What can cause accuracy to fall apart at 700 yards?

[GhostFace]

So before anyone asks, yes I know how to drive a semi and specifically a large frame. I’ve been doing it with great success for 20+ years. I rebarreled said rifle about two years ago with a LW 1/10, I really didn’t get a chance to get behind the rifle a lot because of work. I retired last year but took on another full time job. I had to go through all of their hoops and such for the first year. Now the dust has settled and I have been able to get to the range.

The first time I noticed this issue was about two months ago, I was banging steel from 100-600 yards easily. As soon as I went out to 700 the bullets just danced around the targets. I kinda chalked it up to forgetting my rear bag but deep down I thought I was pretty stable and shouldn’t have missed that much. I went out again last week and this time I brought the bag. I was shot several groups in the .7s at 100/200/300 yards. At 400/500/600 I was shooting steel. 100% hits. As soon as I went out to 700 the bullets just danced around the targets and never hit steel. I checked the scope and its tracking, the rings and mount is tight. The barrel has been bedded into the receiver.

so I am truly puzzled by this. Has anyone else seen this before?

 

[oldrifleman]

Is it hitting Sub-Sonic transition about there? The bullets might have lost stability. What round are you shooting?

 

[hlee]

308? Seems about right…

 

[Bluedog82]

Is it hitting Sub-Sonic transition about there? The bullets might have lost stability. What round are you shooting?

Yeah, OP post your load data.

 

[oldrifleman]

I do know that 168 FGMM starts the transition about 650 -700yrds.

 

[sloporsche]

Tell us all about the ammo and i gather the barrel has a very low rounds out count . How accurate is it on paper at 100 yards ? tack driver ?

 

[BCP]

Either transonic or some weird parallax/mirage issues at longer range.

Or weird wind.

 

[CaptNemo]

Load data ?
Chrono data ?
Next range trip, stake out some wind flags / surveyor's marking tape near the 600 and 700 yard lines to see if there is a weird wind happening in the longer ranges.

 

[Rio Precision Gunworks]

Need to know:

Bullet you're shooting
Ammo avg velocity
Ammo SD. Preferably 10 shots or more
Target size you're missing at distance
Any pattern on the missing (is it always or mostly elevation, is it always or mostly windage, is it just random)

Otherwise, people are just going to post different reasons it could happen without knowing if it's even possible that's your issue.

 

[LRRPF52]

Barrel length
Ammunition

 

[GhostFace]

178s handloads, velocity is (memory is about 2520) not home at the moment. Factory 178s is the same velocity give or take about 30 fps. Shot at 850ish ASL in 75 degree weather.

Barrel is an 18 inch 1/10. The old barrel was a hammer out to 1K . No issues going transonic....

 

[Kfive73]

Mixed lots of bullets?

I had a similar issue with a boutique 6mm bullet. Best groups I’ve ever shot out to 600. At 900, all over the place, couldn’t ring 3 MOA steel. I bought like 140 bullets to try out before committing to a 500 bullet lot. The 140 was a mix of 2-3 lots. I could tell a difference while seating them of the separate lots (seemed like 1 lot had a shorter bearing surface). Switched back to Bergers and haven’t had the issue since.

 

[Rio Precision Gunworks]

Size of target and standard deviation of ammo?

For example, a 178 eld moving 2550avg with 10sd......the smallest it can hold at 700 yds is just under 1moa. That's the smallest if you were able to shoot every shot perfectly. Add in some environment, and not too hard to start missing a lot depending on target size.

Also, considering you said .7 was some of your best groups at closer distances.......it's not surprising that you're going to see some issues at distance.

 

[theLBC]

maybe borderline spin rate?

Twist Rate Stability Calculator

Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.

bergerbullets.com

 

[camocorvette]

178s handloads, velocity is (memory is about 2520) not home at the moment. Factory 178s is the same velocity give or take about 30 fps. Shot at 850ish ASL in 75 degree weather.

