Chasing the lands with 2155 Sierra in 308

[JSC]

When I've developed a load which needs to be below a certain OAL for magazine feeding, I settle on the longest practical OAL which will feed from the magazine and then tune it with the powder charge.

A change in one variable almost always affects something else, so the danger is you start chasing your tail and end up completely confused and without a conclusive result.

If I were you, I'd not worry about jump at all. Just load them out as far as you can so they feed from the magazine and don't fall out of the case too easily and then adjust the other variables.

I did quite a bit of experimenting with N140 & RL15, but there wasn't really a bullet I've used where I'd be 'matching' the RL15 load to the N140 load. With a 155SMK, I'd stick to N140 if I were you and maybe try another (faster) powder if anything.

HTH a little. Laurie's advice is all spot on as usual...

[The Lord Flashheart]

When I've developed a load which needs to be below a certain OAL for magazine feeding, I settle on the longest practical OAL which will feed from the magazine and then tune it with the powder charge.

A change in one variable almost always affects something else, so the danger is you start chasing your tail and end up completely confused and without a conclusive result.

If I were you, I'd not worry about jump at all. Just load them out as far as you can so they feed from the magazine and don't fall out of the case too easily and then adjust the other variables.

I did quite a bit of experimenting with N140 & RL15, but there wasn't really a bullet I've used where I'd be 'matching' the RL15 load to the N140 load. With a 155SMK, I'd stick to N140 if I were you and maybe try another (faster) powder if anything.

HTH a little. Laurie's advice is all spot on as usual...

I fear I have not expressed myself clearly, apologies and thank you for your reply.

The test was not to find an accurate load per se, more to find out whether a method such as :

I settle on the longest practical OAL which will feed from the magazine and then tune it with the powder charge.

Is indeed theoretically valid ( i realise that it is practically speaking valid) or whether the two appraoches are ( within reason) interchangeble given that the load's contribution to accuracy ( i.e. leaving out bullet, barrel and rifle quality) is via barrel time and by extension barrel exit point at the vibration cycle.

So when you select an arbitary seating length and tune with the powder, what you are tuning is this exit time, unless there is more at play here as I asked Laurie.

When settling on an arbitary powder charge ( usually the most accurate at that OAL) and varying the OAL you are doing the same thing, i.e tuning barrel exit time.

This is what Laurie meant in his post when he spoke of establishing a base line and hence my question about "matching" barrel exit points using QL rather in the sense of velocity or powder charge.

I've noticed that RL15 packs a lot better than N140, something like 4 grains more on max loads can be put in the case without compression. I have always found that the slower burning powder for a given calibre tends to produce more velocoity for the pressure than the faster burning powder ( given equivalent burn rate modifier chemistry) as long as one could get enough of it in the case without compression problems.

On the two baseis above I am wondering what the theoretical explanation is for "not liking powders" might be?

[Laurie]

I'd agree with JSC's views. Some bullets are very jump-sensitive; a few won't fit your barrel well and will probably never give consistently good results in it no matter what you do. The 155gn 308 SMK #2155 is never in the former camp and rarely in the latter. You will hardly find a more tolerant design.

With a bullet like this one, I'll usually start on 15 thou' jump and play around with powders and loads. It is very rare that something doesn't do well, or often many things. But if it has to fit a magazine and take a large jump in the process, many SMKs simply don't care. I spent a fair bit of range time on 223 some years ago in a SOuthern Gun SSR-15 with 77s from Lapua, Berger, Nosler, and Sierra - all designed to be loaded very deep to magazine COALs ~2.26" for rapid fire stages in US NRA High-Power Service Rifle XTC using semi-auto AR-15s. In a Wylde chambered 223 that sees a LOT of jump, so I experimented with over-length rounds and got very good results. Just out of interest, I then played around with a couple of these bullets at magazine length and getting on for 200 thou' jump and apart from getting more compressed loads got just as small groups, sometimes smaller after a bit of retuning charge weights.

I had until recently a 223 FTR single-shot rifle chambered with the PT&G 'ISSF' chamber reamer that gives a 0.169" freebore for very long 90gn bullets and for the hell of it had a play with the old 77gn SMK as I had a fair few on hand. I didn't bother measuring base to ogive settings for this chamber - unlikely to get near to the lands in any event - and simply seated the bullets very shallow with shanks in the neck by around 0.15" and worked loads up to see what MVs I'd get. At something over 3,000 fps the two round pressure / velocity work-up loads started to shoot one-hole 100 yard groups and subsequent fives put them into well under the half-inch, some under third-inch. As always as charges rose, the pattern of reducing group size / ES would show then go into reverse as loads went past the sweet spot / node to then start reducing again at around 1gn heavier charges. That would again be with a three figure jump - these bullets like most older tangent ogive SMKs simply don't care!

