Reply With QuoteROFLMAO Now you are hooked :)
Good stuff.. Glad you’re enjoying your new rig.
ROFLMAO Now you are hooked :)
Thanks gents. The last time I shot a rifle at targets at these ranges was when I was working for Uncle Sam back in the 70`s. This is a lot more fun! My performance with an M-16 was "inconsistent " out around 300 yards/meters ( M-14 was another matter! ), so it was nice to get a little " payback" at that range, LOL. Looking forward to getting back out and going further.
Congratulations. I have a Model 12 long range target rifle that I shoot Palma and long range prone. The rifle is great. Ergonomics great on laminate prone stock. I also like the target Accutrigger. The .308 has a 1:13 twist 30 in. barrel meant for 155 gr bullets, but the rifle shoots the heavier 175-178 gr bullets very well which I prefer. I also have a barrel chambered for 6mm SLR that also shoots great.
So enjoy your adventure with your new rifle.
Why did they go with the slow twist, and why does it shoot the heavy bullets so well?Originally Posted by Palmafiddleman
Seems like that would go against most common theories on stabilizing heavy bullets.
Thanks.
It is kinda backwards, but, the longer barrels allow a bit more vel, which means longer/heavier bullets can be stabilized.
The slower twist (and longer barrel) is used with the 155's so a bit more vel could be eeeked out of them. Less energy to spin them up means more energy to push the bullet. The longer barrel is also good for a longer sight radius.
Rules: A Palma rifle consists of a single shot bolt action rifle weighing less than 6 kg (13.2lbs) in 7.62mm NATO caliber (.308 Winchester) firing a 155 grain palma bullet. US Palma rules allow any weight bullets, NRA Match and Service Rifles.
Adding to what Charlie b said, 155 gr bullets are required for those who shoot on the international team. There are three members of my club who are on the current US Palma team. Those of us who will never be on the international team can shoot the bullet we want, even at the nationals (Camp Perry, Camp Atterbury). My club sponsored a "Full Bore" match earlier this year where the 155 gr was required. Situations like this are the only time you see it mandatory. At the full bore match we also shot "two to a mound" rather than a single string. That was a challenge to stay in position a lot longer.
Why does my barrel with the 13 twist shoot the heavier bullets well? I might say that maybe I am lucky it does. Quite possibly not all barrels of same twist/length would do it.
One reason is bullet length, at least for me. The 155 Berger Full Bores that I shoot are longer than the 175SMK's that I like for shooting at 1000yd. (I am using a 10 twist so this is a different issue).
Not just for yours Charlie. That’s how it is for every gun. It’s not weight that dictates twist needed, it’s bullet length. And while the norm has been that typically the heavier the bullet, the longer it is, there have been several lighter bullets in a specific caliber, that are longer than their heavier counterparts.
As Charlie mentioned, those Berger 155 Full Bore’s are a perfect example. Very long for for a 155 30cal. So if that is your specimen for example, that answers why. But in the world of firearms, these contraptions do some strange things at times that defy logic. Just something to ponder.
There is sound physics reasons for all of this. The simplified stability equations work most of the time, but, others require the use of the more detailed equations that take into account the specific aerodynamics of the bullet being used.
And sometimes it can be atmospheric conditions. The bullet stability depends on the density of the air. Most of the time we shoot when it is closer to std conditions, but, if we go out when it is very cold then some of the loads we use might not work.
The manufacturers recommend certain twist rates based on the extremes. They have to. If Sierra made their Match Kings and recommended a twist rate that would not work at below freezing temps, they they would be turned away from military contracts (and many hunters). So, they are very conservative.
Thanks guys.
One more question - is a 175 superior to a 155 in terms of wind deflection?
In general the advise is to use the heavier weight bullet for its caliber for its ability to resist wind deflection. The 155's were chosen to create the maximum test for a rifleman/competitor in wind reading and adjustment before executing the next shot. When shooting "2 or 3 to a mound" you will have a limited time to break your shot when it is your turn. You may not have the luxury of waiting for your preferred condition to re-appear. By the way, .308 FTR shooters use the heavy, 200, 220 grs etc. class of bullet weights.
Blue is the Lapua 155gn Scenar factory load
Green is the Lapua 185gn Scenar factory load
Note the starting velocity, I suspect from a 24" or 26" barrel. I picked a zero range of 300yd
You can notice the wind drift differences in the two bullets. This was for a 5mph wind
Range Drop
(inches)Velocity Energy Wind drift
(inches)Time
(milliseconds)0 -1.4867 -1.4837 2822 2477 2740 2520 0.0156 0.0178 0 0 200 4.9646 6.0442 2471 2280 2101 2135 1.3035 0.9238 228 253 400 -11.5335 -13.2674 2145 2091 1583 1796 5.5292 3.7925 488 528 600 -58.5207 -64.4834 1843 1911 1169 1500 13.3760 8.8903 790 828 800 -146.8517 -153.9021 1566 1740 844 1243 25.7532 16.5333 1143 1157 1000 -292.6009 -289.4278 1310 1577 591 1021 43.9179 27.0994 1562 1519 1200 -520.7133 -481.2653 1099 1422 416 830 69.5685 41.0601 2066 1920 1400 -862.0448 -742.0185 1013 1275 353 668 101.0725 58.9821 2637 2366
I can say I like shooting the 175SMK's at 1000yd more than the 155 Bergers. I can adjust for wind easier. I also think the heavier bullets make for a lower ES/SD for me, which results in smaller groups. The only thing I have to overcome is the recoil. I am not consistent enough with hold (12lb rifle) over a long string. Which is why my 1000yd gun is a 6BR these days. :)
If that ain’t about the most confusing chart I ever done seen! So, “A” (Blue) is the 180gr.. but it’s in green columns? And since when is a 180gr going to be higher velocity than 155gr? Sure those aren’t reversed?
Dave,
The cut and paste messed up the A and B heading. Pay attention to the color.
Fixed it. :)
Now that’s much easier. The first way it was had me thinking I was taking crazy pills, LOL!
Brother…I’ll second your thinking on recoil! I remember in my teens & 20’s I thought recoil was uber kewl! Even in my 30’s I didn’t mind it so much, having a stout physic. Although by then I had come to know it just wasn’t needed. Now in my mid 40’s, with a broken, weak body, I say recoil is for the birds! I learned that having a 15lb rifle that’ll get out to a mile without much recoil is what I like.
Got it - thanks.
Well.......LOL!! I`m glad I can take credit for initiating a thread that has allowed the experts to hold forth! I`ll just crawl back into my little neophyte hole with my .223 " trainer" !!
LOL trainer indeed. Probably one of my better 600yd guns when the wind wasn't blowing.
223 is among my very favorite cartridges my friend. Although I use it in the AR platform. I’ve hand built & owned a horde of AR15’s over the last 17 years, and all but 2 were chambered 223/5.56. While I’ve never had a Bolt Gun in 223 I know what it does in my high end AR15’s. And I also know that performance can only be furthered in a Bolt Gun. Trainer says you? HA, says I!
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