bc vs velocity w/copper solids

[royinidaho]

Listened to Pump and the other fella who seemed to point out that bc of solids drops with velocity reduction much greater than do lead core bullets.

I'd never thought of that.

I'm shooting 377 CEBs at somewhere around 3150 FPS MV with the published G1 bc of 0.950 which is close enough for what I've been doing so far out to 1200 yards.

I'll be shooting paper to that distance one of these first days then jumping to a mile. After that I'll be going as far as the old girl will go.

Any hints on were to learn the bc vs velocity span changes to get "closer" before shooting that first shot at those long distances.

Idaho might be big but finding a 3000 yard shot spot requires miles of travel and those bullets aren't the least expensive things and i'm po and cheap.

 

[mitch260]

Roy,

Your best bet will probably be to use a G7 BC. It should be much more consistent over all velocities. The effect of the G1 changing drastically over the velocity spectrum is due to the bullets shape being drastically different than the G1 standard. The copper Solids tend to be even farther away from the G1 standard than typical lead core bullets, so the G1 will vary more with changes in velocity. The G7 is a much closer fit to all modern long range bullets so there is substantially less BC variation due to velocity changes.

 

[HarryN]

Perhaps you can glean a hint from similar bullets. GS Custom makes an SP series of solid copper bullets that are sort of similar to those cebs.

They publish BC constants for three different velocity ranges for many of their products.

 

[BergerBoy]

Hey Roy come down to Nevada.... I'll take you out shooting.... we have vast amounts of open land down here.

Solids or monolithic bullets are not as heavy as lead core bullets so they have to be longer for the same weight and thus harder to stabilize, as you know. I always look to see if the bullet has an efficient BC- what is the drag coefficient? As a general rule the average needs to be under .99 IMO.

I know the published BC is just an average and the BC changes with velocity but it would be nice to figure out what your "exact average" for your load is. Meaning, if you push it faster or slower than usual it will be different than the published BC.

I have the Horus Kestrel that only has a G1 BC but I went shooting my 300 at 1734 yds. and that thing is dead-nuts on. I know in therory I shoot a G7 profile bullet so a G7 BC program would be closer but so far I have had great luck with it.

Good luck

 

[royinidaho]

BergerBoy,

Thanks for the offer. I may take you up on it sometime.

However, the news is bad.

While the 377 and 350 CEBs shoot lights out at 628 yards 2 of 5 shots @ 1028 went bonkers and the first shot at 1028 with the 350s missed the 4' x 4' target holder.

I gave up and went back to the 350 SMKs but they're not nearly as sexy as the CEBs.

 

[HarryN]

Roy, is that your 375 AM 10 twist?

The reason I ask is that I am curious as heck about the Gs custom 375 sp copper solids.

They have a 375 330 grain sp032 and a similar 375 355 grain sp173, both should be good for a 1:10 twist.

If you are game to try one of them, I will buy a box for you in exchange for your results. If you end up not liking them, just send me the leftovers.

 

[snox801]

Thats not good news. I was looking at the 300 gr 338 ceb for my AM. Got me thinking maybe not now.

 

[royinidaho]

Roy, is that your 375 AM 10 twist?

The reason I ask is that I am curious as heck about the Gs custom 375 sp copper solids.

They have a 375 330 grain sp032 and a similar 375 355 grain sp173, both should be good for a 1:10 twist.

If you are game to try one of them, I will buy a box for you in exchange for your results. If you end up not liking them, just send me the leftovers.

HenryN,

I'm game for the research opportunity. Both the CEB 350s and 377s should have been stable in my 10 twist. Didn't happen though. It seems they were on the very edge of stability.

Compare bullet lengths of CEB and Gs offerings are longer it may be iffy but I don't know what their shape factor is.

Hey, its worth a try.

 

[HarryN]

I have seen Gerald post on here sometimes. Maybe we can entice an opinion from him. I sent a pm to him via the forum for his recommendation.

 

[Gerard Schultz]

royinidaho and HarryN,

The best GSC bullet for a 1:10" twist would be the 355gr SP. The 330gr SP will also work but is intended for work from a slower twist rate or from a 1:10" if the distance varies from point blank to about 800yds. The technical profile on the website of both bullets is still in the old format where the new format profile contains more data and is clearer.

Perhaps it would be an idea to check that the barrel of your rifle is indeed a 1:10" twist. It is relatively easy to do and this device can be made from a paperclip. Below is a 5 shot group that a GSC distributor shot at 1500yds with his 375CT. The rifle has a twist of 1:9" and he is using the 414gr SP.

 

[LR3]

In my .375 AM the 355 gr GS were more accurate from 100-1000 yds but at one mile and beyond the SMK 350gr were more accurate and had a slightly better BC. I suspect the quality of the GS is higher with less variability. At one mile the GS shot about 3MOA lower. At 2200 yds my best group of 6 shots into 12"" was with SMK.