Why did changing buffers change my POI?

[Double Naught Spy]

So if you think changing the buffer changed the POI, then the simple way to verify this and to have conditions that are truly the same (including environmentals) is to go to the range with both buffers and shoot a target. If correct, then the bullets will group in two different locations roughly 2" apart as you note.

If not satisfied, let somebody else shoot for groups with the 2 buffers.

Otherwise, as has been noted, there is not reason to believe that changing buffers should change your POI.

[grayfox]

So...
lots of good and consistent advice.
Pix.
Shoot again with both buffers side by side...
have another shoot same thing, both buffers.

The ball is now in your court sir.

[65Grendelier]

The ball can be in whoever has another explanations court. I can shoot 1/4” groups I’m not sure why I would need someone else to shoot it? I don’t need to go redo anything as I’ve already done it lol. I had to move my elevation down two inches and I’ve shot it since and it’s still on… the only variable that changed is my buffer. I measure and log every round that goes through that pipe…

[imaguy3]

well then problem solved... no reason to keep talking about it...

[Klem]

65,

With respect, this is not supposed to be adversarial. Check your ego at the door please and help us, help you.

Reading the replies, no one is suggesting you cannot shoot, but without knowing all the facts it cannot be discounted as the reason. And what does it matter if it is your ability to shoot; we're all just avatars on a shooting forum? There is a lot of information missing and your claim to a 0.25" average out of an AR is extraordinary. Removing yourself from the equation and letting someone else shoot is a logical way to eliminate one possibility for the POI shift - I can see myself doing that in a similar situation. This given the reasons for where bullets go include the gun, ammo, rest, environment and shooter.

As for the buffers, I'm with B13, Montana and others on this; there is no way an 0.8oz increase in buffer weight will have that much influence on external ballistics. So I think there's a bit of confirmatory bias going on here. For the avoidance of doubt why don't you take both buffers down to the range and shoot some more groups. Swap the buffers while keeping everything else the same. Keep swapping until you prove/disprove your hypothesis - that the buffers are the cause for a 2" POI shift and shrinking the average group size by a factor of 3.

Full disclosure would be helpful. We still don't know at what range are you shooting these groups. Are you measuring centre-to-centre? Any photos of the gun and targets? Claims to an average group size of 0.25" (at 100) implies half are even tighter than 0.25", which is extraordinary out of an AR. The occasional group for sure, but claims to what the gun is capable of imply lots of groups have been fired to form an objective average, and not cherry-picking the best group. So how many shots are we talking about?

If you have kept the suppressor on for both buffer group sessions and shot the same load above then it could be other reasons, like shooter, rest, wind, and other parts of the gun.

I don't clean bolt guns until the groups widen either, but definitely clean suppressed autos every time; shoot 50+ rds and actions, magazines and spent cases get filthy quickly.

[65Grendelier]

It’s okay Klem. I give up dude. This wasn’t a post about group sizes etc. it was about the effect of changing buffers on harmonics and pressure, changing poi and group sizes.

It’s reasonable for me to understand there’s not an easy answer to this. I could rinse repeat do it again and waste my time, but I already know it happened.

I apologize that this somehow turned into me flexing my ego, that was not my intent or original question, I’ll just leave it at that.

Thanks.

[Klem]

65,

So be it - good luck.

[Zeneffect]

We never considered the issue could be before firing, during chambering as we don't know the neck tension.

The additional buffer mass may be carrying through the case and you can be seeing some unwanted coal growth. Not saying this is the case, bit it's a very slight / remote possibility that is easy to check and eliminated. This would conform to both "won't impact haromonics" and "seeing poi shift" theories at the same time.

My second thought on this is weather vs parallax. If you are adjusting parallax focus to cut through mirage, you might have a difference in parallax shift as a result (focal point actually changing at range) this would be the fault of the scope in my opinion. Some will do it more than others, some won't do it at all...

The most likely case.... your weather changed and so did your velocity... which changed the harmonics and bullet exit point during barrel whip. Cfe223 isn't known to be temp stable by any means. Things like humidity, atmospheric density, all impact aerodynamic jump as well. In general, what was the weather like during the before and after tests? I'm guessing... about 15F difference and probably different times of the day?

