Corbon DPX accuracy

[DBR]

I recently sighted in a couple of 16" 1:7 AR15s at 100 yds. One had an Aimpoint ML2 the other had a good quality 1.5-5x scope. After sighting in with Hornady TAP 75gr "Personal Defense" ammo which got better than 1.5 MOA with both guns for 3 shot groups from a cold barrel, I shot Corbon 55gr DPX 3 shot groups from both guns to see if POA was different (cold barrel).

I was not impressed by the results. Both guns shot "patterns" with the Barnes bullet averaging about 8".

Here is what I want to know: I have heard that Barnes bullets want a clean barrel. Does this mean that if I use a more common round as my "standard" like the Hornady 75gr TAP I cannot count on reliable accuracy if I shoot some Hornady and then switch to the Barnes bullet for more barrier penetration without the opportunity to clean the barrel?

This "problem" occurred with two different rifles on the same day at the same time with the same ammo from the same 20rd mag.

Both barrels started off clean. Part of my original test was to determine if a "clean" barrel need "fouling" shots to settle down after cleaning. At least for these barrels they did not.

[alistaire]

Perhaps these barrels don't like light bullets. Try the 62 grain DPX. Have you tried any other 55gr bullets with these to weapons?

[DBR]

Yes, I have shot 55gr Black Hills and Lake City. The Black Hills averages 1-2" and the XM193 goes about 3". These are 5 shot groups from a bipod and bench.

After I posted I spoke with the folks at Corbon. They said that Barnes recommends a clean barrel and cleaning about every 20rds for best results. They were surprised though by the wide "pattern".

I will repeat this test the next time I shoot at 100yds.

[BushmasterFanBoy]

I shot the Federal Premium Loading of the TSX round through my 1/9" 14.5" BM carbine, it grouped to a similar size as Privi at 50yards, (1-1.5" using my M4s)

I was impressed that it shot to virtually the same point of impact as the 55gr. FMJ (this is the reason I decided on a 55gr. load) but didn't get a chance to group it at 100 yards for accuracy. I may buy another box for accuracy testing, but just 120 rounds cost me $200! :eek:

ETA: This gun is run pretty dirty, and the barrel's last good cleaning was ages ago. I was worried that groups might suffer, but at 50 yards, the ammo seemed to slightly shoot tighter than the Privi I normally use.

[SMJayman]

I've had good results with the 62gr TSX bullet as handloaded by me, but I have not tried the Corbon loadings. Try out the 62s and see if they do any better, although if the TAP runs for you, I don't see any pressing need to monkey with the Corbon loads....

[DBR]

I wanted to use the DPX loads for 200-250yd coyote shots. Hopefully they would be effective beyond "fragmentation" range. Two other choices are 60gr Nosler partition either handloaded or from Federal and one of the new Speer Gold Dot loads.

Both of the rifles I used are on the better side of service grade AR accuracy with most ammo averaging about .75-2 MOA at 100yds for 5 shot groups.

On the same day I shot the Corbon through the ARs I sighted in my 243 Winchester Model 70 Classic Feather Weight. Shooting Federal 85gr Barnes TSX from a cold barrel each 3rd group (five in all) was less than 1" at 100yds. This surprised me!

[Molon]

The problem could be something as simple as your barrel just doesn’t like the TSX bullet. I’ve tested the 62 grain and 70 grain TSX bullets and the bullets themselves are capable of some fine accuracy. I don’t see why the 55 grain TSX should be much different.

Hand-loaded 62 grain TSX rounds produced a sub-MOA 10-shot group at 100 yards from an already fouled barrel.

http://www.box.net/shared/static/8ybojjxv1b.jpg

The COR-BON factory loaded 62 grain DPX load produced a 10-shot group with an extreme spread of 1.75” from an already fouled barrel.

http://www.box.net/shared/static/i2b5q3mxql.jpg

Hand-loaded 70 grain TSX rounds turned in a 10-shot group with an extreme spread of 1.12” from 100 yards.

http://www.box.net/shared/static/i3jfs1623r.jpg

[BAC]

Which rifle did you use for those, Molon? (curious about twist rate is all, or if you've noticed a difference between twist rates and precision...)


