120gr 7mm08 troubles- #62 potential issue
- Thread starter WhelanLad
- Start date
Alright
31 Degree evening around 7pm I started, finished at 7:45pm (now).
id set up in the Shade
fired the first of the 41gr loadings.
waited a good while until the tube wasn't warm.. fired.
same again for the first 4! then had trouble chambering one , so I got it in with little bita force an fired it pretty much straight away..
The Result
the first 3 were close to the inch, then with the 5 it went out a little bit but cant be sure with that last round but either way I'm settled... 41 varget
very similar POI to the 139 hornady interlocks, this sits about 3 inch high at 100m though the 139s are around 2/2.5 ... Happy to use both for Deer especially.
31 Degree evening around 7pm I started, finished at 7:45pm (now).
id set up in the Shade
fired the first of the 41gr loadings.
waited a good while until the tube wasn't warm.. fired.
same again for the first 4! then had trouble chambering one , so I got it in with little bita force an fired it pretty much straight away..
The Result
the first 3 were close to the inch, then with the 5 it went out a little bit but cant be sure with that last round but either way I'm settled... 41 varget
very similar POI to the 139 hornady interlocks, this sits about 3 inch high at 100m though the 139s are around 2/2.5 ... Happy to use both for Deer especially.
- Location
- Prince Albert, Sk
It isn't a twist issue , 120 isn't "too light".
No way that a 7-08 could push a 120 grain projectile to the point of having problems.
That 9" twist will work with weights up to bullets in the 160gr ish range for the -08.Anything from 100gr to 160gr will typically work, it is about load tuning.
There are LOTS of loaders using 120gr projectiles in 7/08 with factory twist rates with very good results.
Looks like the OP is getting things settled in.
No way that a 7-08 could push a 120 grain projectile to the point of having problems.
That 9" twist will work with weights up to bullets in the 160gr ish range for the -08.Anything from 100gr to 160gr will typically work, it is about load tuning.
There are LOTS of loaders using 120gr projectiles in 7/08 with factory twist rates with very good results.
Looks like the OP is getting things settled in.
coleman1495
CGN Ultra frequent flyer
- Location
- Whitecourt
I am not sure what you mean by pushing the projectile to the point of having problems. A 1-9 twist is pretty fast for a 120gr bullet. You simply aren't going to see optimal accuracy out of it. The bullet is being overstabilized and any variations in the bullet create inaccuracies.
No big secrets here. 1-9 twist is too fast for being optimal.
Yes, I'm sure your dents are from sizing lube. The ones on my cases were from firing underloads. The reason I got into this mix-up is because Hodgdon has incorrect loads posted for the .264 Win Mag on their web site. I'm 100% sure they have interchanged the loads for the 140 grain bullet and the 160 grain bullets. This results in severe underloads for the 140 and severe overloads for the 160. I've informed Hodgdon of the error a few years ago, but they have not taken any action to correct the problem. In any case you can look up the loads for this cartridge and in particular for the 140 and 160 grain bullets. I don't recall exactly what I loaded those cartridges at, but based on what they have on the site now, it was probably about 6.5 grains of H4831 too light, and the picture shows what happens when you do that!
It could be an issue of bullet quality. However, most quality bullets made today can easily handle the spin of a 9 twist without any significant increase in group size. Dan Lilja did some estimations of the effect of twist and bullet unbalance on accuracy. See this article he wrote. At the bottom of the article is some examples of what effect that twist has.
One thing to consider is that specific bullets sometimes just do not shoot in a gun. I have found in my 6BR that when you go too light and too short it has a major effect on accuracy. A Berger 68 grain will shoot under 0.2" in my gun. However a similar flat base design Berger at 62 grains struggles to produce 2" groups. Yes, 10 times larger! Powder, velocity, seating depth, primers, all made no difference. Shot nearly the whole box of 100 with zero success. In my case, I think the basic problem was that the throat is too long for a short light bullet like the 62 grain.
- Location
- Prince Albert, Sk
Bullet failure from excess speed and rpm.
Sometimes it is only bearing surface causing issues.Lots of variables.
Sometimes it is only bearing surface causing issues.Lots of variables.
Yeah I tend to lean toward some Fact in there that is saying this particular Rifle doesn't like 120gr Sierras too much, an there is some doubt of my shooting, it is not benchrest quality..
