Armory Sponsor
Posted: 5/12/2010 9:08:37 PM EDT
|
Spent an hour at the 100yd range today shooting a test groundhog load in my bull barrel 1x9 AR w/ an old giant 24x scope. I'm tweaking a load that I built from ladder testing (last fall) by playing around with seating depth and adjusting the charge very slightly.
This aggravating pattern occurs several times: 2 rounds touch,the third is about 1/4" away. Great...until the 4th and 5th shots,which repeatedly go wild by about 1"-1.5" from the rest of the group. This happened consistently for 5 5rd groups. Shots were fired at about a 30sec interval. Cheek weld was held throughout each group. The load was 55gr Remington PSPs seated to about 2.23" OAL (just below the cannelure,with the base of the bullet just under the bottom of the neck inside the case). No crimp. 25grs of WC844 (H335 substitute), Remington cases, CCI primers. Cases were FL sized in an RCBS X-die, powder was measured from a Lee PPM. Multiple charges were verified on 2 different scales before I started throwing. All test charges were within .2gr of nominal. My throw technique is pretty consistent. Any guesses as to why this would occur? I'm guessing it may not even be ammo related since the pattern repeats in a consistent manner. I know I had a good hold and follow through, and the shots were shot from a sandbagged rest. It's darned annoying anyway,so I figured I'd ask you all to take a shot at it. My best guess is that I'm treading on the edge of a barrel harmonics "sour spot" so far as my load development goes,and the later rounds are going too fast to catch the same sweet spot as the first three. |
|
Personally I would load the bullets mag length and play with the powder charge weights. COAL lengths, unless single loaded, probably won't make much difference accuracy wise in an AR since the throat area is very long.
Are the flyers in the same area or are they in different positions? If in the same area I think I would look into removing the barrel and true up the receiver face where the barrel extension shoulder meets it. Undue pressure as the barrel warms up can cause a shift in the barrel receiver relationship. |
|
If the barrel is not free floated, I would blame the barrel, and even if it is floated it very well could be stringing as it heats up.
Try shooting a 5 and 10 round group. Let the barrel cool for a minute or two between shots, enough that it cools, but doesn't cool to ambient temperature. If it's too hot to touch, slow down. If the accuracy improves, you'll pretty know the barrel is the problem and the only fix is to change it. Barrels ought to be stress relieved after final machining to contour. If they aren't, the residual stresses cause the barrel to move when it gets hot. This will happen whether the barrel has a heavy contour or light contour. I have a factory TC barrel on a Contender carbine that strings like crazy after the second or third shot. Thing is, it's better after I floated to forearm to get it out of contact. For hunting, this isn't a problem, but shooting a string is aggravating. |
|
I try to seat to 2.250 with every bullet that will allow it.
If it's not your barrel heating up and you are sure the problem is not you, I would suspect the bullets. I have no trouble getting the Hornady 55 gr SP, #2265 or #2266, to shoot good groups. I have never got Rem bullets to shoot with Sierra or Hornady bullets, maybe it's just me. In 22, 7mm, and 30 cal. |
|
To answer some of the questions:
Barrel is free floated. The comment on stress relief is interesting. What does everyone think of cryo for AR barrels? Worth it? The barrel never heated to the point where it was hot to the touch. It simply got warm. I had several minutes between 5 round groups,so it was returning close to ambient temp. My original ladder group was at 2.250" OAL,but I had my doubts as to whether I had sufficient bullet pull with the bullet so far out. It wasn't even filling the case neck at that point,and was very close to going under the magical bullet's diameter worth of seating to maintain neck tension. Then again,it did shoot fairly well. I tested that load at 225yds and shot 5 rounds inside of 1.7" at that distance. However that was last November in Texas,not May in Virginia. :) I could probably do better brass prep as well. I'm not doing any case neck uniforming. This is more of an experiment to get a cheap load set to work well. I've got Sierra 52gr BTHPs available,but wanted to make this load work. The trigger does suck. It's a stock CMMG unit, with one leg of the hammer spring removed,and the hammer and trigger force fitted by hand,but that's it. That trigger is one thing I need to rectify,along with the optics (a 15 year old Taiwan Tasco 6-24x-40mmAO). However I still think I had a good hold and follow through,despite the trigger. |
|
An expert or High Master shooter can put five consecutive shots in the x-ring at 200 yards. Take away his high-dollar competition rifle and his handloaded ammo and give him an average rack-grade AR with military ball ammo, and he will STILL put five shots in the x-ring. That's why he's an expert.
