Adjusting gas block changes velocity?

[GM2B]

Will adjusting my gas block to cycle less gas create a touch more velocity out of my 18 inch rifle length barrel? I could just adjust it chrono and find out but I hit dead on at 200-500 right now sub MOA and I dont think messing with it 12 days before 3 major matches back to back makes any sense. I looked at the JBMballistics.com and it appears 30FPS with 77SMK makes 2.5 inch difference at 500 yards. I cannot imagine it making more than a 10FPS difference but I have never tested this. Has anyone here?

Background: I was shooting 55FMJ @2300 FPS it was working great until I hit 40 degrees at 3 Gun Nation SE regionals and had 3 failure to cycle with it. Now I have found the lot of 2000 I loaded are not consistent with the powder charge and have decided to shoot PMC Bronze but I am way over gassed shoot with PMC. I shot one of my handloads in a match today and it sounded like a .22lr I prayed as I racked the chamber and broke another shot. Luckily the bullet made it out! I have loaded over 50,000 rounds and the past month I have encountered my first squib with my pistol and today was my first rifle "squib like" round.

Edited March 17, 2014 by GM2B

[Mberry]

Good question. I have never chrono'd it to find out, but I would think that a 10 fps shift is not out of the question with a big change.

But... You're probably more likely to see a shift in zero from DA changes in matches across the country, even from morning to afternoon. A 1/2 moa at 500 yards really isn't that big of a shift. Most folks are doing really well to shoot 2 moa at 500 under match conditions with 3-gun gear.

I would tune it and not worry too much about it. I think you're more known for speed than accuracy anyways, right? Are you consistently going one for one on shots past 300?

[BBJones]

You thought you might have a bullet stuck and you pulled the trigger anyway and "prayed" it would be ok? No match is worth serious and permanent injury.

No personal testing on your question but I doubt you could alter the gas enough to drop it even 10fps.

[Religious Shooter]

I'm not sure about velocity. But adjusting the gas block can change your POI.

http://www.youtube.com/watch?v=0bRBEWjsJtI

But I don't think it matters for the typical 3 gun target you will encounter.

[GM2B]

I heard the pop like a .22lr not just a primer. You are right it was a poor decision but luckily the bullet left the barrel.

My money maker is long range. I can keep up with speed but my best stages have always been long range. I dont necessarily go one for one but I hit them quick and in a hurry. Usually for 5 targets at 300 yards 6-8 shots. Yesterday in a match I hit 11 targets 200-300 yards in 41 seconds from 4 positions 3 targets standing supported, 3 kneeling, 3 sitting, run 15 yards and shoot 2 from prone. 20 shots.

Based on the video I just watched and just having the gut feeling of knowing not to change anything before a major I will leave it alone. I appreciate this persons video but his baseline was 2+MOA at 100 with adjustment closed he went to 5+MOA!!!! People can shoot 2moa groups at 500. I will stick with my 3/4 moa and hit more frequently! My background is 3 years of benchrest and 1000 F class style shooting before I ever played 3 gun so accuracy of my equipment is paramount.

[GM2B]

Thanks for your help on solidifying my decision to change nothing!

[Mberry]

Change it all right before the Tarheel Challenge! I'll buy you lunch at the gas station if you do.... You can even get the fresh sushi!

I would have never guessed that you were a BR and F class guy. All that, and you can throw a tomahawk!

[Mark Gale]

Will adjusting my gas block to cycle less gas create a touch more velocity out of my 18 inch rifle length barrel?

No. Everything else being the same, velocity can only be controlled by powder charge.

Don't think for a minute that an adjustable gas block can be fined tuned. There is nothing linear about their operation. Given a specific cartridge, they are either on or off.

[Stlhead]

I am hoisting the bullshit flag. On or off? Specific cartridge? Please share your testing procedures that resulted in you reaching these conclusions. Adjustable gas is not voodoo, big hole = more gas, small hole = less gas. Hell even the tune the port not thebblock guys still adjust the gas, they just do it with a drill instead of a set screw. There are some systems that work better than others, but to paint them all as either on or off is ludicrous.

[GM2B]

I agree with you Stihead.

My logic came from less gas going through the port means more is going out the barrel which I would think would increase the muzzle velocity slightly. Probably more evident in a carbine length gas system. Maybe not even noticable on either barrel using a chronograph due to the extreme spread of any given load. This is something that I would love to tinker with but I have to leave my rifle alone for now!

[mpeltier]

Your logic would be sound except for one thing, the bolt is locked until the bullet leaves the bbl. there is no more or less gas in the entire system. With an adjustable gas block you simply control where some of the "extra" gas goes. It flows into the bolt/carrier and out the muzzle after the bullet in all cases of a functioning bolt carrier. If you shut off the gas block it might give back a little velocity, but even then it probably wouldn't be more than 30-50 fps.

[troupe]

I disagree on the only thing that can change velocity is the powder charge . Have you never notice velocity change as a barrel heats up ??? 30 FPS is not unreal.

[Solidgun]

We should also consider that These speed averages may be from chrono tolerance error as well as factory ammunition variance along with other considerations mentioned.