[Bonas]

OP, the short version of all this is that there are about a gazillion variables involved in producing a group of shots. The buffer is pretty much at the bottom of the list of variables that would produce the changes in group size and POI you reported. Beyond that, despite several requests, you won't provide any additional information that might help isolate variables.

"Harmonics," whatever that's defined as, and changes in case pressures within safe ranges aren't going to reduce your average group size from .85" to .25," even if you were manipulating them intentionally. There is no way changing buffer weights can do that. That's why everyone is pointing to other causes and seeking additional information. Whatever you observed wasn't caused by the buffer. Regardless, if you really got an average group size of .25" at 100 yards with a statistically signficant number of shots in the groups, you probably ought to leave the rifle as is and stop wondering how it got there because you have a unicorn.

[LRRPF52]

Lol I clean my chamber.

I precision reload.

6.5 Grendel:

123 eld-m MV 2425 SD 9
31.2 cfe 223
Bto 1.658”
Cci 450
Starline brass base to shoulder 1.212” fired cases 1.2165-1.217 (.005” bump)
Trim length 1.510”

Charge master link powder measure

Lots of precision shooters don’t clean their barrels until they stop grouping.

I’m not an amateur, well at least not a noob… just trying to understand what I altered, was it barrel harmonics?

I’m the same way. I don’t clean the bore until groups start opening up.

The differences in your groups could just be a fluke since there isn’t a large enough sample size between the different reciprocating mass configurations to establish ant baseline or trends.

I’ve never seen a gas gun that will consistently shoot 1/4 MOA. Most people with bolt guns that think they have consistent 1/4 MOA shooters have 3/4 MOA shooters at best, other than the benchrest rifles.

I would just drive on with your heavier buffer and enjoy.

[Double Naught Spy]

The ball can be in whoever has another explanations court. I can shoot 1/4” groups I’m not sure why I would need someone else to shoot it? I don’t need to go redo anything as I’ve already done it lol. I had to move my elevation down two inches and I’ve shot it since and it’s still on… the only variable that changed is my buffer. I measure and log every round that goes through that pipe…

You asked for help and it was provided. Strangely, you are discounting variables for which you don't have controls and saying the only thing changed is the buffer. You are a variable. If you shot on different days, despite similar conditions, they aren't the same. That is another variable. You could have bumped your scope between shooting sessions, another variable best controlled for by doing the buffer comparison test back to back.

Except for you, it is pretty much a consensus that changing the buffer weight slightly isn't doing anything to affect your POI significantly.

The same conclusion came from the folks on AR15.com several years ago...
https://www.ar15.com/forums/precision-ri...t-/4-4232/


The same here...
https://www.24hourcampfire.com/ubbthread...t-accuracy

There are all sorts of articles on why and when to change buffers, but none that I have read have any comments on changes of POI when changing the buffer.

Bottom line, there is at least one variable for which you are not controlling that isn't the buffer that caused your POI shift.

I would just drive on with your heavier buffer and enjoy.

That would be the easy solution.

[xoon]

it sounds like the bolt was unlocking before the bullet had exited the suppressor and the heavier buffer delayed the bolt just long enough to stop that

i would appreciate input from others if that sounds right as i do not have much confidence in my knowledge on this sort of thing

perhaps the barrel manufactorer sized the gas port so it would run reliably with a carbine buffer weight and 7 inch suppressor but you were running your can in the 9 inch configuration or otherwise had slightly higher back pressure than the conditions the manufacturer had in their R&D

[Klem]

it sounds like the bolt was unlocking before the bullet had exited the suppressor and the heavier buffer delayed the bolt just long enough to stop that

i would appreciate input from others if that sounds right as i do not have much confidence in my knowledge on this sort of thing

perhaps the barrel manufactorer sized the gas port so it would run reliably with a carbine buffer weight and 7 inch suppressor but you were running your can in the 9 inch configuration or otherwise had slightly higher back pressure than the conditions the manufacturer had in their R&D

Xoon,

Unless you are the OP re-registering under a different name I would say that is a very specific reason for the POI shift and group shrink. There are 50 other reasons that are also possible.

There is a lot of information missing in the OP's request for help and for whatever reason he/she chose not to provide it. This raises warning bells that much of what has been reported is either incorrect or exaggerated. Certainly the claim to precision out of an AR is unbelievable, and that casts doubt on the rest. This person has decided to opt out and I would not worry about it.