I don't normally 5 shot group, but did with this particular to eliminate the two in an one out, with that group there is still some user error involved but I was confident in the let off an all that.
slowing them down has definatly helped out.
I don't normally 5 shot group, but did with this particular to eliminate the two in an one out, with that group there is still some user error involved but I was confident in the let off an all that.
slowing them down has definatly helped out.
coleman1495
CGN Ultra frequent flyer
- Location
- Whitecourt
Yeah higher quality bullets are definitely less effected by overspin. The OP is using soft point bullets so combining that with the faster than necessary twist rate so I think the results are to be expected.
The results aren't terrible, just exactly what I would think would happen.
- Location
- Prince Albert, Sk
Most 7/08 factory twists are 9.125 or 9.250 , an eighth or quarter is not going to to create that type of over spin problems you are stating.I have 9" 7mm and 9.25" 7mm , Anything from 100gr and up is all within reasonable parameters and usable and excellent accuracy.This is why I have been suggesting ladder tests to find the nodes where the 120's settle in a bit more efficiently.
We aren't talking about trying to shoot a 90 gr VLD .223 out of a 12 twist barrel here.
If the rifle/barrel is of quality it will shoot 120's with the right combination of components and diligent testing especially in a quality firearm.
We aren't talking about trying to shoot a 90 gr VLD .223 out of a 12 twist barrel here.
If the rifle/barrel is of quality it will shoot 120's with the right combination of components and diligent testing especially in a quality firearm.
interesting and thanks mate
coleman1495
CGN Ultra frequent flyer
- Location
- Whitecourt
Here is the quick reference chart from Berger: http://www.bergerbullets.com/pdf/Quick-Reference-Sheets.pdf
It shows a 1-10 twist as being optimal for 140-168gr depending on the bullet. 1-9 twist is definitely too fast to be optimal for a 120gr. The more uniform a bullet is the less effected by overspin. Soft point bullets are not going to be extremely uniform. A 1-9.5 twist still won't shoot a 120gr bullet optimal. Those twist rates are designed to be optimal for ~>150gr.
I wouldn't be too sure about that. My Sako 85 has a 1-9.5 twist and the load development I did using 120 gr. TTSX for hunting is very accurate and I'm not shooting off the most stable platform,,,usually the tailgate of my truck and I've had lots of grouping in the 1/2" MOA range.
.That being said, maybe my gun shoots most bullet weights well once an OCW load workup is completed. I use 150 gr. BTs for practice shooting and they're very accurate as well.
Five shot group:
Last edited:
coleman1495
CGN Ultra frequent flyer
- Location
- Whitecourt
I wouldn't be too sure about that. My Sako 85 has a 1-9.5 twist and the load development I did using 120 gr. TTSX for hunting is very accurate and I'm not shooting off the most stable platform,,,usually the tailgate of my truck and I've hard lots of grouping in the 1/2" MOA range.
.
That being said, maybe my gun shoots most bullet weights well once an OCW load workup is completed. I use 150 gr. BTs for practice shooting and they're very accurate as well.
Five shot group:
I don't think you read my post.
Wasn't it your post that said a 1-9.5 twist won't shoot a 120 gr. bullet very well?? My mistake if it wasn't. In any event, my 120 gr. bullets shoot like a hot damn with that twist rate.
coleman1495
CGN Ultra frequent flyer
- Location
- Whitecourt
I said that it isn't optimal. Over stabilization of bullets will make defects in the bullet more apparent. Soft point bullets are not going to be totally uniform. Overspinning them will cause a loss of accuracy.
IE, I found that a 1-8 twist Tikka fired a 55gr American eagle bullet like crap. I was able to get good results out of a Hornady 53gr.
Higher quality (or at least more uniform) bullets will be affected less by over stabilization.
prairie lover
CGN Regular
- Location
- southern MB
i have a 8 twist tikka t3 lite in 223. I tried to find the 12 twist version but couldn't so I bought the 8. I had and have no intension of shooting over 55 gr bullets. it shoots my 2 fur getting bullets, a 50 gr nosler bt and 55 sierra gameking excellent. half moa groups are the norm. 2 inch 5 shot groups at 300 yards with a 3-9 scope. twist is way too fast but it still shoots well. so I don't think too much twist is the issue. the barrel just does not like certain bullets.
