Load development with gas off - Am I wasting my time?

[SupressYourself]

-- Thought about posting this to the reloading forum, but it is specific to gas guns, and could be applied to precision testing factory ammo as well --

I have a 6mm creed AR10 that I'm going to start developing a load for.
To minimize some of the accuracy killing factors inherent to gas guns, I'm thinking about turning the adjustable gas block completely off during load development, thereby effectively turning it into a straight-pull bolt action. I shoot suppressed, so the added benefit is it keeps the action a lot cleaner while I do it.

Here's my question: Will the groups I shoot in that gas-off configuration tell me anything about how it will potentially shoot with the gas on?

In my mind, if I find a good velocity "node", and it groups well with the gas off, it should shoot nearly as well with the gas on, and any loss of precision would be the shooter.
I already understand that over-pressure signs occur earlier with the gas on, so I'll need to be careful there, but will velocity or harmonics be different enough to matter?

 

[striped1]

Following to see results.

interested to see if there is a predictable and constant variance in mv and Sd with has block.

May have to test with my 6.5 savage gasser

 

[Gustav7]

This would be interesting to see. I could see it both ways.
The gas porting off could change the vibrations and harmonics, but I feel like the overall accuracy is based off of harmonics of the WHOLE barrel, meaning a gas system probably won’t change the entire harmonics of the whole barrel. It might shift it in a minor way, but I imagine the node would generally still be the same.

following. Always need a guinea pig lol

 

[redneckbmxer24]

Turning gas off will increase velocity and yes will change your nodes and you’d be wasting your time and components.

With a good gas block the regulation is going to be pretty damn close and isn’t going to effect a thing. I’ve done load development for some AR’s with some crazy low ES’s and SD’s.

One thing that I do during load development though is single feed the rounds. I push them all the way up in the chamber and then ride the bolt home using the charging handle so that it only has enough momentum to slip the extractor over the rim and go into battery.

This mitigates potential change in carrier position cause by the next round in the mag, and also eliminates the possibility of pushing the bullet back into the case, tweaking runout, or damaging the tip, all which can and will effect the accuracy.

 

[Gustav7]

I guess my theory was always to do all shooting exactly how I’m going to do shooting. If accuracy is going to be effected while using said rifle then I suppose I’d like to do all shooting in that same condition, to include load development.

 

[redneckbmxer24]

I guess my theory was always to do all shooting exactly how I’m going to do shooting. If accuracy is going to be effected while using said rifle then I suppose I’d like to do all shooting in that same condition, to include load development.

Eliminating variables while doing development is a good thing if you want to get the load as solid as possible. Same reason why you do load development for a hunting rifle off of a bench or prone even though you won’t have a bench on the field and most likely won’t be making a shot prone, you’re eliminating (or significantly mitigating in this case) shooter error.

Something that will completely change the velocity in the barrel is not something you want to eliminate though.

 

[Gustav7]

Eliminating variables while doing development is a good thing if you want to get the load as solid as possible. Same reason why you do load development for a hunting rifle off of a bench or prone even though you won’t have a bench on the field and most likely won’t be making a shot prone, you’re eliminating (or significantly mitigating in this case) shooter error.

Something that will completely change the velocity in the barrel is not something you want to eliminate though.

oh my bad, I didn’t mean shooting position. I was only referring to changes in how the gun is operating both in function and ammo related. So single loading you mentioned could impact accuracy, so my thought was to always have it loaded from the actual mag like it would be done the rest of the time.

Are you single loading to try and avoid random issues? Meaning every bullet that’s loaded out of the mag by the guns normal operation may be impacted marginally, but SOME of those rounds may be impacted significantly, and that’s what you’re trying to avoid. Which in theory would get rid of accuracy outliers?
That makes more sense. Would also help slow you down a little too lol

 

[SupressYourself]

I recently did this with a 6 Grendel, and it seemed to work out. Velocity and groupings with gas on were on-par with my gas-off load. However, # of firings on the brass were different, so not 100% apples to apples, and maybe I just got lucky. I'm going to try it again with the 6 Creed and see what happens.

 

[bfoosh006]

Myself, I would rather shoot with the rifle tuned to run. I would want to know if the rifles cycling is messing with it precision potential.

Make sure the gas tube freely enters the gas key and is not touching the barrel nut and hole through the upper. The gas block should be slightly off the barrels shoulder.

 

[SupressYourself]

Myself, I would rather shoot with the rifle tuned to run. I would want to know if the rifles cycling is messing with it precision potential.

That's what I'm trying to address by turning it off. I feel like I may not know what it's true potential is if the cycling + my poor form causes it to shoot worse than its true potential. In my head, if I can find a good node that shoots, lets say .5 MOA with the gas off, and then I turn it on and it shoots 1 MOA and velocity is close, then I know that extra .5 is me, and I can work on that. Whereas if I'm developing a load with gas on and see a 1 MOA load from the get-go, I'm going to keep searching.

 

[hlee]

Or, the difference is a change in harmonics caused by the system cycling. When you change the gas setting, you are doing more than just affecting your reaction to the rifle.