[LRRPF52]

Gents, let’s keep it polite and not make worst assumptions about people.

I was treated very kindly when I first signed up here back in 2009, whereas other forums have a reputation for treating people like trash.

Let’s not be like them. Keep it technical. I think the OP has received the appropriate technical feedback.

[lazyengineer]

Actually I'm glad we have this thread. I once put a carbine upper on a National Match leaded lower, and found it's POI shifted A LOT. As folks here say though, there are lots of factors in play, ranging from how the gun was being adressed (I was running National Match rapids, and wanted to burn that BBL in practice, rather than my good 20", for some tests), and it doubled the weight of the gun, meaning the mechanical locked-system recoil was different, before the now rifle-buffer ever got touched. But really, it probably had more to do with my significant difference in addressing the gun running a leaded A2NM lower in prone, than a light weight M4 lower from teh bench - is my guess based on the replies. I always wondered, but never chased it further than that.

[LRRPF52]

Actually I'm glad we have this thread. I once put a carbine upper on a National Match leaded lower, and found it's POI shifted A LOT. As folks here say though, there are lots of factors in play, ranging from how the gun was being adressed (I was running National Match rapids, and wanted to burn that BBL in practice, rather than my good 20", for some tests), and it doubled the weight of the gun, meaning the mechanical locked-system recoil was different, before the now rifle-buffer ever got touched. But really, it probably had more to do with my significant difference in addressing the gun running a leaded A2NM lower in prone, than a light weight M4 lower from teh bench - is my guess based on the replies. I always wondered, but never chased it further than that.

Did you mean to say “carbine buffer” inside a National Match lower?

[lazyengineer]

Did you mean to say “carbine buffer” inside a National Match lower?

No, but - I can see the confusion. But naw, I was trying to run NTIT drills (rattle battle) which are 30 rounds in 50 seconds on 600 yard targets, and that will smoke a National Match upper. Especially if you do 3 runs. So I tried being clever on a lark, and took an Carbine upper with a "who cares" Barrel. And dropped it on the lower. So practicing on my trigger and stock still, at least. And do practice on that barrel. It wasn't a good idea regardless,but I sometimes will run stuff on a lark. The (zero'd) carbine upper zero was way off, in that config.

[Darryle]

Dwell time, if your rifle was leaving battery to quickly, then you are experiencing lower velocities/pressures affecting POI. I generally see improved function, lower felt recoil and improved function of the rifle while reducing wear and tear using heavier buffers.

FTR, suppressed or not, I never use an adjustable gas block, I tune using heavier buffers, I start with a H3 and usually go up from there. I have some that are over 8oz.

I have never been and never will be a fan of restricting the one thing your rifle needs to function. My opinion, worthless to most, is that an adjustable gas block is a half hearted attempt at getting a rifle to function properly.

YMMV

[montana]

Dwell time, if your rifle was leaving battery to quickly, then you are experiencing lower velocities/pressures affecting POI. I generally see improved function, lower felt recoil and improved function of the rifle while reducing wear and tear using heavier buffers.

FTR, suppressed or not, I never use an adjustable gas block, I tune using heavier buffers, I start with a H3 and usually go up from there. I have some that are over 8oz.

I have never been and never will be a fan of restricting the one thing your rifle needs to function. My opinion, worthless to most, is that an adjustable gas block is a half hearted attempt at getting a rifle to function properly.

YMMV

With respect, I believe using heavier buffers for an over gassed system is like pressing the gas throttle down all the way in a car, while only using the break pedal to adjust for speed.. Using a heavier buffer can be hard on the firing pin cotter key..Heavier buffers do not effect dwell time, but are used to slow the carrier velocity and prevent bolt bounce on full auto..Dwell time is determined by the ammunition being used, gas port location and cam slot cut timing..Heavier buffers can help with residual gas pressure..The heavier the mass during cycling, the heavier the felt recoil..When discussing gas, more is not always better..

[xoon]

i agree that it is a guess with limited information in a situation in which there are many possible explanations that fit the facts but i do think this is the most likely explanation given my (limited) background knowledge

i dont think unreliable group size methodology or reporting of group sizes makes it likely that someone would lie or be confused about brass being torn up