Bullet Velocity Variation (2)

[Brillo]

I thought it best to start a new post on this subject rather than highjack the original, which was a query about accuracy of reloading scales.

I read with interest the German Salazar article about .308 1000 yard load development because I'm finding 1000 yd shooting particularly challenging (and enjoyable).

My rifle is a .308 Sako TRG-22 with a 26" barrel and up to now I have used, exclusively, the 155 grain SMK #2155 bullet. With this head and various load combinations I have had good results up to 900 yards, but it fails at 1000 yards.

My favourite load has a MV of 2850 and by the time it gets to 1000 yards its velocity is only 1100 fps. I have developed a load that gives me 2920 fps but even this will not get me near to the magic Mach 1.2 number mentioned in the article.

I have been advised to go to a heavier bullet and I'm in the process of developing loads for the 175 grain SMK, coincidentally the same bullet referred to in the article and used in the mentioned ballistics test.

So far I have reached 2730 fps without pressure signs, with the aim of reaching 2750 fps and so replicating an established accuracy load I found on the 6mmBR website. But even this will only get me to Mach 1.147 (1280 fps) at 1000 yards at a range height of 220 feet (this is the height of Stickledown at Bisley).

To reach Mach 1.2 at this height I need to have a MV of 2860 fps. I would have thought that this MV with a 175 grain bullet would produce very high pressures and I'm reluctant to even progress towards it especially when the maximum loads on the Vihtavouri data tables for the 175 SMK is 2631 fps.

Comments?

[Laurie]

The 175gn SMK is virtually a dead end in ballsitic terms. It'll give marginally better 1K results than the 155gn SMK (#2155), but its design is barely improved over the lighter model.

 

The key feature is the i7 or G7 based 'form factor' which compares its ballistic efficiency to that of the G7 reference projectile. The 'reference bullet' always has an i value of 1.0, so the factor for bullets being compared is read against that. With it being a drag based factor, a low value = good; high value = bad.

 

Sierra's original 155 has a Litz calculated i7 value of 1.092 which is poor by today's long-range match bullets getting on for 10% higher drag. The new 155 (#2156) is much improved at 1.018, but it doesn't work well in everybody's barrel.

 

The 175gn SMK is 1.085, barerly better than the older 155 SMK.

 

Here are some of the more efficient bullets in the 175-190gn bracket, which is certainly the weight range to consider with a 26-inch barrel for this distance:

 

Berger 168gn Hybrid (Must be Hybrid, not VLD) which I know from personal experience is a good 1,000 performer: 0.953

Berger 175gn LR BT - an excellent bullet which is usually easy to tune and is used my many US sling shooters in 'US Rules' TR/Palma comps: 0.999

Berger 185gn LRBT 'Juggernaut': 0.985

Berger 190gn VLD: 0.982

 

 

Of the lighter bullets, the ones to go for are:

 

155gn Lapua Scenar: 0.988

155gn HBC (from Brian Fox, £28/100): 0.989

 

On top of that there is a trio whose form factors are nothing special, but have a reputation for handling trans and subsonic transitions very well:

 

190gn Sierra MK

200gn Sierra MK

185gn Lapua D46 FMJBT (step-boat-tail)

 

Don't consider any other Lapua bullet for extreme ranges - the 167 and 185 Scenars are VERY poor LR designs, but good short range numbers.

Don't consider any Hornady A-Max for 1K except the 208gn model which is a superb LR design. The others all have short boat-tail sections with over-steep angles that lead to transonic turbulence, extra drag and instability.

 

Finally, Berger does a 175gn 'OTM Tactical' model that is optimised for the US military's sniper / marksmen rifles' recently adopted standard 1-11.25" rifling twist rate. The 175gn is designed to shoot well at 1K at ~2,600-2,650 fps in this twist rate and may suit a TRG-22 depending on its barrel twist. (The objective is to tune the MV to provide the same rpm as a 2,600 fps in the 11.25-inch rate.)

[Brillo]

Many thanks Laurie. I was 'half' hoping you would respond and your reply has given me the information I need to go forward. I must now give Brian Fox a call to see what he has in stock from the bullets in your list.

Your last paragraph is particularly interesting as my TRG is 1:11 twist so it should be a simple matter of maths to extrapolate the rpm to match the 2600fps of the 11.25 twist for the OTM Tactical bullet..

 

Mark

[Panda]

I tried the Berger 185 LRBT Juggernauts in my 26" Remy 700 and couldn't get them to work at all. I moved to the 185gn OTM Tactical behind 44.5gn of N150 (after a load work up) and used them at the 1000yd benchrest comp at Diggle picking up a 1st in class with an agg of 11.105".

 

It may have been I got the best wind conditions, or the fact I was using a different stock or even that I was using my mate's Seb front rest rather than my Caldwell Fire Control, however I feel that the OTM bullet had a major part to play in the win. It was by far the best 1000yd shoot I've achieved in over a year of competing.

 

I haven't had a chance to put them over a chrono yet, however, given the come up using the android shooter app it looks like it's around 2600fps at the muzzle.

[Dark Star]

I tried the Berger 185 LRBT Juggernauts in my 26" Remy 700 and couldn't get them to work at all. I moved to the 185gn OTM Tactical behind 44.5gn of N150 (after a load work up) and used them at the 1000yd benchrest comp at Diggle picking up a 1st in class with an agg of 11.105".

 

It may have been I got the best wind conditions, or the fact I was using a different stock or even that I was using my mate's Seb front rest rather than my Caldwell Fire Control, however I feel that the OTM bullet had a major part to play in the win. It was by far the best 1000yd shoot I've achieved in over a year of competing.