 

[bfoosh006]

That's what I'm trying to address by turning it off. I feel like I may not know what it's true potential is if the cycling + my poor form causes it to shoot worse than its true potential. In my head, if I can find a good node that shoots, lets say .5 MOA with the gas off, and then I turn it on and it shoots 1 MOA and velocity is close, then I know that extra .5 is me, and I can work on that. Whereas if I'm developing a load with gas on and see a 1 MOA load from the get-go, I'm going to keep searching.

I understand what you mean, and that might work... but that extra .5 MOA difference could also come from the moving parts now being involved.
Something as simple as ...Poor gas tube to gas key interaction, your BCG not returning to a consistent position... basically anything to do with the cyclic part of the action.

I would suggest trying a "Lead Sled" if you truly think your bench technique is causing issues.

Or a bench bag like this... ( Medium size ) ...http://www.dog-gone-good.com/

Those would also help minimize that factor.

You also mentioned brass life... and in my experience, your cyclic speed and bolt unlocking speed / at what chamber pressure has a huge impact on your brass life. And can even have a bearing on primer and their pockets being properly supported.... not to mention consistent 100% ejection and extraction.

I am all for experimentation, so I am looking forward to your results. And truly hope your train of thought works out well.

 

[redneckbmxer24]

If your gas tube is stressing the gas key to one side, or the bolt isn’t consistently coming to rest the same then it’ll do that regardless of whether gas is cycling the action or not.

The theory behind having the gas system on and tubes for development is that gas purging out will change velocity. I’m talking well over 100fps in a 18-20” with rifle gas. That will change you’re node.

The theory behind single feeding one round at a time during development is to eliminate the possibility of the rifle doing anything to the round upon chambering and eliminating that variable to find the true accuracy potential of the rifle as a base line. Once you’ve developed your load and you know what the rifle can do that’s when you start shooting as you would to see if it remains the same. If it doesn’t and some rounds you’ve chambered you pull and measure and it’s an ideal scenario with no setback or bullet deformation then you plug on. If it is setting bullets back and/or causing accuracy issues then you begin to tweak neck tension and/or play with crimping (neck tension is a far more accurate/consistent way if you can make it work). If it’s jacking up bullets to the point it ever throws shots, then you figure out why... after you’ve figured out your absolute baseline.

This is working backwards from the start while only adding a few steps so that you’re not scratching your head down the road.

 

[SupressYourself]

...gas purging out will change velocity. I’m talking well over 100fps in a 18-20” with rifle gas...

I only have a sample of 1 so far, but I did not see that with my Grendel. Velocity was within 15fps. But between gas off and on I switched from 4x brass to new brass, so I don't have the cleanest data.

 

[bfoosh006]

I wonder if the difference in the volume of gas produced... IE, 6.5Grendel v. 6.5CM would produce different FPS loss.

Molon did a 5.56 test and showed a loss of 23fps... sorry the link is older and the photos are gone.
https://www.ar15.com/forums/ar-15/A...mpared_to_Single_Shot_Velocities/118-696525/?

 

[GONE BAD]

What the OP is asking is also something that I have questioned many times while testing load development.

Mainly how hot I can load a particular cartridge in a particular rifle.

As far as the effects of how the gun reacts to gas on or off or single loading may have less effect than what most are stating here.
Take for instance single loading in high power matches where using ammo to long for magazine is used.
They run fine and show excellent accuracy.

Setting that aside, how do we achieve a high node without knowing what is actually happening inside the chamber. I'm talking primary extraction.
In a boltgun it's easy. In a gasgun not as easy unless you turn the gas off or on just enough to get primary extraction.

Just a little food for thought.

 

[sam4886]

I'm interested in results as well. I've got a can coming soon and want to switch brass and maybe powder so I'll have some development to do this spring on a 6mm predator AR. I'll keep this in mind. It might show something with current loads going from normal operation to no gas too.

Aren't the bullets long gone from the barrel before any of the recoil impulse, and maybe gas, has any effect on the rifle? If that is the case, the harmonics that mess with the bullet would be the same either way. The gas tube and everything is still there in either case.

I think the only factor that may be in play for accuracy testing with gas on or off is velocity. Obviously that's a big factor for nodes and stuff, but it could be useful to know when testing other variables or something. Did those velocity tests mentioned above take weather and other stuff into account? Where they done the same day/time?

Again, this is mostly a question, not an educated opinion. Just my thought process.

 

[SupressYourself]

The results are in, and the velocity change is negligible.
Stats: 6 Creed, 90Gr Sierra TGK, Reloader 16, Lapua 3x, CCI 450, 22" bbl, 9" 30cal suppressor.

Gas OFF:
42.3 ~3077
42.4 ~3092

Gas ON:
42.3 ~3079
42.4 ~3086

All are 4 round averages, shot on the same day, only a few minutes apart.
There seemed to be a POI shift, about .5 MOA to the left with the gas on, but the loads grouped just as well or better -- although that piece was likely me settling in, as I shot with gas off first.

I think the suppressor plays a big role in maintaining velocity with the gas on. It creates a ton of back-pressure, so it doesn't take nearly the gas volume to cycle the action.

Overall, I'd call this a win. I found an accurate load while keeping my action clean.

