Range Report Range Report: 243 Win - 110 SMK - 8 twist barrel - No go

[3rdfocal]

Spent some time working up a load in 243 win with a 110smk using an AIAT with a 26" 8 twist barrel. I've got the 110's going about 3015 fps with 47 grains of H1000, zero pressure signs. They could be run way harder with a different powder but I figured I'd get pretty good barrel life with it. Anyways...

- At 100 yards it shoots very well, consistently half MOA.
- I stretched it out a bit a few weeks ago and had great groups at 400 yards, several 3 shot groups under 2". Same day went from 400 to 1k and things got interesting, seemed very inaccurate but it was windy and I only had about 5 rounds to shoot at 1k so I figured I just needed to shoot more to figure the round/wind out.
- Today, I took 50 rounds out to really get it dialed in at longer ranges. Conditions were great, a little overcast, and almost no wind (which is rare here). Again at 400 things were great. At 600 groups on steel opened way up. 800 was wildly unpredictable. And 1k just pissed me off, 1 round on target, next 2 feet high and right, next a foot low.

What I assume, and have learned from others with similar experiences with good close range accuracy but poor long range accuracy is that the bullet probably isn't spinning fast enough? If anyone has any ideas about what else may be going on, I'm all ears. For what it's worth, same day, same gun, 308 barrel, 8/10 hits on 12" plate at 1k.

My belief is that the 110 SMK doesn't work in an 8 twist barrel. Hopefully this saves someone some time in the future. Now I get to start over with a 105.

 

[entropic86]

Actual twist rate can vary from barrel to barrel. Most button barrel makers spec their twist rate at +/- 0.3 in/in. I haven't had these issues with the three 8-twist Bartlein barrels I've run 110s in so far. I get .5-.75" groups at 100, which isn't great but they are hammers at 1000. My next barrel will be a 7.25" twist. Match staff still ask what I'm shooting when they see how flat the trace is.

 

[3rdfocal]

I haven't tried to measure the actual twist of the barrel but it's labeled as an 8 twist AINA barrel. I've spent the last 2 days working up a load with the 105 HVLD's, 47.5 grains of H1000, kissing the lands they are looking very good. Today at 100 I shot a few 3 round groups between .2-.6" and ran a few rounds out to 800, 3/3 hits on a 12" plate after getting the elevation right. That wasn't imaginable with the 110's.

I had about 20 rounds loaded with the 110's left from before I figured out they wouldn't shoot well. I decided to shoot them yesterday instead of pulling them, at 4 and 600 yards they were absolutely hammers but at 800 I couldn't hit a torso sized plate. I really want to keep messing with them but the 243 barrel life has me wanting to give up and switch to what I know will work. The next barrel will be a 7-7.5 twist for sure cause those 110's really are awesome and I want to run them bad. They're the reason I went 243 instead of 6.5 something for this last barrel.

It seems that the accuracy falls apart between 6-800 yards. Not sure if I'm crazy or if anyone else has experienced something similar.

 

[3rdfocal]

Thanks for all the help via the PM's Dave.

 

[CharlieNC]

With a lot of vertical dispersion there are two major possibilities. First the velocity variability is excessive?. Second you did develop a load within a node?

 

[3rdfocal]

Charlie -

The SD for this load is 9 and an ES of 20. They are very accurate out to about 600, group size of only a few inches. At 800 the group goes to about 20"+. I've been told by someone with a lot of experience with these bullets that this is because the bullets are marginally stable. "It is stable enough out of the muzzle to give decent accuracy, but at distance the centerline of the bullet points less and less in the same direction as the velocity vector (due to gravity accelerating the bullet down). This induces instability that can only be overcome with faster twist". They are pretty much a no-go at LR in my barrel. Others have had success with them in 8 twist barrels though. If I could get them to shoot at 1k the way they do at 4-600 we'd be in business. My next barrel will be a 7-7.5 for the 110's.

 

[Hondo1]

I am shooting the 110 out of a 1-8" 6 Creedmoor. WinTac Barrel out of an AIAX. I have had great luck out to 1760. I am at 5800ft though. What is your elevation?

 

[3rdfocal]

I am shooting the 110 out of a 1-8" 6 Creedmoor. WinTac Barrel out of an AIAX. I have had great luck out to 1760. I am at 5800ft though. What is your elevation?

I'm shooting between 4800-5200. I've seen several people report success with them in 8 twist barrels. I don't see why mine would do anything different. What's you MV?

 

[Hondo1]

I'm shooting between 4800-5200. I've seen several people report success with them in 8 twist barrels. I don't see why mine would do anything different. What's you MV?

i am just under 3200 fps

 

[snarkscarbine]

I have a handful of Med Varmint 6mm 7-twist blanks on the shelf right now looking for a good home!