Bullet jump in 223R

[Viperdoc]

Using a comparator, it seems like at magazine length in my AR, Sierra 69MK bullets are jumping 0.048, while the Hornady 75 BTHP are jumping around 0.037. Best groups I'm seeing out of either bullet is around .75 in my Krieger Varmatch barrel. Is this amount of bullet jump too much to expect better accuracy than what I'm seeing? Is it possible to have them set the chamber back to make it tighter? Have worked on combinations of load and powders, new and once fired Lapua brass, primer pockets cleaned, necks chamfered inside and out, etc. Should I be seeing better than this from an AR or is this as good as it's going to get?

 

[dreever]

one thing you have to remember. An AR is not a bolt gun so you can't expect bolt gun accuracy. I have to keep telling myself that from time to time.

Try seating the bullets out to touch the lands then single load them and see if your groups improve. The 69 grain Sierra's are pretty forgiving as to OAL but it's worth a try anyway.

I don't think you want to set the barrel back in an attempt to get mag length rounds into the lands. That coud cause all kinds of feeing problems me thinks.

Danny

 

[shootsanything]

You left out what twist rate your barrel is, if it is 1:9 or faster I would expect better groups. I have a colt H-Bar with a 1:7.5 that shoots under 1/2" at 100 yards with both 69gr SMK and 69gr Nosler CC. Because it is a military chamber the jump is huge when loaded for mag length -I never bothered measuring the jump.

There is another issue with these gas guns. I was told that to get the barrel properly bedded against the upper you need to tighten the nut, losses it and tighten is again. A buddy of mine was having terrible groups on a new barrel until he worked the nut a few times and got the barrel really tight against the upper.

 

[Viperdoc]

The barrel is a 1/9 Krieger Varmatch- have played with a lot of loads and bullet/powder combinations. Still, having a hard time consistently getting ounder around 0.75. Brass: new and once fired Lapua, uniformed primer pockets, CCI small rifle primers, all cases measured and chamfered inside and out, all loads weighed (tried Varget, 2520 for heavier bullets, and TAC for lighter ones), used a comparator to check each round seating depth for consistency. Am I missing something else?

 

[15Tango]

You're not trying to taper crimp or anything are you?

I'd try different powder charges until it tightens up. Might be worth trying something lighter as well, I know Nosler 60 grain Ballistic Tips are fantastic out of my AR.

What speed are you running on the 75 grain? I couldn't get 75 VLDs to shoot out of my 1:9" twist until I got over 2700 FPS - they would just keyhole under that speed.

Is there something else that may be the cause like loose scope rings (if you're running a scope) or maybe the trigger needs some adjustment? I know I need overtravel all but gone or I get screwed up. Maybe the barrel needs a good cleanup with some JB to make sure some fouling isn't throwing things off.

Just some ideas.

Wayne

 

[Mikem]

Bullet Jump vs Jam can be crazy, in my BRs I worry about it a lot, and jamb all loads, and they shoot well under a half, like in the .2s, bolt guns of course.
But I also have a 308, factory semi custom sniper bolt rifle, (not a Remchester) that when loaded to fit its 10 round mag, has a jump of .100 with 168 SMKs, and it can shoot around .250 at 100. Not bad for a 30 cal. And the factory test target was lower than that, so I'm not sure about jump or jam, I think it depends on the rifle.
But one thing for sure, with a gas gun, you don't have the latitude you do with a bolt gun, and I have gas guns.
Try a lighter bullet weight, like 50 to 60g.
Mike.

 

[ForneyRider]

I shoot slightly under .5in at 100 yards with 52 and 55gr bullets. The 69gr SMK and 75gr Hornady BTHP are slightly over .5in. This is with a stock DPMS Panther bull 20in barrel with 1:9 twist rate.

The 52 and 55gr are magazine length (2.26in). The 69 and 75gr bullets are 2.28in COL. The longer bullets get a light scratch on them from the rifling.

I use Benchmark and AA2230 for lighter bullets, and AA2230, R15, and Varget for the larger bullets. Remington brass and Fed 205 primers. Mr. Berger gave me data for his 73gr bullets that were pretty close to 69gr and 75gr info. Going to try those next.

I went from min to max in .3gr increments found top accuracy at just under or at max loads. Velocities are ~3k with the 69gr, slightly slower with 75gr. I think the lighter bullets were 3150fps or so.


Lot of people recommended to me to shoot the AR barrel dirty for best accuracy.

 

[Klong]

Change some of the other components, such as primer, powder, or powder quantity. You may find some help even chaging brass or neck tension. I have several AR's and they will all shoot .5 inch or better. You may try a different scope. You should be able to get to .5 inch. I beleive 1 in 9 to be on the edge for stablizing anything over 55 to 63 grain bullets. A 1 in 8 or a 1 in 7 is what I prefer. Good luck!

 

[people]

klong is right in saying trying different primers. You never know your rifle may not like those cci primers.

 

[Viperdoc]

Thanks for all the great input. So far, I've only used Lapua new brass (and once fired). The cases were all sized and inside/outside chamfered. Tried H335, TAC, AA2520, and of course Varget, with all around around the same results. Bullets: Hornady 55Vmax, 75 BTHP, and Sierra 55BTHP and 69MK. Scope is a Nikon 8-32 (in retrospect would have gone with a Nightforce). Trigger is a Geisselle. Shooting off of rear sand bag and front bipod. Barrel is a 26 Krieger Varmatch in 1/9. Intent is to use it for PD hunting out west.