 

I haven't had a chance to put them over a chrono yet, however, given the come up using the android shooter app it looks like it's around 2600fps at the muzzle.

 

I am a fan of the OTMs because I found exactly the same with my Rem 700. Nothing else would really properly work at 1000+ but the 175 TOTM at 2640fps MV is still supersonic by the time it gets to 1000 but, more importantly, stays much more stable from Mach 1.2 down to < Mach 1 which means they'll still work even in very cold conditions and beyond 1000yds.

[Laurie]

Ah ... now that's an interesting pair of comments that the 185 'Juggernaut' didn't work, but the 'OTM Tactical' did.

 

There is a degree of dispute about these 'two' bullets as many in the US say they're not two designs at all rather a single design with two names and different Berger part numbers, this strange situation created by the US military's demand that any match type bullet bought by them or loaded into sniper / special purpose ammo must be called 'OTM' !! (To keep their Judge Advocate General department happy vis a vis legality under the Hague Convention rules?)

 

The issue is discussed at some length here:

 

http://forum.accurateshooter.com/index.php?topic=3790325.0

 

The third member of the .30 TOTM trio, the 230gn Hybrid Tactical also appears to be identical to the Target Match Hybrid version in everything but its label.

 

The 175gn TOTM on the other hand DOES appear to be a unique design. Although its BC is only marginally below that of the 175gn Berger LRBT, it has a shorter nose section and a noticeably longer boat-tail rear end and a 7.2-deg BT angle v the LRBT's 8.6-deg, a significant change so far as these things go.

 

What it looks like is that Bryan Litz designed the 175gn model specially for the 7.62mm military sniper / .308 Win law enforcement ammunition markets to try and muscle in on Sierra's stranglehold on them with its bullets (168gn used by most LE buyers in preference to 175s). Remember too that Bryan L has his own ammunition manufacturing outfit as part of his 'Applied Ballistics' operation.

 

http://www.appliedballisticsllc.com/Munitions/ABMTactical.html

 

and sells 308 Win loaded with this bullet.

 

The 185 and 230gn 'TOTM' (or non-TOTM it seems) models appear to have been renamed / added as an afterthought with the stated purpose of suiting military / LE outfits that use the .300 Win Mag as well as bolstering the catalogue a bit, likewise the 0.224 77gn TOTM AKA 77gn Berger Target BT bullet. The 'meat' in the Tactical OTM range is the 175gn thirty and the .338 models.

 

I've loaded 25 175 TOTMs over IMR-4895 to try at longer ranges in my 22-inch barrel Howa 1500 Varmint 'affordable F/TR rifle' with MVs selected to provide similar rotational speeds in its 1 in 12-inch rifling twist barrel to that of 1 in 11.25-inch at 2,625 fps. I'll try them in due course in a Diggle 800 yard F-Class match (as far as my £115 Fox scope will adjust up to).

[Panda]

Many thanks for the interesting link Laurie. I'm now beginning to wonder if I tried to push the LRBTs too hard. I started the work-ups higher up after running them through Quickload and as you saw, I ran into pressure marks on the base of the case very quickly.

 

I've got 200+ left of LRBTS so I think I'll have a go at loading them up with less powder and see how they perform.

[Brillo]

I tried the Berger 185 LRBT Juggernauts in my 26" Remy 700 and couldn't get them to work at all. I moved to the 185gn OTM Tactical behind 44.5gn of N150 (after a load work up) and used them at the 1000yd benchrest comp at Diggle picking up a 1st in class with an agg of 11.105".

 

It may have been I got the best wind conditions, or the fact I was using a different stock or even that I was using my mate's Seb front rest rather than my Caldwell Fire Control, however I feel that the OTM bullet had a major part to play in the win. It was by far the best 1000yd shoot I've achieved in over a year of competing.

 

I haven't had a chance to put them over a chrono yet, however, given the come up using the android shooter app it looks like it's around 2600fps at the muzzle.

 

This is very interesting. Did you really mean the 185 grain OTM tactical or did you mean 175 grain?

[Panda]

Hi Brillo. I got your pm but am having trouble replying at the moment.

 

Yes, I'm definitely using the 185gn otms. I've had a look at the Berger data sheet and the OTM & LRBT do indeed seem to be the same bullet. However, and this may be due to batch differences, the oals don't tie in with the data. The LRBTs are consistently running 12 thou short and the OTMs are averaging +12 thou. Using a comparator the OTMs are running 17 thou on average longer than the LRBTs (average taken over 22 bullets of each type).

 

All I can say is this hand loading is confusing!!!

[Spiker]

Panda.

 

PM sent regarding the 30418.

[palo]

I also have a sako trg 22 308 rifle.

I was also looking for a bullet to shoot at 1000 yards so I sent brian litz an email

asking him what bullet he recommended for my particular rifle.

He recommended the berger 175 otm tactical.

I didnt get round to trying them yet though.

[Brillo]

I also have a sako trg 22 308 rifle.

I was also looking for a bullet to shoot at 1000 yards so I sent brian litz an email

asking him what bullet he recommended for my particular rifle.

He recommended the berger 175 otm tactical.

I didnt get round to trying them yet though.

Getting them seems to be like trying to find gold plated rocking horse droppings. I've got some 185 OTM's to try thanks to Panda so I suggest we compare notes if you get any 175 grainers.

[Panda]

+1 on comparing notes on the 175 OTMs. I would be very interested to hear how they perform, especially as my Remy has a 26" barrel. I know Brian Fox has plenty of the 185 OTMs but I'm not sure about the 175s.