Weird grouping issue

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Flatliner
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Re: Weird grouping issue

Post by Flatliner »

I have been following this thread but didn't just reread the whole thing so forgive me if you did this and I am not remembering the post. Did you pull a 'first round' back out and roll it on the table to ensure the bullet (either on a 'first round' or a 'second round') wasn't getting knocked out of square slightly? I remember someone suggesting that and it seems like the only variable (I can think of anyway) is the carrier speed. Alternatively, have you tried magazine loading a group of single shots (essentially duplicating the first shot exactly) multiple times?
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dellet
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Re: Weird grouping issue

Post by dellet »

Ex Umbra wrote:
dellet wrote:
Ex Umbra wrote:
Splayed leaves that have not totally given out. yet.
Why only first round?

Why repeatable?

Why only one type of ammunition/bullet?
1 & 2: With handling and transport, the purchase of the leaves on the erector tube wonders around. This obviously, randomly, moves the erector tube. The first recoil impluse re-splays the leaves to their maximum erroneous position. And that's where they stay, until they get worse or totally fail. Until transport & handling causes them to wiggle around again. This is exactly why Burris, or was it Bushnell? came out with posilock scopes years ago, that would allow you to mechanically lock the erector tube against the turret dowels. This negates leaf or coil spring damage or total failure all together...until you mechanically unlock the erector tube once again.

3. Would have nothing to do with the optics.

Kind regards.
I understand what you are suggesting but, random movement of the tube and repeatable first round only shots doesn't make sense. More so when the only handling is a magazine change.
300 Blackout, not just for sub-sonics.
Whole Bunches
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Re: Weird grouping issue

Post by Whole Bunches »

I do not have a tool to measure if bullet is straight in the case, but I did do the following:

Roll loaded round on flat surface and see no observable bullet wobble at tip and measure the oal. Load round from magazine and eject loaded round. Oal still the same. Roll round on flat surface and see no observable wobble in the tip of the bullet. Fit in Sheridan gage before and after.

I do not have a torque wrench, but did remove bbl from receiver and reinstall, tightening up snug, loosening and relighting x 3. Nothing was loose when I took the upper apart. Again, it shoots fine with other bullets tried. The bbl nut has no notches for the gas tube to pass through, so having to tighten it super hard to line up a notch is not a factor. For tightening the bbl nut I have an action wrench which goes through the receiver and locks into the bbl extension so minimal force actually goes onto the receiver.

Have not choreographed any Barnes 110gr black tip loads in this upper. Was looking for accuracy first and would chronograph later in order to plug velocity into the ballistics program to determine bullet impact at further and closer ranges than what sighted in for.

Did one small group consisting of 1st round loaded (only round loaded) in the mag and chambered and fired. Ejecting empty mag and loading 2 rounds. 1st round of the 2 round loaded mag touched the hole of the very 1st round with the 2nd round (chambered by the autoloading action) going high.

Since it's a side charger upper, I also tried a group doing the following: On the first round chambered, I put the safety on, and pointing in a safe direction I took a rubber mallet and rapped on the charging handle to help ensure the bolt carrier group was all the way forward. I then fired a group with the result that the 1st round loaded and shot was lower than the rest of the group. Also did the following: Chamber first round, pull bolt handle back a little so I can see the case and let the bolt handle go, rechambering the round...made no difference.

Doesn't matter if the first round chambered manually starts on the left or right side of the magazine. Multiple magazines tried. All is not hopeless, as it does like the Nosler's; just want to use Barnes for hogs after being attacked by a boar in which the Nosler needed another half inch of penetration (hit spine mushroomed, but didn't penetrate the spine).

Future efforts include a rifle buffer and A1 stock with rifle spring, Spike's T2 buffer with carbine spring, rifle buffer and A2 stock with Tub's flat wire spring. I keep hoping all this shooting wears the upper parts in and the situation heals itself. I can measure that the throat has worn a little. No H3 buffers in the household, but am willing to buy. I do not intend to use either the A1 or A2 (M16A2) setups for hunting even if they work, as they only have GI type triggers. All my other lowers have LaRue or Geissele. Frustrating, but sorta fun trying to figure it out. I don't know that the OP ever succeeded either in his first round out of the group.

