A "slow barrel" ???

[uvausmc]

I recently sighted in my Savage 12LRP in 6.5 Creedmoor with a 24" barrel. I sighted it in factory Hornady 140gr A-Max ammo. The box states the velocity is 2710fps from a 24" barrel. I know factory velocity claims are usually off, but I chronographed this stuff and I got an avg velocity of 2543 fps with std. dev. of 18. I emailed Hornady to see if they had an answer as to why I was getting almost 200fps slower than the claimed vel. Their response was: "it honestly sounds like you have a slow bbl on the rifle." :banghead:

Is it just me or does this sound like BS response? I know all barrels shoot differently and they test ammo in pressure barrels so they are going to get high velocities but this seems like a big difference. The barrel is still brand new and I'm getting 0.25-.40" 3-shot groups @100 but they are opening up to about 1" with 5 shots.



Here is what I sent Hornady:
"I am writing to question some of the velocity claims on your 6.5 Creedmoor 140gr A-Max ammo (#81494). I shot 10 rounds of this ammo from my Savage Model 12 with a 24" target barrel over my chronograph and only got an average velocity of 2534 fps vs. the 2710 from a 24" barrel stated on the box. Std. dev. was 18. The conditions I was shooting were 75 degrees, sunny, and 60-70% humidity. I was at approximately 100 feet above sea level. I was disappointed to see the nearly 200 fps difference in the velocities. This difference will obviously have a major effect on long range ballistics. Can you explain this difference in advertised velocity vs. actual velocity?"

 

[LoonWulf]

Ive never had hornady ammo chrono that much slower then advertised. Im not sure a barrel could be that much slower. One of my guns is consistently slower then my friends with the same barrel length, but its only about 80-100fps. Have you checked your chrono with a known velocity load? Ive found that with the cheap one i have if the battery gets even a bit low (its kinda like one of my highend paintball guns actually), it reads on the slow side.

 

[jmr40]

Could be a combination of slower than advertised velocity and a slower than normal barrel.

Most of the factory loads I've chronographed have been reasonably close considering most of my guns have 22" barrels and they test at 24". I usually am within 40-50 fps and that is about what I'd expect from a slightly shorter barrel. The Hornady Superformance ammo I've chronographed is closer to 75-100 fps slower than advertised though.

It is also not common for some barrels to shoot faster, or slower than expected. Most of the time you will see 50 fps or less. I once had a couple of 280's with equal barrel lengths. The Ruger was consistently 75-100 fps faster than the Winchester with all ammo.

Couple of weeks ago a friend and I were shooting at the range. He had worked up a load and was testing it. When we shot it over my chronograph it shot a lot slower than the loading manual said it should. We tried several rounds and got the same. We tried a few rounds through 1 of my rifles and it was 130 fps faster. That is by far the biggest difference I've ever noted.

 

[Hardtarget]

How can a barrel be "slow"?

Is it a function of twist rate?
Is the barrel "tight"...as in on the small side if the useable diameter?
Or maybe its too large and letting gas bolw by the bullit?

just wondering.

Mark

 

[bigedp51]

In auto racing the condition of the track or road surface controls top speed........



Which track (bore) is less likely to slow you down due to friction?



Speed bumps on a brand new button rifled bore...........

 

[StrawHat]

Not only a rough bore but an oversized bore can contribute to slower numbers. How does the ammuntion group for you? That is the criteria I would consider.

Speer included an article "Why Ballisticians Get Grey" in one of their manuals. It was reprinted in this link.

http://www.leverguns.com/articles/ballisticians.htm

 

[fal762x51]

I have a 4" S&W 629 in 44 magnum that consistently gives about 100 fps less of velocity than a 4 3/4" Ruger Blackhawk, so yes I believe that your problem could be a slow barrel.

 

[MtnCreek]

Reloaders deal with this same issue when working up loads. Data was generated using barrel / chamber X (typically a universal receiver) and the reloader works up his load, using that data, in chamber/barrel Y. The results are always different than the data, sometimes a lot, sometimes just a little. There’re inconsistencies in the components, but the biggest difference is the chamber and barrel. If you were to reload those cases by only neck sizing (leaving the body of the case as is), you could probably get pretty close to the advertised velocity of the factory ammo with pressure similar to Hornady’s pressure target. When fired, the cartridge cases expanded to fit your chamber; assuming your chamber is larger than Hornady’s test chamber (and it very likely is), pressure was reduced, contributing to the lower velocity. Now you have an already expanded cartridge case; this case can be reloaded with a greater powder charge and will give higher pressure and higher velocity and could theoretically be within the pressures intended by Hornady. I bet most of the difference is in your chamber compared to hornady’s test chamber. It would make sense that Hornady would use the minimum chamber dimension when testing…

The barrel is still brand new and I'm getting 0.25-.40" 3-shot groups @100 but they are opening up to about 1" with 5 shots.

