Altitude vs. Velocity

[nmkid]

Today I finally had the opportunity to shoot my new 22 Creedmoor. I loaded 45.0 grs. of RL 26 behind a 75 gr Hornady ELD Match. Barrel is finished at 28" From what I had read beforehand, I was calculating around 3550 fps. My Magneto said 5 shot average was 3472 fps. Got me to wondering if my altitude, (180' above sea level) had anything to do with my, "lower" velocity.

 

[riflewoman]

Not that much. More likely you have a slightly slower lot of powder and blowing out the case to your chamber.

 

[The German]

My understanding is that the altitude/air pressure, temperature should have almost zero impact when measuring close to V0 (trajectory of course will change).

 

[geraldgee]

The barrel should speed up after 100 or so rounds - mine always do. I resist chrono’ing until I get the barrel broke in.

Good luck with it

Gerald

 

[Bart B.]

A 100 fps spread in muzzle velocities across a bunch of barrels for the same load happens. Almost that much across a given charge weight across all lots of a given powder.

A smaller spread across the same rifle and ammo's velocity with different people and chronographs used.

 

[284winner]

Today I finally had the opportunity to shoot my new 22 Creedmoor. I loaded 45.0 grs. of RL 26 behind a 75 gr Hornady ELD Match. Barrel is finished at 28" From what I had read beforehand, I was calculating around 3550 fps. My Magneto said 5 shot average was 3472 fps. Got me to wondering if my altitude, (180' above seal level) had anything to do with my, "lower" velocity.

What you will read and what you will experience oftentimes are two different things. That I believe is a case of that example. As said all barrels run different speeds. Your Barrel will speed up after break in.

 

[nmkid]

The barrel should speed up after 100 or so rounds - mine always do. I resist chrono’ing until I get the barrel broke in.

Good luck with it

Gerald

Normally, I never chrono until I have found a load that I like. I think I got derailed from my normal procedure because this was my first barrel install, (Savage). Needless to say...Tensions were running high on the first trigger pull. Guess I did everything right, I'm still here and my spent cases looked perfect.

 

[nmkid]

Still looking for a starting load with H-4350 for the 75 gr. and the 80 gr.

 

[Mr.Knowit all]

From Nevada (where I live) to CA (where our ranch is) there is just over 5, 000 ft difference in elevation. The biggest thing for me is....the air is much denser and I start to go trans a couple hundred yards sooner but my MV were the same/very close as in Nevada.

 

[geraldgee]

Normally, I never chrono until I have found a load that I like. I think I got derailed from my normal procedure because this was my first barrel install, (Savage). Needless to say...Tensions were running high on the first trigger pull. Guess I did everything right, I'm still here and my spent cases looked perfect.

Glad it went well for you. I hope it shoots well too. Keep us posted with a review once you get it where you want it. I have a 6.5 Creed that shoots well and a 6 Creed that hasn't been shot besides function testing by the gunsmith . I am interested in how yours does.

Good shooting to you,
Gerald

 

[fredo]

Today I finally had the opportunity to shoot my new 22 Creedmoor. I loaded 45.0 grs. of RL 26 behind a 75 gr Hornady ELD Match. Barrel is finished at 28" From what I had read beforehand, I was calculating around 3550 fps. My Magneto said 5 shot average was 3472 fps. Got me to wondering if my altitude, (180' above sea level) had anything to do with my, "lower" velocity.

Nope, ASL won't affect MV, but it does affect downrange ballistics via the amount of drag against the bullet as it flies through that air...

Sometimes, there's a disconnect from what ya read on the internet and what happens in real life. Based on capacity on your cartridge, you're right in the wheelhouse of expected performance with that bullet weight.
If anything, RL-26 might be too slow a burn rate for that size case? Just speculating, but those I know who shoot .22Creeds are running STOUT loads of 4350 to get their speed. If I were dead set on using an Alliant powder, I suspect RL-22 or '23 might be a better fit?

As has been stated, yes...your barrel might "speed up". But that is not a given. A 75 @ 3475 is still doing sumthin, just keep in mind you might lose some fps during colder months. My old 22-243Win lost over 1fps per °F of temp change when loaded with both RL-25 & '22. But the '22 allowed more initial MV...

Have fun!

P.S.
A 75 VLD or JLK are both more slippery, and might yield more velocity due to their reduced bearing surface...

 

[nmkid]

If anything, RL-26 might be too slow a burn rate for that size case? Just speculating, but those I know who shoot .22Creeds are running STOUT loads of 4350 to get their speed. If I were dead set on using an Alliant powder, I suspect RL-22 or '23 might be a better fit?

Think I might give RL-22 as I have a ton of it. Been searching for some starter loads for H-4350 for the 75 gr. bullet. Good amount of info on H-4350 and the 80-80.2 gr bullets but, pretty sketchy on the 75.

 

[fredo]

Whatever intel you gather for an 80 is directly attributable to to a 75. You should be able to use that data as a guide, backing off a bit for safety. Then, work back up to prove out your own ladder/pressure test for your rifle...

Just like reading glorified velocity claims on the internet, take any & all load recipes with a grain of salt and several ounces of safety! Don't just arbitrarily dump powder cuz some dude in the 'net said his rifle loves it....PROVE IT for yourself by being safe & methodical!