In military rifles, I never bother even trying to measure jump levels with tangent ogive bullets, simply make up some rounds and gradually reduce COALs until they fit the magazine with a bit spare clearance to cope with COAL variations, then if the bullet has enough grip in the neck that's the COAL that is recorded and an inert 'seating dummy' made up and used to reset the seater every time I load that bullet again. It is often astonishing how well these rifles and such bullets will group if it is a good platform such as the Swedish Mausers allied to the 140gn SMK and (currently) a pair of Chilean 7X57 'contract Mausers', the older one of the pair with the old 175gn Hornady RNSP bullet whose shape and weight match the original 173gn RNFMJ and older hunting load rounds. Set it to reliable-feed magazine length, load over Viht N160 and first test session, I'd got both precision and MVs that match the original military loading and therefore suit the sights. Half an hour range time and sorted - no more development or trying any other combination.

So far as chasing the lands go, I have a Palma brass load for 308 for my main FTR rifle that originally gave the 155.5gn Berger BT Fullbore - another supremely tolerant design - 3,050 fps. The barrel has had nearly 3,000 rounds down it and MV has reduced to 3,027 fps at the last time over the chronograph, almost certainly down to throat erosion so jump will have increased substantially. It will still produce 0.2 to 0.4" groups at 100 and hold good long-range elevations same as it did when new and I've never remeasured clearance / jump for that bullet or changed the load at all. For a VLD type (or the 168gn Berger Hybrid that seems to behave like one) that needs seating a little into the lands, I would check and change the COAL at regular intervals, but with bullets like the older tangent ogive Sierra MKs, I'd only do so if the results deteriorated - and that's usually at or near the end of the barrel life.

As John says, don't go changing variables all over the place and certainly never more than one at a time. Even so, it is very easy to shoot barrels out in a vain quest to try and produce better precision than they're capable of producing. This is particularly so with hammer forged factory barrels that sometimes mislead through a lack of consistency, so they'll produce what seems like really promising improvements in one session, then a significant deterioration with the same loads in the next. (Not that custom match barrels and gunsmith chambered set-ups won't do this either on occasions - most frustrating!)

[The Lord Flashheart]

Thanks for you reply Laurie and I fully take on board what you say but fear I have not expressed myself very clearly again.

My original worry wasn't so much about the relationship of the bullets to the lands per se, it was about whether sufficient neck tension was more important than relationship to the lands and you answered that one very well with the example of that BR case with no neck.

What this then set me on was an odyssey ( which is why it has taken me so long to reply) of trying to work out whether that given OAL would be the best across the board for all powders ( a baseline OAL as you mentioned in you earlier post) i.e.

it gives you a seating / COAL set-up to leave as a constant while you play with the other variables.

I developed the RL15 load by working up the powder charge at the arbitary OAL of 2.850 as you suggested, took the best charge and fiddled with the OAL until I found the best load at OAL of 2.800.

I then tried N140, H4895 and BL-C (2) at that OAL up the powder charges and noted the group sizes, firing 3 ten round groups of each.

That done, I then took the most accurate charges from each and played with the OAL of each.

I found that they gave best accuracy at different OALs, varying in each case. I didn't find a better load than the RL15 load above but did manage to better the accuracy of the baseline loads from the last paragraph.

This led me to wonder if we are not in fact dealing with a discrete system and it is in fact impossible to truly say that adjusting one variable at a time is valid for anything other than a particular combination of bullet, powder, case, rifle and primer?

On that basis, I am wondering if the barrel time for a particular bullet is the main factor in determining whether a load is accurate or not as it is a synthesis, or end result if you will, of all of the variables that go to make up a load.

I was wondering if then QL might be able to model this sufficiently accurately?

[Laurie]

I don't believe QuickLOAD is sufficiently accurate to play this sort of game. There are just too many variables. For instance, simply changing the primer model (possibly even the production lot of a single model) will often change results significantly. That's in 308 Palma SR brass which shows a much smaller (~50%) range of performance variations than equivalent LRP brass. .... and you can't model that factor in QL.