This is what I would be concerned with. The Savage 12 is a target rifle with a heavy barrel, correct? I would want to figure out why my 5 shot groups are opening up so much. If your 3 shot groups are consistently repeatable at .40”>, and 5 shot groups are consistently giving you 1”, it sound like your setup is having issues with a warm barrel. IMHO, that’s going to make more difference on target than 200 fps.

 

[Z-Michigan]

I have a 4" S&W 629 in 44 magnum that consistently gives about 100 fps less of velocity than a 4 3/4" Ruger Blackhawk, so yes I believe that your problem could be a slow barrel.

Revolvers have the added and greater issue of cylinder gap and forcing cone dimensions. The difference in those is probably a mix of cylinder gap and the extra 0.75" of barrel for the faster one.

 

[Dr T]

I have a 270 Win that is about 200 fps slow. On the other hand, it shoots 0.75" groups consistently. For all practical purposes, 200 fps is about 20 yards difference in point blank range, so I don't worry about it.

Those are great bore pictures. They make me wonder if the 270 barrel may have speeded up over the last several hundred rounds.

 

[uvausmc]

Reloaders deal with this same issue when working up loads. Data was generated using barrel / chamber X (typically a universal receiver) and the reloader works up his load, using that data, in chamber/barrel Y. The results are always different than the data, sometimes a lot, sometimes just a little. There’re inconsistencies in the components, but the biggest difference is the chamber and barrel. If you were to reload those cases by only neck sizing (leaving the body of the case as is), you could probably get pretty close to the advertised velocity of the factory ammo with pressure similar to Hornady’s pressure target. When fired, the cartridge cases expanded to fit your chamber; assuming your chamber is larger than Hornady’s test chamber (and it very likely is), pressure was reduced, contributing to the lower velocity. Now you have an already expanded cartridge case; this case can be reloaded with a greater powder charge and will give higher pressure and higher velocity and could theoretically be within the pressures intended by Hornady. I bet most of the difference is in your chamber compared to hornady’s test chamber. It would make sense that Hornady would use the minimum chamber dimension when testing…



This is what I would be concerned with. The Savage 12 is a target rifle with a heavy barrel, correct? I would want to figure out why my 5 shot groups are opening up so much. If your 3 shot groups are consistently repeatable at .40”>, and 5 shot groups are consistently giving you 1”, it sound like your setup is having issues with a warm barrel. IMHO, that’s going to make more difference on target than 200 fps.

Yes it's the Savage 12 Long Range Precision. Like I said, these were the first rounds I've put through the gun. I really want to stick with 140gr bullets but I will try the 120-130 range too just to see if it makes a difference in the accuracy. I'm also wondering if the barrel just needs to get more rounds through it to get "broken in." I know these rifles have the potential to be very accurate and produce consistently small groups. I just want to figure out the right formula. I handload for every gun I have and am not the kind of guy that chases velocity but I'm concerned about only getting ~2500 fps because I want to stretch this rifle out to 1000 yds and want to keep all the velocity I can get.

 

[USSR]

Have you checked your chrono with a known velocity load?

+1. Should be the first thing you do.

Don

 

[uvausmc]

+1. Should be the first thing you do.

Don

I haven't. I got the readings on a clear sunny day. I used the diffusers that go on the chrono but could the conditions be causing low readings? That day I also tested some .308, .38 spl, and 10mm. The readings seemed consistent but may have in fact been a little low. I hope this will be the easy answer.

Back to laboratory for more testing...

 

[Hardtarget]

OK. The photos and other info help me see how this slow barrel thing can make a mess of things if a shooter is on the search for truly high speed loads. I don't own a chrno so I never have looked to that facet of shooting. Just if it shoots good or not. Even though I'm not a high end target shooter, I test my reloads to work up a load that my rifle likes.

Good info, guys...like we see here often!

Mark

 

[LoonWulf]

Ive had some issues with lighting and my chrono. Ive been thinking about building a box with a a full ceiling of opaque plastic to see if that helps. My most consistent results are usually on uniformly overcast days.

 

[USSR]

Quote:
Originally Posted by USSR View Post
+1. Should be the first thing you do.

Don

I haven't. I got the readings on a clear sunny day. I used the diffusers that go on the chrono but could the conditions be causing low readings?

The diffusers alone do little to keep the sun off the sensors, which will cause erroneous velocity readings. Late morning and mid-afternoon sun are the worst. Tape a translucent material between the two diffusers and have it overhang all the way around.

Don