Barrel is an 18 inch 1/10. The old barrel was a hammer out to 1K . No issues going transonic....

I had similar experience during load development with 178's with a bolt gun. I can't remember the speed then, but after about 600 the opened up. I've now got a load in lapua brass with varget at 2660-2700 that does great to 1300 yards.

I was using lc brass before and my seating depth was shorter. These are long and make me want to re barrel for a tighter chamber.

You've got a lot of variables. Semis are literally harder to shoot accurately at extended ranges.

So make sure your load is on point and your shooting position is great. I'd try to adjust the load and only shoot at 500 plus during development.

Has it been windy when shooting 700+?

 

[264win]

Bullets starting to de stabilize sounds like the culprit here. This can happen well before transonic as well.

 

[sinister]

178s handloads, velocity is (memory is about 2520) not home at the moment. Factory 178s is the same velocity give or take about 30 fps. Shot at 850ish ASL in 75 degree weather.

Barrel is an 18 inch 1/10. The old barrel was a hammer out to 1K . No issues going transonic....

I've not shot 178s, but the 175 Match King needs to launch around 2550 to reach 1,000 supersonic. Not sure but I think 178 A-Max is longer.

JBM says you should be good-to-go for a Hornady 178 Boat-tail Match with your given met data:

 

[GhostFace]

Thanks Sinister for the JBM, I've used the 178 HPBT in an 18 inch LW 1/10 since forever . I'm thinking this new barrel is the culprit. It's a LW 1/10 too but something just isn't right. I have about 260 rounds on it and the first one took a while to come in but by time I started shooting at distance it was already broke in and settled down. This new one is scratching my head. It's the only thing that's changed in the equation...

 

[oldrifleman]

What’s the barrel?

 

[sinister]

Thanks Sinister for the JBM, I've used the 178 HPBT in an 18 inch LW 1/10 since forever . I'm thinking this new barrel is the culprit. It's a LW 1/10 too but something just isn't right. I have about 260 rounds on it and the first one took a while to come in but by time I started shooting at distance it was already broke in and settled down. This new one is scratching my head. It's the only thing that's changed in the equation...

Is it the VarTac profile? They have it in-stock and I was thinking of getting one.

 

[GhostFace]

It a Lother Walther Medium HB, basically the T profile but in 18 inches with RLGS. This is the chromoly nitride. The last one was stainless. I have about 260 rounds on it.

I just checked their site, it's the Vartac...

 

[sinister]

Hmm. I've only used their stainless barrels so my input won't be the same.

 

[GhostFace]

That SS one I had was absolutely the best. It shot like a custom bolt gun! I was sad as shit when she burnt out....

 

[oldrifleman]

At this point I think I would try a couple of boxes of another bullet, maybe something like the 175 Berger just to see if maybe this barrel does not like your existing stock.

 

[GhostFace]

At this point I think I would try a couple of boxes of another bullet, maybe something like the 175 Berger just to see if maybe this barrel does not like your existing stock.

I thought about this and probably will try something else but if a barrel doesn't like something it shows up close or at least that's been my experience. This barrel groups well with this bullet just not beyond 600...lol

 

[oldrifleman]

Yeah I know, it’s either that or you now have a 600yrd rifle

 

[hafejd30]

Get a chrono reading when shooting. Also try some paper at 700 yds

I had a 20” 308 running 168 smk that the bullets hit the target sideways at about 800.

I’m guessing destabilizing

 

[LRRPF52]

Every time I have seen this with guys coming through courses, it has been a 16” barrel with 1/12” twist start to come apart, but usually once they go from 700yd TGTs to 800yds. POA=POI just fine up until they stretch to 800. This is at 6300ft ASL.

Others on here have said they have no problem with 12 twist from bolt guns running fast, but I’m almost always running classes with gas guns.

Todd Hodnett was/is a big proponent of running 1/9 twist with .308 from 16” gas guns for that reason.

