Hornady 6.5mm bullets are slow?

[Hoon]

So, since i started shooting 6.5CM, i've been running 142gr SMKs on 41.0gr of H4350.

This has yielded 2770 FPS on my chrony, which has been verified accurate over the course of hundreds of rounds on the range.

Accuracy wise, the load was good for about .5 MOA on average, with occasional groups in the high .2s and low .3s.

So, i ran out of 142 SMKs and loaded up some 140 ELD Match on 40.7-41.2gr of H4350 for testing. 40.7gr only produces 2700fps. 41.2gr only produces 2745 FPS.

I loaded up a few Burger 140s on 40.7-40.8gr and got 2750fps out of those.

I will say, the Hornady's are freakin' accurate. No problem putting 5 shot groups into the .3s, but the for some reason the velocity seems noticably slower than the other two bullets ive tested. To make it worse, the best accuracy node i've found is the lowest charge i tested, at 40.7.

Granted, 2700fps is still plenty of steam to go well beyond the 1015 yard max that i shoot the rifle.

 

[jtcoinflip]

Were all of the cartridges tested on the same day? are you adjusting for temperature of the ammo and the external temps if they werent? Also, barrel life could be a factor in the change in velocity.

 

[Hoon]

Were all of the cartridges tested on the same day? are you adjusting for temperature of the ammo and the external temps if they werent? Also, barrel life could be a factor in the change in velocity.

The 142 SMK is my go-to load, it has been tested several times and verified on the range many times. It was about 75 degrees when i shot the Hornadys and Burgers, the SMKs have been done at 70 degrees and yielded 2770.

The ELDs and Burgers were shot back to back.

The barrel has 552 rounds down it - shouldn't be slowing down yet!

 

[Steve Marshall]

JHC. 70 FPS is life changing? .2 MOA in your world sounds like a good trade-off, no? I mean you are shooting at targets after all. Sooooooo how does it perform on target at your 1015 yard max?

 

[Hoon]

JHC. 70 FPS is life changing? .2 MOA in your world sounds like a good trade-off, no? I mean you are shooting at targets after all. Sooooooo how does it perform on target at your 1015 yard max?

It's not life changing, but I don't understand why it's happening and am curious if other people have had the same result.

Berger with 1/2 grain less powder are going faster. Heavier Sierra with less powder are going faster.

 

[jtnf]

What size population? You have "hundreds of rounds" over the chrony with the 142gr SMKs, what about the Hornady?
And, what was the std.dev of the SMKs? If the population of the ELDs was large enough to be a valid sample, what was the std.dev of that population?

 

[jtcoinflip]

What about cartridge length? Are you seating the ogive to the same distance from the lands?

 

[Steve Marshall]

How about bearing length, load density or actual bullet diameter? 70 FPS in this BC class will change your POI what? 15" or so at 1,000 yards. How about the difference in BC of the 2 bullets? OR how about one bullet, under identical conditions HAS to be slower/faster than another?

 

[Mountain]

70 FPS at 1000 yards for those velocities and BC's is going to be a ~20" difference in POI. At least it's 6.5CM- a drop of 70 FPS for .308 could be the difference between staying supersonic or not at 1000. Significant...

Hoon- any difference in bullet diameter and jump to lands?

 

[vicorjh]

As Steve notes, suspect that the bearing surface on the SMKs is measurably less than the ELD-M. This has the potential effect of a reduced amount of friction on the projectile while in the barrel (relative to the ELD-M).
Just a guess since I do not have the measurements handy. Might be worth it to measure bullet base to ogive.

 

[larueminati]

Title should be slow(er)

Bearing surface as mentioned above might be the culprit.

On the positive side if the Hornady's have more bearing surface with the neck they should theoretically be a more concentric round and be more accurate.

You mentioned accuracy node, have you tried going up on the charge to the velocity you want and then running a seating depth test? Sometimes you can tighten the group back up with a slight adjustment.

 

[josh2600]

You mentioned accuracy node, have you tried going up on the charge to the velocity you want and then running a seating depth test? Sometimes you can tighten the group back up with a slight adjustment.

That's true, it's all about timing.

 

[Hoon]

What size population? You have "hundreds of rounds" over the chrony with the 142gr SMKs, what about the Hornady?
And, what was the std.dev of the SMKs? If the population of the ELDs was large enough to be a valid sample, what was the std.dev of that population?

Population for the hornadys is 35 rounds across 6 charge weights. not enough data at any one charge weight for an SD. I'd have to go downstairs and sort through some notebooks for the SD on the SMKs, but it was very low. If it wasn't single digits it was close. Just started testing with this bullet, haven't been back to the range with the 6.5 yet.

What about cartridge length? Are you seating the ogive to the same distance from the lands?

Identical.

How about bearing length, load density or actual bullet diameter? 70 FPS in this BC class will change your POI what? 15" or so at 1,000 yards. How about the difference in BC of the 2 bullets? OR how about one bullet, under identical conditions HAS to be slower/faster than another?

Can't measure bearing length, don't have any more SMKs on hand. Probably won't for awhile...want to spend some time slinging the Hornadys. They're cheap and very accurate so far, i'd like to see what kind of performance i get from them at distance.

70 FPS at 1000 yards for those velocities and BC's is going to be a ~20" difference in POI. At least it's 6.5CM- a drop of 70 FPS for .308 could be the difference between staying supersonic or not at 1000. Significant...

Hoon- any difference in bullet diameter and jump to lands?

Same jump, can't measure diameter, i'll have to pick up another box of SMKs. Not really in a hurry to do that considering the accuracy of the Hornadys, and the new(ish) 147 ELD with a .697 BC is going to have to get tested at some point

Title should be slow(er)

Bearing surface as mentioned above might be the culprit.

On the positive side if the Hornady's have more bearing surface with the neck they should theoretically be a more concentric round and be more accurate.

You mentioned accuracy node, have you tried going up on the charge to the velocity you want and then running a seating depth test? Sometimes you can tighten the group back up with a slight adjustment.

I have not tried to push the velocity yet, this is just the results after the first round of testing. I would have thought it was something besides the bullet, but when i shot the bergers in between and the velocity came up i knew it was the bullet itself...everything else was identical, they were even loaded at the same time.

 

[Mountain]

Damn- .697 BC is really impressive from a normal size caliber. I'm running a 6.5CM gas gun, so that might not make mag length but would be good for single load.