-B

[Ned Christiansen]

Mang!

That first group is more like .74 if you take out that wild one. 9 into .74..... that kind of accuracy eludes me but for an occasional fluke group.

Molon, what is your procedure for bench shooting, I mean, bags or bipod, let it slide in recoil or buck it up, single-loading rounds or careful semi-auto fire?

[DBR]

Molon:

Thanks for chiming in. I too have had excellent accuracy from the Barnes bullets in 243, 30-06 and 30 Carbine after firing other ammo. Maybe the stars just weren't right or maybe there is something not right with this box of ammo - all were from the same box.

I will do a repeat from a clean barrel and a barrel that has fired the same Hornady TAP and see what happens.

I posted because I wanted to see if anyone else had experienced this unusual result.

Thanks

[Molon]

Mang!

That first group is more like .74 if you take out that wild one. 9 into .74..... that kind of accuracy eludes me but for an occasional fluke group.

Molon, what is your procedure for bench shooting, I mean, bags or bipod, let it slide in recoil or buck it up, single-loading rounds or careful semi-auto fire?

When shooting purely to evaluate the accuracy of a rifle/ammunition combination, I attempt to remove as many of the variables as is reasonably practicable. The forend of the rifle rides in a Sinclair Windage Benchrest. The stock rests in a Protektor bunny-ear rear bag. A mirage shade is attached to the scope. Ammunition is usually fed from the magazine, as that’s the way that I personally use my weapons in practical settings. A Wind Probe is used to monitor the wind conditions and I use a hard hold on the rifle.

10-shot groups are an absolute must for your results to have any statistically significant meaning to them; preferably three 10-shot groups. The most accurate AR-15 that I currently own has a free-floated 24” Krieger barrel with a 1:7.7” twist. The groups shown below were fired from that weapon in the manner described above.


http://www.box.net/shared/static/0fuxcv68qk.jpg



http://www.box.net/shared/static/r35j7qm5i1.jpg



http://www.box.net/shared/static/pt7y91nj7y.jpg



http://www.box.net/shared/static/edqv78hn81.jpg



Contrast the above groups with a 3-shot and 5-shot group from the same weapon.

http://www.box.net/shared/static/ft5ummnqrp.jpg


http://www.box.net/shared/static/6nbjg6mxll.jpg


http://www.box.net/shared/static/goznv7cxck.jpg

[DTHN2LGS]

I use Barnes bullets for hunting and reload my own ammo. Barnes recommends that bullets be started at .050" off the rifling and O.A.L. adjusted from there for best accuracy. Maybe factory ammo loaded for "all" guns is just not at the right distance from the rifling for some guns. Just my $.02.

[Ned Christiansen]

Thanks, and I agree on 10-shot groups, it's much more a snapshot of reality. I usually shoot 10-shot groups when it's for an article.

I pet peeve of mine is when an article shows a target with a fantastic 3-shot group, with something like a box of cartridges laying right next to it-- hey, whaddya covering up there? Or a section of target has been cut out that has three touching and the rest of the target is.... gone.

[Molon]

I pet peeve of mine is when an article shows a target with a fantastic 3-shot group, with something like a box of cartridges laying right next to it-- hey, whaddya covering up there? Or a section of target has been cut out that has three touching and the rest of the target is.... gone.

You might enjoy this excerpt from one of my threads.



The Texas Sharpshooter
(Second Cousin of the Internet Commando)


Envious of all the attention his cousin, the Internet Commando, receives at the local tavern, as well as on the popular firearms forums on the Internet, our antagonist decides it is time for him to make his mark in the world. He decides he needs to perform some feat of marksmanship that surpasses even the accomplishments of his cousin, the Internet Commando.