Recently cleaned the barrel with usual Hoppe's 9, then overnight with their BR copper remover, then did a cleaning with bore paste. Ran patches through afterward until completely clean. Haven't shot after this extensive cleaning as of yet.

Made some load ladders, but so far have yet to shoot (chronograph out for repair). Worst part now is that living in Wisconsin it is cold outside. I think it could affect the performance of loads, and it certainly will affect my performance at the range. Supposed to be in single digits tonight- makes it hard to hold still and focus on breathing, etc while the frostbite sets in.

Does anyone try to shoot for groups at the same time they shoot over a chronograph? Seems like trying to line everything up and do it all right could be difficult. Blasting some rounds over the chronograph at a sandbank would go a lot faster.

When referring to groups, I have been meaning five shots. Otherwise, yes I have gotten 0.3 groups of three shots, but I think this is pretty meaningless.

Thanks again for the great tips- maybe if it hits twenty degrees tomorrow I may go out and shoot.

 

[Phil3]

Using a comparator, it seems like at magazine length in my AR, Sierra 69MK bullets are jumping 0.048, while the Hornady 75 BTHP are jumping around 0.037. Best groups I'm seeing out of either bullet is around .75 in my Krieger Varmatch barrel. Is this amount of bullet jump too much to expect better accuracy than what I'm seeing? Is it possible to have them set the chamber back to make it tighter? Have worked on combinations of load and powders, new and once fired Lapua brass, primer pockets cleaned, necks chamfered inside and out, etc. Should I be seeing better than this from an AR or is this as good as it's going to get?

I have an AR with Krieger Varmatch barrel (24", 1:9" twist, .920" muzzle diameter). Using a Sinclair bullet depth seating measurement tool, I found the bullet jump for the Sierra 69g MKs to be at about .037", when bullets are seated for a COL of 2.26" (maximum for the mag). I measured several times and it is always different, but seems .037" is close.

I think your accuracy can be better. My rifle shot a best, so far, off a range sand bag, of .650" for a 5 shot group at 100 yards. This using PMC Bronze 55 grain FMJ ammo, with a cannelure. I expect much better than this with handloaded ammo. Just as a note, Krieger told me that their barrel is capable of .250", IF everything else on the gun and the shooter is equally capable. If shooting off a sand bag, put the bag as close to the receiver as possible. Apparently, this helps. I seem to do equally well off a bipod...go figure.

- Phil

 

[Mikem]

Its my belief that using a good front rest, and rear sand bag, like one of leather will shoot better than just a front bag or bipod.
Mike.

 

[ForneyRider]

I shoot groups with the chrony. I try to forget about the chrony when shooting. I put 2 pieces of paper up with 5 targets each and shoot groups. I have the chrony out about 10-12ft and shoot 100 yards. I haven't hit the chrony yet. I actually have room for about 2.5 of the common backboards room to shoot through the chrony.

of course, I tend to forget to write down the FPS sometimes, but the "recall" function on the chrony helps there.

I've used a few of the cheapy 10-20$ plastic gun rests by Koplin and Caldwell, and for hunting accuracy, they were good enough. They both had simple vertical adjustments that I preferred over the bags.

Sounds like you have the parts to go .25MOA or better on regular occasion. I just went with the 8-32x Burris, because I wanted the fine crosshair and 1/8 MOA adjustments. But I eyed that Nikon for while, as with the Nightforce BR, Zeiss Conquest, and Sightron SIII.

The 5 and 10 shotgroups are more informative to me for .223 AR. But for my 7mm Mag loads, 3 is plenty to get an idea of what it is doing. Ha!

 

[Toms]

I have a Remington LTR 223 1-9 twist. It shoots 1/2 min out to 300 yards with ammo loaded to fit the magazine. I checked the oveerall with a RCBS precision Mic and was shocked to see that the bullets were jumping .230. I have tried seating out tuching and there was not much differance in groups. I use the rifle for varmint shooting and want to run the ammo through the magazine.
I also had a RRA National Match rifle that shot between 7/8" and 1 1/2" at 100 yards with scope. I do not have it any more. My 700 Rem. sporter with tupperware stock and j lock shot better than the RRA. Just my experiance. Hope this helps. Use whatever works. Tom.

 

[jonbearman]

are you shooting with a free float tube and if you are get an accuracy assett from sinclair. it is a bolt on flat bottom adaptor,made one myself and my groups shrunk to .250 with sierra 69 mk's using benchmark. The accuracy assett bolts to the sling swivel stud,works great and it takes more of the human out of the shot.I would also invest in an art jewell trigger(the best I have ever tried).got it set at 2#'s,just right for a semi like the ar. hope this helps. have a good smith look at the crown,you never know,anyone could make a mistake,even the best. I recrowned a brand new armalite barrel,freefloated it ,jewell trigger,and a homemade muzzle brake and I can shoot with the best with 69 gr mk's.The gun you have will shoot awesome with some time behind that trigger. good luck