Hornady 129 SST with 8208 XBR

[BjornF16]

Went to the range this am with some 129 SSTs loaded up with 8208XBR. Also shot some of my previous OCW load (AA Entry) of 129 SST driven by AA2230 for comparison.

My current rig is Satern 18" in AA upper, adjustable gas block, Vortex PST 2.5-10x44, WCI brake.

The XBR loads were 26.2 gr, 26.7 gr and 27.2 gr. The 27.2 looked most promising and I don't believe showed any high pressure signs (I could use some expertise here).

If someone can also explain the variation in groupings (vertical, horizontal spreads), I would appreciate it.

The AA2230 load was 25.5 gr and had proven to be the most accurate of the AA2230 loads I tested in my AA Entry. The velocity is too low for my liking...

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[BjornF16]

Additional pics of 27.2 gr loaded brass:

[LR1955]

Went to the range this am with some 129 SSTs loaded up with 8208XBR. Also shot some of my previous OCW load (AA Entry) of 129 SST driven by AA2230 for comparison.

My current rig is Satern 18" in AA upper, adjustable gas block, Vortex PST 2.5-10x44, WCI brake.

The XBR loads were 26.2 gr, 26.7 gr and 27.2 gr. The 27.2 looked most promising and I don't believe showed any high pressure signs (I could use some expertise here).

If someone can also explain the variation in groupings (vertical, horizontal spreads), I would appreciate it.

The AA2230 load was 25.8 gr and had proven to be the most accurate of the AA2230 loads I tested in my AA Entry. The velocity is too low for my liking...

Attachment 1565Attachment 1566Attachment 1564Attachment 1568Attachment 1562Attachment 1563

Bjorn:

Should have attended the Boomershoot Clinic. You may still have shot those groups but you would also be able to figure out why.

Basically, did your shots land within your call area or not? If they 'went to call', your loads are fine. If they didn't 'go to call', something is wrong. Could be your loads, rifle, optic, or a combination but if they did not go to call, it is a mechanical problem.

Another thing. Five shots isn't enough to make good conclusions, either. Choose the one you think is best and load ten more. Then fire two more strings of five and see.

LR1955

[Bwild97]

How are you supporting the rifle, (Bipod/shoulder), (bipod/mono pod), (bag/shoulder), (bag/bag), benchrest vice.

Group spreads; (in my experiences) The horizontal spread could be a function of your heart beat, the blood that pulses through your veins will slightly alter POA The tighter you hold, the greater the effect. Unless you have your rifle mounted in a benchrest vice, you shouldn't read into the groups too much. (just my Opinion)

The primers look good, but I have learned to not trust small primers for gauging pressure signs. Ejector\Extractor, shadowing/swiping are constant affects that indicate pressures are nearing the dangerous.

[LRRPF52]

What range were these groups printed at? 100yds, or 200yds? It looks like your chrono data doesn't show any crazy spikes in velocity. I would suggest running some ladder tests at 200yds, and marking your bullet tips with a permanent marker for each load. Then see where the nodes are. Shoot from a rest, if possible. At a minimum, use a rear bag in addition to your frontal support.

That Satern barrel should group much tighter than that with the right load.

[BjornF16]

From a concrete bench. The hand guard is resting on sandbag support; my left hand pulls the stock into my shoulder (between deltoid and pectoral) and also fine tunes the elevation (resting on top of a sandbag). My right hand is relaxed, not squeezing the pistol grip, fingertip pressure on SSA-E trigger. I can see my heartbeat moving the sight less than 1/4 MOA. All shots had same aim point at 100 yds. Surprised at each shot. (not saying I'm a great shot, but I have been able to achieve .5 MOA in the past with my former Entry).

For each group, I shot 1, examined the case, then loaded up the next 4. Paused only to record the chrono data. No more than 1 minute between shots in the group of 5.

In my previous load development efforts, I have also seen large horizontal and vertical groupings that tighten up when approaching an optimum load...I just can't remember the reason for the vertical and the reason for the horizontal spreads (other than flinches, which I don't think was really the case today). This was the first attempt at load development for this rifle. Previously I had only shot factory ammo through it, with the Berger 115 being just under 1 MOA. Both of my Grendels did not shoot that well with factory loads.

I followed the OCW load development technique (see http://optimalchargeweight.embarqspace.com/) for the AA2230 load on my 19.5 AA Entry (ER Shaw). Interestingly, it shot well in my Satern Spartan 18" (I rushed this 5 shot group). I think the OCW is similar to the Optimal Barrel Time theory (see http://the-long-family.com/optimal%20barrel%20time.htm).

My game plan is to load 10 each at 27.0, 27.2, 27.4 gr 8208XBR and compare; looking for a good node (I'm using Lyman 1200 DPS2).

I really wanted to attend the Boomershoot clinic, but didn't have enough time to plan for it this year once I learned of it's existence. I'd like to attend the next one, but it is a pretty long haul from Texas.

[bwaites]

Boomershoot is a long trip for you, but we'd really like to have you there. Your technique sounds reasonable, but there may be some pointers that LRRPF52 and LR1955 can help with.

Sounds like you are using a looser hold on the rifle. Some AR's like to be locked in tight, so you might try that. I seem to go back and forth depending on how well I'm shooting. Lately, I've been more relaxed, and seem to be shooting a bit better.

[BjornF16]

I tried a really loose hold in the past...groups really opened up. I wouldn't say that I am locked in tight; maybe halfway between.

I also tried a Caldwell Lead Sled DFT...didn't work so well. Barrel seemed to jump up too much. Not sure if I didn't have enough weight on it or what. I certainly didn't restrain the rifle in the sled.

My left hand rests in the "nook" of the PRS stock, and really "pushes" the stock into my shoulder. Nothing is holding the front of the rifle down on the sandbag.

[LR1955]

I tried a really loose hold in the past...groups really opened up. I wouldn't say that I am locked in tight; maybe halfway between.

I also tried a Caldwell Lead Sled DFT...didn't work so well. Barrel seemed to jump up too much. Not sure if I didn't have enough weight on it or what. I certainly didn't restrain the rifle in the sled.

My left hand rests in the "nook" of the PRS stock, and really "pushes" the stock into my shoulder. Nothing is holding the front of the rifle down on the sandbag.

Bjorn:

Some folks believe horizontal stringing is due to too high a velocity. And vertical due to too low a velocity. I am skeptical to a degree but when other things don't give a solution, I sometimes go with it. Since your groups were vertical more than horizontal, and you think that as you approach max that they tighten up, perhaps there is something to this saying.

Also, if you are shooting on a slow cadence, individually loading and shooting and looking through your scope between shots -- most likely it is you. Load five in your magazine, get into a confident and solid position, and shoot them in about fifteen or twenty seconds without looking between shots. Attend to holding your sight picture throughout the shot, take your breath, settle in and shoot again. All five with your attention focused on sight picture. My bet is that you will see your performance improve with all of your loads.

LR1955

[BjornF16]

Also, if you are shooting on a slow cadence, individually loading and shooting and looking through your scope between shots -- most likely it is you. Load five in your magazine, get into a confident and solid position, and shoot them in about fifteen or twenty seconds without looking between shots. Attend to holding your sight picture throughout the shot, take your breath, settle in and shoot again. All five with your attention focused on sight picture. My bet is that you will see your performance improve with all of your loads.

Well, this gives me a reason to buy a chrono with printer! I've been using a borrowed chrono.

My shooting was better before using the chrono; but I also believe groups will "tighten up" as optimum load is approached (I saw this before using chrono when developing the AA2230 load). I never really thought about it but my shooting was better before borrowing the chrono.