 

[Greg Langelius *]

I agree with about all I read here, including the contradictory stuff.

I develop loads as closely as possible to the manner as I shoot. In my instance, that's being fed from the magazine. If it's a mistake, at least it's my mistake.

I don't shoot suppressors. My curiosity prompts me to ask if/how the suppressor influences dwell time, and whether gas system length works in conjunction.

My accuracy demands have limits; ones I hope are based on reasonability. I'm not seeking BR Grade accuracy, and I'm also trying to reasonably limit the impact load testing will have on overall bore life.

Greg

 

[SupressYourself]

Small update: I found this to be an interesting exercise with another 6 Creed barrel.
22" bbl suppressed, Hornady factory 108 Match, 4 rounds each.
Gas Off: 2843 fps
Gas On: 2849 fps
Both grouped sub-.5 MOA, with an edge to gas off, but with the difference being well within the margin of error for my shooting ability.

 

[KineticPerformance]

I develop my loads with gas turned off, adjust gas until it runs reliably, then make any minor tweaks if needed but it rarely requires any adjustment.

 

[Molon]

gas purging out will change velocity. I’m talking well over 100fps in a 18-20” with rifle gas.

Do you have any statistically significant data to support that claim? The testing that I've done shows the velocity difference with the gas port off is miniscule.

....

 

[redneckbmxer24]

Do you have any statistically significant data to support that claim? The testing that I've done shows the velocity difference with the gas port off is miniscule.

....

I have chronograph data just like you, but I have testing from several rifles and no just one. Does it make it more statistically significant if I made a silly little chart instead of just explaining what I have seen?

 

[Molon]

I have chronograph data just like you, but I have testing from several rifles and no just one. Does it make it more statistically significant if I made a silly little chart instead of just explaining what I have seen?

So you don't have any statistically significant data to support your claim. Thanks for clearing that up.

...

 

[spife7980]

I'm not really sure what I'm supposed to do about last round flyers.

In relation to this, I noticed that the last round was almost always out of group when doing my load development.
So now I will load an extra dummy round in the bottom of the mag so that the final test round isn’t being acted upon differently on from the lack of pressure on the carrier from an empty mag.

 

[Odysseus1911]

I have chronograph data just like you, but I have testing from several rifles and no just one. Does it make it more statistically significant if I made a silly little chart instead of just explaining what I have seen?

Don't take offense, I don't think @Molon was making a dig at you. He was asking a serious question, and I was wondering the same thing.

Everyone makes observations. And if we make the same observation a few times, we naturally conclude that whatever we observed must be what tends to happens in that situation. The problem is that we're wrong half the time. So our conclusions are of questionable value until we test them in a way that definitively proves or disproves them. That's why the scientific method and statistics were invented.

The solution is to run a controlled, well-designed test where you eliminate every variable except the one being tested (chronographing multiple rounds from the same lot of ammo, from the same gun, in the same sitting) so that we're not led to the wrong conclusion by extraneous variables, like using different guns in the same test, or using different lots of ammo in the same test, etc. (Then you can repeat the test with a different gun or a different lot of ammo, but only test ONE variable at a time.) The other half of making sure your data is meaningful is to run each test with enough samples (chrono'd shots in the same sitting) to make it statistically significant. Statistical significance isn't determined by whether you made a chart to explain it or not, but by applying an equation called a power analysis which determines whether you used enough samples (power) to know that your data couldn't support a wrong conclusion.

Molon was just asking if you had applied the scientific method and statistics to definitevely prove or disprove your observation-based conclusion. If you haven't, there's no shame in that, but inquiring minds want to know.

 

[redneckbmxer24]

So you don't have any statistically significant data to support your claim. Thanks for clearing that up.

...

So making a chart which you could literally fabricate whatever numbers you want certifies it? Got it.

You have a test sample of one fucking rifle and made a chart on apple pages or whatever so you’re practically Bryan Litz in your mind.

 

[KineticPerformance]

I also find going from no gas to cycling to have an insignificant effect on MV with a sample of greater than one.

 

[r.tenorio671]

....FWIW, I usually test my development loads with my SLR AGB's turned OFF. My intent is to find the charge weight that will give me my desired FPS (if possible). By using a closed block, I don't have to worry about early unlocking and/or brass issues resulting from it being open. Afterwards I can adjust the AGB to a functional setting and if necessary, tweak the charge weight, seating, etc. to gain accuracy. I haven't seen any really significant changes in the FPS closed -vs- open. Admittedly, I'm looking for FPS as close I can get to my anticipated FPS goal with the powder/bullet/primer combo in use.

 

[MontanaMan]

Unless you plan to use the rifle as a single shot, then anything you do with the gas off is more or less a moot issue.............in the long run.

All the loading variables, as well as the variables in the functioning of the rifle, & you as a shooter will determine the "accuracy" of the rifle in normal operation.

But to get enough rounds through it to assure that you've seen & encompassed all of the variable (ie, a full, normal distribution), IMO is more valuable & more important in the long run than what you are getting with doing load development with the gas off.

And all assuming that all the functioning / fit of the mechanical parts of the rifle are right.

YMMV

MM