200.20x Berger BC

[ARShooter91]

Set up a 300wm to shoot a mile way back in 2020-21 and settled on the 200.20x and Ramshot Magnum as that's all I could get. 1:9 26" Bartlein getting 3160fps safely 75deg and lower, not sure if warmer but I'd caution it as I'm near the top.

Berger list a BC of .328 and I'm seeing a .342 to line up with what I'm seeing at 1007yd and 1730yds. Velocity has been checked on a Garmin,Lab, and pro Chrono as well as trued at 600yds.

Is this because of how fast I'm spinning them?

 

[FredHammer]

Maybe a stupid question, but was your station pressure correct in your ballistic app? If this is off, then one will manipulate the BC in error, giving a false confirmation.

3160 is cooking for starters, and especially out a 26" barrel. That alone could be the cause for the higher BC.
I had 208Amax at 3060 out a 30" barrel in 75-85F. I've since cut that barrel to 24" and moved to the 215 Hybrids at 2925fps. The increase of the Hybrid BC puts me projected same mils to a mile even though I'm running slower. Can't wait to try it out this Spring.

 

[ARShooter91]

Ah, you know I didn't even adjust my pressure at 1730yds which is at a little lower alt. I'll see if my buddy has the pressure from that day and run the ballistics again.

I was shooting for about 100fps less than that but precision and consistency got better the more I pushed it. May have to do with the short bearing surface the 20x has as well.

 

[FredHammer]

Make sure to enter station pressure, and not sea level pressure. I mistakenly entered sea level pressure and it made me inflate the BC to overcome the heavier pressure number. In actuality, the station pressure was lower causing less drag/resistance, not that the bullet had higher BC. Hopefully that makes sense.

Run them hot to trot for that precision, just decide how long you want those primer pockets to last. LOL.

 

[memilanuk]

It's not entirely the same application (.308 Win vs .300 WSM), but I've put quite a few thousand of the 200.20X down range in FTR competition - since before their public release - and my come-ups have always jived with the numbers published with Berger, within the usual +/- tolerance

 

[Rio Precision Gunworks]

Set up a 300wm to shoot a mile way back in 2020-21 and settled on the 200.20x and Ramshot Magnum as that's all I could get. 1:9 26" Bartlein getting 3160fps safely 75deg and lower, not sure if warmer but I'd caution it as I'm near the top.

Berger list a BC of .328 and I'm seeing a .342 to line up with what I'm seeing at 1007yd and 1730yds. Velocity has been checked on a Garmin,Lab, and pro Chrono as well as trued at 600yds.

Is this because of how fast I'm spinning them?

More than likely something to do with settings in the software or some other thing influencing things. Generally speaking, Berger BC's are going to be very close.

 

[hero's machine]

I'm using .328g7 @2830fps / 3.5kasl and hits within predictions to 1600y. This is in a 10tw 300wsm with 200.20x

 

[ARShooter91]

29.92in HG was my input with 29.89 actual. I'm swapping scopes with my 223 Tikka which I have verified dope out to 1265 that lines up perfectly with JBM.

 

[Rio Precision Gunworks]

As long as it consistently works for you, then it's fine. Though I would also be looking at all the details myself if I was using a BC that far off from Berger, so I don't blame you asking and trying things.

Double check everything. Optic over bore height, etc.

 

[ARShooter91]

I'll check everything again and verify the Bushy ERS is tracking well. Same Seekins 1.1" rings on both it and the DMR2. Figured it could be an error at 1k but 1730yd with even a .330G7 would have me hitting .7mil lower than I was..

Let's say hypothetically, is it possible to "boost" a BC significantly by pushing them fast and giving them more spin than needed?

Edit: 2.11 stability on Bergers calculator with my numbers

 

[FredHammer]

I'm no physimachist, but I would think a faster twist barrel would have more contact with the bullet and slow it vs speed it up.
Lets say your data in and data out was spot on. You could of had an updraft wind somewhere down range. The ELR range I shoot is in a quasi valley with a creek at 1350yds. There were days the wind blew from the rear, 5-7 O'clock, and created an updraft hitting the creek and following up a small hill to the target. (Think of a wave hitting a retaining wall and splashing upwards)

One day we were all "no impact no idea" and one of our muppets yelled out, "Dial full mil low!" ShoNuff we were all hitting back in the ballpark. If you've no terrain features on your range to cause this, then it's back to the data in the app, or a positional issue, like buttstock not solid on the chest and recoil sends the gun drooping the stock upon firing and slightly elevating the muzzle. I've had this happen shooting different clothing.

I'm willing to bet the Bushy scopes you mentioned are not the problem. My DMR2 and DMR3 track like micrometers and have presented some sub-MOA groups at the mile with regularity. Well, when I have my shit together at least. Lol.

If all this LR and ELR shooting were that easy, we'd get bored!

 

[ARShooter91]

The 1730 has been at Thunder Valley, wind wasn't bad this week. Still it can do some funky things rolling over those hills and valleys.

 

[FredHammer]

Wind is just invisible water!

 

[TylerN]

More than likely something to do with settings in the software or some other thing influencing things. Generally speaking, Berger BC's are going to be very close.

This is my experience as well. Last time I thought I needed a custom BC's for Bergers I later realized my scope height was way off in my solver.

 

[hero's machine]

For bore height i take half the bolt diameter plus half the scope diameter and add the distance between the two. That's very close to centers.

 

[Taylorbok]

For bore height i take half the bolt diameter plus half the scope diameter and add the distance between the two. That's very close to centers.

I just measure it with a caliper.

 

[ARShooter91]

I typically go firing pin hole to center of rings. I'll check both ways