I’ve also had guys come through with 20” SR-25s with 175s and 178s and literally group sub-MOA at 1000yds on the big gongs. I think those were 1/11.25 twist.

I know if I was spec’ing a .308 gasser right now, I would go with the 9 twist from a shorty and suppress it.

 

[oldrifleman]

He is running a 10 twist barrel so should be able to stabilize the bullet. I agree with others that the bullet is likely destabilized as it loses velocity out past 600yrds. I don't blame the barrel as it seems to hold up well out to 600yrds, that leaves the bullet/load although the ballistics calculator says you are ok. Still it holds up well to a point then fails, that's where I would look.

 

[RTH1800]

When “banging steel” comes up it’s difficult to discuss precision.
Get a target. Post 10 shot groups and load data.
Or, keep banging steel.

 

[918v]

It’s prolly not 1-10”.

 

[oldrifleman]

It’s prolly not 1-10”.

Maybe but that's what he thinks it is based on what he bought.

 

[BCP]

This sort of thing happened to me before and how I figured it out was a big piece of plywood at 750 with sideways bullet holes. I cleaned the barrel with copper solvent and they started flying straight again.

Doubt its bullet or velocity. Wind is a possibility especially if it’s coming towards you or fishtailing.

 

[msgriff]

I'd probably look for copper build-up at the gas port in the bore.

 

[Jsp556]

Like stated above, I’d shoot it on paper at distance with a few different bullets.

I’d look at the entire barrel with a bore scope. Melonited barrels are tough. If there’s a barrel defect that’s damaging the jackets, go ahead and replace the barrel. If the internal finish is good, you’re not going to get much if any copper fouling barring a problem at the gas port.

You’ve probably already checked the crown for damage. Maybe an uneven carbon build up?

 

[joe777]

Idk shit about shooting long range but I've had a couple barrel extensions that really dug grooves into the bullet.

 

[GhostFace]

It’s prolly not 1-10”.

It is, I mentioned it before. The previous barrel was 1/10 from the same manufacturer, Lother Walther. The only difference is the previous barrel was SS and this one is not, this one is CM and factory nitrided.

 

[81STFACP]

It is, I mentioned it before. The previous barrel was 1/10 from the same manufacturer, Lother Walther. The only difference is the previous barrel was SS and this one is not, the one is CM and factory nitrided.

Button or cut? Do you know the twist tolerance of either one?

One time we had one button AR barrel stamped 8T, but it would stabilize any 80 trainer. At 600 it was 8 ring to 8 ring for normal distribution. We handed the shooter another rifle, he shot 200-11X.

We surmised the 8T he had maybe slower than stamped.

 

[308pirate]

Every time I have seen this with guys coming through courses, it has been a 16” barrel with 1/12” twist start to come apart, but usually once they go from 700yd TGTs to 800yds. POA=POI just fine up until they stretch to 800. This is at 6300ft ASL.

Others on here have said they have no problem with 12 twist from bolt guns running fast, but I’m almost always running classes with gas guns.

Todd Hodnett was/is a big proponent of running 1/9 twist with .308 from 16” gas guns for that reason.

I’ve also had guys come through with 20” SR-25s with 175s and 178s and literally group sub-MOA at 1000yds on the big gongs. I think those were 1/11.25 twist.

I know if I was spec’ing a .308 gasser right now, I would go with the 9 twist from a shorty and suppress it.

It's simple math. Short barrels = lower linear velocity. Low rate of twist = fewer revolutions per unit distance. Put the two together and you get much lower rotational velocity in the bullet than usual.

 

[DeathBeforeDismount]

-What solver are you using?
-SD will give you an idea of hit probability on an X sized target at x distance via WEZ.
-Twist rate and short barrels as already mentioned.
- Could be bullet. I would try the new smk 169s. They are shooting REALLY well, as well as the tried and true 185 bergers if you can get coal to play nicely.

