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VarmLR

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About VarmLR

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    http://www.referencefidelitycomponents.co.uk

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    Male
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    Gloucester
  • Interests
    Shooting,
    Hill Walking,
    Loud Harley Davidsons ("another" Mid life crisis!)
    Music & Hifi

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  1. Twist rate

    The required gyroscopic stability of a bullet is related to selection of twist rate, or rather the bullet's stability factor (related to gyroscopic stability) determines whether it will be satisfactorily stabilised for any given twist rate. Brian Litz has published extensive research on this and his first publication of Applied Ballistics for Long Range Shooting, as well as his latest one provides tables which list the Sg (stability Factor) for a whole range of bullets and calibres. A nominal Sg of 1.4 or greater is the desired minimum figure to look for when seeing if a particular bullet might stabilise from specific barrel twist. Stability can be described in general terms as the ability of a projectile to maintain its point forward orientation in flight and return to that point forward orientation if disturbed (Litz, Applied Ballistics Ch10). The only way that a smooth projectile like a bullet can do this is by spinning in flight. The measure for stability is the Stability Factor, given by the ratio of the rigidity of the spinning mass divided by the overturning aerodynamic drag. This then relates to bullet length and twist rate for any given calibre. An Sg of 1.0 or less will be very unstable. 1 to 1.4 will be marginally stable and anything above 1.4 will be stable. However that is just a guide and there may be some leeway either side. However, that is not to say that shooting a light short bullet from a fast twist will always be satisfactory as the high acceleration and velocities reached for these lighter bullets and the corresponding centrifugal forces can combine within the barrel and structurally compromise the bullet's outer jacket causing it to disintegrate. The subject of stability leads onto some interesting related issues of trajectory which, whilst rarely an issue for small arms shooters can become a consideration for artillery pieces (over stabilisation affecting a projectiles ability to follow a trajectory trace, more importantly concerned with whether the projectile lands "nose in" to detonate at all due to maintaining a nose up flight attitude) but that's not something that really concerns sport shooters, although there may be slight effects on drag, hence BC with range/velocity. Such issues as increased drag can be determined by field testing and calibrating DOPE accordingly. This is a simplified explanation. Laurie's really the man to offer more insight.
  2. Neck sizing v full-length sizing

    It's likely in that event that it's due to brass migration from the case head to the shoulder and neck area. Have you checked the brass thickness on the necks for the stiff to load cases and the overall diameter compared to SAAMI?
  3. deer stalking directory

    No issues with me. Logged on to check this morning and all seems normal.
  4. 308 175 gr bullet makes which works best

    Thanks Stu. Yes, a close look reveals hardly any step at all. You can feel the junction with a thumb nail but only just. I'll persevere with them for now but may try some Lapua Scenar 175s for comparison although they'll need driving faster.
  5. 308 175 gr bullet makes which works best

    As per your experience Stu but using a much shorter barrel. About 1moa, plenty of V bulls but in the conditions today with lots of swirl, I wouldn't have expected better whatever I was shooting. It'd take a more experienced shot than me to better moa with a factory rifle in these conditions. A slightly stiffer load I think would have helped a little as the load was only generating 2660 fps. Overall, really happy with the TMKs which shot as well as anything else seemed to on the day and bettered some shooting HME.
  6. 308 175 gr bullet makes which works best

    Good points Stu. I'll report back when I see what I can do with them tomorrow. I checked the batch just loaded and they too appear to have a very slight step between tip and bullet, barely just enough so you can feel the transition with a thumb nail.
  7. long range vermin

    Got to admit that my 6.5 CM recoil is far less unpleasant than (especially) heavy loads shot from my .308. On lighter loads, I hardly notice it but the rifle still jumps a little (poor bipod/bipod use).
  8. 308 175 gr bullet makes which works best

    Sorry, yes, don't know how I missed that! My only observations are that when you mention a drop-off in accuracy from 0.7moa to 1moa, at 1000 yards wouldn't the slightest environmental condition changes contribute as much, if not more, to this difference? After all, shooting a 7.3 inch group one day then shooting a 10.5 inch group the next wouldn't ring alarm bells with me as being anything significant unless the conditions were exactly the same and my own performance was exactly the same. If, playing devil's advocate for one moment, we assume that your starting velocities are the same at 2765 fps, then the difference in drop for the wider group is ((10.5-7.3)/2) = 1.6 inches at 1000 yards assuming everything else is exactly the same (which it won't be) and assuming the use of averages and not extremes (fair enough in the circumstances). Given a G7 BC for the 175 of 0.267 and using standard press/temp, the drop at 1000 yards given a 2765m/s MV is 345.2 inches. To account for the extra 1.6 inch difference, fudging just the MV leads to an difference (average) of just 5 fps which in the grand scheme of things could be down to reloading batch variation or just the conditions on the day being different. I get your point though. Any inconsistency has to be viewed with suspicion and isn't what one looks for in a long range bullet. I'll report back on how I got on with mine later in the week. Best I've managed in my rifle previously at this range was 1.2 moa using 190 SMKs from a 24 inch 1/11 twist so I'll be interested to see how these compare.
  9. long range vermin

