important than bullet length or OAL of a loaded cartridge. I have not used the Stony Point unit because I was shooting M1/M14's and had no access to the chamber. I do use an RCBS device that is best explained here:

https://gswagner.com/headspace/headspace.html

Also, what S.D. are you getting on your Chronograph?

Good Luck and be SAFE!
Steve

Do the tolerances matter? Maybe... only your rifle knows.

May I remind that I have not mentioned shooting the 68 gr Hornady Match bullets yet, and I have not. So, no chrono numbers yet either.

The Stoney Point gauges I mentioned are head and shoulder/(and) bullet gauges creating a repeatable datum on the ogive in the measuring of bullets. Measuring ten 68 gr Hornady Match bullets base to ogive:
.5835, .5835, .5825, .582, .584, .5825, .583, .583, .5825, .582. These pretty much replicate what I have found with SMKs, and indicate the more important bearing surfaces are probably "perfect enough". (another way of saying mil spec? LOL).

My way of measuring distance to rifling lands consists of a sized shell having two cuts longitudinally down through the neck and slightly into the shoulder, spaced 180 degrees. The interior of the neck is smoothed, and holds the bullet firmly, with heavy finger pressure able to move the bullet. I carefully introduce the assembled bullet and modified case into the chamber, and push the device until it firmly stops at shoulder contact.

A gentle push with a cleaning rod dislodges the assembly. Doing this five times and all five measurements agreeing I am confident that I have the COALs required to engage or avoid the rifling.

The Frankenbuild DPMS-based AR with the 1/8.5" Wilson barrel measures 2.975" and the Spikes Tactical 1/7 measures 2.983". I suppose I could add .004" to each to account for headspace as well. Some of my loads will stand off of the lands with deliberate experiment. Some will accommodate mag length of under 2.260".