That's also why the shooter and his technique is more important than the equipment, whether it's service rifle, highpower, benchrest, or whatever. Custom handloaded ammo that is perfectly prepared will improve the results of flawless form by a significant degree, but will have little impact on imperfect form. So before you get too serious about cryogenic barrels, case neck uniforming, etc., you may want to look at the equipment that's pulling the trigger. >> I tested that load at 225yds and shot 5 rounds inside of 1.7" at that distance. That says (A) your rifle, as presently configured, is certainly capable of the performance you want, and (B) your skill, as presently attained, is certainly capable. I'm not a shooting psychologist (wouldn't that be a great job?), but I think the 4th and 5th round stringing is being caused by fixation and inadvertently jerking the trigger ever so slightly. Getting the first bullet where you want it is no big deal. Getting the second one right on top of the first is much harder. With each consecutive shot, the stress and tension rises exponentially as you try to repeat that performance three times, four times and five times. As the tension rises, your breathing and heart rate is affected, and the crosshairs start to wiggle over the bullseye a little more. You're then faced with trying to pull that trigger under stress at the perfect micro-second, and that deliberate action is a jerked trigger. I'm sure you already know this basic theory, and you've probably long known that the last few shots are much harder than the first few, and that proper breathing and relaxation are fundamental. I just think you're stressing out over a bad shot string, and the stress is turning your 5-round groups into self-fulfilling prophecies. It's temporary. There's probably nothing wrong with your rifle and little to improve with your handloaded ammo. Focus on breathing and relaxing and you'll get back to where you were. That being said... an adjustable 2-stage match trigger makes it much easier to let your brain pull the trigger rather than your finger. |
| And as you already said, You shot this load with a COL of 2.250 and it did very well. GO BACK to that COL and start testing again. The "bullet seated at least as deep as the diameter" is a "general" rule (albeit, generally a good one) but not a steadfast rule that can't be deviated from. JMHO for a quick, cheap fix to make some good ammo. You and your rifle have already proven it can be done. |
|
Quoted:
Quoted:
Replace the Remington 55 grain PSP bullets with Sierra 52 or 53 grain Match Kings. Problem solved. That's what I think, change bullets. Me too. I missed the bullets in the first post. At least try one of the two bullets above to regain confidence in your methods. |
|
Long footnote to this load workup.
I tried this bullet again,with the same components and same lot of sized cases, using Newberry's Optimal Charge Weight load method,and dropping the OAL back to about 2.255" (neck just under the cannelure,and just under mag length) I also made a big improvement: changing to extra high Burris XTR rings,adding about .375" to my scope height. Before,I was a bit too low,and had a hard time getting a good picture without grinding my cheek painfully into the stock to avoid a scalloped sight picture at 24x. Now,I can get a perfect sight picture with a comfortable cheek weld. End result: a small accuracy node occurs between 25.8-26.3grs,with POI shifting less than .5" for the center of the groups in that charge weight range. Though it's not relevant to the test particularly, group size for three rounds at 26.1gr was just barely under 1" (.955" at 100yds). So a load in the 26.1gr range should create a good consistent load even if charge weights vary slightly. End result: I was loading too long and too light a charge. The Rem PSP is likely still a turd,but now it's a polished turd that didn't cost much. I'll try developing a larger series to test my chosen "node load" resilience with 5-10 shot groups. Incidentally, some Varmint Nightmare premium HPs (which I suspect are Barnes or Nosler factory seconds)were tested with the same load,loaded to 2.55 roughly. They exhibited a very wide accuracy node,with POI for 3rd groups varying less than .25" from a common center for all charge weight selections from 25.3-26.3gr. Individual group size was still about the same (.950" best),but it could be achieved over a wide range of charges. I think that that the lack of variance across many charge weights indicates a better quality bullet. I plan to retest with some 52gr Sierra's to see if this holds true. |
|
Quoted:
Replace the Remington 55 grain PSP bullets with Sierra 52 or 53 grain Match Kings. Problem solved. Over the course of 38 yrs of reloading metallics, Sierra MatchKings have been the most consistently accurate bullets. Of course, I've gotten some great groups from other brands of bullets, including Remington, but the repeatability of those great groups was difficult in many cases. |
| You want the most consistent bullets. Pay particular attention to how the bases are finished, because what you describe is exactly what happens with Winchester bulk 55gr FMJs; some will hit pretty close to point of aim, and others will veer off by quite a bit. This is due to the inconsistent shape of the bases on the Win bullets. An open-nose bullet won't be as bad, but unless the bases are really smooth AND really consistent, muzzle effects can redirect the bullet enough to do what you're describing. |
|
2nd addendum.
I retested the load with the Varmint Nightmares today,based on the predicted optimal results from my OCW tests. 26gr of WC844 R-P cases (not sorted by weight,but all prepped in the same batch using Lee trimmer/chamferer,RCBS dies) CCI regular SR primers OAL was about 2.55" roughly (varied slightly due to meplat length variation) Temp about 90, slight wind but I tried to avoid the gusts The pic is 10 shots into .983" at 100yds from an already warm,fouled barrel. Given the price of the components, I'm pleased. I think weighing and sorting brass might bring in some of those outlying rounds and shrink groups when I take the load out to 300yds. 
55gr PSPs are a PITA. I ran them today based on my OCW data,and the groups showed rather consistent outlying shots from a central point,grouping between 2-3" for 10rds. All factors except the bullets and OAL were identical to the Varmint Nightmares,so I believe the bullet to be at fault. I may have misread the node in the OCW test for the Rem PSP. It was notably smaller than the node for the Varmint Nightmares. I'm going to try to drop the charge on the PSPs slightly to get closer to the exact middle of the node. Unfortunately these stupid PSPs are too short,and you get a huge degree of bullet jump with them unless you load them out so far that they're barely held by the neck. I may just load the rest of them up as fodder for my lightweight build. |
|
I agree that the bullets are the likely culprit.
The trigger isn't helping. I wouldn't worry about the barrel stringing with heat. This would be unusual with an AR and very unlikely with a bull barrel Simple test would be to wip up a batch with match bullets (I myself like the 52 SMK) to check out yourself and your rifle. Different rifles take a bit of trying to get good groups even off the sandbags |
Armory Sponsor