    Factory production also includes easy access to 1/8 twist rifles and loads of bullet options between 60n and 80 grains in 223, so it shouldn't be discounted. As already mentioned, it uses higher BC heavies than any of the 17's, is cheaper to shoot than the very capable 22-250 and less noisy. If point and shoot to 250 yds is all that's needed, it for all practical purposes matches anything listed above. For mainly LR work (and for me on smaller quarry this would be anything over 200 yds...) then the precision and wind-bucking of a 6mm BR makes sense, just not the costs. There's a really good reason the .223 has been around for so long and if looking for one a little different from the crowd, 1/8 chambered Ackley Improved with its steeper shoulder and slightly greater powder capacity should tick the boxes for improvements to precision and MV's with heavies over the standard 223. I've always found my own 1/8 223 to be one of the most versatile field rifles that I've ever owned. Boringly accurate, dead easy to load for and bullets and cases etc available just about everywhere. Cheap shooting.
  10. 308 175 gr bullet makes which works best

    That's a similar load to mine which is 44.2gr RS50/TMK175 @ 2.8COAL for 2662fps in a 24 inch 1/11 barrel. Will be trying it at LR this week but it gave almost one hole 100yd groups. I haven't checked the tips as you describe and don't know what effect this will have until tested at longer range. I guess that there may be a possibility of inconsistent BC drop-off rates between bullets but we'll see how they group. You haven't mentioned if your 1000 yd groups dropped off in precision with this latest batch? If not, is there anything to worry about?
  11. As Baldie suggests, always a good idea to tumble or U/S clean brass after prep. I tumble, anneal, size, trim to length, chamfer and lightly spin a bronze brush inside the case necks to remove any debris and also to try and consistently clean up the necks. The brass then goes into an U/S bath for 20 minutes, or I tumble it if I have a lot to do. I haven't tried platting rectal hairs but bet there's a reloading tool sold for that as well! (probably comes free with competition die sets)
  12. 308 175 gr bullet makes which works best

    N140 is usable with 175 grain projectiles BUT is not ideal. It is a little peaky and has a tendency to suffer spikes in pressure when used higher up the pressure ladder, especially where heavier bullets are concerned. My shoulder can attest to that! N150 is a more sensible choice. RS62 is also a good choice for 175 and heavier, although you can also use RS50 without the same pressure signs as when using N140 with 175 bullets. Just because Vhit list those powders with those bullet combinations doesn't make them ideal.
  13. 6.5 Creedmoor MV

    Or you could try cleaning the chamber out with a meths soaked mop and dry it off. That worked for me with no need to up charge weights.
  14. Trans sonic performance

    As Laurie says, it's a complex subject and there is no straightforward answer. If the question is re-written as "what bullets are stable through transonic", well that's a different matter and much easier to determine, as you simply load some up and try them. I've done just this with a range of bullets in .308 and .223 and what I've found is (exactly as Laurie hints at) that very few modern high BC designs, particularly some of the secant ogive profiles seem to work well through transonic. The best designs have all been the older tangent ogive heavies, and the "best of the best" for me in .308 have been the 190 SMKs which shoot very well through transonic, retaining very good stability as evidenced by good 900m groups. Only one modern design that I've tried in 223 seems to buck the trend a little and that is the 77 TMK which in still conditions manages very respectably out to 850 yards where it starts to drop below supersonic ans I intend on finding out next week how it fares a little further out. Show it a breath of wind though and that soon changes, unlike the 190 smk. I haven't tried them yet but I imagine that the 90gr smks in 223 might perform well too (Laurie has way more experience of these). There's something about these longer, heavier, older smk designs which despite indicated marginal stability at lower velocities, don't seem to become too unstable.
  15. 308 175 gr bullet makes which works best

    I only use 175 TMKs now for long range work in .308. Nothing else I've tried close to the price matches their performance in my rifle, nor their consistency which on my last batch was within 1 or 2 thou base to ogive measurements. They are incredibly consistent in manufacture and will tolerate long jumps due to their tangent-esque ogive profile. Loaded to mag length, they seem to perform very well indeed. Although I have found several nodes with every TMK in every calibre that I use, most cases it's the faster they're pushed where I seem to get the best results. In .308, I use 44.2gr RS50 and that comfortably makes them a very useful and accurate 1000 yard round at the velocities I'm getting with this combination although not up to the more slippery 6.5 and 7mm bullets in performance.
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