But what can he possibly do that the Internet Commando hasn’t already done? Our antagonist recalls the tales of the Internet Commando. He remembers his cousin boasting of shooting sub-minute of angle groups using XM193. How could he possibly top that? Then, it dawns on him. The Internet Commando was using his sights when he fired those sub-minute of angle groups with XM193. “Anyone can shoot a small group using their sights,” he thinks to himself. “It would take real skill to shoot a good group without using the sights, say . . . as in shooting from the hip!”

Seeing his destiny laid out before him, our antagonist sets up his target at 25 yards and proceeds to fire on the target shooting from the hip. As our antagonist walks towards his target to examine his results he begins to grin from ear to ear. “Wait until my cousin sees this,” he actually speaks aloud.

That night at the local tavern our antagonist shows his target (pictured below) to those who have been hanging on every word that his cousin, the Internet Commando has been saying. The people are absolutely astonished that our antagonist was able shoot such an amazing group firing from the hip at 25 yards. Bewildered by the incredible skill demonstrated by our antagonist, the Internet Commando tells his cousin, “You’re quite the sharpshooter Tex!”



http://www.box.net/public/static/6o6edtcy4l.jpg


While the fiction continues in the above fable, once again it is based on a real target. I actually fired that group from 25 yards while shooting from the hip. For those of you that haven’t already figured out how I was able to perform such a feat, here are the little details that Texas Sharpshooters fail to mention.

I actually fired 30 shots from the hip at the “target” which was a blank piece of paper measuring 36” X 24” (kind of like the broad side of a barn). I then found 3 shots that formed a cluster and “drew” the bulls-eye around the shots. Those 3 shots occurred randomly. Not from any outstanding shooting skills of mine, nor from any outstanding qualities of the rifle or ammunition I was using, but purely by chance. (The actual extreme spread of the 30-shot group was 31”.)

The fallacy of the Texas Sharpshooter is based on the fact that clusters of data can occur randomly or by chance (the clustering illusion). “In making statistical observations, results will not be distributed with total uniformity but will naturally be sparser in some areas and denser in others, purely by chance.” Human beings tend to want to discern patterns in random clusters where none actually exist. We try to assign significance where there isn’t any.

In the case of the Texas Sharpshooter “information that has no relationship is interpreted or manipulated until it appears to have meaning.” More specifically, “although the shots were random, the Texas Sharpshooter makes it appear as though he has performed a highly non-random act. In normal target practice, the bulls-eye defines a region of significance, and there's a low probability of hitting it by firing at random. However, when the region of significance is determined after the event has occurred, any outcome at all can be made to appear spectacular.”

If you had not known that the Texas Sharpshooter had drawn the bulls-eye after the shots were fired, you would “falsely assume he's an excellent marksman by reasoning from effect (bullet holes in the bulls-eye) to cause (he fired the bullets).” The fatal flaw is “assigning significance to the outcome of a random event after it has occurred.” The danger is in “jumping to a conclusion that a random cluster is a causal pattern.” The Texas Sharpshooter “takes a random cluster, and by drawing a bulls-eye onto it makes it appear to be causally determined.”



Here is a pic of the target before the bulls-eye was drawn on it.



http://www.box.net/public/static/rh3dyq9lc1.jpg




Here is the target in negative.



http://www.box.net/public/static/t4pzbt9bf9.jpg




Lastly, the target in negative with the random cluster (actually two random clusters) highlighted.



http://www.box.net/public/static/rg02a5dzgz.jpg

[DBR]

I completely agree that a 10 shot group is necessary for a real accuracy evaluation.

I was trying to duplicate a "real world" scenario where I took my clean rifle out of the locker and fired at a varmint at 100-200yds. Here, first and maybe second and third round POA/POI integrity matters more than statistical group size.