twist rate vs bullet weight

[bdotson]

What would you guys suggest for bullet weight and shape? Shooting targets only. 100 200 300 yds 308 win. factory barrel 1/12 twist. I measured the twist, I come up with 12.375. I guess it is 1/12. I want to shoot this gun in factory class and am looking for extreme accuracy. Who makes the best bullet for this application? Key word being BEST for this application. Thanks Buddy

 

[Travelor]

I would try the Sierra MatchKing in the 168 grain weight. This bullet has performed very well for me in the past. This bullet works well out to 600 yards, but the BC is such that it is almost impossible to stay supersonic out past 900 yards.

I have since changed over to the 175 gr Sierra MatchKing as I am now shooting 600 and 1000 yards with a 1:12 twist 308.

George

 

[shootsanything]

Actually it is not weight but length that is the issue, but most lead core bullets have a similar weight/length relationship which is what makes everyone talk about "twist for a given weight". Having said that with a 1/13 twist barrel you should be OK with anything under a 175 grain bullet but for punching paper I would go well under this. You cannot go wrong with a Berger or Sierra Match King bullet and with the yardages you indicated and the twist you have I would focus on 155 grain pills, should be the best trade off for 300 yards. If I were going to do what you are doing I would look at the Sierra 155gr Palma - and actually I am for a similar application.

 

[bdotson]

Who makes the best bullet for this application? Key word being BEST for this application. Thanks Buddy

I would have never thought sierra would be considered the BEST with all the customs out there. Length is the thing I need to think of the factory barrel has a very long throat. A 168 mk seated anywhere near the lands you will have run out problems. Bullet is seated so shallow in case

 

[therifler]

i have been biulding my 30cal. for 600yd and under with 1-12 twist . works great with bullets up to 185 gr . I prefer 168 for 308 win and have got great results with VLD ans BT bergers . They seem to be more consistent as far as bearing surface goes . The BT may work better in close 100-300 range then the VLD.

 

[shootsanything]

"would have never thought sierra would be considered the BEST with all the customs out there"

Take a look at all the trophys won with Sierra Match Kings. I tend to shoot Bergers because they shoot in my guns, but have had great results with both SMK and Sierra Game Kings. Certain loads are best with the SMK and 30cal 150, 155 and 168 Sierra's seem to win an awful lot.

Your issue with a long throat in a factory rifle is one we all face. Berger says the VLD's fly best when jumped and they make 155 & 168gr VLD. Might be worth a try.

 

[Laurie]

Shooting to a maximum range of 300 yards means you don't have to worry about differences in ballistic performance betwen bullet designs.

Both 155s and 168s are proven performers at these ranges, and also well suited to your rifling twist rate. You'll just get away with the 175gn Sierra MK too.

It's accuracy your're looking for - combinations that will give small 100yd groups - rather than high velocities or very high-BC type bullets. I'd give the Sierra 155, Sierra, Hornady and Nosler 168s a go with Viht N150, Varget or IMR-4064.

Regards and have a Good Christmas,

Laurie,
York, England

 

[bheadboy]

Lilja has an excellent article on this subject, also the major effect of bullet length to twist rate with the new longer bullets/weight, balistic tips etc causes a need for faster twist,
example a 22-250 1x14 may or maynot stabalise a 55 sbk as the bullet weight/length is longer than the 55sbt. etc -- i went to a 1x13 and the 55sbk shoots <.200" at 3700 from my 40x 22-250 26" Hart bbl

here is the link
http://www.riflebarrels.com/articles/bullets_ballastics/bullet_imbalance_twist.htm

you need to go fast enough twist but not too fast or you loose on that end of the sweet spot, if one bullet does not shoot measure the length then compare to the bullet that shoots better, look for the shorter bullet when you loose group size


bheadboy

 

[bheadboy]

I forgot to include this quote from Lilja article in Precision shooting

The other consideration not taken into account so far, is changing bullet styles. The bullet in the examples is typical of most flat base bullets used in benchrest. A Rorschach die bullet or a Euber bullet fall into this category. Adding a boattail or increasing the bullet length will decrease the stability. Going to a shorter bullet such as a 62 grain bullet made on a .750" jacket will increase the stability.
Thus with a fixed twist rate look for the longest bullet that will give the desired results, example the balistic tip bullets are usually .0020" longer than hp bullets so you may have to change design or brand to get one that is short enough to shoot in your twist rate, leaving the longer ones on the shelf.

remember temp and elavation also cause stability changes

Bheadboy

 

[bheadboy]

final input, this formular shows the loss of accurcy with the longer bullet and a fixed twist rate - put in your twist rate, velocity, bullet dia. weight, then measure the length of your bullet and enter that, with temp and barimetric pressure,- then calculate,
If the answer is below 1.0 forget it, work for an answer of 1.2-1.5 for best results.

http://www.jbmballistics.com/cgi-bin/jbmstab-5.0.cgi

for fun just change length of the bullet up and down to see the difference in possible accurcy

bheadboy