 

[TheHorta]

Is your scope in MILs? That’s likely the problem. I was experiencing the same problem and switched to an MOA scope. Now I’m hitting steel out to 1200y with .308 M80 ball.

 

[DeathBeforeDismount]

Is your scope in MILs? That’s likely the problem. I was experiencing the same problem and switched to an MOA scope. Now I’m hitting steel out to 1200y with .308 M80 ball.

You have MOA? LUCKY

 

[GhostFace]

Is your scope in MILs? That’s likely the problem. I was experiencing the same problem and switched to an MOA scope. Now I’m hitting steel out to 1200y with .308 M80 ball.

MOA all the way baby! Seriously it's MOA/MOA, I never switched over. Maybe that's the problem ...

 

[Mike_in_FL]

I'll take a guess. Your bullets are the old AMAX and the tips are melting by then?

 

[GhostFace]

No Mike, I'm using the 178 HPBT, no problems with accuracy until I go beyond 600. I think some of these guys are on to something, it maybe destabilizing even though it has plenty of velocity. I'm going to try some 168 ELDs to see how they fair. The BC is good enough to get out to 1K.

I might pick you up a box of 155s too just in case....

 

[308pirate]

No Mike, I'm using the 178 HPBT, no problems with accuracy until I go beyond 600. I think some of these guys are on to something, it maybe destabilizing even though it has plenty of velocity. I'm going to try some 168 ELDs to see how they fair. The BC is good enough to get out to 1K.

I might pick you up a box of 155s too just in case....

There are bullet stability calculators online......

 

[LRRPF52]

No Mike, I'm using the 178 HPBT, no problems with accuracy until I go beyond 600. I think some of these guys are on to something, it maybe destabilizing even though it has plenty of velocity. I'm going to try some 168 ELDs to see how they fair. The BC is good enough to get out to 1K.

I might pick you up a box of 155s too just in case....

I used to shoot 155gr Scenars in competition, just because we didn’t have good BC data back then and they were listed higher than 175gr SMKs, lol. Kicked ‘em out at 2820fps from a 22” GAP-built rifle with Obermeyer pipe.

 

[sinister]

... I'm using the 178 HPBT, no problems with accuracy until I go beyond 600. I think some of these guys are on to something, it maybe destabilizing even though it has plenty of velocity. I'm going to try some 168 ELDs to see how they fair. The BC is good enough to get out to 1K.

I might pick you up a box of 155s too just in case....

I've tried the new and old Sierra 155 Palmas and Lapua 155 Scenars and haven't had any luck with them past 600 in a 16- or 20" L-W stainless 1-12 (even at 5500 ASL) -- couldn't push them fast enough, and they shed velocity faster than heavies.

My son's long-range SR-25 knock-off has a Satern 1-9 I got from Mike Miller. I'm thinking the Sierra 169s would probably do well.

 

[Mike_in_FL]

No Mike, I'm using the 178 HPBT, no problems with accuracy until I go beyond 600. I think some of these guys are on to something, it maybe destabilizing even though it has plenty of velocity. I'm going to try some 168 ELDs to see how they fair. The BC is good enough to get out to 1K.

I might pick you up a box of 155s too just in case....

It might just be me but I've never been able to get those to shoot as well as the 175 SMK in a gas gun. I never try seating depth tests when you have to load to mag length.

 

[HD1911]

You could also try the Federal LE 168gr TMK load, T308T. I’ve been having good luck with it so far. Consistently been under 10 FPS SDs, groups real tight, has a really good BC for a 168gr, and it does not have the transonic stability issues that the 168gr SMK has.

https://www.luckygunner.com/308-168-grain-tactical-tip-matchking-federal-tactical-tru-20-rounds

I normally get it from here, but it goes out of stock quickly everytime it gets replenished.

https://www.recoilgunworks.com/tactical-tru-308-win-168gr-tactical-tip-matchking/