And just for the fun of it, here's the lower that my A1 (actually a type D earlier Vietnam era stock) is on: https://flic.kr/p/HxqmQy https://flic.kr/p/25BxEvw https://flic.kr/p/24Av5Uo https://flic.kr/p/25Fptzp

My version of what a Mattel M16 would have been, had Mattel made them.
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dellet
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Re: Weird grouping issue

Post by dellet »

The problem may very well be the sticker, The rifle is toying with you :lol:

It might be helpful to have the first round velocity numbers to compare. Maybe nothing, but if there is a noticeable velocity change on first round it would be good to note.

15 rifles and only one with problem suggests something other than the load.

I would probably slug the barrel to get a bore size and possibly feel for a loose or tight spot.
300 Blackout, not just for sub-sonics.
Whole Bunches
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Re: Weird grouping issue

Post by Whole Bunches »

While I stay at home taking care of my post-op wife, I was able to do one test a member requested. I live in the county on my little retirement farm so I can do some testing on the property.

20.0gr H110, Barnes 110gr black tip, CCI 400 primer, LC formed brass, no anneal, mild crimp, 2.25" oal, 16" Green Mountain bbl, CRUX Ark30 suppressor

Loading 2 rounds in a mag at a time, I chronographed the 1st shot chambered by pressing the bolt hold open with the bcg locked back and the 2nd that was chambered by the autoloading action of the AR.

1st rd 2359fps at 4' from the chronograph
2nd rd 2348fps

Let bbl and suppressor cool somewhat with AR bbl cooler, but not completely back to ambient temp.

1st shot 2400fps
2nd shot 2372fps

Not much difference in velocity in my opinion.
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dellet
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Re: Weird grouping issue

Post by dellet »

Whole Bunches wrote:While I stay at home taking care of my post-op wife, I was able to do one test a member requested. I live in the county on my little retirement farm so I can do some testing on the property.

20.0gr H110, Barnes 110gr black tip, CCI 400 primer, LC formed brass, no anneal, mild crimp, 2.25" oal, 16" Green Mountain bbl, CRUX Ark30 suppressor

Loading 2 rounds in a mag at a time, I chronographed the 1st shot chambered by pressing the bolt hold open with the bcg locked back and the 2nd that was chambered by the autoloading action of the AR.

1st rd 2359fps at 4' from the chronograph
2nd rd 2348fps

Let bbl and suppressor cool somewhat with AR bbl cooler, but not completely back to ambient temp.

1st shot 2400fps
2nd shot 2372fps

Not much difference in velocity in my opinion.
I think you’re right.

Did it still have the same spread between impact with first round low and was it possible to compare all four shots as one group?
300 Blackout, not just for sub-sonics.
Whole Bunches
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Re: Weird grouping issue

Post by Whole Bunches »

No targets were shot. Simply set up chrono in yard and shot over it into the dirt.
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dellet
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Re: Weird grouping issue

Post by dellet »

Any updates?
300 Blackout, not just for sub-sonics.
Grouse870
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Re: Weird grouping issue

Post by Grouse870 »

Not yet. I borrowed a spikes t2 buffer to try out and I got some different ammo to try. Hopefully this week I’ll get a chance to try it out
Whole Bunches
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Re: Weird grouping issue

Post by Whole Bunches »

Here's my update to the first round of the group hitting low when using my Barnes 110gr blacktip handloads.

Shot groups using 5 different lowers with 5 different weight buffers. Fired 12 groups total. 11 groups had the first shot chambered from the magazine hit low. 1 group had the first shot in the middle of the group (standard carbine buffer). Hoping that combination or having fired enough rounds had solved the problem, I fired more groups with that combo, but alas the other groups still had the problem.

Used standard carbine buffer, H, Spikes ST2, H2, and rifle buffer and spring. Distance to the target happened to be 44 yards this time. First round low varied from about 1.5 to 1.7" low. All first rounds fired would have made a nice group. All subsequent rounds fired would have made a nice group, just in a different spot. Triggers varied: SSA, SSA-E, MBT, and GI. Lowers were of various makes: KISS, home made, Noveske, Joe Bob, Serbu.

At this time, I give up trying to use the blacktips in this 16" Green Mountain bbl and will use the Nosler 125gr BT that shoot all shots into the group.

Edited to add: In the above tests, the first shot did shift about a half inch to the left, whereas before it was directly under the rest of the group.
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