Range Report Lower than expected MV

[earthquake]

So, I just took my rifle to the range yesterday. Brand new barrel, brand new scope, new DBM, new ammo. Lucky for me another guy there had a nice chrono he let me shoot over and here's what I got:

SW Ammunition's 175 SMK match, from a .308 Bartlein (.299 bore, 1:11.25 twist, M40 contour at 20" long)

1. 2,547 fps
2. 2,517 fps
3. 2,538 fps
4. 2,549 fps
5. 2,541 fps

+ 2,549 fps
- 2,518 fps
E 0031
M 2,537 fps
S 0011

Temperature was ~35 degrees Fahrenheit, altitude was 7,780' ASL.

With my old stock Rem PSS barrel (20" too) and SW's Run 'n Gun and Black Hills 168's I was getting ~2,650...HOWEVER, this was at ~600' ASL and 90 degrees Fahrenheit. With the Run 'n Gun I was having major extraction problems and stopped using it.

Would the large difference in altitude and temp make that big a difference? I thought I'd gain a little fps with a tight-bore. Thoughts? I know I can't really know until I go back there this summer in hot weather, but....

 

[Lowlight]

Re: Lower than expected MV

Those number look right, 2550 out of a 20" with a 175gr bullet is about correct.

You can't compare what you had with your 168gr bullet there is a big difference and they will probably shoot the same.

if you wanted higher MV you needed to get a Tight Bore Barrel, not a standard one.

 

[earthquake]

Re: Lower than expected MV

I thought a .299 was a tight-bore?

 

[Lindy]

Re: Lower than expected MV

Muzzle velocity is a function only of temperature. Altitude has no effect, as the oxidizer is contained in the power.

 

[BryanLitz]

Re: Lower than expected MV

The numbers look right to me as well.

Scaling velocity down from the 168 (~2650 fps) to a 175 grain load, you should expect 2597 fps with the 175's assuming the same pressure. However, it sounds like the 168 grain load was over pressure, so the 2537 fps with the 175's sounds like a good non-over-pressure load.

I get ~2570 fps from my 20" OBR with 175's which is within ~30 fps of what you're seeing so I would not consider your numbers to be fishy.

For effectiveness at long range, it's far more important to know your average MV accurately, and that the SD is low. These factors are far more beneficial to success than running 30 fps hotter.

Take care,
-Bryan

 

[Lowlight]

Re: Lower than expected MV

.298 is a tight bore.

 

[earthquake]

Re: Lower than expected MV

.298 is tight-bore, got it. Thanks for all the help. Damn thing shot really well, so I guess I have nothing to worry about!

I made a typo though, the Run 'n Gun stuff were 175's as well, the Black Hills were 168's. I just went back and looked at my data from June, I was wrong, I was getting averages of 2,570 fps with the old barrel and the 175 Run 'n Gun with one box averaging 2,630 fps...sorry about that. It looks like 2,550 is right in the ball-park then.

Should I seek a higher MV by reloading my own ammo for shooting out to 1k? I expect I'll eventually have to begin reloading my own ammo some day to compete with these other calibers I'm seeing (6.5CM, .260, .284 etc.) it appears they handle wind better with speed etc.

 

[Lowlight]

Re: Lower than expected MV

Yes reloading your own will yield better results.

a 175gr with about 45grs of Varget will do well, in CO you can reach a 1000 yards with no problems at 2550.

 

[earthquake]

Re: Lower than expected MV

Sounds good, thanks LL. My gawd this hobby/sport is expen$ive! I'll add reloading equip to the list of stuff I need to buy.

Oh, one last thing, I was looking for the forum thread on barrel break-in, yeah or nay, and couldn't find it. From what I remember reading, is that it's mostly nay...just go out and shoot. That's what I did. I put 90 rounds down range yesterday, ran a dry patch through it just because after maybe 30(?) and that was it. Should I do anything today? Clean it, let it be? Hope I didn't F'ck it up.

 

[Lowlight]

Re: Lower than expected MV

Shoot it, go home and clean it, you;re done. you can clean it once before you shoot it to make sure nothing is hanging out in there, but after that, shoot it like normal and clean it after

 

[earthquake]

Re: Lower than expected MV

10-4, thanks.

 

[Guest]

Re: Lower than expected MV

Velocities will probably come up as you break that barrel in.

I am very happy with these results. Thank you for the data.

Zach

 

[earthquake]

Re: Lower than expected MV

Zach, I am very pleased with the performance of your Match ammo. Here's a photo of my very first 5-shot group after zeroing my brand new SWFA SS 5-20 HD scope with a brand spanking new barrel.

5 shots, 100 yds. ~7mph cross wind, L --> R. The high-right one was first shot.

 

[Guest]

Re: Lower than expected MV

Thank you for the picture, more results that I am very pleased with.

Zach

 

[Frank Green]

Re: Lower than expected MV

Some ammunition makers will not use a test barrel for recording velocities, accuracy etc... until the barrel has a min. of 100 rounds on it. They want to make sure the barrel has settled down and is producing consistent numbers etc...some barrels as they get some rounds on them can see the accuracy get better and your velocities could change as well. Over time of shooting the barrel these things will change as well.

Bore sizes of .30cal. barrels........

.3000" bore size is standard saami min. spec. with a +.0005" tolerance in the vast majority of .30cal. barrels.

Anything smaller than .300" like a .299 bore, .298 bore etc...is a tight bore barrel.

Besides the saami spec. most factories have they're tolerance or maybe I should say run a what is called a factory/production tolerance. Typically the barrels run bigger/looser on bore sizes as well as chamber sizes. I've seen factory barrels run bigger than a .300 bore x .308 groove. As an example I've seen .301 x .309.

Like Bryan L. said in looking at your velocities etc... your loads look normal and nothing out of the ordinary etc...as well as temperatures, elevations/climate your shooting in etc...can cause variations etc....

Later, Frank
Bartlein Barrels

 

[earthquake]

Re: Lower than expected MV

Thank you for the reply Frank. I'm very please so far with my Bartlein! This is my first aftermarket barrel, and I've only heard good things about Bartleins.