I've generally found that assuming a powder is reasonably well suited to the cartridge and other components used, that best results occur at around the same predicted PMax levels in a cartridge / rifle combination. That of course is fine if one trusts the model's PMax predictions, but there are two powders where I don't believe a word of what the program tells me - Viht N160 and Reload Swiss RS52, and it's not that great on N150 either for that matter in some applications.

So a long time ago, I decided that QL is fine for producing starting points for test loads and saving time / barrel life in that respect, also very useful in doing cartridge v cartridge desktop comparison exercises in conjunction with Bryan Litz's BCs and his Ballistic Solver external ballistics programs, likewise comparing potential powders for a cartridge / bullet combination, but that's about as much as I'll rely on it.

[The Lord Flashheart]

I did have a play with QL but even corrected for my rifles and loads it gave results that didn't translate to reality.

Funny you mention the powders, I have found QL to be decidely off with H4895 with my 3006...

So there seems to be no "magic" OAL for a given rifle with a given bullet, it's all in the specifics of the load from what I have been able to scertain from my experiments.

Thanks for all your help. :)

[JSC]

I did have a play with QL but even corrected for my rifles and loads it gave results that didn't translate to reality.

Funny you mention the powders, I have found QL to be decidely off with H4895 with my 3006...

So there seems to be no "magic" OAL for a given rifle with a given bullet, it's all in the specifics of the load from what I have been able to scertain from my experiments.

Thanks for all your help. :)

There's definitely no magic OAL. QL will often be a long way off unless you tweak some of the variables in it, particularly the powder burn rate. Are you doing that?

Having an accurate chrono you have benchmarked against other known good chronos is also very important if you want to use QL accurately.

Sometimes QL just doesn't quite fit with real world results, but as Laurie says it will save masses of time and ammo tests to get you somewhere in the ballpark with a new rifle/barrel/load.

One last point I always bear in mind about loading:
1. Read as many opinions and theories about this subject as you have time for.
2. Test each one of them yourself. Don't take any for granted.
3. Reject the ones that don't seem to work and accept the ones that do.

[The Lord Flashheart]

Hi John,

Don't I know it buddy, hence asking the Guru up there!

I have tweaked QL as far as it will go, case capcity, bore cross sectional area, fiddling with shot start pressure to simulate throats/primers/fudgefactor, played with powder burn rates, Ba values, the lot. I was hoping that Laurie might have got something I have missed. :)

I have an couple of chronos that I shoot through, comparing both for work like this. I am extremely fortunate to have tried them against an Ohler 35P ( sadly the bloke wouldn't sell it to me) to check accuracy and they are pretty good.

I was just trying to do point 2 in your post above.

The reason I ended up wondering about QL in the first place was that the experiments lead me to look into this barrel time question as a determinate of accuracy as a function of a bullet exiting the bore a relatively "quiet" place in the vibration cycle.

I wonder how to go about testing that theory?

[JSC]

Hi John,

Don't I know it buddy, hence asking the Guru up there!

I have tweaked QL as far as it will go, case capcity, bore cross sectional area, fiddling with shot start pressure to simulate throats/primers/fudgefactor, played with powder burn rates, Ba values, the lot. I was hoping that Laurie might have got something I have missed. :)

I have an couple of chronos that I shoot through, comparing both for work like this. I am extremely fortunate to have tried them against an Ohler 35P ( sadly the bloke wouldn't sell it to me) to check accuracy and they are pretty good.

I was just trying to do point 2 in your post above.

The reason I ended up wondering about QL in the first place was that the experiments lead me to look into this barrel time question as a determinate of accuracy as a function of a bullet exiting the bore a relatively "quiet" place in the vibration cycle.

I wonder how to go about testing that theory?

That is the basic theory of OBT is it not? Do you feel the need to test the theory to prove to yourself it is valid?

It sounded plausible to me. I spent time following the theory. It works for me most of the time. When it doesn't work, I don't really have the time to find out why so I just teak loads using gut feel and instinct. When that doesn't work, I put that gun to one side and and shoot another. :)

Another way might be to do traditional ladder tests and then compare results between that and the QL/OBT way to see if there's a correlation which helps to understand what's going on.

it's not an exact science. It would be a lot less of a challenge if it was

[The Lord Flashheart]

I feel the need to exploit it's validity by working out the practical means of doing so, there may well be no way.

I 'ed about the "put that gun to one side and shoot another", it the truly best way of shrinking groups in extremis...