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Berger 175gr OTM

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/28/2011 at 11:42
jonoMT View Drop Down
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I just (pardon the pun) bit the bullet and ordered 200 of the new Berger 175 grain OTM hybrid ogive. I've been interested in trying these out since I first read about them. Unlike most of the Bergers they're designed to be loadable to magazine length in .308 Winchester and by incorporating the hybrid tangent/secant ogive they still have a high BC (.259 G7) while being more forgiving for rifles with long throats (i.e. most Remingtons). The most interesting thing is their reported stability through the transition from supersonic to subsonic speeds.

While I've been pretty happy with the accuracy and performance of my current .308 load using 165 gr. Nosler Accubonds, I've also felt like I'm not really getting the most out of my Rem. 5R. The faster twist barrel (11.25) is really meant for 175 gr SMKs and the like. Also, the Nosler design is somewhat flawed, making it less stable out past 400 yards. I still will use it for my other rifle (Rem. LTR) because it is a great all-around hunting bullet. But the 5R really is more of a long-range target rifle and if I hunt with it, it will be for antelope, which tend to die rather easily.

Out of curiosity before ordering these, I checked the measurements as best I could.



The OTM is actually shorter than the 165 gr. Accubond (1.321") and has less bearing surface. Since the neck of a .308 cartridge is .30" and I'd like to leave at least .25" of bearing surface inside the neck I will probably seat these at exactly 2.8 OAL and just experiment with different charges. (I currently seat the Noslers @ 2.82"). JBM shows that in my typical shooting conditions, the round should remain supersonic out past 1000 yards. (I use 1.2X the sound barrier crossing as my rule of thumb for going trans-sonic).

I'll follow up with some results as soon as I get them.







Edited by jonoMT - August/28/2011 at 11:43
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/28/2011 at 12:11
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Very interesting... My 178gr amax measure about the same as the Accuonds, and have a bearing surface of about .510"(just eye-balled with my caliper). I wonder if, the smaller bearing surface, the Berger's would be faster? 
The length does not bother me, because of the Savage action length I can load out to over 2.9" and still fit in the mag. But if accuracy is the same, faster is always better... At least to me! 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/28/2011 at 13:23
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There seems to be some great buzz about these, jonoMT, I am curious to see how they do for you.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/28/2011 at 16:22
jonoMT View Drop Down
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It's funny though that Berger isn't really pushing these much. There's nothing much on their website, although I was able to find this: http://www.bergerbullets.com/images/Copy%20of%20Quick%20Reference%20Sheets%207-27-11.pdf, which has the exact dimensions so I've updated the bullet image with those. If your .308 Win cartridges are trimmed to the SAAMI spec length of 2.015 and you seat to an OAL of 2.8 you'd have .273" of bearing surface contacting the case neck. Seems like plenty.

About the only other reference is to their ballistician, Bryan Litz' Applied Ballistics website where you can order his preloaded premium ammo. Several reloading supply houses have published a memo from Berger saying that while they will sell them to whoever wants them, the primary market (military/LEO) relies on manufactured loads. That's true, but if these work well why not promote them more to handloaders? There are a number of us who haven't really gotten into Bergers before because they can be hard to tune for rifles with long throats...although they did put out an article once about a method for using shorter seating depths. I think I was still after mag-length bullets though. Maybe it's because they prefer to steer people to the AB loads, which is fine. Guy's gotta make some money for his efforts.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/28/2011 at 16:30
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These float well loaded forward supersonic or backwards subsonic...

I have only gone through 6 or 7 boxes out of the 10 I bought but I would say my thoughts are pretty solid. 

I would tend to say I'd watch out to 800+ super and 500+ sub...

They grouped real well at about 300 yards supersonic.

I might be able to see if I inadvertently got some pics of them on the table and in a pic of a target...

I will see what data I have as far as development for anyone who wants If memory serves it is actually in the update of Quickload...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/28/2011 at 19:18
jonoMT View Drop Down
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I'd be interested to see what you have. I'm going to do a ladder test with Varget, but first load up just five rounds from 42 to 45 to see how much pressure I hit. I like to find out the upper limit then do 5 loads in .7-.8 grain increments down from that.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/30/2011 at 12:18
jonoMT View Drop Down
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A few more interesting bits of info regarding drag and BCs that I gleaned from one of Litz' articles. You can find out what the form factor of a bullet is relative to the drag model used, e.g. G1 or G7, by dividing the sectional density by the BC. The lower the number, the less drag there is relative to the weight of the bullet. So you can compare various projectiles that weigh the same (or, I suppose, are close in weight). For example, the new OTM form factor is:
 
.264 / .259 = 1.019
 
So it is a little 1.9% higher than the G7 drag model. A 175 gr. SMK is:
 
.264 / .243 = 1.086
 
That is 6.6% higher than the OTM. (You get this same number by dividing the OTM's BC by that of the SMK). Interestingly, the OTM has a better BC than the Berger 175 VLD (although not the Long Range) and is somewhat short. It seems to share a lot in common with the Long Range, having almost the same bearing surface, but a longer boat tail and a shorter ogive. Incidentally, according to Litz (and this makes sense) the portion of the bullet that is bearing surface has no effect on drag. Although certainly it has other effects on mass and stability.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/02/2011 at 13:41
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Follow-up. In short, I really like this bullet. I got my order Weds. afternoon and yesterday evening loaded up 5 loads (specific to my rifle!), using new Lapua brass and Varget: 42, 42.8, 43.5, 44.3 and 45. It was really windy at the range this morning and crowded. The former is not that big a factor in a ladder test because you're just looking at vertical stringing. But I pulled a flyer on my last 45 gr. shot when the guy next to me let loose with his .50-90 Sharps at the same time. Still, I found that 45 was otherwise the best group.

It's not incredible, measuring .86" edge to edge. But in my experience, coming back later with the same load and only one load usually tightens up groups considerably. I'd expect it to stay inside .5 MOA next time:



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